The quaternary paleontology and paleoecology of crystal ball cave, millard county, utah: with emphasis on the mammals and the description of a new species of fossil skunk

Vulpes velox

Material--Left dentary with P/3 and partial M/1 (BYUVP 7477), posterior portion of left M/1 (BYUVP 7479). A partial left dentary with M/2 (BYUVP 7478) also compares favorably with this species.

Discussion--V. velox and V. macrotis are now considered conspecific (Hall 1981). The dentary (BYUVP 7477) lacks the "step" of Urocyon, and the M/1 lacks a small cuspule found on the posterolabial margin of the main cusp of all the Urocyon specimens but none of the Vulpes specimens examined. The Crystal Ball Cave specimens listed above are smaller than U. cinereoargenteus but may be similar in size to the smaller U. littoralis, which is known only from islands along the coast of southern California (Miller 1971).

Since V. velox still lives around Crystal Ball Cave (J. C. Bates 1983 personal communication), its presence in the assemblage is not surprising. Its low frequency compared to the now-extirpated V. vulpes suggests that it may not have always inhabited the area, may have inhabited it in much smaller numbers, or may have had a different microhabitat causing it to frequent the cave area less than V. vulpes. The ranges of V. vulpes and V. velox presently overlap to a degree, especially in the midwest, but in the western United States this overlap is small (Hall 1981). Although V. velox occurs in the Snake Range now, it is a more southern species than V. vulpes so its northern range extensions may be of Recent age.

Family Mustelidae

Mustela cf. frenata

Material--Left M1/ (BYUVP 7487), right dentary with P/2,/3, M/1,/2 (BYUVP 7483), partial right dentary without teeth (BYUVP 7484), left dentary with M/1,/2 (BYUVP 7488), left dentary with M/1 (BYUVP 7485), partial left dentary with M/1,/2 (BYUVP 7486).

Discussion--All these Mustela specimens compare best in size with M. frenata, which presently lives around Crystal Ball Cave. The size range of M. frenata is overlapped by the smaller but more variable M. erminea (Kurten and Anderson 1980) which also ranges in the cave area (Hall 1981). The specimens could belong to M. erminea since this species is dentally similar to M. frenata. M. rixosa is always smaller and M. nigripes and M. vison are always considerably larger than the Crystal Ball Cave specimens. M. frenata was the most abundant mustelid at Smith Creek Cave, but M. erminea was also present (Miller 1979). Since all the Crystal Ball Cave specimens fall in the narrow size range of M. frenata, they are referred to this species.

Mustela cf. vison

Material--Left M1/ (BYUVP 7482). A juvenile left dentary without teeth (BYUVP 7491) also compares well with this species.

Discussion--This isolated tooth was compared with a variety of Recent mustelids and other small carnivores and found most similar to M. vison. This is North America's largest extant species of Mustela (although the extinct sea mink, M. macrodon, was larger) and is distinctly larger than but similar in shape to M. frenata (described above). M. vison was recovered from Smith Creek Cave (Miller 1979) and presently occurs 100 miles (160 km) north and east of Crystal Ball Cave (Hall 1981), but it does not currently live in the Snake Range. This species requires lakes or streams to survive (Hall 1946), so its extirpated nature in the Snake Range may have been due to the recession of Lake Bonneville and/or loss of perennial streams in the area at the end of the Pleistocene.

M. vison is sometimes confused with M. nigripes since both are of similar size (Kurten and Anderson 1980), and no distinction in isolated molars could be found in the literature. M. nigripes is currently endangered, and no comparative material was available. It has never been reported from western Utah or Nevada, so the Crystal Ball Cave specimens are referred to M. vison, which is known to have lived in the area.

Martes americana

Material--Left dentary with M/1 (BYUVP 7480), left M/1 (BYUVP 7481). The anterior portion of a right dentary without teeth (BYUVP 7489) and the posterior portion of a right dentary without teeth (7523) probably also belong to this taxon.

Discussion--Anderson (1970), in her systematic review of the genus Martes, considered M. nobilis (found in four caves in Wyoming, Idaho, and northern California) to be a distinct species from M. americana. Of the two, M. nobilis is larger, and its lower carnasial has a relatively shorter trigonid. The lower canines of M. nobilis sometimes have faint grooves on the external surface not found in M. americana (Anderson 1970). The only other species of Martes presently living in Utah is M. pennanti, the fisher. It is considerably larger than M. americana, M. nobilis, and the Crystal Ball Cave specimens. Neither M. americana nor M. pennanti currently live in the Snake Range, but both occur in the mountains of central Utah and northward.

