Many animals have tusks, from elephants to walruses to hyraxes. But one thing today’s tusked animals have in common is that they’re all mammals — no known fish, reptiles or birds have them. But that was not always the case. In a published Oct. 27 in the Proceedings of the Royal Society B, a team of paleontologists at Harvard University, the Field Museum, the 91̽�� and Idaho State University traced the first tusks back to ancient mammal relatives that lived before the dinosaurs.

“Tusks are this very famous anatomy, but until I started working on this study, I never really thought about how tusks are restricted to mammals,” said lead author , a postdoctoral researcher at Harvard University and a 91̽��doctoral alum.

“We were able to show that the first tusks belonged to animals that came before modern mammals, called dicynodonts,” said co-author , a curator at the Field Museum in Chicago. “Despite being extremely weird animals, there are some things about dicynodonts — like the evolution of tusks — that inform us about the mammals around us today.”

Dicynodonts lived from about 270 to 201 million years ago, largely before the so-called “time of the dinosaurs.” They ranged from rat- to elephant-sized. Modern mammals are their closest living relatives, but they looked more reptilian, with turtle-like beaks. One of their defining features is a pair of protruding tusks in their upper jaws. The word dicynodont means “two canine teeth.”

Not all protruding teeth are tusks. Their composition and growth patterns reveal whether they count.

“For this paper, we had to define a tusk, because it’s a surprisingly ambiguous term,” said Whitney.

For a tooth to be a tusk, the researchers argued it must extend out past the mouth, keep growing throughout the animal’s life and, unlike most mammals’ teeth — including ours — tusks’ surfaces are made of dentine rather than hard enamel.

Under these parameters, elephants, walruses, warthogs and hyraxes have tusks. Other big teeth in the animal kingdom don’t make the cut, though. For instance, rodent teeth, even though they sometimes stick out and are ever-growing, have an enamel band on the front of the tooth, so they don’t count.

Some of the dicynodont tusks that the team observed in Zambia didn’t fit the definition of a tusk either: They were coated in enamel instead of dentine.

The different makeup of teeth versus tusks gives scientists insights into an animal’s life.

“Enamel-coated teeth are a different evolutionary strategy than dentine-coated tusks,” said Whitney. “It’s a trade-off.”

Enamel teeth are tougher than dentine. But because of the geometry of how teeth grow in the jaw, if you want teeth that keep growing throughout your life, you can’t have a complete enamel covering.

Animals like humans made an evolutionary investment in durable but hard-to-fix teeth — once our adult teeth grow in, we’re out of luck if they get broken. Tusks are less durable, but they grow continuously, even if they get damaged. It’s like the compromise of getting a car that’s very reliable but very difficult to get repaired, versus driving a beater that needs frequent repairs but is cheap and easy to fix.

The different kinds of teeth animals have evolved tell scientists about the pressures those animals faced that could have produced those teeth. Animals with tusks might use them for fighting or for rooting in the ground, exposing them to little injuries that would be risky for enamel teeth that don’t grow continuously.

To study whether dicynodonts tusks really were tusks, the researchers cut paper-thin slices out of the fossilized teeth of 19 dicynodont specimens, representing ten different species, and examined their structure under a microscope. They also used micro-CT scans to examine how the teeth were attached to the skull, and whether their roots showed evidence of continuous growth.

The scientists found that some dicynodont teeth are indeed tusks, while others, particularly those of some of the earlier species, were just large teeth. It wasn’t a strict progression from non-tusks to tusks, though — different members of the dicynodont family evolved tusks independently.

They also discovered some adaptations that dicynodonts needed to evolve true tusks, including flexible ligament attachments between tooth and jaw and reduced rates of tooth replacement, according to Angielczyk.

The study, which shows the earliest known instance of true tusks, could help scientists better understand evolutionary processes.

“Tusks have evolved a number of times, which makes you wonder how — and why? We now have good data on the anatomical changes that needed to happen for dicynodonts to evolve tusks,” said co-author , a 91̽��professor of biology and a curator at the UW’s Burke Museum of Natural History & Culture. “For other groups, like warthogs or walruses, the jury is still out.”

Most of the dicynodont fossils analyzed in the study were collected during fieldwork in Tanzania and Zambia. These specimens, which are currently stored at the Burke Museum and other U.S. museums, will be repatriated at the end of the project and become part of the permanent collections at the National Museum of Tanzania and the Livingstone Museum in Zambia. This partnership allows for researchers across the globe to study the fossils, and ultimately bring the specimens back to their home nations for further research.

Future studies could examine other dicynodont species and how their tusks — or non-tusks — developed. Sidor’s lab at 91̽��is one of a handful across the country where the fossilized bones and teeth are routinely analyzed at the microscopic scale.

“Thin-sectioning can also provide a lot of useful information, because bones and teeth can capture a record of an animal’s life in their tissues,” said Sidor. “On a tusk that’s ever-growing, the dentine records a daily measure of how fast the animal was growing. Did it grow faster or slower over certain seasons? Stop growing for a certain period of time? Creating thin sections of bones and teeth opens up a lot of other interesting things about the animal almost like analyzing tree rings. These are the types of questions we can continue to research.”

Co-author is 91̽��doctoral alum , an assistant professor at Idaho State University and assistant curator of vertebrate paleontology at the Idaho Museum of Natural History. The research was funded by the National Science Foundation and National Geographic.

Adapted from a release by the Field Museum and Harvard University.

But at least parts of the show could go on during the pandemic — with some significant changes.

“For paleontologists, going into the field to look for fossils is where data collection begins, but it does not end there,” said , a 91̽�� professor of biology and curator of vertebrate paleontology at the UW’s . “After you collect fossils, you have to bring them to the laboratory, clean them off and see what you’ve found.”

