Animals in the United States

Tyrannosaurus Teeth Were Hidden Behind Lizard-Like Lips

The Tyrannosaurus is typically depicted with its fearsome fangs on full display. But a paper published in Science states that the theropod dinosaurs, such as Tyrannosaurus rex, actually had thin, lizard-like lips that hid their sharp, serrated teeth.

Tyrannosaurus rex bellowing with its mouth shut, like a vocalising alligator. With its mouth closed, all of the enormous teeth of T. Rex would be invisible behind its lips. (Credit: Mark Witton)

Theropod Teeth

The paleontologists and paleoartists who are tasked with depicting dinosaurs have long deliberated about the appearance of the theropods. While some have suggested that these predatory dinosaurs had lizard-like lips that covered and concealed their teeth, others have suggested that they lacked lips, exposing their teeth in a terrifying, snaggletoothed snarl.

"Dinosaur artists have gone back and forth on lips," says study author Mark Witton, a paleontologist and paleoartist associated with the University of Portsmouth, according to a press release. "But lipless dinosaurs became more prominent in the 1980s and 1990s. They were then deeply rooted in popular culture through films and documentaries."

That being said, the scientific basis behind these popular portrayals was thin.

"Curiously, there was never a dedicated study or discovery instigating this change," Witton says in a release. "To a large extent, it probably reflected preference for a new, ferocious-looking aesthetic, rather than a shift in scientific thinking."

Read More: Here's What Dinosaurs Really Looked Like

Lipped or Lipless

Now, researchers have analyzed the teeth of the theropods more thoroughly, alongside the teeth of their more modern reptile relatives, finding that the ancient animals had scaly, soft tissues surrounding their teeth.

"We're upending this popular depiction by covering their teeth with lizard-like lips," Witton says. "This means a lot of our favorite dinosaur depictions are incorrect, including the iconic Jurassic Park T. Rex."

T. Rex skull and head reconstructions (Credit: Mark Witton)

All in all, the researchers say that their paper provides important insights into the diet and dental fitness of these dinosaurs. It also demonstrates the worth of a new approach for reconstructing the appearance of all sorts of ancient animals, including other dinosaurs.

"Some take the view that we're clueless about the appearance of dinosaurs beyond basic features like the number of fingers and toes," Witton says. "But our study, and others like it, show that we have an increasingly good handle on many aspects of dinosaur appearance."

Read More: What a Tyrannosaurus Rex Skull Tells Us About Its Intelligence

Studying Dinosaur Smackers

To arrive at these findings, the researchers compared the tooth and mouth morphologies of the theropods with those of modern reptiles, with and without lips. Their comparisons revealed that the mouths of the theropods were much more similar to those of the lipped reptiles, like lizards, rather than the lipless reptiles, like crocodiles.

Of particular importance to their conclusions were tooth wear and size. While the wear seen in the theropods was very different from that seen in the lipless reptiles, the tooth size of the theropods was very similar to that of the lipped reptiles, relative to the size of their skulls.

"Although it's been argued in the past that the teeth of predatory dinosaurs might be too big to be covered by lips, our study shows that, in actuality, their teeth were not atypically large," says study author Thomas Cullen, a paleontologist associated with Auburn University, according to a press release. "Even the giant teeth of tyrannosaurs are proportionally similar in size to those of living predatory lizards when compared for skull size, rejecting the idea that their teeth were too big to cover with lips."

According to the researchers, the theropod's lips protected their teeth from excessive exposure to their environment, decreasing the amount of damage that their enamel sustained during feeding. And, since most modern lizards aren't able to move their lips independently, the researchers also add that the theropods' lips were not muscular, most resembling those of the monitor lizards.

"It's quite remarkable how similar theropod teeth are to monitor lizards. From the smallest monitor to the Komodo dragon, the teeth function in much the same way," says study author Derek Larson, a paleontologist associated with the Royal BC Museum in Canada, according to a press release, "even though they are not closely related."

Ultimately, the researchers stress that their study applies to the theropods and the theropods, alone. So, while some dinosaurs undoubtedly displayed their teeth, the Tyrannosaurus was not one of them.

