Irritator: Beast of the Week

This week's beast is a special dinosaur that helps us understand more about the appearance and lifestyle of its family.  Check out Irritator challengeri!

Irritator life reconstruction in watercolor by Christopher DiPiazza.

Irritator was a meat-eating dinosaur that lived in what is now Brazil during the early Cretaceous period, between 113 and 110 million years ago. From snout to tail it would have measured between 20 and 26 feet (6 and 8 meters) and was a meat-eater when alive.  The genus name, Irritator, is certainly an unusual name for a dinosaur, and is in reference to the fact that the skull, which was originally found by a fossil dealer who attached fake bones to the end of it in an attempt to make it look cooler.  When paleontologists actually got hold of the specimen they found it extremely irritating to undo all the damage to the specimen the dealer had done, so much so, they literally named it that.  The species name is after the fictional character, Professor George Edward Challenger, from the novel by famous author, Sir Arthur Conan Doyle, The Lost World. (which takes place in Brazil and features dinosaurs)

Irritator was a theropod that belonged to the spinosaurid family, which also includes other dinosaurs, like Baryonyx and the gigantic and extremely popular Spinosaurus, itself.  Most spinosaurs were relatively large theropods, Spinosaurus being arguably the largest theropod ever in some ways, but Irritator, at only 26 feet at the high end was a relatively smaller exception to this trend.  Like all spinosaurs, Irritator possessed a long, narrow snout, lined with pointed cone-shaped teeth.  Its nostrils were midway up the snout, instead of at the tip like those of most dinosaurs.  It also possessed a thin bony crest in the midline of the top of its skull.  Sadly only the skull of Irritator was ever oficially found.  There are other spinosaur bones known from the same time and relative area as Irritator, but because there are no overlapping parts between these bones and the Irritator skull, it is impossible to positively say they are all from the same kind of dinosaur.  That being said, if it was anything like other members of its family, it would have possessed strong arms with three curved claws on each hand, with the first finger of each hand possessing the largest claw.  Irritator may have also possessed proportionally shorter legs, a sail of some sort on the back comprised of extended neural spines, and a flattened tail.  These are all traits seen in Spinosaurus, which is thought to be closely related to Irritator even within the spinosaurid family.  

Left and right sideviews of Irritator's skull.

Irritator lived in an environment that would have been tropical in climate and abundant with large lagoons.  It had a long snout lined with pointed teeth, plus  possessed an extra bony palate on the roof of its mouth which would have helped the skull withstand pressure from twisting, an adaptation helpful if it was grabbing large struggling prey.  A study published in 2023 suggested that Irritator's lower jaws would have actually been somewhat flexible and were able to slightly bow outwards to the sides, expanding he gape of the mouth.  It also pointed out that Irritator's eyes were positioned facing forward, giving it particularly good binocular vision.  All these traits suggest Irritator was adapted to hunting fish, and it probably was, however we also know that Irrirator ate pterosaurs at least some of the time.  This is thanks to an Irrirator tooth found embedded into a pterosaur spine.  We don't know if Irritator was actively hunting the flying reptiles or scavenging them, however.  

When the skull of Irritator was first found by German and English scientists in the early 1990s, it was in the hands of a fossil dealer.  The scientists bought the skull from the dealer and brought it back to Germany where it resides to this day.  Current law in Brazil states that fossils found there must stay there unless given explicit permission by the government.  Many believe, including many paleontologists, that Irritaor's skull should be returned to and housed in a museum in Brazil.  

References

Cisneros, Juan C.; Ghilardi, Aline M.; Raja, Nussaïbah B.; Stewens, Paul P. (November 15, 2021). "The moral and legal imperative to return illegally exported fossils". Nature Ecology & Evolution. 6 (1): 1–3.

Machado, E.B.; Kellner, A.W.A. (2005). "Notas Sobre Spinosauridae (Theropoda, Dinosauria)". Anuário do Instituto de Geociências (in Portuguese). 28 (1): 158–173.

