Sunday, May 19, 2024

Silesaurus: Beast of the Week

 This week we will be checking out an interesting and a mysterious creature, Silesaurus opolensis!

Silesaurus was a reptile, closely related to dinosaurs, that lived in what is now Poland during the Triassic period, between 237 and 227 million years ago.  Footprints that could have been from Silesaurus, or at the least something very closely related to it, have also been found on the east coast of the United States, including Maryland.  When alive it would have been an omnivore, eating plants and also small animals, like insects.  Adult Silesaurus measured about 7.5 feet (2.3 meters) from beak to tail.  The genus name, translates to "Selesia Reptile" In reference to the region in Poland in which its bones were discovered. 

Life reconstruction of Silesaurus in watercolors by Christopher DiPiazza.

Silesaurus had a narrow snout with a beaklike mouth.  Its teeth were somewhat leaf-shaped and lacked prominent serrations.  Microwear studies on Silesaurus teeth suggest it ate lots of plants but fossilized dung associated with Silesaurus was also found to have beetle shells in it, showing it was more likely an omnivore, eating insects and maybe other small animals on occasion in addition to a mostly plant diet.

Silesaurus skeletal mount on display at Jurapark Science Park, in Poland.

Silesaurus would have walked on all fours most of the time but may have been able to rear up on its hind legs on occasion if it needed.  All four of its limbs were long and slender, making it look like a reptilian greyhound of sorts. (in my opinion at least) It had five very short fingers and claws on each of its hands and its feet each had three toes.  Thanks to tracks we know its thumb and pinky fingers were held off the ground when it walked. The neck was relatively slender and would have been held in a gentle S shape most of the time, a feature similar to dinosaurs. 

Hand (left) and foot (right) tracks from what may have been Silesaurus (or a very close relative) that were found in Maryland, United States, on display at the Natural History Society of Maryland in Baltimore.

Silesaurus is an interesting animal because its exact placement on the tree of life is still highly debated.  That by itself wouldn't be that unusual (loads of fossil animals we don't know the exact natural history of) but what makes Silesaurus' identity especially noteworthy is because the discourse is over whether or not it is a dinosaur. (dinosaurs are popular) The original placement of Silesaurus was that it was an extremely close relative of dinosaurs without quite being a true dinosaur, itself.  It shares a number of dinosaur-like characteristics, like having its limbs positioned directly under it's body, resulting in a fully erect posture while standing and walking.  It also has several diagnostic dinosaur characteristics in its leg and hip bones.  Because of these extreme similarities to dinosaurs, some experts are starting to propose that the silesaurid family should be reassigned as true dinosaurs, specifically as the ancestors of the first ornithiscian dinosaurs, the broad branch of dinosaurs which includes famous taxa like Triceratops, Stegosaurus, and Iguanodon.  This is partially due to the fact that there is very little, if any, ornithiscian dinosaur fossils known from the Triassic period. (unless they're the silesaurids). Other expert's, however, are still unconvinced, since Silesaurids still don't possess some other key dinosaur characteristics, like a specialized ridge on the anterior of the humerus for muscle attachments, called the deltopectoral crest, as well hip sockets that forms an open window completely through the pelvis. 

Images of the humerus of Silesaurus (left) from Piechowski's 2020 paper alongside the humerus of early ornithiscian dinosaurs, Heterodontosaurus (middle) and Abrictosaurus (right) from Galton's 2014 paper. Note the Silesaurus bone is lacking the deltopectoral crest at the top of the bone compared to the other two. 

Regardless if Silesaurus was a true dinosaur or not, it very well may have sported feathers of some kind when alive.  This is because both dinosaurs and pterosaurs are believed to have shared a common ancestor with some kind of feathers.  Since silesaurids were at least very closely related to dinosaurs (moreso than to pterosaurs) they likely would have had feathers as well.  This method of predicting features in fossil groups based on known features in surrounding groups is known as phylogenetic bracketing.  


Dzik J (2003). "A beaked herbivorous archosaur with dinosaur affinities from the early Late Triassic of Poland" (PDF)Journal of Vertebrate Paleontology23 (3): 556–574.

