Class Mammalia Order Lagomorpha Family Leporidae

HYPOLAGUS

DESCRIPTION The defining character of this genus is the p3, which has a posterior external reentrant (PER; figure 15.1) extending no more than halfway across the tooth, a very shallow anterior external reentrant (AER), and usually no other reentrants. Species in this genus show a wide range of size, from that of a small cottontail to that of a large hare. The degree of cursoriality ranges from less cursorial than Sylvilagus to typical jackrabbit ecomorph (Dawson, 1958; Campbell, 1969; White, 1984).

geographic DISTRIBUTION This extinct genus was widespread throughout North America and Europe in the Pleistocene.

TEMPORAL DISTRIBUTION Species of this genus are known from the early Miocene to the early Pleistocene in North America, but only from the Late Miocene in Asia and the Late Pliocene in Europe (White, 1984, 1991b).

HYPOLAGUS SPP.

REFERRED SPECIMENS DMNH 33269, 38978, 38983, 38988, 38997, 39060, 39081, 39111, 39150, 39168, 39172, 39175, 39194, 39300, 39304, 39349, 393 62.

COMMENTS This genus was a surprise at Porcupine Cave because it was thought to have gone extinct at the end of the Pliocene (White, 1987). However, Repenning et al. (1995) reported Hypolagus from the earliest Irvingtonian at Froman Ferry Fauna. In addition to the p3 characteristics noted previously, the P2 has a single anterior reentrant (AR), which is similar to that in Brachylagus. There may be three species of Hypolagus present in the DMNH Velvet Room sites. One is represented by two jaws with teeth present, as well as numerous p3s. This is a small rabbit, about the size of Sylvilagus bachmani and somewhat larger than Brachylagus coloradoensis. Of the two larger potential species, one is about the size of a large Sylvilagus or L. americanus and has a triangular p3 with very thick enamel. It is known from a few scattered p3s. The other

Anterior AR

Anterior AR

FIGURE 15.1 Terminology for leporid p3 morphology. AER, anterior external reentrant; AIR, anterior internal reentrant; AR, anterior reentrant; PER, posterior external reentrant; PIR, posterior internal reentrant.

Posterior

FIGURE 15.1 Terminology for leporid p3 morphology. AER, anterior external reentrant; AIR, anterior internal reentrant; AR, anterior reentrant; PER, posterior external reentrant; PIR, posterior internal reentrant.

is known from a single p3. It is large, nearly the size of that in Lepus townsendii.

LEPUS

DESCRIPTION These are medium to large leporids, of which there are approximately 29 species (Chapman and Flux, 1990). The interparietal is lacking in adults, and the postorbital processes are triangular and arched over the orbits (2n = 48; Robinson et al., 1983). These hares are typically somewhat cursorial (L. americanus) to highly cursorial (L. alleni), and most prefer open habitats.

GEOGRAPHIC DISTRIBUTION Extant species of Lepus are found throughout Europe, Asia, Africa, Greenland, and North America (Flux and Angermann, 1990).

TEMPORAL DISTRIBUTION Specimens referable to Lepus are known from the early Pliocene to the present (Kurten and Anderson, 1980).

LEPUS AMERICANUS ERXLEBEN, 1777

REFERRED SPECIMENS DMNH 6709, 8932, 9402, 10700, 11067, 11153, 11199, 11911, 14697, 37076, 37079, 39052, 39080, 39103, 39106, 39119, 39137, 39198, 39308, 39318, 39367.

DESCRIPTION Lepus americanus, the snowshoe hare, is the smallest of the North American species of Lepus. Its skull is small, the size of that in some Sylvilagus, arched over the orbits and lacking anterior supraorbital processes. The p3 is simple, with a single AR and with little to no crenulation in the PER. This species molts into a pale or white winter pelage, a trait also expressed by L. arcticus, L. othus, L. townsendii, and L. timidus.

