Siats – large Cretaceous theropod

Siats (Siats meekerorum)

Probably one of the North American largest theropods is also one of the greatest mysteries of paleontology. It was discovered relatively recently, in 2008, yet it is still unclear how big could the mature dinosaurs grow. Why? The answer is pretty straightforward – the discovered Siats fossils belonged to an adolescent specimen. Despite this, the specialists managed to learn quite a few interesting facts related to this large theropod, which inhabited the North American continent in the Late Cretaceous.


  • Kingdom: Animalia
  • Clade: Dinosaurs (Dinosauria)
  • Order: Saurischia
  • Suborder: Theropods (Theropoda)
  • Clade: Megaraptors (†Megaraptora)
  • Genus:Siats
  • Species:Siats meekerorum
Siats (Siats meekerorum)
Siats (Siats meekerorum). Image credit: Jorge Gonzales.


It is estimated to have lived in the Late Cretaceous, about 100 million years ago.

Areas of occurrence

The Siats remains were found in Utah, USA (Emery county). The discovery was made in the Cedar Mountain geological formation.


Lindsay Zanno unearthed the fossilized bones of a previously unknown dinosaur in 2008. These excavations were part of a larger geological project under Peter Makovicky’s guidance. These fossils were collected between the years 2008 and 2010. The first scientific description was comprehended in 2013 – it was created by Lindsay Zanno and Peter Makovicky. As a result, this duo was responsible for proposing the name of the genus and species we use today.

Siats (Siats meekerorum)
Siats (Siats meekerorum). Image credit: Zeherfoto



It is accepted that the first found specimen was over 9 meters (29ft 6in) long and could weigh over 4 tons.

There is much evidence for the found specimen to be physically immature, which would suggest that adult dinosaurs of this genus reached substantially larger size than it is estimated for the discovered animal. Conceivably a fully grown Siats could be even 12 meters  (39ft 4in) long. Therefore it would be one of the largest theropods of North America, second to T. rex. The described specimen is comparable in terms of size to such theropods as Saurophaganax and Acrocanthosaurus.

However, these estimates may only be confirmed after the fossils of an adult dinosaur are found.

Siats (Siats meekerorum).
Siats (Siats meekerorum). Image credit: Jorge Gonzales.

Dietary habits and hunting strategy

Besides the giant sauropods such as Cedarosaurus weiskopfae, Siats could also hunt for tyrannosauroids, which were as large as a dog or a lion at the time (Lythronax genus being the exception – 80 million years ago – as well as Teratophoneus – 77 million years ago; they could measure several meters, but they lived ‘a little bit’ later).

Although the tyrannosauroids of that time were small, their hind legs allowed them to achieve great speeds even on large distances. As a result, they were capable of outrunning a larger attacker. Their speed stemmed from their slender physique and aerodynamic chest.

The Siats bone structure indicates that, as well as allosaurs, it was a rather slow creature. Therefore Siats probably preferred (at least to a certain degree) a carrion-based diet. On the other hand, their legs were similarly built to modern emus, which would suggest that Siats could be not so bad sprinter on short distances.

Siats (Siats meekerorum).
Siats (Siats meekerorum) – size comparison with Sue (the adult T. rex.).

Detailed characteristics / size

Siats (Siats meekerorum)

  • Body length: over 9 meters (29ft 6in), adult dinosaurs could be even 12 – 13 meters (39ft 4in – 42ft 8in) long
  • Height: 4.5 meters (14ft 9in)
  • Weight: more than 4 tons (more than 8800lb)
  • Dating: 100 – 98.5 million years ago
  • Epoch: Late Cretaceous
  • Age: Cenomanian
  • Siats holotype:
    • length: 9.8 m (32 ft 2in)
    • weight: 4-4.6 tons /holotype is a juvenile/
Siats (Siats meekerorum).
Siats (Siats meekerorum) on the left vs Neovenator on the right. Image credit: Scott Hartman

Siats – interesting facts

  • The name Siats is derived comes from a mythological monster that devoured humans. Its name can be roughly translated into ‘man-eater monster’. This horrifying behemoth figure was created by Ute tribe native Americans, whereas the species – meekerorum – is named after the founder of paleontological studies -the geologist John Caldwell Meeker.
  • If the estimated adult dinosaurs’ size proves true, Siats will become not only one of the largest North American predators, but one of the largest predators in the world as well.
  • The Siats fossils are currently in the Natural History Museum in Chicago.
  • The Siats bones bear crocodile bite marks – shape of the teeth marks being the evidence of such state of matters. According to Dr Zanno it is an indication of the presence of giant crocodiles at that time.
Siats (Siats meekerorum).
Siats (Siats meekerorum).

Main photo – Siats (Siats meekerorum). Image credit: Jorge Gonzales.


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