Among other adaptations during the pandemic, Sidor and his 91̽��colleagues have spent more time cleaning, preparing and analyzing fossils excavated before the pandemic, as well as managing new pandemic-related struggles — such as a misplaced shipment of irreplaceable specimens.

For Sidor’s team, a recent triumph came from an analysis — led by 91̽��postdoctoral researcher — of fossils of Micropholis stowi, a salamander-sized amphibian that lived in the Early Triassic, shortly after Earth’s largest mass extinction approximately 252 million years ago, at the end of the Permian Period. Micropholis is a temnospondyl, a group of extinct amphibians known from fossil deposits around the globe. In a published May 21 in the Journal of Vertebrate Paleontology, Gee and Sidor report on the first occurrence of Micropholis in ancient Antarctica.

“P���𱹾��dzܲ�����, Micropholis was only known from South African specimens,” said Gee. “That isolation was considered fairly typical for amphibians in the Southern Hemisphere during the Early Triassic. Each region — South Africa, Madagascar, Antarctica, Australia — will have its own set of amphibian species. Now, we’re seeing that Micropholis was more widespread than previously recognized.”

Out of more than 30 Early Triassic amphibians in the Southern Hemisphere, Micropholis is now only the second found in more than one region, according to Gee. That is surprising given Earth’s geography. In the Early Triassic, most of Earth’s continents were connected as a part of a single, large landmass, Pangea. Places like South Africa and Antarctica were not as far apart as they are today, and may have had similar climates. Some scientists theorize that these closely placed regions could harbor different amphibian species as a consequence of the end-Permian mass extinction.

“It had been proposed that there were only small populations of survivors and low movement of species in the Early Triassic, which could have explained these regional differences,” said Gee.

Finding Micropholis in two regions may indicate that this species was a “generalist” — adaptable to many types of environments — and could easily spread after the mass extinction.

Alternatively, it’s possible that many other amphibians actually lived in multiple regions, like Micropholis, but paleontologists haven’t found evidence yet. While some Southern Hemisphere regions like South Africa have been well sampled, others have not — like Antarctica, which in the Early Triassic was relatively temperate, but is today largely covered by ice sheets.

Sidor’s team collected skulls and other fragile body parts from four individuals of Micropholis during a 2017-2018 collection trip to the Transantarctic Mountains. In 2019, Gee agreed to come to the 91̽��to lead the analysis of amphibian fossils from that trip after completing his doctoral degree at the University of Toronto. He completed his degree early in the pandemic and moved to Seattle during the second wave of COVID-19.

With social distancing measures in place on campus, Sidor delivered the fossils and a microscope to Gee’s home, where he analyzed the specimens in his living room.

“Having access to the microscope was really the most essential piece of equipment, to be able to identify all the small-scale anatomical features that we need to definitively prove these were Micropholis fossils,” said Gee.

On the same trip, Sidor’s team collected another rare find: a well-preserved skull of a therocephalian, a group of extinct mammal relatives that lived in the Permian and Triassic periods. Therocephalians were a widespread group of both herbivores and carnivores.

“But the Antarctic record for these animals is very poor,” said Sidor. “So this was a rare find.”

It was a rare find that nearly went extinct again. Sidor shipped the therocephalian skull in October 2019 to Chicago’s Field Museum, where it was cleaned and prepped by his longtime colleague .

“Not being able to travel to museums to do research, we’ve been shipping fossils to each other — which we don’t like to do, but sometimes we have to in order to keep the work going,” said Sidor.

In early April, Shinya shipped the finished specimens overnight back to Sidor in Seattle, but the package did not show up at the projected time. As Sidor , the skull was apparently lost in a transfer facility in Indiana — he feared for good. After several days, the package was found, and was promptly transported to Seattle and delivered safely to the UW.

“I was so relieved,” said Sidor. “When I thought it was lost, I had been thinking about the insurance forms. How do you put a dollar value on a specimen that you needed an LC-130 Hercules to collect?”

The skull is undergoing analysis at the UW. As for the Antarctic Micropholis specimens, they’ll soon receive a new home. Later this year, they’ll go on display at the Burke Museum.

The research was funded by the National Science Foundation.

For more information, contact Sidor at casidor@uw.edu and Gee at bmgee@uw.edu.

Reference: “” by Whitney MR and Sidor CA. Communications Biology. DOI: 10.1038/s42003-020-01207-6

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Major findings

We provide evidence for a hibernation-like condition in Lystrosaurus, a mammal relative that lived in the Antarctic portion of Pangea about 250 million years ago. This discovery was enabled by high-resolution of incremental growth marks preserved in the tusks of Lystrosaurus.

Frequently Asked Questions

What is Lystrosaurus?

• is a type of , a major group of primarily herbivorous vertebrates that were common during the Permian and Triassic periods. Dicynodonts are characterized by their turtle-like beaks and ever-growing tusks, which are present in most species. They are distantly related to modern mammals.
• Lystrosaurus is known from rocks from about 253-248 million years ago and ranged from about the size of a corgi to slightly smaller than a cow.
• Fossils of Lystrosaurus are known from China, Russia, India, South Africa and Antarctica and this geographic distribution was one of the early pieces of evidence used in support of a large supercontinent called Pangea.
• Fossils of Lystrosaurus have been found in burrow structures in South Africa and similar burrow trace fossils have been recovered from Antarctica, but not with Lystrosaurus inside them.

What is torpor?

