Spinosaurus: Beast of the Week

Make way (lots of room...back up more...keep going...keep going...backbackbackback) for the mighty Spinosaurus Aegyptiacus!

Spinosaurus was a meat-eating dinosaur that lived in what is now Africa, including Egypt, Morocco, and Niger during the late Cretaceous Period, about 97-95 million years ago.  It was a massive animal, the biggest known individuals possibly measuring 49 feet (about 15m) long from snout to tail as an adult, making it the longest meat-eating dinosaur known to science.  The genus name, Spinosaurus, translates to "Spined reptile" in reference to the extremely long neural arches on it's back vertebrae. (We have neural arches too, just smaller.  If you run your finger down your spine, you can feel them.) Some of these spines were almost six feet tall, giving the animal a very striking profile in life.

Life reconstruction of a Spinosaurus aegyptiacus ambush hunting a crocodile while underwater by Christopher DiPiazza.

Spinosaurus has one of the richest histories behind its discovery.  It was first unearthed back in 1912 and published in 1915 by German Paleontologist, Ernst Stromer.  Back then all he had to work with was very fragmented remains including a part of a lower jaw, some vertebrae, and a few ribs, not enough to know for sure what the whole animal looked like, but certainly enough to tell it was something new and exciting.  For decades the remains of Spinosaurus remained in a museum in Munich, Germany, on display.  During World War II, allied forces bombed the area where this museum was.  Luckily some small fossils, including the first discovered Pterodactylus, and arguably the most valuable fossil in the world, Archaeopteryx, were able to be evacuated ahead of time but the poor bones of Spinosaurus were destroyed.  For decades the world had no real Spinosaurus fossils to study beyond the photographs and drawings left behind of the originals and small bits and pieces that didn't give any real new information found here and there every so often.  In fact, Spinosaurus teeth are actually quite common and are frequently sold in fossil and mineral stores.

Illustration of the original fossils found of Spinosaurus from Ernst Stromer's 1915 publication.  You can see three of the vertebrae with the tall neural arches on the left and the lower jaw piece on the lower right.  The straight, cone-shaped teeth are illustrated larger above the jaw.

It wasn't until the year 2005 that another big piece of Spinosaurus was found.  Italian Scientists digging in Morocco found pieces of a Spinosaurus skull, including most of the snout and the nostrils.  This showed that Spinosaurus had a much narrower snout than previously thought.  Then, this past year in 2014, paleontologist, Nizar Ibrahim, published a paper about even more material from this amazing animal, which included more of the spine and the hind legs that he and his team had uncovered in Morocco.  It was this discovery that changed Spinosaurus' image from unique to something that looks more at home in mythology. (Yes, even by dinosaur standards.)

Spinosaurus had many unique features about it that pretty much break all the rules of what we thought we knew about theropod dinosaurs.  We will start with the head and work our way back.  Spinosaurus belongs to a family of dinosaurs called spinosauridae (named after it, the first known member) which are all characterized by having very long, narrow snouts.  Their snouts are often compared to those of modern crocodiles, but this is mostly a superficial resemblance since they aren't mechanically that similar.  Spinosaurids all had pointed, cone-shaped teeth, and their nostrils were not at the tip of the snout, but higher up towards the middle.  These characteristics led scientists to believe that spinosaurids were adapted to hunting fish.  Their arms were powerful and possessed three fingers on each hand.  Digit one of each hand had an enormous, hooked claw on it, much larger than the other two.  This was probably another adaptation to hunting.

Spinosaurus skeletal mount on display at the National Geographic Museum.

As stated before, Spinosaurus had extremely long neural arches on its back that would have been covered in skin and other living tissue when the dinosaur was alive, giving it a sail-like appearance.  This is not completely unlike the sail of the also famous mammal-like reptile (and totally not a dinosaur), Dimetrodon, which lived millions of years earlier.  Despite the similarities, these two animals are not directly related to each other and is just another beautiful example of convergent evolution.  The function of the sail on Spinosaurus is something nobody can quite agree on.  There are always those who will say an adaptation like that was for display within the species.  Others believe it was to help regulate the animal's body temperature, having possibly been rich in blood vessels in life and easier to heat up in the sun.  This is a good hypothesis especially if Spinosaurus was spending a lot of its time near or in the water to hunt.  Bodies of water always cool an area down, conducting warmth more slowly than land does, and being in or near it can lower an animal's body temperature to the point where it needs to leave the area to warm up again.  Those that don't leave the water would need adaptations to help them stay warmer longer.  Think about ducks and geese (which produce their own heat, being endothermic) and how they have a layer down feathers against their bodies.  Also think about modern Marine Iguanas (cannot produce their own body heat as ectothermic) and how they can only stay in the ocean for a few minutes at a time until they need to haul out on shore to absorb more warmth from the sun.  A good way to experience this is going out on a boat during the summer, it may be hot on the land but the farther out the boat goes, the more everyone wishes they brought a jacket.  The sail on Spinosaurus may have been a way for it to increase its surface area to warm itself up in the sun as efficiently as possible while still being able to hang out in places with lots of water for long periods of time. 