Galton, P.M. (2014). "Notes on the postcranial anatomy of the heterodontosaurid dinosaur Heterodontosaurus tucki, a basal ornithischian from the Lower Jurassic of South Africa" (PDF)Revue de Paléobiologie, Genève. 1. 33: 97–141.

Nesbitt, Sterling J. (2011). "The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades"Bulletin of the American Museum of Natural History352: 1–292.

Piechowski, Rafał; Tałanda, Mateusz (2020). "The locomotor musculature and posture of the early dinosauriform Silesaurus opolensis provides a new look into the evolution of Dinosauromorpha"Journal of Anatomy236 (6): 1044–1100. 

Sunday, April 21, 2024

Acrocanthosaurus: Beast of the Week

This week we are checking Acrocanthosaurus atokensisAcrocanthosaurus was a meat-eating dinosaur that lived in what is now the United States, including Oklahoma, Texas, Wyoming, and even as far east as Maryland, during the Early Cretaceous Period, between 125 and 100 million years ago.  Acrocanthosaurus measured about thirty eight feet (11.5 meters) long from snout to tail, and was likely the top predator in its environment.  The name Acrocanthosaurus, translates to "High Spine Lizard" and is in reference to this dinosaur's particularly tall neural arches, which gave it a distinctive ridge down its back.

Watercolor reconstruction of Acrocanthosaurus by Christopher DiPiazza.

Acrocanthosaurus' spine was interesting in that we haven't found another theropod dinosaur with anything similar.  It is often compared to the unrelated, Spinosaurus' sail-like structure, but Acrocanthosaurus' runs all the way from the back of the skull to about midway down the tail, rather than just the back like in SpinosaurusAcrocanthosaurus also has a close relative from Spain, Concavenator, which has a triangular-shaped hump over its hips, but again, this is concentrated to one area of the spine. The purpose of this ridge-like look is a mystery.  Some believe it would have formed a hump rather than a ridge, like what you might see on a modern bison's skeleton.  (Which also have extended neural arches, but mostly over the shoulders.)   As of now the safe answer could always be that Acrocanthosaurus possessed this ridge down its spine for display purposes to other members of its species.  Maybe they were larger in males than in females and played a role in mate selection?  Perhaps it was significantly shorter in juveniles?  There is still a lot we don't know!

Bison skeleton.  Note the tall neural arches above the shoulders.  The living animal has a hump there.

The skull of Acrocanthosaurus is long, low, and narrow in the front, but the back of the lower jaw become increasingly deep, suggesting there was a lot of muscle there in life, allowing this dinosaur to bite down hard.  The teeth of Acrocanthosaurus were slightly curved and serrated on both the front and back edges.  They were also thicker than the very blade-like teeth of its later relatives, like Giganotosaurus and Cacharodontosaurus, suggesting Acrocanthosaurus was more of a generalist hunter.  This is also further supported by the fact that Acrocanthosaurus' range was so widespread across what is now the United States, which would have consisted of multiple different kinds of habitats.

Acrocanthosaurus skull from the North Carolina Museum of Natural Sciences.

The front limbs of Acrocanthosaurus were short, but powerful and had a decent range of motion to them.  Each hand possessed three hooked claws.  It is difficult to say exactly how Acrocanthosaurus would have utilized these arms since they were so short, but they may have played a part when it was going after large prey, like a sauropod, at close quarters.

Acrocanthosaurus skeletal mount on display at the North Carolina Museum of Natural Sciences.

When alive, Acrocanthosaurus, would have coexisted with many other dinosaurs, including the much smaller predator, Deinonychus, the ornithopod, Tenontosaurus, and a few different kinds of large sauropods, like Sauroposeidon and Astrodon on the east coast.  In fact, there is a dinosaur track way in Texas consisting of large theropod prints that are believed to have been made by Acrocanthosaurus along with those of a large Sauropod.  These tracks show, since at times the theropod prints overlap the sauropod ones, that those of the theropod were made later, and could have possibly been tracking the larger herbivore.  At one point some scientists believe the theropod even attacked the sauropod, since the meat-eater tracks skip for a while where they finally intersect. (did it latch onto the side of its intended prey?)  This hypothesis can't be fully proven, however.  Even though no bones from either dinosaur were found with this trackway, it is predicted the predator was Acrocanthosaurus because the size, location, and age of the tracks.

