Paleo Profile: Mexico’s Mystery Dinosaur

Centrosaurine sites in North America. From Rivera-Sylva et al., 2016.
Centrosaurine sites in North America. From Rivera-Sylva et al., 2016.

A few years back, while crashing at my apartment for the night during a long trip west, a friend of mine asked me “Haven’t paleontologists found all the dinosaurs already?” Museums from coast-to-coast seem well-stocked with primordial reptiles, and, really, when dealing with such giants, how many species could there possibly be? I had to chuckle at my friend’s question. Not only were there more dinosaur species than we ever imagined, but we’re still a long way from finding them all.

I can’t think of a place that better exemplifies the dinosaur boom than North America’s southwest. Hell, the fantastic new species coming out of the area from the four corners on south was half the reason I moved to Utah. New explorations in the western deserts have yielded an increasing array of new dinosaur species, and paleontologists already know that there’s more out there than has been formally identified. Take, for example, an animal represented by a smattering of bones found in northern Mexico.

There is no formal name for this dinosaur yet. There’s too little of it to justify a permanent identification. But, as described by paleontologist Héctor Rivera-Sylva and colleagues, the fossils appear to represent a horned dinosaur not seen before.

The bones were found in Coahuila, northern Mexico, between 2007 and 2011. And while paleontologists named another horned dinosaur – Coahuilaceratops – from this area in 2010, the bones described by Rivera-Sylva and coauthors are from something different. That’s because Coahuilaceratops is what experts call a chasmosaurine – the lineage that contains Chasmosaurus and Triceratops – while this new dinosaur belongs to a separate lineage called centrosaurines that includes Centrosaurus, Nasutoceratops, and their relatives. This makes CPC 274 the southernmost occurrence of a centrosaurine dinosaur yet found.

This is how some dinosaurs make their debut. Not as beautiful skeletons with names as awesome as their osteology, but as fragments and pieces that hint at what’s left to find. The recently-named tyrannosaur Timurlengia, for example, first came to paleontologists as a smattering of tantalizing fragments before a braincase tied everything together. Hopefully the Coahuila centrosaurine will follow the same pattern, new finds filling in the identity of what must have been a gnarly herbivore with its own splay of spikes and horns.

I look forward to the day that paleontologists will be able to organize an unveiling for Mexico’s mystery dinosaur, but that’s not the point of this post. I picked this unnamed enigma for my last Paleo Profile here at National Geographic because of what it represents. The unknown is what calls to scientists, both in the lab and in the layers of time laid out in the desert. For every fact or fossil we find, we get a bloom of new questions that itch at the brain and the soles of your boots. That’s the drive to seek out unknown dinosaurs in their remote, ancient tombs, and, truly, we are just getting started.

centrosaurine-squamosal

Fossil Facts

Name: There is no genus and species name yet. For now the dinosaur is designated as specimen CPC 274.

Age: About 80 million years ago.

Where in the world?: Coahuila, Mexico.

What sort of critter?: A horned dinosaur related to Centrosaurus.

Size: Unknown.

How much of the creature’s body is known?: A partial skull and several pieces of the postcrania.

Reference:

Rivera-Sylva, H., Hedrick, B., Dodson, P. 2016. A centrosaurine (Dinosauria: Ceratopsida) from the Aguja Formation (Late Campanian) of northern Coahuila, Mexico. PLOS ONE. doi: 10.1371/journal.pone.0150529

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief
The Purgatoire River’s Whale Fish
Russia’s Curved Blade
The Dawn Mole
The Oldest Chameleon
The Wandering Spirit
Teyú Yaguá
New Caledonia’s Giant Fowl
The Giant Tarasque Tortoise
The Giant, Bone-Crushing Weasel
The Dawn Rough Tooth

Paleo Profile: The Dawn Rough Tooth

The reconstructed skull of Eotrachodon. From Prieto-Márquez et al., 2016.
The reconstructed skull of Eotrachodon. From Prieto-Márquez et al., 2016.

Eastern dinosaurs are hard to find. Between geologic happenstance, suburban sprawl, and forests that blanket what would otherwise be promising outcrop, we know frustratingly little about the dinosaurs of Appalachia compared to their relatives exposed in the deserts to the west. But every now and then paleontologists are able to pull a prize out of the difficult eastern exposures. The hadrosaur Eotrachodon is one such case.

Paleontologists  Albert Prieto-Márquez, Gregory Erickson, and Jun Ebersole named the dinosaur earlier this year from bones found in Alabama. The remains are pretty scrappy, which is typical for Appalachian finds, but Eotrachodon is nevertheless known from a nearly-complete skull that provides a rich source of osteological comparison for other hadrosaurs. After all, most hadrosaurs are primarily identified by their skulls – different ornamentation on a very conservative chassis.

At about 85 million years old, Eotrachodon lived about 10 million years before the great profusion of its more famous cousins in the west like Parasaurolophus, Lambeosaurus, and their ilk. In fact, Prieto-Márquez and colleagues found, Eotrachodon seems to fall right outside the split between the major crested and crestless hadrosaur lineages, hinting that the eastern half of North America was the place hadrosaurs started to take off before conquering so much of the west.

But there’s another reason I picked Eotrachodon for this week’s Paleo Profile. When I was a kid the hadrosaur Trachodon often made appearances in books and movies, but paleontologists abandoned the name. That’s because the name Trachodon is formally chained to a handful of isolated teeth that can’t be tied back to a body. By coining the name Eotrachodon, however, Prieto-Márquez and coauthors found a workaround to revive the classic title and give poor “Trachodon” a new dawn.

The right maxilla of Eotrachodon. From Prieto-Márquez et al., 2016.
The right maxilla of Eotrachodon. From Prieto-Márquez et al., 2016.

Fossil Facts

Name: Eotrachodon orientalis

Meaning: Eotrachodon means “dawn Trachodon” (or “dawn rough tooth” fully translated), and orientalis is a reference to the fact this dinosaur was found in America’s southeast.

Age: About 85 million years ago.

Where in the world?: Montgomery County, Alabama.

What sort of critter?: A hadrosaur, or “duck-billed” dinosaur.

Size: Comparable to other North American hadrosaurs such as Hadrosaurus and Gryposaurus.

How much of the creature’s body is known?: A nearly-complete skull and fragmentary elements of the postcrania.

