Conepatus sanmiguelensis, Wang & Carranza-Castañeda, 2008

Wang, Xiaoming & Carranza-Castañeda, Óscar, 2008, Earliest hog-nosed skunk, Conepatus (Mephitidae, Carnivora), from the early Pliocene of Guanajuato, Mexico and origin of South American skunks, Zoological Journal of the Linnean Society 154 (2), pp. 386-407 : 388-398

CONEPATUS GRAY, 1837

CONEPATUS SANMIGUELENSIS SP. NOV.

( FIGS 4–10 ; TABLE 1)

Holotype: IGM 7800 , nearly complete cranium with left I1-M1 and right I1-2, I3 alveolus, C, P2 alveolus, and P3-M1; proximal end of left humerus, complete right tibia, one complete and one partial thoracic, complete sacrum, and rib fragments. Collected by Hilda Tronconso and volunteers of the Earth Watch programme in July 2002.

Type locality and geology: GTO 75 (MPGJ 272), Coecillos area, Arroyo de Emilio (20°59.97′N 100°45.88′W), San Miguel de Allende Basin, State of Guanajuato, Mexico ( Miller & Carranza-Castañeda, 1984; Carranza-Castañeda, 2006). The GTO 75 locality sits on top of a ravine ( Fig. 1 ), and the sediments are thin-bedded, thinly laminated, light grey to light buff coloured mudstones.

Referred specimens: IGM 7801 , isolated left C and P3–4, right C, P3–M1, partial left dentary with c and p2–m1, partial right dentary with i1–c and p4–m1, 4 partial cervicals, 1 thoracic, 3 caudals, partial right scapular, proximal right humerus and partial left humerus, partial left and right radius–ulna, partial left and right hands with two pathological proximal and middle phalanges, distal right tibia, distal left tibia–fibula, left and right calcanea and astragali, partial left and right feet. From GTO 75 locality, in the same horizon as the holotype ( Fig. 2 ). Collected in 2005.

IGM 7802, right mandible fragment with m1 and m2 alveolus, from locality JAL TECO 9 La Asunción in a deep arroyo located in the Santa Maria village in the southern part of the Tecolotlán basin about 100 km south of Guadalajara City, in Tecolotlán (Jalisco) graben. The associated fauna is of late Hemphillian age and consists of Dinohippus mexicanus , Astrohippus stockii , Neohipparion eurystyle , Nannippus aztecus , Teleoceras fossiger , Megatylopus matthewii , Hexobelomeryx sp. and? Gomphotherium .

Fauna, strata, and age: The Coecillos area (GTO 30) is an extensive area in San Miguel de Allende basin, where abundant Hemphillian fossil material was discovered. It is located in the middle of a small valley surrounded by small hills of andesitic basalt. Continued search in the well-exposed badlands allowed the discoveries of additional localities with Hemphillian, Irvingtonian and, recently in a small hill in the northeast of the area, Blancan faunas. The oldest fossils discovered in this area were Calippus (Grammohippus) hondurensis and Dinohippus interpolatus in La Presa locality (GTO 44), and we assign an age of earliest late Hemphillian. Typical Hemphillian fossils have been collected from the GTO 30 locality, including Astrohippus stockii , Dinohippus mexicanus , Neohipparion eurystyle , Nannippus aztecus , Teleoceras fossiger , Machairodus sp. , Notolagus velox , Hypolagus sp. and Paenemarmota cf. P. barbouri , as well as Catagonus cf. C. brachydontus , Megatylopus cf. M. matthewi , Texoceros sp. and Hexobelomeryx fricki ( Fig. 3 ).

