Lindsay Kastroll

March 31, 2021 by wpengine

MESOZOIC MONTHLY: Volaticotherium

by Lindsay Kastroll

Once again, spring has sprung. Prepare to see the gorgeous forests of Pennsylvania launch back into action. I, for one, can’t wait to get outside and explore as the weather continues to improve. I was recently reminded of the fact that Pennsylvania is home to two species of flying squirrels, and I am definitely adding them to my list of things to see. But of course, this is Mesozoic Monthly, so flying squirrels can’t be the stars of this article. Instead, the superficially flying squirrel-like “ancient gliding beast” Volaticotherium antiquum is stealing the spotlight!

Although Volaticotherium was about the size of a modern flying squirrel at 5–6 inches (13–15 cm) long, it belonged to a group of early mammals called eutriconodonts that includes some of the largest mammals that lived alongside non-avian dinosaurs. “Eutriconodont” means “true three-coned tooth,” in reference to the three longitudinally aligned cusps on their molars. Although not all mammals today have three-cusped molars, the ancestors of modern mammals did. Does this mean that modern mammals evolved from a eutriconodont? The answer is no, though they did evolve from a mammal with eutriconodont-like teeth.

We can split modern mammals into two main groups: the monotremes, which are egg-laying mammals like the platypus, and the therians, which include both marsupial and placental mammals (like kangaroos or humans, respectively). The ancestors of monotremes diverged (meaning, formed their own ‘branch’ of the evolutionary tree) before eutriconodonts and therians evolved. Eutriconodonts and therians share a different, more recent, and as-yet unknown common ancestor. Monotremes, therians, and eutriconodonts actually lived alongside one another for over one hundred million years before eutriconodonts became extinct near the end of the Cretaceous Period (the third and final division in the Mesozoic Era, or ‘Age of Dinosaurs’).

This flowchart represents a simplified phylogeny (aka, evolutionary tree) of the relationships discussed in the previous paragraph. A lot of ‘branches’ and intermediate steps are missing from this phylogeny to make it easier to follow.

The canines and molars of eutriconodonts were pointy, suggesting that these mammals were carnivores or insectivores. Volaticotherium is no exception, which makes it particularly unique, as most other gliding mammals are herbivores! Because it was so small, Volaticotherium was probably an insectivore, but a larger cousin, Jugulator, could probably eat small vertebrates. As an arboreal glider, Volaticotherium could soar from tree to tree to catch insects in midair. Instead of wings, it had a patagium, a broad flap of skin that stretched between the fore- and hind limbs, creating enough surface area to achieve gliding descents. The various limb adaptations necessary to make Volaticotherium an efficient glider also made it poor at maneuvering on the ground. It can be hard to understand why an animal would evolve features that would hinder its terrestrial movement, and multiple hypotheses have been put forth to try to explain this. Most of these focus on the benefits of leaping out of trees to escape predators or to quickly traverse territory between arboreal food sources, scenarios based on herbivorous mammals. Because Volaticotherium was a gliding predator, perhaps gliding conferred other advantages to this eutriconodont.

Restoration of *Volaticotherium* in mid-glide by Jose Antonio Peñas, used with permission. Take note of those sharp canine teeth, useful for catching tasty insects! You can find more of Peñas’ art on their DeviantArt, ArtStation, or YouTube.

The fossilized remains of Volaticotherium were found in a layer of rock called the Daohugou Bed in China. This deposit consists of lakebed sediment and volcanic ash compacted into solid rock over millions of years as more heavy sediment was deposited on top of it. There is a debate about how old the Daohugou Bed is, but most estimates place it near the middle or end of the Jurassic Period (the middle period of the Mesozoic). Getting the timing right is important. Because Volaticotherium is among the oldest known gliding mammals, its discovery pushes the origin of mammalian gliding back as much as 70 million years earlier than previously thought!