Read More: T. Rex Developed Different Shaped Eye Sockets For a Forceful Bite

Predatory Dinosaurs Such As T. Rex Sported Lizard-like Lips, Suggests Study

A new study suggests that predatory dinosaurs, such as Tyrannosaurus rex, did not have permanently exposed teeth as depicted in films such as Jurassic Park, but instead had scaly, lizard-like lips covering and sealing their mouths.

Researchers and artists have debated whether theropod dinosaurs, the group of two-legged dinosaurs that includes carnivores and top predators like T. Rex and Velociraptor, as well as birds, had lipless mouths where perpetually visible upper teeth hung over their lower jaws, similar to the mouth of a crocodile.

However, an international team of researchers challenge some of the best-known depictions, and say these dinosaurs had lips similar to those of lizards and their relative, the tuatara—a rare reptile found only in New Zealand, which are the last survivors of an order of reptiles that thrived in the age of the dinosaurs.

In the most detailed study of this issue yet, the researchers examined the tooth structure, wear patterns and jaw morphology of lipped and lipless reptile groups and found that theropod mouth anatomy and functionality resembles that of lizards more than crocodiles. This implies lizard-like oral tissues, including scaly lips covering their teeth.

These lips were probably not muscular, like they are in mammals. Most reptile lips cover their teeth but cannot be moved independently—they cannot be curled back into a snarl, or make other sorts of movements we associate with lips in humans or other mammals.

Study co-author Derek Larson, Collections Manager and Researcher in Paleontology at the Royal BC Museum in Canada, said, "Paleontologists often like to compare extinct animals to their closest living relatives, but in the case of dinosaurs, their closest relatives have been evolutionarily distinct for hundreds of millions of years and today are incredibly specialized.

"It's quite remarkable how similar theropod teeth are to monitor lizards. From the smallest dwarf monitor to the Komodo dragon, the teeth function in much the same way. So, monitors can be compared quite favorably with extinct animals like theropod dinosaurs based on this similarity of function, even though they are not closely related."

Co-author Dr. Mark Witton from the University of Portsmouth said, "Dinosaur artists have gone back and forth on lips since we started restoring dinosaurs during the 19th century, but lipless dinosaurs became more prominent in the 1980s and 1990s. They were then deeply rooted in popular culture through films and documentaries—Jurassic Park and its sequels, Walking with Dinosaurs and so on.

"Curiously, there was never a dedicated study or discovery instigating this change and, to a large extent, it probably reflected preference for a new, ferocious-looking aesthetic rather than a shift in scientific thinking. We're upending this popular depiction by covering their teeth with lizard-like lips. This means a lot of our favorite dinosaur depictions are incorrect, including the iconic Jurassic Park T. Rex."

The results, published in the journal Science, found that tooth wear in lipless animals was markedly different from that seen in carnivorous dinosaurs and that dinosaur teeth were no larger, relative to skull size, than those of modern lizards, implying they were not too big to cover with lips.

Also, the distribution of small holes around the jaws, which supply nerves and blood to the gums and tissues around the mouth, were more lizard-like in dinosaurs than crocodile-like. Furthermore, modeling mouth closure of lipless theropod jaws showed that the lower jaw either had to crush jaw-supporting bones or disarticulate the jaw joint to seal the mouth.

"As any dentist will tell you, saliva is important for maintaining the health of your teeth. Teeth that are not covered by lips risk drying out and can be subject to more damage during feeding or fighting, as we see in crocodiles, but not in dinosaurs," said co-author Kirstin Brink, Assistant Professor of Paleontology at the University of Manitoba.

She added, "Dinosaur teeth have very thin enamel and mammal teeth have thick enamel (with some exceptions). Crocodile enamel is a bit thicker than dinosaur enamel, but not as thick as mammalian enamel. There are some mammal groups that do have exposed enamel, but their enamel is modified to withstand exposure."

