Cardiatherium paranense ( Ameghino, 1883a ) Francis and Mones, 1965a

Vucetich, María Guiomar, Deschamps, Cecilia M., Vieytes, Emma Carolina & Montalvo, Claudia I., 2014, Late Miocene capybaras from Argentina: Skull anatomy, taxonomy, evolution, and biochronology, Acta Palaeontologica Polonica 59 (3), pp. 517-535 : 523-528

Cardiatherium paranense ( Ameghino, 1883a) Francis and Mones, 1965a

Figs. 4 , 5 .

1883 Hydrochoerus paranensis ; Ameghino 1883a: 104–105.

1883 Cardiatherium Doeringi ; Ameghino 1883b: 270–274.

1885 Contracavia matercula ; Burmeister 1885: 158–159.

1885 Cardiatherium petrosum ; Ameghino 1885: 50–51.

1885 Cardiatherium denticulatum ; Ameghino 1885: 51.

1885 Cardiatherium minutum ; Ameghino 1885: 54.

1885 Procardiatherium simplicidens ; Ameghino 1885: 55–58.

1885 Procardiatherium crassum ; Ameghino 1885: 58–59.

1885 Cardiodon Marshii ; Ameghino 1885: 61–64.

1885 Cardiodon? Leidyi ; Ameghino 1885: 64–65.

1886 Plexochoerus paranensis ( Ameghino, 1885) ; Ameghino 1886: 58.

1886 Anchimys Leidyii ( Ameghino, 1885) ; Ameghino 1886: 72–74.

1889 Plexochoerus adluis ; Ameghino 1889: 252–253.

1889 Plexochoerus lynchi ; Ameghino 1889: 910.

1891 Eucardiodon affinis ; Ameghino 1891: 247.

1891 Procardiotherium denticulatum (Ameghino) ; Ameghino 1891: 248.

1891 Eucardiodon marshi ; Ameghino 1889: 249.

1927 Procardiotherium septemlaminatus ; Kraglievich 1927: 597.

1927? Procardiotherium octolaminatus ; Kraglievich 1927: 598.

1934 Procardiotherium septemlaminatus ; Kraglievich 1934: 83–84.

1934 Cardiotherium sp. ; Rusconi 1934: 180.

1940 Anchimysops radicei ; Kraglievich 1934: 322.

1940? Anchimysops dubius ; Kraglievich 1934: 323–324.

1940 Procardiotherium (Eocardiotherium) septemlaminatus ; Kraglievic 1940: 326–329.

1945 Plexochoerus paranensis (Ameghino) ; L. Kraglievich in Kraglievich 1945: 453–454.

1

1

2

2

3

3

1945 Plexochoerus petrosus (Ameghino) ; L. Kraglievich in Kraglievich 1945: 455.

1945 Cardiotherium rothi ; Kraglievich 1945: 456.

1961 Plexochoerus sp. ; Pascual and Bondesio 1961: 106.

1965 Cardiatherium lynchi (Ameghino) ; Francis and Mones 1965a: 31. 1965 Cardiatherium paranensis (Ameghino) ; Francis and Mones 1965a: 30.

1965 Cardiatherium rothi ; Francis and Mones 1965a: 27.

1965 Cardiatherium adluis (Ameghino) ; Francis and Mones 1965a: 31. 1979 Eucardiodon cf. marshi ; Mones and Castiglioni 1979: 80–81.

1984 Anchimys marshi (Ameghino) ; Mones 1984: 3.

1984 Kiyutherium denticulatum (Ameghino) ; Mones 1984: 4.

1984 Procardiatherium matercula (Burmeister) ; Mones 1984: 5.

1985 Kiyutherium scillatoyanei ; Bondesio 1985a: 276.

1986 Procardiatherium (Eocardiotherium) septemlaminatum ; Mones 1986: 204.

1991 Cardiatherium sp. A (Pascual and Bondesio); Mones 1991: 31.

1991 Anatochoerus inusitatus ; Vucetich and Mones in Mones, 1991: 32.

1991 Contracavia minuta (Ameghino) ; Mones 1991: 35.

1993 Kiyutherium aff. orientalis ; Yrigoyen 1993b; nec Pascual and Bondesio, 1985.

For further details regarding changes and modifications to this systematic list, see Mones (1991).

