Struthiomimus: Beast of the Week

All birds are dinosaurs, but not all dinosaurs were birds.  This week's beast is a perfect example of that.  Let's check out Struthiomimus!

Struthiomimus was a theropod dinosaur that lived in what is now Alberta, Canada, and parts of the Western United States, during the Late Cretaceous Period between 75 and 66 million years ago.  From beak to tail Struthiomimus measured about 14 feet (7.3m) long.  The name, Struthiomimus, translates to "Ostrich Mimic" because...look at it.

 

Struthiomimus altus life reconstruction in watercolors by Christopher DiPiazza

Struthiomimus was a member of the ornithomimosaur aka "bird mimic" group of dinosaurs.  These theropods are characterized by their long slender limbs and necks, with proportionally small heads.  The later-living members, including Struthiomimus, had toothless beaks.  Struthiomimus is probably the most famous member, and is particularly similar-looking to modern ratites, the group of birds that includes ostriches and emus.  Despite both being groups of theropod dinosaurs, ornithomimosaurs are not the direct ancestors of ratites.  Each group evolved extremely similar traits completely independently of one another, a concept in biology called convergent evolution.

Struthiomimus skeletal mount on display at the American Museum of Natural History.

Like modern ratites, Struthiomimus would have likely been a very fast runner in life.  In fact, later members of the ornithomimosaur group, like Struthiomimus, are thought by experts to probably be the fastest running non-avian dinosaurs, able to sprint at high speeds to evade predators when they had to.  This is due to their proportionally long lower leg and foot bones and overall gracile build.  It is difficult to say exactly how fast Struthiomimus could have ran, but today's ostriches can sprint close to 50 miles (80km) per hour and sustain long distance speeds of around 30 miles (48km) per hour.  Some experts think ornithomimosaurs evolved this fast-running body plan as a result of an evolutionary arms race with tyrannosaurs, which also had proportionally long-slender legs for running, even the largest taxa, like T. rex, which was probably too bulky to catch a Struthiomimus as a mature adult, would have been a much faster runner as a juvenile, and therefore a prime threat to the ornithomimosaurs.  

A different Struthiomimus skeleton on display at the American Museum of Natural History.

Struthiomimus' diet is pretty mysterious.  Its head and mouth were proportionally very small so it was likely not attacking large animals.  Its actual beak was toothless and had somewhat sharp edges on the sides, which could have been an adaptation for clipping plants or cutting up small animals.  Struthiomimus' arms were long and but didn't have the ability to reach up that high past their normal resting position.  The fingers were all about the same length, which is unusual for theropod dinosaurs, and wouldn't have been very dexterous, despite many older outdated reconstructions of ornithomimids show them holding and carrying items in an almost primate-like fashion.  It is possible Struthiomimus used its forelimbs as hooks, to bend plants closer to its mouth, which it could reach easier with the help of its long neck. 

Close up of a Struthiomimus' hand at the Oxford University Museum of Natural History.

In life, Struthiomimus almost definitely had feathers.  We know this because specimens of its close relative, Ornithomimus, were discovered with amazingly preserved long feathers that were attached to the arms, making it look even more like an ostrich in life.  The arm feathers probably aided these dinosaurs in brooding eggs and young, or possibly display within their species.  

When alive Struthiomimus altus shared its environment with many other dinosaurs, Parasaurolophus, Lambeosaurus, Anodontosaurus, Chasmosaurus, Styracosaurus, and its close cousin, Ornithomimus, to name a few.  It would have been running from large tyrannosaurs, like Gorgosaurus and Daspletosaurus.  Struthiomimus sedens was living alongside Edmontosaurus, Triceratops, Ankylosaurus, Pachycephalosaurus, Ornithomimus (different species), and would have needed to run from the likes of Tyrannosaurus and Nanotyrannus.  

References

Barrett, Paul M. (2005). "The diet of ostrich dinosaurs (Theropoda: Ornithomimosauria)". Palaeontology 48 (2), 347–358. 

Longrich, N. (2008). "A new, large ornithomimid from the Cretaceous Dinosaur Park Formation of Alberta, Canada: Implications for the study of dissociated dinosaur remains." Palaeontology, 51(4): 983-997.

Nicholls, Elizabeth L.; Russell, Anthony P. (1985). "Structure and function of the pectoral girdle and forelimb of Struthiomimus altus (Theropoda: Ornithomimidae)". Palaeontology 28: 643–677.