Machado, E.B.; Kellner, A.W.A.; Campos, D.A. (2005). "Preliminary information on a dinosaur (Theropoda, Spinosauridae) pelvis from the Cretaceous Santana Formation (Romualdo Member) Brazil". Congresso Latino-Americano de Paleontologia de Vertebrados. 2 (Boletim de resumos): 161–162.

Martill, D.M.; Cruickshank, A.R.I.; Frey, E.; Small, P.G.; Clarke, M. (1996). "A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil" (PDF). Journal of the Geological Society. 153 (1): 5–8.

Schade, Marco; Rauhut, Oliver; Foth, Christian; Moleman, Olof; Evers, Serjoscha (2023). "A reappraisal of the cranial and mandibular osteology of the spinosaurid Irritator challengeri (Dinosauria: Theropoda)". Palaeontologia Electronica. 26 (2). a17.

Mirasaura: Beast of the Week

 This week we will be checking out a newly published and super unique little creature, Mirasaura grouvogeli!

Watercolor life reconstruction of Mirasaura grouvogeli by Christopher DiPiazza.

Mirasaura was a reptile that lived in what is now France, during the late Triassic period, 247 million years ago.  Adults of this species may have grown to about 8-10 inches (20-25cm), The genus name translates to "Marvelous Reptile".  The species name, grouvogeli, honors Louis Grouvogel, who originally discovered the first fossils of Mirasaura and helped with its excavation. Mirisaura is known from two almost complete, likely juvenile specimens, as well as eighty specimens of isolated parts of the crest structure found on the animal's back.  Some of these isolated crests are much longer than those of the two nearly complete individuals, implying they could have grown larger than the two actual skeletons on the fossil record.  

Despite being recently published, Mirasaura was actually discovered back in the 1930s.  Its crest was initially believed to have been a disembodied fish fin and then an insect wing.  It wasn't until 2019 that it was reexamined again and realized to be the elaborate and unusual crest of a reptile.  

Photograph of one of the nearly complete, likely juvenile, Mirasaura specimens.

Mirasaura was a member of a family of interesting creatures called drepanosaurs.  Drepanosaurs were small, tree-dwelling reptiles, that lived during the Triassic period.  They all exhibit traits similar to modern lizards, in particular chameleons, but are not directly related to them.  Narrow, beaklike snouts with small teeth on the sides of the jaws and a hunched back are common to members of this group, including Mirasaura.  Some of them, like Mirisaura, sported flamboyant crests on their backs, which were made of soft, yet rigid structures that were actually extremely similar to feathers.  Thanks to Mirasaura, of which many fossil specimens preserved these soft feather-like structures, it is possible other members of this group, which only preserved bones, had similar crests.  Sadly the limbs and tail from both known skeletons of Mirasaura are missing, but other drepanosaurs had limbs and feet adapted for grasping branches and some had a single claw on the tip of the tail.  

Possibly the most interesting thing about Mirasaura's crest is the fact that the individual structures that form it are arranged slightly overlapping but in a single file down the midline of the animal, making it not symmetrical. (Best analogy I can think of is when you pose for a group photo at a wedding or something.)  So far experts do not know exactly why this is.  The exact function of the whole crest is also still a mystery.  Like modern reptiles it may have been a signal to members of its own species for impressing mates or intimidating rivals.  If they sported them before they were fully grown, however, they may have had other uses.  Perhaps they could have been for camouflage, obscuring Mirasaura's outline and making it look more like part of a tree?  We may never know for sure.

Mirasaura may have specialized in eating small insects, rooting them out of crevices in trees with its pointed snout, and then crunching them up with the teeth in the sides of its jaws.  Because it was so small, it would have needed to be weary of many of its own predators when alive, ranging from pterosaurs, to dinosaurs, to crocodilian relatives, and even early mammals, all of which were around during the late Triassic.  Because of this, living up in the trees may have been an effective way to minimize predation.  