References:

Prieto-Márquez, A., Erickson, G., Ebersole, J. 2016. A primitive hadrosaurid from southeastern North America and the origin and early evolution of ‘duck-billed’ dinosaurs. Journal of Vertebrate Paleontology. doi: 10.1080/02724634.2015.1054495

Prieto-Márquez, A., Erickson, G., Ebersole, J. 2016. Anatomy and osteohistology of the basal hadrosaurid dinosaur Eotrachodon from the uppermost Santonian (Cretaceous) of southern Appalachia. PeerJ. doi: 10.7717/peerj.1872

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief
The Purgatoire River’s Whale Fish
Russia’s Curved Blade
The Dawn Mole
The Oldest Chameleon
The Wandering Spirit
Teyú Yaguá
New Caledonia’s Giant Fowl
The Giant Tarasque Tortoise
The Giant, Bone-Crushing Weasel

Paleo Profile: The Giant, Bone-Crushing Weasel

Three views of Megalictis: restoration, skull reconstruction, and original skull. Art by Adam Hartstone-Rose.
Three views of Megalictis: restoration, skull reconstruction, and original skull. Art by Adam Hartstone-Rose.

Some beasts catch you by surprise. I’m not talking about ambush predators – though such a statement would hold true – but rather prehistoric mammals whose very existence comes as something of a shock. The latest to make me go “What the hell?” is an enormous weasel that used to prowl western North America.

Paleontologist William Diller Matthew named carnivore Megalictis ferox way back in 1907. The mammal’s teeth and osteology clearly showed it to be a cousin of martens and stoats, yet their dimensions “indicate an animal which may best be described as a gigantic wolverene [sic], equaling a jaguar or a black bear in size.” And given that cats were meek little things at the time Megalictis lived, paleontologists thought that this weasel had evolved to take on a lion-like lifestyle during North America’s long Cat Gap.

But now paleontologist Alberto Valenciano and colleagues have discovered that Megalictis was no feline wannabe. Through a new analysis of previously-undescribed skull material, the researchers not only refine the evolutionary relationships of America’s giant weasels, but they also make the case that the teeth and jaws of Megalictis were more like those of hyenas and some deep-jawed dogs than to cats. In other words, this huge weasel was a bone-crusher.

Additional Megalictis skull material. From Valenciano et al., 2016.
Additional Megalictis skull material. From Valenciano et al., 2016.

Fossil Facts

Name: Megalictis ferox

Meaning: The entire name translates roughly to “fierce giant wolverine.”

Age: Between 22.7 and 18.5 million years ago.

Where in the world?: South Dakota, Nebraska, and Wyoming.

What sort of critter?: A mustelid, or a member of the group that includes weasels and their relatives.

Size: Estimated as being about the size of a jaguar.

How much of the creature’s body is known?: The new study focused on skull material from several individuals, including a nearly-complete cranium and almost-perfect lower jaws.

References:

Matthew, W. 1907. A lower Miocene fauna from South Dakota. Bulletin of the American Museum of Natural History. 23 (9): 169-219

Valenciano, A., Baskin, J., Abella, J., Pérez-Ramos, A., Álvarez-Sierra, M., Morales, J., Hartstone-Rose, A. 2016. Megalictis, the bone-crushing giant mustelid (Carnivora, Mustelidae, Oligobuninae) from the Early Miocene of North America. PLOS ONE. doi: 10.1371/journal.pone.0152430

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief
The Purgatoire River’s Whale Fish
Russia’s Curved Blade
The Dawn Mole
The Oldest Chameleon
The Wandering Spirit
Teyú Yaguá
New Caledonia’s Giant Fowl
The Giant Tarasque Tortoise

We Still Don’t Know What Killed the Biggest Shark of All Time

We just can’t let Carcharocles megalodon rest. From Peter Benchley’s JAWS to the dreck that regularly bobs up to the surface of basic cable “science” channels, we can’t seem to resist invoking the specter of a shark so large that it could easily engulf a person without a drop of blood spilled into the sea.

Art by Fernando G. Baptista; Research by Ryan T. Willians, Fanna Gebreyesus; Source: STEPHEN J. GODFREY, CALVERT MARINE MUSEUM
Art by Fernando G. Baptista; Research by Ryan T. Willians, Fanna Gebreyesus; Source: STEPHEN J. GODFREY, CALVERT MARINE MUSEUM

Despite our fascination with this enormous, extinct relative of today’s great white shark, there’s still a great deal we don’t know about the life and death of the biggest shark that ever lived. For starters, we still don’t know why the last of the megatooths died over 2.5 million years ago.

In the entire history of cartilaginous fish, Carcharocles megalodon was a huge success story. And that’s not just because of the predator’s size and inferred ferocity. This species patrolled the coasts of the Atlantic, Pacific, and Indian Oceans for about 20 million years. Few creatures can claim such a record. And that only makes the disappearance of the shark all the more puzzling.

Changes brought on by a cooling climate have been the focus of the traditional explanation for the monstrous shark’s demise. C. megalodon has often been thought of as a warm-water hunter, and so, the argument goes, as sea temperatures dipped at the end of the Pliocene the whales, seals, and other fatty mammals the shark relied upon migrated to chilled seas where the shark couldn’t follow. The pitiful selachian was simply left behind as cetaceans spouted off for the poles.

But was the great shark so restricted by temperature? To find out, paleontologist Catalina Pimiento and colleagues drew from the Paleobiology Database to analyze occurrences of C. megalodon over time in relation to climate.  Contrary to what had previously been thought, temperature probably didn’t freeze the shark into extinction.

Curator Jeff Seigel stands in the five–-foot mouth of a fossil shark jaw. The shark is called Carcharoles Megalodon and was large enough to swallow a small car. Photograph by Rick Meyer, Los Angeles Times, Getty
Curator Jeff Seigel stands in the five–-foot mouth of a fossil shark jaw. The shark is called Carcharoles Megalodon and was large enough to swallow a small car. Photograph by Rick Meyer, Los Angeles Times, Getty

The big picture looks something like this. During the shark’s early years, around 20 million years ago, C. megalodon primarily swam through waters of the northern hemisphere. Populations expanded around 15 million years ago to include every major ocean basin on the planet, the researchers write, but from there the sharks populations steadily declined.

All of this happened irrespective of climate. During times of major temperature spikes and dips, Pimiento and coauthors note, C. megalodon occurrences didn’t seem to show any direct response. Not to mention that the shark seemed fully capable of coping with a range of temperatures from 53 to 80 degrees Fahrenheit, and there have been waters in this range from the shark’s time until today. As Pimiento and coauthors write, “C. megalodon would have not been affected significantly by the temperature changes during the Pleistocene, Holocene and Recent.”

Populations of C. megalodon over time. From Pimiento et al., 2016.
Populations of C. megalodon over time. From Pimiento et al., 2016.

So if it wasn’t cooler waters, what drove the shark to extinction? There’s still no definitive answer. Even today, when we can witness species disappear, it’s often difficult to precisely retrace the road from the vanishing point back to the first signs of trouble. In the case of C. megalodon, though, Pimiento and coauthors have some ideas about possible killswitches.

