A team of paleontologists led by Michelle Stocker of Virginia Tech and Sterling Nesbitt of the Department of Geoscience identified fragments of fossils from what is believed to be the oldest known frog in North America.
The fossils are made up of several small pieces of hip bones, called ilium, from Chinese frogs, a distant and long-extinct branch of the modern frog, but not its direct ancestor. The fragments are packed in rock and are smaller than a pink nail. They represent the earliest and oldest known Equatorial remains of a salientien – the group containing living frogs and their most closely related fossil relatives – dating from the Upper Triassic, about 216 million years ago.
The name of the fossil comes from where they were found, the Chinle Formation in Arizona.
Stocker, assistant professor of geosciences at Virginia Tech College of Science, explains that the fossils discovered in May 2018 highlight the importance of collecting and analyzing microfossils to understand extinct species whose total length is less three feet.
"This new discovery highlights just how much remains to be learned about the late Triassic ecosystem and how much we find when we look a little closer to us," said Stocker. "We are familiar with the charismatic archosaurs of the Chinle Formation, but we know that on the basis of other ecosystems they should represent a small percentage of the animals that lived together." With this new orientation, we are able to fill a lot of these small missing components with new discoveries ".
Coming from many individuals, the hip bones are long and hollow, with an offset hip grip rather than centered. The bones of the frogs show how tiny they were: a little over half an inch long. "The Chinle frog could fit on the tip of your finger," added Stocker.
Stocker and his team include researchers from Virginia Tech, Petrified Forest National Park, Arizona, and the Natural History Museum of the University of Florida, whose results were published today in the online journal. Biology Letters. Although the fossils are part of the Chinle frog family, they have not yet named them.
"We refrain from naming this Chinle frog because we are continuing to treat a matrix of micro-vertebrates that will likely produce additional cranial and post-cranial material that could be even more informative," added Stocker.
The Chinle Frog shares more features with live frogs and Prosalirus, an ancient Jurassic frog found in the sediments of the current Navajo Nation, triadobatrachus, an early Triassic frog found in modern times in Madagascar, Africa. "These are the oldest frogs near the equator," added Stocker. "In total, the oldest frogs are about 250 million years old from Madagascar and Poland, but these specimens come from higher latitudes and are not equatorial."
Nesbitt, also an assistant professor of geoscience, added, "Now that we know that tiny frogs are present about 215 million years ago in North America, we may be able to find other members modern vertebrate communities of the Triassic period ".
(During the Triassic, the distinct continents that we recognize today formed the only land mass named Pangea.At Arizona today was located about 10 degrees north of l & # 39; equator).
The team added that this discovery also marks the first time that fossils of frogs have been discovered directly with other primitive dinosaurs and phytosaurs.
The Virginia Tech team included undergraduate and graduate students from the university, using fossils found in the field and repeatedly sprinkling other rock samples into water buckets. . Further study of fossils has been completed by scanners. Undergraduate students who accompanied Stocker and Nesbitt during the spring 2018 Arizona expedition included Elizabeth Evans, a major of the School of Performing Arts; Rebecca Hawkins, specialization in the Department of Fish and Wildlife Conservation; and Hector Lopez, who specializes in biological sciences.
"Thanks to my internship with Drs Stocker and Nesbitt in Arizona, I've seen the hard work of paleontologists in finding fossils," said Hawkins, a sophomore at the College of Natural Resources and Environment. "Every day you have to face long hikes, heavy loads, scorching heat, etc. And, with the right combination of patience and luck, you can find something really amazing that is worth it to be hard, like a little frog hip that tells a great story. "
"Our development of methods to recover the delicate bones of small vertebrates has made this discovery exciting," said Ben Kligman, Ph.D. geoscientist student from Philadelphia, Pennsylvania. "Our goal is to use similar techniques in the Chinle Formation to discover the early life of other small animals, including lizards, salamanders, turtles and mammals."
The study was funded by the National Science Foundation, the National Geographic Society, the David B. Jones Foundation, the Petrified Forest Museum Association and the Friends of the Petrified Forest National Park.
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