One of the important localities discovered in recent years in the middle of this area is GTO 75 Arroyo de Emilio (type locality of Conepatus sanmiguelensis ). It is a small ravine where Hemphillian fossils were collected. The lower layer of the stratigraphic sequence is a deposit of about 40–60 cm of grey volcanic ash. Above this, the sediment is composed of laminated sandy clay with abundant irregular concretions of calcium carbonate ( Fig. 3 ). The thickness of this layer is variable from 2 to 5 m. Almost all of the fossil materials known from this site were collected in the top of this layer, including Dinohippus mexicanus , Astrohippus stockii , Catagonus brachydontus , Paenemarmota cf. P. barbouri and Hexobelomeryx fricki, ( Carranza-Castañeda, 2006: 53) . This layer is covered by light-yellow clay, when exposed to weathering, but has a brownish colour when freshly exposed. The thickness of this layer is about 0.75– 1.50 m. It is in this layer where the skunk material was collected, associated with Paenemarmota cf. P. barbouri , as well as some isolated teeth of Dinohippus mexicanus and other materials.

In erosional unconformity, all of the Hemphillian sequence is covered by a very fine clay of grey colour when freshly exposed. The thickness of this layer is variable, 1– 2 m. In this layer a Glyptotherium shield with an associated jaw was collected, a site named GTO 78 Arroyo de Emilio-Gliptodon. In the same layer at different sites, a jaw, one fragment of a skull and several isolated teeth of Equus were collected, in addition to Thomomys and Hypolagus sp. This fauna is assigned to the Irvingtonian based on the horse material and the presence of Thomomys sp.

The stratigraphy of the JAL TECO 9 Santa Maria area consists of layers of oxidized clay with reddish colour, sandy clay and several palaeochannels with sandy gravels. The Conepatus specimen (IGM 7802) was collected in a clay layer towards the top of this sequence. All of the fossiliferous sediments are covered by lacustrine sandy layers that crop out in almost all the Santa Maria area. Above the lacustrine sediments is an important clay-bed sequence that contains volcanic ash dated at 4.89 ± 0.16 Ma by the 40 Ar/ 39 Ar method ( Kowallis et al., 1998).

Fossils associated with the skunk jaw fragment (IGM 7802) in the JAL TECO 9 locality are isolated teeth and plates of Crocodylu s sp., Megalonyx sp. , abundant horse material belonging to Dinohippus mexicanus , Neohipparion eurystyle and Nannippus aztecus , a few isolated upper teeth of Astrohippus stockii , Teleoceras fossiger , Machairodus cf. M. coloradensis , Canis ferox , Rhynchotherium sp. , Megatylopus matthewi and Hexobelomeryx fricki .

Etymology: Referring to the San Miguel de Allende Basin, from where the holotype was collected.

Diagnosis: Among genera of mephitids, Conepatus sanmiguelensis possesses the following derived characters to indicate membership within the Conepatus clade: retracted external nasal opening (presence of a ‘hog-nose’), loss of condyloid canal, elongation of M1, high-crowned P4 and m1 talonid equal or longer than trigonid. C. sanmiguelensis is distinguished from South American species ( C. talarae , C. chinga and C. humboldtii ) in its large size, condyloid foramen merged within the posterior lacerate foramen, presence of a P2, more quadrate M1 (anteroposterior length = transverse width) and more elongated M1 relatively to P4. In contrast to North American species ( C. leuconotus and C. robustus ), C. sanmiguelensis is distinct in the following primitive characters: frontal sinuses less inflated, paroccipital process horizontally orientated, P2 present, P4 shearing blade less high-crowned and more dorsally curved, M1 protocone low-crowned and M1 lingual cingulum lacking a ridge connecting to postprotocrista. C. sanmiguelensis is distinguishable from the Central American C. semistriatus plus the extinct South American C. altiramus in the lack of an entoconulid on m1 and in the presence of a P2.

DESCRIPTION

The following description of Conepatus sanmiguelensis is based mainly on material from San Miguel de Allande Basin. A single jaw fragment from the Tecolotlán basin is too poorly preserved to offer significant morphological insight. Both specimens from San Miguel, IGM 7800 and 7801, are generally well preserved, but have suffered from various degrees of fracturing. The two specimens complement each other in preserved elements such that a nearly complete composite skeleton is preserved. The palate and pterygoid regions on IGM 7800 were separated from the dorsal half of the skull and were later restored in the laboratory .

