An early nimravid from California and the rise of hypercarnivorous mammals after the Middle Eocene Climatic Optimum

Carnivoraforms (crown carnivorans and their closest relatives) first occupied hypercarnivorous niches near the dawn of the late Eocene, 40–37 million years ago. This followed the decline or extinction of earlier carnivorous groups, Mesonychia and Oxyaenodonta, leaving carnivoraforms and hyaenodontan meat-eaters as high trophic level consumers. The pattern of this change and the relative contributions of the taxonomic groups has hitherto been unclear. We report a new genus and species of the sabretoothed mammalian carnivore family Nimravidae, Pangurban egiae, from the Eocene Pomerado Conglomerate of southern California, with strongly derived hypercarnivorous features. While geochronologically the oldest named nimravid in North America, Pangurban egiae is recovered as phylogenetically derived, with affinities to Hoplophoneus. This provides unequivocal evidence for rapid radiation and spread of nimravid carnivores across Asia and North America and constrains the timing of early divergences within the family. Pangurban egiae narrows the gap between convergent iterations of sabretoothed mammalian carnivores and demonstrates swift diversification of the hypercarnivorous nimravids during a period of global climatic instability. Furthermore, it highlights the top-to-bottom restructuring North American ecosystems underwent during the Eocene–Oligocene transition, resulting in carnivoraforms taking positions as trophic specialists for the first time, a niche they still occupy today

Our past creates our present: a brief overview of racism and colonialism in Western paleontology

As practitioners of a historical science, paleontologists and geoscientists are well versed in the idea that the ability to understand and to anticipate the future relies upon our collective knowledge of the past. Despite this understanding, the fundamental role that the history of paleontology and the geosciences plays in shaping the structure and culture of our disciplines is seldom recognized and therefore not acted upon sufficiently. Here, we present a brief review of the history of paleontology and geology in Western countries, with a particular focus on North America since the 1800s. Western paleontology and geology are intertwined with systematic practices of exclusion, oppression, and erasure that arose from their direct participation in the extraction of geological and biological resources at the expense of Black, Indigenous, and People of Color (BIPOC). Our collective failure to acknowledge this history hinders our ability to address these issues meaningfully and systemically in present-day educational, academic, and professional settings. By discussing these issues and suggesting some ways forward, we intend to promote a deeper reflection upon our collective history and a broader conversation surrounding racism, colonialism, and exclusion within our scientific communities. Ultimately, it is necessary to listen to members of the communities most impacted by these issues to create actionable steps forward while holding ourselves accountable for the past

Expanding the paleontological record of semiaquatic and marine mammals: Adaptations to freshwater in Coryphodon and the history of pinnipeds in the eastern Pacific

Major evolutionary innovations in lifestyle can lead to adaptive radiations, change the nature of selective forces, and rearrange ecological interactions. One of the many determinants of lifestyle is body mass, and so change in body mass is often accompanied by change in lifestyle. In the case of mammals, their earliest members from the Late Triassic were small. They remained relatively small throughout the Mesozoic, most likely due to interactions with the diverse large bodied diapsids that dominated Mesozoic large-body ecomorphs, especially dinosaurs in the terrestrial realm. It was not until the early Cenozoic, after the extinction of the non-avian dinosaurs and large bodied marine diapsids, that the body size of mammals expanded, which lead to new mammalian ecomorphs. The initial stages of the Cenozoic mammalian exploration of large-body ecomorphs included at least two novel semiaquatic forms – large amphibious herbivores and large coastal marine carnivores. These ecomorphs were to evolve multiple times throughout the Cenozoic and led to the freshwater Hippopotamidae, the marine Pinnipedia (seals and sea lions), as well as to the fully aquatic marine mammals, the sirenians (manatees and dugongs) and cetaceans (whales and dolphins).This dissertation employes bone histological methods and the analysis of new fossil specimens to add to our paleontological knowledge of large bodied semiaquatic mammals. The earliest occurrences of these large-bodied semiaquatic forms are poorly understood, and gaps exist in our knowledge of their evolution and distribution. To help address these deficiencies I used bone histological methods to establish the lifestyle of the earliest large-bodied mammal, the Paleocene-Eocene Coryphodon. I follow this with the description and analysis of new fossil material that expand our knowledge of the diversity and biogeography of fossil pinnipeds and their earliest stem-relatives, the geologically longest-lived lineage of semiaquatic marine carnivores. The Late Paleocene to Early Eocene Coryphodon was a member of the Pantodonta, the first mammalian group to achieve large body size following the end-Cretaceous mass extinction. Using histological and microanatomical techniques to examine the structure and growth of its bones, I show that Coryphodon was semiaquatic and further demonstrate that it had significant adaptations to this way of life rather than merely occupying waterways in a transient manner. A framework for behavioral inference for extinct taxa is presented, which incorporates evidence from multiple timescales. I argue that this approach facilitates the framing of the causal relationships between, and interpretation of, the different kinds of evidence that can be brought to bear on our understanding of the origins of major changes in lifestyle. In the case of Coryphodon, the concurrent achievement of large body size and semiaquatic lifestyle suggests a reciprocal rather than unidirectional causal relationship between body size and specialization at the beginning of the Cenozoic. Turning to the origins and biogeography of the pinnipeds, the Pleistocene sea lion Proterozetes ulysses belongs to a monophyletic group of North Pacific otariids that includes the living genera Eumetopias (Stellar’s sea lion) and Zalophus (California sea lion). Fossil mandibles of Proterozetes from the Port Orford Formation of Oregon are described and found to be intermediate in morphology and size to the other North Pacific otariids, most resembling Eumetopias. The presence of this distinct but morphologically intermediate taxon in the eastern North Pacific during the Pleistocene establishes the Pleistocene as a time of increased otariid diversity, in contrast to diversity decline seen in other marine mammal clades. The timing of sea lion diversification along the west coast of North America appears to follow diversification in Japan, reinforcing the possibility of an eastward dispersal trend in the North Pacific after the end-Pliocene. Pleistocene sea lions in the Eastern North Pacific similarly show multitaxon assemblages with overlapping body size and feeding styles, indicating the high diversity possible once the coastal carnivore ecomorph was achieved. Finally, paleontological investigation of the early history of pinnipeds similarly reveals assemblages of increased diversity and overlapping body size. The pinnipedimorph Enaliarctos was a marine-adapted carnivore with dental and locomotor features intermediate between terrestrial arctoid carnivores and living pinnipeds. Newly discovered fossils, described herein, fill a major biogeographic gap in the record of the genus, previously known nowhere between southern California and central Oregon, and show that stem pinnipeds existed for longer and survived later than previously thought, from the latest Rupelian to the late Burdigalian (28.1-16.6 mya). This discovery of an increased biogeographic and temporal range of Enaliarctos indicates that the genus may have interacted with a much wider range of other taxa than previously thought, including plotopterid birds, odontocete whales, and crown pinnipeds such as early odobenids, early otariids, and desmatophocids. The expansion of the known ranges of Enaliarctos species and the description of previously undescribed morphological attributes, particularly of the mandible and lower dentition, provides insight into the origins of pinniped diversity and their possible interactions with other early Neogene coastal marine organisms. Though early pinniped relatives were smaller than living members, increasing body size does not appear to have been necessarily superior once the coastal marine ecospace was colonized