Thomas Cullen, Assistant Professor of Paleobiology at Auburn University and study lead author, said, "Although it's been argued in the past that the teeth of predatory dinosaurs might be too big to be covered by lips, our study shows that, in actuality, their teeth were not atypically large. Even the giant teeth of tyrannosaurs are proportionally similar in size to those of living predatory lizards when compared for skull size, rejecting the idea that their teeth were too big to cover with lips."

The results provide new insights into how we reconstruct the soft-tissues and appearance of dinosaurs and other extinct species. This can give crucial information on how they fed, how they maintained their dental health, and the broader patterns of their evolution and ecology.

Dr. Witton said, "Some take the view that we're clueless about the appearance of dinosaurs beyond basic features like the number of fingers and toes. But our study, and others like it, show that we have an increasingly good handle on many aspects of dinosaur appearance. Far from being clueless, we're now at a point where we can say 'oh, that doesn't have lips? Or a certain type of scale or feather?' Then that's as realistic a depiction of that species as a tiger without stripes."

The researchers point out that their study doesn't say that no extinct animals had exposed teeth—some, like saber-toothed carnivorous mammals, or marine reptiles and flying reptiles with extremely long, interlocking teeth, almost certainly did.

More information: Thomas M. Cullen et al, Theropod dinosaur facial reconstruction and the importance of soft tissues in paleobiology, Science (2023). DOI: 10.1126/science.Abo7877. Www.Science.Org/doi/10.1126/science.Abo7877

Citation: Predatory dinosaurs such as T. Rex sported lizard-like lips, suggests study (2023, March 30) retrieved 8 April 2023 from https://phys.Org/news/2023-03-predatory-dinosaurs-rex-sported-lizard-like.Html

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Smithsonian Scientists Discover One Of The Earliest Mammal Ancestors That Ate Its Veggies

An artist's rendering of Melanedaphodon hovaneci, a reptile-like mammal ancestor that lived in what is now Ohio more than 300 million years ago. Henry Sharpe

While plants first colonized land 470 million years ago, there haven't always been animals able to eat them. Being a herbivore requires specialized traits like durable teeth to break down tough plant material and a large gut housing microbes capable of digesting cellulose. As a result, researchers have long thought that large animals did not start chowing down on greens until the early Permian period around 300 million years ago.

But the discovery of a new fossil critter may push this dietary revolution back millions of years. In a study published today in the journal Scientific Reports, Smithsonian paleontologists  Arjan Mann and Hans Sues named a new species of ancient reptile-like mammal ancestor that had chompers reminiscent of living lizards like blue-tongued skinks who devour everything from fruits and veggies to insects.

"The similar tooth morphology present in this fossil animal may indicate the earliest inklings of herbivory," said Mann, a Peter Buck Postdoctoral Fellow at the National Museum of Natural History and the lead author of the new study. "The adaptation of herbivory is now much earlier than previously recognized."

Museum paleontologist Arjan Mann holds the fossilized skull of a Gorgonops, another type of reptile-like mammal ancestor that lived around 260 million years ago in what is now Zambia. Arjan Mann

These fossils hail from the site of a now-defunct coal mine near the eastern Ohio town of Linton. During the Late Carboniferous period, this area was a balmy stretch of wetlands whose waters contained coelacanths, spiny freshwater sharks and an abundance of amphibians. One of the stranger inhabitants was Colosteus, a large amphibian with fangs and reduced limbs that ruled these primeval swamps like a crocodile. According to Sues, these communities were also home to the earliest reptiles and the earliest forerunners of mammals.

 307 million years ago, a meandering river changed course here, leaving an isolated riverbed called an oxbow lake in its wake. Eventually plant material from the surrounding swamp built up in the stagnant water and decomposed into peat. The decomposition process siphoned oxygen from the surrounding water, dooming the bog's inhabitants. The lack of oxygen also kept scavengers at bay, ensuring the fish, amphibians and whatever else washed in was peacefully interred in the peat.

Over time, heat and pressure transformed the peat into slabs of cannel coal, a type of coal that was used to create kerosene during the nineteenth century. Between 1855 and 1921, miners extracted cannel coal out of the local Diamond Coal Mine. Almost immediately they started discovering the well-preserved remains of ancient fish and amphibians etched into the coal's waxy, black surface.