BYUVP 7480 is as large as the largest M. americana specimen to which it was compared, and judging from the incisor socket, its incisor was slightly larger. The other specimens are the same size as most Recent M. americana specimens. Both lower carnasials match perfectly in shape with M. americana and do not show a relatively shorter trigonid, so they are assigned to M. americana. A right M1/ of M. nobilis was recovered from Smith Creek Cave (Miller 1979) but M. americana has never been reported. The ecological and chronological separation of these two species in the Snake Range is, therefore, problematic. Brown (1971) listed M. americana as one of eight species of boreal mammals that presently range in the Sierra Nevada and the Rocky Mountains but on none of the isolated Great Basin ranges in between. This citing demonstrates that M. americana did range at least as far east in the Great Basin as the Snake Range before becoming extirpated.

Brachyprotoma brevimala, sp. nov.

Type--Anterior portion of skull including a complete palate except the most posterior (smallest) socket of each M1/ and extending posteriorly to include the entire anterior wall of the braincase (BYUVP 7490, see figure 5). Only the right P4/ was found in situ, but a right and left M1/ (previously cataloged as BYUVP 7492 and 8298 respectively) fit perfectly into the sockets of the type specimen where they have been permanently mounted. The type specimen is of a young adult based on complete fusion of the premaxillae, maxillae, nasals, and frontals and on lack of significant tooth wear. Both the skull and isolated M1/'s were recovered from Site 1, Channel A, Crystal Ball Cave, Millard County, Utah (see figures 1 and 3) by Wade E. Miller and party on March 19, 1977. The type specimen is housed at the Brigham Young University Vertebrate Paleontology Laboratory.

Diagnosis--Brachyprotoma brevimala has a short face and a maxillary tooth formula of I3/-3/, C1/-1/, P2/-2/, M1/-1/ as in B. obtusata. Face and maxillary dental measurements average 15% smaller than those of B. obtusata. B. brevimala is distinguished from B. obtusata by P4/ being transversely narrower and having a more posteriorly directed lingual cusp, and by M1/ being more reduced and distinctly shorter anteroposteriorly. In other known characters B. brevimala is equivalent to B. obtusata. B. brevimala has the most reduced P4/ and M1/ of any known skunk.

Description--The maxillary dental formula of I3/-3/, C1/-1/, P2/-2/, M1/-1/ is known among the mustelids only in two genera of skunks, Conepatus and Brachyprotoma (although I found one abnormal Recent Spilogale putorius specimen with this formula). The Crystal Ball Cave specimen is clearly a skunk (subfamily Mephitinae) based on the presence of only 2 pairs of upper premolars (mephitines have 2 or 3, all other mustelids have 3 or 4), the small size (only the subfamilies Mustelinae and Mephitinae have such small adult individuals), the lingual cusp of P4/ extending from the middle of the tooth (as opposed to the more anterior extension in the mustelines), M1/ being anteroposteriorly shorter labially than lingually (mustelines have the opposite condition), and the internal nares extending almost as far anteriorly as the posterior end of the tooth row (they are much more posterior in mustelines).

Compared to extant mephitines the Crystal Ball Cave specimen represents an individual of similar size to Spilogale but much smaller than Conepatus and Mephitis. The palate is shorter and wider than that of Spilogale putorius, but the interorbital breadth shows that the type specimen represents a larger individual than the average S. putorius. The P4/ is similar to Spilogale, differing only in having the lingual cusp slightly more posterior, but it is proportionally much narrower than the P4/ of Mephitis and Conepatus. The M1/'s are proximo-distally shorter than any of the living mephitines (especially Conepatus and Mephitis that have large square M1/'s) and are closest to Spilogale in shape and cusp pattern. The rostrum of the type specimen is shorter than that of Spilogale, matching that of Conepatus in proportions. The external nare is steep as in Conepatus, but it is relatively small and round as in Spilogale. Both infraorbital canals are single rather than double or triple, a species-diagnostic character in Conepatus (Hall 1981) but variable in Mephitis and Spilogale.