Expanding the paleontological record of semiaquatic and marine mammals: Adaptations to freshwater in Coryphodon and the history of pinnipeds in the eastern Pacific

Major evolutionary innovations in lifestyle can lead to adaptive radiations, change the nature of selective forces, and rearrange ecological interactions. One of the many determinants of lifestyle is body mass, and so change in body mass is often accompanied by change in lifestyle. In the case of mammals, their earliest members from the Late Triassic were small. They remained relatively small throughout the Mesozoic, most likely due to interactions with the diverse large bodied diapsids that dominated Mesozoic large-body ecomorphs, especially dinosaurs in the terrestrial realm. It was not until the early Cenozoic, after the extinction of the non-avian dinosaurs and large bodied marine diapsids, that the body size of mammals expanded, which lead to new mammalian ecomorphs. The initial stages of the Cenozoic mammalian exploration of large-body ecomorphs included at least two novel semiaquatic forms – large amphibious herbivores and large coastal marine carnivores. These ecomorphs were to evolve multiple times throughout the Cenozoic and led to the freshwater Hippopotamidae, the marine Pinnipedia (seals and sea lions), as well as to the fully aquatic marine mammals, the sirenians (manatees and dugongs) and cetaceans (whales and dolphins).This dissertation employes bone histological methods and the analysis of new fossil specimens to add to our paleontological knowledge of large bodied semiaquatic mammals. The earliest occurrences of these large-bodied semiaquatic forms are poorly understood, and gaps exist in our knowledge of their evolution and distribution. To help address these deficiencies I used bone histological methods to establish the lifestyle of the earliest large-bodied mammal, the Paleocene-Eocene Coryphodon. I follow this with the description and analysis of new fossil material that expand our knowledge of the diversity and biogeography of fossil pinnipeds and their earliest stem-relatives, the geologically longest-lived lineage of semiaquatic marine carnivores. The Late Paleocene to Early Eocene Coryphodon was a member of the Pantodonta, the first mammalian group to achieve large body size following the end-Cretaceous mass extinction. Using histological and microanatomical techniques to examine the structure and growth of its bones, I show that Coryphodon was semiaquatic and further demonstrate that it had significant adaptations to this way of life rather than merely occupying waterways in a transient manner. A framework for behavioral inference for extinct taxa is presented, which incorporates evidence from multiple timescales. I argue that this approach facilitates the framing of the causal relationships between, and interpretation of, the different kinds of evidence that can be brought to bear on our understanding of the origins of major changes in lifestyle. In the case of Coryphodon, the concurrent achievement of large body size and semiaquatic lifestyle suggests a reciprocal rather than unidirectional causal relationship between body size and specialization at the beginning of the Cenozoic. Turning to the origins and biogeography of the pinnipeds, the Pleistocene sea lion Proterozetes ulysses belongs to a monophyletic group of North Pacific otariids that includes the living genera Eumetopias (Stellar’s sea lion) and Zalophus (California sea lion). Fossil mandibles of Proterozetes from the Port Orford Formation of Oregon are described and found to be intermediate in morphology and size to the other North Pacific otariids, most resembling Eumetopias. The presence of this distinct but morphologically intermediate taxon in the eastern North Pacific during the Pleistocene establishes the Pleistocene as a time of increased otariid diversity, in contrast to diversity decline seen in other marine mammal clades. The timing of sea lion diversification along the west coast of North America appears to follow diversification in Japan, reinforcing the possibility of an eastward dispersal trend in the North Pacific after the end-Pliocene. Pleistocene sea lions in the Eastern North Pacific similarly show multitaxon assemblages with overlapping body size and feeding styles, indicating the high diversity possible once the coastal carnivore ecomorph was achieved. Finally, paleontological investigation of the early history of pinnipeds similarly reveals assemblages of increased diversity and overlapping body size. The pinnipedimorph Enaliarctos was a marine-adapted carnivore with dental and locomotor features intermediate between terrestrial arctoid carnivores and living pinnipeds. Newly discovered fossils, described herein, fill a major biogeographic gap in the record of the genus, previously known nowhere between southern California and central Oregon, and show that stem pinnipeds existed for longer and survived later than previously thought, from the latest Rupelian to the late Burdigalian (28.1-16.6 mya). This discovery of an increased biogeographic and temporal range of Enaliarctos indicates that the genus may have interacted with a much wider range of other taxa than previously thought, including plotopterid birds, odontocete whales, and crown pinnipeds such as early odobenids, early otariids, and desmatophocids. The expansion of the known ranges of Enaliarctos species and the description of previously undescribed morphological attributes, particularly of the mandible and lower dentition, provides insight into the origins of pinniped diversity and their possible interactions with other early Neogene coastal marine organisms. Though early pinniped relatives were smaller than living members, increasing body size does not appear to have been necessarily superior once the coastal marine ecospace was colonized

