Taxonomy and notes on the paleobiology of the late Pleistocene (Rancholabrean) antilocaprids (Mammalia, Artiodactyla, Antilocapridae) from the state of Hidalgo, central Mexico (original) (raw)
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A set of cranial and dental material of Antilocapridae was recovered from Quaternary deposits that outcrop in southeastern Hidalgo, central Mexico. The fossil bearing unit consists of clay, silt, sand, and scarce conglomeratic lenses in a fluvial environment; the specimens are associated with Bison indicating a Rancholabrean Land Mammal Age. The comparative study of the material with selected specimens of North American antilocaprids, allowed its identification as the small-sized species Capromeryx minor and the medium-sized Stockoceros conklingi. The sample referable to C. minor shows a combination of cranial and dental characters typical of this species, including a large posterior tine that is curved upward and forward, posterior horn core with a deep sulcus on its posterior side that extends from the base to the tip, and well-developed heel on M3. The isotopic analysis of teeth referable to this species from Hidalgo indicates a mixed feeding dietary behavior. A partial skull and associated horn core fragments were assigned to Stockoceros conklingi, considering its larger size than C. minor and shorter than the extant pronghorn Antilocapra americana, as well as for having symmetrical and diverging horn cores, and more outwardly flaring horn cores. The recognition of these antilocaprids in southeastern Hidalgo represents one of the southernmost occurrences within temperate North America. The tiny Capromeryx minor is known in North American localities of lower altitude (0-100 m a.s.l.) compared to those of the medium-sized Stockoceros conklingi . Hence, body size differences between both species and altitude differences between some of their localities suggests minimal direct competition between these antilocaprids.
Creek is an open site in Union County, northeastern New Mexico, which has produced a Rancholabrean vertebrate fauna characterized by the presence of Bison and Mammuthus. A partial skull with both right and left horn cores of Capromeryx furcifer is described from this site in which the anterior prong of the horn core is reduced to little more than a nubbin of bone about 3 mm in height. This represents the most extreme reduction in the anterior prong of the horn core of Capromeryx yet known. We suggest that the anterior prong may not have been expressed at all in the keratinous horn sheath, or that, alternatively, a fairly substantial keratinous expression of the anterior sheath may have been present despite the absence of a concomitantly developed horn core. We further speculate that the reduction in the anterior prong may have been associated with a progressive invasion of less-open vegetation and the adoption of a more solitary life style, paralleling similar differences in the elaboration of cranial appendages in living bovids and cervids.
Pleistocene Microvertebrates from Santa Cruz Nuevo, Puebla, México
The Pleistocene was characterized by drastic climatic changes that influenced patterns of evolution and geographical distribution of the biota. At the end of this period occurred an important event, the extinction of megafauna; however, few genera of microvertebrates have been reported as extinct. Holman (1995) notes that no family or genus of herpetofauna became extinct and that only 12 of 129 taxa are in doubt. In Mexico, 776 Pleistocene-age localities bear mammal remains in which 286 species and 146 genera are identified; 30 percent of the species are not present today in Mexico (Arroyo-Cabrales et al. 2002). There are 29 registered localities with 98 genera and 118 species of birds, of which 17 species are reported as extinct (Corona 2002). Present in 27 localities are remains of herpetofauna, including 10 genera and 19 species of amphibians with no extinct species, and 27 genera and 39 species