GEOGRAPHIC DISTRIBUTION Lepus americanus is found throughout much of Canada and Alaska, and in the Sierra Nevadas, Cascades, Rocky Mountains, and Appalachian Mountains of the coterminous United States. It prefers the dense understory of subclimax forests but can be found in a variety of forest types. L. americanus is still present in South Park, although not in areas immediately adjacent to the site.

TEMPORAL DISTRIBUTION This species has a fairly long history. Besides being known from the middle Irvingtonian sediments of the Velvet Room, L. americanus has been reported from several late Rancholabrean sites, some of which are well south of its current distribution (Kurten and Anderson, 1980).

COMMENTS This species is very common in the DMNH Velvet Room sites and is easily distinguished from most other leporids, even with fragmentary material. L. americanus has a p3 pattern that places it in the Arctic hare clade, but many extant specimens exhibit a greater degree of crenulation in the posterior fold of the PER than in any other species in this clade. However, most of the L. americanus specimens from Porcupine Cave either lack this crenulation or have very little.

LEPUS CALIFORNICUS GRAY, 1837

REFERRED SPECIMENS DMNH 39059, 39324.

DESCRIPTION Lepus californicus, the black-tailed jackrabbit, is a large, lean, highly cursorial hare that is well adapted to both deserts and plains. Molecular and morphological evidence indicates that it is more closely related to L. alleni and its allies than to L. townsendii (Nelson, 1909; Halanych and Robinson, 1997; Ramos, 1999). The skull is long and narrow with a flattened profile. The p3 is quite crenulated, more so than in L. townsendii and its allies but less so than in L. alleni or L. callotis.

geographic DISTRIBUTION L. californicus can be found from the Pacific Coast of Baja California and California, across the Great Basin, and into the Great Plains, reaching south into central Mexico.

TEMPORAL DISTRIBUTION This species is reported from both early Irvingtonian (Curtis Ranch, southern Arizona) and late Irvingtonian sites (Slaton, west Texas), and is common in Rancholabrean sites within its present range (Kurten and Anderson, 1980).

COMMENTS L. californicus is an inhabitant of open grasslands and shrub desert. This highly cursorial hare is present in Colorado but is not found in South Park today. It is distinguished from L. townsendii by having a more slender dentary, slightly smaller teeth, and more crenulation on the enamel reentrants of the p3. This hare is known from the early Irvingtonian, and possibly earlier (Kurten and Anderson, 1980).

REFERRED SPECIMENS DMNH 9630, 9923, 11202, 11769, 20776, 23436, 27078, 38982, 38986, 38996, 39053, 39058, 39063, 39073, 39074, 39095, 39115, 39118, 39178, 39183, 39196, 39302, 39317, 39322, 39330, 39339, 39340, 39351, 39354, 39358, 39369.

DESCRIPTION This is a medium to large hare with a heavy body and moderately long ears. Its skull shape and p3 patterns closely resemble those of L. arcticus, L. othus, and L. timidus. There is geographic variation in the shapes of the supraorbital processes and incisors. Specimens from the northernmost reaches of the range lack an anterior supraorbital process. In addition, northern specimens have the Sylvilagus pattern of incisor, in which the groove is simple and divides the tooth into rounded, anterior surfaces that are roughly equal in size. This pattern of incisor is also found in L. arcticus, L. timidus, and L. othus (Ramos, 1998, 1999).

geographic distribution Lepus townsendii, the white-tailed jackrabbit, is found from above treeline to the plains. Its range extends from the Sierra Nevada and Cascade Mountains, across the northern Great Basin, through the Rocky Mountains and the Great Plains. The southern limits of its range have been receding since the turn of the century, while the range of the black-tailed jackrabbit has been expanding. Ramos (1998) reported evidence of this trend dating from the Rancholabrean.

TEMPORAL DISTRIBUTION The oldest record for the white-tailed jackrabbit comes from Mullen II and is late Irving-tonian. The species is also known from several Rancholabrean sites within it present range (Kurten and Anderson, 1980).

COMMENTS The white-tailed jackrabbit still inhabits areas immediately surrounding the cave site. Its presence in the early and middle Irvingtonian sediments of Porcupine Cave is a temporal extension of its known distribution.

