Sarah L Shelley

University of Colorado Boulder | CUB

Following the end-Cretaceous mass extinction, mammals underwent an increase in body size, taxonomic diversity and ecological specialization throughout the Paleocene, exemplifying their adaptability. One especially enigmatic group is the “Triisodontidae”, medium- to large-sized ungulate-like placentals from the Paleocene which are best known from th...

Conoryctes comma is a member of the enigmatic group Taeniodonta, Paleogene mammals that have been found only in North America. Taeniodonts were part of the first wave of placental mammal diversification after the end-Cretaceous extinction. The lack of postcranial elements has limited the understanding of the anatomy and locomotion of Conoryctes, an...

Ever since the discovery of Macrauchenia patachonica by Charles Darwin in 1834, the affinities of litopterns—a group of extinct South American Native Ungulates (SANUs)—have been elusive. In particular, the interfamilial relationships and timing of the familial diversification within the order Litopterna have not been addressed with adequate taxon a...

After successfully diversifying during the Paleocene, the descendants of the first wave of mammals that survived the end-Cretaceous mass extinction waned throughout the Eocene. Competition with modern crown clades and intense climate fluctuations may have been part of the factors leading to the extinction of these archaic groups. Why these taxa wen...

We describe a new macraucheniine macraucheniid, Micrauchenia saladensis gen. et sp. nov., from the late Miocene (Huayquerian SALMA). This is the first litoptern from Bahía Inglesa Formation, Chile. The specimen includes a partial mandible, cervical and thoracic vertebrae fragments, and portions of the forelimbs (a scapula fragment, an ulna-radius f...

After the end-Cretaceous extinction, placental mammals quickly diversified1, occupied key ecological niches2,3 and increased in size4,5, but this last was not true of other therians6. The uniquely extended gestation of placental young7 may have factored into their success and size increase8, but reproduction style in early placentals remains unknow...

Mammals are the most encephalized vertebrates, with the largest brains relative to body size. Placental mammals have particularly enlarged brains, with expanded neocortices for sensory integration, the origins of which are unclear. We used computed tomography scans of newly discovered Paleocene fossils to show that contrary to the convention that m...

We describe the tympanic anatomy of the petrosal of Deltatherium fundaminis, an enigmatic Paleocene mammal based on cranial specimens recovered from New Mexico, U.S.A. Although the ear region of Deltatherium has previously been described, there has not been a comprehensive, well-illustrated contribution using current anatomical terminology. The den...

To date, a complete auditory apparatus (with malleus, incus, stapes, ectotympanic, and perhaps surangular) is known for only three Mesozoic mammals, the haramiyidan Arboroharamiya allinhopsoni 1 , the multituberculate Sinobaatar pani 2 , and the zhangheotheriid Origolestes lii 3 , with subsets of these bones preserved in a handful more, including t...

A small piece of cartilage or bone, the element of Paaw, occurs in the tendon of the stapedius muscle in some extant marsupial and placental mammals. It has been nearly a century since the last comprehensive treatment of the distribution of the element of Paaw in mammals. The current report updates knowledge on this structure by synthesizing the su...

Mammals exhibit vast ecological diversity, including a panoply of locomotor behaviours. The foundations of this diversity were established in the Mesozoic, but it was only after the end-Cretaceous mass extinction that mammals began to increase in body size, diversify into many new species and establish the extant orders. Little is known about the p...

Among extant vertebrates, mammals are distinguished by having a chain of three auditory ossicles (the malleus, incus and stapes) that transduce sound waves and promote an increased range of audible—especially high—frequencies¹. By contrast, the homologous bones in early fossil mammals and relatives also functioned in chewing through their bony atta...

The end-Cretaceous mass extinction, 66 million years ago, profoundly reshaped the biodiversity of our planet. After likely originating in the Cretaceous, placental mammals (species giving live birth to well-developed young) survived the extinction and quickly diversified in the ensuing Paleocene. Compared to Mesozoic species, extant placentals have...

Conference talk

Colbert Poster Prize, Mesozoic & Early Cenozoic Mammalian Evolution

Colbert Poster Prize, Mesozoic & Early Cenozoic Mammalian Evolution

The anatomy of the petrosal and associated middle ear structures are described and illustrated for the brown rat, Rattus norvegicus (Berkenhout, 1769). Although the middle ear in this iconic mammal has been treated by prior authors, there has not been a comprehensive, well-illustrated contribution using current anatomical terminology. Descriptions...