• is a term that refers to the general pattern of vertebrate physiology where there are periodic reductions in metabolic activity. These periods of slower metabolism are often related to seasonal changes in the environment that create unfavorable conditions.
• Hibernation is one form of torpor and is found in warm-blooded animals today. Hibernation is marked by reduction of metabolic activity with periodic small reactivations of activity throughout the hibernation period. This is in contrast to a different kind of torpor called brumation which is common in cold-blooded animals. In brumation, metabolic activity is completely inactive for the entirety of the torpor period.
• Modern examples of hibernators include many North American bear, echidnas, many rodents, hedgehogs, badgers and some lemurs during dry seasons. Modern examples of daily torpor, a form of torpor characterized by daily reductions in metabolic activity, include many birds and bats, as well as bushbabies. Modern examples of brumation include many reptiles such as lizards, turtles and snakes.

What was Antarctica like in the Early Triassic?

• In general, the Early Triassic (252-247 million years ago) was a warm period in Earth history.
• The climate of Antarctica during the Early Triassic is still a subject of active research, but it is clear that the continent was NOT under a thick ice sheet like today. The discovery of fossil plants — including fossil forests — as well as a wide variety of land-living vertebrate fossils demonstrate that the continent was habitable for at least part of the year.

What is thin-sectioning?

• We make thin-sections of fossil bones and teeth so that we could study the fine, inner details that are preserved in these hard tissues. These small, microscopic details act as storybooks, preserving a lot of information about the biology of these animals while they were alive. As is easy to imagine, studying the biology of animals that lived millions of years ago can be challenging. These details, in this case the tree-ring-like growth marks, preserve critical clues into the biology of fossilized animals.

How did you analyze the tusks?

• The way that these tusks grow is layer by layer, growing inward toward the pulp cavity.
• Growth of the tusk happens periodically during both normal and stressful times for the animal. Each increment of growth will leave behind a ring. We looked at both normal growth mark rings and growth marks that were especially thick, which represent a stressful time for the animal.
• We counted how much growth had occurred between rings, and also measured the thickness of the stressful rings.
• We compared periods of regular growth and stress in polar Antarctic tusks to those from non-polar South African localities from the same time period.

Has torpor been found in the fossil record before?

• Torpor has been reported in some fossil rodents, where hibernation marks were found in their ever-growing incisors. But these relatively recent fossils are from the Pleistocene, on the order of hundreds of thousands of years old.
• Our study is by far the oldest evidence of torpor.
• Given how widespread torpor is in modern vertebrates, it is expected that this is not a trait that evolved recently, and instead has likely been widespread throughout the vertebrate evolutionary history. However, torpor is a difficult feature to study in the fossil record.
• This study provided a unique opportunity to study torpor in the fossil record. First, Lystrosaurus had ever-growing tusks, which provide a lengthy record of regular and stress growth rings. Second, we have two populations to compare, a polar population from Antarctica and a non-polar population from South Africa.
• This study suggests torpor was present even 250 million years ago and lends support for the idea that having a flexible physiology may serve as a key feature in surviving mass extinctions.

What this paper does NOT say:

• This paper does not say that Lystrosaurus was a reptile — or a dinosaur! Though it is only a distant relative to mammals, Lystrosaurus is actually more closely related to mammals, including humans, than to any reptile. Lystrosaurus is a member of a very early branch on the lineage that eventually gave rise to mammals.
• This paper does not say that Lystrosaurus was the only animal experiencing torpor in the Early Triassic. This is the first study of its kind. There is a rich assemblage of vertebrates from the Early Triassic of Antarctica and similar studies on their seasonal physiologies have not yet been launched.
• This paper does not prove that Lystrosaurus was hibernating. This is a preliminary study that puts forward a hypothesis. Our hope is that there is continued testing of this hypothesis and additional sampling of Lystrosaurus and other polar vertebrates to look for signals of hibernation or other forms of torpor.

For additional information, contact Christian Sidor at casidor@uw.edu and Megan Whitney at meganwhitney@fas.harvard.edu. 91̽�� press release here.

Hibernation is a familiar feature on Earth today. Many animals — especially those that live close to or within polar regions — hibernate to get through the tough winter months when food is scarce, temperatures drop and days are dark.

According to new research, this type of adaptation has a long history. In a published Aug. 27 in the journal Communications Biology, scientists at the 91̽�� and its report evidence of a hibernation-like state in an animal that lived in Antarctica during the Early Triassic, some 250 million years ago.

The creature, a member of the genus , was a distant relative of mammals. Antarctica during Lystrosaurus’ time lay largely within the Antarctic Circle, like today, and experienced extended periods without sunlight each winter.

The fossils are the oldest evidence of a hibernation-like state in a vertebrate animal, and indicate that — a general term for hibernation and similar states in which animals temporarily lower their metabolic rate to get through a tough season — arose in vertebrates even before mammals and dinosaurs evolved.

“Animals that live at or near the poles have always had to cope with the more extreme environments present there,” said lead author , a postdoctoral researcher at Harvard University who conducted this study as a 91̽��doctoral student in biology. “These preliminary findings indicate that entering into a hibernation-like state is not a relatively new type of adaptation. It is an ancient one.”

Lystrosaurus lived during a dynamic period of our planet’s history, arising just before Earth’s at the end of the Permian Period — which wiped out about 70% of vertebrate species on land — and somehow surviving it. The stout, four-legged foragers lived another 5 million years into the subsequent Triassic Period and spread across swathes of Earth’s then-single continent, Pangea, which included what is now Antarctica.

“The fact that Lystrosaurus survived the end-Permian mass extinction and had such a wide range in the early Triassic has made them a very well-studied group of animals for understanding survival and adaptation,” said co-author , a 91̽��professor of biology and curator of vertebrate paleontology at the Burke Museum.