Russell D (1972). "Ostrich dinosaurs from the Late Cretaceous of Western Canada". Canadian Journal of Earth Sciences 9 (4): 375–402.

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". Science 338 (6106): 510–514. 

Siats: Beast of the Week

This week belongs to a mysterious theropod dinosaur.  Check out Siats !  Siats was a large, meat-eating dinosaur that lived in what is now Utah, USA,  during the middle Cretaceous period, about 98 million years ago.  The individual found would have been about 30 feet (9 meters) long from snout to tail, but appeared to have been still growing when it died so it may have been able to grow larger.  The genus name is after a terrifying man-eating monster from the local Ute tribe's mythology, called a siats. 

Life reconstruction of what Siats may have looked (mostly based on other megaraptorans) like by Christopher DiPiazza.

Unfortunately the known remains of Siats are only fragmentary, consisting of vertebrae, legs, and part of the pelvis, but enough for experts to identify it as a large theropod.  Despite being large, the parts of the vertebra that were found were not fully fused, implying it was still a juvenile when it died, implying it could have gotten even larger!  

Megaraptorans appear to have shared a close common ancestor with tyrannosaurs (or were tyrannosaurs themselves).  Thanks to Siats, we know they were already large in the middle Cretaceous, when the line that would give rise to the giant two-fingered tyrannosaurids was still small.

When it was discovered, Siats was identified as being from the megaraptoran group of theropods.  At the time megaraptorans were considered related to the group of meat-eating dinosaurs that includes Allosaurus and Acrocanthosaurus, called allosauroids.  As time went on, however, and more megaraptoran fossils were found around the world, inlcuding a skull from South America, many experts reclassified them as being more closely related to the tyrannosauroid group of theropods, than the allosauroid group.  Depending on the experts you ask, megaraptorans were either just outside the tyrannosaur group or within it but near the base.  If this is true, Siats likely would have had a long narrow snout filled with proportionally small, curved teeth, and three-fingered hands with scythe-like claws.   

Some of the bones unearthed belonging to Siats.

Siats is an important fossil to our understanding of theropod evolution because we have so few fossils from the time period in which it lived, the middle Cretaceous.  The fact that it was so large is also interesting, especially if it was indeed closely related to tyrannosaurs.  It implies that a branch of (or close to) the tyrannosaur group grew to extremely large sizes all the way back during the middle Cretaceous.  This would have been independent of the later group of extremely large tyrannosaurs, which includes T. rex, which didn't start to get large until millions of years later.  In fact, there is even a small tyrannosauroid that lived alongside Siats, called Moros, that likely was part of the lineage that would produce this second group of giants. 

Fossils from the middle Cretaceous are still rare, but other known dinosaurs that Siats would have lived alongside are its smaller relative, Moros, the large ankylosaur, Peloroplites, as well as a number of giant long-necked sauropods.

References

Coria, Rodolfo A.; Currie, Philip J. (20 July 2016). "A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia". PLOS ONE. 11 (7) e0157973.

Naish, Darren; Cau, Andrea (7 July 2022). "The osteology and affinities of Eotyrannus lengi, a tyrannosauroid theropod from the Wealden Supergroup of southern England". PeerJ. 10 e12727.

Porfiri, Juan D.; Novas, Fernando E.; Calvo, Jorge O.; Agnolín, Federico L.; Ezcurra, Martín D.; Cerda, Ignacio A. (1 September 2014). "Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation". Cretaceous Research. 51 (Supplement C): 35–55.

Zanno, L. E.; Makovicky, P. J. (2013). "Neovenatorid theropods are apex predators in the Late Cretaceous of North America". Nature Communications 4. doi:10.1038/ncomms3827.

Tromerosaurus: Beast of the Week

 This week we are checking out a newly described predatory dinosaur with a truly frightening and fantastical name.  Look out for Tromerosaurus solumons!

Tromerosaurus was a theropod dinosaur that lived in what is now Southern Alberta, Canada, during the late Cretaceous period, between 76 and 77 million years ago.  It measured about 30 feet (7meters) from snout to tail and would have been a meat-eater when alive.  It's genus name translates to "frightening lizard/reptile" and the species name to "lonely mountain".  This is because the small horn (the "mountain" in question) just before its eye socket was isolated by a wider flat shelf of bone behind it.  This is also in reference to the Lonely Mountain from the famous book by J.R.R. Tolkien, The Hobbit, where the dragon, Smaug, lived.  (The venn diagram of Tolkien fans and paleontologists has a gigantic overlap section.)