References

Calzavara M., Muscio G. & Wild R. (1980). "Megalancosaurus preonensis, n. g., n. sp., a new reptile from the Norian of Friuli". Gortania. 2: 49–63.

Senter, P. (2004). "Phylogeny of Drepanosauridae (Reptilia: Diapsida)". Journal of Systematic Palaeontology. 2 (3): 257–268.

Spiekman, Stephan N. F.; Foth, Christian; Rossi, Valentina; Gascó Martín, Cristina; Slater, Tiffany S.; Bath Enright, Orla G.; Dollman, Kathleen N.; Serafini, Giovanni; Seegis, Dieter; Grauvogel-Stamm, Léa; McNamara, Maria E.; Sues, Hans-Dieter; Schoch, Rainer R. (2025-07-23). "Triassic diapsid shows early diversification of skin appendages in reptiles".

Ceratosaurus: Beast of the Week

This week we shall be looking at a popular meat-eater with some truly unique features.  Enter Ceratosaurus!

Watercolor life reconstruction of Ceratosaurus nascornis eating the ancient lungfish, Ceratodus robustus by Christopher DiPiazza.

Ceratosaurus was a meat-eating dinosaur that lived during the late Jurassic period, about 150 million years ago, in what is now the United States, specifically Utah and Colorado.  Bones thought to be from Ceratosaurus have also been unearthed in Portugal.  As an adult it would have measured about twenty feet from nose to tail but one specimen suggests it may have grown even larger in some cases.  The genus name, "Ceratosaurus" translates to "Horned reptile/lizard" and refers to the horn-like protrusions on the animal's snout and over its eyes.

Bronze cast of a Ceratosaurus skull on display at the Mesalands Dinosaur Museum in Tucumcari new Mexico.

The most notable feature about Ceratosaurus is the presence of its "horns".  These bony structures aren't really horns as much as they are crests, however, since they were extremely thin and delicate.  Whereas the horns of certain other dinosaurs, like Carnotaurus, were robust enough to have been effective weapons in life, the "horns" of Ceratosaurus would have easily broken if they were used in any sort of violent activity.  They were most likely used for display rather than for physical fighting.  Keep in mind that these crests would have had a layer of keratin growing over them, so they might have appeared even longer and possibly even a slightly different shape in life.  A juvenile Ceratosaurus skeleton that was discovered showcases proportionally smaller crests on its skull, supporting the idea that they were for display, possibly helping individuals within the species to identify others as sexually mature or not.  They may have also been for display against other species, making Ceratosaurus' head look bigger and therefore more intimidating to rival meat-eaters, like Allosaurus. 

Juvenile Ceratosaurus skull on display at the North American Museum of Ancient Life. Note the smaller crests on the nose and above the eyes. (Photo credit: Jens Lallensack)

The crests weren't Ceratosaurus' only unique feature.  This dinosaur also had a row of small bony plates, called osteoderms, running down the center of its back.  This is a feature common in certain groups of dinosaurs, like the thyreophorans, like Stegosaurus, but is extremely rare in theropods.  The exact purpose is a mystery, but we can make some educated guesses.  As with the head crests, these bony structures may have aided in display to other dinosaurs.  Perhaps males had longer plates than females?  Perhaps they were absent in juveniles?  Maybe they helped camouflage Ceratosaurus slightly by breaking up its basic body shape?  We may never know for sure.

Neck of the Ceratosaurus skeleton on display at the Smithsonian National Museum of Natural History in Washington D.C.  I circled a group of the osteoderms in yellow.

Ceratosaurus' tail was particularly deep and flattened laterally. This lead some to hypothesize that Ceratosaurus may have been a decent swimmer and specialized in hunting aquatic prey. (although there is little other evidence that suggests this)  Ceratosaurus also had short, but fully functional arms each tipped with four fingers and three claws.