Neotype: MLP 40-XI-15-1 designated by Mones (1991), right mandibular fragment with p4–m3 (see Mones 1991; Vucetich et al. 2005: fig. 9E). The holotype, currently lost, was an isolated and fragmentary M3, the only cranial material so far assigned to this species.

Type specimens of synonymised species: Anatochoerus inusitatus Vucetic and Mones in Mones, 1991, MLP 87-XI-1-27, incomplete skull with both P4–M3; Anchimys leydi ( Ameghino, 1885) , MLP 73-I-10-5, anterior fragment of mandible with both incisors and right p4 alveolus; Anchimys marshii ( Ameghino, 1885) , MLP 73-I-10-7, right mandible with i, p4–m3;? Anchimysops dubius Kraglievich, 1934 , MACN 9055, right M3; Anchimysops radicei Kraglievich, 1934 , MACN 3353, right M3; Cardiatherium denticulatum Ameghino, 1885 , MPCNP? (lost specimen, cast MLP M-27), isolated right m1 or m2; Cardiatherium doeringi Ameghino, 1883b , MLP 73-I-10-11, fragment of left mandible with p4–m1; Cardiatherium minutum Ameghino, 1885 , MLP 69-XII-2-19, anterior left palatal fragment with anterior root of the zygomatic arch and P4–M1; Cardiatherium petrosum Ameghino, 1885 , MLP 69-XII-2-16, fragment of left mandible with i, p4–m1; Cardiotherium rothi Francis and Mones, 1965a , MACN unknown number (lost specimen), right M3; Contracavia matercula Burmeister, 1885 , MACN 1049, anterior fragment of palate with anterior root of the zygomatic arch and both P4; Contracavia matercula Burmeister, 1885 , MACN 1050, anterior fragment of palate with anterior root of the zygomatic arch, both P4, and anterior prisms of both M1; Eucardiodon affinis Ameghino, 1891 , MACN 5890, fragment of right mandible with the base of incisor and m1–2; Kiyutherium scillatoyanei Bondesio, 1985a , MLP 78-II-27-1, fragment of right mandible with p4–m3; Plexochoerus adluis Ameghino, 1889 , unknown repository (lost specimen), left M3 ( Ameghino 1889: pl. 79: 4, 4a); Plexochoerus lynchi Ameghino 1889 , unknown repository (lost specimen), palatal fragment with both M1–3 ( Ameghino 1889: pl. 79: 6, 13); Procardiatherium crassum Ameghino, 1885 , unknown repository (lost specimen, cast MLP M-22), left p4; Procardiatherium octolaminatum Kraglievich, 1927 , MACN 8934, M3 and part of the skull including the left parietal and frontal; Procardiotherium (Eocardiotherium) septemlaminatum Kraglievich, 1927 , MACN 3336, incomplete skull with both P4–M3; Procardiatherium simplicidens Ameghino, 1885 , MLP 73-I-10-8, fragment of left mandible with p4–m2.

Referred material.—MACN 13434, anterior fragment of palate with anterior root of the zygomatic arch, both P4 and right M1; MACN 13465, fragment of palate with left P4–M3 and right M1–2; MACN 13469, anterior fragment of palate with anterior root of the zygomatic arch, right P4–M2 and left P4–M3; MLP 40-XI-15-2, anterior fragment of palate with anterior root of the zygomatic arch, right P4–M2 and left P4–M3; MLP 41-XII-13-1, isolated M3; MLP 41-XII-13- 153, right anterior fragment of palate with anterior root of the zygomatic arch and P4–M3; MLP 41-XII-13-161, isolated M3; MLP 41-XII-13-161a, isolated M3; MLP 41-XII-13- 171, isolated M3; MLP 41-XII-13-233, isolated M1 or M2; MLP 41-XII-13-233a, isolated M2?; MLP 41-XII-13-291, isolated M3; MLP 52-X-5-75a, isolated M3; MLP 71-VI-16-1, anterior portion of skull with complete dentition, albeit somewhat damaged ( Fig. 4B ; see Historical background); MLP 87-XI-1-1, anterior fragment of palate with anterior root of the zygomatic arch, both P4 and left M1; MLP 87- XI-1-2, isolated M3; MLP 87-XI-1-3, anterior fragment of palate with anterior root of the zygomatic arch, left P4 and both M1; MLP 87-XI-1-3a, anterior fragment of palate with anterior root of the zygomatic arch and both P4–M2. For material not included in this analysis (mandibles and lower teeth), see Vucetich et al. (2005).

