Sinosaurus: Beast of the Week

This week we will be looking at one of the first large predatory dinosaurs.  Make way for Sinosaurus triassicus!

Sinosaurus triassicus life reconstruction in watercolors by Christopher DiPiazza

Sinosaurus was a meat-eating dinosaur that lived in what is now Southwest China during the early Jurassic period, between 201 and 196 million years ago.  From snout to tail it measured 18 feet (5.5 meters) long. It's genus name translates to "Chinese Lizard/Reptile" and the species name is in reference to the Triassic period which is when it was first believed to have lived upon its discovery. (We now know it was in the Jurassic.)

Sinosaurus is a dinosaur that underwent a few identity changes as paleontologists discovered more fossils and learned more about it over the years.  Most prominently it was believed to be an Asian species of the more popular North American theropod, Dilophosaurus, and was originally named Dilophosaurus sinensis.  This makes sense at first since both of these dinosaurs are known for having two bony crests on the top of their snouts.  They both also even have a similar notch towards the front of their upper jaws.  However, as more material from Sinosaurus was unearthed over the years, it was determined that it was more closely related to later kinds of theropods, called the tetanurans, and therefore was given its own genus name, Sinosaurus.  Tetanurans are a broad group of theropods characterized by how their tails were stiffened in life thanks to how their tail vertebrae interlock together.  Tetanurans are also all more closely related to birds than to other dinosaurs, including other kinds of theropods.  According to this updated idea, Sinosaurus was particularly closely related to another crested theropod from the early Jurassic, Cryolophosaurus.  

Sinosaurus skeletal mount on display at the Maryland Science Center in Baltimore, Maryland, USA.

Sinosaurus had curved serrated teeth that would have been ideal for slicing through and stripping off chunks of meat from bodies.  The upper jaw notch towards the front of its snout may have been an adaptation for hooking into and ripping through the skin of other dinosaurs to get into the meat inside, similar to the hooked beaks of modern carnivorous birds, like hawks, eagles, and vultures.  Sinosaurus is probably most known for its bony crests which adorned the top of its skull.  These crests had holes in them, making them lightweight, and may have served as visual display adaptations within the species or even possibly could have helped absorb impact, allowing Sinosaurus to bite harder without injury.

Sinosaurus skull from in Zhang's 2023 paper. (listed below)

Sinosaurus shows evidence of tooth injury in life in the form of what is called alveolar remodeling.  This means that it experienced a broken tooth and the ridge of bone in the jaw that includes the tooth sockets, called the alveolar bone, changed shape in the healing process following the loss of the tooth.  Dinosaurs losing and replacing teeth is common in the fossil record, but this is the only recorded instance of an actual tooth related injury that healed in this way known so far for a dinosaur.  

Sinosaurus lived during a time when predatory dinosaurs were first starting to get truly large.  Prior to this most meat-eating dinosaurs were much smaller and more gracile, like Coelophysis, and even the biggest plant-eaters, like Plateosaurus, weren't that huge compared to what would later evolve.  At 18 feet long, Sinosaurus was likely the top of the food chain in its environments.  

References

Chung-Chien, Young (1940). "Preliminary Notes on the Lufeng Vertebrate Fossils*: Young:-Lufeng Vertebrate Fossils". Bulletin of the Geological Society of China. 20 (3–4): 235–240.

Dong, Z.M. (2003). "Contribution of New Dinosaur Materials from China to Dinosaurology" (PDF). Memoir of the Fukui Prefectural Dinosaur Museum. 2: 123–131.Xing, L.D.; Bell, P.R.; Rothschild, B.M.; Ran, H.; Zhang, J.P.; Dong, Z.M.; 

Rauhut, O.W.M. (2003). "The interrelationships and evolution of basal theropod dinosaurs". Special Papers in Palaeontology. 69: 215.

Zhang, W.; Currie, P.J. (2013). "Tooth loss and alveolar remodeling in Sinosaurus triassicus (Dinosauria: Theropoda) from the Lower Jurassic strata of the Lufeng Basin, China". Chinese Science Bulletin. 58 (16): 1931–1935.

Zhang, Z.-C.; Wang, T.; You, H.-L. (2023). "A New Specimen of Sinosaurus triassicus (Dinosauria: Theropoda) from the Early Jurassic of Lufeng, Yunnan, China". Historical Biology. in press.