Skull ( Fig. 4 )

The nasal is completely fused with the frontal and maxillary and no suture is visible. The anterior tips of the nasals display a nearly transverse edge with a slight curve bending posteriorly. Such a gentle curve is similar to those in living species of Conepatus and thus suggests that the anterior edge of the nasals is essentially intact. On the internal surface of the nasal, the root of the nasal turbinate can be seen to taper toward the anterior edge of the nasal, as can be seen in skulls of living hog-nosed skunks, further evidence of an intact nasal in IGM 7800. However, a small, anterior protrusion along the medial contact of the left and right nasals, commonly seen in extant Conepatus , is broken off. Other than this damage, we judge the nasal to be essentially intact and show the true extent of its anterior edge. If this is the case, then the nasal displays the retraction of the external naris in hognosed skunks. In lateral view, the anterior edge is at the same level as the posterior edge of the upper canines, a stage of retraction more advanced than in C. humboldtii but similar to that in C. leuconotus .

The frontal area is gently domed, but not as inflated as in extant species of Conepatus . In dorsal view, a postorbital process of the frontal is barely visible, common for most species of Conepatus , although the temporal crest leading from the postorbital process is elevated enough to indicate the position of the postorbital process. The distance between the postorbital process and postorbital constriction is fairly long (12 mm) among known species of Conepatus . A discrete central (single) sagittal crest is low (shallow) and becomes slightly deeper near the posterior end. A nuchal crest is well developed, which projects posteriorly beyond the posterior margin of the occipital condyles. The zygomatic arch is only partially preserved on the left side, and it exhibits the typically slender, rod-like structure in all extant mephitids.

In ventral view, the palate is extensively fractured, although its overall dimension is more or less intact. The premaxillary–maxillary suture is fully fused, and it is not possible to ascertain the position of this suture, a character useful for species identification in Conepatus . The posterior border of the palatine is nearly at the same level as the posterior edge of the M1, a primitive condition as in C. humboldtii in contrast to a more posteriorly positioned border in more advanced species of Conepatus , such as C. leuconotus .

In the basicranium area, the bulla is strongly fused to the surrounding regions. A long tube for the external auditory meatus is also heavily fused to the postglenoid process. The area surrounding the mastoid process is inflated, as is typical of all mephitids. The paroccipital process is short and directed posteriorly. A concave fossa is present on the broad tip of the paroccipital process. This fossa is the largest in IGM 7800 among all species of Conepatus that we have examined, and the paroccipital process is largely horizontally orientated (with the above fossa facing essentially ventrally) in contrast to a more vertically orientated process in all other species. The condyloid foramen opens on the posterior rim of the posterior lacerate foramen, i.e. the former merges with the latter to open into the same pit as the posterior lacerate foramen, a condition seen in C. leuconotus but not in southern species such as C. humboldtii and C. chinga . The condyloid canal is absent from the internal surface of the occipital condyle.

Mandible ( Figs 5 , 8 )

The mandible has strong and thick (mediolaterally) horizontal rami, as is typical of Conepatus . A mental foramen is visible at the level of the anterior root of the p4. A blunt and deep angular process has an enlarged fossa for the inferior ramus of the medial pterygoid muscle at the expense of the fossa for the superior ramus of the same muscle, a character shared by Mephitis and Conepatus .

Teeth ( Figs 6–8 )

Dentally, Conepatus sanmiguelensis possesses a combination of primitive and derived characters for a transitional species. Apart from the right I3 and right P2, all other upper teeth are preserved. The incisors sustained little wear and the enamels on the occlusal surface are still intact. I1–2 show no sign of cuspules on either sides of the main cusp, and I3 has a basal, longitudinally orientated ridge on the lingual side. The canines are strong and straight. The enamel surface has no ornamentation but there is a weak cingulum on the lingual side.

A residual P 2 in IGM 7800 is present on the left side and that on the right side is lost. This tiny P2 is so small, measuring 1.7 ¥ 1.1 ¥ 0.9 mm (length vs. width vs. crown height), that it probably does not occlude with the lower premolars. However, the P2 is not crowded to the lingual side of the P3, as is the case in a similar stage of P2 reduction in Promephitis ( Wang & Qiu, 2004) , i.e. it maintains a space for itself between the C1 and P3, in contrast to a closed space in extant species of Conepatus that have lost the P2.