Through hindsight, we can see that the road to extinction for the megatooth shark started in the middle of the Miocene. This coincided with two major events, as previously pointed out by paleontologist Dana Ehret as well as the authors of the new study. Against a background of crashing whale diversity during this time, the world saw the evolution of some stiff competition for C. megalodon: large sharks close to the ancestry of the great white and sperm whales that behaved and hunted more like today’s orcas. This trend continued only through the Pliocene, with fewer big baleen whales and an increasing array of predators that young megatooth sharks would have struggled against to get enough food down their throats. There was less food to go around for an expanding guild of predators who relied upon warm, blubbery prey.

The case isn’t closed yet, though. So much of what’s known about C. megalodon comes from teeth, the occasional vertebra, and some bite marks. Those pieces only reach so far in revealing the massive shark’s biology, including how much the fish actually relied on filter-feeding whales for food or the other predators it was striving against to survive.

We can be sure the megatooth shark is dead. The fish’s fossil record taps out by 2.5 million years ago, and we surely wouldn’t miss populations of fifty-foot-long sharks patrolling the global coastlines. But why the shark vanished is a secret still waiting to be dredged from the fossil record.

Reference:

Pimiento, C., MacFadden, B., Clements, C., Varela, S., Jaramillo, C., Velez-Juarbe, J., Silliman, B. 2016. Geographical distribution patterns of Carcharocles megalodon over time reveal clues about extinction mechanisms. Journal of Biogeography. doi: 10.1111/jbi.12754

Getting to the Root of How Earth’s Massive Coal Seams Formed

Close-up of a lycopsid tree. Did fungus break down these plants? Image from Wikipedia.
Close-up of a lycopsid tree. Did fungus break down these plants? Image from Wikipedia.

Writing about science is a tightrope walk. You can practice as much as you want, and during preparation you have lifelines in the form of editors and experts you can phone for answers, but in the end it’s just you out there, trying to toe the line suspended between attention and accuracy. Eyes are on you for any misstep, and even a perfect performance comes with an often-unrecognized risk. That’s because science is a process, not a static collection of facts, and in an instant a new discovery or study can make the rope vanish beneath your feet.

A few months back my Phenomena neighbor Robert Krulwich wrote a post titled “The Fantastically Strange Origin of Most Coal on Earth.” It’s a lovely little story, all about how a delay in microbial evolution allowed the vast forests of over 300-million-years-ago to become compressed into the fossil fuels we rely on. “[W]hen those trees died,” Krulwich writes, “the bacteria, fungi, and other microbes that today would have chewed the dead wood into smaller and smaller bits were missing.”

Paleontologists call this the “lag hypothesis.” And it turns out to be wrong.

Back in March, about two months after Krulwich’s post went up, Stanford University geoscientist Matthew Nelsen and colleagues published a paper in PNAS that set the record straight in the very title: “Delayed fungal evolution did not cause the Paleozoic peak in coal production.” What seemed like a neatly-solved question once again turned into a conundrum.

The key to the puzzle is lignin. This is the sturdy stuff that often gives bark, wood, and even the cell walls of many plants their resilience. And in the thick forests of the Carboniferous, over 300 million years ago, lignin was supposed to be the stuff that microoganisms and fungi just couldn’t chew up. With no decomposers up to the task, the enormous trees of the time and other plant material piled up for burial rather than breaking down.

A 19th century rendition of a Carboniferous forest. Source.
A 19th century rendition of a Carboniferous forest. Source.

Yet new discoveries have totally reversed what paleontologists expected of those primordial forests. The bulk of the great Carboniferous swamp biomass consisted of trees called lycopsids, Nelsen and colleagues write, but up to 80% of these plants was made of a kind of bark that has no modern equivalent. In other words, these trees did not rely on lignin to support themselves.

And it gets better. “Carboniferous fossils provide direct evidence that fungi were taxonomically and ecologically diverse,” Nelsen and coauthors point out, and paleontologists have already uncovered Carboniferous wood “infiltrated with fungi and possessing damage consistent with white rot decay or other forms of fungal degradation of lignified tissue.”

The lag was in our understanding, not fungus evolution. Lignin wasn’t as critical as had been thought, and, even then, fungus and other decomposers were still capable of busting up the material. And this makes the vast coal seams created by these forests even stranger. If not a reprieve from becoming compost, what could have made such a glut of fossil fuels? The answer, Nelsen and colleagues suggest, probably has to do more with how those forests became buried.

Carboniferous forests were incredibly productive, throwing up plant life faster than the dead plants could decay, creating a literal logjam of organic material in the hot, humid habitats. This happened in a glacial world, but as those stores of ice melted the thick tangles of slowly-decaying plants were buried and eventually compacted down. The Earth’s crust had its own role to play, too. The sweltering forests grew in areas of the planet that were shunted beneath the surface as Pangaea coalesced, the movement of the Earth providing the geological forces necessary to create the fuel for the Industrial Revolution and the climate change we’ve brought upon ourselves.

Reference:

Nelsen, M., DiMichele, W., Peters, S., Boyce, C. 2016. Delayed fungal evolution did not cause the Paleozoic peak in coal production. PNAS. doi: 10.1073/pnas.1517943113

Paleo Profile: New Caledonia’s Giant Fowl

A restoration of Sylviornis. From Worthy et al., 2016.
A restoration of Sylviornis. From Worthy et al., 2016.

Life gets weird on islands. Some species, such as elephants, shrink over time, while forms of life that are tiny on the mainland expand to unheard of sizes. Among the best examples of this Island Rule—which is really more of an Island Puzzle—are birds. Over and over again, islands have hosted populations of ground-dwelling, supersized birds, such as one hefty fowl that strutted around New Caledonia.

François Poplin named the bird Sylviornis neocaledoniae in 1980. Exactly what sort of avian it was, however, has been in dispute ever since then. Poplin considered the helmet-headed bird to be related to cassowaries and emus, while other experts suggested that Sylviornis was much closer to turkey-like megapodes. Then further analysis of the skull led other avian experts to put Sylviornis in its own special lineage, the Sylviornithidae, asserting that the turkey-like features of the birds bones were a case of convergence.

In order to sort through this tangle, paleontologist Trevor Worthy and colleagues had a look at about 600 bones of the bird’s body. What they found supported some earlier suggestions about where the bird nested in the greater avian family tree – Sylviornis was a stem galliform, or a relatively archaic member of the group that contains turkeys, pheasants, and chickens. And this might rule out Sylviornis as the answer to a New Caledonian mystery.