Photograph of the tracks believed to have been from Acrocanthosaurus possibly stalking a sauropod in the field in Texas.  You can now see these tracks in person on display at the American Museum of Natural History in New York City.

That is all for this week!  As always please comment below or on our facebook page!


Currie, Philip J.; Carpenter, Kenneth. (2000). "A new specimen of Acrocanthosaurus atokensis (Theropoda, Dinosauria) from the Lower Cretaceous Antlers Formation (Lower Cretaceous, Aptian) of Oklahoma, USA". Geodiversitas 22 (2): 207–246.

Lockley, Martin G. (1991). Tracking Dinosaurs: A New Look at an Ancient World. Cambridge: Cambridge University Press. p. 252pp.

Senter, Phil; Robins, James H. (2005). "Range of motion in the forelimb of the theropod dinosaur Acrocanthosaurus atokensis, and implications for predatory behaviour". Journal of Zoology 266 (3): 307–318.

Stovall, J. Willis; Langston, Wann. (1950). "Acrocanthosaurus atokensis, a new genus and species of Lower Cretaceous Theropoda from Oklahoma". American Midland Naturalist (American Midland Naturalist, Vol. 43, No. 3) 43 (3): 696–728.

Thomas, David A.; Farlow, James O. (1997). "Tracking a dinosaur attack". Scientific American 266 (6): 48–53.

Sunday, April 14, 2024

Rhamphorhynchus: Beast of the Week

Rhamphorhynchus was a pterosaur that lived in what is now Germany during the late Jurassic period, between 150 and 148 million years ago.  The adults measured about four feet (1.2 meters) long from beak to tail and had wingspans of about six feet (1.8 meters) wide.  When alive Rhamphorhynchus would have eaten meat, mostly in the form of fish and other marine life.  The genus name translates to "Beak Snout" from Greek.  Rhamphorhynchus muensteri is by far the most well known species of Rhamphorhynchus, known from many individual specimens, however, there is also a species known from a single wing fossil found in what is now Dorset, England, called Rhamphorhynchus etchesi.

Rhamphorhynchus muensteri life reconstruction in watercolors by Christopher DiPiazza.

Rhamphorhynchus belonged to the group of pterosaurs that existed from the Triassic to the early Cretaceous periods, characterized by their proportionally smaller heads short legs, and long narrow tails, called rhamphorhynchoids. (named after Rhamphorhynchus, itself.)  In addition to their wings, which form from flexible skin attached from the tip of their fourth finger (which was extremely long and sturdy) to about the ankle, pterosaurs from this group also sported a membrane between their legs, which likely aided in flight.  Pterosaurs from this also sported teeth, and Rhamphorhynchus was no exception.  The teeth of Rhamphorhynchus, were particularly long, slightly curved, and interlocked when the jaws were closed.  The tip of its jaws also curved into each other and were beaklike.  This seems to be an adaptation for grasping fish, cephalopods, and other slippery marine prey.  

Rhamphorhynchus skeleton on display at the Royal Ontario Museum that showcases preserved soft tissue, like wing membranes and the tail vane.

At the tip of its tail, Rhamphorhynchus sported a fan-like structure, called a tail vane, which may have helped it steer during flight.  Since Rhamphorhynchus is known from many individuals of different stages of maturity when they died with soft tissue preserved, we know that the shape of this structure changed as the animal aged.  The youngest individuals sported narrow, oval-shaped vane, slightly older individuals had vanes that were more pointed and diamond-like, while in the most mature individuals the tip of the vane flared out into an almost sideways triangle shape.  Because of this change it is possible the vane may have had a role in some sort of communication, like sexual display within the species, as well.  Originally, scientists thought Rhamphorynchus consisted of several more species than the two listed at the top of this post, grouping them based on size and tail vane shape.  More recently, however, it was determined they were all the same species at different developmental stages of life. 

