Discovery of new small fish, species of lizards re

image: Baby Deinonychus investigates a Sciroseps pawhuskai on the charred remains of a cycad.
to see After

Credit: Illustration by Brian Engh,

Two tiny new species that inhabited part of what is now the southern United States around 100 million years ago have been discovered by a team of researchers that includes a paleontologist from the University of Wisconsin at Oshkosh .

Joseph Frederickson, a vertebrate paleontologist and director of the Weis Earth Science Museum on the Fox Cities campus, is among the authors of a recent paper published in PeerJ, highlighting these new discoveries in southwestern Arkansas. The species is a small lizard named by researchers Sciroseps pawhuskai and a fish named Anomoeodus cadoi.

The paper is titled A new vertebrate fauna from the Lower Cretaceous Holly Creek Formation of the Trinity Group, southwestern Arkansas, USA. Celina Suarez, an associate professor of geosciences at the University of Arkansas, was lead author on the paper, which brings together decades of research in the region known as the Holly Creek Formation. Frederickson is the second author.

“The Holly Creek Formation is interesting because few fossils have been described in the literature, although it did produce dinosaur fossils in the past,” Frederickson said. “Features like these help us better understand how the continent was connected and the diversity of living animals in the early Cretaceous.”

The finds serve both to highlight the variety of fossils found at this site, including dinosaurs, mammals, fish, amphibians and reptiles, and to reinforce the general lack of variety of fossils found throughout America. North at that time.

“The fish and the lizard represent material, albeit small and fragmentary, that retains enough detail to call them new species,” he said. “The lizard jaw is particularly interesting because normally fossils are limited to small broken pieces, whereas the specimen we describe in this article is mostly a complete lower jaw.”

Frederickson began working on the project in 2017. The previous year, he began working with Suarez at a fossil site in Montana.

His part of the Arkansas Project included the study of micro-fossils, or small materials that required microscopes to see in detail. This included the teeth of fish, amphibians, reptiles and dinosaurs. He compared these fossils with those of similarly aged rocks in Oklahoma, Montana and Maryland to determine which species were present, then photographed the material using a scanning electron microscope.

This latest publication work comes a year after Frederickson made headlines in another published article. In 2020 he presented evidence that Velociraptors probably did not hunt in large, coordinated groups as described by the famous jurassic park movies. This latest research, of course, focuses on creatures far less glamorous than the raptor immortalized by Hollywood.

“I think this article is a good reminder that the fossil record preserves many different animals, not just dinosaurs,” he said. “This article focuses heavily on the tiny organisms crawling or swimming at the feet of giant dinosaurs, which are too often undocumented because they can be difficult to study. However, it is often these small animals that tell us the most about the environment in which they lived.

The study resulted from long-term investigations that began in Arkansas in the 1970s. It was in this area that thousands of sauropod and theropod tracks were discovered beginning in the 1980s.

Previously preserved dinosaurs from the site include at least one long-necked sauropod (probably Sauroposeidon), large theropods (a juvenile Acrocanthosaurus), an ankylosaurus (armored dinosaur) and the small raptor kickboxer, Deinonychus.

A variety of very small fossils have also been discovered, including the remains of sharks, bony fish, frogs, lizards, turtles, crocodilians and mammals. Although unspectacular, these tiny bones and teeth document the presence of many species essential to understanding the ecosystem that lived in Arkansas millions of years ago.

The remains have been preserved in rock which represents a brackish to fresh water environment which was probably a marshy area just inland from the ancient coast.


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