Dino of the Week: Yangchuanosaurus

Type Species: Yangchuanosaurus shangyouensis

Classification: Dinosauria – Saurischia – Theropoda - Carnosauria - Allosauroidea - Metriacanthosauridae 

Time Period: Middle to Late Jurassic

Location: China 

Diet: Carnivore 

a pair of Huayangosaurus keep a wary eye on a Yuangchuanosaurus

Yangchuanosaurus was the apex predator of China during the Callovian stage of the Middle Jurassic and the Oxfordian stage of the Late Jurassic. It likely preyed upon sauropods such as Mamenchisaurus and Omeisaurus, and it may have dodged spikes and plates to take down stegosaurs such as Tuojiangosaurus and Huayangosaurus. It was similar in size and appearance to the North American Allosaurus, though it was likely slower (top running speed has been clocked around 25 miles per hour). Yangchuanosaurus was a large, powerful carnivore that walked on two muscular legs. The first digit of its foot was a small dewclaw, a vestigial toe that generally grows higher on the leg and doesn’t make contact with the ground when walking. The three outer toes bore its weight, and each was armed with a large claw. Yangchuanosaurus  had short arms, a strong but short neck, a big head with powerful large, and large, serrated teeth. Because its jaws were relatively weak in regards to bite force, it may have brought down prey in the same manner as has been suggested for Allosaurus: the ‘hatchet-bite’ technique in which the attacker swings its head down like a hatchet to club or stun its prey to submission. Yangchuanosaurus  had characteristic growth on top of its nose along with smaller horns and ridges, similar to Ceratosaurus. Its tail made up half its length.

Yangchuanosaurus may have hunted in packs like the North American Allosaurus. While direct evidence is lacking, the similarities between the two theropods imply such behavior wouldn’t be surprising. Adding credibility to the theory is that we have two specimens of this dinosaur, and they are of different sizes (the first’s skull is 2.5 feet long, and the second’s is 3.5 feet long; the first grew to 26 feet in length whereas the second grew up to 36 feet in length); while these differences could be attributed to different ages of the specimens, it could also be due to sexual dimorphism. Sexual dimorphism – wherein one sex has different sizes or morphologies than the other – is often seen in gregarious creatures, and pack-hunting is a facet of gregarious hunters (think: wolves). By hunting in packs, Yangchuanosaurus could bring down large sauropods. The meet of a full-grown Mamenchisaurus could feed the pack for a whole week and still leave some leftovers for scavengers.