A variety of factors have led geologists to struggle in determining the age of the Daohugou Bed. In an ideal geologic record, rock layers would be perfectly horizontal, creating a continuous stack with the oldest layers on the bottom and the newest layers on top. However, this is rarely the case. Sediment may be eroded before new layers are deposited, creating a gap of time without record in that sequence of rocks. This phenomenon, where two rock layers do not represent a continuous progression of time and have a gap of data missing between them, is called an unconformity. Other issues with dating rock layers involve the squeezing, stretching, folding, melting, and chemical alteration of rock layers when they’re subjected to geologic processes. These forces can result in old rock layers being placed on top of younger ones, making it hard to determine the actual sequential order of the rocks. Changes can also occur within the minerals that compose the rocks, making radiometric dating much more difficult.

The Daohugou Bed has an unconformity above and below it, and it has been folded, which makes attributing an exact age to it that much harder. When you go out hiking in the beautiful spring weather on the horizon, take a moment to look at the rock outcrops you pass and think about what those layers might have experienced on their journey to where they are today. And if you continue your hike after sunset, be sure to keep your eyes peeled. If you’re lucky, you might just catch a glimpse of a flying squirrel gliding through the forest!

Lindsay Kastroll is a volunteer and paleontology student working in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum staff, volunteers, and interns are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

Mesozoic Monthly: Nasutoceratops

Although much of the Western world recognizes January 1 as the first day of the new year, many other cultures around the globe celebrate Lunar New Year, an alternate calendar system based on the cycles of the moon. Lunar New Year began on February 12 this year, ushering in, according to repeating cycles of the traditional Chinese zodiac, the Year of the Ox. While bovines hadn’t evolved by the Mesozoic Era, there were plenty of dinosaurs that could be compared to an ox. So, in honor of Lunar New Year, this month’s Mesozoic Monthly features Nasutoceratops titusi, a ceratopsian with a rounded nose and curving, bull-like horns!

An anterior (head-on) view of the skull of *Nasutoceratops*, clearly displaying its most iconic features: the frill and horns. You can view this skull in the temporary exhibition *Dinosaur Armor* at Carnegie Museum of Natural History until July 5, 2021.

Ceratopsian dinosaurs are famous for their huge, elaborate skulls adorned with ornate frills and large horns. Several different bones make up these unique structures. If you haven’t taken an anatomy class, you may not have realized that your skull is made up of several bones that fuse together as you age (fun fact: baby humans have more bones than adults, and this is why!). The horns above a ceratopsian’s eye arise from the postorbitals, bones that sit right behind the eye hole in the skull. The frill is made of two types of bones: the parietals, which make up the central part of the frill, and the squamosals, which act as the corners. Humans actually have both of these bones: the parietal is the large bone at the crown of your head, and the squamosal is fused into the temporal bones above your ears. The bones that form the nose horn of a ceratopsian are aptly named nasals, and we have them too, supporting the cartilage structure of our noses. Of course, our bones are shaped markedly different from those of Nasutoceratops, but the fact that we (and all other vertebrates, aka animals with backbones) have similar skeletal compositions is a feature we inherited from our most recent common ancestor.

Life restoration of a herd of *Nasutoceratops* providing a convenient perch for a flock of enantiornithine birds in what’s now southern Utah roughly 75 million years ago. Artwork by Harrison Keller Pyle. You can find more of Keller Pyle’s work on DeviantArt under kepyle2055.

The skulls of ceratopsians are huge: they grow as long as one third of their body length! The skull of Nasutoceratops was almost five feet (1.5 meters) long, and although we don’t have many bones from the rest of its body, paleontologists estimate that the animal was almost 15 feet (4.5 meters) long. But Nasutoceratops wasn’t even the largest ceratopsian! The most famous ceratopsian, Triceratops, has a skull that can reach a whopping 8.2 feet (2.5 meters) long, but even that isn’t the largest. The largest skull of all dinosaurs belongs to Pentaceratops (sometimes called Titanoceratops), a ceratopsian with an absolutely massive 8.7 foot (2.7 meter) skull!