For decades, everyone just assumed Spinosaurus' legs were the same as those of its close relatives like Suchomimus and Baryonyx, fellow spinosaurids which scientists had more complete skeletons of and were relatively typical for theropods, long and powerful, supporting an obligatory bipedal posture.  A discovery of more Spinosaurus bones that was published in 2014 changed all that, however.  According to what was unearthed,  Spinosaurus had short legs...like really short legs.  Initially some people proposed Spinosaurus may have been a quadroped, possibly walking on its knuckles to keep its claws sharp, making it the only known quadrupedal theropod known in history.  (which is mostly not accepted.)  Right after this publication was released many people thought that perhaps the paleontologists suggesting these odd proportions had not considered maybe their new leg material was from a juvenile specimen and was not scaled up to the other already-known material which was from adults.  The problem with that argument is that the new leg material was found with other bones that were almost certainly all from the same individual, including some of the long spine vertebrae, which were big just like the other adult-sized material already on the fossil record from Spinosaurus.  The mighty Spinosaurus really did have the proportions close to that of a dachshund mythical Asian Dragon!

Despite its proportionally small legs, assuming its front limbs were similarly built to those of any other theropod's, Spinosaurus still almost certainly only walked on its hind legs.  It was likely slower and clumsy on land, possibly dragging its tail for extra support.

The 2014 discoveries didn't end with the legs, however.  Spinosaurus' feet were unique in that the toes were flatter and wider than what is typically seen in theropod dinosaurs, except for certain birds that have webbed toes for paddling, like penguins and ducks, suggesting Spinosaurus had webbed toes as well.   Spinosaurus' bones were also not hollow like those of most other theropods.  Instead they were dense and solid.  Penguins are another kind of theropod with solid bones so that they can swim under water more easily.  These two amazing discoveries, combined with what we already knew about Spinosaurus' snout and teeth, lead us to believe that this dinosaur was specially adapted for a life in the water.  Even having short legs makes more sense.  Think of the legs of hippos and otters.  These are animals that, although capable getting around on land, really move best when under the water.  Also, if Spinosaurus was under the water a lot, having a large sail on its back which may have been more often poking above the surface to soak up some warmth from the sun, it would have been able to help prevent its body from getting too cold.  All of these strange adaptations which confused scientists for many years all start to come together a little more with the help of just a few more new (yet strange) discoveries!

In 2020 yet another previously absent part of Spinosaurus was published on, the tail, which was also unique.  The neural arches and chevrons (bony protrusions on the top and bottom of the vertebra) on the tail bones were greatly extended, implying Spinosaurus had a broad, paddle-shaped tail, like a gigantic newt! This actually makes sense since by this point scientists already had reason to think Spinosaurus was spending most of its time in the water.  This tail would have only helped Spinosaurus to move around in its environment better.

Photograph of Spinosaurus' newly published tail bones from Ibrahim's 2020 paper.

Finally, if Spinosaurus was an aquatic dinosaur, it would also make more sense of what we know about its environment.  The areas that Spinosaurus bones have been discovered in have a lot of other fossils in them too, most notably lots of other species of meat-eating dinosaur, and also lots of aquatic creatures like fish, turtles, and crocodiles.  Before this year, it was assumed that Spinosaurus was so large because it was competing with other predatory dinosaurs, like the slightly smaller allosauroid, called Carcharadontosaurus, and various ceratosaurs.  Despite this, it still always seemed strange to have that many predators but not so many plant-eating dinosaurs in the community.  Now we know that Spinosaurus probably evolved in a completely different direction to avoid competition altogether.  It was more likely an aquatic predator, spending more of its time in the water hunting fish and other aquatic prey.  This way it wasn't occupying the same space, nor was it competing for the same food as its fellow theropods.  Since it was the only dinosaur to exploit such a unique niche, it could have evolved to be extremely large without any competition.

Spinosaurus running under the water like a boss...or a hippo.  I have my doubts if this dinosaur was actually good at swimming, through the water like a crocodile, but walking/running around under it, sure, given its anatomy.

Note I haven't specifically said Spinosaurus would have been swimming underwater.  That's because despite how there is much evidence that suggests it spent time in and near the water, there is evidence that without contradicting any of this, suggests it was a poor swimmer.  That sounds contradictory at first but consider the fact that hippos don't really swim, despite spending most of their time in the water.  Birds, like herons, storks, and cranes also don't swim well, while spending lots of time in and around the water.  A paper published in 2021 investigated Spinosaurus' body proportions to test how well it would actually be able to swim in deep water, and found that because of its sail and upright dinosaurian posture (having its legs directly underneath the body) it would have been very top heavy and therefore at best a very clumsy swimmer.  That being said, it still appears to be adapted for living near and in the water, it was just more likely wading or walking around in it, not openly swimming.

Image of the skull of Spinosaurus mirabilis by Daniel Vidal.  Areas highlighted in red are what was actually found.  Gray areas are based on other spinosaurs to fill the gaps.

Finally, in 2026, a completely new species of Spinosaurus was published on!  The new species, called Spinosaurus mirabilis, was discovered in what is now Niger, Africa.  It was the younger of the two Spinosaurus species, living 95 million years ago, and its environment would have been more inland, farther away from the ocean.  It is only known from a skull, a few vertebra, and a leg bone, which is enough to identify it as a new species.  It's jaws were skinner than those of its older, Egyptian cousins'.  It also would have had proportionally slightly longer legs. (not a high bar just sayin) Most interesting, however, is probably the huge crescent-shaped bony crest growing out of the middle of the forehead.  The texture of the bone of this crest is highly vascularized, which means there was likely a layer of keratin over it in life and could have been much longer than what the bone core alone shows.  

sketches of both species of Spinosaurus known to science.

