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Yuma Geoscientist Sparks Debate on Fossil Porcupines

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. Maya Springhawk Robnett of the Arizona Science desk says the debate over migration vs. evolution has become rather…prickly.

Fred Croxen has been a professor of Geosciences at Arizona Western College in Yuma for thirty-nine years. And he’s built up a large fossil collection in that time—more than twelve-thousand specimens.
“It’s just more cluttered," he says as he walks into his lab, "But it’s an organized clutter!”
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. “I don’t know if you can hear my voice over the thing there," he shouts over the machine, "but you can see the matrix just flaking off as I touch it!”
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," Croxen explains, "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… However, porcupines that live in the neo-Tropics, when they get up to eat, they have a year-round salad bar.”
Croxen says 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 fifteen years in the making. But the conclusion doesn’t sit well with everyone in the paleontological community.
“Well, what about all this other information?" asks one paleontologist. "What about limb bones? What about skulls?”  Gary Morgan is a curator of vertebrate paleontology at the New Mexico Museum of Natural History. Morgan says 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.”
Morgan says 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. 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,” he says.
Professor Croxen at Arizona Western College agrees to disagree. But that’s okay 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!”
The article and its controversy will be published in the Natural History Museum of Los Angeles County’s Contributions in Science on July 20.