P3 is well preserved in both specimens. It has a single, high-crowned main cusp and lacks a posterior accessory cusp. A very weak anterior ridge leads down toward the tip of the main cusp, whereas a more distinct posterior ridge trails behind the main cusp. A lingual cingulum is well developed, especially along the posterior half of the tooth.

Both P4s are preserved in IGM 7800 and 7801. The shearing blade of P4, particularly the posterior half, is higher-crowned than in Mephitis , about the same crown height as in Conepatus humboldtii , but not as high as in C. leuconotus . In C. leuconotus it has lost the sharp bend in lateral view around the area where the carnassial notch should be (all mephitids have lost the notch). The protocone is crest-like on IGM 7800 but shows signs of initial development of a low cusp on IGM 7801, and is posterior to the anterior edge of the paracone. The protocone crest is also relatively lowcrowned compared with that in C. leuconotus .

Both M1s on IGM 7800 and the right M1 on IGM 7801 are well preserved and suffered little wear. The outline of the M1 is quadrate with its length/width ratio is approximately 1. The lingual cingulum is expanded posteriorly, but not as much as in Conepatus leuconotus . The protocone is also not as crowded toward the paracone as in the latter. The protocone is relatively low crowned compared with that in C. leuconotus . There is no ridge connecting the posterior end of the postprotocrista and lingual cingulum, a structure present in C. leuconotus .

The i1–i3 are preserved on IGM 7801. The roots of the lower incisors are imbricated with that of the i2 shifted lingually relative to those of the i1 and i3. The crown size increases from i1 to i3, and the tips of the crowns are too worn to discern cusp morphology. The lower canine is strongly curved, more so than seen in other species of Conepatus . There is a very weak lingual and posterior cingulum.

Only the left p2–3 are preserved and both have double roots. Both of these premolars are less reduced, relative to p4, than in living C. leuconotus . The p2 main cusp is very low and the posterior end of the tooth is broad. The p3 main cusp is also low, and there is a ridge along its posterolingual side. A prominent posterior cingulum is present in p3. Both p4–m1s are well preserved in IGM 7801. The p4 is high crowned and is higher than the tip of m1 paraconid. The main cusp is weakly ridged on the anterior surface and a slightly more distinct posterior ridge, as well as a lingual ridge, is present. The lingual ridge extends down toward the posterior root and forms a bulge at the base of the crown. There is a small, but distinct, anterior cingular cusp and a larger posterior cingular cusp. A weak anterior cingulum and more distinct posterior cingulum are present.

The m1s are moderately worn, although most cusp shapes are still readily distinguishable. The lengths of trigonid and talonid are approximately equal ( Figs 7 , 8 ; Table 1). The shearing blade (labial edge of the paraconid–metaconid) of the trigonid is the longest and most longitudinally orientated among all known species of Conepatus . Such a long trigonid also gives it a more open appearance, i.e. the paraconid is more anteriorly positioned. A weak ridge is present on the posterior face of the trigonid, as is typical for all New World skunks ( Wang et al., 2005b). The talonid is slightly wider than the trigonid. The hypoconid occupies about two-thirds of the talonid and the entoconid takes up the lingual one-third of the talonid. The hypoconid is also significantly higher than the entoconid, and the two cusps enclose a longitudinally orientated talonid basin, which is enclosed posteriorly by a rim formed by the merging of these two cusps. A shallow notch is present at the anterior end of the entoconid, where no sign of an entoconulid is present. The m2s are lost in both jaws. That on the left side left a single-rooted alveolus (4.8 mm in anteroposterior dimension).