Spinosaurus holds many titles as a dinosaur.  Not only was it the longest known meat-eater, it was also the first known non-avian dinosaur to have actually been at least somewhat aquatic.  This long-snouted, short-legged, webbed-footed, sail-backed, paddle-tailed beastie would have truly been a sight to behold!

References

dal Sasso, C.; Maganuco, S.; Buffetaut, E.; Mendez, M.A. (2005). "New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities". Journal of Vertebrate Paleontology 25 (4): 888–896. 

Hone; Holtz, Thomas R. Jr. (2021). "Evaluating the ecology of Spinosaurus: Shoreline generalist or aquatic pursuit specialist?". Palaeontologia Electronica. 24

Ibrahim, N.; Sereno, P. C.; Dal Sasso, C.; Maganuco, S.; Fabbri, M.; Martill, D. M.; Zouhri, S.; Myhrvold, N.; Iurino, D. A. (2014). "Semiaquatic adaptations in a giant predatory dinosaur". Science.

Ibrahim, Nizar; Maganuco, Simone; Dal Sasso, Cristiano; Fabbri, Matteo; Auditore, Marco; Bindellini, Gabriele; Martill, David M.; Zouhri, Samir; Mattarelli, Diego A.; Unwin, David M.; Wiemann, Jasmina (2020). "Tail-propelled aquatic locomotion in a theropod dinosaur". Nature. 581: 1–4. 

Sereno et al (2026) "Scimitar-crested Spinosaurus species from the Sahara caps stepwise spinosaurid radiation" Science. vo391 issue6787: 

Smith, J.B.; Lamanna, M.C.; Mayr, H.; and Lacovara, K.J. (2006). "New information regarding the holotype of Spinosaurus aegyptiacus Stromer, 1915". Journal of Paleontology 80 (2): 400–406. 

Stromer, E. (1915). "Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens. II. Wirbeltier-Reste der Baharije-Stufe (unterstes Cenoman). 3. Das Original des Theropoden Spinosaurus aegyptiacus nov. gen., nov. spec". Abhandlungen der Königlich Bayerischen Akademie der Wissenschaften, Mathematisch-physikalische Klasse (in German) 28 (3): 1–32.

Corythosaurus: Beast of the Week

This week we will take a look at a well known duckbill dinosaur.  Enter Corythosaurus!  

Corythosaurus was a plant eater that belonged to the lambiosaurine group within the family, Hadrosauridae. (duckbills)  Lambiosaurine hadrosaurs typically had hollow crests on their heads and narrower beaks compared to other kinds hadrosaurs.  It was closely related to other lambiosaurine hadrosaurs such as Parasaurolophus, Hypacrosaurus, Lambeosaurus, and Velafrons.  It lived in what is now Alberta, Canada, during the Late Cretaceous period, between 77 and 76 million years ago.  Corythosaurus could have measured up to 30 feet (about 9m) long from beak to tail and its genus name translates to "helmet lizard/reptile" because of its tall disc-shaped crest, which in profile resembles a helmet.  

Corythosaurus cassuarius life reconstruction in watercolors by Christopher DiPiazza.

Corythosaurus actually includes two distinct species.  Corythosaurus cassuarius was had a larger crest and was found in rocks that about 1 million years older, and Corythosaurus intermedius, which had a slightly smaller crest and was found in slightly younger rocks.

There are two species of Corythosaurus currently known.

The crest of Corythosaurus, despite the name, wasn't really a helmet.  (Although another group of dinosaurs, the pachycephalosaurs, did have skulls that were more literally helmet-like.)  Its crest was semi-circular, and hollow on the inside, housing a network of tubes that likely connected the animal's nostrils to its windpipe.  Originally scientists thought this was an adaptation for a semi-aquatic lifestyle, but they were most likely for amplifying the sounds that Corythosaurus made.  Corythosaurus could inhale through its nostrils, where the air would pass through the series of tubes before being released through the mouth, thus producing a louder sound, much like the inner workings of trumpets or other brass wind instruments.  Sound was probably a very important method of communication for Corythosaurus and its relatives.  

Juvenile Corythosaurus skull on display at the Royal Ontario Museum in Canada.  Note the proportionally much smaller crest.

Thanks to a beautifully preserved specimen of Corythosaurus, paleontologists were able to discover highly developed inner ear bone, further supporting this idea.  The Corythosaurus genus used to consist of several species with similar crests of varying sizes.  It was later realized, however, that these specimens were more likely different ages and sexes of the same species since they were all found in the same area together and the largest specimens had the largest crests.  Furthermore, if adult male and female Corythosaurus also had different looking crests, they would have had different sounding calls.  We can see this today with their modern relatives, the birds and crocodilians, as well as other kinds of animals like frogs and insects.  It is possible lambiosaurid dinosaurs practiced similar behaviors, using sound to announce their age and sex over longer distances than they could with just looks.  Since more than one different kinds of these duckbills would have lived in the same place during the same time (Corythosaurus and Parasaurolophus, for instance.) it would make sense that each would have different crests to make different sounds and thus, preventing any identity confusion just like all the kinds of birds and frogs within the same community each have their unique calls today. 

Corythosaurus skeleton, which includes patches of skin and other soft tissue, on display at the American Museum of Natural History in New York.