Rhamphorhynchus fossil with imprints of the wing membranes and tail vane cast on display at the American Museum of Natural History in New York.

Since Rhamphorhynchus is known from many specimens of various sizes, paleontologists were able to study and predict how it would have grown as it aged when alive.  Thanks to a study in 2012, examining various specimens of different stages when they died, it was determined that like many modern reptiles, Rhamphorhynchus would have been able to fly on its own soon after hatching and would have grown rapidly early in life.  This growth spurt seemed to slow down at about three years of age, which also seems to be when they were fully mature.  

The environment that Rhamphorynchus lived in would have been a series of islands with lagoons in a relatively shallow sea.  It likely would have hunted over the water, snatching small fish and other marine animals off the surface of the water while flying.  It would have coexisted with fellow pterosaur, Pterodactylus, and the dinosaurs Archaeopteryx and Compsognathus.  


Bennett, S. C. (1995). "A statistical study of Rhamphorhynchus from the Solnhofen Limestone of Germany: Year-classes of a single large species". Journal of Paleontology69 (3): 569–580.

Prondvai, E.; Stein, K.; Ősi, A.; Sander, M. P. (2012). Soares, Daphne (ed.). "Life history of Rhamphorhynchus inferred from bone histology and the diversity of pterosaurian growth strategies"PLOS ONE7 (2): e31392.

O'Sullivan, Michael; Martill, David M. (June 2015). "Evidence for the presence of Rhamphorhynchus (Pterosauria: Rhamphorhynchinae) in the Kimmeridge Clay of the UK" Proceedings of the Geologists' Association126 (3): 390–401.

Sunday, March 3, 2024

Mei: Beast of the Week

 This week we will look out a dinosaur that helped solidify the connection between extinct dinosaurs and modern birds.  Let's check out Mei long!

Mei was a theropod dinosaur that lived in what is now China, during the Early Cretaceous period, about 125 million years ago.  It only measured about two feet (60cm) long as an adult, about the size of a modern duck, and would have eaten meat and possibly some plant material when alive.  The genus and species name, Mei long, translates from Chinese to "sleeping dragon" in reference to how this amazing fossil was discovered.  

Life reconstruction of Mei in watercolors by Christopher DiPiazza.

Mei's biggest claim to fame is how it was unearthed in a sleeping position, similar to how modern birds sleep with their head curled back and tucked under one wing and legs folded under the rest of the body.  Not only is this interesting purely because we know what kind of posture a dinosaur had millions of years ago, but it also strongly implies this dinosaur had feathers when alive, since the pose of the head tucked under the arm is so often done by modern birds with the use of wing feathers to shield the eyes.  The minerals between and over the bones of Mei imply the dinosaur was buried alive extremely quickly by ash from an erupting volcano, resulting in a beautifully preserved complete dinosaur skeleton for paleontologists to learn from.  

Cast of the juvenile specimen of Mei on display at the American Museum of Natural History in the seasonal "Dinosaurs Among Us" exhibit in 2014.

Mei was a member of the troodontid family of theropods.  Troodontids were birdlike, typically smaller dinosaurs that appear to have specialized in hunting small animals and possibly some plants when alive.  Troodontids typically had proportionally large eyes, narrow snouts, short arms, and long slender legs tipped with sharp claws, including a retractable second toe claw, which could have been an adaptation for pinning prey.  

Mei is known from two specimens, one young juvenile and one adult.  The adult retains what are generally considered juvenile characteristics, like proportionally short snout and large eyes.  Both specimens also exhibit relatively large nares (nostril holes in the skull) which is unusual for troodontids.  

Photograph of the second discovered specimen of Mei from the 2012 paper by Gao et al., which was an adult when it died. 