Skeleton ( Figs 9 , 10 )

For anatomical terminologies, we use those in Evans & Christensen (1979). We have access to one skeleton for each extant genera of North American skunk ( Spilogale , Mephitis , Conepatus ), and the following descriptions thus concentrate on generic comparisons. Four partial cervicals are preserved. Three are mostly centrum, and only one is essentially complete. The centra in all four cervicals are relatively long compared with that of Conepatus chinga (MVZ 114941), suggesting a long neck for C. sanmiguelensis . A single thoracic from IGM 7801 is probably near the region of T3–5, with the dorsal (spinous) process mostly missing. It has well-developed, rugose transverse process. Another thoracic is associated with IGM 7800 and judging by its lack (or very weak) caudal coastal fovea and its elongated, posteriorly projecting transverse process, it is probably near the posterior region (last or penultimate) of the thoracic series. It has a strong and erect dorsal process. Two sacral vertebrae from IGM 7800 are well fused, as in living hog-nosed skunks. The suture surface with the pelvic is very rugose. Two caudals are preserved in IGM 7801. Their long centra suggest a long tail.

Only the articulation fossa is preserved for the right scapula in IGM 7801. It has a much stronger coracoid process than in C. chinga . A proximal humerus in IGM 7801 has a relatively large greater tubercle, a character shared with Mephitis but is in contrast to a smaller tubercle in Spilogale . The head is also more convex in anterior view than a more rounded profile in Spilogale . The tuberosity for teres major is more prominent than in C. chinga . Between the left and right partial radio-ulna on IGM 7801, the entire anatomy of these two bones can be observed. As in living hog-nosed skunks, the ulna shaft is bowed and the olecranon slanted toward the medial side, characters of a non-cursorial limb. The styloid process of the radius has a posterior ridge that is absent in living C. chinga . Nearly the entire left and right hands are preserved in IGM 7801. Metacarpal V is reduced and much thinner than the remaining metacarpals. Two proximal (probably III and IV; these were not preserved in original articulation) and one medial phalange show clear signs of pathological conditions. The distal ends of the proximal phalanges are enlarged, probably due to injuries, and movements are severely restricted due to extra growth ( Fig. 10 ). Front limb terminal phalanges are much longer and deeper than those in the hindlimbs among living skunks, presumably a fossorial adaptation. This is also true for C. sanmiguelensis .

Only a left head (IGM 7800) and two distal condyle fragments (IGM 7801) are preserved for the femur. A complete right tibia in IGM 7800 and partial left and right tibiae in IGM 7801 are available. Beside being larger in size (maximum length 88.8 mm), the tibia is very similar in overall morphology to that in C. chinga (length 73.3 mm). Both calcanea and astragali are present in IGM 7801. The astragalar trochlear has a similarly shallow groove as in C. chinga , and the shortness of the trochlear and presence of an astragalar foramen suggests little rotation with regard to tibia articulation. A plantar tendinal groove ( Wang, 1993: fig. 5) is distinct and is in contrast to its absence in C. chinga . The posterior articular surface of the calcaneum and its corresponding posterior calcaneal process of the astragalus are relatively flat as compared with a more curved articulation surface in C. chinga . Both feet in IGM 7801 are preserved. As in the hands, metatarsal V shows a similar degree of reduction compared with the other digits. The terminal phalanges are significantly shorter and shallower than those in the hands.

COMPARISON

Conepatus is morphologically distinctive and generally not easily confused with other genera of skunks. By its large size and advanced cranial and dental morphology, Conepatus is far removed from basal North American skunks such as Martinogale , Buisnictis and Spilogale (see Phylogeny for a list of derived characters in Conepatus that distinguish the latter from the basal forms). The Pleistocene Brachyprotoma has a short rostrum as in Conepatus , but the former is like Spilogale in size and has a swollen, conical P4 protocone, a character that suggests a relationship with Mephitis ( Wang et al., 2005b) . Another North American Pleistocene genus, Osmotherium , is poorly known and generally shows a stage of evolution equivalent to Mephitis . The Guanajuato species shares with Conepatus the following derived characters: retracted external nasal opening, high-crowned P4 and m1 talonid equal to or longer than trigonid. Its membership within Conepatus is thus secure.