You can view the skull of *Nasutoceratops* (foreground) alongside those of other ceratopsians (including *Utahceratops* and *Kosmoceratops*, mentioned below) in the temporary exhibition *Dinosaur Armor* at Carnegie Museum of Natural History until July 5, 2021.

Nasutoceratops shared its environment with several other species of ceratopsian, including Kosmoceratops richardsoni and Utahceratops gettyi. Each of these had very different-looking headgear. Nasutoceratops, as previously mentioned, had bull-like horns and a big round nose. Kosmoceratops, in contrast, had weird horns at the top of its frill that curled forward and down, almost like it had bangs, and Utahceratops had short postorbital and nasal horns but a large frill surrounded by spikes. Since all these ceratopsian species lived together, it’s likely that the unique skull ornamentation of different species helped with intra-species recognition (in addition to other functions such as sexual signaling or defense from predators). This meant that each animal could regard shared cranial features as a way to tell who was part of their species. These visual cues might have been especially important for ceratopsians born during the Year of the Ox – according to the Chinese zodiac, “oxen” have poor communication skills, so clear and direct signaling is crucial!

Mesozoic Monthly: Dreadnoughtus

Last January, we started out hopeful for 2020, but unfortunately it ended up being a very difficult year for almost everyone. After an equally challenging start to 2021, I think it is safe to say our attitudes toward this year are more guarded, but nonetheless brave. We know that more hard times might be approaching, but if we could make it through 2020, we can make it through its successor. It is in this spirit that this edition of Mesozoic Monthly features Dreadnoughtus schrani, a colossal sauropod dinosaur whose genus name literally means “fearer of nothing.”

Dreadnoughtus has many connections to Carnegie Museum of Natural History (CMNH). Starting in 2005, a team that included CMNH’s own Dr. Matt Lamanna collected the only known fossil skeletons of the ginormous species in Santa Cruz Province of southern Patagonia, Argentina. Matt was also one of the authors of the paper that officially named the beast in 2014. Furthermore, many of the bones were scientifically prepared by staff and volunteers in the museum’s on-exhibit fossil lab, PaleoLab. Preparation involves freeing the fossils from the rock in which they were preserved (called matrix) using special tools, and then gluing/reinforcing the fossils back together as needed. Next time you visit CMNH, make sure to take a peek in PaleoLab to see our preparators in action!

CMNH Scientific Preparator Dan Pickering carefully removes rock from a gigantic cervical vertebra (neck bone) of *Dreadnoughtus*, ca. 2012. The top of the vertebra is projecting toward the viewer; the front is toward the left of the image. Photo courtesy Matt Lamanna.

Sauropod dinosaurs such as Dreadnoughtus are easily recognized by their frequently huge size, long necks, and long tails. CMNH’s Dinosaurs in Their Time (DITT) exhibition features real fossil skeletons of three different sauropods: Camarasaurus, Apatosaurus, and Diplodocus. Brachiosaurus, one of the stars of Jurassic Park, is also a sauropod, and is featured in the mural in the Jurassic Period atrium in DITT.

Dreadnoughtus belongs to a group of sauropods called titanosaurs that lived during the following Cretaceous Period, largely in the Southern Hemisphere. Titanosaurs have many interesting features that make them unique, such as simplified front feet with very few bones, extra-wide shoulders and hips, and even (in some species) bony plates called osteoderms embedded in the skin. However, as their name implies, titanosaurs’ primary claim to fame is their generally titanic size. Many titanosaurs were absolutely enormous – the smallest members of the group, such as Magyarosaurus, were outliers likely produced by insular dwarfism, a phenomenon in which typically large-bodied animals evolve smaller sizes that are more sustainable in geographically restricted habitats such as islands. Magyarosaurus lived in what’s now the Transylvania region of Romania, which was part of an island at the end of the Cretaceous. In contrast, Dreadnoughtus, which lived in prehistoric South America, was not restricted by an island habitat, and grew to an estimated 85 feet (26 meters) long. And, based on studies of the microscopic internal structure of its bones, it’s possible that the already-immense name-bearing specimen wasn’t even done growing before it died!