The environment that Mei lived in during the early Cretaceous appears to have been heavily forested with rivers and lakes throughout with nearby active volcanoes.  Since Mei was so small, it may have relied on hiding in the underbrush, or possibly even climbing trees to avoid predation from larger predators that shared its environment, like the gliding dinosaur, Changyuraptor, or even the large tyrannoysauroid, YutyrannusMei also would have crossed paths with dinosaurs like Beipiaosaurus and Tianyulong to name a few more.


Gao C, Morschhauser EM, Varricchio DJ, Liu J, Zhao B (2012) A Second Soundly Sleeping Dragon: New Anatomical Details of the Chinese Troodontid Mei long with Implications for Phylogeny and Taphonomy. PLoS ONE 7(9): e45203.

Junchang Lü; Li Xu; Yongqing Liu; Xingliao Zhang; Songhai Jia & Qiang Ji (2010). "A new troodontid (Theropoda: Troodontidae) from the Late Cretaceous of central China, and the radiation of Asian troodontids" (PDF)Acta Palaeontologica Polonica55 (3): 381–388.

Xing Xu & Mark A. Norell (2004). "A new troodontid dinosaur from China with avian-like sleeping posture" (PDF)Nature431 (7010): 838–841.

Sunday, February 25, 2024

Miragaia: Beast of the Week

This week we will be checking out a unique plated dinosaur.  Enter Miragaia longicollum.  Miragaia was a plant-eating dinosaur that lived in what is now Portugal during the Late Jurassic Period, about 150 million years ago.  From beak to tail it measured roughly twenty feet (6m) long.  The genus name is in honor of the village of Miragaia, near where its bones were first uncovered in eastern Portugal.  However, "Miragaia" also translates to "wonderful Gaia".  Gaia, in Greek mythology, was the titan of the earth, and mother to many of the gods.   The species name, longicollum, translates to "long neck" for reasons that don't need explaining once you see what this dinosaur looks like.

Watercolor life reconstruction of Miragaia by Christopher DiPiazza.

Long necks are nothing new or unusual for dinosaurs.  Sauropods, being the most famous for having them, as well as many theropods, including lots of living birds!  Miragaia, however, was none of those things.  Miragaia was a stegosaurid, a close relative to the more famous, Stegosaurus.  Among stegosaurids, Miragaia had a noticeably long neck, which consisted of seventeen vertebrae.  Stegosaurids in general tended to have relatively long-ish necks, consisting of between nine and thirteen vertebrae (depending on the species) possibly to help them access as much low-growing vegetation as possible without having to move their bodies while feeding.  The specific reason why Miragaia's neck was as long as it was is still somewhat of a mystery.  What's even more interesting is the fact that since it lived during the late Jurassic, Miragaia was coexisting with sauropods, which also had extremely long necks.  Perhaps it was evolving to compete with its sauropod neighbors?  Keep in mind, despite a quadruped, Miragaia was probably able to rear up on its hind legs for short periods of time, perhaps to reach higher vegetation while feeding.  This is because its center of gravity would have been in its hips, making its front end much lighter.  Maybe its neck allowed it to feed in a space just below the larger sauropods, but beyond other stegosaurids?  We may never know for certain. 

Miragaia is an interesting find because it was not discovered by paleontologists looking for fossils.  Its remains were found on accident by construction workers, while building a road.  Because of this, only the front half of Miragaia's skeleton was initially found, the back part unknowingly may have been destroyed during the construction. Years later a stegosaur, currently called Alcovasaurus but possibly a different species of Miragaia, was published on, which included elements of the back half of the body, including long spikes that would have been on the tail.  

There are a number of interesting things to note about this Miragaia other than the neck.  Part of Miragaia's skull was preserved, including the beak.  Miragaia's beak was relatively small, but flared out slightly on either side, making an almost upside-down heart shape.  This beak was likely ideal for clipping vegetation to be processed by the small teeth farther back in the mouth.

Photograph of most of Miragaia's bones that are on the fossil record.  Photo credit: Dr. Mateus.

