Rare Florida fossil finally ends debate over porcupine jaw and tail evolution

A rare, almost complete fossil of an extinct North American porcupine helped me and my colleagues resolve a decades-long debate about how modern North American porcupine developed from its ancestors.

In our paper published in Current Biology, we argue that the ancestors of North American porcupines could well be 10 million years old, but wouldn’t be recognizable until about 8 million years later.

By comparing the bone structure of porcupines in North and South America, we found that, surprisingly, during those 8 million years, North American porcupines still looked like their cousins, the Neotropical porcupines that now live within the tropical regions of Central and South America.

Our findings make clear the evolution of the North American porcupine from South America – and at the identical time solve the mystery of why it was so difficult to seek out its ancestors.

I’m a paleontologist who studies the fossilized bones and teeth of extinct animals. With Museum curator Jon Bloch, I created a course where we analyzed bone structure to succeed in the conclusions of our study.

Why it can be crucial

Modernity North American porcupine differs from its spiny relatives. It has a brief tail, a jaw with which it may well scrape bark from trees and weighs between 10 and 25 kilos (4.5 and 11.3 kilograms).

Although clearly related, Neotropical porcupines look different. They have long, grasping tails, weaker jaws and weigh between 1.5 and 10 kilos (0.68 and 4.5 kilograms).

DNA analyses of recent animals estimate that these two groups are about 10 million years before.

This is where the mystery is available in. Fossils of the North American porcupine are all younger than 1.8 million yearsIn other words, fossils of the North American porcupine dating back about 8.2 million years were missing.

All the researchers had were parts of jaws and tails that looked like they belonged to Neotropical porcupines.

Two competing hypotheses could explain the similarity.

Some scientists have argued that the jaw and tail fossils of early ancestors of North American porcupines should more closely resemble their modern descendants. Researchers who support this concept have said that the fossil record is incomplete for unknown reasons, but that it continues to be possible that fossils supporting their hypothesis will eventually emerge.

Other scientists have suggested that each one early porcupine ancestors could have had jaws and tails much like those of recent neotropical porcupines. The ancestors of North American porcupines could also be hidden in the present fossil record because, based on their jaws and tails alone, they give the impression of being an identical to the ancestors of neotropical porcupines. Only more moderen fossils would show distinctive features because these features appeared at the moment.

The debate continued for many years. With the available fossils it was inconceivable to resolve the issue.

How we worked

Then researchers from the Florida Museum of Natural History excavated a 2 million 12 months old almost complete skeleton of a porcupine in north central Florida in 2005.

The fossil had an extended tail and no jaws to chew bark, much like neotropical porcupines. But it also had dozens of other bones that we could use to elucidate the relationships.

To gather this evidence, we needed to comb through all of the bones, on the lookout for lots of of tiny details – just like the shape of ridges or patterns of bone edges – and compare those details to skeletons of recent North American and Neotropical porcupines. Bloch and I developed a course through which each student took on a component of the project.

Together, we compiled a listing of nearly 150 insightful details. Although the specimen had some features much like those of neotropical porcupines, additional evidence supported the concept that this fossil was a more in-depth relative of North American porcupines.

Since this porcupine had a jaw and tail like its neotropical cousins, it is probably going that the majority of the North American porcupine's older relatives also lacked the characteristic features of their modern descendants.

In other words, the reply to the puzzle is that the fossil record of North American porcupines appears young since the stronger jaw and shorter tail evolved relatively recently. Porcupines looked different than we expected for much of their 10-million-year-old ancestry.