An artist’s impression of the Tetrapodophis amplectus in its Cretaceous environmentAn artist’s impression of the Tetrapodophis amplectus in its Cretaceous environment. Illustration courtesy Julius Csotonyi

Researchers suggest that a study claiming to have found an ancestral snake had no legs after all

Cristina Miceli

When in 2015, David Martill of the University of Portsmouth in the U.K., and coauthors claimed they had have found the first ever four-legged snake fossil, dubbed Tetrapodophis amplectus, in a Science paper (paywall), the scientific community and the lay public took notice. But recent research by Michael Caldwell of the University of Alberta in Canada, and others suggests that they really needn’t have bothered.

In a world where language is usually arcane and couched in subtlety, the headline Caldwell et. al. used in their headline in their article in the Journal of Systematic Paleontology was uncharacteristically blunt: ”Tetrapodophis amplectus is not a snake…

The Tetrapodophis amplectus fossil to scale
The Tetrapodophis amplectus fossil, to scale. Pic courtesy Michael Caldwell

Caldwell had heard about the Martill paper before it was published in 2011. In fact, he requested that he be allowed to review it.

“I was suspicious from the very first time I saw the paper,” Caldwell told Truly Curious. “When it was published in Science, I was actually surprised because I wasn’t asked to read it again. I think I was probably excluded from the process because my opinion was counter to the perspective being proposed…”

The Long Way Home

Before Caldwell got around to pointing out misidentified fossils, his road to research had quite a few turns and detours.

As he put it, “My story about how I got interested in paleontology is more like a drunk spider web than it is a straight and linear story.”

In grade school, he did want to be a paleontologist, but went to university and did two years studying history and political science, with the intent of becoming a lawyer. But because he was passionate about rock-climbing and mountaineering, he earned a second degree in physical education and outdoor recreation.

But then, in 1986, while mountain-climbing with friends, Caldwell got interested in high-altitude physiology and its effects on the lungs, brains and more, and started collecting blood and urine from friends.

Michael Caldwell
Michael Caldwell. Pic courtesy Michael Caldwell

“That was when I realized that science was the thing I was more interested in than anything else – and suffered yet another epiphany when I was out with two youngest sons on a backpacking trip, and one of them found a fossil,” he said.

So, in that summer of 1987, thus reminded of his childhood dream, Caldwell went back to school to get another degree – in geology and biology at the University of Alberta.

In 1991, he went to McGill University to do a PhD in paleontology, doing a thesis on limb evolution in reptiles, including mosasaurs, an early lizard that died out after the same asteroid hit that ultimately put paid to most dinosaurs. Yes, birds are dinosaurs that missed the extinction memo.

A Complicated Story

So Caldwell was well qualified to judge the age and provenance of the fossil found in Brazil. He had a background in geology, which is useful to gauge the age and behavior of the material and depth a fossil is found in, and training and experience in the biology of lizards and snakes.

While Martill had studied the fossil in Brazil, it had found its way to Germany.

“The specimen left Brazil somehow, which means it left it illegally because there are no export permits or papers associated with this specimen,” Caldwell said. “So, it was collected in Brazil by someone – we don’t know how. We don’t even know exactly where it came from. And no one would talk about it.”

It did not help that Martill first dismissed the Brazil’s requirement that any research done on fossils found there needed at least one researcher to be Brazilian.

The recent paper argues that the teeth did not naturally point backward like snakes, as earlier suggested, but had shifted after death.
The recent paper argues that the teeth did not naturally point backward like snakes, as earlier suggested, but had shifted after death. Pic courtesy Michael Caldwell

Caldwell described Martill as “very vocal and colonial in his attitude towards fossils specimens from Brazil,” even describing him as “rude, and bigoted and chauvinistic and misogynistic.” Very strong words for an academic.

Indeed, in an interview with Estadão in 2015, Martill had described his objections to Brazilian laws about fossils, describing the measures as xenophobic and limiting.

When pressed, Martill told the journalist that when he had started out he didn’t know of a Brazilian fossil snake expert, before adding, “But what difference would it make? I mean, do you want me also to have a black person on the team for ethnicity reasons, and a cripple and a woman, and maybe a homosexual too just for a bit of all round balance?” While he did clarify that nationality and sexuality – and presumably gender and ableness, too – did not matter, the attention had already shifted from the scientific to the political.

A Second Opinion

That same year, Caldwell and fellow author Robert Riesz (also from the University of Alberta) got a permit to see the fossil, now in a private collection in Germany. Suddenly, Caldwell was not seeking out possible errors in a paper; he was looking at the fossilized bones of a creature he was trained to study.

Caldwell quickly concluded it was clear that while Tetrapodophis amplectus was a lizard, it certainly not a snake.

For instance, in his paper, Martill and coauthors state that, as seen in snakes, the fossil is characterized by a very short tail. However, Caldwell says it’s not relative length, but the number of bones in it that matter.

“The tail actually had 120 vertebrae,” Caldwell said. “A typical snake tail has only 40 or 50..”

More evidence comes from the skull, which was poorly preserved but for one bone: the left lower jaw.

“Not a single feature of that left lower jaw was similar to what we see in a snake,” said Caldwell, whose paper suggests that Tetrapodophis amplectus was, in fact, a dolichosaur, a group of lizards closer to the mosasaurs that he had studied for his thesis.

The whole fossilized skull does not look like that of a snake, but a lizard, the authors argue
The whole fossilized skull does not look like that of a snake, but a lizard, the authors argue. Pic courtesy Michael Caldwell

Yes, researchers agree that the ancestors of snakes had legs; even today, pythons and boas have the stunted remnants of legs – called pelvic spurs. There is no convincing case for snakes not having descended from lizards. What we are not sure about is which type of lizard they evolved from. This is called the snake ancestry problem, the subject of academic debate for more than a century.

“That’s also where paleontologists at conferences would sit in bars and throw beer bottles at each other,” Calwell said with a smile to make clear that it was a joke.

What Went Wrong?

So how did the earlier researchers miss this evidence – of the jaw, the lack of deeply curved teeth, or ribs and other bones that resemble a lizard more closely.

“People do science in very different ways,” Caldwell said. “I’m very focused on the dataset, on the anatomy of the animal that I’m studying… If you don’t focus as much on data you can sometimes get your paper published in a high-profile journal with simply a good narrative. And good narrative is not necessarily good science.”

Despite not being a snake, Tetrapodophis amplectus is a unique fossil – a lizard with that many vertebrae in the body that still has four legs.

The legs bones of the fossil, which an earlier study asserted was the sign of a snake ancestor
The leg bones of the fossil that an earlier study asserted were just vestiges of a lizard ancestor. Pic courtesy Michael Caldwell

“This is like no other lizard I have ever seen before,” Caldwell said. “It’s kind of breaking the rules with elongation of the body and still maintaining the front legs.”

According to him, by the time lizards get that long, they usually lose their limbs. Caldwell pointed out to many living examples of legless lizards.

“So this is a really cool animal all on its own without being a snake,” Caldwell said. “It doesn’t need to be a snake to be interesting.”

For a variety of reasons, it certainly is.

Christina Micelli

Cristina Miceli is a freelance writer with a master’s degree in journalism from the University of Limerick

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