Strange earthen mounds on New Caledonia were thought to be the nests of the massive Sylviornis. But this connection relied on the idea that the big bird was a megapode, as these birds characteristically deposit warm their eggs in holes or little hillocks of soil to gain warmth from rotting vegetation, the earth, or some other outside source. Now that Worthy and coauthors have pushed Sylviornis further away from the megapodes, the idea that the mystery mounds were made by Sylviornis now seems less likely. The anatomy of the bird’s feet, the researchers conclude, was at best suited to scratching at the dirt as if it were a supersized chicken. Perhaps, as paleontologists scratch at the soil themselves, they’ll uncover more clues about the life and times of this long-lost fowl.

Some of the Sylviornis long bones examined in the study. From Worthy et al., 2016.
Some of the Sylviornis long bones examined in the study. From Worthy et al., 2016.

Fossil Facts

Name: Sylviornis neocaledoniae

Age: Over 5,500 years ago until about 3,000 years ago.

Where in the world?: New Caledonia

What sort of critter?: A bird related to landfowl like turkeys and pheasant.

Size: Over two and a half feet tall and more than 60 pounds.

How much of the creature’s body is known?: Thousands of individual elements from the skeletons of multiple individuals.

Reference:

Worthy, T., Mitri, M., Handley, W., Lee, M., Anderson, A., Sand, C. 2016. Osteology supports a steam-galliform affinity for the giant extinct flightless birds Sylviornis neocaledoniae (Sylviornithidae, Galloanseres). PLOS ONE. doi: 10.1371/journal.pone.0150871

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief
The Purgatoire River’s Whale Fish
Russia’s Curved Blade
The Dawn Mole
The Oldest Chameleon
The Wandering Spirit
Teyú Yaguá

Paleontologists Uncover the Tiniest Bonehead Dinosaur

Pachycephalosaurus at the North Carolina Museum of Natural Sciences. Photo by Brian Switek.
Pachycephalosaurus at the North Carolina Museum of Natural Sciences. Photo by Brian Switek.

The trio of bones were some of the smallest pieces of dinosaur I had ever seen. Royal Ontario Museum paleontologist David Evans brought the rugose, chocolate colored pieces in a box smaller than my hand, set down next to a cast of a young dinosaur’s skull that looked absolutely enormous by comparison. Despite the difference in scale, though, the facsimile cranium and the authentic fossils shared a great deal in common and revealed the identity of the animal Evans had brought out to show me. What I was looking at was the smallest Pachycephalosaurus ever found.

Pachycephalosaurus stands out in the dinosaur pantheon as the largest, last, and, thanks to The Land Before Time and Jurassic Park: The Lost World, most famous of the “bonehead” dinosaurs. They roamed western North America in the same haunts as Tyrannosaurus and Triceratops between 68 and 66 million years ago, their thick, rounded skull domes highlighted by a tonsure of little spikes surrounding the outer edge. And, as is the case with most dinosaurs, the name of the species conjures up images of the adult animals in the prime of life, yet we know that Pachycephalosaurus started out life as tiny hatchlings. The small skull bones Evans and Mark Goodwin have described get us closer than every before to the early days of this thick-skulled dinosaur.

The bones of the young Pachycephalosaurus next to a cast of "Dracorex" in the ROM collections. Photo by Brian Switek.
The bones of the young Pachycephalosaurus next to a cast of “Dracorex” in the ROM collections. Photo by Brian Switek.

The three bones—part of the cheek, the midline bone at the back of the skull, and a bone with small spikes jutting from it—were found in two Hell Creek Formation bonebeds in Garfield County, Montana. It’s literally a handful of material, but the combination of bumps and knobs and spikes on the three bones allowed Evans and Goodwin to confirm that the pieces really did belong to a very young Pachycephalosaurus. In fact, the three help tie together a hypothesis that has turned three different dinosaurs into one.

Up until about 2009, paleontologists identified three different pachycephalosaurs from the Hell Creek Formation. There was a small, flat-headed form called Dracorex, a dome-headed mid-size species with large spikes called Stygimoloch, and the classic, large Pachycephalosaurus. But in that year Goodwin and Jack Horner proposed that Dracorex and Stygimoloch were really just immature Pachycephalosaurus, the differences in their skulls being signs of growth rather than different species.

Here’s where the baby skull comes in. The stubby points on the bone from the back of the skull, the squamosal, are clustered in the same way as “Dracorex,” “Stygimoloch,” and some adult-stage Pachycephalosaurus skulls. These spikes became set very early in life. Likewise, the flat bone from the skull roof shows ornamentation similar to that of “Dracorex” as well as the beginnings of a “void space” inside from the beginnings of dome growth. So even though some aspects of skull ornamentation changed throughout the growth of Pachycephalosaurus, the anatomical groundwork was already set in place when these dinosaurs were juveniles.

So Pachycephalosaurus were fairly spiky early on. They didn’t start to grow ornaments with the onset of sexual maturity, but already had knobbly skulls in the early years of their lives. And while distinctive, these points and bumps wouldn’t have offered any defense against predators lurking in those Cretaceous woodlands. Instead, Evans and Goodwin point out, the spikes and domes in different arrangements might have been signals of age class, allowing Pachycephalosaurus to pick out who’s who in a crowd. In other words, these dinosaurs were showoffs from the time they were born.

Reference:

Goodwin, M., Evans, D. 2016. The early expression of squamosal horns and parietal ornamentation confirmed by new end-stage juvenile Pachycephalosaurus fossils from the Upper Cretaceous Hell Creek Formation, Montana. Journal of Vertebrate Paleontology. doi: 10.1080/02724634.2016.1078343

Paleo Profile: Teyú Yaguá

Teyujagua-skull
The skull of Teyujagua paradoxa. From Pinheiro et al., 2016.

Do a Google Image search for the word “Triassic” and you’re going to see variations of the same scene over and over again. Svelte little dinosaurs snap and squawk around an ancient lake or river, with the also-rans of their era – such as the armored aetosaurs and superficially-crocodile-like phytosaurs – shuffling through the undergrowth and basking at the water’s edge. Such vignettes are classic Triassic imagery, and yet they’re only a narrow view of one part of the opening chapter in the Age of Reptiles triology. There’s far more to the Triassic story than Coelophysis and its neighbors, with the latest wrinkle to the tale arriving in the form of a beautiful skull found in Brazil.

The fossil, described by paleontologist Felipe Pinheiro and colleagues, was that of an archosauromorph. This was a line of reptiles that first evolved back in the Permian, when the protomammals held sway, and underwent explosive diversification during the Triassic, eventually sprouting branches that would include dinosaurs, pterosaurs, and crocodiles.

