Using extant patterns of dental variation to identify species in the primate fossil record: a case study of middle Eocene Omomys from the Bridger Basin, southwestern Wyoming.
ABSTRACT Patterns of extant primate dental variation provide important data for interpreting taxonomic boundaries in fossil forms. Here I use dental data from several well-known living primates (as well as data from selected Eocene forms) to evaluate dental variation in Middle Eocene Omomys, the first North American fossil primate identified by paleontologists. Measurements were collected from a sample of 148 omomyid dental specimens recovered from Bridger B localities in the Bridger Basin, Wyoming. Most of these specimens have not previously been described. Nonmetric traits were also scored for this sample. Lower molar coefficients of variation range from 4.01 for M2 length (n = 80) to 6.73 for M3 talonid width (n = 57). All of the nonmetric traits scored exhibit less than 100% presence in the overall sample, including traits previously described as representative of Omomys (e.g., P4 metaconids present in 91%, n = 55; M2 pericones present in 80%, n = 15). Dental traits also vary in a set of spatially restricted localities from the same fossil horizon and in a separate, single fossil locality (DMNH 868, P4 metaconids present in 67%, n = 6). An increasing frequency in several premolar traits across time in these more restricted samples suggests an anagenetic change in Bridger B Omomys. However, this degree of morphological variability is consistent with that seen in extant primate species from single locations. Metric variation in this sample is comparable to that seen in other Eocene primates, such as new data presented here for the omomyid Arapahovius gazini from the Washakie Basin, southern Wyoming. Omomys metric variation is also comparable to that found in several samples of well-known extant primates from single localities (e.g., ring-tailed lemurs and gray-brown mouse lemurs). These metric data also correspond to the patterns of variability described in previously published studies of Omomyscarteri. In sum, a single species interpretation (O. carteri) for this new Bridger B Omomys sample from southern Wyoming is affirmed, and this study illustrates the usefulness of dental data from extant primates for evaluating primate fossil samples.
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ABSTRACT: The earliest euprimates to arrive in North America were larger-bodied notharctids and smaller-bodied omomyids. Through the Eocene, notharctids generally continued to increase in body size, whereas omomyids generally radiated within small- and increasingly mid-sized niches in the middle Eocene. This study examines the influence of changing body size and diet on the evolution of the lower fourth premolar in Eocene euprimates. The P4 displays considerable morphological variability in these taxa. Despite the fact that most studies of primate dental morphology have focused on the molars, P4 can also provide important paleoecological insights. We analyzed the P4 from 177 euprimate specimens, representing 35 species (11 notharctids and 24 omomyids), in three time bins of approximately equal duration: early Wasatchian, late Wasatchian, and Bridgerian. Two-dimensional surface landmarks were collected from lingual photographs, capturing important variation in cusp position and tooth shape. Disparity metrics were calculated and compared for the three time bins. In the early Eocene, notharctids have a more molarized P4 than omomyids. During the Bridgerian, expanding body size range of omomyids was accompanied by a significant increase in P4 disparity and convergent evolution of the semimolariform condition in the largest omomyines. P4 morphology relates to diet in early euprimates, although patterns vary between families. Am J Phys Anthropol 153:15-28, 2014. © 2013 Wiley Periodicals, Inc.American Journal of Physical Anthropology 01/2014; 153(1):15-28. · 2.51 Impact Factor
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ABSTRACT: Small mammals are rarely reported from subfossil sites in Madagascar despite their importance for paleoenvironmental reconstruction, especially as it relates to recent ecological changes on the island. We describe the uniquely rich subfossil small mammal fauna from Ankilitelo Cave, southwestern Madagascar. The Ankilitelo fauna is dated to the late Holocene (,500 years ago), documenting the youngest appearances of the extinct giant lemur taxa Palaeopropithecus, Megaladapis, and Archaeolemur, in association with abundant remains of small vertebrates, including bats, tenrecs, carnivorans, rodents, and primates. The Ankilitelo fauna is composed of 34 mammalian species, making it one of the most diverse Holocene assemblages in Madagascar. The fauna comprises the 1st report of the short-tailed shrew tenrec (Microgale brevicaudata) and the ring-tailed mongoose (Galidia elegans) in southwestern Madagascar. Further, Ankilitelo documents the presence of southwestern species that are rare or that have greatly restricted ranges today, such as Nasolo's shrew tenrec (M. nasoloi), Grandidier's mongoose (Galidictis grandidieri), the narrow-striped mongoose (Mungotictis decemlineata), and the giant jumping rat (Hypogeomys antimena). A simple cause for the unusual small mammal occurrences at Ankilitelo is not obvious. Synergistic interactions between climate change, recent fragmentation and human-initiated degradation of forested habitats, and community-level processes, such as predation, most likely explain the disjunct distributions of the small mammals documented at Ankilitelo.Journal of Mammalogy 10/2009; 90(5):1111-1131. · 2.23 Impact Factor
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ABSTRACT: A thorough knowledge of biological variation in extant primates is imperative for interpreting variation, and for delineating species in primate biology and paleobiology. This is especially the case given the recent, rapid taxonomic expansion in many primate groups, notably among small-bodied nocturnal forms. Here we present data on dental, cranial, and pelage variation in a single-locality museum sample of mouse lemurs from Amboasary, Madagascar. To interpret these data, we include comparative information from other museum samples, and from a newly collected mouse lemur skeletal sample from the Beza Mahafaly Special Reserve (BMSR), Madagascar. We scored forty dental traits (n = 126) and three pelage variants (n = 19), and collected 21 cranial/dental measures. Most dental traits exhibit variable frequencies, with some only rarely present. Individual dental variants include misshapen and supernumerary teeth. All Amboasary pelage specimens display a "reversed V" on the cap, and a distinct dorsal median stripe on the back. All but two displayed the dominant gray-brown pelage coloration typical of Microcebus griseorufus. Cranial and dental metric variability are each quite low, and craniometric variation does not illustrate heteroscedasticity. To assess whether this sample represents a single species, we compared dental and pelage variation to a documented, single-species M. griseorufus sample from BMSR. As at Amboasary, BMSR mouse lemurs display limited odontometric variation and wide variation in non-metric dental traits. In contrast, BMSR mouse lemurs display diverse pelage, despite reported genetic homogeneity. Ranges of dental and pelage variation at BMSR and Amboasary overlap. Thus, we conclude that the Amboasary mouse lemurs represent a single species - most likely (in the absence of genetic data to the contrary) M. griseorufus, and we reject their previous allocation to Microcebus murinus. Patterns of variation in the Amboasary sample provide a comparative template for recognizing the degree of variation manifested in a single primate population, and by implication, they provide minimum values for this species' intraspecific variation. Finally, discordance between different biological systems in our mouse lemur samples illustrates the need to examine multiple systems when conducting taxonomic analyses among living or fossil primates.Journal of Human Evolution 12/2012; · 4.09 Impact Factor