About

Professor Eric Sargis leads research in the Mammalian Evolutionary Morphology Lab at Yale University, focusing on the morphology of living and fossil mammals, including primates. As curator of the Mammalogy and Vertebrate Paleontology collections at the Yale Peabody Museum, he integrates museum-based research with fieldwork, conducting summer expeditions to collect new specimens. His laboratory offers opportunities for students to engage in laboratory, museum, and paleontological field research, emphasizing the study of mammalian form and function through morphological analysis. Professor Sargis's work supports a broad range of investigations into evolutionary biology, functional morphology, and taxonomy, contributing to the understanding of mammalian evolutionary history and diversity.

Research topics

• Paleontology
• Biology
• Evolutionary biology
• Zoology
• Geology
• Ecology

Selected publications

• Rapid weight increases in a primate population: evidence of a plastic response to climate change?

  Proceedings of the Royal Society B Biological Sciences · 2026-05-20

  articleOpen access

  Climate-change-associated decreases in body weight are often predicted because of changing thermoregulatory costs in warmer environments, but evidence for and mechanisms underlying such changes remain elusive. We leverage over two decades of research and 287 weight measurements of Azara's Owl Monkeys (Aotus azarae azarae) to investigate the relationships among temperature, weight and various confounders and report, for the first time in a non-human primate population, rapid mean weight increases. Owl monkey individuals are 50 g heavier in 2023 than in 1999, coinciding with a >1℃ temperature rise. Although heavier individuals may be more likely to reproduce, the potential response to selection is too small to explain this increase. Furthermore, elevated temperatures during post-natal development, not adulthood, are associated with higher weights, suggesting that warmer temperatures during growth may decrease thermoregulatory costs and promote weight acquisition. These results align with the mean weight increase representing a plastic response to a changing environment. These findings highlight the complexity of primate body weight as a plastic phenotype and the need for further research on climate and ecogeographical rules.

  PublisherDOI

• A new species of tree hyrax (Procaviidae: Dendrohyrax) from West Africa and the significance of the Niger-Volta interfluvium in mammalian biogeography

  The Catalogue of Life · 2026-02-16

  datasetOpen access
  PublisherDOI

• New remarkably complete skeleton of Mixodectes reveals arboreality in a large Paleocene primatomorphan mammal following the Cretaceous-Paleogene mass extinction

  Scientific Reports · 2025-03-11 · 3 citations

  articleOpen accessSenior author

  Mixodectids are poorly understood placental mammals from the Paleocene of western North America that have variably been considered close relatives of euarchontan mammals (primates, dermopterans, and scandentians) with hypothesized relationships to colugos, extinct plagiomenids, and/or microsyopid plesiadapiforms. Here we describe the most complete dentally associated skeleton yet recovered for a mixodectid, specifically Mixodectes pungens from the early Paleocene of the San Juan Basin, New Mexico. A partial skull with all the teeth erupted and associated axial skeleton, forelimbs, and hind limbs, with epiphyses fused, indicate that it was a mature adult. Results from cladistic analyses incorporating new data robustly support primatomorphan (Primates + Dermoptera) affinities of Mixodectidae, but relationships within Euarchonta are less clear, with Mixodectes recovered as a stem primatomorphan, stem dermopteran, or stem primate. Analyses of postcrania suggest that M. pungens was a relatively large (~ 1.3 kg), claw-climbing arborealist capable of frequent clinging on large diameter vertical supports. With teeth suggesting an omnivorous diet that included leaves, M. pungens occupied a unique ecological niche in the early Paleocene of North America that differed from contemporary, arboreal plesiadapiforms that were smaller and more frugivorous. Euarchontans were thus a more diverse radiation in the early Cenozoic than previously appreciated.