In addition to the three extant genera, three fossil genera have been named: Buisnictis, Brachyprotoma, and Osmotherium (Kurten and Anderson 1980). Osmotherium can be ruled out since it is large and very similar to Mephitis (Kurten and Anderson 1980), the living skunk genus that is most distinct from the Crystal Ball Cave specimen. Both Buisnictis and Brachyprotoma are small and have proportionally short jaws like the Crystal Ball Cave specimen. Buisnictis has been recovered from Late Pliocene deposits of southwestern Idaho (Bjork 1970) and Middle Pliocene to Early Pleistocene deposits of Kansas and Oklahoma (Hibbard 1941, 1950, 1954), but it has no record in the Late Pleistocene or Recent. Buisnictis has a short jaw with crowded premolars, but it differs from the Crystal Ball Cave specimen in having 3 pairs of upper premolars instead of 2 (Kurten and Anderson 1980). Based on an illustration by Hibbard (1954), the P4/ of Buisnictis has its lingual cusp extending from the anterior part of the tooth as in the mustelines, and the M1/ is distinctly longer than that of the Crystal Ball Cave specimen. These morphologic and age differences show that the Crystal Ball Cave specimen is distinct from Buisnictis.

The Crystal Ball Cave specimen matches the genus Brachyprotoma in having short jaws, only 2 pairs of upper premolars, P4/ and M1/ similar in shape and cusp pattern to Spilogale, and in the age of deposits in which they have been recovered. Until recently Brachyprotoma was only known from a few early Pleistocene to early Recent age ave deposits in the eastern United States. But during the period of this study P. M. Youngman (1984 personal communication) recovered several Brachyprotoma specimens from two cave deposits in the Yukon Territory of Canada. Although no previous Brachyprotoma specimens have been reported closer than 1130 miles (1880 km) from Crystal Ball Cave, morphology clearly allies the Crystal Ball Cave specimen with this genus. But there are specific differences between the Crystal Ball Cave specimen and other skulls which have been assigned to the genus Brachyprotoma. To test the amount of variation to be expected within a species of skunk, I measured 73 specimens of Recent Spilogale putorius, 60 from the Harvard University Museum of Comparative Zoology and 13 from the Brigham Young University Monte L. Bean Museum. Spilogale putorius makes a good standard for the expected individual variation in species of Brachyprotoma, both because Spilogale is probably the most closely related extant genus to Brachyprotoma and because S. putorius borders on being divisible into multiple species (although most workers presently consider it a single species). Based on the great amount of variation seen between the Crystal Ball Cave specimen and other skulls assigned to the genus Brachyprotoma compared with the amount of variation seen among individuals of S. putorius, I believe the Crystal Ball Cave specimen warrants the status of a new species.

The B. brevimala type is smaller than specimens of B. obtusata in most measured characters, averaging about 15% smaller (see table 3). The greatest differences occur in P4/ and M1/, which are the most varied maxillary teeth between skunk taxa. The mean length of P4/ in B. obtusata is only 7% greater than in B. brevimala while the mean width is 22% greater. The lingual cusp of P4/ in B. brevimala also points more posteriorly than in B. obtusata, being nearer M1/ at its lingual tip rather than closer at its base or parallel as in B. obtusata. The M1/ of B. obtusata is 16% transversely wider on the average, but the labial anteroposterior length is 30% greater and the lingual anteroposterior length is 59% greater than in the B. brevimala type on the average. Since there is only minor variation in these characters among B. obtusata skulls (see table 3) but distinct difference between them and the Crystal Ball Cave specimen, and because the differences between the B. brevimala type and specimens of B. obtusata are far greater than would be expected within a species (based on the variation found among 73 individuals of Spilogale putorius, the most closely related extant species), erection of a new species for the Crystal Ball Cave specimen is clearly justified.

Discussion--Brachyprotoma specimens have been previously recovered from the following deposits of Early Pleistocene to Early recent age: Port Kennedy Cave and Frankstown Cave, Pennsylvania (Cope 1899, Peterson 1926), Cumberland Cave, Maryland (Gidley and Gazin 1938), Crankshaft Cave and Brynjulfson Cave, Missouri (Oesch 1967, Parmalee and Oesch 1972, Parmalee et al. 1969), Connard Fissure, Arkansas (Brown 1908), and two caves in northern Yukon Territory, Canada (P. M. Youngman 1984 personal communication). Most of these specimens are lower jaws, and the only 7 skulls (or skull fragments) that have been previously reported are Carnegie Museum 11057A and 20233, American Museum of Natural History 11772 and 12426, U.S. National Museum 8155 and 11960, and a specimen identified as Carnegie Museum 308 by Oesch (1967) but which does not correspond to that number in the Carnegie Museum catalogs (M. R. Dawson 1984 personal communication). Parmalee et al. (1969) illustrated this latter specimen but did not identify it by catalog number.