Lastly, Ceratosaurus had the longest teeth proportional to its body of any known dinosaur.  The teeth were curved and serrated, like steak knives.  They look to be ideal for slashing chunks of flesh from bone, rather than crushing through armor and bone.  This is further supported by the fact that Ceratosaurus' lower jaw was rather thin, and therefore wouldn't have been capable of applying too much force or withstanding too much pressure before being injured.

Almost-complete(no arms!) Ceratosaurus skeletal mount on display at the National Museum in Washington D.C. 

Ceratosaurus bones have been found in the same formations as other, larger Jurassic meat eaters, like Allosaurus and Torvosaurus.  Most scientists agree that Ceratosaurus may have specialized in hunting a different kind of prey than its larger contemporaries, perhaps going after smaller animals, rather than giant sauropods and heavily-armed stegosaurs.  This is further supported by the fact that Ceratosaurus bones are particularly less common than most of the other dinosaurs known from the Late Jurassic of North America.  This could mean that Ceratosaurus typically dwelled in habitats slightly different from the rest of those dinosaurs where fossilization didn't take place as easily.

Sometimes I wonder what exactly prevented Ceratosaurus from existing close to the other megapredators of it's time...

They said it couldn't be done but I managed to make a cartoon merging Late Jurassic predators with Mean Girls.  It wasn't even that hard.

That's all for this week!  As always feel free to comment below!  Want to see a particular prehistoric beastie reviewed?  Let me know and I'll make it happen!

Works Cited

Carrano, M.T.; Sampson, S.D. (2008). "The Phylogeny of Ceratosauria (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 6 (2): 183–236.

Foster, John (2007). "Gargantuan to Minuscule: The Morrison Menagerie, Part II". Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 162–242. 

Gilmore, C.W. (1920). "Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus". Bulletin of the United States National Museum 110: 1–154.

Marsh, O.C. (1884). "Principal characters of American Jurassic dinosaurs, part VIII: The order Theropoda". American Journal of Science 27 (160): 329–340.

Rowe, T.; Gauthier, J. (1990). "Ceratosauria". In Weishampel, D.B.; Dodson, P.; Osmólska, H. The Dinosauria. University of California Press. pp. 151–168. 

Lepidotes: Beast of the Week

 This wee we will look at a unique kind of prehistoric fish that swam in rivers and lakes while some of the largest dinosaurs walked on land.  Check out Lepidotes!

Watercolor reconstruction of Lepidotes gigas by Christopher DiPiazza.

Lepidotes was a genus of heavily scaled bony fish that lived in what is now Europe and North America during the early Jurassic between 180 and 175 million years ago.  The genus may have even persisted into the Early Cretaceous, as recent as 115 million years ago, but the identity of these later species has been proposed to be from a separate genus by some experts.  In life Lepidotes lived in mostly fresh water and some shallow salt water environments, and would have eaten small invertebrates.  The genus name translates to "covered with scales" in Greek.  From nose to tail most Lepidotes grew to about a foot in length (30 cm).  

Fossil of Lepidotes gigas (photo credit: Ghedo) Note the hard scales, which fossilized extra dark compared to the other parts of the fish.

Lepidotes is most known for its scales, which are by far the most commonly fount fossil from it, and were particularly hard and shiny.  Its closest living relatives are gars, which also have extremely tough armored scales.  Like Gars, the scales of Lepidotes acted as as armor against predators. Gars, however, are also known for their long bodies and snouts, lined with pointed teeth, while Lepidotes was convergently more shaped like a carp, with a taller, rounder body, and proportionally small round mouth.  

In the back of Lepidotes' mouth were rounded teeth, ideal for crushing shelled invertebrates on which it likely preyed on when alive.  Another interesting characteristic of Lepidotes was that both the upper and lower jaws were not attached directly to the rest of its skull, allowing it to have stretched its mouth out into a tube-like structure while sucking up food.  In addition to its body shape, this is another trait present in modern carp.  