The end‐Cretaceous mass extinction allowed placental mammals to diversify ecologically and taxonomically as they filled ecological niches once occupied by non‐avian dinosaurs and more basal mammals. Little is known, however, about how the neurosensory systems of mammals changed after the extinction, and what role these systems played in mammalian d...

The superfamily Djadochtatherioidea is a distinctive clade of multituberculates from Upper Cretaceous beds of Mongolia and Inner Mongolia, China. Because many of the 11 included genera are known from skulls, more is known about the cranial anatomy of djadochtatherioids than any other clade of multituberculates. Within Djadochtatherioidea, the most...

SIZE VARIATION IN POPULATIONS OF TETRACLAENODON (MAMMALIA, ‘CONDYLARTHRA’), FROM THE TORREJONIAN NALMA OF THE SAN JUAN BASIN (NEW MEXICO) REVEALS NEW INSIGHTS INTO THEIR EVOLUTION AND PALEOENVIRONMENT HOLPIN, Sofia, University of Edinburgh, Edinburgh, Scotland; WILLIAMSON, Thomas E., New Mexico Museum of Natural History, Albuquerque, NM, United St...

Colbert Prize Poster Session

Conference talk

In non-mammalian amniotes, the parasphenoid is a midline dermal element with a narrow rostral portion, the cultriform process, linked to the interorbital septum and an expanded distal portion, the alae or wings, forming part of the ventral skull base. In mammals, the parasphenoid has not been found in extant monotremes and only a handful of reports...

Mammals underwent a profound diversification after the end‐Cretaceous mass extinction, with placentals rapidly expanding in body size and diversity to fill new niches vacated by dinosaurs. Little is known, however, about the brains and senses of these earliest placentals, and how neurosensory features may have promoted their survival and diversific...

Periptychus is the archetypal genus of Periptychidae, a clade of prolific Paleocene ‘condylarth’ mammals from North America that were among the first placental mammals to radiate after the end-Cretaceous extinction, remarkable for their distinctive dental anatomy. A comprehensive understanding of the anatomy of Periptychus has been hindered by a la...

Periptychus carinidens raw anatomical measurements. This file is formatted as an excel file and includes raw measurements for the Periptychus specimens described in this paper. Individual bones are listed in separate tabs. (XLSX)

Eutherian mammals—placentals and their closest extinct relatives—underwent a major radiation following the end-Cretaceous extinction, during which they evolved disparate anatomy and established new terrestrial ecosystems. Much about the timing, pace, and causes of this radiation remain unclear, in large part because we still know very little about...

The diversification of eutherian mammals following the end-Cretaceous mass extinction was a critical period in evolutionary history. The Palaeocene is marked by the proliferation of archaic mammals which exhibit a mosaic of primitive and derived anatomies and whose phylogenetic affinities with extant mammals remain contentious. Consequently, macroe...

Triisodontids are an archaic group of mammals that possess dental adaptations for carnivory, but are not members of the order Carnivora. They were probably apex mammalian predators for much of the early Paleocene. The wolf-sized species of Triisodon were the largest triisodontids and were also among the largest mammals of their time. A new specimen...

the Palaeocene, reaching their zenith in diversity and body size in the Palaeocene. Taeniolabidoidea, the topic of this paper, includes the largest known multituberculates, which possess highly complex cheek teeth adapted for herbivory. A new specimen from the early Palaeocene (middle Puercan; biochron Pu2) of the Nacimiento Formation, New Mexico r...

The phylogenetic relationships among archaic taxa of the Paleocene remain poorly resolved and as such hinder our understanding about how mammals recovered following the end-Cretaceous mass extinction and how extant members of Placentalia subsequently radiated. The “Triisodontidae” are a group of medium sized eutherian mammals known predominantly fr...

Multituberculates were among the most abundant and taxonomically diverse mammals of the late Mesozoic and Paleocene, reaching their zenith in diversity and body size in the Paleocene. Taeniolabidoidea includes the largest known multituberculates that possess highly complex cheek teeth adapted for herbivory. A new specimen from the early Paleocene (...

The early Paleocene was a time of rapid faunal and floral reorganization following the end-Cretaceous mass extinction. The mammal record is punctuated by intervals of substantial turnover, yet it is unclear if these changes are due to extrinsic factors, such as climate change, or intrinsic factors, such as rapid evolution. The San Juan Basin (SJB)...