Peer-Reviewed Publications

Shark-on-Shark Predation in the Fossil Record

Evidence of shark-on-shark predation is largely absent from the fossil record due to a taphonomic filter. Direct evidence of shark predation in the fossil record is largely limited to bite traces on prey items but may also be found within the gut contents of exceptionally well-preserved individuals or as inclusions within coprolites. Shark bite traces are typically observed on durable, bony skeletal elements. Previous publications have shown shark bite traces on skeletal elements of fossil fishes, marine mammals, marine reptiles, and even a pterosaur, offering direct evidence of active predation, failed predation, and/or scavenging. This study describes the first evidence of shark bite traces preserved on cartilaginous vertebral centra of other sharks. Four carcharhiniform centra have been identified from the Neogene Atlantic Coastal Plain, bearing chondrichthyan bite traces, of which two have partial teeth still embedded within them. In one specimen, CT scans showed remodeling of the tissue around two partial teeth embedded in the centrum, indicating that the bitten individual survived the encounter. While shark-on-shark predation is common among living taxa, capturing evidence of these interactions in the fossil record is exceptionally rare. 

Read the full paper here: Rare Evidence of Shark-on-Shark Trophic Interactions in the Fossil Record

The Fossil Record of Sharks & Rays in Florida

I completed a review of the fossil record of sharks and rays from Florida based on over 117,000 specimens conserved in the Florida Museum of Natural History. I documented 70 different species of sharks and rays, of which 20 had never been reported from the state before. I evaluated trends in taxonomic and ecological diversity from the Eocene through the Pleistocene [~45 million years to 10 thousand years ago]. The most notable trend, was a major turnover in the dominant shark order (lamniform to carcharhiniform) across the Eocene-Oligocene boundary, a global cooling event. However, the transition occurred gradually across the climate event and was also associated with a shift in the dominant functional morphology from grasping to cutting type. This implies a possible biotic driver and increased predation on larger prey, likely associated with the evolution of marine mammals. This study also identifies major gaps in sampling and provided a roadmap to direct future research.

Read the full paper here: The Chondrichthyan Fossil Record of the Florida Platform (Eocene-Pleistocene) 

Training Citizen Scientists in Paleontology

As part of the NSF-funded FOSSIL Project, I led field trips to the Belgrade Quarry in Maysville, North Carolina, with other staff from the Florida Museum, Smithsonian, and members of the North Carolina Fossil Club. We organized a professional development workshop, the Belgrade PaleoBlitz, in which avocational paleontologists were invited to the Florida Museum to contribute to the curation of the specimens from Belgrade. Through this experience, participants learned about best practices in paleontology, increased their confidence in museum curatorial practices, and expanded their personal paleontology networks. Participant engagement was sustained through the online community on the myFOSSIL website. Participants demonstrated what they learned by sharing their experiences with others through newsletters, field trips, and workshops. 

Read the full paper here: The Belgrade PaleoBlitz: A pilot project to engage amateur paleontologists

Body Size of Megalodon & Relatives

The megatooth shark, Otodus megalodon, is widely accepted as the largest shark that ever lived; and yet, despite over a century of research, its size is still debated. The great white shark, Carcharodon carcharias, is regarded as the best living ecological analog to the extinct megatooth shark and has been the basis for all body length estimates to date. The most widely accepted and applied method for estimating body size of O. megalodon was based upon a linear relationship between tooth crown height and total body length in C. carcharias. However, when applying this method to an associated dentition of O. megalodon, the estimates for this single individual ranged from 11.4 to 41.1 m. These widely variable estimates showed a distinct pattern, in which anterior teeth resulted in lower estimates than posterior teeth. Consequently, previous paleoecological analyses based on body size estimates of O. megalodon may be subject to misinterpretation. Herein, we describe a novel method based on the summed crown width of associated fossil dentitions, which mitigates the variability associated with different tooth positions. The method assumes direct proportionality between the ratio of summed crown width to body length in ecologically and taxonomically related fossil and modern species. Total body lengths were estimated from 11 individuals, representing five lamniform species: Otodus megalodon, Otodus chubutensis, Carcharodon carcharias, Carcharodon hubbelli, and Carcharodon hastalis. The method was extrapolated for the largest known isolated upper tooth of O. megalodon, resulting in a maximum body length estimate of 20 m. 

Read the full paper here: Body length estimation of Neogene macrophagous lamniform sharks (Carcharodon and Otodus) derived from associated fossil dentitions

Megalodon Evolutionary Trends

This study documents evolutionary trends in the megatooth lineage based on specimens found along the Calvert Cliffs and adjacent tributaries. The megatooth lineage represents a chronospecies, with very gradual morphological change from the Paleocene Otodus obliquus to the Mio-Pliocene Otodus (=Carcharocles) megalodon. This morphological transition from the Paleocene through the Pliocene reflects a long-term macroevolutionary shift in tooth function from grasping to cutting, coincident with the evolution of marine mammals. Along the Miocene Calvert Cliffs, the final transition from O. chubutensis to O. megalodon is preserved. Using stratigraphically controlled specimens, the rate and timing of lateral cusplets being lost was documented. It took more than 10 million years for lateral cusplets to finally disappear, suggesting that there was not a strong selective pressure to drive their loss. 

Read the full paper here: The transition between Carcharocles chubutensis and Carcharocles megalodon (Otodontidae, Chondrichthyes): lateral cusplet loss through time

First Fossil Records of the Cookiecutter Shark and Angel Shark from Florida

In 2015, the Florida Museum received an email from Ken Marks, inquiring about the age of some fossil cookiecutter shark, Isistius, teeth that he had found. At this point, cookiecutter shark teeth had never been reported in the published literature from Florida. Consequently, I began collaborating with Ken Marks to document the site where the cookiecutter shark teeth originated. As a result, we also were able to document the first records of angel shark, Squatina, teeth from the Florida fossil record. These taxa were the first representatives of their entire orders (Squaliformes and Squatiniformes) from the state. However, both species were known to the avocational paleontology community for more than a decade. This study documented a significant Florida fossil site and highlighted the importance of professional-avocational partnerships in paleontology research. 

Read the full paper here: The first documented fossil records of Isistius and Squatina (Chondrichthyes) from Florida, with an overview of the associated vertebrate fauna

Fossil Sharks & Rays from Panama

The timing of Panama's formation is extremely important because it connected North and South America and separated the Caribbean from the Pacific. This had major impacts on biogeography, oceanography, and global climate. There are two main theories for when Panama formed: the classic late closure model (~6 million years ago) and an early closure model (~10-15 million years ago). This study documented the first late Miocene shark and ray fauna from the Pacific shelf of Panama. Based on strontium isotopes preserved in fossil scallops, we determined an age of 9.5 - 10 million years for the site. Taxonomic and functional diversity were evaluated and a novel method for estimating paleobathymetry was developed. The fauna was dominated by littoral generalists (Carcharhinus) and filter-feeding specialists (Mobula). The community composition indicates a nearshore environment, with an estimated average depth of 110m. Based on the biogeography of extant analogs, the fossil shark and ray fauna indicate that there was still a marine connection between the Caribbean and the Pacific, which supports the late closure model.

Read the full paper here: Late Miocene chondrichthyans from Lago Bayano, Panama: Functional diversity, environment and biogeography