Haplomastodon chimborazi ( Proaño, 1922 )

Ferretti, Marco P., 2010, Anatomy of Haplomastodon chimborazi (Mammalia, Proboscidea) from the late Pleistocene of Ecuador and its bearing on the phylogeny and systematics of South American gomphotheres, Geodiversitas 32 (4), pp. 663-721 : 670-707

Haplomastodon chimborazi ( Proaño, 1922)

Mastodonte del Chimborazo Proaño, 1894: unnumbered page.

Mastodon waringi Holland, 1920: 229 , nomen dubium.

Masthodon chimborazi Proaño, 1922 : unnumbered page.

Tetrabelodon ayora Spillmann, 1928 : unnumbered page preceding p. 70.

Bunolophodon ayorae ( Spillmann, 1931) : 67.

Bunolophodon postremus Spillmann, 1931: 73 .

Cuvieronius ayora – Osborn 1936: 567.

Cuvieronius postremus – Osborn 1936: 595.

Haplomastodon (Haplomastodon) chimborazi – Hoffstetter 1952: 192.

Haplomastodon (Aleamastodon) guayasensis Hoffstetter, 1952: 208 .

Haplomastodon waringi – Simpson & Paula Couto 1957: 171.

Haplomastodon waringi – Ficcarelli et al. 1993: 233. — Casamiguela et al. 1996: 316.

Stegomastodon waringi – Alberdi & Prado 1995: 283. — Alberdi et al. 2004: 433. — Prado & Alberdi 2005: 4. — Prado & Alberdi 2008: 905.

HOLOTYPE. — A nearly complete adult skeleton of which only the right ( MICN-UCE 1981 ) and left ( MICN-UCE 1982 ) humeri are now preserved.

OTHER MATERIAL EXAMINED. — See Tables 1-19.

ORIGINAL DIAGNOSIS. — Gomphothere with high-domed cranium; upper tusks massive, with converging tips, lacking an enamel band ( Proaño 1922). Hoffstetter (1952) listed the following diagnostic characters of Haplomastodon chimborazi : 1) cranium high, elephant-like; 2) mandible with short symphysis (brevirostrine); 3) atlas and axis lack transverse foramina; 4) lower tusks absent; 5) upper tusks are relatively short, upturned with no torsion; 6) enamel band present in some juvenile tusks, never at adult age; 7) molars show slight tendency to anancoidy (displacement of buccal and lingual half-lophs); 8) posttrite central conules absent to poorly developed; 9) third molar tetra- to pentalophodont.

Characters 1, 2, 4, and 7 are shared with “ Stegomastodon ” platensis, whilst characters 3, 8 and 9 have a wider distribution within SA gomphotheres, with character 3 showing intraspecific variability.Characters 5 and 6 are derived relative to the condition in Cuvieronius hyodon . The phylogenetic significance of these two latter characters, in particular concerning the relationships between Haplomastodon and SA “ Stegomastodon ” will be discussed below.

REVISED DIAGNOSIS. — Medium to large brevirostrine gomphotheriid of trilophodont grade that differs from other South American gomphotheres by the presence of relatively short, massive and upwardly curved upper tusk, which always lacks an enamel band in the adult growth stage, and in possessing only slightly divergent tusk alveoli in the premaxillaries. In addition, H. chimborazi has a unique combination of the following characters: 1) high, elephantine skull; 2) inflated frontals and parietals forming sagittaly a wide fronto-parietal plane; 3) anterior border of bony orbit laying forward of the mesialmost cheek tooth in use; 4) nasal aperture wide and shallow, separated by a thin bony lamina from a deep subnasal fossa; 5) supraorbital foramen of maxillary absent; 6) alveolar portion of premaxillaries relatively long and robust; 7) presence of a shallow fossa for muscular insertion (lateral coronoid fossa) at the base of the ascending ramus of the mandible; 8) position of the mandibular foramen on the medial side of the ascending ramus markedly higher than the occlusal plane; 9) transversal foramina of the first and second cervical vertebrae with tendency to obliterate; 10) dorsal arch of atlas very thick, with strong dorsal concavity; 11) large and robust ventral tubercle of transverse process of atlas; 12) lower tusks absent; 13) DP3/dp3 trilophodont; 14) P3-P4/p3-p4 absent; 15) M3 with fully developed tretraloph; m3 with 4 to 5 lophids; 16) posttrite central conules (forming secondary trefoils under wear) absent to weakly developed.

Character 1, is shared with “ S.” platensis. Characters 2-10 and 12-15 are shared with both “ S.” platensis and C. hyodon , whilst character states 11 and 16 are as in C. hyodon .

TYPE LOCALITY. — Quebrada de Chalán near Punin, Chimborazo province, Central Ecuador ( Proaño 1922; Hoffstetter 1952).

TYPE HORIZON. — No stratigraphic data were provided by Proaño (1894, 1922). Recent geological investigations in the Punin area, however, indicate that the sedimentary sequence cropping out at Quebrada Chalán is part of the Late Pleistocene Cangahua Formation and contains a typical Lujanian fauna ( Ficcarelli et al. 1997; Coltorti et al. 1998). A radiometric dating of bone carbonate from mammalian fossil remains newly collected from Q. Chalán gave an age of 20 980±530 years BP ( Coltorti et al. 1998).

OCCURRENCE. — Late Pleistocene to earliest Holocene ( Ficcarelli et al. 2003; Coltorti et al. 1998). Ecuador: it is distributed both in the Andean provinces (Carchi, Pichincha, Chimborazo) and on the coast (Santa Elena Peninsula, Guayas province). Remains referable to this species have been collected from many other sites in South America, including Brazil ( Simpson & Paula Couto 1957), Colombia, Venezuela ( Hoffstetter 1986), and Peru ( Alberdi et al. 2004).

Measures Specimen MECN 82 1. Total length: akrokranion-prosthion 930 2. Akrokranion-rhinion (base of nasal aperture) 270 3. Tusk alveolus length 590 4. Length of zygomatic arch 450 5. Greatest breadth of neurocranium c. 780 6. Diameter between most lateral points of orbital processes of frontals c. 550 7. Breadth of tusk alveoli between infraorbital foramina 422 8. Greatest breadth of tusk alveoli 515 9. Maximum dorso-ventral diameter of tusk alveoli 213

10. Greatest length of occipital condyle 110

11. Transversal diameter of occipital condyle 75

ANATOMICAL DESCRIPTION AND COMPARISONS Cranium ( Figs 2-5 ; Table 2)

The description of the cranium of H. chimborazi is mainly based on the study of the Bolivar specimen (MECN 82). Additional data were obtained from Spillmann’s (1928, 1931) description and figures of the Punin ( Fig. 2 ) and Alangasi skulls. Though these three specimens are at slightly different ontogenetic stage (see the Material and methods section), they represent adult individuals as in all of them the M3 is completely formed. Th e skull of the Bolivar skeleton suffered a dorso-ventral crushing of the neurocranium and a distortion that altered in part the orientation of the distal end of the premaxillaries, that of the right tusk, and of the molars along the tooth row (see below). Th e Punin and Alangasi skulls were, on the other hand, in good state of preservation. Unfortunately, some aspects of these skulls were not figured before they were lost, so we have a partial knowledge of their morphology. Of the Punin skull only the left lateral aspect was figured by both Proaño (1894, 1922) and Spillmann (1928, 1931). Of the Alangasi skull the anterior, antero-lateral and ventral aspects were figured by Spillmann (1931).

Antero-dorsal view ( Figs 3A, B ; 4A ). The parietal bones are transversally expanded and dorsally form two small bulges separated by a sagittal depression. The forehead (fronto-parietal plane) is wide, sagittally convex, and transversely flat. The temporal lines are very faint and smooth postero-ventrally. The postorbital process of the frontal bone is relatively small. The nasals are bounded posteriorly by a sulcus for the attachment of the m. maxillo labialis (levator of the trunk), marking the limit between the nasals and the frontals. Th e sulcus is shallow medially and deeper laterally. It continues laterally into the nasal process of the premaxillary bone, along the limit between the premaxillary and frontal.Rostrally, the nasals constitute the dorsal limit of the external nasal aperture. The nasal processes are very small. Th e external nasal aperture is wide and low ( Fig.4A ).Th e dorsal margin, formed by the nasals and the nasal processes of the premaxillaries, is thick, forming a step-like border. Laterally, the nasal aperture is delimited by the nasal processes of the premaxillaries. The thickness of the lateral border of the nasal aperture rapidly decreases ventrally. Th e ventral border, made up by the body of the premaxillary, is not very distinct. The lateral and dorsal inner walls of the nasal aperture do not show any opening communicating with the paranasal sinuses, or with the lacrimal conduct. Medially, just below the ventral margin of the nasal aperture is a fossa that deepens into the body of the premaxillary ( Fig.4A ).Th is structure,here called the sub-nasal fossa, is contiguous anteriorly with the incisive fossa, from which it is clearly distinct. Th e alveolar processes of the premaxillaries, bearing the alveoli for the tusks, are long and very robust. In particular, the distal anterior margin is very thick. Seen in anterior view, the tusk alveoli only slightly diverge distally. The maximum distal width of the premaxillaries do not exceed the diameter between the orbital processes of the frontals. The incisura dentalis only slightly separates distally the two premaxillaries.

Lateral view ( Figs 2 ; 5A, B ). In lateral view, the outline of the cranial vault is regularly convex (Punin skull; Fig. 2 ). Th e skull vertex is on the perpendicular passing just behind the tuber maxilla. Th e orbits are large, with their anterior margin laying at the front of the mesial-most molar. The proximo-distal axis of the tusk alveoli is parallel to the plane of the forehead, and forms a wide open angle with the occlusal plane. The dorsal side of the alveolar processes of the premaxillaries is longitudinally concave.