References

 Agassiz, L. (1832), Untersuchungen über die fossilen Fische der Lias-Formation. Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde 

Frederickson, Joseph A.; Lipka, Thomas R.; Cifelli, Richard L. (2018-08-28). "Faunal composition and paleoenvironment of the Arundel Clay (Potomac Formation; Early Cretaceous), Maryland, USA". Palaeontologia Electronica.

Lambe, L.M. (1902). "New Genera and Species from the Belly River Series (mid cretaceous)". Geological Survey of Canada. Contributions to Canadian Palaeontology. 3: 25–81.

López-Arbarello, Adriana (2012-07-11). Steinke, Dirk (ed.). "Phylogenetic Interrelationships of Ginglymodian Fishes (Actinopterygii: Neopterygii)". PLOS ONE. 7 (7): e39370.

Polycotylus: Beast of the Week

 This week we will be checking out a beast that helps us understand how some prehistoric marine reptiles reproduced.  Check out Polycotylus latipinnis!

Polycotylus was a plesiosaur that lived in what is now Kansas, USA, during the late Cretaceous period, about 83.6 million years ago.  From snout to tail adults could grow to 18 feet (5.4 meters) long, and would have been a predator when alive, using its long snout full of interlocking cone-shaped teeth to capture smaller marine prey, like fish or squid.  The genus name, Polycotylus, translates to "many cupped vertebrae" in reference to the shape of its backbones.  

Polycotylus about to chomp a baby mosasaur.  Watercolor reconstruction by Christopher DiPiazza.

Plesiosaurs are most famous for having proportionally small heads with extremely long necks, but many kinds, like Polycotylus, were actually the opposite, possessing proportionally large heads and short necks.  They all had sturdy, somewhat turtle-shaped bodies, short tails, and four powerful flippers for swimming in the ocean.  Polycotylus' flippers were especially long and tapered at the tips, suggesting it was a particularly fast swimmer in life, which would have allowed it to pursue prey and also avoid becoming prey, itself, to predators, like the enormous mosasaurs it coexisted with.  

The famous Polycotylus specimen containing the bones of an unborn fetus (circled in white) on display at the Natural History Museum of LA County.

What Polycotylus is probably most famous for is the skeleton that was found with an unborn fetus still inside, showed Polycotylus gave birth to live young.  This is unusual since most reptiles reproduce by laying hard-shelled eggs, or sometimes, like with boas and rattlesnakes, keep the eggs inside until the babies hatch.  That being said, since very similar evidence of live birth has also been found in ichthyosaurs, a completely separate kind of prehistoric marine reptile, live birth seems to be more the norm in ancient marine reptiles, but also must have evolved convergently multiple times in these different groups.  This makes sense since the bodies of plesiosaurs and ichthyosaurs seem completely unfit for land, even for short periods of time, unlike modern sea turtles and some sea snakes endure to lay eggs on beaches.  What's even more interesting about Polycotylus' case is the fact that there was only one single unborn baby inside that measured almost a whopping five feet long.  Birthing one big baby, opposed to many smaller ones, is not a reproduction strategy typically seen in reptiles.  This implies that parents likely cared for the baby after birth, instead letting them go off on their own, like many modern reptiles do today.  

References

O'Keefe, F.R. (2004). "On the cranial anatomy of the polycotylid plesiosaurs, including new material of Polycotylus latipinnis, Cope, from Alabama". Journal of Vertebrate Paleontology. 24 (2): 326–340.

O'Keefe, F.R.; Chiappe, L.M. (2011). "Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia)". Science. 333 (6044): 870–873.

o'Keefe, F. R.; Sander, P. M.; Wintrich, T.; Werning, S. (2019). "Ontogeny of Polycotylid Long Bone Microanatomy and Histology". Integrative Organismal Biology. 1 (1): oby007.

Schumacher, B.A.; Martin, J.E. (2016). "Polycotylus latipinnis Cope (Plesiosauria, Polycotylidae), a nearly complete skeleton from the Niobrara Formation (early Campanian) of southwestern South Dakota". Journal of Vertebrate Paleontology. 36 (1). el031341.

