Moros: Beast of the Week

 This week we'll be looking at an important little dinosaur that helps us understand the backstory of the most famous dinosaur ever known.  Check out Moros intrepidus!

Moros was a relatively small meat-eating dinosaur that lived in what is now Utah, USA, during the Cretaceous period, between 97 and 96 million years ago.  From snout to tail Moros is estimated to have measured about 10 feet (3 meters) long based on fragmented remains.  The genus name is after the deity from Greek Mythology, Moros, who was the personification of impeding doom, appearing to those who were about to die. The reasoning for this name is because Moros is thought to be the ancestor of later apex predators, like Tyrannosaurus rex.

Watercolor reconstruction by Christopher DiPiazza of a trio of Moros.

Even though Moros is only known from an incomplete skeleton, paleontologists can deduct that it was indeed a member of the tyrannosaur group based on the leg and foot bones, and the teeth that were uncovered.  They were also able to identify the individual as an almost fully grown adult based on growth rings in the leg bone.  

It may seem odd to associate such a relatively small, lanky dinosaur like Moros, with giant monsters like Tyrannosaurus or Gorgosaurus, but when looking at the fossil record this actually makes sense.  The fossil record actually has many smaller species of tyrannosaurs found in North America, Europe, and Asia, ranging in age from 160 to 96 million years old.  The larger trannosaurids don't start showing up until millions of years later.  Different large-bodied meat-eaters, called the carnosaurs (like Sinraptor in Asia), existed alongside the smaller, earlier tyrannosaurs, and went extinct before the large, two-fingered tyranosaurids appeared in the same places.  It is thought that the smaller, more adaptable, early tyrannosaurs were able to survive whatever  wiped out the carnosaurs in the northern hemisphere, and then went on to occupy their niche as giant predators in the form of the two-fingered tyrannosaurids.  To put it into perspective, Tyrannosaurus is more closely related to birds than to dinosaurs like Allosaurus, and fossils like those of Moros help fill in the gaps that prove it.

Different views of the femur of Moros featured in the 2019 paper by Zano et al., including cross section and growth rings.

Moros had proportionally long, slender legs, which suggest it was a fast runner when alive, and possibly could have hunted smaller prey.  Since paleontologists have found feathers in other tyrannosauroid fossils, it is likely Moros had some sort of feathers in life too.  

References

Zanno, Lindsay E.; Tucker, Ryan T.; Canoville, Aurore; Avrahami, Haviv M.; Gates, Terry A.; Makovicky, Peter J. (February 2019). "Diminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American fossil record". Communications Biology.