Within Conepatus , C. sanmiguelensis is distinct from all known species, fossil or extant, by its primitive possession of a small P2. The single skull from Guanajuato does not permit an assessment of variations in the reduction or loss of the P2. However, a similar stage of P2 reduction is seen in the Eurasian Promephitis . In a large series of Promephitis skulls from Hezheng, Gansu Province, China, a tiny P2 is consistently present when this area of the skull is preserved ( Wang & Qiu, 2004). Therefore, it seems likely that the small P2 on IGM 7800 is a consistent character and represents a transitional stage of tooth reduction. In addition, its quadrate M1 is also a transitional feature for species of Conepatus ( Fig. 11 ). With the exception of the Rancholabrean C. robustus (see discussion below), C. sanmiguelensis is the largest among all fossil and living species of Conepatus . The m1 shearing blade (trigonid) in C. sanmiguelensis is also the longest among all known species of the genus.

The m 1 in IGM 7802 is 22% smaller than those in IGM 7891 ( Table 1). Its trigonid is also slightly shorter than in the latter. Given the limited materials at hand, we cannot determine if these differences are due to morphological or chronological variations. We tentatively place IGM 7802 in Conepatus sanmiguelensis pending better material from the Tecolotlán graben.

The above combination of characters (most of them primitive conditions for Conepatus ) allows clear contrast between C. sanmiguelensis and other known species. That C. sanmiguelensis represents the earliest representative of Conepatus distinct enough from other species seems to be readily born out by the above comparisons. In the phylogeny section below, we further demonstrate that C. sanmiguelensis is also a basal species in a North American Conepatus clade.

PHYLOGENY

The phylogenetic position of the skunks is traditionally regarded as a clade within the Family Mustelidae based on such commonly recognized characters as anal glands, reduced dental formula and loss of a carnassial notch on the P4 (e.g. Muizon, 1982; Bryant, Russell & Fitch, 1993; Wyss & Flynn, 1993; Baskin, 1998; Wolsan, 1999). This position has been increasingly challenged by recent molecular studies that place the skunks outside the clade formed by the living members of Procyonidae and Mustelidae and thus advocate a distinct family ( Mephitidae ) ( Wayne, Benveniste & Janczewski, 1989; Vrana et al., 1994; Ledje & Arnason, 1996a, b; Dragoo & Honeycutt, 1997; Flynn et al., 2000, 2005a; Marmi, López-Giráldez & Domingo- Roura, 2004; Sato et al., 2004, 2006); Delisle & Strobeck, 2005; Fulton & Strobeck, 2006). The above controversies aside, however, both traditional (morphological and palaeontological) and molecular approaches agree that skunks originated from Eurasia sometime in the early Miocene (possibly earlier if their deep split from other arctoids is true) and immigrated to North America during the late Miocene.

The earliest and most primitive skunk in North America is Martinogale Hall, 1930 in the late Clarendonian (see Wang et al., 2005b for a recent summary). Through a transitional genus, Buisnictis Hibbard, 1950 , the living North American skunk clade began to emerge, which includes Spilogale Gray, 1865 , Mephitis Geoffroy Saint-Hilaire & Cuvier, 1795 , and Conepatus Gray, 1837 ; as well as two fossil genera in the Pleistocene, Brachyprotoma Brown, 1908 and Osmotherium Cope, 1896 , that are nested within the extant clade ( Wang et al., 2005b).

By comparison with such outgroups as Martinogale and Buisnictis , Conepatus is morphologically the most derived, both cranially and dentally, and tends to be the largest in size among extant genera of North American skunks ( Wang et al., 2005b). Various DNA sequence studies, however, are either consistent with such an assessment ( Dragoo, Honeycutt & Schmidly, 2003) or suggest a more basal position for Conepatus among extant mephitids ( Dragoo & Honeycutt, 1997; Flynn et al., 2005a). If the latter is true, then some of the derived dental characters must have been acquired independently.