Cope (1899) named Mephitis (Spilogale) obtusatus, for a single small dentary from Port Kennedy Cave, but E. D. Cope died before the completion of this paper, and a footnote stated that "none of the specimens labelled by Prof. Cope bear this name." Brown (1908) named the genus Brachyprotoma, and he considered M. obtusatus to belong to this genus as well as M. fossidens and M. leptops, two species named by Cope previous to the naming of M. obtusatus. From Connard Fissure Brown (1908) reported B. fossidens, B. leptops, and B. obtusatus based on dentaries, and he named B. pristina based on two partial skulls and three dentaries (the skull cataloged as American Museum of Natural History 12426 is the type for the genus and species) and B. spelaea based on one dentary. The dentaries Brown (1908) identified as B. fossidens and B. leptops are far too large to belong to the same genus as the small specimens he identified as B. obtusatus, B. pristina, and B. spelaea, and no one since has considered these two species as belonging to the genus Brachyprotoma. Later Hay (1923) named B. putorius from Frankstown Cave. Peterson (1926) identified material from Frankstown Cave as B. obtusata, correcting the specific ending to match the gender of the generic name.

The naming of multiple species of Brachyprotoma in the early publications listed above has been widely criticized by later workers because the variation among specimens is less than that seen within living species. Hall (1936) and Kurten and Anderson (1980) considered the genus Brachyprotoma to be clearly monotypic with the only valid species being B. obtusata, the earliest named species that can be applied to the genus. The Brachyprotoma skull from Crystal Ball Cave is the first specimen of Brachyprotoma distinct enough from B. obtusata to warrant the erection of an additional species of this genus.

Concerning the paleoecology of Brachyprotoma, Kurten and Anderson (1980) stated that this genus has always been associated with boreal faunas although other skunk genera were also recognized at each site. This matches the "more boreal than present" nature of the Crystal Ball Cave assemblage and suggests that the post-Pleistocene climatic shift may have lead, directly or indirectly, to the extinction of Brachyprotoma. Since fossils of Brachyprotoma are only found in a few deposits and even then are few in number, this genus probably never had a high density of individuals in life.

The Brachyprotoma brevimala type was first misidentified as Spilogale (Heaton 1984), the most similar living genus. Miller (1982) reported cf. Spilogale from Crystal Ball Cave, possibly based on this same specimen. Mephitis was also mentioned in my preliminary report (Heaton 1984), but further examination proved that the anterior right dentary (BYUVP 7489) upon which the identification was based was equally referable to Martes americana, which is represented by additional material. Although both Mephitis mephitis and Spilogale putorius (=gracilis) now inhabit the Snake Range (Hall 1981), and Spilogale has been recovered from deposits over 12,000 years old in Smith Creek Cave (Mead et al. 1982), their presence is unconfirmed in the Crystal Ball Cave assemblage.

Since Brachyprotoma seems to have lived contemporaneously with other skunk genera, it is interesting to speculate about how their niches varied. All living skunks tend to be nocturnal and omnivorous, so they are rarely tied to specific foods or habitats. Minor niche differences do occur between living North American genera: Spilogale is the most carnivorous, Mephitis the most herbivorous, and Conepatus the most insectivorous. Spilogale has narrow sharp teeth, Conepatus at the other extreme has very broad teeth, and Mephitis is intermediate but has the longest tooth rows. Brachyprotoma (especially B. brevimala) has pushed the narrowing of the teeth seen in Spilogale to an extreme, converging on the carnivorous genus Mustela. This suggests that Brachyprotoma was more carnivorous than any of the living skunks.

Why Brachyprotoma lost P2/ and shortened its tooth rows, paralleling the genus Conepatus, is a mystery. Members of the genus Mustela have longer tooth rows than skunks, so in that respect Brachyprotoma diverged from Mustela. Brachyprotoma was trending in a direction that is difficult to explain. Brachyprotoma also did not survive the post-Pleistocene changes as did the aforementioned genera (although some species were lost and ranges altered). I propose that these two facts are correlated. Brachyprotoma was probably adapting to a specialized niche that existed during the Pleistocene but disappeared during the Recent. I also propose that this specialization was a feeding habit and/or preference for a particular prey item since the specializations discussed are all dental. No postcranial material has been reported to document additional specializations, and skunks' most diagnostic characters, scent glands and color patterns, are in the soft anatomy which is obviously unavailable. With such limited data (about 27 specimens from 9 sites), further speculation would be unwarranted. All that can be concluded is that Brachyprotoma was restricted to boreal conditions, was widespread in North America, was probably low in density, and did not survive the post-Pleistocene changes.