Paleontologists today find Lystrosaurus fossils in India, China, Russia, parts of Africa and Antarctica. These squat, stubby, creatures — most were roughly pig-sized, but some grew 6 to 8 feet long — had no teeth but bore a pair of tusks in the upper jaw, which they likely employed to forage among ground vegetation and dig for roots and tubers, according to Whitney.

Those tusks made Whitney and Sidor’s study possible. Like elephants, Lystrosaurus tusks grew continuously throughout their lives. The cross-sections of fossilized tusks can harbor life-history information about metabolism, growth and stress or strain. Whitney and Sidor compared cross-sections of tusks from six Antarctic Lystrosaurus to cross-sections of four Lystrosaurus from South Africa.

Back in the Triassic, the collection sites in Antarctica were at about 72 degrees south latitude — well within the Antarctic Circle, at 66.3 degrees south. The collection sites in South Africa were more than 550 miles north during the Triassic at 58-61 degrees south latitude, far outside the Antarctic Circle.

The tusks from the two regions showed similar growth patterns, with layers of dentine deposited in concentric circles like tree rings. But the Antarctic fossils harbored an additional feature that was rare or absent in tusks farther north: closely-spaced, thick rings, which likely indicate periods of less deposition due to prolonged stress, according to the researchers.

“The closest analog we can find to the ‘stress marks’ that we observed in Antarctic Lystrosaurus tusks are stress marks in teeth associated with hibernation in certain modern animals,” said Whitney.

The researchers cannot definitively conclude that Lystrosaurus underwent true hibernation —which is a specific, weeks-long reduction in metabolism, body temperature and activity. The stress could have been caused by another hibernation-like form of torpor, such as a more short-term reduction in metabolism, according to Sidor.

Lystrosaurus in Antarctica likely needed some form of hibernation-like adaptation to cope with life near the South Pole, said Whitney. Though Earth was much warmer during the Triassic than today — and parts of Antarctica may have been forested — plants and animals below the Antarctic Circle would still experience extreme annual variations in the amount of daylight, with the sun absent for long periods in winter.

Many other ancient vertebrates at high latitudes may also have used torpor, including hibernation, to cope with the strains of winter, Whitney said. But many famous extinct animals, including the dinosaurs that evolved and spread after Lystrosaurus died out, don’t have teeth that grow continuously.

“To see the specific signs of stress and strain brought on by hibernation, you need to look at something that can fossilize and was growing continuously during the animal’s life,” said Sidor. “Many animals don’t have that, but luckily Lystrosaurus �徱��.”

If analysis of additional Antarctic and South African Lystrosaurus fossils confirms this discovery, it may also settle another debate about these ancient, hearty animals.

“Cold-blooded animals often shut down their metabolism entirely during a tough season, but many endothermic or ‘warm-blooded’ animals that hibernate frequently reactivate their metabolism during the hibernation period,” said Whitney. “What we observed in the Antarctic Lystrosaurus tusks fits a pattern of small metabolic ‘reactivation events’ during a period of stress, which is most similar to what we see in warm-blooded hibernators today.”

If so, this distant cousin of mammals isn’t just an example of a hearty creature. It is also a reminder that many features of life today may have been around for hundreds of millions of years before humans evolved to observe them.

The research was funded by the National Science Foundation.

For more information, contact Sidor at casidor@uw.edu and Whitney at meganwhitney@fas.harvard.edu.

: “Evidence of torpor in the tusks of Lystrosaurus from the Early Triassic of Antarctica” by Whitney MR and Sidor CA.

DOI: 10.1038/s42003-020-01207-6

Antarctica wasn’t always a frozen wasteland. About 250 million years ago, it was covered in forests and rivers, and the temperature rarely dipped below freezing. It was also home to diverse wildlife, including early relatives of the dinosaurs. Scientists have just discovered the newest member of that family — an iguana-sized reptile whose genus name, Antarctanax, means “Antarctic king.”

“This new animal was an archosaur, an early relative of crocodiles and dinosaurs,” said Brandon Peecook, a researcher and lead author of a in the describing the new species. “On its own, it just looks a little like a lizard, but evolutionarily, it’s one of the first members of that big group. It tells us how dinosaurs and their closest relatives evolved and spread.”

Collected during a 2010-2011 expedition to Antarctica led by senior author , professor of biology at the 91̽�� and curator of vertebrate paleontology at the UW’s , the fossil specimen consists of portions of the backbone, limbs and skull. The specimen is now part of the permanent collections at the Burke Museum and is one of more than 300 vertebrate fossils from Antarctica in its collection, collected over the course of four expeditions and resulting in one of the largest Antarctic vertebrate fossil collections in the country. During the Burke’s most recent Antarctic expedition in 2017-2018 Sidor led his team back to Graphite Peak, the site where Antarctanax had been found, which was also where the first vertebrate fossils in Antarctica were discovered in 1967.

Although the new specimen is an incomplete skeleton, paleontologists still have a good feel for the animal, named Antarctanax shackletoni — the latter part a nod to polar explorer . Based on its similarities to other fossil animals, the researchers surmise that Antarctanax was a carnivore that hunted bugs, amphibians, and relatives of early mammals.

The most interesting thing about Antarctanax, the authors say, is where and when it lived.

“The more we find out about prehistoric Antarctica, the weirder it is,” says Peecook, who was a doctoral student in the 91̽��Department of Biology at the time the fossil was collected and is now also a research associate at the Burke Museum. “We thought that Antarctic animals would be similar to the ones that were living in southern Africa, since those landmasses were joined back then. But we’re finding that Antarctica’s wildlife is surprisingly unique.”