  PublisherOA PDFDOI

• Additional morphological evidence for taxonomic diversity in the Pen-tailed Treeshrew (<i>Ptilocercus</i>, Scandentia)

  Journal of Mammalogy · 2025-05-07

  article

  Abstract The Pen-tailed Treeshrew Ptilocercus lowii Gray, 1848 is a small arboreal mammal known from Southeast Asia. Two subspecies are currently recognized, P. l. lowii from Borneo and some nearby offshore islands, and P. l. continentis from the Malay Peninsula, Sumatra, and the surrounding islands of Lingga, Karimunbesar, Bangka, Siberut, and Pini. Previous work demonstrated that these 2 subspecies are distinctive in aspects of their osteology, especially their postcranial morphology, which suggests that they may be distinct species. We sought to further investigate taxonomic boundaries of the Pen-tailed Treeshrew by examining museum specimens for differences in linear dimensions of the manus and pes (methods previously shown to reflect species boundaries among treeshrews), as well as in the geometry of the lower second molar using an automatic landmarking algorithm for geometric morphometrics known as auto3dgm and SAMS. Results of the linear measurements suggest that these 2 subspecies are subtly different from one another, though not consistently so, and that P. l. lowii is slightly larger than P. l. continentis in dimensions of the manus and pes. Results of the geometric morphometric analysis suggest that these 2 taxa are distinctive in their molar morphology. Comparisons of gross molar morphology demonstrate that the lower second molar of P. l. lowii is wider crowned, has more lingually placed cusps, and a buccally inflated cingulid. Our work provides further evidence that these subspecies may represent distinct lineages worthy of species-level recognition. This work highlights the need for additional genomic data and the need to reassess the conservation status of Ptilocercus, particularly in light of global climatic change and local deforestation.

  PublisherDOI

• Craniometric variation and taxonomic boundaries in the Madras Treeshrew (Scandentia, Tupaiidae: Anathana ellioti [Waterhouse, 1850]) from India

  Journal of Mammalian Evolution · 2024-01-25 · 3 citations

  articleOpen accessSenior author

  Abstract The Madras Treeshrew, Anathana ellioti (Waterhouse, 1850), is a small, poorly studied mammal from South Asia. It is the only treeshrew found across the southern half of the Indian subcontinent and is the westernmost member of its order (Scandentia). The phylogenetic relationship between Anathana and its putative sister genus, Tupaia , remains unresolved, and the morphological differences between these two genera have yet to be analyzed with craniometric data. Here we describe some features that distinguish Anathana from other treeshrews. However, our comparative morphometric analyses reveal that Anathana overlaps with Tupaia in morphospace; it is smaller than most species (including the only other species found on the Indian mainland, T. belangeri ) but larger than T. minor , Dendrogale melanura , and Ptilocercus lowii . At the infraspecific level, there is some separation between eastern and western populations, but this requires further investigation with larger sample sizes. Unfortunately, Anathana is disproportionately scarce in museum collections relative to other scandentians, and additional biological surveys across South India will be critical for future research on the taxonomy, distribution, and conservation of this elusive taxon.

  PublisherOA PDFDOI

• A new species of fossil guenon (Cercopithecini, Cercopithecidae) from the Early Pleistocene Lower Ngaloba Beds, Laetoli, Tanzania

  Journal of Human Evolution · 2022-01-13 · 7 citations

  article
  PublisherDOI

• Taxonomic boundaries in Lesser Treeshrews (Scandentia, Tupaiidae: <i>Tupaia minor</i>)

  Journal of Mammalogy · 2022-10-05 · 5 citations

  articleSenior author

  Abstract The Lesser Treeshrew, Tupaia minorGünther, 1876, is a small mammal from Southeast Asia with four currently recognized subspecies: T. m. minor from Borneo; T. m. malaccana from the Malay Peninsula; T. m. humeralis from Sumatra; and T. m. sincepis from Singkep Island and Lingga Island. A fifth subspecies, T. m. caedis, was previously synonymized with T. m. minor; it was thought to occur in northern Borneo and on the nearby islands of Banggi and Balambangan. These subspecies were originally differentiated based on pelage color, a plastic feature that has proven to be an unreliable indicator of taxonomic boundaries in treeshrews and other mammals. To explore infraspecific variation among T. minor populations across the Malay Peninsula, Borneo, Sumatra, and smaller islands, we conducted multivariate analyses of morphometric data collected from the hands and skulls of museum specimens. Principal component and discriminant function analyses reveal limited differentiation in manus and skull proportions among populations of T. minor from different islands. We find no morphometric support for the recognition of the four allopatric subspecies and no support for the recognition of T. m. caedis as a separate subspecies on Borneo.