The well-preserved material of Conepatus sanmiguelensis offers a unique opportunity to evaluate character polarities among species of the genus. We scored a data matrix using a combination of a previous framework for early North American mephitids ( Wang et al., 2005b) and a species-level analysis of Conepatus by examining extant osteological collections and previously described fossil taxa. Our matrix, 19 taxa by 38 characters, includes all living species plus fossil species that are well preserved and described in sufficient detail ( Table 2 and Appendix 1). We treat all South American species ( C. chinga , C. humboldtii , C. primaevus , and C. talarae ) as a group of small-sized skunks with a mediolaterally widened M1 and shortened m1 trigonid (we do not have a sufficiently large series of living South American samples to evaluate variations; nor do we have access to the two fossil species). However, we individually coded the Argentinean C. altiramus because of its shared character (presence of an entoconulid on m1) with C. semistriatus and its possible special status as the first South American immigrant (see Zoogeography below). Parsimony analysis results in six shortest trees, a strict consensus of which is shown in Figure 12 . Species relationship within Conepatus is fully resolved (except the South American clade).

Figures

Figure 1. Map and satellite image of the locality GTO 75, north of San Miguel de Allende Basin, Guanajuato State, Mexico.

Figure 2. Photograph of locality GTO 75 in the Coecillos area, San Miguel de Allende Basin, Guanajuato State, Mexico. Arrow indicates sites where IGM 7800 (middle) and IGM 7801 (far right) were collected. White vertical bar indicates the layer where associated fauna was found. Black horizontal lines (middle and far right) mark the lower boundary of Pleistocene deposits that cap the Tertiary exposures. Photo by X. Wang, 2 June 2006.

Figure 3. Stratigraphic columns and faunal compositions of GTO 75 and related localities.

Figure 4. Conepatus sanmiguelensis sp. nov., IGM 7800, holotype: A, lateral, B, ventral and C, dorsal views of the skull.

Figure 5. Conepatus sanmiguelensis sp. nov., IGM 7801, referred specimen: A, medial and B, lateral views.

Figure 6. Conepatus sanmiguelensis sp. nov., Stereophotos of polyester casts of upper teeth. Occlusal views of A, IGM 7801, referred specimen, and B, IGM 7800, holotype.

Figure 7. Conepatus sanmiguelensis sp. nov., IGM 7801, referred specimen. Stereophotos of polyester casts of lower teeth. Occlusal views of A, right jaw, and B, left jaw. The p2–3 were collected as isolated teeth, and their position and imbrications on the left jaw are reconstructions based on the orientation of the p4, which is preserved in situ. This type of imbrication (clockwise rotation) is less common among Conepatus, and the more common type is an anticlockwise rotation on the left jaws.

Figure 8. Conepatus sanmiguelensis sp. nov., IGM 7802, referred specimen from JAL TECO 9: A, occlusal, and B, lingual views.

Figure 9. Conepatus sanmiguelensis sp. nov., IGM 7801, referred specimen: A, lateral view of right proximal scapula; B, anterior view of proximal humerus; C, anterior view of left ulna; D, anterior view of left radius; E, dorsal view of right hand (terminal phalanges shown in lateral view); F, anterior view of left distal fibula; G, anterior view of left distal tibia; and H, dorsal view of left foot (terminal phalanges shown in medial view).

Figure 10. Conepatus sanmiguelensis sp. nov., IGM 7801, referred specimen. Pathological proximal and medial phalanges. A, medial, and B, dorsal views.

Figure 11. Plots of fossil and extant species showing relationship of A, M1 lengths vs. widths; and B, m1 length vs. m1 trigonid length. See text for explanations.

Figure 12. Strict consensus of six shortest trees of North American skunks found by Branch and Bound option of the PAUP program. Solid bars indicate synapomorphies and open bars indicate homoplasies and reversals. Numbers to the left of the bars are character numbers that correspond to those in Appendix 1 and Table 2, and numbers to the right of the bars are character states. Numbers at nodes are bootstrap values (> 50%, 100 replications). Tree length = 67, consistency index = 0.7, retention index = 0.82. Character 25 (loss of P2) is optimized as independently occurring in the C. leuconotus–robustus clade and in the C. semistriatus–South American clade, rather than a single occurrence at Conepatus and then reversals.