Named Teyujagua paradoxa by the researchers, the 251 million year old animal lived just before the great reptilian radiation really took off. So while not necessarily the ancestor of the various lineages that would come later, Pinheiro and coauthors point out that the skull of Teyujagua is a significant part of the story given that it exhibits some characteristics of older forms of reptiles as well as novelties that would come to mark the “ruling reptiles” such as serrated teeth and an opening in the sidewall of the lower jaw. When you look at the skull of Teyujagua, you’re looking at a face that helped set evolutionary trends from the dawn of the Triassic until today.

A close-up of Teyujagua. From Pinheiro et al., 2016.
A close-up of Teyujagua. From Pinheiro et al., 2016.

Fossil Facts

Name:Teyujagua paradoxa

Meaning: The genus was named after Teyú Yaguá, a dog-headed lizard in Guarani mythology, while paradoxa underscored the “unusual” combination of characteristics.

Age: Around 251 million years ago.

Where in the world?: Southern Brazil.

What sort of critter?: An archosauromorph, or an ancient member of the lineage that includes dinosaurs, pterosaurs, crocodiles, and their relatives.

Size: The skull is about four and a half inches long.

How much of the creature’s body is known?: A nearly-complete skull and several neck vertebrae.

Reference:

Pinheiro, F., França, M., Lacerda, M., Butler, R., Schultz, C. 2016. An exceptional fossil skull from South America and the origins of the archosauriform radiation. Scientific Reports. doi: 10.1038/srep22817

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief
The Purgatoire River’s Whale Fish
Russia’s Curved Blade
The Dawn Mole
The Oldest Chameleon
The Wandering Spirit

Most Dinosaur Species Are Still Undiscovered

Just about every two weeks, we meet a new dinosaur species. Some come fresh from the desert. Others have been hiding in museum collections for decades, or were misidentified as different species. However they’re found, though, dinosaurs are stomping out onto the public stage at a greater rate than ever before. Just last week, for example, paleontologist Hans-Dieter Sues and colleagues named a new, tiny tyrannosaur that once scampered around prehistoric Uzbekistan.

And if the latest estimate is correct, we’re not even close to hitting Peak Dinosaur yet.

We’ll never know precisely how many non-avian dinosaurs roamed the planet between their origin 235 million years ago and their decimation 66 million years ago. The fossil record is not complete—animals that lived in upland environments scoured by erosion had poor chances of being preserved, for instance—and that’s not accounting for sampling bias dictated by researcher interests and what field specialists can actually remove from the rock.

Even then, most of what we know about dinosaurs comes from their skeletal remains. This lets us tell the difference between Tyrannosaurus and Triceratops, but, like some modern birds and reptiles, some non-avian dinosaur species may have differed only in color, geographic range, or other squishy features that we just don’t have access to. Even if we had the bones of every single dinosaur, we’d still probably underestimate the true number of species.

Still, given these caveats, University of Oslo researchers Jostein Starrfelt and Lee Hsiang Liow have created a new model they call TRiPS to estimate how many dinosaur species were around during the Triassic, Jurassic, and Cretaceous chapters of their history.

Visitors passing by the skeletons of dinosaurs in the Humboldt Museum fur Naturkunde in Berlin, Germany. Photograph by VPC Photo, Alamy
Visitors passing by the skeletons of dinosaurs in the Humboldt Museum fur Naturkunde in Berlin, Germany. Photograph by VPC Photo, Alamy

Drawing from known dinosaur records in the Paleobiology Database, the researchers extended the known record into estimations of origin and extinction for dinosaur species throughout their history and included a simulation of how likely it’d be for species to enter the fossil record.

In all, Starrfelt and Liow write, the heyday of the dinosaurs saw the comings and goings of about 1,936 different species. About half this count are expected to be theropods—the lineage that includes T. rex and birds—with the rest split between the long-necked sauropodomorphs and ornithischians such as the armored, horned, and duckbilled dinosaurs.

Starrfelt and Liow acknowledge that they’re dealing with estimates and that refinements will likely alter their dinosaur count. But, for a first run, the results came out similar to what’s been proposed before. In 2006 paleontologists Steve Wang and Peter Dodson estimated that around 1,844 genera of dinosaurs lived during the Mesozoic. While the categories are different—a genus can contain multiple species, like Triceratops horridus and Triceratops prorsus—many dinosaurs described so far are what paleontologists call monospecific, or have only one species in a genus. This affects estimates drawn from the known span of dinosaur discoveries, and might be why the species count isn’t even higher.

The last time anyone did a major count, about eight years ago, paleontologists recognized about 648 valid genera and 675 species of Mesozoic dinosaur, including birds. Those numbers have continued to shift. In 2010, eight new dinosaur species were found in Utah alone, and debates over lumping genera or species continue, as tortured Torosaurus knows. And if the current estimates of dinosaur diversity are correct, discovery and debate will keep a frantic pace for decades to come. We’ve only just started to find all the dinosaurs, much less understand the lives of these impressive creatures.

Reference:

Starrfelt, J., Liow, L. 2016. How many dinosaur species were there? Fossil bias and true richness estimated using a Poisson sampling model. Philosophical Transactions of the Royal Society B. doi: 10.1098/rstb.2015.0219

Paleo Profile: The Wandering Spirit

The skull of Mupashi migrator. From Huttenlocker and Sidor, 2016.
The skull of Mupashi migrator. From Huttenlocker and Sidor, 2016.

There’s no foolproof way to avoid extinction. A disease, a global cold snap, an asteroid with a deadly trajectory – these are all things that every other species in the entire history of life hasn’t been able to foresee or plan for. One day the world changes, and only the lucky survive.

But there are a few ways that entire lineages of organisms have inadvertently made themselves resistant to extinction. One of the best, it seems, is to spread far and wide over the planet. At least then there’s a chance that some members of the family will persist in a refuge, able to stick it out through the worst of the extinction pulse.

This is just the sort of good fortune that was with the therocephalians. These were the “beast heads”, ancient protomammal relatives of ours that could be found all over the ancient Northern and Southern Hemispheres during the Permian period of Earth history. That distribution was helpful during the catastrophic mass extinction at the end of the Permian, around 252 million years ago, as some therocephalians managed to survive the disaster in pockets of prehistoric Africa, Europe, Asia, and Antarctica.

How and when did these ancient cousins of ours expand to inhabit so much of the Permian world? The fossil record has kept the answer a secret, but, paleontologists Adam Huttenlocker and Christian Sidor report, a new protomammal from Zambia helps flesh out the story.

They named the little creature Mupashi migrator. The protomammal wasn’t very big – you could have held it’s arrow-shaped skull in the palm of your hand – but it’s not the size that matters most. The closest known relatives of Mupashi, the paleontologists found, were species that lived in prehistoric Russia, far, far away from ancient Zambia. It’s a long-distance connection that hints at pathways, perhaps along the prehistoric coastlines, that let therocephalians disperse to different landmasses, and in time many of these animals split off into new forms. This was not preventative planning – the protomammals couldn’t have known what was coming – but they way they shuffled around the world gave them an edge when their world came crashing down.