About two million years before Antarctanax lived — the blink of an eye in geologic time — Earth underwent its largest mass extinction. Climate change, caused by volcanic eruptions, killed 90 percent of animal life. The years immediately after that extinction event were an evolutionary free-for-all. With the slate wiped clean by the mass extinction, new groups of animals vied to fill the gaps. The archosaurs, including dinosaurs, were among the groups that experienced enormous growth.

“Before the mass extinction, archosaurs were only found around the equator, but after it, they were everywhere,” said Peecook. “And Antarctica had a combination of these brand-new animals and stragglers of animals that were already extinct in most places — what paleontologists call ‘dead walking.’ You’ve got tomorrow’s animals and yesterday’s animals, cohabiting in a cool place,” he added.

“Fossil exploration in Antarctica is really difficult, given all of the logistics involved. But since so little work has been done the potential for making important new discoveries is high — and that’s what Antarctanax represents,” said Sidor. “The same rocks that yielded Antarctanax also yield some of the earliest mammal relatives from after the mass extinction.”

The fact that scientists have found Antarctanax helps bolster the idea that Antarctica was a place of rapid evolution and diversification after the mass extinction.

“The more different kinds of animals we find, the more we learn about the pattern of archosaurs taking over after the mass extinction,” said Peecook. “Antarctica is one of those places on Earth, like the bottom of the sea, where we’re still in the very early stages of exploration. Antarctanax is our little part of discovering the history of Antarctica.”

Co-author on the paper is of the University of the Witwatersrand in Johannesburg and the Iziko South African Museum.

###

For more information, contact Andrea Godinez at burkepr@uw.edu.

Adapted from a by the Field Museum.

After a great mass extinction shook the world about 252 million years ago, animal life outside of the ocean began to take hold. The earliest mammals entered the scene, and reptiles — including early dinosaurs — lived on Pangea, the name given to the giant landmass in which all of the world’s continents were joined as one.

A project spanning countries, years and institutions has attempted to reconstruct what the southern end of this world looked like during this period, known as the Triassic (252 to 199 million years ago). Led by paleontologists and geologists at the 91̽��, the team has uncovered new fossils in Zambia and Tanzania, examined previously collected fossils and analyzed specimens in museums around the world in an attempt to understand life in the Triassic across different geographic areas.

Findings from the past decade of fieldwork and analysis are reported March 28 in a publication of the . In total, 13 research papers detailing new fossils, geologic discoveries and ecological findings in the Triassic make up the society’s 2018 special-edition volume, published once a year in a competitive submission process.

“Most of what we know about the major mass extinction is from the South African Karoo Basin. I was always interested in understanding, do we see the exact same pattern around the world, or do we not?” said co-editor , a 91̽��biology professor and curator of vertebrate paleontology at the Burke Museum of Natural History and Culture.

“The fossil record can be great to understand timing and sequence, but not always great at looking at things in a geographic context.”

Since 2007, Sidor and his team of students, postdoctoral researchers, paleontologists and geologists have visited the Ruhuhu Basin of Tanzania five times and the Luangwa and mid-Zambezi basins of Zambia four times. They lived there for about a month at a time, often hiking for miles to find fossil sites and camping in villages and national parks. Once, they were even awakened by the stomping and calls of elephants only feet from their camp.

Each site in Tanzania and Zambia contains its own collection of fossils from the Triassic and other periods, but the goal of this decade-long project was to look across locations hundreds and thousands of miles apart to find similarities in the fossil records. Two papers describe the regional patterns and similarities across much of what used to be Pangea.

“These papers highlight what a regional perspective we now have — we have the same fossils from Tanzania, Antarctica, Namibia and more,” Sidor said. “We’re getting a much better Southern Hemisphere perspective of what’s going on in the Triassic.”

Most of the papers in the special edition discuss new fossil findings from the paleontological digs. One explains the discovery of a new species of lizard-like reptile called a procolophonid. Another details Teleocrater, an early dinosaur relative that walked on four crocodile-like legs. This finding in Nature last year, but the new paper describes the animal’s anatomy in fuller detail.

Most of the remaining papers describe other animals that were present in the Triassic besides the early dinosaurs.

“This was a time when dinosaurs were just stepping onto the stage, and they were not very big and not very remarkable animals then,” Sidor said. “These papers really round out what dinosaurs were competing with before they became the dominant reptiles on land.”

In addition to the 13 papers that make up the special edition, the team has published 24 peer-reviewed papers as part of this project in the past decade.

More than 2,200 fossils were collected across Tanzania and Zambia over the last decade of fieldwork. Of the special edition’s 27 authors, many participated in fieldwork with Sidor since 2007, including co-editor , a former postdoctoral researcher at the 91̽��and now an assistant professor at Virginia Tech.

Fossil hunting is an experience every member of Sidor’s lab can have, from undergraduates through postdoctoral researchers. Sidor and a team are going again this August.

“This has been what my lab has done, and all of my students have been involved in some way,” he said. Four of Sidor’s students and two postdoctoral researchers are co-authors of papers in the new special edition.

Other co-authors are from The Field Museum; London’s Natural History Museum; University of Birmingham; Virginia Tech; Royal Ontario Museum; California Academy of Sciences; Southern Methodist University; Petrified Forest National Park; Iziko: South African Museum; Muséum national d’Histoire naturelle (Paris); University of Chicago; University of the Witwatersrand; National Museum (Bloemfontein); Museo Argentino de Ciencias Naturales; Rowan University; and North Carolina Museum of Natural Sciences.

Fieldwork in Tanzania and Zambia was supported by the National Science Foundation, the��National Geographic Society, The Grainger Foundation and The Field Museum/IDP Foundation, Inc., African Partners Program. Additional support for analysis and museum research are noted in the individual papers.