The maxillary bones have a single large orbital perforation, ventral to the orbit, corresponding to the infraorbital foramen.Th e foramen is oval-shaped and relatively large, with a maximum diameter comparable to that of extant Loxodonta africana . The infraorbital process of the maxillaries, forming the lateral wall of the infraorbital foramen, is thick and antero-posteriorly expanded. The zygomatic arch is deep and robust. The anterior half of the zygomatic is deep, with a straight dorsal margin. On the ventral margin, is a slightly concave surface, possibly representing the origin of the m. masseter. A marked step separates dorsally the anterior half of the zygomatic from the shallower posterior portion (pars temporalis), whose dorsal side is occupied by the elongated articular surface for the zygomatic process of the temporal. Th e zygomatic ends posteriorly in a small tuberosity.

Posterior view ( Fig. 3C ). Th e dorso-ventral crushing of the MECN 82 cranium caused the posterior tilting of the occipital squama. Dorsally and laterally, the occipital squama is bounded by the nuchal crest. Th e latter is a thick and markedly wrinkled crest, evidence of a powerful dorsal nuchal musculature (m. splenius capits and m. semispinalis capitis). Viewed from behind and slightly from above, the cranium shows two lateral swellings separated by a median depressed area at the bottom of which is the nuchal fossa.

Ventral view ( Fig. 3D ). Because of the post-mortem crushing, the occipital and basicranial regions of the Bolivar cranium are quite damaged preventing a detailed anatomical description. Anterior to the condyles is the stoutly built basilar process (basioc- cipital). Along its lateral margins are two contiguous depressed areas, likely representing the area for insertion of the m. rectus capitis ventralis and m. longus capitis. Th e auditory bullae are not preserved, except for the anterior portion of the right one, represented by a thin bony lamina (muscular process). Anterior and lateral to the muscular process is an aperture here interpreted as the foramen lacerum orale (= foramen lacerum medium + foramen ovale; Eales 1928). Anterior and lateral to the basioccipital are, on both sides, the pterygoid processes of the sphenoids, extending to the palatine region.

The angle between the plane of the basicranium and the occlusal plane in H. chimborazi is greater than in G. angustidens and G. productum , approaching the condition in L. africana . The articular-mastoid region is characterized by the stout zygomatic process of the temporal and by its auricular part. The area posterior to the articular fossa is not preserved in the Bolivar skull, so it is not possible to control the occurrence of a retroarticular fossa (present in elephants and stegodonts, and absent in primitive gomphotheres and in mammutids; Tassy 1985).

The palate is relatively long and narrow. Sagittally there is a prominent crista palatina. Lateral to the palatine crista, on both sides, are two sulci deepening posteriorly. No palatine foramina are discernable in both the MECN 82 and Alangasi skull. Both the palatine crista and the palatine sulci gradually weaken and eventually disappear anteriorly. The palatines reach posteriorly and laterally the pterygoid processes at the contact with the sphenoids, where they form a stout protuberance. Th e posterior border of the palatines lays well behind the distal end of the posteriormost molar (MECN 82, Alangasi skull). In MECN 82, the left and right dental rows diverge at the level of the distal-most and yet non completely erupted molar (M3) to became parallel to each other at the level of the molars in use (M2). Medial to the mesial-most molar (M2) originates, on both side, the interalveolar crest. Th e two interalveolar crests diverge anteriorly so that their anterior ends are well separated from one another.

Discussion. Compared to Gomphotherium angustidens and G. productum , H. chimborazi is more derived in possessing larger and more robust premaxillaries, whose dorsal face is slightly upwardly concave, a wider and more rounded forehead, and a more pronounced pneumatization of the bones forming the dorsal, lateral, and posterior walls of the braincase, which produces a moderate lateral swelling of the parieto-occipital bulges.Th ese characters are also present in Rhynchotherium cf. falconeri (LVNHM 871; Ferretti 2008: fig. 3), as well as in the other American brevirostrine gomphotheres considered (i.e. Stegomastodon texanus , C. hyodon , and “ S. ” platensis). Sinomastodon hanjiangensis , the only species of this Old World brevirostrine gomphothere genus whose cranial morphology is sufficiently well-known ( Zong et al. 1989), possesses a similar derived morphology of the neurocranium, while retaining a primitive premaxillary morphology. Haplomastodon chimborazi and the other brevirostrine gomphotheres considered are derived with respect to G. angustidens and G. productum in having the anterior margin of the orbit laying just at the front of the mesial end of the tooth row. The more forward position of the orbit in the brevirostrine forms with respect to the condition in G. angustidens and other longirostrine gomphotheres (e.g., Eubelodon morilli , R. cf. falconeri), is correlated to a modification of the skull toward a more “elephant-like” morphology, characterized by a relatively higher, vertically tilted, and more for-aft compressed cranium than that of primitive gomphotheres. Such derived skull shape is likely linked to the development of a large proboscis, and evolved in parallel in other elephantoid lineages, such as Elephantidae Gray, 1821 and Stegodontidae Hopwood, 1935 . Another derived character of the skull of H. chimborazi with respect to primitive gomphotheriids, is the absence of a supraorbital foramen.Th is last character is shared, among American gomphotheres, with R. cf. falconeri, C. hyodon (Tarija sample), and “ S. ” platensis (MLP 8-1, MLP 8-3). It is noteworthy that Stegomastodon texanus (AMNH 10622) retains a well-defined supraorbital foramen ( Osborn 1936). On the basis of the figures provided by Zong et al. (1989), Sinomastodon hanjiangensis seems also to possess a supraorbital foramen. Haplomastodon chimborazi shares with “ S. ” platensis similarly large and robust premaxillaries, but in the latter (skulls MLP 8-1 and NHM M-19951) these are relatively shorter and distally wider than in Haplomastodon . In these characters, “ S. ” platensis appears morphologically intermediate between C. hyodon , that possesses extremely flaring premaxillaries, distally divided by a deep and wide incisura, and H. chimborazi . The configuration of the external nasal aperture of H. chimborazi , with the occurrence of a deep sub-nasal fossa, differs from the condition seen in Mammut americanum , G. angustidens , G. productum , Anancus Aymard, 1855 and elephantines, whereas it is shared by R. cf. falconeri, C. hyodon , and “ S. ” platensis (MLP 8-1, MLP 8-3, NHM M-19951). Th e wide external nasal aperture, the evidence for a strong trunk musculature, and the large infraorbital foramen indicate that H. chimborazi possessed a well-developed, elephant-like proboscis.

Mandible ( Figs 3C ; 5A ; 6 ; Table 3)

The mandibular corpus is relatively long and its labial side is moderately inflated. The corpus becomes deeper anteriorly at the level of the posterior mental foramen. Th e symphyseal portion is short (“brevirostrine”), massive, with no tusk or vestigial tusk alveoli ( Fig. 6 A-C). In MECN 82, on the labial side, there are three mental foramina: the most posterior one is the largest and is positioned at the level of mesial root of the m2 ( Fig. 6D ). The ascending ramus is slightly posteriorly inclined. Its anterior and posterior borders are parallel to one another. Th e posterior margin of the ramus is straight. It continues dorsally into the condylar process. Th is is dorso-caudally directed and bears a large and transversely elongated condyle. In anterior view, the condyle is very slightly medially inclined ( Fig. 6B ). Th e coronoid process is significantly lower than the condyle. On the lateral side of the ramus, there is a deep masseteric fossa, dorsally positioned, just below the sigmoid incisure ( Fig. 6D ). Th e posteroventral margin of the

C D E

fossa makes a marked step with the lateral surface of the ascending ramus. Anteriorly, the fossa becomes gradually shallower and the anterior margin is poorly defined.

At the very base of the anterior margin of the ramus, posterior to the linea obliqua, is a small and not well-delimited depressed surface ( Fig. 6D ). This structure is here named the lateral coronoid fossa (LCF). Th e LCF could represent the ventral-most point of insertion of the m. temporalis on the lateral side of the coronoid process (see Laub 1996).

The mandibular foramen is small and dorsally positioned on the medial side of the ramus, about 5 cm from the posterior border of the ramus. The ventral border of the foramen is V-shaped ( Fig. 6E ). The anterior border bears a small tuberosity, here interpreted as homologous to the lingula (linguoid process) described in elephants ( Beden 1979) and mammutids ( Laub 1996). Behind the mandibular foramen, at the posterior margin of the ascending ramus, below the condyle, there is a small depression probably for the m. pterygoideus externus. Still, on the medial side of both rami, near to the trigonus retromolares, is a well-developed coronoid foramen ( Fig. 6E ).

Discussion. The mandible of H. chimborazi closely resembles those of C. hyodon and “ S. ” platensis. Among the C. hyodon sample examined there are specimens (e.g., MUT J1, MUT J2) with relatively long and downward deflected symphyses. This primitive morphotype is unknown in H. chimborazi and “ S. ” platensis. Several juvenile mandibles of C. hyodon from Tarija, Bolivia (MUT) present small alveoli for the deciduous lower tusks ( Hoffstetter 1952; Ferretti 2008b). In one specimen (MUT-J69), a left deciduous tusk was indeed found in situ (Ferretti pers. obs). Both the tusk and the alveolus have an oval cross-section. No traces of lower incisors were found in the mandibles of any of the other brevirostrine gomphotheres considered. Stegomastodon texanus (AMNH 10622) differs from the SA gomphotheres here examined in possessing a lower and more backwardly oriented ascending ramus and the posterior opening of the mandibular canal (mandibular foramen) placed more ventrally on the medial side of the ascending ramus. Absence of a lateral coronoid fossa as described in H. chimborazi , in M. americanum , G. angustidens , G. productum , R. cf. falconeri, S. texanus , Anancus arvernensis , and elephants and its presence in “ S. ” platensis and C. hyodon suggests this is a derived feature of SA gomphotheres. Th e mandibles of Sinomastodon intermedius and S. hanjiangensis are morphologically very similar to those of South American gomphotheres, but apparently lack a coronoid fossa ( Teilhard de Chardin & Trassaert 1937; Tobien et al. 1986; Zong et al. 1989).