Heyuannia: beast of the Week

This week we will be checking out a dinosaur they helps us better understand dinosaur eggs, Heyuannia huangi!

Heyuannia was a theropod dinosaur that lived in what is now China and Mongolia during the latest Cretaceous period, between 70 and 66 million years ago. From beak to tail it measured almost 5 feet long (1.5meters) and was likely an omnivore when alive.  It's name translates to "from Heyuan" in reference to the region of China where its bones were first found. 

Watercolor life reconstruction of Heyuannia by Christopher DiPiazza.

Heyuannia was a member of the oviraptorosaur group of dinosaurs, known for being bird-shaped with long necks and short boxy skulls with powerful beaks.  Many of them also sported tall bony crests on their heads, but sadly the whole skull of Heyuannia has not been found so we don't know that part of it's anatomy for sure.  Like its relatives, Heyuannia may have been an omnivore, using its short, but powerful beak to process seeds, fruits, and other tough plant material, but would have also been equally efficient at eating small animals, including hard-shelled invertebrates.  

Heyuannia skeleton on display at the Heyuan City Museum in China.

Heyuannia had proportionally short arms and fingers compared to many oviraptororsaurs.  Each finger was armed with a curved claw.  We don't know why its arms and fingers were so short.  It may have been exhibiting a different feeding style that utilized its head and neck more, but it is almost impossible to predict exactly what that would have been.  Like all Oviraptorosaurs, it is almost certain Heyuannia had feathers in life. 

Photograph of a fossilized Heyuannia nest from the paper by Wiemann et. al. referenced below.  Note how the eggs are in a ring pattern and arranged in pairs.

Heyuannia is also known from many eggs and embryos which were found in the same place as many of the adult skeletons.  The nests of eggs are arranged in a ring pattern and don't appear to have been buried in life.  This implies that the parent would have guarded the nest with its body, likely with its feathered arms spread over the ring of eggs and their body in the middle of the ring.  (We have actual fossils of close relatives that died doing exactly this.) In addition the eggs are arranged in pairs, which implies they were laid two at a time.  This is notable since modern birds do not lay eggs in pairs because they only have one functioning oviduct, an adaptation to lighten their bodies for flight. Oviraptorosaurs, which did not fly, likely had both oviducts in use due to the way we find their eggs.

The most exciting thing about Heyuannia's eggs is the fact that scientists were able to examine the shells closely enough to identify the chemical makeup of some of them, specifically the part that reflects what color the shells would have been.  According to what they found, the eggs of Heyuannia would have been blue-green in color! 

References

Lü, J (2002). "A new oviraptorosaurid (Theropoda: Oviraptorosauria) from the Late Cretaceous of southern China". Journal of Vertebrate Paleontology. 22 (4): 871–875.

Lü, J. (2005). Oviraptorid dinosaurs from Southern China. Beijing: Geological Publishing House. ISBN 7-116-04368-3. 200 pages + 8 plates. (In Chinese: pp 1-83, including 36 figures & 3 tables. In English: pp 85-200, including 5 geological figures.)

Wiemann, J.; Yang, T.-R.; Sander, P.N.; Schneider, M.; Engeser, M.; Kath-Schorr, S.; Müller, C.E.; Sander, P.M. (2017). "Dinosaur origin of egg color: oviraptors laid blue-green eggs". PeerJ. 5: e3706.

Platyhystrix: Beast of the Week

 This week we will be talking about an unusual little amphibian that predates the dinosaurs by about 100 million years.  Check out Platyhystrix rugosus!

Platyhystrix was a kind of prehistoric amphibian that lived in what is now the United States, in Texas, New Mexico, and Kansas, during the early Permian period, about between 300 and 279 million years ago.  From snout to tail measured about 3 feet (1 meter) long.  Like most amphibians it was a predator, likely swallowing smaller animals whole.  The genus name translates from Greek to "Flat Porcupine" (which I find delightful) because of its unusual back ornamentation.  