The skull of Mupashi from above. From Huttenlocker and Sidor, 2016.
The skull of Mupashi from above. From Huttenlocker and Sidor, 2016.

Fossil Facts

Name: Mupashi migrator

Meaning: Mupashi is the Bemba word for spirit or ancestor, while migrator is a reference to the wide geographic range that the protomammal’s family occupied during the Permian.

Age: Between 259 and 254 million years ago.

Where in the world?: Northern Zambia.

What sort of critter?: A protomammal belonging to a group called karenitids.

Size: The skull is a little more than three inches long.

How much of the creature’s body is known?: A nearly-complete skull with several articulated neck vertebrae.

Reference:

Huttenlocker, A., Sidor, C. 2016. The first karenitid (Therapsida, Therocephalia) from the upper Permian of Gondwana and the biogeography of Permo-Triassic therocephalians. Journal of Vertebrate Paleontology. doi: 10.1080/02724634.2016.1111897

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief
The Purgatoire River’s Whale Fish
Russia’s Curved Blade
The Dawn Mole
The Oldest Chameleon

It’s a Girl! Paleontologists Examine Pregnant T. rex

Sexing a dinosaur isn’t easy.

As far as gross skeletal anatomy is concerned, male and female dinosaurs are practically identical. And the shape of saurian bones provides no help. So far as anyone has been able to tell, the skeletons of dinosaurs were not sexually dimorphic (or, in other words, different between males and females). Even in highly-ornamented species of horned dinosaurs, armored dinosaurs, and others, all the gnarly spikes and plates and crests don’t show a definitive split in form that can be taken as a marker of different sexes.

But the evolutionary architecture of bones isn’t everything. A pair of surprises provided opportunities for paleontologists to identify some female dinosaurs, at least. In 2005 paleontologist Tamaki Sato and coauthors reported on a fossil of a parrot-like oviraptorosaur that had been preserved with a pair of eggs nestled between her hip bones. This dinosaur was definitely a female.

Better yet, just a few months later molecular biologist Mary Schweitzer and her colleagues reported on another way female dinosaurs could be identified through their pregnancies. A thigh bone of a Tyrannosaurus rex—MOR 1125 or “B. rex” to fossil fans—had a special tissue inside the main cavity called medullary bone. The same type of bone is seen in living birds, and is laid down when estrogen skyrockets following ovulation. In short, if you see medullary bone, you’ve found a pregnant female.

Art by Mark Hallett.
Art by Mark Hallett.

Not everyone agreed with this interpretation. Other experts suggested that the messy, rapidly-deposited bone tissue inside the T. rex was from a disease and that similar types of bone found in the jaws of male and juvenile pterosaurs—the flying relatives of dinosaurs—meant that medullary bone can’t be taken as a reliable indicator of a dinosaur’s sex.

But Schweitzer and a multidisciplinary team of experts have now answered these criticisms with a new study of the original T. rex clue. What did they find? That MOR 1125 truly was pregnant when she died.

Schweitzer and her colleagues approached the bone tissue from multiple avenues, re-examining the structure of the tissue with CT scans but also looking at its chemical composition. This is the key in teasing out tricky tissues, the researchers write, because medullary bone is chemically different from other bone types.

That’s because true medullary bone contains a higher proportion of mineral content and biomolecules called glycoaminoglycans than the surrounding tissue. So when the researchers used a stain to reveal the presence of biomolecules known to be abundant in medullary bone, the reaction fit with what they had suspected: the stain literally highlighted the fact that MOR 1125 had a femur infilled with the mineral-rich tissue.

Watch: Dinosaurs May Have Danced Like Birds. According to famed paleontologist Jack Horner, dinosaurs may have had courting behaviors similar to today’s birds.

The bone in MOR 1125 was not a pathology, and the superficially similar tissues in the pterosaurs must be attributable to some other condition or process. (Medullary bone is estrogen-dependent, Schweitzer and coauthors point out, so similar tissues in male and immature animals have to be something different.)

Pregnant dinosaurs really did lay down true medullary bone inside themselves, and this discovery holds fantastic possibilities for investigating how dinosaurs actually lived. But there’s a more subtle point that’s just as important to the way we think about these animals.

In fossiliferous shorthand, it’s easy to say that dinosaurs turned to rock during their long tenure in the earth. And yes, their bones and other tissues come down to us as permineralized versions of the originals. But it’s not as if everything of the real creatures was obliterated.

“Original organic components are assumed to be completely destroyed during burial and fossilization processes over millions of years,” Schweitzer and colleagues write. “However, we have shown that tissues, cells, and fragments of original molecules can persist across geological time.” Dinosaurs didn’t turn to stone like mythological trolls caught in sunlight. After all this time, tatters of the living creatures remain.

Look at dinosaurs as once-living animals, not piles of bone-shaped rocks, and you can start to see them.

References:

Schweitzer, M., Zheng, W., Zanno, L., Werning, S., Sugiyama, T. 2016. Chemistry supports the identification of gender-specific reproductive tissue in Tyrannosaurus rex. Scientific Reports. doi: 10.1038/srep23099

Schweitzer, M., Wittmeyer, J., Horner, J. 2005. Gender-specific reproductive tissue in ratites and Tyrannosaurus rex. Science. doi: 10.1126/science.1112158

Paleo Profile: The Oldest Chameleon

Lizards in amber. The earliest known chameleon is on the bottom right corner. From Daza et al., 2016.
Lizards in amber. The earliest known chameleon is on the bottom right corner. From Daza et al., 2016.

[Note: In a previous version of this post I wrote that the amber specimens were donated to the American Museum of Natural History. That was a mistake. These lizards, like many other important amber-bound fossils, are still held in a private collection and could be sold off tomorrow if the owner so chose.

The wording concerning where the fossils are reposited – or in this case, not – confused me, and I feel especially frustrated by this because I didn’t want to highlight fossils kept out of the public trust. Paleontology, like all science, relies on reproducibility, and that can only happen if significant fossils are held at accredited institutions in perpetuity. That’s the standard, and it’s past time for scientific journals to step up their requirements to match the ethics of the field.]

If you want to follow Earth’s constant and exuberant evolutionary dance, you’ve got to get in touch with the fossil beat. The stacked remains of creatures long extinct provide the essential backstory for every species alive today, marking who emerged onto the stage when and how drastically, or not, their routine has changed through the ages. A single discovery can quickly change the program, however, as a tiny lizard just did for chameleons.