of reptiles with 4 extinct species. It is clear that the avian and herpetofauna fossil record in Mexico is poor. In the southeastern part of the state of Puebla, near the village of Santa Cruz Nuevo, a sequence of ca. 38 m of fluvial late-Cenozoic sands, silts, and gravels outcrops. During the last four years sediment from different sites was collected for screen washing, and Pleistocene remains of anurans, reptiles, birds and micromammals were recovered. The objective of the study was to evaluate change in the microfaunal assemblage from the late Pleistocene to the present. Until now, 22 families, 24 genera, and 11 species of vertebrates identified include Ambystoma sp., Bufo occidentalis, Bufo cf. valliceps, Bufo sp., Rana sp., Kinosternon sp., Rhinoclemys sp., Gopherus cf. berlandieri, Sceloporus cf. grammicus, Sceloporus cf. horridus, Conopsis sp., Lampropeltis sp., Leptodeira sp., Senticolis sp., Thamnophis sp., Trimorphodon sp., Crotalus sp., remains of plethodontids, spade-foot frogs, skinks, Neotoma mexicana, Peromyscus difficilis, Reithrodontomys sp., Sylvilagus floridanus, Sylvilagus sp., and Bassariscus cf. sumichrasti. Megafauna identified includes Odocoileus sp., Pampatherium mexicanum, Glyptotherium sp., Equus conversidens, Mammuthus sp., and unidentified genera of deer, bear, goat, and mastodont. The presence of Peromyscus difficilis, Neotoma mexicana, and Pampatherium mexicanum confirms a late-Pleistocene age for the deposit. Excellently preserved fossil remains suggest the identified taxa probably lived near the deposit area. Of the family-level taxa identified, 50 percent are present today in the study area (Bufonidae, Scaphiopodidae, Ranidae, Phrynosomatidae, Colubridae, Viperidae, Kinosternidae, Leporidae, Muridae, Procyonidae, and Cervidae) 18 percent are reported extinct in North America (Pampatheriidae, Glyptodontidae, Equidae and Elephantidae); and 32 percent have experienced a change in their geographic distribution (Ambystomatidae, Plethodontidae, Bataguridae, Testudinidae, Scincidae, Antilocapridae, and Ursidae). As expected, most of the megafauna taxa became extinct, and some of them (Antilocapridae and Ursidae) today are distributed differently. The presence of the gopher turtle Gopherus is noteworthy because it represents the southernmost record of the genus in North America. At present, four species range from southern Nevada in the United States to southeastern San Luis Potosí in Mexico. Recently Gopherus was reported in the state of Hidalgo (Nájera-Hernández and Castillo-Cerón 2004a, 2004b), filling the gap between northern Mexico and Puebla. This faunal association is a mixture of taxa with different ecological requirements. Although most of the fossil taxa inhabit a semiarid environment (Bufo occidentalis, Sceloporus cf. horridus, Gopherus cf. berlandieri, Peromyscus difficilis, and the family Scaphiopodidae), they are found together with taxa usually associated with more humid (tropical and subtropical) conditions, such as the frog B. valliceps and the turtle Rhinoclemmys (Ernst and Barbour 1989; Porter 1970). Giant armadillos (Pampatherium and Glyptotherium) are considered tropical or semitropical organisms (Gillete and Ray 1981). Salamanders of the genus Ambystoma live in rivers or lakes in temperate subtropical areas; on the other hand, salamanders of the family Plethodontidae are partially or completely arboreal species that inhabit cloud forest or wet montane forest (Wake and Lynch 1976). Bears inhabit the oak forest. The presence of different species with disparate ecological requirements suggests the existence of a disharmonious or ecologically incompatible association, as proposed by Fay (1988) and Graham and Lundelius (1984). Bufo occidentalis, Sceloporus cf. horridus, Sceloporus cf. grammicus, and the genera Rhinoclemmys and Senticolis are here reported for the first time in North America. The genera Conopsis and Leptodeira and the families Plethodontidae and Scincidae are new fossil records for Mexico.