  PublisherDOI

• Recent and rapid ecogeographical rule reversals in Northern Treeshrews

  Scientific Reports · 2022-11-29 · 14 citations

  articleOpen accessSenior author

  Two of the most-studied ecogeographical rules describe patterns of body size variation within species. Bergmann's rule predicts that individuals have larger body sizes in colder climates (typically at higher latitudes), and the island rule predicts that island populations of small-bodied species average larger in size than their mainland counterparts (insular gigantism). These rules are rarely tested in conjunction or assessed across space and time simultaneously. We investigated these patterns in the Northern Treeshrew (Tupaia belangeri) using museum specimens collected across a wide spatial and temporal range. Contrary to Bergmann's rule, size increases with temperature in T. belangeri, a signal that is highly consistent across space and time. We also show that these rules are intertwined: Bergmann's rule is reversed on the mainland but holds on islands, and therefore the island rule is upheld at higher, but not lower, latitudes. Moreover, we demonstrate a rapid reversal of both rules over time. The mechanism behind these inversions remains unclear, though temperature and precipitation are significant predictors of body size. Ecogeographical rules rely on the assumption of a constant relationship between size and the factors driving its variation. Our results highlight the need to question this assumption and reevaluate these rules in the context of accelerating and uneven climate change.

  PublisherOA PDFDOI

• Skeletal Variation and Taxonomic Boundaries in the Pen-tailed Treeshrew (Scandentia: Ptilocercidae; Ptilocercus lowii Gray, 1848)

  Journal of Mammalian Evolution · 2021-12-01 · 7 citations

  articleSenior author
  PublisherDOI

• The limitations of external measurements for aging small mammals: the cautionary example of the Lesser Treeshrew (Scandentia: Tupaiidae: <i>Tupaia minor</i> Günther, 1876)

  Journal of Mammalogy · 2021-05-04 · 2 citations

  articleOpen accessSenior author

  Abstract Age is a basic demographic characteristic vital to studies of mammalian social organization, population dynamics, and behavior. To eliminate potentially confounding ontogenetic variation, morphological comparisons among populations of mammals typically are limited to mature individuals (i.e., those assumed to have ceased most somatic growth). In our morphometric studies of treeshrews (Scandentia), adult individuals are defined by the presence of fully erupted permanent dentition, a common criterion in specimen-based mammalogy. In a number of cases, however, we have had poorly sampled populations of interest in which there were potentially useful specimens that could not be included in samples because they lacked associated skulls. Such specimens typically are associated with external body and weight measurements recorded by the original collectors, and we sought to determine whether these data could be used successfully as a proxy for age or at least to establish maturity. We analyzed four traditional external dimensions (head-and-body length, tail length, hind foot length, and ear length) and weight associated with 103 specimens from two allopatric populations of the Lesser Treeshrew (Tupaia minor Günther, 1876) from Peninsular Malaysia and from Borneo, which we treated as separate samples (populations). Individuals were assigned to one of eight age categories based on dental eruption stage, and measurements were compared among groups. In general, mean sizes of infants and subadults were smaller than those of adults, but the majority of subadults fell within the range of variation of adults. The large overlap among infants, subadults, and adults in external measurements and weight indicates that such measures are poor proxies for age in this species, probably for treeshrews in general, and possibly for other small mammals. This has significant implications for any investigation wherein relative age of individuals in a given population is an important consideration.

  PublisherOA PDFDOI

Recent grants

• Doctoral Dissertation Improvement Grant: Origin and Early Evolutionary History of Primates

  NSF · $14k · 2010–2013

• Collaborative Research: Systematics, Biogeography, and Ecogeographic Variation in Treeshrews (Mammalia, Scandentia)

  NSF · $90k · 2006–2010

Frequent coauthors

• Neal Woodman

  Eastern Ecological Science Center

  129 shared

• Link E. Olson

  University of Alaska Fairbanks

  118 shared

• Aspen T. Reese

  University of California, San Diego

  73 shared

• Stephen G. B. Chester

  The Graduate Center, CUNY

  71 shared

• Christopher C. Gilbert

  61 shared

• Mary Silcox

  University of Toronto

  46 shared

• Jonathan I. Bloch

  Florida Museum of Natural History

  36 shared

• Ananth Miller-Murthy

  30 shared

Labs

• Mammalian Evolutionary Morphology LabPI