Miocene marine macropaleontology of the fourth bore Caldecott Tunnel excavation, Berkeley Hills, Oakland, California, USA

Excavation of the new fourth bore of the Caldecott Tunnel in the Berkeley Hills, Oakland, California reveals two faunas attributed to an unnamed glauconitic mudstone (=Sobrante Formation and mapped as Tsm) and the Claremont chert (both of Graymer 2000). The fossil assemblage from the unnamed glauconitic mudstone, referred to here as the Tsm Caldecott Tunnel fauna, consists of 32 taxa: one bryozoan, 22 Mollusca (16 Bivalvia, five Gastropoda and one Scaphopoda), two Arthropoda (one Decapoda and one Maxillopoda), two Echinodermata (one Crinoidae and one Echinoidea), and five Chordata. Mollusks indicate a middle Miocene age based on the co-occurrence of the provisionally identified bivalves Acila empirensis, Anadara osmonti, Yoldia submontereyensis, Y. supramontereyensis and the gastropod genera Bruclarkia and Trophoscyon. This fauna was likely deposited at water depths between 350 and 400 m. Although several taxa from shallower depths are present, these are assumed to have washed in from shallower depths. Only one taxon was found that typically occurs in deeper water. The fauna lived in a methane-rich environment based on the occurrence of vesicomyid bivalves and on a vesicomyid/lucinid bivalve association shown elsewhere to be associated with cold seep environments. Vertebrates include great numbers of small, pelagic fish and the piscivorous sharks and marine mammals which likely took advantage of them for food. The Tsm Caldecott Tunnel fauna represents the second fauna from a methane-rich environment from the greater San Francisco Bay area and the first attributed to a methane seep environment. In addition, this fauna contains the first reported Cenozoic crinoid from California and the new species Dentalium (Fissidentalium?) mcganna (Mollusca: Scaphopoda) is described. The fauna from the Claremont chert includes two bivalve mollusks, one scaphopod, one barnacle and three vertebrates. These taxa are all represented by single specimens. They represent a marine environment likely at continental shelf or slope water depths. The occurrence of the shark Carcharhinus obscurus may indicate water temperatures warmer than off the central California coast today

TABLE S1. Carnivore occurrences from An early nimravid from California and the rise of hypercarnivorous mammals after the middle Eocene climatic optimum

Carnivore occurrences in late Uintan–Duchesnean of southern California and western Texas

SUPPLEMENTARY TEXT. from An early nimravid from California and the rise of hypercarnivorous mammals after the middle Eocene climatic optimum

Additional description, geological context, expanded methods, references, and additional phylogenetic trees

Pangurban BEAST file. from An early nimravid from California and the rise of hypercarnivorous mammals after the middle Eocene climatic optimum

BEAST run file, in xml format

Figure S2. Three-dimensional surface model from An early nimravid from California and the rise of hypercarnivorous mammals after the middle Eocene climatic optimum

Data file for three-dimensional surface model of of SDSNH 60554

Pangurban phylogenetic matrix from An early nimravid from California and the rise of hypercarnivorous mammals after the middle Eocene climatic optimum

Phylogenetic matrix used in the analysis, in nexus format