Differential diagnosis.—Portion of rostrum anterior to the anterior margin of the zygomatic root wider than in C. aff. orientalis Pascual and Bondesio, 1965b and C. patagonicum Vucetich, Deschamps, Olivares, and Dozo, 2005 ; palate at the level of M3 wider than in C. aff. orientalis and C. patagonicum ; attachment areas for masseter superficialis muscle anteriorly convergent; angle formed by anterior root of the zygomatic arch and alveolar plane smaller than 20° in lateral view; distance between base of the incisive foramen and middle point between both P4s shorter than in C. aff. orientalis ; broad incisive foramen; base of P4 projected lateral to the occlusal surface in ventral view, thus forming a conspicuous bulge immediately dorsal to the anterior margin of the anterior root of the zygomatic arch; cheek teeth with flexi/flexids deeper than in C. chasicoense ( Pascual and Bondesio, 1968) ; lower cheek teeth with secondary internal flexid and tertiary internal flexid shallower than in C. patagonicum .

Description

Skull.—The description of the skull is mostly based on MLP 87-XI-1-27, the holotype of Anatochoerus inusitatus , because it is the most complete ( Figs. 4A , 5 ). This specimen, originally described by Vucetich and Mones (in Mones 1991), is marked by peculiar roll-shaped expansions located at the anterior part of the rostrum involving the dorsolateral margin of the premaxilla and a short anterolateral portion of the maxilla, which led to the description of the genus Anatochoerus and its own subfamily Anatochoerinae (see Mones 1991). The porous appearance of the bone forming these protuberances is different from the rest of the skull, changing transitionally within the premaxillae and maxillae. Work is in progress to determine whether these structures are normal or represent a pathological condition. The premaxillae are absent in all other specimens from the “conglomerado osífero”, except for MACN 3336 (holotype of Cardiatherium septemlaminatum ), in which the ventromedial portions of these bones have been preserved. The specimen from Tupungato (MLP 71-VI-16-1, described below) lacks such expansions ( Fig. 4B ), but it should be noted that it is a juvenile.

In ventral view, the palate is relatively flat (as opposed to concave in H. hydrochaeris ), and the tooth rows are conspicuously divergent, with M3 being approximately in line with P4–M2. The length of the diastema located between the anterior margin of the alveolus of P4 and the posterior margin of the alveolus of I1 exceeds the combined length of P4–M3, and is comparatively much longer than in H. hydrochaeris . In the juvenile MLP 71-VI-16-1, the diastema is 3.2% longer than P4–M3 (diastema: 32 mm; P4–M3: 31 mm), which increases to 27% in the largest available specimen, MLP 87-XI-1-27 (75 mm and 59 mm, respectively). This demonstrates the lengthening of the rostrum with age, which is also seen in H. hydrochaeris , although in the modern species the diastema is always shorter than the combined length of P4– M3 (25.1/ 37.2 mm in the juvenile MLP 2033, and 67.9/ 79.3 mm in the adult MLP 2031). The rostrum is wider than in any other hydrochoerine, and almost doubles in width both anterior and posterior to the anterior root of the zygomatic arch, relative to its width at the level of prism I of P4 ( Fig. 5A ). This relative increase in rostral width—at least along the posteriormost part of the diastema—is related to the lateral projection of the base of P4 relative to both its own occlusal surface and the rest of the upper dentition (e.g., MLP 87-XI- -3a, MLP 87-XI-1-3, MLP 41-XII-13-153, MACN 13468), which forms a conspicuous bulge immediately dorsal to the anterior margin of the anterior root of the zygomatic arch Figs. 4A 1 , 5A ). By contrast, the base of P4 is not so conspicuous and is completely located above the anterior root of the zygomatic arch in H. hydrochaeris . Both the width of the rostrum and the degree of outward protrusion of P4 seem to increase with age, although this is not certain owing to the incompleteness of the available material.

