Discovery of ‘rare’ fossil in Florida solves evolutionary mystery

An exceptionally rare porcupine fossil skeleton discovered in Florida has helped solve a long-standing evolutionary mystery.

The research, published in the journal Current biologysheds new light on the evolutionary history of North American porcupines.

The origin of North American porcupines has long been the subject of debate among scientists who study these animals.

Central and South America are home to 16 species of porcupines, all belonging to the genus (species group) Coendou. In contrast, only one species of porcupine lives in the United States and Canada today: the North American porcupine, known scientifically as the Erethizon dorsatum. This species belongs to the genus simply called Erethizon, of which it is the only living member.

Previous DNA evidence suggested that the genus Erethizon arose around 10 million years ago, when the North American and South American continents were still separated by a vast sea route. On the other hand, fossil evidence suggests that North American porcupines may have evolved around 2.5 million years ago after the emergence of a land bridge connecting the two continents.

The latest discoveries, based on an analysis of the Florida fossil, seem to reconcile these different chronologies, according to the authors.

The fossil, which was found in a limestone quarry, is the oldest documented nearly complete porcupine skeleton in North America, according to researchers. They determined that it belonged to a species known as Erethizon poyeri, which is an extinct member of the genus Erethizon that lived around 2 million years ago.

Analysis of the fossil indicated that rather than originating in North America, the genus Erethizon likely originated and existed for much of its evolutionary history in South America, with a body form and role ecological which largely resembled those of its sister group, Coendou.

Both Coendou and Erethizon belong to a larger group known as New World porcupines. These animals originated in South America before dispersing to North America as part of the Great American Exchange.

This exchange occurred about 3 to 4 million years ago, after the Isthmus of Panama rose above sea level, connecting the two continents by a land bridge. This stretch of land allowed animals to migrate in both directions, with porcupines being among those heading north.

Today, Coendou porcupines live in the rainforests of Central and South America. They exhibit several characteristics that have allowed this group to adapt to life in the treetops. These characteristics include relatively small body size, long fingers tipped with sickle-shaped claws for grasping branches, and long prehensile tails capable of grasping, which can be used for climbing and reaching fruit.

North American porcupines, on the other hand, are adapted to temperate forests. They have larger bodies, shorter tails, and a different jaw shape, the latter adaptation allowing them to eat tree bark when food is scarce during cold winters.

The scarcity of fossils has prevented biologists from understanding the timing of these ecological adaptations in relation to the dispersal of porcupines from South America to North America. But the Florida fossil sheds new light on this question, indicating that it was only after Erethizon’s expansion into temperate North American habitats that it acquired the characteristics for which the group is known Today.

“When they first brought (the fossil) in, I was amazed,” Jonathan Bloch, a paleontologist and lead author of the study at the Florida Museum of Natural History, said in a press release.

“It’s so rare to get fossil skeletons like this with not only a skull and jaws, but also many bones associated with the rest of the body. This allows for a much more complete picture of how this extinct mammal would have interacted with its environment. We immediately noticed that it was different from modern North American porcupines.

Unlike the modern North American porcupine, Erethizon poyeri had traits similar to the tropical genus Coendou, including a long prehensile tail specialized for clinging to branches and grasping feet. It also lacked a jaw and teeth specialized for chewing bark.

However, others Erethizon poyeri some traits, such as the shape of the middle ear bone and the shape of the lower front and back teeth, appear to more closely resemble those of North American porcupines.

E. poyeri had been described by scientists before the latest study, but only from a much less complete fossil: the species was mainly known from its jaws and middle ear bones.

“This incompleteness explains part of the origin of the controversy,” said the study’s lead author, Natasha Vitek, a former doctoral student at the Florida Museum who now works at Stony Brook University in New York. News week.

“The jaws had features surprisingly more similar to those of their distant tropical relatives than to those of the temperate porcupines that live closer to them today. But paleontologists weren’t sure if they looked similar because they ate similar foods and chewed in similar ways, or because they were surprisingly closely related to more tropical porcupines.

The Florida fossil helps explain why scientists have had difficulty identifying the ancestors of North American porcupines, the researcher said.

“Today, these animals have distinct tails, jaws and legs, and other cold adaptations, and we look for these features as markers of relationships and ancestry in fossils,” Vitek said. “It turns out that these features tell us about function, but they are not reliable markers of ancestry.”

“Once we found a nearly complete fossilized skeleton with dozens of additional data points in other body parts telling us about relationships, we discovered that the ancestors of these porcupines did not share their distinctive adaptations to survive cold winters and move around trees like modern North American porcupines do, move and eat much more like their tropical cousins,” she added.

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Updated 5/30/24, 1:29 p.m. ET: This article has been updated with additional comment from Natasha Vitek.