When you’re 85 feet long from head to tail, you tend to dwarf everything around you! I bet you didn’t even notice the two 13-foot-long *Talenkauen santacrucensis* at the bottom right – ornithischian dinosaurs that lived alongside *Dreadnoughtus* in the ~75-million-year-old ecosystem of southern Argentina’s Cerro Fortaleza Formation. This digital painting of *Dreadnoughtus* and company is by artist Charles Nye, used with permission. You can find more of his art under the name @thepaintpaddock on Instagram and Twitter!

As you can imagine, it’s very hard to determine how much a dinosaur would have weighed when it was alive, especially for a dinosaur as large as Dreadnoughtus! Although multiple methods for calculating the weight of an extinct animal have been proposed, one of the most commonly employed techniques is volumetric mass estimation. Paleontologists using this method work with typically incomplete skeletons to first estimate how much of each type of tissue (like muscle or fat) covered the skeleton; afterward, they calculate how much each tissue type (including bone) weighed. It’s a difficult, somewhat speculative process that can result in different researchers producing wildly different estimates for the same animal’s weight. Estimates for Dreadnoughtushave been anywhere between 24.4 and 65.4 US tons (22.1 and 59.3 metric tons), but the most recent estimate was 54.0 US tons (49 metric tons). For comparison, a typical school bus weighs around 12.5 US tons (11.3 metric tons)! Clearly, no matter how you estimate it, Dreadnoughtus was a massive animal.

It’s notoriously hard to find complete sauropod skeletons – because their bodies and bones were so large, they tended to break apart and to be at least partially destroyed before they could be buried and preserved. The holotype, or name-bearing, specimen of *Dreadnoughtus* is among the most complete giant titanosaur skeletons ever found. This reconstruction by scientific illustrator Lindsay Wright (a former volunteer here at CMNH) shows which bones of this titanosaur have been discovered (in white).

Gargantuan size has its drawbacks, but it also brings enormous benefits. It takes an absurd amount of resources to grow this large and power the organs needed to support life. However, if enough food is present to sustain this growth, predators are no longer an issue. Not even the largest meat-eating dinosaurs could pose a threat to something as large as an adult Dreadnoughtus. The only chances predators had to taste this sauropod were to hunt it when it was a small juvenile or to scavenge it when it was dead or dying. That seems to be what happened, too, because teeth of carnivorous dinosaurs were found scattered around the fossils.

So, as we continue our journey through 2021, let us think of ourselves like the unassailable Dreadnoughtus: the challenges of 2020 helped us to grow tremendously resilient, and the trials coming our way will not fracture our resolve. Times may be hard, but we are gigantic dinosaurs with no natural predators. We can do this.

Mesozoic Monthly: Vegavis

Disclaimer: Our dinosaur paleontologist Matt Lamanna typically edits Lindsay Kastroll’s Mesozoic Monthly posts before they go live, but due to some much-needed holiday revelry he was late in getting to this one. As such, it’s being posted in January rather than in December as Lindsay had intended. Matt sends his apologies!

‘Tis the season for eating candy canes, singing Christmas carols, and kicking off a new year of Mesozoic Monthly! That’s right – one year ago, the first Mesozoic Monthly debuted in December 2019, spotlighting the ceratopsian dinosaur with a candy cane-shaped nasal horn, Einiosaurus. This December, we’ll move from candy canes to carols as we feature Vegavis iaai, the first Mesozoic bird known to have had a syrinx (the avian “voice box”)!

