BOZEMAN – A Montana State University alumna’s research on the nesting behaviors of modern crocodiles was featured on the cover of an international journal dedicated to sedimentary geology and the impact of life on Earth’s history. The research may help scientists recognize successfully hatched nesting sites in the fossil record and shed light on how ancient crocodilians parented their young.
Ashley Ferguson of Burley, Idaho, is lead author of a paper published in the May issue of the geoscience journal Palaios that details her study of the nests and nesting habits of the American crocodile and the broad-snouted caiman, a small crocodile found in Central and South America.
“The research might help us recognize some nesting sites in the fossil record that we might not have noticed before,” said Ferguson, who earned her master’s degree in May 2016 in the Department of Earth Sciences in MSU’s College of Letters and Science.
The paper “From Eggs to Hatchlings: Nest Site Taphonomy of American Crocodile (Crocodylus acutus) and Broad-Snouted Caiman (Caiman latirostris),” is one chapter of her thesis into what characteristics make up a nesting site.
For the study, Ferguson, along with her adviser, MSU paleontologist David Varricchio, and MSU assistant research professor Frankie Jackson, looked at the nests of American crocodiles in Florida and broad-snouted caiman nests in Argentina. Varricchio and Jackson are co-authors of the paper, along with Carlos Ignacio Piña, a scientist with the National Scientific and Technical Research Council in Argentina.
“We wanted to see what types of nests the crocodiles made, such as whether they constructed cavities, like turtles, or mounds, as well as what type of material the nest was made of,” Ferguson said. “Then, we wanted to know if there was anything around the nest. Were there eggshells scattered around it; were there any bones or any traces left by the animals from walking around the nest?”
Eggshell fragments, a fairly common occurrence in the fossil record, may have been mistakenly believed to be remnants left by predators that attacked a nest to feast on eggs or hatchlings, or material transported by streams or floods, but were instead an indication of a successful hatching site, Ferguson said.
Ferguson also compared the orientation of eggshell fragments found around the nest – whether the concave, or open, portion was facing up or facing down – to previous studies on tortoise and bird nests that showed that 60 percent of the eggshell fragments in successful nesting sites were oriented with the concave portion facing up and 40 percent facing down.
“Because of the scattered eggshell distribution associated with the nests, we might have assumed that the eggshell was dispersed by predators or perhaps by flooding,” Ferguson said. “Looking at the eggshell orientation is just another way to tease that out and also to be able to recognize if we’re looking at a successfully hatched nest.”
In addition to the two species of crocodiles, Ferguson’s thesis research included applying similar techniques to four species of colonial ground nesting birds at the Bowdoin National Wildlife Refuge near Malta. She is currently constructing a paper to include results from the crocodylian and avian sites.
By including various species in their research, the scientists were able to recognize relationships between the types and abundance of debris generated by nesting and the reproductive behaviors of the animals, Varricchio said.
“For example, crocodylian hatchlings spend little time at the nesting site and the resulting assemblage consists only of eggs and eggshell,” he said. “In contrast, Ashley found that for birds with young that remain in the nest for some time, the nesting site preserves many bones of both prey (fish, rodents) and hatchlings and actually very little eggshell.
“Ashley’s work on these crocodylians, as well as on the nesting colonies of birds she examined in Montana, will allow us to better recognize and interpret fossil nesting sites whether from (ancient crocodiles) or dinosaurs.”
Before coming to MSU, Ferguson earned her bachelor’s degree in geology from Idaho State University. She has since returned there to pursue her doctorate in geology. She said she chose MSU for her master’s degree because of the first-rate reputation of its paleontology program.
“I knew the paleontology program here was excellent and I’ve wanted to come here since I was 8 years old,” Ferguson said. “My background was more of a generalist, so I came here to study more about vertebrates, having published before on oysters and trace fossils.”
Ferguson said she learned much while working alongside Varricchio, and was also excited about interacting with other students who share her passion for Earth sciences, even while pursuing other types of research.
At Idaho State, Ferguson will conduct research under the guidance of geoscientist Leif Tapanila, director of the Idaho Museum of Natural History. There, she will study eggshell ornamentation to see if she can determine the reason for the bumps and ridges that appear on the shells of some reptiles and birds.
She hatched upon the idea while she was in Argentina digging through caiman nests and noticed that the eggshells were bumpy and rough, like sandpaper.
“I thought it was interesting because I had always thought ornamented eggs were a dinosaur thing,” Ferguson said. “Nobody has really determined the reason for this ornamentation, although there have been some hypotheses, such as for water retention. I want to try to tease that out.”
Ashley Ferguson, email@example.com