MINI-PAPERS, 2001
Most of the vertebrate fossils from Tijeras Arroyo, located just south of the Albuquerque International Airport in Bernalillo County, are derived from the Sierra Ladrones Formation and are early Irvingtonian in age (Lucas et al., 1993). However, one locality (New Mexico Museum of Natural History and Science [NMMNH] site L-1458) at the base of the exposed stratigraphic section in Tijeras Arroyo (Fig. 1) has produced two species that are indicative of a Blancan age. The fossils from this site were derived from a sandstone comprising unit 1 in the stratigraphic section of Lucas et al. (1993, fig. 2). The lowermost part of the section in Tijeras Arroyo, including unit 1, was recently referred to the Ceja Member of the Arroyo Ojito Formation (Connell and Hawley, 1998; Connell et al., 1999). Both mammals identified from site L-1458 in the Tijeras Arroyo section, Hypolagus cf. H. gidleyi and Equus cf. E. cumminsii, are typical of Blancan faunas, and do not occur in the Irvingtonian. The extinction in the late Pliocene (about 2.2 Ma) of several characteristic Blancan genera, including Hypolagus, Borophagus, Rhynchotherium, and Nannippus, is considered one of the most important biochronological events in the late Blancan (Lindsay et al., 1984). The presence of Hypolagus thus indicates that site L-1458 is older than 2.2 Ma. Equus cf. E. cumminsii appears to be absent from early Blancan faunas, so L-1458 is probably middle or early late Blancan in age. Ten stratigraphically higher localities in Tijeras Arroyo have produced a significant vertebrate fauna of early Irvingtonian age (Lucas et al., 1993; Morgan and Lucas, 2000). More than 75 m of the Sierra Ladrones Formation are exposed in Tijeras Arroyo, consisting of sandstones, pumiceous sandstones, and gravels, with minor amounts of mudstone and diatomite. These sediments represent axial river deposits of an ancestral Rio Grande. The most distinctive lithologic chracteristic of these beds is the presence of reworked Guaje Pumice derived from the Bandelier Tuff, Ar/Ar dated at 1.61 Ma (Izett and Obradovich, 1994), in the units associated with an Irvingtonian fauna (units 3-8 of Lucas et al., 1993). An extensive flora of leaves and pollen from a localized volcanic ash bed was collected in the Tijeras Arroyo section (NMMNH Site L-1445). The Tijeras Arroyo flora indicates that the cottonwood forest or bosque currently found along the banks of the Rio Grande in New Mexico dates back to at least the early Pleistocene (Knight et al., 1996).
Fossil specimens of American mastodons (Mammut americanum) that have been recovered from fluvial sedimentary deposits of the late Pleistocene of southeastern Hidalgo, central Mexico, are formally described. The sample includes cranial and postcranial remains of an adult male that represents one of the most complete mastodons that have been found in Mexico, as well as a molar belonging to an old individual. The material from Hidalgo shows the following diagnostic features of M. americanum: well-developed tusks that curved upward; upper and lower molars with a simple occlusal pattern; last molars with four to five lophs/ids; a medial sulcus between the lophs/ids; a scapula with a straight caudal border, a short and expanded neck, and a glenoid cavity that is oval in outline; a short and robust humerus with a prominent epicondylar crest; a radius with a wide distal end; and an ulna with a well-developed olecranon process and a deep trochlear notch. The dental size of the mastodon from Hidalgo is comparable to that of mastodons from the Gulf Coastal Plain and the Great Lakes region, whereas the limb dimensions are similar to those of the Watkins Glen Mastodon from the late Pleistocene of New York. In order to characterize the diet and habitat of the mastodons from Hidalgo, a stable carbon and oxygen isotope analysis in tooth enamel apatite was performed. The results indicate that studied specimens were mainly C3 browsers (mean δ13C isotope value of -10.06 ‰) that thrived in closed habitats covered by high vegetation, such as trees (mean δ18O isotope value of -4.31 ‰). This information suggests the presence of closed habitats in the southeastern region of Hidalgo, during the second half of the Pleistocene.
White et al Antilocapridae from Nueces River Texas proofs
Three extinct genera and species of Antilocapridae (Mammalia: Artiodactyla), Tetrameryx shuleri, Stockoceros conklingi, and Capromeryx furcifer, are reported from the latest Pleistocene (Rancholabrean NALMA) Nueces River Fauna on the Gulf Coastal Plain of southeastern Texas. A fourth extinct genus and species of antilocaprid, the early Pliocene (latest Hemphillian NALMA) Hexameryx simpsoni, is represented by two reworked specimens from the Pliocene Goliad Formation. The largest of the three Rancholabrean antilocaprids in the Nueces River Fauna, Tetrameryx shuleri, is represented by a sample of nine horn cores, each with two prominent prongs, one oriented anteriorly and the other oriented posteriorly, with the posterior prong much longer. Five horn cores are identified as Stockoceros conklingi, intermediate in size between the larger Tetrameryx and smaller Capromeryx. S. conklingi also has two prongs on each horn core, oriented anteriorly and posteriorly but compared to Tetrameryx the anterior and posterior prongs are about the same length. A single two-pronged horn core of Capromeryx furcifer is considerably smaller than horn cores of Tetrameryx or Stockoceros. The horn core of C. furcifer also has a different configuration than the other two genera, with two vertically oriented prongs, a much larger posterior prong and a tiny anterior prong. Two partial horn cores from the same gravel pit that produced the Rancholabrean Nueces River Fauna are similar in size and shape to horn cores of the six-horned antilocaprid Hexameryx simpsoni, originally described from the latest Hemphillian Palmetto Fauna in Florida and are here referred to the early Pliocene (latest Hemphillian) Lake Corpus Christi Local Fauna. The Nueces River fauna is the only Rancholabrean fauna in the United States that, together with two faunas from Mexico, contains three genera of antilocaprids, Tetrameryx, Stockoceros, and Capromeryx. The easternmost Rancholabrean records of both Stockoceros and Capromeryx are from the Nueces River Fauna. Late Pleistocene records of Tetrameryx are limited to Texas and Mexico, but are more widely distributed in the early and middle Pleistocene. Stable isotope studies suggest Tetrameryx was a grazer, Stockoceros a mixed feeder, and Capromeryx a browser, indicating that a wide range of habitats were present along the Nueces River on the Texas Gulf Coast Plain in the late Pleistocene, supporting a diverse biota of large mammals in the Nueces River Fauna.