Photo (left) and computed tomographic (CT) scan image (right) of the type, or name-bearing, specimen of *Vegavis iaai*, a partial skeleton inside a ~70-million-year-old rock concretion from Vega Island, Antarctica. Photo from the Antarctic Peninsula Paleontology Project website.

Birds evolved during the Mesozoic Era, the so-called “Age of Dinosaurs,” before non-avian dinosaurs became extinct. Last month, for the November edition of Mesozoic Monthly, we discussed what makes modern birds members of the group of theropod dinosaurs, but what I didn’t mention is that birds lived alongside non-avian dinosaurs! Birds evolved around 165 to 150 million years ago during the Jurassic Period, the second of three time periods in the Mesozoic. The Jurassic dinosaur Archaeopteryx represents a transitional stage between birds and non-avian dinosaurs: its fossils display obvious flight feathers like a bird, but it also has many non-avian dinosaur characteristics such as a toothy mouth, a long bony tail, and even a miniature version of a killing claw like that of Velociraptor.

Replica skeleton of *Archaeopteryx lithographica* on display here at CMNH. Photo from Wikimedia Commons.

Birds lived and evolved alongside their non-avian relatives for almost 100 million years, and by the end of the Cretaceous Period (the third and final time period of the Mesozoic), the distinct groups of birds that we recognize today were beginning to originate. Vegavis was an ancient relative of ducks and geese discovered on Vega Island, an island off the coast of the Antarctic Peninsula (the part of Antarctica that juts northward towards South America). At that time, Antarctica was warmer than it is now and home to lush temperate forests.

Sandwich Bluff, the site on Vega Island, Antarctica that has produced all known fossils of *Vegavis*. Photo by Eric Roberts, James Cook University.

With many skeletal features suggesting that it was a diving bird that propelled itself with its feet, Vegavis was probably as well-adapted to life in the water as it was to life in the skies. While it’s certainly incredible that scientists are able to deduce this much information about its behavior from just its skeleton, the story gets better: one specimen of Vegavis includes a fossilized syrinx, the organ that birds use to produce sound! A syrinx’s shape is directly related to the sounds it can make, and the fossilized syrinx of Vegavis was a distinctively goose-like asymmetrical shape. So, this ancient bird may well have honked! If it did, it would have sounded much more like six geese-a-laying than, say, four calling birds, three French hens, two turtle doves, or a partridge in a pear tree.

Mesozoic Monthly: Scipionyx

My high school calculus teacher, Mr. Surovchak, once told me about a competition he and his brother had every Thanksgiving. They would weigh themselves before and after dinner to indisputably measure who was able to eat the most. When it comes to dinosaurs, it’s typically much harder to tell what and how much they ate. However, a few fossils give us windows into the guts of dinosaurs – literally! Paleontologists are extremely thankful for spectacular fossils like that of Scipionyx samniticus, a small theropod dinosaur with several internal organs preserved!

Oil painting of *Scipionyx samniticus* in its Early Cretaceous environment by Emiliano Troco, used with permission. You can find more of their work on their Tumblr and contact them via their WordPress site.

Theropods, like Scipionyx, are dinosaurs that stand on two legs, usually with only three prominent toes on each hind foot. Some of the most famous dinosaurs are theropods, like Tyrannosaurus, Velociraptor, and previous Mesozoic Monthly honoree Citipati (does that make it famous? I like to think so). Most theropods interacted with the world primarily with their heads rather than their hands, hence why several of them look like they have oversized skulls and relatively underdeveloped forelimbs. Many also had hollow bones, and, as we can see in extremely well-preserved fossils, feathers. Is this all starting to sound familiar? That’s because these are also features of birds! If you’ve ever heard someone say that birds are dinosaurs, that’s because modern birds, which are called Aves or Neornithes, are just one evolutionary subset of theropod dinosaurs! Birds have all these features of theropod dinosaurs, plus others like toothless beaks and wings made partly from fused wrist and hand bones. If you are eating turkey for Thanksgiving dinner, remember that you’re eating a dinosaur!