The small squamate, encased in amber, was not a new find from a scientific expedition. The lizard was one of many sold in the private fossil trade out of the amber-rich deposits of Myanmar, winding up in the private collection of James Zigras now made available through cooperation with the American Museum of Natural History. It was one of eight cut-and-polished pieces containing lizards so spectacular that their little scales can be seen, now shown off in high-resolution CT scan detail in a paper by herpetologist Juan Daza and colleagues. Out of this handful of fossils, though, it’s the chameleon that has made headlines.

At less than an inch long, the 99 million-year-old lizard looks like a little scribble in the rock. But thanks to high-tech imaging, Daza and coauthors were able to identify the reptile as a very close relative of chameleons. It didn’t belong to the strictly-defined group that contains modern chameleons, in other words, but is the closest known relative to the group or what paleontologists call a stem chameleon. This must have come as something of a shock. Up until now, the oldest fossil chameleon came from Miocene deposits much closer to us in time. This new lizard stretches the lineage of these charismatic lizards back about 78 million years earlier, meaning that there are a hell of a lot of fossil chameleons waiting to be found in the new gap.

Close-up of the protochameleon's claw. From Daza et al., 2016.
Close-up of the protochameleon’s foot. From Daza et al., 2016.

Fossil Facts

Name: There isn’t an official name yet, but the specimen is known as JCZ Bu 154.

Age: About 99 million years old.

Where in the world?: Myanmar.

What sort of critter?: The closest known relative of all chameleons.

Size: Less than an inch long.

How much of the creature’s body is known?: A single, nearly-complete body encased in amber.

Reference:

Daza, J., Stanley, E., Wagner, P., Bauer, A., Grimaldi, D. 2016. Mid-Cretaceous amber fossils illuminate the past diversity of tropical lizards. Science Advances. doi: e1501080

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief
The Purgatoire River’s Whale Fish
Russia’s Curved Blade
The Dawn Mole

Giant Flesh-Eating Koala of Legend Was Real

The skeleton of Thylacoleo in Naracoorte Caves National Park. Photo by Karora.
A skeleton of Thylacoleo in Naracoorte Caves National Park. Photo by Karora.

If you ever go on a camping trip to Australia, you might be told to beware the dreaded drop bear. There won’t be a chase. You’ll just be walking along, minding your own business, when a dark shape plummets onto you from above, pinning you down before your realize that you’re being eaten alive by an overgrown koala. The only way to protect yourself, the locals will advise, is to slather yourself in Vegemite and speak in an Australian accent. The efficacy of changing your name to Bruce is unknown.

This is all nonsense, of course. There are no carnivorous koalas with a taste for tourists hanging around the eucalyptus trees of Australia. Yet, despite the fact that the drop bear is a modern hoax, I’m still tickled by the fact that the mythical animal’s description closely matches a very real animal that prowled Australia during the last Ice Age. Paleontologists and fossil fans know this beast as Thylacoleo carnifex, the “marsupial lion.”

Despite the mammal’s name, Thylacoleo doesn’t hold much leonine resemblance. The carnivore’s skull is a modified version of a koala’s or wombat’s, just with cleaver-like shearing teeth at the cheek instead of grinders. That fits given that Thylacoleo belonged to the group of marsupial mammals called the diprotodonts, which includes kangaroos, wombats, koalas, and possums today. Thylacoleo was closer to being a carnivorous koala than a pouched cat.

The kinship of Thylacoleo is only half of the drop bear equation, though. The other has to do with its hunting habits. Back in 2010, paleontologist Roderick Wells and colleagues found that the paws of this marsupial predator would have been just as useful for climbing trees as grappling with the large prey of its era. Now Samuel Arman and Gavin Prideaux have forwarded even more evidence that Thylacoleo was a skilled climber: thousands of scratch marks in the lair of Australia’s real drop bear.

Southwestern Australia’s Tight Entrance Cave yielded the essential clues. In addition to a bonebed cradling the bones of both living and extinct marsupial species, the main chamber of the cavern is marked here and there by V-shaped scratch marks. Only one animal in the cave matches the size and anatomy required to make the largest scratches: Thylacoleo. And while Arman and Prideaux concede that some of the smaller scratches could have been made by other animals trying to find their way out of the cave, from possums to Tasmanian tigers, their preferred interpretation is that most of the smaller scratches were left by Thylacoleo joeys who were reared in the safety of the cave.

Scratches likely made by Thylacoleo in Tight Entrance Cave. From Arman and Prideaux, 2016.
Scratches likely made by Thylacoleo in Tight Entrance Cave. From Arman and Prideaux, 2016.

The nature of the bones in Tight Entrance Cave bolsters this vision of Thylacoleo hunkering down in the dark. Relatively few of the bones in the cave show bite marks. This means that the cave was not the habitat of bone-eaters, like Tasmanian devils, and might indicate that Thylacoleo was much like a cat in primarily dining on flesh and viscera, leaving bones mostly intact.

At different times, off and on between 140,000 and 51,000 years ago, Thylacoleo apparently used the cave as a refuge. And from where the claws marks are situated among the inclines and boulders, it seems that these predators had qualms about taking difficult routes through the dark. “Many claw marks within TEC are located on steep surfaces, despite more gradual inclines being available on other sides of the central rock pile and boulder,” Arman and Prideaux write, and the entrance to the cave itself appears to have been a steep deadfall for other creatures. This suggests that Thylacoleo was a skilled and confident climber, clambering in and out of a cave that trapped other species. And if Thylacoleo could haul itself around rocky caves, it could almost certainly scale trees.

Humans undoubtedly saw Thylacoleo. The mammal was still very much alive when people arrived on Australia around 50,000 years ago, and there may even be Pleistocene art of the mammal. The mythical drop bear, however, didn’t appear as a tall tale until the 20th century, so there’s no link between what people actually saw and stories used to make tourists shudder at the sound of a creaking branch in the night. It’s convergence, but it’s a wonderful sort of convergence. So much of prehistoric life was so strange that we could have never imagined those species if we hadn’t come across their remains. The drop bear is a rare case when our species, in jest, stumbled upon something real and just as scary as our  imaginations can muster.

Bonus: In response to a piece I wrote for Slate about real creatures that could inspire Hollywood monsters, artist Ted Rechlin made this wonderful poster for a Drop Bear movie starring Thylacoleo.

Reference:

Arman, S., Prideaux, G. 2016. Behaviour of the Pleistocene marsupial lion deduced from claw marks in a southwestern Australian cave. Scientific Reports. doi: 10.1038/srep21372

Paleo Profile: The Dawn Mole

The jaw of Eotalpa anglica. From Hooker, 2016.
The lower jaw of Eotalpa anglica. From Hooker, 2016.