Corythosaurus is amongst the most well-studied of the non-avian dinosaurs because one specimen that was unearthed in the early 1900s not only included nearly every single bone in the skeleton, but it also preserved skin, organs, and even the animal's last meal!  Thanks to this individual, now on display at the American Museum of Natural History in New York, we know that Corythosaurus would have had pebbly, mosaic-like scales that varied in size to form patterns on its skin.  It also had padding under its feet and hands, which scientists in the early 1900s originally thought would have been webbing for swimming, further supporting the now debunked aquatic hypothesis.  In the stomach cavity were the remains of conifer needles, sticks, and seeds.  These plant foods would have been plucked with Corythosaurus' narrow, flat beak and chewed up with its hundreds of tiny teeth lining the back of its jaws. 

When alive, Corythosaurus would have coexisted with many other well-known dinosaurs, like close relative, Parasaurolophus, the horned ceratopsian, Chasmosaurus and, the tyrannosaur, Gorgosaurus.

That is all for this week!  As always feel free to comment below!

References

Barden, Holly. "Sexual dimorphism in dinosaurs: a review of the evidence and approaches" (PDF). APS 402 Dissertation. University of Sheffield. Retrieved 13 August 2013.

Bell, P. R. (2012). "Standardized Terminology and Potential Taxonomic Utility for Hadrosaurid Skin Impressions: A Case Study for Saurolophus from Canada and Mongolia". In Farke, Andrew A. PLoS ONE 7 (2): e31295.

Dodson, P. (1975). "Taxonomic implications of relative growth in lambeosaurine dinosaurs". Systematic Zoology 24 (1): 37–54.

Torvosaurus: Beast of the Week

Today we are going to look at a huge Jurassic predatory dinosaur, Torvosaurus tanneri! 

Torvosaurus lived about 150 million years ago during the Late Jurassic period. Its bones have been unearthed in Colorado, USA, Portugal, and possibly Germany (Europe and North America were not as vastly separated back then, remember, so a lot of the dinosaurs on each of them from that time shared recent ancestors).  From nose to tail it measured up to 36 feet (about 11m) and would have been among the largest, most formidable meat eaters of its time.  The name, Torvosaurus, translates to "Fierce Reptile".
  

Torvosaurus in watercolors life reconstruction by Christopher DiPiazza.

Torvosaurus is a member of the megalosaurid family, and is closely related to the more famous, Megalosaurus.  Megalosaurids are mostly known from the middle and late Jurassic period, and are not super well known, since not many of them have ever been found compared to most other dinosaurs.  That being said they tend to have long, low skulls with large robust teeth with serrations for cutting meat.  Their arms were powerful with three fingers, tipped with proportionally large hooked claws.  Their legs also tend to be proportionally shorter.  The more popular spinosaurs are currently thought to be closely related to the megalosaurids (both are classified within the broader megalosauroid group), and it is likely that the megalosaurids gave rise to the first spinosaurs, although we currently don't have any obvious transition fossils that demonstrate this yet.

Torvosaurus, itself, currently contains two distinct species.  Torvosaurus tanneri from North America, and the slightly larger Torvosaurus gurneyi, from Europe.

Torvosaurus tanneri Skeletal mount on display at the Mesalands Dinosaur Museum in New Mexico.

Torvosaurus is especially important to paleontology because its one of the few dinosaurs paleontologists have actually found eggs from.  The nest of eggs found in Portugal, appeared to have been methodically buried in life by the parent.  They were close to hatching because the bones of embryos were also found inside, making them the oldest theropod dinosaur embryos known to science.  

When alive Torvosaurus tanneri would have coexisted with many famous dinosaurs, including the long-necked sauropods, Apatosaurus, Brontosaurus, Diplodocus, Barosaurus, Camarasaurus, and Braciosaurus, the armored Stegosaurus and Gargoyleosaurus, and the ornithopod Camptosaurus, all of which it may have hunted.  It also would have coexisted with fellow predators, Allosaurus and Ceratosaurus.  In Europe Torvosaurus gurneyi lived alongside Allosaurus (European species) and the long-necked stegosaur, Dacentrurus, to name just a few.

References

Araújo, Ricardo; Castanhinha, Rui; Martins, Rui M. S.; Mateus, Octávio; Hendrickx, Christophe; Beckmann, F.; Schell, N.; Alves, L. C. (2013). "Filling the gaps of dinosaur eggshell phylogeny: Late Jurassic Theropod clutch with embryos from Portugal". Scientific Reports. 1924 1924: 8.

Chure, Daniel J.; Litwin, Ron; Hasiotis, Stephen T.; Evanoff, Emmett; and Carpenter, Kenneth (2006). "The fauna and flora of the Morrison Formation: 2006". In Foster, John R.; and Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin, 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 233–248.

Mateus, O., Walen, A., and Antunes, M.T. (2006). "The large theropod fauna of the Lourinha Formation (Portugal) and its similarity to that of the Morrison Formation, with a description of a new species of Allosaurus." New Mexico Museum of Natural History and Science Bulletin, 36.

 Mateus, O., & Antunes, M. T. (2000). Torvosaurus sp.(Dinosauria: Theropoda) in the late Jurassic of Portugal. In I Congresso Ibérico de Paleontologia/XVI Jornadas de la Sociedad Española de Paleontología (pp. 115-117).

Ribeiro, Vasco; Mateus, Octávio; Holwerda, Femke; Araújo, Ricardo; Castanhinha, Rui (March 4, 2014). "Two new theropod egg sites from the Late Jurassic Lourinhã Formation, Portugal". Historical Biology. 26 (2): 206–217.