Tromerosaurus life reconstruction in watercolors by Christopher DiPiazza.

Tromerosaurus was a tyrannosaurid, meaning it was closely related to the famous Tyrannosaurus, and likewise had all the typical tyrannosaurid features, like having long, backwards-curved teeth on the sides of its jaws and smaller, narrow teeth in the front of the snout with "D" shaped cross sections.  It had a bony crest running down the midline of its snout and around its eyes, plus small horns jutting out just before the eyes.  It would have had proportionally small bust strong arms with two fingers on each hand and a hooked claw on each finger.  Its feet were made up of three bones, called metatarsals, but the middle one was pinched between the outer two in an upside down "v" shape, present in all tyrannosaurs. 

"Frighteing Lizard from the Lonely Mountain" is a nod to Smaug, the dragon, regardless of how pronounced this dinosaur's horns are. Cartoon by Christopher DiPiazza.

Tromerosaurus is important because it helps paleontologists get a more detailed idea of how tyrannosaurs were evolving in North America during the late Cretaceous.  Within its family it was most closely related to relatives, like Gorgosaurus and Albertosaurus, which are in an even more specific group, called the albertosaurines. Like them, Tromerosaurus had proportionally longer legs than what is typical for large theropods, implying it was a fast runner in life.  That being said, Tromerosaurus also possessed traits in line with yet another branch in its family, called the tyrannosaurines, which includes T. rex itself and are characterized by being the largest and most robust of the tyrannosaurs. Like them, Tromerosaurus had a notably wide skull base, around where the jaw muscles would have been.  This implies that despite its gracile body, it would have also had a powerful bite, even among tyrannosaurs! 

Skull of Tromerosaurus, photo credit: Khoi Nguyen

When alive Tromerosaurus would have been a top predator in its community.  It wasn't the only one, however, and would have shared space with fellow tyrannosaur, Daspletosaurus, which was similar in size to it but slightly more heavily-built.  Tromerosaurus also would have lived alongside many other dinosaurs, including the ornithomimid Struthiomimus, and hadrosaurs, Corythosaurus, and Maiasaura.(which it probably ate.)

References

Powers, Mark J.; Napoli, James G.; Coppock, Colton C.; Sharpe, Henry S.; Garros, Christiana W.; Demers-Potvin, Alexandre V.; Raun, Gorm S.; Stock, Jordan C.; Miyashita, Tetsuto; Currie, Philip J. (2026-10-02). "A new albertosaurine from the Oldman Formation, Alberta, Canada, illuminates ambiguity between albertosaurine and tyrannosaurine characteristics".

Eukritta- Beast of the Week

 This week we will be checking out a beast that is named after one of the most iconic movie monsters.  Watch out for Eucritta melanolimnetes!

Eucritta was an early tetrapod (animal with four limbs or that evolved from a four limbed ancestor...basically any vertebrate that's not a fish) that lived in what is now Scotland during the Carboniforous period, between 344 and 331 million years ago.  It measured about 10 inches (25.4cm) long from snout to tail and would have been a meat-eater when alive.  The genus and species name together, Eucritta melanolimnetes, translates to "True Creature from the Black Lagoon", after the famous 1954 monster movie.  This is in reference to how, like the movie monster, Eukritta exhibited features from multiple different kinds of other animals and would have spent time on both land and in the water when alive.

Life reconstruction of Eucritta in watercolors by Christopher DiPiazza.

When Eucritta was alive, none of the land vertebrates we are familiar with today were around yet.  The ones that did exist would have had the most in common with modern amphibians but were still pretty different even from them.  Eucritta stands out among these ancient animals because it possessed a number of features associated with multiple different varieties of early land creatures that were evolving around that time, placing it somewhere between the early ancestors of the first reptiles and the amphibian-like temnospondyls.  

