Crinoids in Lilliput: Morphological Change in Class Crinoidea across the Ordovician-Silurian Boundary

Winner Denman Undergraduate Research Forum - Math and Physical SciencesWinner Math and Physical Sciences Undergraduate Research Forum - Geological ScienceThe Ordovician-Silurian (O-S) transition marks the second most catastrophic mass-extinction event to impact life on Earth. A rapid global cooling event led to a glacial epoch that devastated biological communities around the world, leaving a depauperate group of survivors to diversify and repopulate the biosphere. In this project we address how members of the Crinoidea (Phylum Echinodermata) responded morphologically to the ecological stressors at the end of the Ordovician. In addition to suffering a mass extinction and undergoing a macroevolutionary faunal change, crinoids experienced a morphological response of severe reduction in body size, an evolutionary trend recently termed “The Lilliput Effect.” To test this hypothesis, crinoids from the Ordovician-Silurian stratigraphic sections on Anticosti Island, Quebec are examined. Anticosti Island has the best-preserved shelly fossil record through this evolutionary boundary. This class-wide shrinking was documented by measuring the width and length of fossil crinoid calyxes from before, during, and after the O-S transition. These data were then used to calculate the volume of individuals. An 85% reduction in body size is documented during the mass extinction interval. Nonparametric statistics are used to demonstrate significant or not significant body size reductions through the Anticosti section. After this interval, average body volume increased by 1074%. The Lilliput Effect has been documented in more recent mass extinctions (Late Cretaceous, Late Eocene), but never observed in any group of organisms from the Paleozoic Era. This Lilliput response does not correlate to changes in depositional environments through the Anticosti section. It is presumably a biological response to a collapse in the biosphere, but whether this is a global paedomorphic shift or a product of more local selective factors is unclear. To test this question, the manifestation of the Lilliput Effect among “winning” and “losing” crinoid clades across this macroevolutionary change is evaluated

Digging Past the Dinosaurs?: Locomotor Trends and Mammalian Survivorship at the K–Pg (Cretaceous/Paleogene) Boundary

Winner Denman Undergraduate Research Forum - Biological SciencesWinner Math and Physical Sciences Undergraduate Research Forum - Geological ScienceSixty-five million years ago a bolide approximately 10 km in diameter collided with the Earth. This event triggered global devastation and a mass-extinction event, the Cretaceous-Paleogene (K-Pg) extinction, signaling the end of the “Age of Dinosaurs.” Non-avian dinosaurs are the most famous victims of the impact, but other groups such as ammonite cephalopods, angiosperms and mammals were severely affected by the ecological consequences of this catastrophic event. However, there were survivors. In 2004 Douglas S. Robertson et al. described the geophysical scenario surrounding the impact event including a global thermal pulse lasting 2 to 20 hours caused by infrared radiation (IR) from falling impact ejecta. The authors suggested all terrestrial survivors of the impact event were capable of buffering the resulting 10 kW.m-2 of power (the thermal equivalent of an oven on broil) by insulating themselves below ground or underwater. Called the “Sheltering Hypothesis” the hypothesis suggests the survivors of the impact event were morphologically equipped for fossorial or semi-aquatic locomotion. To test the hypothesis I turned to the mammalian fossil record. Other groups such as arthropods and birds exhibit differential survival patterns, but poor sampling and conservative morphologies make it difficult to test the Robertson hypothesis. Regardless of clade, specific locomotor demands produce predictable post-cranial skeletal structures in mammals that indicate ecological roles in ancient and modern contexts. In order to conduct this study, indicators of locomotor behavior were based on isolated post-crania as the mammalian fossil record near the K-P does not preserve articulated specimens or complete disarticulated specimens. One of the most reliable indicators of fossorial (digging) behavior is the relative length of the olecranon process of the ulna. Utilizing Ohio State’s Higher Vertebrates collections, I first demonstrate extant mammals can be grouped into locomotor guilds based on this feature using linear measurements and linear regression. Unfortunately, complete fossil ulnae are usually not preserved, so a novel proxy based on the length of the semi-lunar notch is described. This proxy is based on correlations to ulnar length based on linear regression analysis. This proxy allows us to understand the locomotor guilds of mammals before and after the K-P impact. Using fossils from the Pioneer Trails Regional Museum in North Dakota and the University of California Museum of Paleontology at Berkeley I compare the locomotor diversity of mammals before and after the impact event. Preliminary results refute the Robertson hypothesis and suggest mammalian survivorship was more closely related to body size than locomotor guild. Derived adaptations for fossorial or semi-aquatic locomotion are apparent before the boundary including the likely swimmer Didelphodon vorax, a large marsupial that went extinct at the boundary. Survivors appear to be scansorial generalists. Future areas of inquiry include incorporating more post-cranial structures and material into the sample, and examining the consequences of a “Lilliputian” mammalian community on extinction recovery patterns throughout the ecosystem.Arts and Sciences Honors Research GrantHonors Collegium Research and Travel GrantThe Pressey Honors EndowmentNo embarg

Craniodental and humeral morphology of a new species of <i>Masrasector</i> (Teratodontinae, Hyaenodonta, Placentalia) from the late Eocene of Egypt and locomotor diversity in hyaenodonts