Scipionyx didn’t look much like a turkey, though. It belonged to a group of theropods called compsognathids, which were long-tailed, slender, and relatively small predators. It wasn’t imposing size or an especially fascinating appearance that made Scipionyx special – it was the way the only known specimen was fossilized. It is so well preserved that many of its internal organs are intact in its body cavity! Petrified tissue from the trachea, small intestine, and even rectum can be seen in the fossil, as well as muscle tissue, blood vessels, and traces of other organs. We can tell from the bones and scales in its digestive tract that it ate several meals of lizards and fish before it died. There is such a wealth of biological information preserved in this single specimen, and we can learn even more when we consider its relatives. Although skin didn’t preserve in Scipionyx, at least one fossil of another compsognathid named Sinosauropteryx has such well-preserved skin and filament-like ‘protofeathers’ that we can even see pigments preserved! Based on Sinosauropteryx, we can assume that Scipionyx had some sort of filamentous or fuzzy covering as well, at least over some parts of its body.

The incredible fossil of *Scipionyx* preserves the dinosaur’s internal organs in 3D! For example, the sinuous shape of the small intestine is visible immediately behind the right elbow. Photo by *Giovanni Dall’Orto on Wikimedia Commons*. You can read more about this specimen in *a paper by Dal Sasso and Maganuco (2011).*

The fossil of Scipionyx is very small because the individual in question was just a hatchling when it died. Paleontologists can tell it was a hatchling, and not a small adult animal, because its proportions are similar to those of other juvenile dinosaur fossils and many of its bones had not yet fused together (you can learn more about how bones fuse as organisms get older in the Nemicolopterus edition of Mesozoic Monthly). The baby Scipionyx individual represented by the fossil would have measured around 18 inches (46 cm) long in life, and estimates based on how other compsognathids grew suggest that its species reached about 7 feet (2.1 meters) in length at adulthood. Not much is known about its habitat, but it was likely one of the largest animals around. Scipionyx was found in deposits laid down in a marine environment in what is now Italy. Back in the early part of the Cretaceous Period (the third and final division of the Mesozoic Era, or ‘Age of Dinosaurs’), when Scipionyx was alive, Italy was mostly under a shallow sea dotted with small islands, and the dinosaur would have lived on one of these. Since then, tectonic activity has dramatically changed the region, creating new mountains and lowering sea level to what it is today.

So, this Thanksgiving, if you’re looking for a conversation starter at the dinner table/family video call (or if you urgently need to divert discussion from a more sensitive topic), here’s an idea: ask your dining partners whether they think non-avian theropods like Scipionyx would have tasted more like turkey or chicken! Or, if your loved ones would rather learn than debate, you could perhaps offer to read them any of the 12 Mesozoic Monthly animal spotlights (that’s right, December makes one whole year of Mesozoic Monthly!). I’d certainly feel honored to make an appearance at your Thanksgiving feast.

Mesozoic Monthly: Gargoyleosaurus

Do you know what you’re going to dress up as for Halloween? This year, I’ll be going to work dressed as Velma Dinkley from Scooby-Doo. For the October edition of Mesozoic Monthly, I’ll be ‘unmasking’ a dinosaur with a monstrous name: Gargoyleosaurus parkpinorum, an armored dinosaur from the Jurassic Period!

Handy infographic of the ankylosaur *Gargoyleosaurus parkpinorum* showing its appearance, size, geographic and temporal occurrence, and more. Art by cisiopurple on DeviantArt, used with permission.