Dentition

Upper incisor (tusk; Figs 3A ; 5A, B ). Adults of H. chimborazi posses massive and relatively short upper tusks, oval in cross-section. The longitudinal axis of the tusk is distinctly upwardly curved and with no trace of torsion. The curvature becomes more evident as the tusk increases its length during growth, so that adult or, more in general, larger tusks are more curved than smaller juvenile tusks.In MECN 82, the left tusk has a maximum diameter of 115 mm and the length of the extralveolar part on the outer side is of 880 mm.

All known adult tusks of H. chimborazi lack enamel. Contrary to what was reported by Ficcarelli et al. (1995), the juvenile tusk MECN 258 from Bolivar also has no trace of enamel. However, a juvenile fragmentary skull with the DP 4 in use from the Late Pleistocene of Quebrada Los Milagros near Llano Chico (EPN V-1980; Hoffstetter 1952), bears a tusk with a distinct lateral enamel band. Th e enamel band is very thin and straight. The tusk is rectilinear, with a flattened sub-circular cross section and no torsion, that would exclude it from C. hyodon .

Cheek teeth ( Figs 7 ; 8 ; Table 4). Cheek tooth categories represented at the Bolivar sites are DP4- M3 and m1-m3. No permanent premolars (P3- P4-p3-p4) are present in the Bolivar sample nor among the La Carolina and Punin samples studied by Hoffstetter (1952). All intermediate cheek teeth (DP4-M2 and m1-m2) are trilophodont. M3s posses four lophs and a small distal talon ( Fig. 7C, D, I, J ). Th e fourth loph is sensibly narrower and with a more simple structure than the preceding ones. Th e lower m3s have four to five lophids and a distal talonid. Th ey possess welldeveloped pretrite central conules. The emerging wear figure is a typical trefoil pattern. In all molar categories, posttrite central conules could be either absent (morphotype a) or moderately developed (morphotype b). In the latter morphotype a poorly defined secondary trefoil pattern emerges in advanced stages of wear. Cement is absent or filling the very base of the interloph(id)s. Enamel is even and never wrinkled as in “ S. ” platensis. Two complete m3s from Bolivar (MECN 133, MECN 438;

A

Fig. 8F, H ) preserve their roots. Th e root of the second lophid is divided into two branches, with the mesial one joining the main anterior root and

the posterior one coalescing with the posterior root system, formed by the fusion of the roots of the third to fifth lophids.

Though no DP3s are present in the Bolivar dental sample, information on the anatomy of this tooth is given by Hoffstetter (1952) who describes, without figuring them, two isolated H. chimborazi DP 3s from the Late Pleistocene of Alangasi and Calderon, in the surrounding of Quito. Th e specimen from Alangasi (EPN V1244) is formed by three lophs and a small distal talon. Its size (length 56 mm; width 43 mm) is comparable to that the DP3 of C. hyodon from Tarija, where complete upper molar series are known (Boule & Th evenin 1920). Specimen EPN V1244 is, on the other hand, significantly smaller than the DP4s of C. hyodon and also than that from Q. Pistud, described above. In EPN V1244 only pretrite trefoils are present. Between the first and second lophs, at the labial end of the interlpohid, is a small cone (“bouton”). Th e enamel sectioned on the occlusal surface is rather wrinkled.

The second DP3 from Calderon (EPN V1231) is very similar to that from Alangasi both in size (57.3 mm in length; 47.5 mm in width) and morphology.

Discussion. The tusks of H. chimborazi differ from those of primitive gomphotheres (e.g., G. angustidens ) in being more robust, not downwardly curved and with no enamel band in adults.With respect to “ S. ” platensis and C. hyodon , the tusks of H. chimborazi are relatively shorter. Th e type specimen of “ S. ” platensis (MLP-8-1) possesses long and nearly straight tusks, a morphotype absent in Ecuadorian H. chimborazi . No adult tusks from Ecuador show traces of an enamel cover. Also, in the Aguas do Araxá sample described by Simpson & Paula Couto (1957), all tusks are without enamel. On the other hand, this occurs in some “ S. ” platensis isolated tusks from Argentina (MLP; material previously referred to a distinct taxon, Notiomastodon ornatus Cabrera, 1929 ) belonging to both juvenile and adult individuals (Ferretti pers. obs.). Therefore, even though the occurrence of an enamel band is a variable character in both H. chimborazi and “ S. ” platensis, the latter has a tendency to retain an enamel band in later stages of growth.

The morphology of H. chimborazi molars is generally conservative (as far as South American gomphotheres is concerned), very similar to the condition in C. hyodon , but with morphotypes that approach the more derived complex structure of “ S. ” platensis. Haplomastodon chimborazi is more progressive than species of Gomphotherium Burmeister, 1837 and Rhynchotherium Falconer, 1868 in the greater development of the accessory conules and in possessing well-developed tetraloph and pentalophid on M3 and m3 respectively. Th e most primitive NA bona-fide species of Stegomastodon , S. primitivus Osborn, 1936 from the Late Hemphillian to Early Blancan (Latest Miocene-Early Pliocene) of North America, is already more derived than H. chimborazi in possessing a more developed pentaloph on the M3 ( Osborn 1936). Ecuadorian H. chimborazi possesses DP3 with three lophs and a distal talon. This character is also present in C. hyodon and “ S.” platensis. As evidenced by Tassy (1990) and Shoshani (1996), the full development of a third loph in the DP3/dp3 could represent a distinct feature of SA gomphotheres, and a convergence with tetralophodont gomphotheres ( Tetralophodon Falconer, 1857 , Anancus , Paratetralophodon Tassy, 1983 ; Tassy 1985, 1990). Primitive trilophodon gomphotheres, like G. angustidens and G. productum , posses DP3/dp3s formed by two loph(id)s and a distal talon. Savage (1955) described a dp3 (UCMP 44749) of Stegomastodon mirificus from Cita Canyon, Texas, as consisting of three lophids, though the third one is much lower and structurally less complex than the anterior ones. A similar incipient development of the third loph(id) of the third deciduous premolars is observed in the juvenile material of Rhynchotherium edensis from Mt Eden, California, described by Frick (1926) and Osborn (1936).

Available evidence from Ecuador and Brazil ( Simpson & Paula Couto 1957) indicates that in Haplomastodon deciduous premolars are not replaced by permanent premolars. Th is derived feature is also known in C. hyodon (Boule & Th evenin 1920), in “ S.” platensis ( Cabrera 1929; Ferretti pers. obs.) and in NA Stegomastodon ( Shoshani 1996) . In contrast, P3-P4 are present in more primitive gomphotheriids from NA and Europe, like G. productum and G. angustidens ( Frick 1926; Tassy 1985, 1990). Evidence from a juvenile skull and mandible (AMNH 18218, 18216a, 18216b) of Rhynchotherium edensis from Mt. Eden, with the DP2-DP3/dp2-dp 3 in use and the M1/m1 already formed, indicates that this taxon also lacks permanent premolars ( Frick 1926; Osborn 1936). Loss of permanent premolars and the acquisition of a “horizontal tooth succession” is a derived trait among proboscideans, that evolved independently in several elephantoid lineages (e.g., mammutids, Anancus , and elephants; Tassy 1990). Shoshani (1996) regarded this trait as a possible synapomorphy of SA gomphotheres and NA Stegomastodon .

Axial skeleton

Atlas ( Fig. 9 A-G; Table 5). Th e dorsal arch is very stout, dorsally convex,with a strong dorsal tuberosity. Th e foramen for the passage of the vertebral artery

(lateral vertebral foramen), is large, oval in shape, and located near the cranial margin of the dorsal arch. Lateral and slightly ventral to the outer opening of the lateral vertebral foramen, a shallow groove extends to the cranial opening of the transverse foramen. Th e articular facets for the occipital condyles are deep and concave. Th e articular facets for the axis are almost circular in shape, low, and slightly concave dorso-ventrally.Th e transverse processes are large and well extended dorso-ventrally. The dorsal tubercle of both processes is strongly developed, and projects lateralward and dorsalward ( Fig. 9F ). The ventral tubercle is well developed though smaller than the dorsal one. Th e dorsal and ventral tubercles are separated by a notch. Th e transversal foramina are in most specimens unequally developed, with

Specimen Measures

MECN 82 1. Greatest breadth 251 2. Breadth of cranial articular surface 208 3. Breadth across the postzygapophyses 154 4. Breadth of caudal articular surface 154 5. Height of caudal articular surface 134 6. Greatest height 296 7. Height of the dorsal process 106 8. Greatest length 125

one foramen markedly larger than the opposite one (e.g., MECN 82 ; Fig. 9F ). Noticeably, in some specimens, as first noted by Hoffstetter (1952), one or both foramina are completely obliterated (e.g., EPN V2010; Fig. 9C, D ). A similar variability in size and presence/absence of transverse foramina of the atlas has been observed in the C. hyodon and “ S. ” platensis samples analyzed for this study. On the other hand, none of the other proboscideans examined show this feature .