Eucritta is known from several skeletons so we actually know quite a bit about its anatomy.  It possessed a wide, semi-circular skull and its eye sockets were proportionally large and round, suggesting it had good vision in life, and it possessed many small pointed teeth, ideal for grabbing and swallowing small prey.  The top of its mouth also possessed small tooth-like protrusions, which would have helped ensure live prey did not escape once grabbed.  Despite its amphibian-like skull, it also possessed a bony pallet on the roof of its mouth separating its mouth from its nose, which is something amphibians do not have, but an ancestral trait to the group of animals that would become the first reptiles.  It's arms were short and robust, and its legs were proportionally longer and also powerfully built, suggesting that Eucritta could have spent considerable time walking around outside the water.  Sadly its tail was never found so we do not know if it was stubby or longer and possibly paddle-shaped to aid in swimming. 

Photograph of the skull and shoulder girdle of Eucritta from the paper by Clack et. al. referenced below.

Eukritta's low flat skull and short, straight ribs, give us clues as to how it breathed.  Modern ampbibians, like frogs and salamanders have the same traits and get their oxygen by buccal pumping, which is when they use muscles in their throat to pump air into their bodies. (Ever notice how the skin under a frog's chin is always moving up and down? that's buccal pumping in action.)  This is because they do not have a diaphragm, a muscle which other land animals (including us) use to breathe instead. Animals with diaphragms also have longer ribs that curve around their torso to better support their organs. 

References

Clack, J. A. (March 2001). "Eucritta melanolimnetes from the Early Carboniferous of Scotland, a stem tetrapod showing a mosaic of characteristics". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 92 (1): 75–95.

Clack, Jennifer A. (2 July 1998). "A new Early Carboniferous tetrapod with a mélange of crown-group characters". Nature. 394 (6688): 66–69.

Garudimimus: Beast of the Week

This week we're checking out a feathered dinosaur that helps us understand the evolution of the "bird mimic" family of dinosaurs.  Enter Garudimimus brevipes!

Garudimimus was a theropod dinosaur that lived in what is now Mongolia during the Cretaceous period, between 96 and 89 million years ago.  From beak to tail it would have measured about 11.5 feet (3.5 meters) long and it likely would have been an omnivore when alive.  The genus name translates to "Garuda Mimic", in reference to Garuda, the half bird half human Hindu deity.  The species name, brevipes, translates to "short foot".

Watercolor life reconstruction of Garudimimus by Christopher DiPiazza.

Garudimimus was a member of the ornithomimosaur family of theropod dinosaurs that are famous for resembling ostriches while not being directly related to them, rather evolving a similar body plan independently millions of years prior.  Garudamimus is interesting because it can be considered a transition fossil, possessing characteristics of both older and more recent relatives of this family, and thus helping us understand how this group evolved.  Earlier members of the ornithomimosaur family, like Harpymimus, are known for having teeth and still possessing four toes on each foot, the first of which was very short and probably had no purpose, like the dewclaw on a dog.  Later living members, like Ornithomimus and Struthiomimus, had much longer, more slender limbs, with only three toes per foot and toothless beaks.  Garudimimus possesses a mix of these traits, having a stockier build with the vestigial fourth toe on each foot, but also a toothless beak.  Many paleontologists currently believe that Garudimimus is actually more closely related to the extremely large and unusual member of the ornithomimosaur family, Deinocheirus.    

Skull of Garudimimus on display at the Mongolian Natural History Museum.

Garudimimus' skull had a relatively narrow beak with a weak bite force, even compared to other ornithomimosaurs, suggesting it was more specialized to eating plants.  The sides of its beak had a sharper edge which may have helped it cut bite-sized pieces of leaves as it ate.  Its eye sockets were proportionally huge and round, implying it had a strong sense of sight and its neck would have been long and flexible, which would have been helpful for looking out for potential predators.  Some experts have suggested Garudimimus would have been active at night, but having large eyes doesn't always reflect a nocturnal lifestyle. (modern ostriches are a good example of this)

Garudimimus' legs were proportionally shorter and stockier than those of its later relatives, but it still would have been comparably fast, especially compared to other dinosaurs in its environment, likely relying on speed to avoid predation.  Like all members of its family it likely would have had feathers in life, which would have aided in regulating its body temperature, caring for eggs and young, and possibly for display within its species.  

References

Barrett, P. M. (2005). "The diet of ostrich dinosaurs (Theropoda: Ornithomimosauria)". Palaeontology. 48 (2): 347−358.

Hughes, G. M.; Finarelli, J. A. (2019). "Olfactory receptor repertoire size in dinosaurs". Proceedings of the Royal Society B. 286 (1904) 20190909.