Gargoyleosaurus belongs to my favorite group of dinosaurs: the ankylosaurs! The group Ankylosauria is comprised of many big-bodied herbivores covered in osteoderms, which are pieces of bone embedded in the skin that act like armor. Their osteoderms came in many shapes and sizes, from tiny ossicles that protected their bellies, to large, fused pieces of bone that formed club-like structures on their tails. In most cases you can easily distinguish between the two major groups of ankylosaurs based on their style of osteoderms (though there are other features that distinguish them as well). Ankylosaurids are famous for their tail clubs: the last vertebrae in their tail overlap to form a rigid ‘handle’ that ends with a mass of fused osteoderms akin to a club. Nodosaurids, their sister group, sported massive osteoderm spikes on their shoulders instead of clubs on their tails. Some paleontologists distinguish a third group of ankylosaurs, called polacanthids, which have a rectangular ‘pelvic shield’ made of fused osteoderms that rests over the hips. There’s a lot of overlap between ‘nodosaurid’ and ‘polacanthid’ characteristics, though, so ankylosaurs with pelvic shields are typically grouped in with the nodosaurids instead of being recognized as their own group.

Conveniently, the Dinosaur Armor temporary exhibition at Carnegie Museum of Natural History features representatives of all three (or both, depending on your taxonomic preference!) ankylosaur subgroups: the ankylosaurid Akainacephalus, the nodosaurid Peloroplites, and the polacanthid (= nodosaurid?) Gastonia.

The imposing nodosaurid ankylosaur *Peloroplites* as seen in CMNH’s *Dinosaur Armor* exhibition. Check out those giant, spike-shaped shoulder osteoderms, a nodosaurid hallmark. Photo by Matt Lamanna.

There’s been some debate over where to place Gargoyleosaurus on the ankylosaur family tree because it displays a range of features from both major groups. It has pointy, horn-like osteoderms on the back of its head, which is a feature of ankylosaurids, but its skeleton lacks evidence of a tail club or other ankylosaurid characteristics. It also has a long snout, shoulder spines, and a pelvic shield, all features of nodosaurid (or polacanthid) ankylosaurs. The best explanation for the mix of features seen in Gargoyleosaurus is that it was one of the most basal nodosaurids, meaning it was one of the earliest nodosaurids to evolve and is therefore located at the base of the group’s evolutionary tree. If Gargoyleosaurus was a basal nodosaurid, that would explain why it still had features similar to those of ankylosaurids: because it had only recently evolved from the common ancestor of ankylosaurids and nodosaurids, not enough time had elapsed for features of that common ancestor (such as ankylosaurid-like skull osteoderms) to be removed by natural selection. This would be in keeping with the status of Gargoyleosaurus as one of the geologically oldest ankylosaurs of any kind discovered to date.

Albany County, Wyoming, ca. 150,000,000 B.P.: a solitary *Gargoyleosaurus* enjoys a shady spot by a stream in its Morrison Formation ecosystem. Art by Batavotyrannus on DeviantArt, used with permission.

No matter which ankylosaur subgroup Gargoyleosaurus belongs to, everyone can agree that it was a well-armored tank. Armor is a very useful defense against predators, since it generally covers the most vulnerable places on the body, such as the neck. Gargoyleosaurus lived in what is now the Morrison Formation, a famous set of rocks in the western US made of sediment deposited during the late Jurassic Period (the second of three periods in the Mesozoic Era, or Age of Dinosaurs). Most of the Jurassic dinosaurs on display at CMNH come from the Morrison Formation, such as our beloved long-necked sauropod Diplodocus, the even more massive sauropod Apatosaurus, and the forever popular Stegosaurus. But the Morrison ecosystem was home to a horde of formidable carnivores too—Allosaurus, Ceratosaurus, and Torvosaurus among them—so the armor of Gargoyleosaurus undoubtedly came in very handy. Contrary to what certain “Jurassic” franchises would lead you to believe, though, Tyrannosaurus rex did not live during the Jurassic Period, and so it never interacted with Gargoyleosaurus or any other members of the Morrison dinosaur community. That said, if trick-or-treating had been a possibility in the Jurassic, I’d imagine those inflatable T. rex Halloween costumes might have been very popular. Who doesn’t love those silly costumes?!

MESOZOIC MONTHLY: Volaticotherium

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