Cervical vertebrae 2 to 7 ( Figs 9 H-K; 10A-H; Tables 6; 7). Five other cervical vertebrae of the Bolivar skeleton are preserved, identified as C2, C3, C5, C6, and C7 respectively. Th e axis possesses a very high dorsal arch ( Fig. 9H ) The spinous process is transversally enlarged and terminates with two dorsal tuberosities, separated by a central depression. On the caudal aspect of the process runs a narrow crest, and, lateral to this, on both sides, two intensely wrinkled grooves are present. The pedicles are long and robust. Th e vertebral body has a ventral crest that terminates caudally in a small tuberosity. Lateral to this crest, the ventral face of the body is cranio-caudally concave and transversally convex. Cranially, the two wide articular surfaces for the atlas are situated lateral to the stout odontoid process. Th e transverse processes are short and weak and are pierced by an oval-shaped transverse foramen. The process ends laterally with a tuberosity. Medial and ventral to the transverse process there is a small bony spine. A second, nearly complete axis from Punin (EPN V 3744) shows no traces of transverse foramina. On the other hand, two axes from La Carolina (EPN 1265, EPN 1287) described by Hoffstetter (1952) possess well-developed transverse foramina.

The body of C3 has a sub-circular shape in cranial view ( Fig. 10A, B ). On the ventral side runs a thin median crest. Th e laminae are thick. The spinous process is broken just above its base. It seems, however, to have been slender and not caudally bent. The vertebral foramen is triangular-shaped with a rounded vertex. Th e caudal vertebral incision consists, on both sides, in a groove running from the vertebral foramen to the transverse foramen. The transverse process is slender, and its dorsal root is ventrally sloping.Th e dorsal tubercle of the transverse process is caudally directed. Th e ventral tubercle forms a thin process, cranially directed.

The morphology of C5 is very similar to that of C3 ( Fig. 10C, D ). Th e transversal foramina are however larger than those of C3, while the ventral tubercle of the transverse process is smaller.

The body of C6 of MECN 82 is crushed dorsally ( Fig. 10E, F ). Th e vertebral foramen is wide. The spinous process is slender. Th e transverse processes are more robust relative to those of the previous vertebrae. Ventrally and caudally there is a robust process whose extremity forms a large tubercle (tuberculum caroticus) cranially directed.

In C7 the spinous process is incomplete; however, it was evidently larger than in the previous cervical vertebrae. Th e ventral portion of the body and the transverse processes are crushed and partly broken off. The facet for the articulation with the first left rib is partly preserved on the caudal face of the body. Th e transverse processes are dorso-ventrally expanded, laterally flattened and without transversal foramina.

Thoracic vertebrae ( Fig. 10 I-T; Table 7). Eleven vertebrae of the thoracic segment of the backbone of MECN 82 are preserved. Th e approximate position of each vertebra along the vertebral column was assessed by comparison with associated vertebrae of E. maximus and C. hyodon from Tarija. The cranialmost preserved thoracic vertebra is identified as a T2 or T3 (thereafter T2/T3) based on the size of the spinous process and the fact that it seems not to articulate with C7. Th e body is heart-shaped and its lateral sides are concave ( Fig. 10I, J ). On both sides, ventral to the base of the transverse process, there are two demi-facets, which articulate, with the heads of the second and third ribs. The incom- plete spinous process is large, caudally bent, and originally terminated into an apical tubercle. The cranial margin of the spinous process is sharp. The caudal one, on the contrary, is characterized by a

and lumbar vertebrae (see Appendix 2).

feeble median groove. Th e vertebral foramen is triangle-shaped. The very thick transverse processes end in a robust lateral tubercle, on the cranial side of which is present a small, dorsally oriented spine. The cranial articular processes (prezygapophyses) are well separated from each other.

In T3/T4 the body is longer than that of the preceding vertebra ( Fig. 10K, L ). Th e vertebral foramen is narrow, due to the position of the cranial articular processes. Th e spinous process is similar to that of T2/T3. The transverse processes are stout and laterally directed. The articular facet for the tubercle of the fourth rib is not evident. Also the cranial articular facet for the head of the rib is not well defined; it seems however to be positioned on the cranio-ventral margin of the transverse process. The caudal one is positioned laterally with respect to the body, near the dorsal margin.

The corpus ofT4/T5is heart-shaped ( Fig.10M, N ). The spinous process is strongly deflected caudally, probably as a consequence of taphonomic distortion. Th e cranial margin of the process is flattened, while on the caudal one runs a very deep groove. The transverse processes are more slender and the lateral tubercle is less pronounced with respect to the preceding vertebrae. Th e cranial articular facet for the head of the fourth/fifth rib is concave and dorso-ventrally elongated. Th e caudal one is wide, concave, semicircular-shaped and positioned lateral to the corpus.

T6/T7 has the same general characteristics as T4/ T5. It is missing its spinous process ( Fig. 10O, P ). The transverse processes are more dorsally positioned than in the preceding vertebrae. The caudal facet for the sixth/seventh rib is smaller than that of T4/T5.

Also in T7/T8 the spinous process is broken ( Fig. 10Q, R ). This vertebra is very similar in shape to the previous one. Th e transverse processes are incomplete, laterally and slightly cranially directed.

The shape of T9/T10 is similar to that of the preceding one ( Fig. 10S, T ). Only the proximal half of the spinous process is preserved. The groove occurring on the caudal side of the process is very deep, and the spine has a V-shaped cross section. Th e lateral processes are broken.

T11/T12 has a heart-shaped, and dorso-ventrally elongated body. Th e costal facets are close to each other and positioned dorsally on the body. Their dorsal margin is situated at about half of the ver- tebral foramen. Th e vertebral foramen has an oval outline. Th e spinous process is rather long and possesses a very sharp cranial margin. The lateral processes are broken.

T12/T13 is very similar in shape to the preceding vertebra. Th e spinous process is slender, long, and caudally inclined. A narrow notch with a rounded floor is found in a median position on the cranial margin of the dorsal arch. The transverse processes are laterally and dorsally directed. Th e costal articular facets are close to one another. The cranial facet is particularly deep and concave.

In T14/T15, the cranial and caudal costal articular facets are small, and well separated from one another. Th e spinous process is short and not so much inclined caudally. Th e cranial notch on the dorsal arch is deep. Th e transverse processes are dorso-laterally directed. Th ey have a dorsoventrally flattened base and each ends in a clubbed extremity. A stout crest, possibly homologous to the accessory tubercle of the lumbar vertebrae, is present on caudal margin of the transverse processes.

Two more posterior thoracic vertebrae are present, whose position is between T15 and the last thoracic vertebra. Th e corpus of the more anterior one is rather long. Th e spinous process is broken at its very base. A deep cranial groove runs on the dorsal arch. Th e right transverse process is broken, whilst the left one is only slightly damaged on its ventral side. Th e left process is short, dorsoventrally flattened and horizontal in direction. Dorso-cranially there is an elongated tubercle, which is homologous to the mammillary process of the lumbar vertebrae.

The second posterior thoracic is morphologically similar to the preceding one. It is damaged on the right side. It has, on both sides, only one cranial facet for the head of a rib. It bears a short spinous process, caudally inclined. The mammillary processes are large and positioned laterally to the cranial articular processes. The right transverse process is short, flattened and dorsalward and lateralward directed. It articulates with a rudimentary rib. Between the latter and the ventral side of the transverse process persists a small fissure. The caudal articular facet for the rib is absent.

Lumbar vertebrae ( Fig. 11 A-C, F; Table 7). Three lumbar vertebrae are preserved in MECN 82. The body of L1 is wide and thick ( Fig. 11A ). The pedicles diverge. Th e spinous process is broken. The cranial articular processes are very close to one another, and are separated only by a narrow fissure. The left transverse process is not preserved. The right one is short, thick and latero-caudally directed. The mammillary processes end in two small tubercles. Lateral to each mammillary process arises a bony lamina that reaches the cranio-dorsal margin of transverse processes, bounding a small foramen dorsally.

The body of L3 is subcylindrical in shape and dorso-ventrally flattened ( Fig. 11B ). The dorsal arch is thin. Th e distal part of spinous process is not preserved. It has a wide base. Th e vertebral foramen is wide. Th e transverse processes are broken at their bases. Th e mammillary processes end into two small tubercles cranially directed.

L4 has a markedly dorso-ventrally flattened body ( Fig. 11C ). Th e spinous process has a wide base. It is laterally flattened, short and caudally inclined. The cranial articular processes and the mammillary processes, on both sides, are fused together into a unique strong process, cranio-dorsally oriented. The transverse processes (costal processes) are thick and are laterally expanded, making up, caudally, a wide articular surface for the ileum ( Fig. 11F ).

Sacrum ( Fig. 11 D-F; Table 8). Th e sacrum of MECN 82 consists of the first, second and third sacral vertebra (in adult elephants the sacrum is formed usually by five sacral vertebrae that are fused at different times during the individual life history). Th e width of the vertebrae diminishes in a caudal direction. Th e ventral face of each vertebra is concave ( Fig. 11E ). Th e neural arch is low. All three vertebrae bear a spinous process strongly inclined caudally (in the third one it is broken) and two cranial articular processes, dorso-cranially directed ( Fig. 11F ). Th e vertebral canal is flattened and it narrows caudally. The first sacral vertebra has, lateral to the articular facets, a large mammillary process. Th e transverse processes are wide and flattened, ventrally directed and blended together to form the wrinkled lateral crest. Th e sacral wing is poorly developed. Laterally, the vertebrae are

Specimen Measures MECN 82 1. Greatest length c. 280 2. Greatest breadth 290 3. Breadth of second sacral vertebra 280 4. Breadth of thirdh sacral vertebra 253 5. Breadth of cranial articular surface 150 6. Height of cranial articular surface 92

separated from each other by a wide intervertebral space, where the supra- and sub-sacral foramina, respectively, are visible.