Miragaia had bony plates on its back, just like all known stegosaurids.  These plates (at least the ones that were found) were relatively small, and were arranged in pairs.  The plates may have been for display between members of the species.  They also might have had a role in temperature regulation or even could have helped with camouflage by obscuring the animal's profile, depending on what kind of environment it was in.  Many living reptiles have similar adaptations today, like spines and sails for those purposes.  Stegosaurids are also known for having spikes, usually, but not limited to the tail.  Two spikes were unearthed in association with a possible Miragaia specimen, suggesting it may have had an arrangement similar to that of its relative, Kentrosaurus, with the front half of its back adorned with plates that turn into long spikes around the hips and continue to the tip of the tail.  These spikes were extremely long and would have been potentially deadly defensive weapons against potential predators, like Allosaurus or Torvosaurus.

That is all for this week!  As always feel free to comment below or on our facebook page!


Costa, Francisco; Mateus, Octávio (13 November 2019). "Dacentrurine stegosaurs (Dinosauria): A new specimen of Miragaia longicollum from the Late Jurassic of Portugal resolves taxonomical validity and shows the occurrence of the clade in North America"PLOS ONE14 (11): e0224263.

Mateus, O.; Maidment, S. C.R.; Christiansen, N. A. (2009). "A new long-necked 'sauropod-mimic' stegosaur and the evolution of the plated dinosaurs". Proceedings of the Royal Society B: Biological Sciences. 276 (1663): 1815–21.

Waskow, Katja; Mateus, Octavio (2017). "Dorsal rib histology of dinosaurs and a crocodylomorph from western Portugal: Skeletochronological implications on age determination and life history traits". Comptes Rendus Palevol.

Sunday, February 4, 2024

Ornithomimus: Beast of the Week

 This week we will be looking at a fast-running dinosaur that looked like modern birds. (but wasn't directly related to them) Make way for Ornithomimus!

Ornithomimus was a theropod dinosaur that lived in what is now mostly western North America, although some fragmentary fossils that appear to be from it have also been found on the east coast of the United States, including New Jersey.  It lived during the late Cretaceous period, between 76.5 and 66 million years ago, and therefore was one of the dinosaurs wiped out by the meteorite that ended the Mesozoic.  From beak to tail it would have measured about 12 feet (3.6 meters) long and was either an herbivore, or possibly an omnivore when alive.  Its genus name translates to "Bird Mimic" because of its birdlike (specifically ostrich) appearance.  

Ornithomimus edmontonicus life reconstruction in watercolors by Christopher DiPiazza.

Ornithomimus was a member of the ornithomimosaur family of theropods, characterized by their long, slender necks, long legs, long arms, and beaked faces.  Like Ornithomimus, many were toothless, but a few earlier members had small teeth.  Struthiomimus, Gallimimus, Harpymimus, and even the gigantic Deinocheirus, are all also members of this group.  Like many of its relatives, Ornithomimus had proportionally long arms with three fingers on each hand and long powerful legs, suggesting it was a fast runner.  A large number of Ornithomimus foot bones on the fossil record were found by paleontologists to be devoid of stress fractures, further supporting the idea they were adapted to running in life. Ornithomimus also had a slender beak with proportionally large eye sockets, suggesting it had strong eyesight in life.  

Ornithomimus edmontonicus skeleton on display at the Royal Tyrell Museum in Alberta, Canada.

Ornithomimus is currently known from two species.  The earliest of the two, called Ornithomimus edmontonicus, lived between 75.5 to 72 million years ago, in what is now Alberta, Canada.  It would have coexisted with other dinosaurs, like Albertosaurus, Anodontosaurus, Pachyrhinosaurus, Sphaerotholus, Hypacrosaurus, and its close relative, Struthiomimus.  The later species, Ornithomimus velox, was the slightly smaller species based on known material, and lived more in what is now the United States, from the very end of the late Cretaceous.  This species would have crossed paths with Tyrannosaurus, Triceratops, Pachycephalosaurus, Anzu, and Ankylosaurus to name a few, and like them, would have gone extinct when the asteroid that ended the Mesozoic hit the earth, 66 million years ago.  In the past Ornithomimus actually included a whopping seventeen more species that have since mostly been lumped into one of the two previously mentioned, or found to be different genera.

