Temporal range: Late Cretaceous
|An artist's interpretation of Siats meekerorum|
Zanno & Makovicky, 2013
Zanno & Makovicky, 2013
Siats meekerorum, meaning Man-Eating Monster, was the apex predator of the Cenomanian Stage. It was named after a man eating monster and the Meeker family, who are museum donors. Holotype specimen is found in Utah, Cedar Mountain formations, which also gave us well-known Deinonychosaurs - Utahraptor and Deinonychus. The holotype is also the only known specimen from this genus, discovered by paleontologist Lindsay Zanno in year 2009. It is the fourth largest theropod dinosaur known from North America. Skeleton includes traces of wide, crocodilian - shaped teeth. Dr. Zanno thinks that is a clue that giant crocodiles. Today, Siats is generally known for being the fourth largest terrestrial carnivore North America has ever known. It was initially classified as a megaraptoran, a group with controversial relations. The group may be tyrannosauroids, allosauroids, or basal coelurosaurs.
First when Zanno and Makovicky discovered the skeleton, they thought it belongs to carcharodontosaurid type of dinosaur, possibly close related to Acrocanthosaurus or Shaochilong. Later and closer analysis of skull shape revealed that this dinosaur is rather neovenatorid than carcharodontosaurid. The paper describing a juvenile Megaraptor suggested that Siats is not a megaraptoran, and instead is likely a neovenatorid, as it shares several traits with Neovenator, but differs from megaraptorans in the structure of its dorsal vertebrae, ilium, and fibula. Even later studies suggesting that megaraptorans are neovenatorids, placed Siats outside of Megaraptora.
Holotype specimen is about 9 m long and 3.5m tall, what's pretty large to neovenatorid standards. However, Dr. Lindsay Zanno says that holotype did not belong to an adult, but to the juvenile. She also says this dinosaur can be about 4.5m tall at most and about 12.5 m long, what surely makes this Theropod one of the largest predators in the North America. It is spectacularly large.
Hunting tactics and behavior
In early Cretaceous, there were no known large predators, until now. Tyrannosauroids were small, about the size of a lion or a dog. Only larger species were Lythronax and Teratophoneus, but they were also small for Tyrannosauroid standards. Also, large herbivores dominated in this environment, and these small Tyrannosaurs could not hunt them. Now, we have found answers - Siats Meekerorum was the natural predator of gigantic sauropds, but they were also the reason why Tyrannosauroids were so small and swift. They evolved gracile and aerodynamic design of thorax and body at all, alongside with long legs, with very large metatarsals and obviously smaller "upper leg" (tibia and femur). Also, tibia was a bit longer than femur. This leg type design was perfect for very fast running in long distances. They are actually not able to hunt well- because of their small size, so they evolved larger and yet more agile legs to escape from Siats and his cousins, what indicates Siats did not eat just large Sauropods such as Cedarosaurus, but also Tyrannosauroids. On the other side, like most other Allosaurs, Siats was a slow creature and partially scavenger. However, because of this emu-like design of hindlimbs, they were able to run pretty fast on short distances. When Siats and similar theropods died off about the beginning of middle Cretaceous, Tyrannosaurids were finally able to grow to immense sizes and dominate the landscape.