The evolution of the genus Brachyprotoma has been discussed by Kurten and Anderson (1980). They stated that it seems most closely related to Spilogale, but both were probably derived from the Mio-Pliocene genus Promephitis. No intermediate forms are available to show the exact phylogeny, however. Some speculation can be made about the relationship of B. brevimala to B. obtusata. B. brevimala has gone to a greater extreme in the characters that differentiate Brachyprotoma from other skunks (shorter face and narrower teeth) and is therefore more specialized. Since specialists almost always evolve from generalists, B. brevimala probably evolved from B. obtusata. The fact that B. obtusata has been found in deposits from early Pleistocene to early Recent age (Kurten and Anderson 1980) while B. brevimala is known only from a late Pleistocene to Recent deposit also supports this conclusion.

Family Felidae

Smilodon cf. fatalis

Material--Partial left ectocuneiform (BYUVP 7530), claw (BYUVP 7497). Miller (1982) reported cf. Smilodon from Crystal Ball Cave based on a single vertebra (W. E. Miller 1983 personal communication), but this specimen is apparently lost (possibly due to an explosion that affected the collection).

Discussion--The ectocuneiform is dense, worn, and coated with a calcite crust. The claw is missing the outer plates but is otherwise in good condition. The specimens were compared with Smilodon and Felis atrox, the only two late Pleistocene cats large enough to be considered, and both compare best with Smilodon (W. E. Miller 1984 personal communication). The ectocuneiform was previously referred to Panthera atrox (Heaton 1984), but comparison with actual specimens rather than casts shows that it was clearly Smilodon. The only previous citing of Smilodon in Utah is from the Silver Creek fauna of north-central Utah (Miller 1976), but it has been found in Pleistocene assemblages throughout North America.

Kurten and Anderson (1980) considered S. fatalis to be the only valid species of late Pleistocene Smilodon in North America, but it has been known by many other names. Based on this synonymy, the Crystal Ball Cave specimens are referred to S. fatalis although they are doubtfully species specific.

Felis concolor

Material-First right metacarpal (BYUVP 7502), 4 claws (BYUVP 7498-7501).

Discussion-F. concolor is the only cat of its size presently living in North America, but similar-sized species of Acinonyx and Homotherium existed during the Pleistocene. Lynx and other species of Felis (disregarding those often placed in the genus Panthera) are distinctly smaller than F. concolor, and Smilodon, Panthera atrox, and P. onca are distinctly larger. The Crystal Ball Cave specimens were compared with material of Felis species, Acinonyx, and Homotherium at the Los Angeles County Museum and found to match perfectly in size and shape with F. concolor but to clearly differ from the other felids mentioned. F. concolor presently lives throughout the Snake Range (Hall 1981), and J. C. Bates (1983 personal communication) reported a citing in the Snake Valley near Gandy as well as many higher in the mountains.

Lynx cf. rufus

Material--Right C1/ (BYUVP 7494), right P/4 (BYUVP 7496). The anterior portion of a right maxilla without teeth (BYUVP 7495) is probably also referable to Lynx.

Discussion--L. rufus currently inhabits the area of Crystal Ball Cave (J. C. Bates 1983 personal communication) while L. canadensis ranges only as close as central Utah and northward and prefers colder climates (Hall 1981). L. canadensis is slightly larger than L. rufus and has considerably larger feet (Ingles 1965). The specimens recovered fall in the size range of both L. rufus and L. canadensis, but they tend to be closer in size to L. rufus. None of the claws recovered could be referred to this genus, so the difference in foot size was not helpful. Since L. rufus presently lives around the cave, the specimens are referred to it.

Order Perissodactyla
Family Equidae
Equus cf. scotti

Material--Left cuneiform (BYUVP 7542), right lunar (BYUVP 7544), 2 right scaphoids (BYUVP 7549, 7550), right magnum (BYUVP 7561), second phalanx (LACM 123683), third phalanx (BYUVP 7595). A juvenile left P/2 (BYUVP 7623), a partial juvenile first phalanx (BYUVP 7586), a second phalanx (BYUVP 7588), 3 partial third phalanges (BYUVP 7596, 7607, 7608), and a distal sesamoid (BYUVP 7622) probably belong to this species also. Phalanx measurements are listed in tables 4, 5, and 6.