Caudal vertebrae ( Fig. 11 G-L). Th ree caudal vertebrae are attributable to individual MECN 82. All three vertebrae have an elongated body. The two most anterior caudals have cranial and caudal convex articular surfaces. Transverse processes are flattened, horizontal, and their length diminishes from the anterior-most to the posterior-most one. The dorsal arches have a base cranio-distally expanded. Cranial and caudal articular processes are button-like. Th e spinous process is extremely reduced and caudally oriented.

Ribs ( Fig. 11 M-W). Among the collected material, four ribs surely pertain to individual MECN 82. Most probably also specimens MECN 112, MECN 207, MECN 208, MECN 409, MECN 410, MECN 411, MECN 412, MECN 457 and MECN 470 belong to the same individual. The first rib is complete. It is short and slightly curved ( Fig. 11M, N ). Th e tuberculum is large and separated by a notch from the head. Th e latter has two facets, respectively for the seventh cervical and the first thoracic vertebrae. Th e tubercula of the consecutive ribs become gradually smaller and eventually disappear, while the bodies become longer and more curved.

Discussion. The observed asymmetry and variability in the degree of closure of the transverse foramina on the atlas and axis of H. chimborazi , C. hyodon and “ S. ” platensis could be consistent with a regres- sive process affecting skeletal structures no longer functional. A similar pattern can be observed in C7 of most mammals. In humans, for instance, the transverse foramina of the seventh cervical vertebra rarely give passage to the vertebral artery and vein, and they are generally smaller on one side or even absent ( Bell et al. 1950). The vertebral artery in humans usually passes in front of the transverse process of C7. A similar condition for the atlas and axis of H. chimborazi (and the other SA gomphotheres) is suggested here. According to this hypothesis, in H. chimborazi the vertebral artery ran cranially through the transverse foramina of C6-C3 and then just below the transverse processes of the axis and the atlas ( Fig. 9 ). Th en it turned upward passing laterally to the articular surface for the occipital condyle and entered the vertebral foramen passing through the lateral vertebral foramen. The latter is present in all the atlases of H. chimborazi examined, even in those with completely closed transversal foramina.It is diffi cult to assign any adaptive significance to the lack of transverse foramina on the first cervicals. Rather, it might represent an anatomic variation, quite frequent among SA gomphotheres, while extremely rare (if present at all) in other proboscideans (actually no other case has been described so far). In this case, it could represent the results of the so-called founder effect, supporting the hypothesis that all South American taxa derived from a single dispersal event.

The preserved vertebrae of MECN 82 indicate that the trunk region of H. chimborazi contained a minimum of 16-17 vertebrae (extant elephants typically possess from 19 to 21 thoracic vertebrae). All thoracic vertebrae of H. chimborazi possess backwardly bent spinous processes. The inclination increases in the anterior thoracics (T2 to T5), remains nearly constant from T5 to about T12 and then decreases in the remaining posterior vertebrae. Compared to G. sylvaticum and G. productum , the spinous processes of the anterior thoracics of H. chimborazi are more backwardly bent, suggesting the head was kept in a more elevated posture in the latter taxon. In H. chimborazi , the length of the spinous processes increases from (T1) T2 to T5 and rapidly decreases passing from the fifth thoracic to consecutive vertebrae.

On the basis of the preserved thoracic vertebrae of MECN 82, it can therefore be deduced that the dorsal outline originally produced by their spinous

processes ( Fig. 20 ) should have been similar to that observed in complete specimens of M. americanum (see Olsen 1979) and in “ S. ” platensis ( Ferretti 2008a).

Appendicular skeleton

Scapula ( Fig. 12 A-C; Table 9). In both scapulae of the Bolivar skeleton, the ossified dorsal cartilage is not fused, and only that of the right scapula was retrieved ( Fig. 12A ). Th e supraspinous fossa is subrectangular and fairly concave. The infraspinous fossa, more extended caudally than the former, is sub-triangular. Its cranial portion is concave and the caudal portion is convex. The scapular spine is prominent and terminates ventrally into an anterior acromian process (processus hamatus) and a posterior metacromian process (processus suprahamatus), separated by a shallow triangular surface. Th e acromian process is more developed than the metacromian one. Th e medial (costal) face cranially displays a shallow subscapular fossa and is rather convex in the central portion ( Fig. 12B ). In the dorsal half of the costal surface there is a wide, extremely rough triangular area for the origin the m. serratus ventralis. Caudally, the surface is flat and is delimited by the caudal angle of the scapula. The glenoid cavity is sub-rectangular, with the main axis directed cranio-caudally. Th e cavity is markedly concave cranio-caudally, and is less concave transversally. Th e supraglenoid tubercle is situated cranially to the glenoid cavity. The coracoid process is poorly developed and forms a short crest along the medial aspect of the glenoid cavity. The supraglenoid tubercle is not ventrally bent to a great extent ( Fig. 12A ).

Humerus ( Fig. 12 D-G; Table 10). In the MECN 82 skeleton the left humerus is fractured at the epicondylar crest, while the right one is complete and undeformed. Th e epiphyses are fused to the shaft. Th e bone appears rather massive. The epicondylar crest, for the extensor of the forearm, is well developed. Th e deltoid tuberosity is moderately developed.

The tuberosity for m. teres major and m. latissimus dorsi is weakly pronounced and proximally positioned. Th e proximal epiphysis is massive and dominated by the articular head. Th is is very convex both dorso-caudally and latero-medially. The articular surface is wide at the center, tapers cranially and caudally. Medially and posteriorly, it is limited by a sulcus. Th is is distinct on the medial side, separating the articular surface from the medial tuberosity (trochine). Th e articular head is separated from the bicipital groove by the lateral tuberosity, which projects above the head. The distal articular surface is strongly convex antero-posteriorly. The trochlea is well developed, with a deep median depression, while the lateral border is weak and practically integrated with the condyle. Th e articular surface is delimited antero-proximally by a large coronoid fossa confluent to the radial fossa. Posteriorly, there is a deep olecranon fossa, bordered by the epicondyle and epitrochlea. Relative to the humerus long axis, the distal articular surface is latero-distally sloping. The humerus to ulna physiological length ratio in MECN 82 is 1.4.

Ulna ( Fig. 13 A-D, H, I; Table 11). The ulna is relatively slender. Th e medial margin is flat and displays marks for the interosseous tendon. The epiphyses are completely fused with the shaft. The olecranon is massive and medially bent. The top of the olecranon is enlarged and rough with two tuberosites, one proximal, the latter medial. The semilunar notch is deeply concave vertically, convex transversally. Th e medial articular surface for the trochlea of the humerus is more developed than the lateral one, for the condyle, and dorsally-medially has a small articular area for the radius. The distal extremity of the ulna is slightly bent laterally. A strong styloid process occurs laterally. On the medial side, there is a wide diarthrodial surface for the radius. A subtriangular surface occurs distally for the pyramidal, formed by a palmo-lateral condyle, and is concave dorsally. Dorso-medially there is a small articular facet for the lunar. The articular surface for the pyramidal continues palmarly in a proximal direction and fuses with the facet for the pisiform.

Among the H. chimborazi remains from the Q. Cuesaca site there is a juvenile right ulna (MECN 458; Fig. 13H, I ) belonging to a calf. The olecranic epiphysis is not fused to the shaft and was not retrieved. Distally the shaft is fractured at is palmar side, while dorsally it reaches to the diarthroidal surface for the distal epiphysis. A likely juvenile character is the slenderness of the shaft.

Radius ( Fig. 13 E-G; Table 12). In MECN 82, the radii do not have completely fused distal ends. The shaft is narrow and flat is its proximal part, and thickens distally, assuming a triangular cross section. Th e bone axis in concave palmarly and has a lateral bending in its upper part. The proximal end, bearing the surface for the humerus and the ulna is laterally expanded. Th e surface for the humerus is trapezoidal and concave antero-posterirorly. It is divided in three parts: the lateral-most part contributes with the ulna to the articulation with the condyle of the humerus. Th e middle part is convex and forms the coronoid process. The medial-most part is part of the articulation for the humeral trochlea. Palmarly and distally is the articular facet for the ulna and distally to it, an extremely rough triangular area for the insertion of tendons. The distal end, more voluminous than the proximal one, displays a triangular cross section. The articular facets for the lunar and the scaphoid are found on distal face of the radius. Both facets continue for a short distance on the palmar side. The articular facet for the lunar is laterally positioned and has a saddle form: palmarly convex and dorsally concave. The surface for the scaphoid is medial to the convex portion of the articulation for the lunar, and is also concave. In dorsal view the two surfaces form an angle of about 160°.

Carpus ( Figs 14 ; 15 ; Table 13). Only three carpals from the right side and four from the left side of the Bolivar skeleton are preserved.Articular surfaces of each element of the carpus are schematically depicted in Figure 14 .

In lateral view the scaphoid (radial carpal bone; Figs 14B, C ; 15 A-C) is triangular. Th e medial aspect is concave and rough. A large tuberosity, that projects above the proximal margin, is found on the dorsal margin of the scaphoid. A groove occurs distal to this tuberosity, and reaches to the distal margin of the bone. With its upper extremity it articulates with the radius (proximally) and with the lunar (medially). Th e lower extremity presents the facets for the lunar (dorsally), the magnum (palmarly), the trapezoid, and the trapezium (distally and palmarly).