We review seven Pliocene and early Pleistocene (Blancan) vertebrate faunas from the Palomas Formation near Elephant Butte Lake and Caballo Lake in Sierra County, southwestern New Mexico. These faunas occur in a narrow (<10 km wide), north-south trending belt of sediments in the Rio Grande Valley that are exposed over a distance of about 40 km. The three northernmost faunas (Elephant Butte Lake, Cuchillo Negro Creek, and Truth or Consequences) are located in the Engle basin and are late early Blancan in age. The Elephant Butte Lake Fauna is composed of 8 species-the land tortoise Hesperotestudo and 7 species of mammals. The Cuchillo Negro Creek Local Fauna (LF) is somewhat more diverse with 12 species-4 turtles/tortoises and 8 mammals. The Elephant Butte Lake and Cuchillo Negro Creek faunas are composed primarily of large mammals, including the gomphothere Stegomastodon primitivus and the horses Equus simplicidens and E. scotti. S. primitivus is limited to early Blancan faunas and the earliest co-occurrence of E. simplicidens and E. scotti is during the late early Blancan. The canid Borophagus hilli from Cuchillo Negro Creek is known only from latest Hemphillian and early Blancan faunas. The Mud Springs pumice dated at 3.1 Ma can be correlated with the Cuchillo Negro Creek Fauna, and both faunas occur in strata beneath the 2.9 Ma Mitchell Point basalt. The co-occurrence of B. hilli, E. simplicidens, E. scotti, and S. primitivus, absence of South American immigrant mammals from the Pliocene phase of the Great American Biotic Interchange (GABI), and association with the 3.1 Ma Mud Springs pumice, indicate a latest early Blancan age (~3.0-3.3 Ma) for the Cuchillo Negro Creek and Elephant Butte Lake LFs. The Truth or Consequences LF has at least 25 species, including several small fish, an anuran, several lizards and snakes, 3 freshwater turtles, 3 birds, and 15 mammals. The fauna primarily consists of small vertebrates, including several small mammals typical of the early Blancan: the leporids Hypolagus vetus and Notolagus lepusculus and the rodents Geomys minor, Neotoma cf. N. fossilis, and Jacobsomys. This small mammal assemblage is similar to those found in the early Blancan Rexroad Fauna in Kansas and Benson Fauna in Arizona. Like those two faunas, the Truth or Consequences LF occurs in normally magnetized strata correlated with the lowermost Gauss Chron (3.33-3.58 Ma). Magnetostratigraphy and occurrence 40 m below the Mud Springs pumice suggest that the Truth or Consequences LF is somewhat older (~3.3-3.6 Ma) than other two faunas from the Engle basin. The four southernmost faunas from the Palomas Formation (Williamsburg, Palomas Creek, Kelly Canyon, and Caballo) are in the Palomas basin and are late Blancan in age. The Williamburg LF consists of only 7 species of mammals, but documents the association of the three-toed horse Nannippus peninsulatus and the small mylodont ground sloth Paramylodon cf. P. garbanii, a South American immigrant that participated in the late Pliocene/early Pleistocene phase of the GABI. These two species coexisted only during a short interval in the latest Pliocene (early late Blancan), after the onset of the Interchange in the southwestern United States at about 3.0 Ma and before the extinction of Nannippus at about 2.5 Ma. Paramylodon and Nannippus also co-occur in the Pearson Mesa LF in southwestern New Mexico in strata magnetostratigraphically correlated with the uppermost Gauss Chron (2.58-3.04 Ma). The Palomas Creek Fauna consists of a tortoise and 10 mammals, including N. peninsulatus, but lacks Interchange mammals. Palomas Creek also has the larger horses E. calobatus, E. cumminsii, and E. simplicidens, and shares