Hesperosuchus: Beast of the Week

This week we will be checking out a relative of modern crocodilians that has tricked scientists multiple times!  Enter Hesperosuchus agilis!

Hesperosuchus was a pseudosuchian (related to crocodilians) that lived in what is now Arizona and New Mexico, USA, during the late Triassic period, about 210 million years ago.  It would have been a meat-eater and from snout to tail the most complete skeleton measures about four feet (1.2m) but other fossils suggest it could have grown larger, up to about six feet (1.8m).  The genus name translates to "Western Crocodile" due to where it was fond and its relation to modern crocodilians, and the species name to "agile" in reference to how it was likely a swift and agile runner in life.

Hesperosuchus stealing an egg from the dinosaur, Coelophysis. Watercolor reconstruction by Christopher DiPiazza.

When Hesperosuchus was first discovered it was initially thought to be a kind of dinosaur.  This is due to the fact that it had hollow bones, a trait that at that time was not known to be in pseudosuchians.  Hesperosuchus is just one of many examples of how the group that includes modern crocodilians was extremely diverse and evolved into many different forms during the Mesozoic, especially the Triassic.  Not only did Hesperosuchus have hollow bones, but it also possessed fully erect upright posture with long slender limbs.  It may have even been able to run on its hind legs.  

Hesperosuchus also possessed a laterally compressed skull (again like most theropod dinosaurs) which is in contrast to modern crocodilians, all of which have skulls that are more flattened top to bottom, an adaptation for spending much of their time in the water.  Aquatic crocodilians had not yet evolved in the Triassic and all of their closest relatives from then, like Hesperosuchus, were actually land animals.  Hesperosuchus possessed pointed teeth that were serrated on both the front and rear edges, implying it at meat when alive, probably focusing on snatching up small animals.  Like modern crocodiles it had a slight notch in its snout where its bottom teeth interlocked with its top jaws.

Hesperosuchus skull image from the 2012 paper by Nesbitt et al., referenced below.

 Like most pseudosuchians, Hesperosuchus also had osteoderms, bony armor that exists in the skin, in the form of two rows of almost square-shaped scutes running down its back.  This was likely for defense against predators, of which there were many Hesperosuchus had to be weary of.  That being said it appears this armor may not have protected Hesperosuchuchus every time since there is a famous skeleton of the dinosaur, Coelophysis, has what appears to be bones from Hesperosuchus (which were initially thought to be from a baby Coelophysis) inside its stomach cavity. 

When alive, Hesperosuchus would have lived alongside other pseudosuchians, like the herbivorous aetosaurs and shuvosaurs, and the large  carnivore, Postosuchus.  It also would have shared its environment with the not-crocodile-but-crocodile-resembling phytosaurs, as well as the carnivorous dinosaur, Coelophysis.  

References

Clark, James M.; Sues, Hans-Dieter; Berman, David S. (19 January 2001). "A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs". Journal of Vertebrate Paleontology. 20 (4): 683–704.

Colbert, E. H. 1952. A pseudosuchian reptile from Arizona. Bulletin of the American Museum of Natural History 99:561–592.

Nesbitt, Sterling J.; Turner, Alan H.; Erickson, Gregory M.; Norell, Mark A. (22 December 2006). "Prey choice and cannibalistic behaviour in the theropod Coelophysis". Proceedings of the Royal Society B. 2 (4): 611–4.

Nesbitt, Sterling J.; Turner, Alan H.; Weinbaum, Jonathan C. (September 2012). "A survey of skeletal elements in the orbit of Pseudosuchia and the origin of the crocodylian palpebral". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 103 (3–4): 365–381.

Pachycephalosaurus: Beast of the Week

This week we shall be checking out a well-known dinosaur with an iconic skull.  This dinosaur is one of my personal all time favorites.  I will never forget seeing it's awesome representation in The Lost World: Jurassic Park in the movie theater when I was only eight years old.  The way it smashed that truck...it changed me.  Say hello to Pachycephalosaurus wyomingensis!

Pachycephalosaurus life reconstruction in watercolor by Christopher DiPiazza.

Pachycephalosaurus was the largest known member of the pachycephalosaur family at about 15 feet (4.5m) long from beak to tail.  In life, it was most likely a plant-eater, but some have suggested it may have supplemented its diet with meat in the form of small animals and possibly carrion.  The genus name, Pachycephalosaurus, translates to "Thick Head Lizard" in reference to the dinosaur's skull, which is almost ten inches thick in the biggest specimens.  Pachycephalosaurus lived during the very end of the Cretaceous period, between 70 and 66 million years ago, in what is now the Western United States, specifically Montana, South Dakota, and Wyoming.  In fact, its full genus and species name is Pachycephalosaurus wyomingensis, in reference to this.  
Sadly, none of Pachycephalosaurus' body beyond the skull has ever been discovered.  However, we can guess what the rest of the body looked like thanks to more complete skeletons of other kinds of Pachycephalosaurids it was closely related to.  It was most likely a biped, with short front arms, each ending in a five-fingered hand.  The hips were probably relatively wide with a thick tail base.  The end of the tail would have been stiffened with ossified tendons. (bony rod-like structures found in the tails of many dinosaurs)

Pachycephalosaurus' head was its trademark feature, however.  Like I said earlier, its skull was extremely thick, and made of solid bone, encasing a relatively small brain, forming a round, dome-shaped cranium.  Around the back of the head, over the eyes, and on the top of the snout, were a series of short horns.  The mouth was tipped with a short beak and the jaws were lined teeth were small and leaf-shaped, most likely for shredding tough plants.  There were also a set of unusual pointed teeth in the front of the jaws which experts are still about the use of, but are the main reason why some have suggested an omnivorous diet.  The eye sockets of Pachycephalosaurus skulls are large, and face partially forward.  This indicates that this dinosaur would have had good vision and also had a sense of depth perception in life.  The heavy skull would have been held up by a short, muscular neck.

