DESCRIPTION AND COMPARISONS

Horn Core

The left horn core (52139A) is complete and contains some fragmentary adjoining frontal bone (Figure 2). The horn core is short, nearly straight (no divergence), with a slight posterior curvature (recurved). The horn core is medio-laterally (transversely) compressed, with the medial side somewhat flattened and the lateral side more convex, producing an ovate cross section. The relatively smooth surface lacks both anterior and posterior keels and longitudinal grooves. There is no evidence of torsion (spiral twist to horn core and horn sheath). Sinus cavities extend into the basal portion of the horn core (Figure 2). The cranium is broken immediately adjacent to the position of a postcornual fossa (pf, Figure 2). If this fossa was small, it would probably be absent from the portion of the fossil preserved. Until more complete specimens can be located, there is no evidence that a postcornual fossa occurred on Sinocapra willdownsi Extant Ovis, Capra, Hemitragus, and Oreamnos have a highly reduced to absent postcornual fossa, whereas a shallow yet distinct fossa occurs on the holotype of S. minor (Figure 3; Chen 1991).

The horn core length is measured from the pedicle base (where the burr would be located; arrows in Figure 2; equals base of horn sheath) to the tip. Medio-lateral and nasal-nuchal (antero-posterior) measurements, taken at pedicle base, are included in Table 1.

Discussion: Although the horn core of Sinocapra willdownsi is unusually small relative to those of living caprines and the extinct S. minor (Table 1), we interpret that the small horn cores do not indicate a juvenile growth stage. Figure 4 contains a series of skulls showing ontogenetic growth stages for male and female Ovis canadensis (Rocky Mountain bighorn) and illustrates the sexual dimorphism that is expressed at an early age. Using even this small series of skulls, it is easy to determine the sex and approximate age of the wild sheep. At about three months of age, the horn core begins to appear on the frontal (Figure 4A). The horn core develops more rapidly on males. At an early age the horn core has a wide pedicle base yet little length (male and female); torsion begins early for males (arrow in Figure 4C). The young female (Figure 4B) still has a wide base to the horn core yet no torsion develops. These sexual dimorphic traits occur because the horn core and horn sheath in male Ovis spp. is highly twisted at maturity, providing the characteristic lateral curl to wild sheep rams (Figure 4E, Figure 5I-L). Horn cores of female Ovis spp. are not twisted and are more-or-less straight with a slight posterior curvature (Figure 4D). The horn sheaths (therefore the horn cores also) of adult female Ovis spp. show little growth after about 2.5 years age (Geist 1971). Using horn growth of Ovis as a model for Sinocapra, it would appear that the individual from Panaca was likely at full growth stage of development.

Table 1 illustrates the small size of the Panaca caprine horn core in comparison to horn cores of other adult caprines including Sinocapra minor (sex not designated by Chen [1991]; see discussion below), Ovis dalli (Dall’s bighorn; male and female), Ovis nivicola (Snow sheep; male), and Ovis shantungensis (extinct bighorn; assumed to be male), and the two ‘rupicaprines’ Neotragocerus (two species, extinct) and Oreamnos (two species, one extinct; male and female). Clearly the horn cores of the Panaca caprine are small, yet based on length and diameter measurements, the horn core is considered to be from an adult individual (a determination that is supported by tooth eruption; see below).

There is a slight posterior curvature orientation to the horn core of S. willdownsi, with no indication of torsion (such as would be found with the Oioceros (extinct) and members of the Bovini, Ovibovini, and many males of taxa within Caprini; e.g., Ammotragus (aoudad), Pseudois (bharal), Ovis, and some forms of Capra (goat); Figure 5). The surface of the horn core of S. willdownsi is relatively smooth (as is found in Capra, Hemitragus (tahr), Oreamnos, Ovis, and Sinocapra minor) and lacks the deep grooves found with members of the Bovini, Ovibovini, Oioceros, and Saiga.