The lunar (intermedium carpal bone; Figs 14 D-F; 15D-H) is proximo-distally fl attened, and subtriangular in proximal view. Th e proximal face bears the articulation for the radius and the ulna. The former is saddle-like. A strong margin divides, laterally, the surface for the radius from that for the ulna. Th e latter is very small, laterally facing, palmodorsally concave and convex proximo-distally. The dorsal aspect of the bone is sub-rectangular and very rough. Th e palmar angle is formed by a voluminous square tuberosity. Th e lateral and medial faces are irregular and dorso-palmarly elongated. Both bear on the proximal and distal margins the articular surfaces for the neighbouring carpals.

The lateral process of the pyramidal (ulnar carpal bone; Figs 14G ; 15 I-K) is not palmarly curved as in elephants. Th e pisiform (accessory carpal bone; Fig.14H ) is massive, with the distal tubercle slightly bent medially. It possesses two articular surfaces: proximally is a smaller one for the tibia and below, on the anterior face, a larger one for the pyramidal. The trapezoid (second carpal bone; Figs 14 I-L; 15L-O) has a triangle-like shape in proximal view. The proximal face is occupied by the articulation for the scaphoid. Th is is wide dorsally and narrow palmarly. The medial margin is straight, while the lateral one forms a saddle-like articulation for the magnum. In specimen MECN 82 the sinuosity of the lateral margin of the trapezoid is indeed not particularly pronounced. There is no evidence of a distinct facet for the lunar on the proximal face of the trapezoid, even though the latter might have articulated with the lunar along its dorso-lateral edge. Th e distal face has the articular face for Mc2. The dorsal face is planar and rough. Th e palmar margin is made up by a rounded tuberosity. Th e articulation for the trapezium is found on the medial face of the pyramidal. On the lateral face there are three facets for the magnum. Th e dorsal one is the larger, running from the proximal to the distal margin. A third, smaller facet for the magnum occurs in a palmar position, near the distal margin of the bone.

The magnum (third carpal bone; Figs 14 M-P; 15P-S) is a quadrangular bone. Th e dorsal face has a squared outline and is very rough. Th e lateral face is trapezoidal and bears a large facet for the unciform. A second oval facet for the unciform is present dorsally, in proximity of the distal margin of the bone. Palmarly and distally there is a large hooked tubercle, distally directed. Th e medial side of the magnum has centrally a deep fossa for the interosseous ligaments. A quadratic articular facet for the trapezoid is present along the dorsal margin of the medial side. This facet has a prolongation running palmarly and proximally bordening the central fossa.Th e prolongation reaches the proximo-palmar facet for the trapezoid. A small fiissure separates the proximal facet from the distal facet for the trapezoid. The latter is linked to the dorsal facet through a dorsally sloping crest. The proximal face is quadrangular. Palmarly, on the medial margin, a process bears the articular surface for the scaphoid. For this reason, the medial margin has a sinuous outline, complementary to that of the lateral margin of the trapezoid. The proximal face is occupied by the articular surface for the lunar and, on the palmar angle, by that for the scaphoid. The articular surface is markedly convex palmarly and concave dorsally. Th e palmar face has a triangular outline. At the distal vertex of the triangle is a large tubercle, distally bent. Th e distal face is concave palmo-dorsally, and bears the articular facets for Mc2 and Mc3. Th e articular facet for the Mc2 does not reach the dorsal margin.

The unciform (fourth carpal bone; Figs 14 Q-S; 15T-W) is a massive bone, possessing a trapezoidal outline.Th e proximal face slopes laterally and articulates with the pyramidal. Th e unciform articulates distally with the third, fourth and fifth metacarpals. Palmarly, the surface for the Mc5 is contiguous with that of the pyramidal. Two large surfaces for the magnum occur on the medial face.

Metacarpus ( Fig. 16 ; Table 14). Three metacarpals are preserved. Mc5 is very short ( Fig. 16A, E, H ). The proximal articular surface is divided into two facets: a medial one for the unciform and a lateral one articulating with the lateral process of the pyramidal. Th e lateral face is proximally protruding, forming a tubercle from which a crest departs, dividing the facet for the unciform from that for the pyramidal.

Mc4 Mc3

Measures MECN 82 1. Maximum length of pelvis 1110 2. Maximum length of ilium: from tuber coxae to tuber sacrale 840 3. Length of the symphysis 420 4. Diagonal height of pelvic aperture: from the pubic symphysis to the lowest point

490 of the tuber sacrale

5. Diagonal height of pelvic aperture: from the pubic symphysis to the most caudal point

480 of the tuber sacrale

6. Maximum width of pelvic aperture, between the iliac crests 460 7. Maximum breadth across the acetabula 760 8. Width between eminentiae iliopubicae 420 9. Smallest height of caudal margin of cranial branch of pubis 80 10. Smallest height of cranial margin of cranial branch of pubis 63 11. Smallest height of medial branch of ileum 54 12. Smallest breadth of the shaft of ileum 207

Mc4 is shorter than Mc3 ( Fig. 16B, F, I ). The proximal articular surface is convex and articulates with the unciform. Medially, the surface for the Mc3 does not reach the dorsal margin. Th e palmar tubercle is more slender than that of the Mc3.

The body of Mc3 is sub-cylindrical, sturdy, and flattened dorso-palmarly ( Fig. 16C, G, J ). Its dorsal face is convex, the lateral and medial faces are flat,and the palmar face is slightly concave proximo-distally. The proximal extremity is palmo-dorsally elongated. Proximally, it bears an extended articular surface divided by a sagittal crest. Th e medial articular facet is for the magnum. This has a trapezoidal outline and narrows palmarly. It is dorso-palmarly convex and medially sloping. Th e lateral facet articulates with the unciform. It is dorso-palmarly convex, transversely concave except in its palmar edge, where it is strongly inclined laterally. It is less extended palmarly than the facet for the magnum. Th e two facets are at an angle to one another. Th e crest dividing the two facets is dorsally elevated, forming a prominence,which slopes and then rises again palmarly. In proximal view the crest appears slightly wavy. Articulations for Mc4 and Mc2 are located, respectively, on the lateral and medial sides. A large tubercle is present palmarly, hanging over the palmar face.Th e distal extremity is larger than the proximal one. Th e large articulation for the proximal phalanx is concave transversely and convex dorso-palmarly. A slightly convex facet for the sesamoids bones is found palmarly.

A second right metacarpal (MECN 462; Fig.16D ), not belonging to the MECN 82 skeleton, is present among the Bolivar sample. Th e facet for the trapezoid is dorso-palmarly extended, while that for the trapezium occupies only the palmar half of the proximal surface.

Pelvis ( Fig.17 ; Table 15). Both halves of the pelvis of the MECN 82 skeleton are preserved. The acetabulum is directed caudally and ventrally. It is bounded by a sub-circular rim, and interrupted ventrally by a deep acetabular notch. Th e cranial portion of the lunate surface is less developed than the caudal one. Dorsally to the acetabulum, the ischial spine forms a sturdy and short tuberosity.On the cranial surface, at the point of junction with the pubis, the prominent ileo-pubic eminence reaches dorsally and laterally the short and weak arcuate line. Lateralward to the iliac eminence, a wide surface for the attachment of the m. rectus femuris is present.

The iliac wing arises from the median part of the hipbone through a short, cranially flattened and transversely broad, neck. Th e iliac wing is greatly extended transversally, and is cranially inclined. The gluteal (external) surface is plane, and it bends caudally at the level of the sacral tuberosity. The gluteal lines are well marked. Th e pelvic (internal) surface has a sub-triangular outline, is cranially oriented and it is bounded by the arcuate line medially and by the ventral margin of the ilium laterally. The internal surface is slightly concave. Along the arcuate line no tuberculum for the m. psoas minoris has been observed.

The arcuate line reaches dorsally the sacral tuberosity, and separates the pelvic surface from the sacral one. Th e latter is medially oriented, at an angle with the pelvic surface. Th e sacral surface is rough. Ventrally, an amphiarthrosial surface articulates with the sacrum, just below the iliac tuberosity. A cranially oriented amphiarthrosis for the fourth lumbar vertebra is situated cranially to the sacral surface. The crest of the ilium is thick and rough, ventrally and laterally directed.Th e crest ends ventro-laterally into an expanded coxal tuberosity. The ischiopubic part of the hipbone has a squared outline, with one of the vertex represented by the acetabulum. At the center, the great obturate foramen displays an oval outline, with the greater axis sagittally oriented. The body of the pubis enters into the formation of the acetabulum, of which it forms the ventral and cranial parts. Th e cranial branch of the pubis is robust and has an oval cross-section. Its dorsal surface is transversely concave, while the anterior one (pectineal surface) is planar. The caudal surface is crossed by the oblique obturator crest, which forms part of the medial margin of the obturator sulcus. Th e medio-cranial angle of the ischiopubic part is thick. Ventrally, it supports a robust ventral pubic spine. The caudal branch of the pubis is thin, depressed and fully fused to the ischium. Its medial border presents the symphysial surface.

The medial branch of the ischium is flattened and very short. It is continuous with the caudal branch of the pubis. Th e lateral branch of the ischium is characterized by torsion and joins the body of the ischium. Th e latter forms the caudal portion of the acetabulum. Th e cranial portion of the medial margin of the lateral branch of the ischium participates in the formation of the pubic symphysis. The caudal margin of the ischiatic table forms a thick and rough vertical margin, ventrally and medially directed. Th e dorsal extremity forms the tuberosity of the ischium. With its fellow the caudal margin constitutes the ischiatic arch. This has a V shape and its vertex is open ventrally.