SYLVILAGUS

DESCRIPTION Cottontails are small to medium or large rabbits with agouti coloring and complex p3 patterns. They retain many ancestral characters, such as keeping the interparietal into adulthood, short limbs, and less specialization for locomotion than is found in jackrabbits. Cottontails are often confused with the European rabbit (Oryctolagus cunicu-lus) but differ in that true cottontails do not burrow, do not live in social groups, and generally have shorter ears.

GEOGRAPHIC DISTRIBUTION Species of this genus are known only from North and South America (Chapman and Ceballos, 1990).

TEMPORAL DISTRIBUTION The oldest known Sylvilagus species are reported from Blancan sites in southern California, southern Arizona, northern Texas, and Florida (White, 1984, 1991a).

SYLVILAGUS AUDUBONII (BAIRD, 1857)

REFERRED SPECIMENS DMNH 27084, 39146.

DESCRIPTION This rather small rabbit has relatively longer ears and legs than other cottontails, reflecting its adaptation for arid, open terrain. However, there is a significant amount of geographic variation in these traits. The skull is arched posterior to the orbits as in S. nuttallii, and the p3 has moderate crenulation.

geographic DISTRIBUTION This species is found throughout the Great Plains, Great Basin, and Southwest and down into the central and western regions of northern Mexico. It can be found in sagebrush plains and pinyon-juniper stands. This cottontail is the most cursorial of its congeners and will tolerate less cover than other cottontails. Genetically it is closely related to S. nuttallii (Robinson et al., 1984), and its skull and p3 morphology substantiate this relationship because these two cottontails are the most difficult to distinguish from one another using only skull fragments (Ramos, 1999).

TEMPORAL DISTRIBUTION The species was known only from Recent and Rancholabrean sites (Kurten and Anderson, 1980) until it was identified in Porcupine Cave deposits.

COMMENTS It is quite difficult to distinguish S. audubonii from S. nuttallii. Enamel patterns of the p3 between the two show a high degree of variation and overlap and cannot be relied upon for confident identifications. Much of the material was assigned to S. nuttallii based upon size. However, some specimens were significantly larger than the usual range for S. nuttallii. These were assigned to S. audubonii, which is somewhat larger. The desert cottontail does not inhabit South Park at present and, owing to the apparently close phylogenetic and geographic proximity between it and the mountain cottontail (Findley et al., 1975; Robinson et al., 1984; Chapman and Ceballos, 1990), it is possible that the two had not completely diverged by the early and middle Irvingtonian.

SYLVILAGUS NUTTALLII (BACHMAN, 1837)

REFERRED SPECIMENS DMNH 10555, 11200, 39056, 39065, 39068, 39077, 39087, 39092, 39141, 39158, 39321.

DESCRIPTION This is a small cottontail, genetically and morphologically similar to S. audubonii. Cranial characters do not easily distinguish this species from S. audubonii. The skull is arched posterior to the orbits with small anterior supraorbital processes that do not fuse with the skull, and the auditory bullae tend to be small. The p3 shows a fair amount of variation, but in general it is not nearly so complex as that of S. aquaticus or S. palustris, but not so simple as that of S. flori-danus. It has relatively short ears and a more grayish pelage than S. floridanus.

GEOGRAPHIC DISTRIBUTION The mountain cottontail is a small rabbit that occurs in the intermountain region of

North America. Its distribution includes much of the southern and central Rocky Mountains, north across the Great Basin to the Sierra Nevada and Cascade Mountains, where it can be found in rocky areas with brush, sagebrush (Artemisia spp.), or both.

TEMPORAL DISTRIBUTION The species is known from late Rancholabrean deposits within its current range (Kurten and Anderson, 1980).

COMMENTS The mountain cottontail currently inhabits South Park, but it is not common in the Porcupine Cave sediments. The distinction between this species and S. audubonii is not clear from the fragmentary remains, and it may reflect a taxonomic indistinction during the time frame represented at Porcupine Cave.

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