The horn core of S. willdownsi is medio-laterally flattened (ovate cross section), typical of most Caprini and unlike the circular to nearly circular horn cores found within the ‘rupicaprine’ Capricornis (serow), Nemorhaedus (goral), Neotragocerus, and Oreamnos, and also within Pachygazella (extinct), Oioceros, Saiga, and the ovibovines. Medio-laterally compressed horn cores occur on female caprines (e.g., Ovis and Hemitragus), perhaps because their small horns are not used for extreme butting. In contrast, adult males of the living Caprini use their horns for extensive butting. Their horn cores typically have rounded lateral surfaces and anterior surfaces (contact when butting) that range from comparatively flat (Ovis, Ammotragus, Pseudois, and some forms of Capra) to highly ridged, forming an acute triangular cross section (Hemitragus, most forms of Capra; Figure 5 shows the horn sheath expressions of the horn cores).

The horn core, type, for Sinocapra minor, is larger than that of S. willdownsi, yet it, too, shows little posterior curvature and lacks torsion (Figure 3). Similar horn cores were referred to Sinocapra minor by Chen (1991; see Teilhard de Chardin and Trassaert 1938). They are all short, moderately straight with minor posterior curvature, lack divergence, and have a comparatively wide pedicle base (one with a postcornual fossa; Figure 3). Because of this wide pedicle base, we assume that the illustrated horn cores for S. minor are from male members of a genus with relatively small horn sheaths that are curved posteriorly and exhibit no torsion. Because the pedicle base on the type for S. willdownsi is not significantly larger than the burr base, as observed on S. minor horn cores and typically found on male caprines, the Panaca caprine specimen is considered to be a female.

Maxillary Teeth

The right P3-M2 (52319 B) were recovered together in a small fragment of the maxilla (Figure 6). The posterior edge of the M2 has a contact mark showing that there was an M3 in the toothrow; this tooth was not recovered. The right P2 and left M1 were recovered as isolated teeth. The molars lack entostyles. Crown height is relatively low, mesodont. Strong labial ribs occur between the parastyle, mesostyle, and metastyle. Distinct internal cavities occur between the protocone and metaconule on the M1-2 (Figure 6).

Discussion: The teeth do not show extreme wear, indicating that the low crowns on the Panaca caprine are not to the result of abrasion (Figure 6). The M2 comes into full functional wear at about two years of age, and the M3 is in complete functional wear at about 3.0 to 3.5 years in Ovis spp. (Cowan 1940). Assuming a similar tooth eruption phase in Sinocapra, the individual from Panaca would have been at least three years old.

The observed occlusal characters of Sinocapra willdownsi are consistent within Caprini but appear undiagnostic to genus. Measurements of the molars and premolars of S. willdownsi are compared with Ovis ammon (argali), O. canadensis, O. catclawensis (extinct bighorn), O. dalli (female), O. shantungensis, and O. zdanskyi (extinct bighorn) in Table 2 (no dentition is known for S. minor). The length and width of the premolars of S. willdownsi fit within the variability observed among these taxa. The size of the molars indicates some variation among genera. These initial data imply that the teeth and toothrow of S. willdownsi are at the small end of the observable range of living and some fossil caprines. The mesodont characteristic may be of importance as the teeth of Sinocapra willdownsi are distinctly lower crowned than any living Ovis spp. or Oreamnos spp.

Humerus

Fragmented left and right humeri (52319E) are known (Figure 7). The left humerus preserves the distal three-fourths while the right humerus is represented by only the distal quarter. Measurements are shown in Table 3.

Ulna

A fragment of the proximal end of the left ulna (52319E) is recovered (Figure 8). The conical impression on the medial surface (Figure 8.1), is consistent with a canine impaction but there is no corresponding indentation on the lateral side.

Lunar

The right lunar (52319E) is complete but not remarkably different from that of other taxa.

Metacarpal

The distal fragment of a right metacarpal (52139E) has a distinctive sulcus (su) with slight crests (not sharp) parallel to the sulcus and is widely open (sagittal groove) at the distal epiphysis (Figure 9). Although the entire bone is not preserved, there is enough (approximately the distal third) preserved to indicate that the bone is from the right side and progressively widens from the diaphysis at the distal end, as occurs on a metacarpal and unlike the rapid expansion observed in metatarsals (see discussion below).

The width of the distal articular surface of the metacarpal of Sinocapra willdownsi and other caprine taxa are included in Table 4. The articular condyles of the first phalanges (verticilli of Köhler 1993) are high and sharply delineated, as seen in Ovis, Oreamnos, and other inhabitants of mountainous terrain.