Femur ( Fig. 18 A-E; Table 16).Th e femora of MECN 82 have both epiphyses fused to the shaft. Th e shaft is long, subcylindrical and flattened cranio-caudally. Narrow in the central portion, it widens approaching the extremities.Proximally, at about one third of the length of the medial margin, there is an elongated prominence slightly caudally placed, probably a homologue of the lesser trochanter. The head of the femur is perfectly hemispheric and delimited by a thick crest from the neck ( Fig. 18E, B ). Caudally there is, along the crest, a small round depressed surface for the femural ligament. Th e trochanter is massive, less elevated than the head and expanded cranio-caudally. Distally, the trochanter forms a robust margin, which integrates into the caudal margin of the lateral face of the shaft.

The distal extremity presents the condyles and, anteriorly, the patellar surface ( Fig. 18E ). The medial condyle is larger and more elongated than the lateral one. It is also slightly bent laterally, while the lateral one is rotated clockwise. From this it follows that the lateral condyle reaches a more distal plane than the medial one. Th e medial epicondyle is more developed than the lateral one. Two deep fossae, possibly for the insertion of the lateral knee ligament and m. popliteus, respectively, are found on the lateral side of the lateral condyle. The patellar surface is relatively large and characterized by wide median concavity.

Patella ( Fig. 18F, G ). Th e kneecap has an elliptic outline. Th e cranial face is convex and rough. The caudal face is flat and bears the articulation for the trochlea. The proximal margin has a small tubercle. Th e distal margin is flat.

Tibia ( Fig. 18 H-M; Table 17). Th e tibia has a prismatic-shaped shaft. Th e proximal portion is more expanded than the distal one. Th is is very evident in lateral view. Th e articular surface for the lateral condyle of the femur is sub-oval and concave. Caudally is the small facet for the fibula. The articulation for the medial condyle is circular and more expanded cranio-caudally. The distal extremity is trapezoidal in outline. On the distal face there is a square surface for the astragalus and latero-caudally a smaller facet of the fibula. A strong medial malleolus borders medially the articulation for the astragalus, on the medial side.

Fibula ( Fig. 18M ; Table 18). In the MECN 82 skeleton, the left fibula lacks the proximal epiphysis, while the right one is complete. Th e proximal extremity of the fibula widens to form the head of the bone. On the cranio-medial faces a rounded surface for the tibia occurs. Caudally and laterally there are two tuberosities for ligaments. The lateral face of the distal extremity is convex and very rugose. The medial face bears a complex set of articular surfaces. At the base of a large fossa there is the articulation for the tibia, dorsally oriented.Ventrally and laterally to this there is a triangular articulation surface for the astragalus. On the ventral face there is a concave surface, which articulates with the calcaneum.

Tarsus ( Fig. 19 A-E; Table 19). Of the tarsus of the MECN 82 skeleton, only the astragalus is represented. No other tarsals are present in the Bolivar sample. The right astragalus is complete and not deformed. The surface for the tibia is rectangular, and mediolaterally more elongated in comparison with that of elephants. On the lateral margin is the surface for the fibula. The medial tubercle is poorly developed. The surface for the navicular (central tarsal bone) occupies the two thirds of the antero-distal (dorso-distal) side. The two surfaces for the calcaneum are well separated from each other by a deep sulcus for the attachment of ligaments on the postero-distal (palmo-distal) side ( Fig.19E ). Th e ligamentous surface widens anteriorly. The medial surface (sustentacular) for the calcaneum is bean-shaped and dorso-palmarly directed.The lateral surface (ectal) is oval, with its major axis directed laterally and anteriorly (dorsally).

Metatarsus ( Fig. 19 F-Q; Table 14). Five metatarsals of the Bolivar skeleton are preserved.Th ese are markedly shorter than the metacarpals.Th e proximal extremity of Mt1 ( Fig.19 F, J, N ) has an oval outline.The distal one is much more transversely expanded.

The proximal articular surface of Mt3 (Fig. G, K, O) is triangular and transversely concave. The articulation for the sesamoids forms two distinct condyles.

The proximal extremity of Mt4 is medially rotated ( Fig. 19H, L, P ). Th e proximal articular surface is triangular and almost entirely devoted to the articulation with the cuboid.

Discussion. The postcranial material of H.chimborazi from Bolivar is characterized by a large amount of size variability, without exhibiting any clear (sexual) dimorphic pattern. Th e mean size of the gompho- there from Bolivar, as can be deduced from the skeletal elements ( Tables 2-19), is greater than that of C. hyodon , while it is similar to that of “ S.” platensis. The postcranium of H. chimborazi shows a typical elephantoid pattern. Haplomastodon chimborazi displays, however, a more robust skeleton than both Gomphotherium (e.g., G. sylvaticum ; Tassy 1977) and more derived elephantoids such as A. arvernensis and elephantids.

Brevirostrine and longirostrine elephantoids are characterized by a different proportion between the bones of the anterior limb ( Ferretti 1998). In many longirostrine forms (e.g., Gomphotherium ), the humerus to ulna physiological length ratio is about 1, whilst in brevirostrines it is usually higher than 1.2 (e.g., A. arvernensis = 1.3-1.4; in elephantines is>1.25). In H. chimborazi (MECN 82) the humerus to ulna ratio is 1.4, displaying thus a typical “brevirostrine” limb proportion.

The structure of the basipodial of H. chimborazi is typically elephantoid. Haplomastodon chimborazi possesses relatively short basipodials,similarly to other gomphotheres ( Fig. 16K ). Some elements posses interlocking surfaces.Th e whole structure appears very robust and firm, a possible adaptation to traversing uneven grounds. Th e available material prevents us from knowing whether in H. chimborazi the lunar articulated distally with the trapezoid, producing the so-called aserial carpus ( Weithofer 1889). However, the condition in C. hyodon and “ S. ” platensis, as reported by Boule & Th evenin (1920: 60), is aserial. In A. arvernensis , a brevirostrine ghomphotere from the Old World, the superposition of the lunar on the trapezoid is markedly more developed than in SA gomphotheres.Such differences could have important functional implications related to limb posture and feeding habits ( Ferretti & Croitor 2001).

SIZE, ONTOGENETIC STAGE AND GENDER DETERMINATION OF INDIVIDUAL MECN 82 Estimates based on humerus length using Harington et al. (1974) methods and direct measurements of the associated anterior limb, indicate a shoulder height for individual MECN 82 of about 2.5 m. Body mass estimates for MECN 82, obtained using shoulder height-mass equation based on exant Asian elephant ( Roth 1990), is 3125 kg.

The ontogenetic stage of individual MECN 82 was assessed through the stage of skeletal fusion (especially that of the bones of the skull and of the limbs) and, independently, on the base of the molar progression (dental stage), by comparison with the pattern of skeletal fusion and dental progression in living elephants ( Sikes 1966; Roth 1994). Th e cranial sutures of MECN 82 are not discernible, except for the zygomatics, which are yet not fused with the zygomatic processes of the maxillary and of the temporal, and were collected separately from the cranium. In extant elephants the zygomatic remains detached until late in the life of the animal. Among the Elephas maximus samples examined (ACM, MNHN, MSNFZ, NHM) there are specimens with the M 3 in use that still have not completely fused zygomatic arches. In the MECN 82 postcrania, the dorsal epiphysis of the scapula is completely detached, and the distal radius suture is still open, while in the rest of the bones the epiphyses are well knit. MECN 82 has the M 2 in use and the M3 erupting, with wear facets on the first three loph(id)s.

Both the stage of skeletal fusion and the dental progression methods are consistent with MECN 82 representing a prime adult individual (see Roth 1994; Sikes 1966). In terms of African elephants molar age (AEMA; Sikes 1966) MECN 82 died at an age of approximately 25-30 years.

Sexual dimorphism in proboscideans is well marked. In osteological specimens it is revealed by the larger size of the skeletal elements of the males ( Deraniyagala 1955; Haynes 1991), the size and robusticity of the tusks ( Haynes 1991; Averianov 1996), the morphology of the skull ( Beden 1979; Averianov 1996) and by the morphology of the pelvis ( Haynes 1991; Kroll 1991; Lister & Agenbroad 1994; Lister 1996; Göhlich 2000). A number of studies have demonstrated that fossil probo- scideans display an amount of sexual dimorphism comparable to that of modern elephants (see Tassy 1996b and Haynes 1991 and citations therein).The strength and size of the skeletal elements, and of the tusks, indicate that MECN 82 is a male. The proportions of the pelvis, in particular the relative width of the pelvic aperture and the thickness of the acetabular region, are comparable with those reported for male elephants ( Table 20; Haynes 1991; Kroll 1991; Lister & Agenbroad 1994; Lister 1996; Göhlich 2000).

Figures

FIG. 2. — Diagrammatic representation of the skull of Haplomastodon chimborazi (Proaño, 1922) from Q. Chalán, Punin, Ecuador (holotype, now destroyed), left lateral view (based on Spillmann 1931). Scale bar: 10 cm.

FIG. 3.— Haplomastodon chimborazi (Proaño,1922) from Q.Pistud,Bolivar,Ecuador,skull (MECN 82):A, cranium,anterior view;B, cranium (cast),antero-dorsal view (tusks havebeen removed);C, cranium andmandible,posterior view;D, cranium (cast),ventral view.Abbreviations used in Figures 3-5: eam, external acustic meatus; ena, external nasal aperture; FR, frontal; id, incisura dentalis;if, infraorbital foramen; inf, incisive fossa; ipm, infraorbital process of maxillary; MX, maxillary; M2, second upper molar; M3 third upper molar; mf, mandibular fossa; NA, nasal;nc, nuchal crest;nf, nuchal fossa;npp, nasal process of premaxillary; o,opening on the internal lateral face of the nasal aperture, leading to perinasal fossae; OC, occipital; occ, occipital condyle; PA, parietal; PM, premaxillary; ppf, post-orbital process of frontal; snf, subnasal fossa; TE, temporal; zpm, zygomatic process of maxillary; zpt, zygomatic process of temporal. Scale bar: 10 cm.