Kobayashi, Y.; Barsbold, R. (2005). "Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia" (PDF). Canadian Journal of Earth Sciences. 42 (9): 1501−1521.

Kurumada, Y.; Aoki, S.; Aoki, K.; Kato, D.; Saneyoshi, M.; Tsogtbaatar, K.; Windley, B. F.; Ishigaki, S. (2020). "Calcite U–Pb age of the Cretaceous vertebrate-bearing Bayn Shire Formation in the Eastern Gobi Desert of Mongolia: usefulness of caliche for age determination". Terra Nova. 32 (4): 246−252.

Schmitz, L.; Motani, R. (2011). "Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology". Science. 332 (6030): 705−708.

Muttaburrasaurus: Beast of the Week

 This week we will be checking out a mysterious plant-eating dinosaur that called what was once Australia home.  Enter Muttaburrasaurus langdoni!

Muttaburrasaurus was a plant-eating dinosaur that lived in what is now Northern Australia during the early to middle Cretaceous period, between 103 and 113 million years ago.  From snout to tail it measured about 23 feet (7m) long.  Its name translates to "Muttaburra Reptile/Lizard" in reference to the part of Queensland in Australia where its fossils were first found. 

Muttaburrasaurus life reconstrucion in watercolors by Christopher DiPiazza.

Muttaburrasaurus would have stood on powerful hind legs, and possessed short but strong arms. It likely normally walked on two legs but would have been capable of dropping down to all fours at times if it wanted.  Scientists were able to predict this not only based on the proportions of its limbs, but also the shape of it's inner ear bones, which often can indicate an animal's posture and preferred head orientation.  

Skeletal mount of Muttaburrasaurus on display at the National Museum of Australia.

Muttaburrasaurus had a relatively long neck and proportionally small head with a snout was originally thought to have ended in a tall crest, similar to those of some hadrosaurs, but it was more recently found, thanks to finding additional missing parts of its skull, that it actually had a rather pointed, narrow snout with a bony bulge midway up the nose, making it much more unique looking.  We still don't know the exact purpose of this feature.  It probably had something to do with display within the species.  Others have suggested it perhaps had something to do with the dinosaur possessing salt glands to help it eat plants that grew in ocean water near where it lived.

Remember putting a plastic cup over your mouth as a kid?  It looks like that.

The back of Muttaburrasaurus' jaws were lined with leaf-shaped teeth for slicing through plants.  Unlike its distant relatives, the hadrosaurs, these teeth were arranged in a single row in each jaw with the new replacement teeth growing directly from below.  Muttaburrasaurus also possessed teeth at the very front of its snout, which is actually rare among ornithopod dinosaurs, notably also present in Thescelosaurus. (which it was also maybe closely related to?)  Like all ornithopods, the tip of its snout was a beak, which would have been for clipping vegetation. 

Skull of Muttaburrasaurus (missing the tip of the snout) (Photo courtesy of Alcharinga Journal of Paleontology.)

The environment Muttaburrasaurus would have lived in was near an ocean coast and would have been seasonally cold.  This is because during that part of the Cretaceous, Australia was much further south and still attached to Antarctica.  Some experts suggest Muttaburrasaurus may have even been adapted to eat plants and algae that grew in salt water, possibly as a food source during the colder months when other plants were more scarce.

Muttaburrasaurus was a member of the ornithopod group of dinosaurs, most famous for including distant relatives like Iguanodon and the "duck-billed" hadrosaurs.  Its identity within this group has proven to be more difficult to pin down.  It was originally considered a close relative of Iguanodon and was even reconstructed with thumb spikes to reflect this. Other experts have since suggested  it was more closely related to dinosaurs like Camptosaurus, and others more to the big-headed rhabdodontid family, like Zalmoxes. (The taxonomy of ornithopod dinosaurs is currently very complicated and tends to change as we discover more fossils.)

References

Bartholomai, Alan and Molnar, R.E. (1981). "Muttaburrasaurus: a new Iguanodontid (Ornithischia:Ornithopoda) dinosaur from the Lower Cretaceous of Queensland". Memoirs of the Queensland Museum. 20 (2): 319–349.