The incisive foramen is sub-rectangular in outline and equidistant between P4 and the incisors, with the premaxillary portion of the premaxillary septum being divided into two rami; the foramen is large, but looks narrow transversely when compared with the wide diastema. The transversely oriented premaxillary-maxillary suture crosses the incisive foramen at its midpoint and is broadly exposed on the wide palate. The suture is mostly straight, but turns anteriorly near the lateral border of the rostrum. The base of the zygomatic arch is oriented posterolaterally (MLP 87-XI-1-3a; Fig. 3C ), rather than laterally as in H. hydrochaeris , and bears the origin of the masseter superficialis muscle. The muscle scars are oval, run parallel to the dental series, and converge anteriorly Fig. 5A ). They begin on the posterior margin of the anterior root of the zygomatic arch (corresponding to the level of prisms I/II of P4), and extend up to half the distance between the base of the incisive foramen and the anterior margin of the alveolus of P4, but never beyond the anterior margin of the anterior root of the zygomatic arch. In other specimens, these scars begin at the level of the posterior border of P4 MLP 87-XI-1-3a; Fig. 3A, B ).

The suture between the maxilla and the palatine originates from the alveolar margin next to prism V of M3, and then abruptly turns medially at the level of prism II, before turning again and running anteriorly to the base of the palatine foramen ( Figs. 4A 1 , 5A ). Thus, the anterior portion of the palatine is reduced to one third of its posterior width, which results in the maxilla forming a relatively large part of the palate. By contrast, the palatines are V-shaped in H. hydrochaeris , and the maxillary-palatine suture diverges from the alveolar margin gradually at the level of prism X of M3. The large palatal foramina (MLP 87-XI-1-3a, MACN 13469) are located at the level of M2 and extend anteriorly, before merging with each other at the level of P4. The mesopterygoid fossa is wide and has a straight anterior margin reaching the last prism of M3. In other specimens (e.g., MACN 3336), the fossa is deeper and reaches the antepenultimate prism (note that the number of prisms increases with size/age). Between the mesopterygoid fossa and M3, there is a conspicuous sulcus.

In dorsal view ( Fig. 5C ), the ascending apophyses of the premaxillae are slightly convergent posteriorly, whereas they are parallel in Hydrochoerus hydrochaeris . The naso-frontal suture is concave anteriorly, instead of almost straight as in H. hydrochaeris , and extends posteriorly beyond the fronto-premaxillary suture, with the frontals protruding as a wedge between the posteriormost portions of the nasals. The maxilla is broadly exposed on the skull roof, dorsal to the posterior portion of the rostral masseteric fossa, and is limited anterodorsally by the ascending apophysis of the premaxilla, posterodorsally by the frontal, and posteriorly by the lacrimal. The fronto-parietal suture is almost straight. The skull roof is depressed medially along the posterior portions of the frontals and the interparietal suture. In MACN 8934, the single specimen in which the posteriormost part of the skull is preserved, this depression does not continue posteriorly beyond the anterior portions of the parietals. The latter narrow posteriorly to form temporal fossae separated by a plane area without a sagittal crest, as in H. hydrochaeris .

In lateral view, the nasals are domed, facing mostly laterally and forming roughly half of the height of the rostrum in lateral view ( Fig. 5B ). At their centre, the nasals form a gibbous prominence. The masseteric fossa is short anteroposteriorly, with an anterodorsally oriented dorsal border (as opposed to being slightly anteroventral as in H. hydrochaeris ) ( Fig. 5B ), and does not extend anteriorly beyond the anteriorly convex portion of the premaxillary-maxillary suture. The dorsal root of the antorbital bar is located ventral to the level of the dorsalmost portion of the masseteric fossa. The anterior root of the zygomatic arch is inclined anterodorsally-posteroventrally with respect to the alveolar plane, at an angle of less than 20º ( Fig. 5B ). Dorsal to the roots of M1–2, and posterior to the protuberance formed by P4, there is a large and ventrally concave foramen representing the most anterior part of the nasolacrimal canal, which runs between P4 and M1 and opens into the nasal cavity.