<div><p>Hyaenodonta is a diverse clade of carnivorous mammals that were part of terrestrial faunas in the Paleogene of Eurasia and North America, but the oldest record for the group is Afro-Arabian, making the record there vital for understanding the evolution of this wide-spread group. Previous studies show an ancient split between two major clades of hyaenodonts that converged in hypercarnivory: Hyainailourinae and Hyaenodontinae. These clades are each supported by cranial characters. Phylogenetic analyses of hyaenodonts also support the monophyly of Teratodontinae, an Afro-Arabian clade of mesocarnivorous to hypercarnivorous hyaenodonts. Unfortunately, the cranial anatomy of teratodontines is poorly known, and aligning the clade with other lineages has been difficult. Here, a new species of the phylogenetically controversial teratodontine <i>Masrasector</i> is described from Locality 41 (latest Priabonian, late Eocene) from the Fayum Depression, Egypt. The hypodigm includes the most complete remains of a Paleogene teratodontine, including largely complete crania, multiple dentaries, and isolated humeri. Standard and “tip-dating” Bayesian analyses of a character-taxon matrix that samples cranial, postcranial, and dental characters support a monophyletic <i>Masrasector</i> within Teratodontinae, which is consistently placed as a close sister group of Hyainailouridae. The cranial morphology of <i>Masrasector</i> provides new support for an expanded Hyainailouroidea (Teratodontinae + Hyainailouridae), particularly characters of the nuchal crest, palate, and basicranium. A discriminant function analysis was performed using measurements of the distal humerus from a diverse sample of extant carnivorans to infer the locomotor habits of <i>Masrasector</i>. <i>Masrasector</i> was assigned to the “terrestrial” locomotor category, a result consistent with the well-defined medial trochlear ridges, and moderately developed supinator crests of the specimens. <i>Masrasector</i> appears to have been a fast-moving terrestrial form with a diverse diet. These specimens considerably improve our understanding of Teratodontinae, an ancient member of the Afro-Arabian mammalian fauna, and our understanding of hyaenodont diversity before the dispersal of Carnivora to the continent near the end of the Paleogene.</p></div

The first hyaenodont from the late Oligocene Nsungwe Formation of Tanzania: Paleoecological insights into the Paleogene-Neogene carnivore transition

<div><p>Throughout the Paleogene, most terrestrial carnivore niches in Afro-Arabia were occupied by Hyaenodonta, an extinct lineage of placental mammals. By the end of the Miocene, terrestrial carnivore niches had shifted to members of Carnivora, a clade with Eurasian origins. The transition from a hyaenodont-carnivore fauna to a carnivoran-carnivore fauna coincides with other ecological changes in Afro-Arabia as tectonic conditions in the African Rift System altered climatic conditions and facilitated faunal exchange with Eurasia. Fossil bearing deposits in the Nsungwe Formation in southwestern Tanzania are precisely dated to ~25.2 Ma (late Oligocene), preserving a late Paleogene Afro-Arabian fauna on the brink of environmental transition, including the earliest fossil evidence of the split between Old World monkeys and apes. Here we describe a new hyaenodont from the Nsungwe Formation, <i>Pakakali rukwaensis</i> gen. et sp. nov., a bobcat-sized taxon known from a portion of the maxilla that preserves a deciduous third premolar and alveoli of dP⁴ and M¹. The crown of dP³ bears an elongate parastyle and metastyle and a small, blade-like metacone. Based on alveolar morphology, the two more distal teeth successively increased in size and had relatively large protocones. Using a hyaenodont character-taxon matrix that includes deciduous dental characters, Bayesian phylogenetic methods resolve <i>Pakakali</i> within the clade Hyainailouroidea. A Bayesian biogeographic analysis of phylogenetic results resolve the <i>Pakakali</i> clade as Afro-Arabian in origin, demonstrating that this small carnivorous mammal was part of an endemic Afro-Arabian lineage that persisted into the Miocene. Notably, <i>Pakakali</i> is in the size range of carnivoran forms that arrived and began to diversify in the region by the early Miocene. The description of <i>Pakakali</i> is important for exploring hyaenodont ontogeny and potential influences of Afro-Arabian tectonic events upon mammalian evolution, providing a deep time perspective on the stability of terrestrial carnivore niches through time.</p></div

Tooth size and carnassialization in Afro-Arabian carnivora and Hyaenodonta.

<p>Tooth size and carnassialization in Afro-Arabian carnivora and Hyaenodonta.</p

Left humerus specimens referred to <i>Masrasector</i>.

<p>DPC 10831 in (<b>A)</b> anterior view, (<b>B)</b>, posterior view, (<b>C)</b>, distal view, medial to left. DPC 15436 in (<b>D)</b> anterior view, (<b>E)</b> posterior view, (<b>F)</b> distal view, medial to left. DPC 11670 in (<b>G)</b> anterior view, (<b>H)</b> posterior view, (<b>I)</b> distal view, medial to left. Digital models were generated in Avizo and are available on Morphosource.</p

Cranium of <i>Masrasector nananubis</i> (DPC 11990).

<p>Cranium of <i>Masrasector nananubis</i> sp. nov. (DPC 11990 with P²–M³) in (<b>A)</b> dorsal view, rostrum points left, (<b>B)</b> ventral view, rostrum points left.</p