Pachycephalosurus skull on display at the American Museum of Natural History in New York.

The exact purpose of Pachycephalosaurus' thick skull has been debated much over the years.  The most common idea, especially in the beginning, was that rival Pachycephalosaurus would have ran into each other, head first, like modern day rams do, to establish dominance.  This idea became so popular, that you would be hard pressed to find imagery of Pachycephalosaurusdoing anything other than running with its head down about to ram something in every bit of media it was included in.  More recently, however, there have been paleontologists who have challenged this, saying the shape of Pachycephalosaurus' skull would not have allowed it to have sustained crashing into other hard objects at a high force without causing serious injury.  Many believed that the large domes of 

Pachycephalosaurus were mostly for display within the species instead.  Was it really possible that those thick skulls were just for show, though?  It seems unlikely considering how thick they were.  (Something that isn't entirely visual.)  Finally in 2013, a study on the skulls of pachycephalosaurs discovered evidence of injuries that had healed over on the skulls of many individual specimens.  In fact, the kind of bone that the skulls of pachycephalosaurs were made of seems to have been especially good at healing and repairing itself after damage was inflicted on them.  This supported the idea, once again, that Pachycephalosaurus and its kin were indeed using their skulls as weapons.  That being said, they may have swung their heads into each other at close quarters, instead of charging into each other from a running distance.  You can observe modern giraffes (like in the video below), and many other animals that sport weapons on their heads, combating each other in the same way.  If this indeed was the method used for Pachycephalosaurus fighting, the small horns on the sides of the head could have been utilized as painful weapons backed up be the force caused by the mass of the thick skull. 

Some still argue that using their heads as weapons would have injured Pachycephalosaurus in life too much and was thus, is still an unrealistic idea or real life.  These folks need to remember, however, that many animals do get injured quite a lot when fighting rivals.  In fact, many species of animals become permanently maimed, or even die fighting peers for dominance.  If a Pachycephalosaurus did hurt itself or die in combat with another back in the Cretaceous, it would have just been another example of natural selection in the works. Evolution is never perfect.  If it was nothing would ever go extinct!

Pachycephalosaurus is believed to have changed its form drastically as it matured into an adult by certain paleontologists.  The other two, slightly smaller, pachycephalosaurs, Dracorex (sported lots of horns but no dome) and Stygimoloch (long horns and a smaller dome), are believed by some to have actually been juvenile and subadult forms, respectively, of Pachycephalosaurus, which would have been the mature adult.  If this is the case, Pachycephalosaurus would have had no dome at all when young, and its horns would have become shorter, being absorbed into the growing thickness of the skull as it matured.  In contrast to this, the more recently discovered close relative, Zavacephale, was a juvenile when it died and had a fully formed dome.  This doesn't necessarily disprove the idea about Pachycephalosaurus' juvenile state (different kinds of animals grow can grow differently) but it is definitely worth noting. Since the number of pachycephalosaur specimens on the fossil record is still very limited, this hypothesis still needs a more evidence to be verified.

Quick sketch of Dracorex, Stygimoloch, and Pachycephalosaurus, which are thought by many to be different growth stages of the same species.  This might not be true, or maybe true for two of the three.  More fossils and research may tell in the future.

When alive Pachycephalosaurus would have coexisted with many other well known dinosaurs, including Triceratops, Edmontosaurus, Ankylosaurus, Thescelosaurus, Acheroraptor, Anzu, Pectinodon, Ornithomimus, and Tyrannosaurus to name just a handful of names.

That is all for this week!  As always feel free to comment below!

References

Carpenter, Kenneth (1 December 1997). "Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior" (PDF). Contributions to Geology 32 (1): 19–25.

Chinzorig, Tsogtbaatar; Takasaki, Ryuji; Yoshida, Junki; Tucker, Ryan T.; Buyantegsh, Batsaikhan; Mainbayar, Buuvei; Tsogtbaatar, Khishigjav; Zanno, Lindsay E. (2025-09-17). "A domed pachycephalosaur from the early Cretaceous of Mongolia". Nature: 1–8.

Horner J.R. and Goodwin, M.B. (2009). "Extreme cranial ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus." PLoS ONE, 4(10): e7626.

Peterson, J. E.; Vittore, C. P. (2012). Farke, Andrew A, ed. "Cranial Pathologies in a Specimen of Pachycephalosaurus". PLoS ONE 7 (4): e36227.

Peterson JE, Dischler C, Longrich NR (2013) Distributions of Cranial Pathologies Provide Evidence for Head-Butting in Dome-Headed Dinosaurs (Pachycephalosauridae). PLoS ONE 8(7): e68620. doi:10.1371/journal.pone.0068620

Sullivan, Robert M. (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria:Ornithischia)" (PDF). Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35: 347–366.

Ajkaceratops: Beast of the Week

This week we will be checking out a unique dinosaur that lived in an even more unique environment.  Let's talk about Ajkaceratops kozmai!