Discussion: Ovis spp. and Oreamnos spp. do not have the prominent sulcus found on the metacarpal as seen in Sinocapra willdownsi. Living Caprini, ‘Rupicaprini,’ and Ovibovini have a superficial sulcus or none at all on the metacarpal. The measurements of the distal articular surface of various caprines indicate that the metacarpal of S. willdownsi is of about average size, compared to other living caprines (Table 4). The data presented for the metatarsal are similar.

Phalanges

The first, second, and third (fragment) phalanges (52139E) appear to fit together and articulate precisely with the right metacarpal fragment, and therefore, they are assumed to be medial manus phalanges (third digit). An additional first phalanx is known but does not adequately articulate with either the right metacarpal or the right metatarsal and is therefore not described.

The first phalanx measures 47.1 mm long (greatest length between medial condyles) and 17.2 mm wide at the proximal end. The additional first phalanx measures 49.2 mm long and 16.8 mm wide at the proximal end. Interdigital ligament insertion ridges are short but prominent on both specimens (Figure 10B.1).

The second phalanx is short and broad (27.6 mm long, following von den Driesch 1976), 13.9 mm wide at the proximal end. A postarticular plateau is lacking (Figure 10A.2), and the dorsal extensor protuberance (dexp) is elongate (Figure 10C). The insertion of the interdigital ligament is weak to almost absent (Figure 10C.3).

The third (distal) phalanx is fragmented, missing the distal half. A robust protuberance for the extensor tendon insertion (exp) is preserved (Figure 10D). A portion of the dorsal ridge is preserved distal to the extensor tendon insertion and appears to be at a more horizontal angle implying at least a slight convex appearance (typical of caprines, and not the highly slanted and straight ridge as in cervoids). The horizontal platform of the articular surface (hpe) is well established (Figure 10D).

Discussion: Although these phalanges are not taxonomically diagnostic, they do indicate that the joint was designed for tensor and flexor motion with a horizontal component that permits notable shock absorbency (see Leinders 1979; Köhler 1993). This implies that Sinocapra willdownsi was more of a mountainous and rocky terrain climber and not an animal adept at sustained, rapid locomotion on fairly level topography.

Femur

Highly fragmented left and right femora (52319E) are known, but will not be discussed here.

Navicular-cuboid

A complete right navicular-cuboid (52139E; central and fourth tarsal) is recovered. The comparative morphology used here is located in Figure 11 and Figure 12. The patterns of the various articular facets and processes of the distal surface are within the realm of variation observed in modern Ovis canadensis and O. dalli, and therefore, are of little use to distinguish the new taxon. However, the articular facets and processes are distinctly unlike those found on cervoids and antilocaprids (see Lawrence 1951; Heintz 1970).

The plantar surface of 52139E contains the calcaneal articular facet (caf), a flange with its length truncated distally by the lateral groove of the tendon to the musculus peroneus longus (tmpl; Figure 11, Figure 12). This groove on the lateral surface or its truncation by the tmpl is rarely observed in Ovis, Ammotragus, Oreamnos americanus (male and female), or the extinct Oreamnos harringtoni.

The medial process (mp; Figure 11B, Figure 12B) on the anterior surface is a pronounced articular process with distinct dorsal and plantar facets on Sinocapra willdownsi and on some specimens of Oreamnos harringtoni (GRCA 509044, 509160, 509273). This differs from the minute projections observed on Ovis spp. and Oreamnos americanus.

The navicular-cuboid of Sinocapra willdownsi is square in shape as in Ovis spp., whereas it is medio-laterally wider in Oreamnos spp. (with its wider foot for mountain climbing). This width on Oreamnos comes from the lateral expansion of the antero-external metatarsal facet (amf) and the postero-external metatarsal facet (pmf) along with their adjacent ligament attachments (Figure 12A). Widening of the Oreamnos navicular-cuboid situates the pmf near the middle of the plantar surface, as viewed posteriorly, whereas in Sinocapra willdownsi and Ovis spp. this process is at the lateral-plantar border of the bone (Figure 11.2). The widening within Oreamnos spp. is also caused by the medial widening of the internal astragal articular facet, a character not found in Sinocapra willdownsi or in Ovis spp. This character indicates that the foot of Sinocapra willdownsi was not as wide and sturdy as that of the mountain goats, but is comparable with the mountain sheep.

