Research

Mass Extinction Ecological Response and Recovery in the Cretaceous-Paleogene Gulf Coastal Plain

The Cretaceous-Paleogene mass extinction is a pop-culture phenomenon replete with imagery of the last roars of T. rex as an fiery asteroid whizzes by. Meanwhile, the ocean was full of exquisite vertebrate and invertebrate life that suffered a 70% species loss and almost unprecedented ecological reshuffling. Our project is part of an interdisciplinary and multi-institution team striving to document survivorship and radiation of shallow marine invertebrates following the end-Cretaceous mass extinction in the U.S Gulf Coastal Plain.

• We will reconstruct ancient U.S. Gulf Coast environments using sedimentological and geochemical proxies.

• We will use the novel approach of Paleoecological Niche Modeling to investigate how suitable habitat and niche stability influenced survivorship across the boundary.

• This work will contribute to our understanding of species-environment interactions in extreme climate change events.

Learn more about our ongoing research here: https://youtu.be/EnDRa73bLoU

This work is funded by NSF EAR 1924749

Extreme conditions at the end-Permian mass extinction

252 million years ago approximately 95% of all life on the planet went extinct. I study the aftermath, the ecological recovery of the surviving marine fauna. The Earth was a diverse place in the Permian, directly before the extinction with unique animals and plants living on land and in the ocean. Imagine almost every mammal, reptile, flower, insect, and snail species you know today all dying in a geologic instant. That is what the transition from the Permian to the Triassic time period was like. The most likely cause was the eruption of volcanic material in present day Siberian Russia. The greenhouse and toxic gasses that erupted warmed the Earth and the oceans, changing circulation patterns and oxygen content, much like modern climate change is altering Earth today!

To study the recovery I collect the fossilized remains of animals that lived on the seafloor; clams and snails (bivalves and gastropods), echinoderms (like modern day sea urchins), and ammonoids (an extinct cousin of squid). My field sites have spanned from the deserts of the Southwest United States to the Dolomite Mountains of Northern Italy. (See the field excursions tab for more scenic images!)

I have found that extremely high ocean temperatures and low oxygen environments directly following the mass extinction may have lead to the development of "alternative ecological state" communities. These assemblages of microbialites, opportunistic bivalves, short-lived foraminifera, and microconchids are unique to the stressful environments in the immediate aftermath of the extinction. As conditions improved, diverse mollusc faunas replaced the disaster community. However, an additional volcanic eruption, leading to a second extreme temperature event, about 2 million years after the end-Permian extinction event led to another paleoecological change. Along with high temperatures, sediment weathering from the continent re-set the recovery trajectory. Diversity was lost in many regions and replaced by gastropods (snails) which were able to diversify in the these hot oceans but remained very small, smaller than your fingernail in most cases (<1cm in length) as well as infaunal (burrowing) bivalves.

Specifically, extreme temperature environments limited the diversification and abundance of echinoderms like sea urchins and crinoids. In low oxygen environments, echinoderms fared better and were abundant, but the overall diversity of clams, snails, and echinoderms was low. The waxing and waning of environmental perturbations led to rebounds and resets in the recovery from the extinction event.

Swimming ammonoids (a cousin of squid) which lived in the water column show booms in taxonomic diversity followed by decreases in taxonomic diversity throughout the Early Triassic.

Gastropod Ecology, Growth, and Biominerlization

I favor gastropods as a study organism. They preserve a record of their growth in their spiral shell which can be used to interpret their life history through multiple proxies. Evidence for interactions with predators include the cannibalistic drillholes of other snails, octopus predation drillholes, and scars left behind on snail shells from the attacks of crabs or fish. On going work uses changes in predation frequency provide clues to how the marine trophic structure changes through time.

Gastropods employ various life history strategies which can be inferred from adult shell size and growth rate. Ongoing work uses changes in gastropod growth rates and size through time and space to test evolutionary processes.

The microstructure of gastropod shells viewed through scanning electron microscopy (SEM) allows me to understand how mollusks control shell growth and how new species evolve novel shell structures through modification over time. Ongoing work examines the evolution of gastropod shell callus that appears in multiple lineages.

Header photo: Overlooking the Augusta Mountains in Nevada