Ajkaceratops was a small plant-eating dinosaur that lived in what is now Hungary during the late Cretaceous period, about 85 million years ago.  From beak to tail it likely measured a little over 3 feet (1m) long.  The genus name translates to "Ajka Horned Face", referencing the town in Hungary near where its fossils were found.  

Watercolor of Ajkaceratops by Christopher DiPiazza.

Ajkaceratops was initially published in 2010 from the front of the beak. The beak itself was curved and pointed, much like a ceratopsian, the "horned dinosaurs", like Triceratops, so it was placed in that family alongside dinosaurs like Protoceratops.  Later on, the beak was re-examined and many unique traits were noted about it compared to other ceratopsians, like the fact that it has a more rounded cross-section and its pitted texture.  It also appears to be completely fused to the rest of the jaw, which is only seen in mature members of the larger members of the ceratopsian group, like Triceratops.  Based on this it was deemed not a ceratopsian at all, but rather an unusual kind of ornithithopod dinosaur, related to Zalmoxes, which was also found in Europe.  Then most recently more fossils from Ajkaceratops were found, including a more complete skull, and in 2026 they were published on.  Based on this new material it was found to be a ceratopsian after all.  Not only that but a few members of the ornithopod group it was previously grouped with, called the rhabdodontids, were also thought to be unusual ceratopsians as well.  This is an important determination since prior to this, ceratopsians were only ever found in North America and Asia, and it was odd that they wouldn't be in Europe.  Ajkaceratops proves they were.  

Ajkaceratops' skull.  Image from the most recent paper by Czepinski et al. referenced below.

It's not surprising the identity of Ajkaceratops was not clear since it is indeed unusual for a ceratopsian.  As mentioned, it beak is extremely long, narrow, and curved, even for a ceratopsian, which are known for having curved beaks.  In fact, its whole skull is pretty elongated, and almost rectangular in profile.  As mentioned, the beak was completely fused to the rest of the jaw, and not a separate bone as it is in vast majority of other ceratopsians, called a rostral bone.  Lastly its extremely small size is also unusual especially for living in the late Cretaceous.  The teeth were more typical and appear to be ideal for shredding plants.  They show a high amount of wear on them, suggesting Ajkaceratops could have been regularly chomping through tougher plant material like twigs and pine needles.  

Teeth of Ajkaceratops.  Image from paper by Osi et at. referenced below.

The part of Hungary that Ajkaceratops was found in was actually an island when it was alive.  That part of Europe was known to be a series of island chains during that time, and paleontologists think the ancestors of Ajkaceratops may have actually have swam there from either Asia or North America. (since ceratopsians were living on both those continents already before Ajkaceratops' time) 

References

Czepiński, Łukasz; Madzia, Daniel (2024). "Osteology, phylogenetic affinities, and palaeobiogeographic significance of the bizarre ornithischian dinosaur Ajkaceratops kozmai from the Late Cretaceous European archipelago". Zoological Journal. 202 (4).

Ősi, Attila; Butler, R.J.; Weishampel, David B. (2010-05-27). "A Late Cretaceous ceratopsian dinosaur from Europe with Asian affinities". Nature. 465 (7297): 466–468.

Maidment, Susannah C. R.; Butler, Richard J.; Brusatte, Stephen L.; Meade, Luke E.; Augustin, Felix J.; Csiki-Sava, Zoltán; Ősi, Attila (2026-01-07). "A hidden diversity of ceratopsian dinosaurs in Late Cretaceous Europe". Nature: 1–7.

Parasaurolophus: Beast of the Week

This week we will be taking a look at a very popular duck-billed dinosaur.  Say hello to Parasaurolophus!  Parasaurolophus was a plant eater that lived in what is now North America during the Late Cretaceous, about 77 to 73 million years ago.  Parasaurolophus measured about 30 feet (9.1 meters) long from beak to tail, but certain incomplete specimens show evidence of having been a bit larger.  Parasaurolophus is most well-known for its long, curved crest that grew from the back of its head, giving it one of the most iconic profiles of any dinosaur.  The name Parasaurolophus translates to "Near Crested Lizard/Reptile" and is in reference to it being compared to another duck-billed dinosaur with a smaller crest, called Saurolophus (just "crested lizard/reptile"), which was discovered earlier.  Turns out that Parasaurolophus and Saurolophus, although both hadrosaurs (duck-billed dinosaurs), weren't really that closely related.  Parasaurolophus belongs to what is called the lambeosaurine branch of hadrosaurs which had hollow crests and narrower beaks, which Saurolophus did not have.  Parasaurolophus was much more closely related to Corythosaurus, Velafrons, and Tsintaosaurus, to name a few examples.

Parasaurolophus walkeri by Christopher DiPiazza.

There are actually a few different named species of Parasaurolophus.  The most well-recognized is called Parasaurolophus walkeri, and it lived in what is now Alberta, Canada, and would have coexisted with other well-known dinosaurs like Styracosaurus, Chasmosaurus, Struthiomimus, Corythosaurus, and Eouplocephalus.  From the southwestern United States, however, there was also Parasaurolophus tubicen, which is incompletely known, but was probably the largest species, and Parasaurolophus cyrtocristatus, which had a much shorter, more curved crest, and would have coexisted with (and ran away from) Teratophoneus.  

Parasaurolophus walkeri skull on display at the American Museum of Natural History in New York City.