###

For more information, contact Sidor at casidor@uw.edu.

Images available for download: https://drive.google.com/drive/folders/1IguAX2X2tFS5oC3Rnq7nv4mR6hupPQa7?usp=sharing

Prepared by and with the 91̽�� and the Burke Museum of Natural History & Culture. 91̽�� press release .

Major findings

demonstrates that this type of tumor has existed for at least 255 million years and predates mammals.

Frequently Asked Questions

What are gorgonopsians?

• Gorgonopsians were a group of carnivorous, land-based vertebrates that lived between about 270 to 252 million years ago during the middle and late Permian Period. Their fossils are known from Africa and Russia.
• Gorgonopsians are distantly related to living mammals, but they lie “on the mammalian line,” meaning that they are more closely related to humans than to dinosaurs or other reptiles.
• Gorgonopsians ranged in body size from 2 to 10 feet long, from the length of a bobcat to that of a polar bear.
• Gorgonopsians are sometimes known as the “saber-tooths of the Permian,” for their enlarged canine teeth.

What is an odontoma?

• The World Health Organization defines a compound odontoma as: “A malformation in which all the dental tissues are represented in a more orderly pattern than in the complex odontoma, so that the lesion consists of many tooth-like structures. Most of these structures do not morphologically resemble the teeth of the normal dentition, but in each one enamel, dentine, cementum and pulp are arranged as in the normal tooth.”
• Odontomas are one of the most common odontogenic tumors, constituting approximately 20 percent of odontogenic tumors. Ameloblastoma is the most common with 39.6 percent of odontogenic tumors.
• Odontomas are not cancer. They are considered benign tumors, though in humans they are often surgically removed.

Where was this specimen found?

• The gorgonopsian jaw with the odontoma was found in southern Tanzania in the Ruhuhu Valley in 2007.
• The specimen is about 255 million years old, based on dating of similar fossils in South Africa.

How did we find this pathology?

• There were no external indications of a pathology. We were thin-sectioning this specimen for an entirely different project —examining the tissues involved in tooth attachment.
• 91̽��undergraduate researcher Larry Mose noticed a pathology along the root of the canine only after the specimen had been cut.

What is thin-sectioning?

• We make thin-sections of fossil bones and teeth so that we can study the fine, inner details of their hard tissues. These small details act as storybooks, preserving a lot of information about the biology of these animals while they were alive. As is easy to imagine, studying the biology of animals that lived millions of years ago can be challenging. We use the microstructure of fossil hard tissues to reveal aspects of their biology like growth rate, age and disease that otherwise would be inaccessible for us to study in these ancient animals.

Has an odontoma been found in the fossil record before?

• This is not the first time an odontoma has been reported in the fossil record. Previous instances include:
  • A Woolly mammoth from the Netherlands from the last glacial age, known as the Weichsel Glacial in Northern Europe, ca. 115,000-10,000 B.C.
  • Fossil red deer from France from 12,200-11,400 B.C.
  • Several recorded instances in archaeological material.
• All reported instances, however, are relatively recent in the history of life on earth —to within the last 1 million years or so.

Is this the oldest occurrence of tumors in the fossil record?

• There is a decisive case of cancer reported in a lower Carboniferous fish (300 million years ago), and a possible case of cancer in fossil fish from the Devonian (350 million years ago).
• But this is the oldest reported case of an odontoma. See above question.

How do teeth form?

• Teeth are derived from two major tissue layers, the outer epithelial layer that gives rise to enamel and an ectomesenchyme layer that gives rise to dentine and pulp.
• Odontomas arise when there are developmental anomalies involving both the epithelial and ectomesenchymal tissues. These anomalies give rise to tooth-like structures that have enamel, cementum, dentine and pulp in their normal anatomical relationships.

What did we learn? What are the implications?

• This is the oldest occurrence of odontoma in a mammal relative. Odontoma has remained relatively unchanged for 255 million years.
• Paleontology can contribute to medicine by shedding light on the history of disease.

Acknowledgements

• Laurent Nampunju and Anthony Tibaijuka (Antiquities Division, Ministry of Natural Resources and Tourism) for assistance with fieldwork in Tanzania.
• Field team for helping to collect the fossil (Ken Angielczyk, Sterling Nesbitt, Roger Smith, Linda Tsuji).
• Oral Biology group at the 91̽�� for helpful discussions.
• Royal Ontario Museum histology lab for use of thin section and imaging equipment.

Grant support

• National Geographic Society (NGS 7787-05) to C. Sidor (for fieldwork to collect fossils)
• National Science Foundation (DBI 0306158) to Ken Angielczyk, Field Museum of Natural History, Chicago (for fieldwork to collect fossils)
• National Science Foundation (EAR 1337569) to C. Sidor (for research and analysis)

For additional information, contact Christian Sidor at casidor@uw.edu and Megan Whitney at megwhit@uw.edu. 91̽�� press release .

When paleontologists at the 91̽�� cut into the fossilized jaw of a distant mammal relative, they got more than they bargained for —��more teeth, to be specific.

As they report in published Dec. 8 in the , the team discovered evidence that the extinct species harbored a benign tumor made up of miniature, tooth-like structures. Known as a , this type of tumor is common to mammals today. But this animal lived 255 million years ago, before mammals even existed.

“We think this is by far the oldest known instance of a compound odontoma,” said senior author , a 91̽��professor of biology and curator of vertebrate paleontology at the . “It would indicate that this is an ancient type of tumor.”

Before this discovery, the earliest known evidence of odontomas came from Ice Age-era fossils.