MLP 69-XII-2-19 (holotype of Cardiatherium minutum ) is a left anterior skull fragment preserving P4–M1 and the anterior root of the zygomatic arch. It is markedly smaller than MLP 87-XI-1-27 ( Tables 1 and 2). According to Mones (1991), the rostrum of this specimen is not as broad as that of MLP 87-XI-1-27, but our new data demonstrate that it is also rather wide. The scar marking the origin of the masseter superficialis muscle also resembles that of MLP 87-XI- 1-27 in its orientation and shape, but is deeper and has clearly defined margins. This is the only specimen that preserves a small portion of the zygomatic arch. The latter is dorsoventrally compressed near the base, in the area of the origin of the masseter superficialis muscle, before becoming laterally compressed further anteriorly. This condition is also seen in other Plio-Pleistocene genera (e.g., “ Chapalmatherium ”, Neochoerus Hay, 1926 ), but not in H. hydrochaeris , in which the zygomatic arch remains dorsoventrally compressed up to the antorbital bar.

The small individual from Tupungato (MLP 71-VI-16-1; Fig. 4B ) is here considered to be extremely young because of its size and the porous condition of the bone in some areas. In this specimen, the maxillo-palatine suture is completely open, although it should be noted that even in adult individuals of H. hydrochaeris the number of open sutures may be high ( Wilson and Sánchez-Villagra 2009). MLP 71-VI-16-1 shares with the specimens from the “conglomerado osífero” a wide rostrum, large incisive foramina, a laterally displaced socket of P4 located immediately dorsal to the anterior root of the zygomatic arch, laterally facing nasals forming almost half of the height of the rostrum in lateral view, and markedly divergent tooth rows. It differs from MLP 87-XI- 1-27 in having a masseteric fossa extending anteriorly beyond the premaxillary-maxillary suture ( Fig. 4B 2 ), as well as the lack of rostral protuberances. This is the only specimen preserving a large portion of the lacrimal, which is a very large bone occupying the anterodorsal part of the orbit. The lacrimal foramen is located far ventrally.

Upper dentition ( Fig. 6A–L ).—Incisors: Only MLP 71-VI-16-1 preserves small, extra-alveolar fragments of both incisors ( Fig. 4B 2 ). Unlike in H. hydrochaeris , the latter lack a longitudinal furrow and are subtriangular in cross section, with their anteroposterior diameter exceeding their transverse one.

P4: Like M1–2, P4 comprises two prisms separated lingually by the fundamental internal flexus. Labially, each prism shows an additional flexus, the primary external flexus in prism I, and the secondary external flexus in prism II. The primary external flexus is oriented posterolingually and extends along more than 50% of the total transverse width of prism I in the largest specimens. The secondary external flexus is shallower than the primary one, V-shaped, and extends beyond the end of the fundamental internal flexus ( Fig. 6I–K ). The first prism of P4 is transversely narrow, and the labial margin of its posterior portion (prism Ib) bears an incipient flexus in some specimens. This feature does not seem to be size-related. Prism II is wider transversely than prism I, and longer anteroposteriorly than the second prisms of the molars, which tend to be laminar.

M1–2: The anterior two molars resemble each other, and differ from P 4 in their anteroposteriorly somewhat shorter, but transversely wider, prism I. As in P4, prism Ib shows a slight flexus on the labial margin in some specimens. Prism II is almost laminar. In the largest specimens, the primary external flexus extends along more than 50% of the total transverse width of prism I.

M3: The number of prisms increases with size, ranging from six plus a little incipient last prism in the smallest specimen (MACN 3353, holotype of Anchimysops radicei ; Fig. 6A ), to seven plus an incipient last one in MLP 87- XI-1-2 and MLP 40-XI-15-2 ( Fig. 6D, E ), to eight with an incipient last one in MLP 87-XI-1-27 ( Fig. 6J , holotype of Anatochoerus inusitatus ), and finally nine plus an incipient last one in MLP 41-XII-13-161a and MLP 41-XII-13-161, the largest complete specimen ( Fig. 6L ). The number of prisms seems to become stable at ten, since the latter two specimens have the same number despite differing in size (see Table 2). Prism I is heart-shaped as in the other cheek teeth, with the primary external flexus being deeper than the other external flexi. The rest of the prisms are laminar with a labial flexus, except for the ninth. The two last prisms are narrow transversely.