the rodents Geomys paenebursarius and Sigmodon medius with Williamsburg, all of which co-occur in the late Blancan. The faunas from Palomas Creek and Williamburg are similar in age (early late Blancan age, ~2.6-3.0 Ma), and correlate with other early late Blancan faunas in New Mexico (Anapra, Pearson Mesa), Texas (Hudspeth, Red Light), and Arizona (111 Ranch). The Caballo LF includes small fish, a toad, a salamander, a snake, 2 tortoises, several birds, and 15 mammals. Caballo documents the association of the glyptodont Glyptotherium arizonae, a large species of the mole Scalopus, and E. scotti. Glyptotherium is a member of the South American Interchange fauna; however, the large species G. arizonae did not appear until the late Blancan (~2.4 Ma) and is also known from the early Irvingtonian (~1.0-1.6 Ma). E. scotti is also known from both late Blancan and early Irvingtonian faunas. However, Scalopus is unknown in New Mexico after the late Blancan, and the mammoth Mammuthus, the defining genus for the Irvingtonian, is absent in the Caballo LF. Magnetostratigraphy of the nearby Las Animas Creek stratigraphic section indicates that the Caballo LF was derived from strata correlating to the middle of the Matuyama Chron (latest Blancan; ~1.8-2.2 Ma). The Kelly Canyon LF consists almost entirely of small vertebrates, primarily aquatic, including many species of fish, frogs, salamanders, a diverse avifauna, and 4 mammals. The only agediagnostic mammal from Kelly Canyon is the extinct muskrat Ondatra idahoensis, a species typical of the late Blancan. Lithostratigraphic correlation suggests that Kelly Canyon and Caballo are similar in age (latest Blancan). Amphibia Anura Remarks: The three microvertebrate faunas screenwashed from the Palomas Formation, Truth or Consequences, Caballo, and Kelly Canyon, all contain small samples of frogs and/or toads (Anura). Several elements, in particular the ilium, have been identified to the generic level, including the toad Bufo from Caballo and frog Rana from Kelly Canyon. The most common taxa in the Caballo microfauna are rodents, rabbits, and snakes, suggesting a terrestrial depositional environment, which is supported by the presence of Bufo. The Kelly Canyon microfauna is dominated by fish, and also contains salamanders and ducks, strongly indicating a freshwater depositional environment, supported by the presence of Rana. Although present in small numbers in most Blancan microfaunas from New Mexico, anurans are common in only one of these sites, the early Blancan Buckhorn LF from the Gila Group in the southwestern part of the state. Rana is by far the most common vertebrate at Buckhorn, which, together with the presence of small fish, flamingos, salamanders, and other aquatic taxa, as well as the lithology of the sediments, indicates a likely lacustrine origin for the Buckhorn microfauna (Morgan et al., 1997). Caudata Ambystomatidae Ambystoma sp. Remarks: Salamanders of the genus Ambystoma occur in the Caballo and Kelly Canyon sites from the Palomas Formation. Small samples of less than 10 vertebrae of Ambystoma identified from screenwashed samples from each of these sites are similar to vertebrae of the modern tiger salamander Ambystoma tigrinum. However, without further study, we hesitate to identify the Blancan vertebrae beyond the generic level. Other Blancan records of Ambystoma from New Mexico include the early Blancan Buckhorn LF from Grant County and the latest Blancan La Union Fauna from Doña Ana County (Morgan et al., 1997). At the present time, A. tigrinum occurs in a wide variety of habitats in New Mexico provided there is a nearby source of nonflowing freshwater water for breeding (Degenhardt et al., 1996