FIG. 4. — Anterior view of skull, showing anatomical details of the anterior nasal aperture: A, Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador (MECN 82); B, Elephas maximus Linnaeus, 1758 (Recent; MCZR). Abbreviations: see Figure 3. Scale bar: 10 cm.

FIG. 5. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, skull (MECN 82); A, cranium and mandible in right lateral view; B, cranium in left lateral view; C-E, right molar in medial, lateral, and anterior views. Abbreviations: see Figure 3. Scale bars: 10 cm.

FIG. 6. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, mandible (MECN 82): A, B, D, mandible in occlusal, anterior (cast), and left lateral view; C, detail of the ventral aspect of the symphysis (anterior to the bottom); E, medial view of the left ascending ramus. Abbreviations: cf, coronoid foramen; lcf, lateral coronoid fossa; ling, linguoid process; m2, second lower molar; m3, third lower molar; maf, masseteric fossa; mf, mandibular foramen; pmf, posterior mental foramen. Scale bar: 10 cm.

FIG. 7. — Haplomastodon chimborazi (Proaño, 1922) from Bolivar, Ecuador, upper and lower second and third molars (M2/m2 and M3/ m3): A, B, left M2 (MECN 82) in occlusal and lingual views; C, D, left M3 (MECN 82) in occlusal and oblique lingual views; E, F, left m2 (MECN 82) in occlusal and oblique labial views; G, H, left m3 (MECN 82) in occlusal and oblique labial view; I, J, left M3 (MECN 4) from Q. Cuesaca, in occlusal and labial (reversed) views. Abbreviations: aprcc, anterior pretrite central conule; lamc, labial main cone; limc, lingual main cone; mscl, mesoconelets; pprcc, posterior pretrite central conule. In all figures, mesial is to the left. Scale bar: 5 cm.

FIG. 8. — Haplomastodon chimborazi (Proaño, 1922) from Bolivar, Ecuador, mandibles and lower molars: A, B, left mandibular body with m3 (MECN 437; Q. Pistud) in lateral and occlusal views; C, D, incomplete right half mandible with m3 (MECN 147; Q. Cuesaca), in lateral (reversed) and occlusal view; E, F, right m3 (MECN 189; Q. Pistud), in occlusal and lingual views; G, H, right m3 (MECN 438; Q. Pistud), in occlusal and lingual views; I, J, left m3 (MECN 272; Q. Cuesaca), in occlusal and lingual (reversed) views. Abbreviation: mar, main anterior root. In all figures, mesial is to the left. Scale bar: 5 cm.

FIG. 9. — Haplomastodon chimborazi (Proaño, 1922),from Ecuador (various localities), first (atlas) and second (axis) cervical vertebrae: A, B, atlas (MECN 271; Q.Cuesaca, Bolivar) in cranial and caudal views; C, D, atlas (EPN V2010; La Carolina, S. Elena Peninsula), in cranial and caudal views; E-G, atlas (MECN 82; Q. Pistud, Bolivar), in cranial, caudal, and left lateral views; H-K, axis (MECN 82), in cranial, caudal, ventral and left lateral views. Abbreviations: dt, dorsal tubercle of transverse process; ovf, outer opening of lateral vertebral foramen; tf, transversal foramen; vt, ventral tubercle of transverse process. Scale bar: 5 cm.

FIG. 10. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, posterior (C3-C7) cervical and anterior dorsal (T2-T9) vertebrae (MECN 82): A, B, C3, in cranial and caudal views; C, D, C5, in cranial and caudal views; E, F, C6, in cranial and caudal views; G, H, C7, in cranial and caudal views; I, J, T2, in cranial and caudal views; K, L, T3 or T4, in cranial and caudal views; M, N, T4 or T5, in cranial and caudal views; O, P, T6 or T7, in cranial and caudal views; Q, R, T7 or T8, in cranial and caudal views; S, T, T9 or T10, in cranial and caudal views. Abbreviation: ct, carotic tubercle. Scale bar: 5 cm.

FIG. 11. — Haplomastodon chimborazi (Proaño,1922) from Q.Pistud,Bolivar,Ecuador,lumbar vertebrae,sacrum and caudal vertebrae (MECN 82): A, L1, cranial view; B, L3, cranial view; C, L4, cranial view; D, E, sacrum, in cranial and ventral view; F, L3-L4 and sacrum in anatomical connection, dorsal view; G-L, caudal vertebrae in dorsal and cranial views; M, N, first left and right costae;O-R, anterior costae; S-U, intermediate costae; V, W, posterior costae. Scale bars: A-L, 5 cm; M-W, 10 cm.

FIG. 20. — Reconstruction of the skeleton of Haplomastodon chimborazi (Proaño, 1922), based on MECN 82 and the Punin skull. Scale bar: 10 cm.

FIG. 12. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, anterior limb bones (MECN 82): A-C, right scapula, in lateral, medial, and articular views; D-G, right humerus, in anterior, lateral, posterior, and medial views. Abbreviations: dt, deltoid tuberosity; ec, epicondilar crest; lt, lateral tuberosity; mt, medial tuberosity. Scale bar: 10 cm.

FIG. 13. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, anterior limb bones: A-D, right ulna (MECN 82), in anterior, proximal, lateral and medial views; E-G, right radius (MECN 82), in lateral, anterior and medial views; H, I, incomplete right ulna of a newborn calf (MECN 458), in proximal and anterior views. Scale bars: A-G, 10 cm; H, I, 5 cm.

FIG. 14. — Schematic representation of Haplomastodon chimborazi (Proaño, 1922) carpals and third metapodial, showing extention of articular surfaces for contiguous bones (based on the Bolivar sample). All bones are from the right manus. A, reconstruction of the right manus, dorsal aspect (based on “S.” platensis, MNHN-PAM191) showing the position of various autopodial bones; B, C, scaphoid in lateral and distal views; D-F, lunar, in dorsal, lateral, and medial views; G, pyramidal, proximal view; H, pisiform, dorsal view; I-L, trapezoid, in distal, proximal, medial and lateral views. It is not possible to asses if the trapezoid articulates with the lunar (area enclosed by dotted line); M-P, magnum, in proximal, distal, medial, and lateral views; Q-S, unciform, in proximal, distal, and medial views; T, U, proximal end of right Mc3, in dorsal and proximal views. Abbreviations: lu, lunar; ma, magnum; Mc1, first metacarpal; Mc2, second metacarpal; Mc3, third metacarpal; Mc4, fourth metacarpal; Mc5, fifth metacarpal; pi, pisiform; py, pyramidal; ra, radius; sc, scaphoid; td, trapezoid; tr, trapezium; ul, ulna; un, unciform.

FIG. 15. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, carpal bones (MECN 82): A-C, left scaphoid, in dorsal, medial and lateral views; D-H, left lunar, in dorsal, medial, lateral, proximal and distal views; I-K, right pyramidal, in dorsal, proximal and distal views; L-O, left trapezoid,in dorsal,medial,lateral and proximal views;P-S, right magnum,in dorsal,lateral,medial and proximal views; T-W, right unciform, in dorsal, lateral, medial and proximal views. Scale bar: 5 cm.

FIG. 16. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, metacarpals and partial manus: A, E, H, right Mc5 (MECN 82), in dorsal, medial, and proximal view; B, F, I, right Mc4 (MECN 82), in dorsal, medial and proximal views; C, G, J, right Mc3 (MECN 82), in dorsal, medial and proximal views; D, right Mc2 (MECN 462), dorsal view; K, partial manus (cast) with magnum (ma), unciform (un), third (Mc3), fourth (Mc4), and Fifth (Mc5) metacarpals in anatomical connection, dorsal view. Scale bar: 5 cm.

FIG. 17. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, pelvis (MECN 82): A, cranial view; B, caudal view. Abbreviations: ac, acetabulum; al, arcuate line; arf, area for m. rectus femoris; carp, caudal ramus of pubis; crp, cranial ramus of pubis; ct, coxal tuberosity; il, corpus of ileum; ilc, iliac crest;ilt, iliac tuberosity;ilv, iliac wing; ipe, ileo-pubic eminence; is, ischium; isi, incisura ischiatica; iss, ischiatic spine; ist, ischiatic tuberosity; obc, oblique obturator crest; of, obturator foramen; sas, sacral surface; st, sacral tuberosity; sy, ischio-pubic symphysis. Scale bar: 10 cm.

FIG. 18. — Haplomastodon chimborazi (Proaño, 1922), from Q. Pistud, Bolivar, Ecuador, hindlimb bones (MECN 82): A-E, left femur, in anterior, proximal, posterior, medial and distal views; F, G, right patella, in anterior and posterior views; H-L, left tibia, in proximal (anterior to the bottom), anterior view, posterior, distal (anterior to the bottom) and lateral views;M, N, right tibia and fibula in anatomical connection, in posterior and distal views. Scale bars: A-E, H-N, 10 cm; F, G, 5 cm.

FIG. 19. — Haplomastodon chimborazi (Proaño, 1922) from Q. Pistud, Bolivar, Ecuador, astragalus, metatarsals and phalanx (MECN 82): A-E, right astragalus, in dorso-distal, proximal, medial, dorsal and distal views; F, G, N, right Mt1, in dorsal, medial and proximal views; G, K, O, left Mt3,in dorsal, medial and proximal views; H, L, P, left Mt4,in dorsal,medial and proximal views; I, M, Q, left proximal phalanx, in dorsal, medial and proximal views. Abbreviations: ecs, ectal surface; fis, articular surface for the fibula; nas, articular surface for the navicular; sus, sustentacular surface; tis, articular surface of the tibia. Scale bar: 5 cm.