Geographic and stratigraphic range.—All of the specimens except MLP 71-VI-16-1 come from the “conglomerado osífero” (“bonebed conglomerate” sensu Behrensmeyer 1991; Rogers et al. 2007), exposed at the cliffs of the Paraná River near Paraná City, Entre Ríos Province; Huayquerian South American Land Mammal Age (SALMA), Late Miocene ( Cione et al. 2000). MLP 71-VI-16-1 comes from the Río de los Pozos Formation, exposed at Tupungato, Mendoza Province

Fig. 1 : locality 6), estimated to be no younger than 5.8 Ma and no older than 8.2-7.4 Ma, Late Miocene ( Chiaramonte et al. 2000; Irigoyen et al. 1995).

Figures

Fig. 4. Late Miocene capybara Cardiatherium paranense (Ameghino, 1883a). A. MLP 87-XI-1-27, holotype of Anatochoerus inusitatus Vucetich and Mones in Mones, 1991, Río Paraná cliffs. B. MLP 71-VI-16-1, juvenile specimen, Tupungato. In ventral (A , B ), lateral (A , B ), and dorsal (A , B ) views.

Fig. 5. Late Miocene capybara Cardiatherium paranense (Ameghino, 1883a), MLP 87-XI-1-27, holotype of Anatochoerus inusitatus Vucetich and Mones in Mones, 1991 from Paraná River cliffs, Huayquerian SAL- MA, in ventral (A), lateral (B), and dorsal (C) views.

Fig. 1. Map showing the localities mentioned in the text. 1, Paraná, Entre Ríos Province; 2, Laguna Guatraché and Laguna Chillhué, La Pampa Province; 3, Arroyo Chasicó, Buenos Aires Province; 4, Albardón, San Juan Province; 5, Rincón Chico, Chubut Province; 6, Tupungato, Mendoza Province; 7, Barrancas de San Gregorio, San José, Uruguay.

Fig. 3. Late Miocene capybara Cardiatherium paranense (Ameghino, 1883a), MLP 87-XI-1-3a, from Paraná River cliffs, Huayquerian SALMA, in ventral (A, B) and left lateral (C, anterior to left) views. A. Skull measurements. B. Skull landmarks: 1, posterior limit of anterior root of the zygomatic arch; 2, lateralmost point of prism I of P4, measured on the alveolar rim; 3, anteriormost point of scar marking the origin of the masseter superficialis muscle; 4, anterior limit of anterior root of the zygomatic arch; 5, midpoint of posterior margin of incisive foramen; 6, midpoint between both P4s at the level of prism I on the maxillary suture.C. Skull landmarks: 1, posterior end of incisive foramen; 2, anterior limit of anterior root of the zygomatic arch; 3, posterior limit of anterior root of the zygomatic arch; 4, point between M1 and M2 on the alveolar plane; 5, point between P4 and M1 on the alveolar plane; 6, point in front of P4 on the alveolar plane; α, angle formed by the anterior root of the zygomatic arch and the alveolar margin of the cheek teeth in lateral view.

Fig. 2. Tooth nomenclature (A), measurements (B), and landmarks (1–8)/ semilandmarks (small circles) (C) on right P4 of Cardiatherium paranense Ameghino, 1883a). 1, labial end of prism I; 2, lingual end of prism I; 3, maximum depth of fundamental internal flexus; 4, lingual end of prism II; 5, labial end of prism II; 6, maximum depth of primary external flexus; 7, labialmost point of isthmus; 8, maximum depth of secondary external flexus.

Fig. 6. Occlusal view of the right upper teeth of Late Miocene capybaras Cardiatherium paranense (Ameghino, 1883a) (A–L) and C. aff. orientalis (M, N). C–E, H, N, reversed. A. MACN 3353, M3. B. MLP 71-VI-16-1, P4–M2. C. MLP 69-XII-2-19, P4–M1. D. MLP 87-XI-1-2, M3. E. MLP 40-XI-15- 2, P4–M3. F. MLP 87-XI-1-3, P4–M1. G. MLP 41-XII-13-153, P4–M3. H. MLP 87-XI-1-1, P4–M1. I. MLP 87-XI-1-3a, P4–M2. J. MLP 87-XI-1-27, P4–M3. K. MACN 13434, P4–M1. L. MLP 41-XII-13-161, M3. M. GHUNLPam 5236, P4–M1. N. GHUNLPam 14452, P4–M3.