Watercolor life reconstruction of Platyhystrix by Christopher DiPiazza.

Platyhystrix was a member of the extremely successful and widespread group of ancient amphibians, called the temnospondyls.  Temnospondyls are sadly extinct now, but they persisted from 300 to 120 million years ago. (210 million years total!)  Eryops, Mastodonsaurus, and Metoposaurus are three other examples from this group that have been covered on this blog in the past.  Unsurprisingly for a group that persisted so long, temnospondyls diversified into many different forms during their time on the planet, exhibiting some traits we don't normally associate with amphibians like frogs and salamanders.  One example of this is the presence of bony armor plates, a trait normally associated with reptiles, like crocodilians and dinosaurs.  Platyhystrix not only had this armor, but it evolved a version of it that is completely unlike that of any other animal armor that ever existed, forming a tall semi-circular crest on its back made up of a single row of flat plates growing from the midline attached to the spine.  At first glance this looks like the kind of sail-like structure that has evolved many times in other animals, including but not limited to, the synapsid, Dimetrodon, the dinosaurs, Spinosaurus and Ouranosaurus, the pseudosuchian, Arizonasaurus, as well as many living lizards, like chameleons, basilisks, and sailfin dragons.  These sail structures are all made of extra long top sections of the vertebra, called neural arches.  Despite the resemblance, this is not the case for Platyhystrix, since its crest was made of bony plates that aren't actually part of its vertebrae, but appear to be their own separate body parts that were instead fused to the top of the spine.  The exact function of this structure is still very much a mystery.  Some suggest it had to do with thermoregulation, but others think it was more of a display structure for communication within the species. Maybe both?

Photo of the elongated armor plates of Platyhystrix from Vaughn's paper referenced below.

  The texture on the top of Platyhystrix's skull is rough with many grooves and pits in it, implying there was a tough keratin layer there in life.  This may have been an adaptation for combat within the species, possibly shoving or headbutting each other for dominance.  Modern amphibians, like frogs, can get extremely physical with each other, especially males around breeding time, so maybe Platyhystrix was similar in some ways?  It may also have had to do with controlling the animal's body temperature or maybe even defense against predators.  The teeth of Platyhystrix were small and cone-shaped, ideal for grabbing and holding onto prey that it could swallow whole.  

Illustration of the underside of Platyhystrix's (crushed) skull.  Note the small teeth at the top.  Image from paper by Berman referenced below.

Platyhystrix's environment would have been very different from what the American Southwest is today.  During the early Permian there would have been many rivers intersecting a landscape that would change between seasonally wet and humid to dry.  Despite being a predator, itself, when alive Platyhystrix would have needed to avoid predation from some of its larger contemporaries, including fellow temnospondyl, Eryops, and the large carnivorous synapsid, Dimetrodon.  

References

Berman DS, Reisz R, Fracasso MA. 1981. Skull of the Lower Permian dissorophid amphibian Platyhystrix rugosus. Annals of Carnegie Museum 50:391-416.

Bowler, Neven; Sumida, Stuart S.; Huttenlocker, Adam K. (2022-12-21). "Histological evidence for dermal-endochondral co-ossification of the dorsal blades in the late Paleozoic amphibian Platyhystrix rugosus (Temnospondyli: Dissorophidae)". Journal of Vertebrate Paleontology. 42 (2).

Case, E.C. (1910). "New or little known reptiles and amphibians from the Permian (?) of Texas". Bulletin of the American Museum of Natural History. 28: 163–181.

Mack, Greg H. (2003). "Lower Permian terrestrial Paleoclimatic indicators in New Mexico and their comparison to paleoclimate models". Geology of the Zuni Plateau. New Mexico Geological Society: 231–240.

Vaughn, Peter Paul (1971). "A Platyhystrix-like Amphibian with Fused Vertebrae, from the Upper Pennsylvanian of Ohio". Journal of Paleontology. 45 (3): 464–469.