Fossilized remains of Ornithomimus feathers circled in yellow.  Specimen at the Royal Tyrell Museum.

For decades most experts suspected Ornithomimosaurs, like Ornithomimus, sported feathers in life based on its resemblance to modern birds and the presence of fossilized feathers in other kinds of dinosaurs.  More recently, however, this hypothesis was confirmed thanks to not one, but several separate specimens of Ornithomimus edmontonicus that sport fossilized remains of feathers.  Thanks to these exquisite fossils, we now know that young Ornithomimus had shaggy down-like feathers on their bodies, much like many modern birds.  We also know that adult Ornithomimus sported long feathers on its lower arms, like the wings of modern ostriches. It is worth noting that the Ornithomimosaurs were NOT direct ancestors of modern ostriches or any other birds (modern types of birds already existed during the time ornithomimosaurs were alive), but a beautiful example of convergent evolution, when two different kinds of animals independently evolve similar features and end up looking more closely related than they really are.


Makovicky, P.J., Kobayashi, Y., and Currie, P.J. (2004). "Ornithomimosauria." In Weishampel, D.B., Dodson, P., & Osmólska, H. (eds.), The Dinosauria (second edition). University of California Press, Berkeley: 137-150.

Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.

Zelenitsky, D. K.; Therrien, F.; Erickson, G. M.; Debuhr, C. L.; Kobayashi, Y.; Eberth, D. A.; Hadfield, F. (2012). "Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins". Science338 (6106): 510–514.

Sunday, January 14, 2024

Stegosaurus: Beast of the Week

This week we will be looking at one of the most instantly recognizable dinosaurs.  Let's check out Stegosaurus

Stegosaurus was a plant-eating dinosaur that lived in what is now the Western United States, including Wyoming and Colorado, during the Late Jurassic Period, between 155 to 150 million years ago.  Some Stegosaurus remains have also been found in Portugal.  The genus name, Stegosaurus, actually translates to "roofed reptile" because its iconic plates were at first believed by scientists to have laid flat on the animal's back like shingles on a roof.  As adults, most Stegosaurus hovered in size at around twenty to twenty five feet, but some individuals could have grown to about thirty feet long from beak to tail.  When alive, it would have coexisted with other famous dinosaurs, including Apatosaurus, Brontosaurus, Camarasaurus, Ceratosaurus, Torvosaurus, and Allosaurus.

Life reconstruction in watercolors of Stegosaurus stenops by Christopher DiPiazza.  Since its center of gravity was over the hips, it may have been easier for Stegosaurus to rear up on its hind legs than most quadrupedal dinosaurs, especially if it used its strong tail as a third support.

Stegosaurus is most well-known for its plates, which varied slightly between species, but more or less were diamond-shaped, depending on the species.  The speceis, Stegosaurus ungulatus, had more narrow and pointier plates.  Stegosaurus stenops had plates that were wider and more rounded.  On average, Stegosaurus possessed seventeen to nineteen of these impressive plates running down its back.  The evolutionary function of these bony structures remains a mystery but paleontologists have come up with a few ideas.  When first discovered, it was believed that these plates served as armor, but it was soon realized that in life, they were arranged sitting erect on the animal's back which wouldn't do much good for physical protection from predators.  Furthermore, the plates of a Stegosaurus are extremely thin and actually quite delicate!  A predator, like Allosaurus or Torvosaurus, would surely have had no problem biting right through them.

Stegosaurus stenops skeleton on display at the American Museum of Natural History in New York.

A second, possably more likely idea for these plates, was to help control Stegosaurus' body temperature.  Upon close inspection, they were found to have had many blood vessels in them in life.  If a Stegosaurus wanted to warm up in the morning, the blood in these plates could have been heated by the sun and then circulated to the rest of the body.  If the Stegosaurus wanted to cool off in the afternoon, the heated blood would cool off slightly when closer to the outside air while in the plates, and like before, be circulated to the rest of the body, cooling the animal down.  Many other animals use this method of temperature control, by using large ears like elephants and rabbits, or reptiles with sails or extendable ribs.  It is plausible that Stegosaurus' plates were also display adaptations, having possibly been brightly colored to impress potential mates or intimidate rivals.  