Herne, M. C.; Bevitt, J. J.; Milan, L.; Hocknull, S. A.; Tait, A. M.; Allen, C. M.; Rozefelds, A. C.; Molnar, R. E.; Weisbecker, V.; Bell, P. R. (2026). "Cranial anatomy, palaeoneurology, palaeobiology and stratigraphic age of the large-bodied ornithopod, Muttaburrasaurus langdoni Bartholomai and Molnar, 1981, from the mid-Cretaceous of Australia". PeerJ. 14 e20794.

Molnar, Ralph E. (1996). "Observations on the Australian ornithopod dinosaur, Muttaburrasaurus"". Memoirs of the Queensland Museum. 39 (3): 639–652.

Arundelconodon: Beast of the Week

 This week we will be looking at a unique mammal that lived alongside some of the largest dinosaurs!  Check out Arundelconodon hottoni.  

Arundelconodon was a small mammal that lived in what is now Maryland, in the United States, during the early Cretaceous Period, about 115 million years ago, making it one of the oldest known mammals from the east coast of the US.  It is estimated to have measured about eight to ten inches (20-25cm) long from nose to tail, roughly the same size as a rat.  Based on the teeth it would have been a meat-eater when alive.  It's genus name translates to "Arundel Cone Tooth" after the county in Maryland the location of its fossils is name after.  The species name is in honor of paleontologist, Nicholas Hotton.  

Despite its size Arundelconodon may have attacked larger animals, like this Aquilops, a roughly housecat-sized dinosaur.

Mesozoic mammal fossils are generally extremely difficult to find because the animals they would come from tended to be small and therefore delicate and unlikely to fossilize well.  When they do preserve, it is usually in the form of their teeth, which are made of more durable material, called enamel, than bones.  Luckily teeth are also extremely diagnostic for mammals, so scientists can deduct at least the group of mammals a tooth belongs to most of the time even with no other parts available. Based on teeth and jaws, Arundelconodon was identified as a member of the family of mammals called the triconidontids.  This was a now extinct group of mammals that flourished during the Jurassic and Cretaceous periods that are identified by having three distinct cone-like points on their molars. (The name even translates to "three cone tooth")  Triconidontids would have branched off the mammal family tree relatively early in their history, being more ancient than the first placental mammals but more recent than monotremes.  Because of this it is thought that they birthed live young instead of laying eggs, but little else is currently known about their reproduction, like if they kept their young in a pouch, like marsupials.  Like all mammals, however, they would have produced milk for their young.

Jaw and teeth of Arundelconodon.  This entire fossil is about 1cm long. Image from the Prince George County website.

The teeth of Arundelconodon were notably long compared to the jaw.  The three prongs on the molars were also arranged in a single line, and would have self-sharpened against the teeth of its upper jaw as it opened and closet its mouth.  It is because of this that we are almost certain it was a meat-eater in life.  It may have specialized in hunting small prey, like insects, but it also may have even been able to take down larger prey similar to how certain mammals, like weasels and shrews do today.  It is interesting to imagine Arundelconodon possibly attacking small or baby dinosaurs!

Like most mammals of the Mesozoic, it is likely Arundelconodon was nocturnal or crepuscular (active at dawn and dusk) to avoid predatory dinosaurs, many of which were likely diurnal.  During the day it may have spent time hiding and sleeping underground or maybe even in trees.  It would have needed to look out for predators like the sickle-clawed, Deinonychus and the several different kinds crocodilians that are known from the same fossil site.  The extremely large meat-eating dinosaur, Acrocanthosaurus, also probably would have posed a threat to Arundelconodon when it was a juvenile. (As an adult it may not have noticed it altogether.) Other dinosaurs Arundelconodon would have coexisted with were the small ceratopsian, Aquilops, the sauropod, Astrodon, and the extremely large armored dinosaur, Priconodon.   

References

Celik, Mélina A.; Phillips, Matthew J. (8 July 2020). "Conflict Resolution for Mesozoic Mammals: Reconciling Phylogenetic Incongruence Among Anatomical Regions". Frontiers in Genetics. 11: 0651.

Cifelli, Richard L.; Lipka, Thomas R.; Schaff, Charles R.; Rowe, Timothy B. (1999). "First Early Cretaceous Mammal from the Eastern Seaboard of the United States". Journal of Vertebrate Paleontology. 19 (2): 199–203.

Luo, Zhe-Xi; Kielan-Jaworowska, Zofia; Cifelli, Richard L. (2002). "In quest for a phylogeny of Mesozoic mammals". Acta Palaeontologica Polonica. 47 (1): 1–78.