At one time, some paleontologists made a hypothesis that Parasaurolophus cyrtocristatus was actually a female of one of the other two species, due to its smaller crest, but further research concluded this was probably not true since they did not live during the exact same time period.  This being said, it is not unreasonable to guess that the Parasaurolophus females could have had shorter crests anyway, since we can observe similar trends of sexual dimorphism (males and females look different) in other lambeosaurine hadrosaurids that are known from a bigger pool of specimens, like Corythosaurus.

Parasaurolophus cyrtocristatus skeleton on display at the Field Museum of Natural History, in Chicago.

In 2013, a specimen of a baby Parasaurolophus was published by scientists at the Raymond M. Alf Museum of Paleontology in California, shedding more light on the growth and development of this interesting dinosaur.  The specimen, which was just under six feet long from beak to tail (small when you consider how large it could have grown), is estimated to have only been one year old when it died.  Paleontologists could tell this by looking at the cross-section of a the dinosaur's bone and counting the ring-like patterns on the inside, similar to a tree. This specimen hadn't developed any rings yet at the time of its death.  Despite this, the tiny dinosaur's crest had already started to grow from the front of  its skull, between its eyes.  At the age that it died that specimen may have still been under it's parent's care, according to the information and evidence on the fossil record about other hadrosaurid mothers.

Fossil remains of the baby Parasaurolophus published in 2013.  Photograph is from Dr. Andrew Farke's paper, cited below.

The crest of Parasaurolophus, which is actually a huge extension of its nasal bones, starting at the very front of the skull, is its most notable characteristic and what gives it its iconic profile. (I will never forget one of my students referring to it as "that pickaxe-head dinosaur")  At first some people thought that hadrosaurs, like Parasaurolophus, were amphibious, and spent a lot of their time in the water because the skin that preserved around the toes of one specimen (an Edmontosaurus) that looks like webbing at first glance (it turned out to have been more like padding for walking) and the fact that they had flat bills like ducks (which weren't really that similar to a duck bills)  To go with this incorrect idea, some proposed the crest of Parasaurolophus was a snorkeling adaptation, since it was hollow on the inside and would have connected to the animal's airways.  A more likely reason for this crest, however, is to help the animal to produce a distinctive sound.  the dinosaur would inhale through it's nose, the air would pass through the tubes inside the crest and become amplified, then released through the mouth as a loud bellow.  The mechanics would have been very similar to playing a trombone, actually.  With the help of some more modern technology, scientists were able to scan the inside of a Parasaurolophus crest and reproduce what they might have sounded like based on their findings.  According to what they came up with, the sounds of Parasaurolophus would have been pretty eerie!  Check out the audio below!

The fact that Parasaurolophus probably used its crest to make sounds, combined with the fact that we know the young had short crests, leads us to the undeniable fact that the young and adults must have sounded different.  (young would have been higher pitched)  This makes sense for communication reasons.  A mom would have an easier time finding her babies by their calls if they ever became separated.  You can actually observe very similar baby to parent vocalizations in modern birds(dinosaurs) and crocodilians.  The sounds were also probably a good way for adults to attract mates and establish dominance, which can also be seen in a myriad of modern animals.

There was more to Parasaurolophus than just the crest, remember.  In the front of its mouth, it had a flat, and relatively narrow beak, which would have been good for selectively foraging its favorite plants to eat.  This is different from the widened, bills of other hadrosaurs, like Edmontosaurus', which were probably more adapted for a generalist plant diet.  Like all hadrosaurs, Parasaurolophus had hundreds of tiny teeth in the back of its mouth, which were tightly packed together to form what is called a dental battery.  these structures were perfect for chewing tough plants much like molars.

Parasaurolophus had relatively long arms and could have walked on four or two limbs depending on how fast it wanted to move.  Its vertebrae had tall neural arches, especially on its back, which would have given it a hump-like profile in life.  Like all hadrosaurs, Parasaurolophus' tail was especially thick, and also pretty rigid.  The tail would have probably been its weapon of choice if it needed to defend itself.

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

References

Barden, Holly. "Sexual dimorphism in dinosaurs: a review of the evidence and approaches" (PDF). APS 402 Dissertation. University of Sheffield.

Currie, Phillip J.; Koppelhus, Eva, eds. (2005). Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Bloomington: Indiana University Press. pp. 312–348. ISBN 0-253-34595-2.

Evans, David C. "Nasal Cavity Homologies and Cranial Crest Function in Lambeosaurine Dinosaurs." Paleobiology 32.1 (2006): 109-25. Web.

Farke, Andrew A., Derek J. Chok, Annisa Herrero, Brandon Scolieri, and Sarah Werning. "Ontogeny in the Tube-crested Dinosaur(Hadrosauridae) and Heterochrony in Hadrosaurids." PeerJ 1 (2013): E182.

Sullivan, R.M.; Lucas, S.G. (2006). "The Kirtlandian Land-Vertebrate "Age"-Faunal Composition, Temporal Position, and Biostratigraphic Correlation in the Nonmarine Upper Cretaceous of Western North America". In Lucas, S.G.; Sullivan, R.M. Late Cretaceous vertebrates from the Western Inter(PDF). New Mexico Museum of Natural History and Science Bulletin 35. pp. 7–23.

Weishampel, D.B. "Acoustic Analysis of Vocalization of Lambeosaurine Dinosaurs." Paleobiology 7.2 (1981): 252-61. 

Wilfarth, Martin (1947). "Russeltragende Dinosaurier". Orion (Munich) (in German) 2: 525–532.