Stegosaurus stenops skeletal mount on display at the London Museum of Natural History.

The position of Stegosaurus's plates has also been the subject of some debate over the years.  Like I stated earlier, originally the plates were believed to have laid flat on the dinosaur's back, like shingles on a roof, for protection.  It was later realized that these plates belonged erect  growing off of the back.  The first version of this idea showed two rows of paired plates but the more recent idea is that the plates were still in two rows, but alternating, not parallel.  Other members of the stegosaurid family, like Kentrosaurus, for instance, did actually have parallel paired plates, however.

Stegosaurus had actual protective armor too!  Right under the chin, extending down the throat of a well-preserved Stegosaurus specimen, many small pieces of bony armor were discovered.  These small chunks of armor would have been embedded in the dinosaur's neck skin and acted like chain mail, protecting the throat from biting predators.  This neck armor is called gular armor. ("Gular" means throat.)  

The actual skull of Stegosaurus was extremely small in comparison to the rest of the body.  The skull of Stegosaurus was narrow, and was tipped with a short beak, which the dinosaur used to clip vegetation.  This food then would have been processed with Stegosaurus' small teeth further down into the mouth, which were also adapted for clipping and shearing vegetation.

Skeletal mount of Stegosaurus showcasing the gular armor.

At the opposite end of the body, at the very tip of the tail, Stegosaurus possessed four long spikes.  Stegosaurus would have been able to swing its tail around with deadly accuracy to keep any potential predators at bay if it was ever attacked.  Since Stegosaurus' hind limbs were so much longer than its front limbs, its center of gravity was near its hips rather than closer to the rib cage like it is with many other quadrupedal dinosaurs.  This would have enabled Stegosaurus to use its front limbs to help it rotate its body around more rapidly than one would expect from an animal of that size, greatly increasing its tail-swinging range.  This makes sense since potential predators would likely be aiming for its head and trying to specifically avoid its tail.

Tail of Stegosaurus.

 The pelvis of Stegosaurus also possessed an odd hollow section which is still somewhat of a mystery to scientists.  At first, this area was believed to be the site of a swelling of nerves, which could have acted as a "second brain" to control the animal's back half, since the actual brain was so small.  Scientists now know this is untrue and that this area appears to be for storing glycogen, a kind of molecule which animals can use for energy.  Glycogen bodies, similar to the one found in Stegosaurus', pelvis can also be found in the hips of modern birds and other reptiles.

That is all for this week!  As always feel free to comment below or on our facebook page!  Have a particular beast you would like to see painted and reviewed?  Let me know and I will add it to the list!


Buchholz (née Giffin) EB (1990). "Gross Spinal Anatomy and Limb Use in Living and Fossil Reptiles". Paleobiology 16: 448–58.

Buffrénil (1986). "Growth and Function of Stegosaurus Plates". Paleobiology 12: 459–73.

Carpenter K, Sanders F, McWhinney L, Wood L (2005). "Evidence for predator-prey relationships: Examples for Allosaurus and Stegosaurus.". In Carpenter, Kenneth(ed). The Carnivorous Dinosaurs. Indiana University Press. pp. 325–50. ISBN 0-253-34539-1.

Czerkas SA (1987). "A Reevaluation of the Plate Arrangement on Stegosaurus stenops". In Czerkas SJ, Olson EC. Dinosaurs Past & Present, Vol 2. University of Washington Press, Seattle. pp. 82–99. ISBN.

Lull, R. S. "The Armor of Stegosaurus." American Journal of Science S4-29.171 (1910): 201-10. Web. 

Saitta ET (2015) Evidence for Sexual Dimorphism in the Plated Dinosaur Stegosaurus mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Upper Jurassic) of Western USA. PLoS ONE 10(4): e0123503. doi:10.1371/journal.pone.0123503