The insertion of the tendon on the plantar side (Figure 11.1) is centrally located on Sinocapra willdownsi, yet continues as a groove proximally. No such groove is observed in Ovis spp. or Oreamnos spp.

The attachment area for the long medial ligament, the plantar ligament, and the long lateral ligament is robust and extensive on Oreamnos spp. and Ovis spp., yet is minute on Sinocapra willdownsi (Figure 11.3). Various muscles attach to these ligaments with tendons. Although the ligaments restrict the amount of absolute movement at the joint, the tendons and muscles attaching on the plantar side permit various flexor and tensor motions of the foot and digits (see Sisson and Grossman, 1938 and subsequent editions).

The internal process (ip) of the internal astragal articular facet (iaaf) permits the attachment of a number of tendons on the plantar and medial sides (Figure 11B, Figure 12B). This process also allows for the formation of a groove that accommodates passing the tendon of the tibialis posterior. It is in this groove that a ligament attaches (in part the tarso-metatarsal ligament). In Ovis, the ligament attachment blends in with the form of the groove. The anterior end of the groove contains a large bony lump for this ligament attachment, similar to, but not as massive as, that found on Oreamnos.

Discussion: The navicular-cuboid 52319E is similar in size and shape to that found on Ovis and dissimilar to that of Oreamnos. Although similar to that of Ovis, differences indicate a different animal and one that, although an inhabitant of mountainous terrain, was not as adept to this habitat as Ovis spp. and Oreamnos americanus are today.

Metatarsal

The right metatarsal (52139E) is nearly complete (Figure 13). A sulcus (su) occurs on the dorsal surface and proceeds from proximal to distal epiphyses, distinct most of its length, prominent and open the distal third with crests on both sides of the sulcus, and widely open (sagittal groove) at the distal epiphysis (Figure 13A), a character typical of bovids but not cervoids (Heintz 1970; Leinders 1979; Köhler 1993). This sulcus is wide and shallow to almost non-existent on Ovis spp. and Oreamnos spp. The goat-like caprines (Capra, Hemitragus) possess a slightly more distinct sulcus at the distal end than do the sheep-like caprines (Ovis; along with the ovibovines and ‘rupicaprines’). The volar or plantar surface (posterior of Heintz 1970) has almost no trace of a groove except near the epiphyses (Figure 13B), similar to that observed on Ovis spp. and Oreamnos spp.

The distal end flares abruptly with a broad ‘V’ from the epiphysis to the intertrochlear notch (in) on 52139E. The connections of the lateral extensor tendon (lext) and the medial extensor tendon (mext) are prominent on Sinocapra willdownsi (Figure 13A). This character set is not significant in Ovis spp. but is robust in Oreamnos spp.

The posterior sub-facet of the navicular-cuboid facet (psfncf) is completely abraded, and it cannot be determined if this facet was raised or level with the rest of the naviculo-cuboid facet (Figure 13B.1 and Figure 14.2). The posteromedial projection (pp; Figure 14) is prominent and has a hooked-appearance on 52139E. However, this is due to abrasion and to the deep fossa below. Due to the abraded state of the fossil, this character (= character 93 of Gentry 1992) cannot be used. The articular condyles for the first phalanges (verticilli of Köhler 1993) are high and sharply delineated, as found with Ovis, Oreamnos, and other mountainous terrain inhabitants (Figure 13).

The metatarsal is neither excessively long nor short, nor narrow or wide, when compared with other caprines (Table 5). To observe its size relative to other caprines, we made a comparison between the overall length and the width of metatarsals, at the distal end. Figure 15 illustrates this comparison among the various caprines. The length/distal width ratio of Sinocapra willdownsi is analogous to those of some Capra ibex and Pseudois nayaur, and not all that dissimilar with some Ammotragus lervia and Ovis orientalis. These similarities, although not helpful with the identification of the specimen, do indicate that S. willdownsi had a relatively short and wide foot, one very capable of mountain terrain. The size of the metatarsal on S. willdownsi indicates that the individual described here was not a large or heavy animal.