In Search of the Last Cretaceous Turritellid Gastropod, and the Aftermath

Cori Myers and Warren Allmon wrap fossils and take notes on a sand bar at Owl Creek. (Photo by Rob Ross)

Cori Myers and Warren Allmon wrap fossils and take notes on a sand bar at Owl Creek. (Photo by Rob Ross)

by Dr. Warren D Allmon, Director

George Phillips (Mississippi Museum of Natural Science) puts his finger on the Cretaceous-Paleocene boundary. (Photo by Warren Allmon)

George Phillips (Mississippi Museum of Natural Science) puts his finger on the Cretaceous-Paleocene boundary. (Photo by Warren Allmon)

What exactly happened in the mass extinction at the end of the Cretaceous Period, approximately 66 million years ago? And how did whatever happened affect what came next in the history of life? 

In June 2021, PRI staff were in northern Mississippi participating in field work as part of a multi-institution, multi-disciplinary, NSF-funded project trying to answer these questions. The project team included researchers and students from the American Museum of Natural History, Brooklyn College, University of Michigan, University of New Mexico, San Jose State University, College of William and Mary, and the Mississippi Museum of Natural Science. (The team is something of a PRI alumnae reunion; fellow principal investigators include Carlie Pietsch (Cornell ’10, former PRI Postdoctoral Fellow, now an Assistant Professor at San Jose State) and Corinne (Cori) Myers (Cornell ’04, former PRI staff member, now an Assistant Professor at New Mexico). )

The goal of the project is to better understand the ecological consequences of this enormous extinction. The end-Cretaceous extinction is publicly famous because it included the disappearance of non-avian dinosaurs. Instead of dinosaurs, however, our team is investigating extinction among marine invertebrates, including clams, snails, and ammonite cephalopods (relatives of modern octopus and squid). The researchers are attempting to discover what was different in the world’s oceans after this event, which may have seen the extinction of more than 75% of species. 

Scientists are almost unanimous in assigning primary responsibility for the end-Cretaceous extinction to the impact of an asteroid in what is now the Yucatan Peninsula of Mexico (there was likely also some effect of massive volcanic eruptions that were happening at the same time in India). The U.S. Gulf Coast received some of the first and harshest effects of this gigantic impact, including a giant tsunami and sudden environmental devastation. Remarkably, these extraordinary events can be reconstructed in great detail, even after the passage of so much time. 

Over the past several decades, researchers from the Mississippi Museum of Natural Science, American Museum of Natural History, and Brooklyn College have discovered many previously unknown locations – from New Jersey to Alabama -- where the geological record of these events can be studied. Among their fascinating findings is that small number of ammonites – those distant relatives of modern chambered nautilus which are well-known poster children for the extinction – actually survived for a few thousand years after the impact. https://bioone.org/journals/acta-palaeontologica-polonica/volume-57/issue-4/app.2011.0068/Short-Term-Survival-of-Ammonites-in-New-Jersey-After-the/10.4202/app.2011.0068.full 

They also have been able to dissect the effects of the tsunami on various sites along the Coastal Plain. One of the signatures at these sites is the “spherule layer”, composed of countless numbers of round particles less than 1 mm (0.04 inch) in diameter. As a result of the enormous heat of the impact, rock from the asteroid and surrounding ground was instantly melted and flung high into the atmosphere. The very cool temperatures in the upper atmosphere caused the tiny molten droplets to freeze quickly into perfect spheres, which then rained to Earth as glass beads. These beads -- spherules -- were deposited in thick layers across the globe. In the ocean, the deposits of spherules and other debris from the impact and tsunami were shifted by waves. Buried in these layers are fossil shells of animals that may have perished on literally the last day of the Cretaceous period. https://www.sciencedirect.com/science/article/pii/S0195667118300090?casa_token=SXvEiNnx1w4AAAAA:uC47trH9-8jRGQzQpevGGXGB2iY3q_rJ1uYDtvep7anIMgJWYlAW_8IEKMgBvUMA6rrStXZ3DaA 

Numerous specimens of Turritella tippana, packed into a “shell stringer” at the type section of the Owl Creek Formation, in Union County, Mississippi. These fossils were found about 20 feet below the Cretaceous-Paleocene boundary. (Photo by Warren Allmon)

Numerous specimens of Turritella tippana, packed into a “shell stringer” at the type section of the Owl Creek Formation, in Union County, Mississippi. These fossils were found about 20 feet below the Cretaceous-Paleocene boundary. (Photo by Warren Allmon)

The goal of the new research project is to build on these previous results, to figure out what the ecology of the shallow ocean was like just before the extinction, in the last few thousands and millions of years of the Cretaceous, and just afterward, in the first few thousands and millions of years of the Paleocene Epoch (the oldest interval of the Cenozoic Era). To do this, the team will be documenting all of the species that were present, reconstructing their respective environmental and ecological requirements, and try to determine why some species became extinct while others did not. We will also try to reconstruct the evolutionary relationships of the species above and below the boundary, to see who is related to whom, which we hope will tell us how the Paleocene ocean was eventually repopulated by new species after the disaster. 

My own small part of the project lies in this final aspect. I study turritellid gastropods – a group of marine snails that has been a major part of shallow sea communities for the past 140 million years. There are probably 150 living species and more than 1000 described fossil species, from every continent. On paper, almost all turritellids became extinct at the end of the Cretaceous – that is, there are almost no described Cretaceous species known to have survived into the Paleocene (only two in the entire world, to be exact). In the Gulf Coast, there are about a dozen species on just one or the other side of the extinction boundary, but not one crosses that boundary. There were clearly survivors, because the group persisted to the present, but we have no idea where they were, why they survived, or how they led to the diversity of species that filled early Cenozoic seas.  

Two generations of Cornell women paleontologists: Corrine Myers (Cornell ’04) and Kiera Crowley (Cornell ’22). (Photo by Warren Allmon)

Two generations of Cornell women paleontologists: Corrine Myers (Cornell ’04) and Kiera Crowley (Cornell ’22). (Photo by Warren Allmon)

The problem is that, despite their commonness, no one has carefully investigated the relationship between the latest Cretaceous and earliest Paleocene turritellid species to see which of the latter evolved from which of the former. It is possible, for example, that every single turritellid in the Gulf Coast died at the end of the Cretaceous, and that new species migrated from elsewhere in the early Paleocene. But it is also possible that some Cretaceous species survived in small pockets – called refugia – from which evolved new descendant species. In order to figure out which was more likely, we need to compare Cretaceous and Paleocene Gulf Coast species to see if they are closely related (that is, if any ancestor-descendant pairs are identifiable).  

During our field work in northern Mississippi, we collected as many fossil turritellids as we could. They will be studied by Cornell undergraduate Kiera Crowley, who will be doing her senior honors thesis on the topic during the coming year.  

Another major goal of our project is to share the results of the scientific research with the general public, and especially with teachers and students in the Gulf Coast region. PRI staff members Rob Ross and Don Haas spent many days capturing video and still images for future use in a new virtual field experience, which will allow students and teachers to explore these sites online. Our goal is that teachers and students be able to experience some of the thrill of exploring fossils and strata from this extraordinary moment in Earth history. 

This project is supported by NSF grant EAR-1925627.

Warren Allmon