The word “mole” is practically synonymous with an underground lifestyle. The little mammals that bear the name are supposed to be near-blind denizens of the world beneath our feet, tunneling through gardens for tasty worms and other morsels. And, fair enough, some moles live this way. But not all. The desman is a snouty mole that swims, some moles forage above the ground but beneath the cover of leaf litter, and the tiny shrew mole Uropsilus doesn’t seem to show any acumen for digging at all. Thanks to some tiny fossils recently found in England, however, it seems that this variety of moles sprung from ancestors that were skilled at scratching into the soil.

Paleontologist Bernard Sigé and colleagues named the critical mole in 1977 from the basis of molars found on the Isle of Wight. They called it Eotalpa anglica, and at 37 to 33 million years old it has stood as the oldest mole ever since. And now, thanks to tiny fossils sifted out of the Eocene rock, it appears that Eotalpa was already doing what moles are famous for.

Natural History Museum paleontologist Jerry Hooker has described the smattering of new bones. The feet of Eotalpa don’t show the swimming adaptations of the star-nosed moses and desmans, Hooker writes, meaning that moles did not start off as semiaquatic mammals as had once been suggested. And while the mole’s hands weren’t quite as extreme as some of its living relatives, their anatomy is more consistent with moles that are dedicated diggers. Even older moles, which Hooker expects might be found in Asia, may help flesh out how moles switched surfaces, but for now Eotalpa indicates that these beasts were underground before it was cool.

eotalpa-claws
The reconstructed finger of Eotalpa anglica in multiple views. From Hooker, 2016.

Fossil Facts

Name: Eotalpa anglica

Meaning: England’s dawn mole.

Age: Between 37 and 33 million years old.

Where in the world?: The Hampshire Basin, England.

What sort of critter?: A mole.

Size: Not estimated, but within the range of living moles.

How much of the creature’s body is known?: Isolated microfossils consisting of the upper and lower jaws, parts of the hand and arm, ankle, and lower leg.

Reference:

Hooker, J., 2016. Skeletal adaptations and phylogeny of the oldest mole Eotalpa (Talpidae, Lipotyphla, Mammalia) from the UK Eocene: the beginning of fossoriality in moles. Palaeontology. doi: 10.1111/pala.12221

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief
The Purgatoire River’s Whale Fish
Russia’s Curved Blade

Prehistoric Animal Bit Like a Sabercat, Crunched Like a Bear

The skull of Kolponomos, with jaw muscles in red. From Tseng et al., 2016.
The virtual skull of Kolponomos, with jaw muscles in red. From Tseng et al., 2016.

Stroll through any museum hall well-stocked with fossil mammals and it’s tempting to look at the extinct beasts as variations on familiar themes. There’s a sloth, but bigger. There’s a camel, but smaller. I guess that weirdo in the corner looks something like a pig. We shove the remains of the extinct into expectations of the familiar even if the fit isn’t particularly good. And that’s a shame. Fossil mammals were stranger than we often give them credit for, and they often behaved in ways that no modern animal does. Just look at Kolponomos.

In the wide spread of the mammal family tree, Kolponomos was a carnivoran. That’s the group that includes cats, seals, bears, civets, and the dog snoring on the couch next to me as I write this. From there the phylogenetic haze sets in, however, with the 20 million-year-old Kolponomos fitting in somewhere around bears and their extinct relatives the bear-dogs, but not really belonging to either line. Regardless of which group can claim Kolponomos, however, what makes this beast so strange was the way it fed. This almost-bear bit like a sabertoothed cat, crunching mollusks in grizzly-like jaws studded with otterish teeth.

The idea that Kolponomos fed on shellfish has been around for a while. The mammal has been found in marine rocks from Oregon, Washington, and possibly Alaska, and the cheek teeth of these fossils show extreme wear from a diet of hard foods. In fact, Kolponomos so regularly dined on clams and mussels that the blocky crushing teeth are often “lakes” of softer dentine with the harder enamel fencing them in. Yet no one had tested this idea, nor how Kolponomos went about prying its food up from rocky shores. Now paleontologist  Jack Tseng and colleagues have finally looked Kolponomos in the mouth.

A restoration of Kolponomos by
A restoration of Kolponomos by Ken Kirkland.

From the anatomy of the shoreline mammal’s jaws, Tseng and coauthors expected that it shared a habit in common with saber-toothed cats. The front of the jaw in Kolponomos is deep and buttressed, giving it a prominent chin just like the famous sabercat Smilodon. In the cats this condition is thought to reflect an attack strategy of anchoring the head with the lower jaw and then using the leverage to drive the famous canines through their prey with a powerful contraction of neck muscles. Kolponomos was no sabertooth, but Tseng and coauthors thought that the mammal could have used the same strategy to detach mollusks from their beds.

To find out, Tseng and colleagues took a multi-pronged approach involving virtual models of Kolponomos, Smilodon, and five other carnivorans to examine bone stress during simulated bites and compare shape, adding examination of tooth wear patterns to see how the hypothesis held up. What they found was that Kolponomos fed like no mammal alive today.

Kolponomos bite sequence. Courtesy Jack Tseng.
Kolponomos bite sequence. Courtesy Jack Tseng.

Tseng and coauthors were on the mark with their Smilodon suspicion. Despite being distant relatives and feeding on entirely different prey, the lower jaws of both Kolponomos and Smilodon were extremely similar in their anatomy, shape, and response to anchor bite stress. The anchor bite was the key. More than that, the researchers found that even though the teeth of Kolponomos resemble those of sea otters the crushing portion of the extinct mammal’s jaw was actually much more like that of a bear in being stiffer but with less mechanical efficiency. Otters show the opposite condition, indicating that there’s more than one way for a carnivoran to be a shell-crusher as far as lower jaws are concerned. This makes the jaws of Kolponomos a multitool, the front strengthened for prying up shellfish and the back stiffened to crush through those defenses.

So if you were to visit coastal Washington about 20 million years ago, you might have seen something almost like a bear, but not quite like a bear, ambling along the rocky shorelines. Sniffing out a shellbed, the burly carnivore opens its jaws to jam its lower teeth into the colony of clams, biting and jerking its neck. The first shove doesn’t work, but the beast bites again and with another spasm the clam comes free with an audible pop and a little arc of spray as Kolponomos tosses its head back. There’s no hope for the bivalve now – with a swipe of its tongue the mammal shoves the snack to its cheek, and you can hear the shell give way beneath molars flattened through repetition. A quick swallow and the mammal’s snout is back in the shallows, ready to pry out another morsel as well as our preconceived notions about what fossil mammals were really like.

Reference:

Tseng, Z., Grohe´, Flynn, J. 2016. A unique feeding strategy of the extinct marine mammal Kolponomos: convergence on sabretooths and sea otters. Proceedings of the Royal Society B. doi: 10.1098/rspb.2016.0044