The prehistoric inhabitants of Linton, Ohio, like these microsaur amphibians, are preserved as fossil impressions in chunks of cannel coal. Jack Tamisiea, NMNH

"These fossils are basically negative impressions in the coal," Mann said. Paleontologists have been studying these imprints for more than a century in order to understand this cache of Carboniferous creatures. Recent technological advancements like CT scans even allow researchers to digitally recreate the flattened fossils in three dimensions.

Most local fossils preserve aquatic inhabitants of these ancient bogs like amphibians and fish. But the remains of terrestrial animals also washed into these swamps. Their fossils turn up from time to time.

Parts of the skulls of two such creatures were entombed in two blocks of cannel coal now housed in the Carnegie Museum of Natural History's collection in Pittsburgh. Together, these slabs contained jaws studded with teeth that ended in rounded, blunt points. According to Mann, who first came across the fossils in 2019 while wrapping up his PhD at Carleton University, the shape of these teeth was very odd for this type of animal at the time.

The original tooth-studded jaw fossil Mann and Sues examined in the new paper (top left). Also depicted are a CT scan (top right) and a detailed illustration of the fossil. Mann et al.

He never forgot about those strange teeth. During the pandemic, he finally had a chance to examine them in depth when he was back home in Toronto. "I decided to get off my butt and did most of the anatomical work as a pandemic project," Mann said. To peer inside the mouth of this ancient animal, researchers had previously used a CT scanner to digitally recreate the animal's jaws. Using these scans, Mann was able to create accurate 3D models of the original fossils, allowing him to analyze the animal's dentition without having to travel to Pittsburgh.

In the new paper, Mann and Sues worked with paleontologists at the Carnegie Museum and Harvard University to describe the ancient animal. They christened the creature Melanedaphodon hovaneci. The genus is a mashup of the Greek word "melanos," which means black—referring to the fossil's dark color—and the words for "pavement" (edaphon) and "tooth" (odon), which refer to the animal's dense clusters of teeth. The species name refers to George Hovanec, a Carnegie Museum donor who helped fund the team's use of CT scanners to analyze the fossils. Holvanec recently passed away, and Mann and his coauthors hope the new fossil will honor his memory.

The animal was a close relative of Edaphosaurus, a reptile-like mammal ancestor called a synapsid who lived during the early Permian. The alligator-sized, sail-backed Edaphosaurus was among Earth's earliest large herbivores. It used its thick tooth plates to grind down tough plants and had a wide ribcage that housed a substantial gut to digest its leafy meals. This skull of the early Permian Edaphosaurus in the museum's collections shows off the animal's set of blunt chompers. Jack Tamisiea, NMNH

Melanedaphodon's teeth, which end in bulbous points, are unique. But they do possess some similarities to the chompers of both Edaphosaurus and several living lizards that eat plants as part of their diets. These include large skinks and tegus, a group of stout lizards native to South America that devour everything from fruits and eggs to rodents and table scraps. "Those animals will eat insects if you put them in there, but will also eat fruit, vegetables and all sorts of things," Mann said. He thinks Melanedaphodon had similarly diverse tastes. "It probably ate a mix of plant material and the occasional insect that was in its way."

The researchers concluded that Melanedaphodon is the oldest known amniote (the animal group that includes all reptiles, birds and mammals) to subsist on a diet that included a healthy portion of low-fiber plant byproducts like seeds and bark. "Not only are we presenting a new type of herbivory present in the early fossil record, but the earliest record of such low-fiber feeding," Mann said.

Melanedaphodon lived during a dynamic era in Earth's history. Not long after the ancient inhabitants of Linton, Ohio, were buried inside the bog, the vast coal rainforests that dominated the Carboniferous began giving way to drier environments, sparking an extinction event. When the Permian period began around 299 million years ago, true herbivores like Edaphosaurus had become major components of terrestrial ecosystems for the first time.

But it appears that a few adventurous eaters like Melanedaphodon were already munching on greens long before herbivory went mainstream.

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