“Until now, the earliest known occurrence of this tumor was about one million years ago, in fossil mammals,” said Judy Skog, program director in the ‘s , which funded the research.�� “These researchers have found an example in the ancestors of mammals that lived 255 million years ago.��The discovery suggests that the suspected cause of an odontoma isn’t tied solely to traits in modern species, as had been thought.”

In humans and other mammals, a compound odontoma is a mass of small “toothlets” amalgamated together along with tooth tissues like dentin and enamel. They grow within the gums or other soft tissues of the jaw and can cause pain and swelling, as well as disrupt the position of teeth and other tissues. Since odontomas do not metastasize and spread throughout the body, they are considered benign tumors. But given the disruptions they cause, surgeons often opt to remove them.

Surgery was not an option for the creature studied by Sidor’s team. It was a , a distant mammal relative and the apex predator during its pre-dinosaur era about 255 million years ago. Gorgonopsians are part of a larger group of animals called , which includes modern mammals as its only living member. Synapsids are sometimes called “mammal-like reptiles” because extinct synapsids possess some, but not all, of the features of mammals. The first mammals evolved over 100 million years ago.

“Most synapsids are extinct, and we —��that is, mammals —��are their only living descendants,” said , lead author and 91̽��biology graduate student. “To understand when and how our mammalian features evolved, we have to study fossils of synapsids like the gorgonopsians.”

Paleontologists have categorized many “mammal-like” features of gorgonopsians. For example, like us, they have teeth differentiated for specialized purposes. But Whitney started studying gorgonopsian teeth to see if they had another mammalian feature.

“Most reptiles alive today fuse their teeth directly to the jawbone,” said Whitney. “But mammals do not: We use tough, but flexible, string-like tissues to hold teeth in their sockets. And I wanted to know if the same was true for gorgonopsians.”

A purely external examination of gorgonopsian fossils wouldn’t answer this question. Whitney had to take the risky and controversial approach of slicing into a fossilized gorgonopsian jaw: looking at thin sections of jaw and tooth under a microscope to see how the tooth was nestled within its socket. Since this technique would damage the fossil, Whitney and Larry Mose, a 91̽��undergraduate student working with her, used a solitary or “orphan” gorgonopsian lower jaw that Sidor had collected in southern Tanzania.

Mose prepared multiple thin slices from the gorgonopsian jaw —��each only about as thick as a sheet of notebook paper —��and mounted them onto slides. He and Whitney immediately noticed something unexpected within the jaw: embedded next to the root of the canine were irregular clusters of up to eight tiny, round objects.

At higher magnification under a microscope, Whitney discovered that the objects within each cluster resembled small, poorly differentiated teeth, or toothlets. The toothlets even harbored distinct layers of dentin and enamel.

“At first we didn’t know what to make of it,” said Whitney. “But after some investigation we realized this gorgonopsian had what looks like a textbook compound odontoma.”

At 255 million years, this is by far the oldest reported evidence for an odontoma —��and possibly the first case in a non-mammal. According to Sidor, odontomas have been reported in archaeological specimens, as well as fossilized mammoths and deer. But those cases all date to within the last million years or so. Since this synapsid had an odontoma, it would indicate that this mammalian condition existed well before the first mammals had evolved.

“This discovery demonstrates how the fossil record can tell us a lot about our present-day lives —��even the diseases or pathologies that are part of our mammalian heritage,” said Sidor. “And you could never tell that this creature had it from the outside.”

The research was funded by the National Science Foundation and a 91̽�� Mary Gates Research Fellowship.

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For more information, contact Sidor at casidor@uw.edu and Whitney at megwhit@uw.edu. Sidor and Whitney have also prepared answers to a list of frequently asked questions, which can be found , regarding gorgonopsians, tooth development, odontomas and more.

Grant number: NSF EAR-1337569.

Paleontologists with the 91̽��’s����have a Tyrannosaurus rex, including a very complete skull. The find, which paleontologists estimate to be about 20 percent of the animal, includes vertebrae, ribs, hips and lower jaw bones.

The team, led by 91̽��biology professor and Burke Museum Adjunct Curator of Vertebrate Paleontology��, discovered the T. rex during an expedition to the Hell Creek Formation in northern Montana — an area that is world-famous for its fossil dinosaur sites. Two Burke Museum paleontology volunteers, Jason Love and Luke Tufts, initially discovered pieces of fossilized bone protruding from a rocky hillside. The bones’ large size and honeycomb-like structure indicated they belonged to a carnivorous dinosaur. Upon further excavation, the team discovered the T. rex skull along with ribs, vertebrae, and parts of the jaw and pelvis.

T. rex was one of the largest meat-eating dinosaurs to ever roam the Earth. Measuring an average of 40-feet long and 15 to 20-feet tall, T. rex was a fierce predator with serrated teeth and large jaws. Fossil evidence shows it ate other dinosaurs like Edmontosaurus and Triceratops, with crushed bones from the animals even showing up in the its fossilized poop. T. rex lived about 66–68 million years ago in forested river valleys in western North America during the late Cretaceous Period.

The T. rex found by the UW/Burke��team is nicknamed the “Tufts-Love Rex” in honor of the two volunteers who discovered it. The skull is about 4 feet long weighs about 2,500 pounds in its protective plaster jacket. Excavation in the field revealed the right side of the skull from base to snout, including teeth. Burke paleontologists believe it is very probable the other side of the skull is present, but will need to carefully remove the rock surrounding the fossil before they can determine its completeness.

“We think the Tufts-Love Rex is going to be an iconic specimen for the Burke Museum and the state of Washington and will be a must-see for dinosaur researchers as well,” said Wilson.

Based on the size of its skull, Burke paleontologists estimate this dinosaur is about 85 percent the size of the largest T. rex found to date. At the hips, the T. rex would have been nearly as tall as a city bus, and as long as a bus from tail to head.

