A professor at Arizona Western College in Yuma has caused a stir in the world of paleontology. His research suggests that an ancestral porcupine evolved as a result of migration, causing a debate over migration vs. evolution that has become rather ... prickly.
Fred Croxen has been a professor of geosciences at Arizona Western College in Yuma for 39 years. And he’s built up a large fossil collection in that time — more than 12,000 specimens.
The fossils are housed in a small building on the edge of the college property, one which isn’t even identified on the campus maps. Croxen calls it the Lake Woebegone of Arizona Western College — it’s here, but no one knows it exists.
Croxen dedicates dozens of hours to single bones by use of air pressure tools to remove the matrix, or sand, surrounding them. Croxen explained the process as he worked.
“I don’t know if you can hear my voice over the thing there, but you can see the matrix just flaking off as I touch it!” he said.
Croxen and several colleagues have traveled into Sonora, Mexico, for more than two decades. There, the El Golfo badlands is home to a treasure trove of fossils that date back over a million years.
That’s where they found several ancient porcupine jawbones. Croxen and his colleagues began to notice they were similar to the shape of the modern South American porcupine, of the Coandou genus.
That surprised them because another porcupine, the Erethizon genus of North America, is traditionally considered to be this ancient porcupine’s closest relative.
“Our porcupines in North America, during the winter they kind of slow down. But what’s available to eat is not as luscious and diverse so they have to scrape bark from trees," said Croxen. "However, porcupines that live in the neo-Tropics, when they get up to eat, they have a year-round salad bar.”
Croxen said the porcupine in North America had to develop a steeper-angled incisor as an evolutionary result of these eating habits. But established thought for this porcupine says evolution came first, then migration. If the porcupine jaws Croxen has don’t have those incisors, how could they have evolved before migrating north from South America?
That’s why Croxen and four other geoscientists have collaborated on an article 15 years in the making. But the conclusion doesn’t sit well with everyone in the paleontological community, including Gary Morgan, curator of vertebrate paleontology at the New Mexico Museum of Natural History.
“Well, what about all this other information? What about limb bones? What about skulls?” said Morgan.
Morgan said Croxen and the other authors have only looked at jaws.
“Their sample that they’re looking at is too limited, and it may not actually be diagnostic of the different porcupines when you look at a larger, broader sample than you’re seeing — that most of the features do look like this Erethizon," said Morgan.
Morgan said there’s a large porcupine fossil collection in Florida from around the same time period. He believes when you look at the whole animal, these ancient porcupines seem more closely related to the modern North American porcupine than its South American cousin.
“They think it’s one animal. I think it’s another. And I think I’m right, only because they don’t have any limb bones, they don’t have any skulls," said Morgan. "All these things that we have in the Florida sample that indicate the animal belongs to the Erethizon genus, they lack that in the samples they’re looking at.”
Croxen at Arizona Western College agrees to disagree. But that’s OK with him.
“We’re more than happy to have any folks who wish to disagree with us and show us some other interpretations of our data. We’ll find out. That’s part of science!” Croxen said.
The article and its controversy will be published in the Natural History Museum of Los Angeles County’s Contributions in Science on July 20.