The Tufts-Love Rex is 66.3 million years old. T. rex lived at the end of the Cretaceous Period, 145–66 million years ago, and became extinct during the Cretaceous-Paleogene mass extinction 66 million years ago. Burke paleontologists could determine that the Tufts-Love Rex lived at the very end of the Cretaceous because it was found at the bottom of a hill; a rock layer at the top of that hill marks the Cretaceous-Paleogene mass extinction. Based on the size of the skull — a good indicator of T. rex age — the team estimates the dinosaur was about 15 years old when it died. Adult T. rex lived up to 25-30 years.

Although arguably the most iconic and well-known dinosaur, T. rex fossils are rare. This remarkable find is one of only about 25 of this level of completeness. The skull is the 15^th reasonably complete T. rex skull known to exist in the world. Next summer, Burke paleontologists will search for additional parts of the dinosaur at the site.

More than 45 people helped excavate the T. rex over the course of a month this summer. The team was collecting fossils in the area for the Hell Creek Project, a multi-disciplinary project examining vertebrates, invertebrates, plants and geology of the area to learn more about the final 2 million years of the dinosaur era, the mass-extinction event that killed off the dinosaurs, and the first 1.5 million years post-extinction that gave rise to the age of mammals. The project, currently led by Wilson, was founded by and Nathan Myhrvold. Burke paleontologists, volunteers, undergraduate and graduate students from the 91̽��and other universities and K–12 educators participating in the Burke’s contribute to the project.

“This is really great news. The Hell Creek Project is responsible for finding the most T. rex specimens in the world, with 11 to date,” said Myhrvold, Intellectual Ventures CEO and Paleontologist. “The T. rex has always been my favorite dinosaur and I’m really pleased that this one is going to make its home at the Burke Museum.”

“Having seen the ‘Tufts-Love Rex’ during its excavation I can attest to the fact that it is definitely one of the most significant��specimens yet found, and because of its size, is sure to yield important information about the growth and possible eating habits of these magnificent animals,” said Horner, former curator of paleontology at the Museum of the Rockies and current Burke Museum research associate.

The T. rex skull and other bones are currently covered in a plaster jacket — similar to a cast used to cover a broken bone — in order to protect the skull during transport. The public can see the plaster-covered T. rex skull, along with other T. rex fossils and paleontology field tools, in a lobby display at the UW’s Burke Museum from August 20 to October 2. Special T. rex-themed activities will take place over Labor Day Weekend and on Sunday, September 25.

After removing the fossil from display, the Burke’s paleontology team will begin preparing the fossil by removing the rock surrounding the bone, which may take a year or more. The museum plans to display the T. rex skull in the when it opens in 2019.

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For more information, contact Andrea Godinez at 206-616-7538 or��burkepr@uw.edu.

Its discoverers include , professor of biology at the 91̽�� and curator of vertebrate paleontology at the . Sidor and his colleagues, who announced their finding , have named the creature Ichibengops munyamadziensis — or “Scarface of the Munyamadzi River.” This colorful designation combines the discovery location with the Bemba word for scar, “ichibenga,” since this long-extinct cousin of the mammalian lineage sported a unique groove on its upper jaw.

“Discoveries of new species of animals like Ichibengops are particularly exciting because they help us to better understand the group of animals that gave rise to mammals,” said senior author of Chicago’s .

Ichibengops was a member of an extinct lineage of mammal-like reptiles called therocephalians or “beast-heads,” which refers to the mammal-like qualities of their skulls. Its closest known relative is a therocephalian that lived in Russia at about the same time. Therocephalians are a sister lineage to the reptilian ancestors of modern day mammals and may have independently evolved some mammal-like characteristics. Ichibengops, for example, had a hard, bony palate. But the diminutive carnivore also sported an unexpected feature.

“One interesting feature about this species in particular is the presence of grooves above its teeth, which may have been used to transmit venom,” said Angielczyk.

If so, this would be a rare finding among therocephalians, mammal-like reptiles and even mammals. Among mammals alive today, only the duck-billed platypus and several shrew species produce venom.

“There is only one other therocephalian that seems to show indications of being venomous,” said Sidor, referring to the extinct therocephalian Euchambersia. “However, it’s very difficult to assess function in fossils, so we can never be 100 percent certain.”

Therocephalians thrived during Earth’s Permian Period, which came to a cataclysmic end about 252 million years ago in in history. Some 90 percent of species went extinct, though some therocephalian species survived into the Triassic Period, the beginning of the so-called “age of dinosaurs.”

“In the grand scheme of things, therocephalians did quite well, considering that they didn’t go extinct at the Permian-Triassic mass extinction,” said Sidor. “However, their diversity was greatly decreased and the group never fully recovered. They went extinct about 8 million years later.”

Though nearly 250 million years have passed since Ichibengops and its relatives roamed underfoot, the curious case of therocephalians at such a turbulent time in Earth’s history still holds relevance today.

“By studying the effects of the Permian-Triassic mass extinction and the subsequent recovery, we can apply the lessons we learn to the mass extinction being caused by humans today,” said Angielczyk.

The paper’s lead author was , who earned his doctoral degree in biology at the 91̽��under Sidor, and is now a postdoctoral researcher at . Grants from the National Science Foundation funded all three researchers. Sidor received additional support from the National Geographic Society, and Angielczyk was also funded by the Granger Foundation and the Field Museum/IDP Foundation, Inc. African Partners Program.

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For more information, contact Sidor at 206-221-3285 or casidor@u.washington.edu.

Adapted from the following Field Museum press materials: “” and “FAQ: Prehistoric Carnivore ‘Scarface’ Discovered in Zambia”