PALEO PROFILE - Siats meekerorum

What better way to start this blog with a profile of my favourite dinosaur, Siats meekerorum.


Siats seen here on the third row, the third from left, in transparent aquamarine
Credit: veterufreak.deviantart.com

Statistics
Length: 10,4 metres (holotype) at sub-adult stage, likely around 12 metres fully grown
Weight: 3800 kilograms (holotype) at sub-adult stage, likely around 5600 kilograms fully grown
Formation: Cedar Mountain Formation, Mussentuchit Member, Utah, USA
Time range: Cenomanian, 95-100 Million years ago (Holotype found 98.5 mya)
Relation: Dinosauria > Saurischia > Theropoda > Neotheropoda > Averostra > Tetanurae > Orionides > Avetheropoda > Carnosauria > Allosauroidea > Allosauria > Carcharodontosauridae > "Neovenatorinea" > Siats > S.meekerorum



My own depiction of Siats meekeroum, shown with adult speculation, and size comparative to 1.8m tall human
  Discovered in 2008, fully collected in 2010 and described in 2013, Siats meekerorum (pronounced See-ots or see-atch) was published by Lindsey Zanno and Peter J Mackovicy. It's genus name refers to the Siat, a large clown-like monster from Native American Ute mythology that devoured hunters. Its species is in honour of geologist John Caldwell Meeker, who donated massive amounts of money to paleontological research before his death.

Siats made headlines around the world, as its presence in Cenomanian America was the final piece of the puzzle surrounding North American carnivorous dinosaurs and their progression. In the Early Cretaceous, the Aptian and Albian (113-110 mya), the large 6.1 tonne Carcharodontosaur Acrocanthosaurus atokensis was the dominant apex predator. As the Cretaceous drew on, and dinosaurs like the Ankylosaurs and Ceratopsids began to evolve, prey became scarcer for weak biters like Acrocanthosaurus, which only had the Ornithopod Tenontosaurus and giant Sauropod Sauroposeidon for prey. In the Turonian (93.8-89.8 mya) The first true Tyrannosauroids, who would become the Tyrannosaurids like Tyrannosaurs, were present, in the shape of Timurlengia euotica, a recent Uzbekistani find with excellent hearing. By the Campanian (72.1-83.6 mya) Tyrannosaurids like Albertosaurines had became dominant apex carnivores, and had moved to America. The Maastrichtian brought the rise of Tarbosaurus bataar, and Tyrannosaurus rex, the last tyrannosaurids before the K-Pg extinction event. But what occupied the apex carnivore spot after Acrocanthosaurus, and before the Tyrannosaurs? Enter Siats.


Phylogeny showing Siats and its relation to other Allosaurs
Credit: veterufreak.deviantart.com

The Fossil
FMNH PR 2716 is currently the only fossil of Siats meekerorum. It resides in the Field Museum of Natural History, in Chicago, the same museum that houses Sue the T.rex, everyone's favourite dinosaur on Twitter. FMNH PR 2716 was a juvenile, around sub-adult stage of growth. It consists of several vertebrae, pelvis, ischia, fibula and other indeterminate post-cranial remains. The animal was immediately identified as a "Neovenatorid" Carcharodontosaur, Zanno and Mackovicy forgetting that an -id family cannot reside within another -id family. How callous. Amateur results have given Siats and the other "Neovenatorids" new places in the dinosaur family tree; Megaraptorans, the hollow-boned predators with giant index claws residing just outside of Tyrannosaurus' circle, Gualicho and Deltadromeus pushed into the long necked herbivore family of Elaphrosaurs, and this new solution has even absorbed another dinosaur, Kelmayisaurus petrolicus, from the Mid Cretaceous of China. However, Siats was also cast into becoming a Megaraptoran. But this changed in 2017, when amateur analysis showed that its vertebrae were far unlike that of any known megaraptoran, and more like Neovenator. And so "Neovenatorinae" was born and the Etymologists rejoiced, and Siats, Neovenator and Kelmayisaurus were pulled into this family.



Drawing depicting Siats hunting the hadrosaur Eolambia caroljonesi
Credit: randomdinos.deviantart.com

Ecology
As a large, five tonne apex carnivore, Siats  likely predated upon the vast amount of herbivorous dinosaurs in the region with no competition. The only possible contenders for Siats' throne were:

• A 'Xiongguanlong-type' Tyrannosauroid known from tooth fragments, likely approx. 5-6 metres and 600 kilograms
• At least one Dromaeosaurid dinosaurs, likely around 1-3 metres and 150 kilograms, known from tooth fragments
• At least one Velociraptorine dromaeosaur, likely around 2 metres and 160 kilograms, known from tooth fragments
• A "Troodontid"/"Stenonychosaurid" dinosaur, likely around 0.5-2 metres and 50-150 kilograms

 
Skeletal reconstruction of Xiongguanlong baimoensis, likely comparative to the Mussentuchit tyrannosauroid.
Credit: getawaytrike.deviantart.com

All of these carnivores, likely smaller in magnitude by at least 10x would have posed little threat to a large adult Siats, but in its adolescent stages, some of these predators would have been viable competition. All of these carnivores need a food source, and the Mussentuchit had herbivores-a-plenty:

• Abydosaurus mcintoshi, a giant 20+ metre long, 40 tonne brachiosaur, likely too large for a single, or even group of Siats, but ill and young Abydosaurs would have been in range.
• Eolambia caroljonesi, A 7 metre long, 1-2 tonne hadrosaurine, just like Siats, found at immature stage, and likely around 10 metres and 4-5 tonnes at full size, an ideal prey item for Siats, and in younger stages, likely the Mussentuchit Tyrannosaur.
• Tenontosaurus sp, a dubious find of the usually-later found 6 metre Tenontosurus, this could have fell victim to any of these carnivores, with the relatively small dromaeosaur Deinonychus antirrhoppus found hunting the animal in other formations.
• Peloroplites cedrimontanus, Average sized for a Nodosaur at 6 metres and 5 tonnes, but some fragmentary remains seem to indicate a (very) unlikely 10 metre and 12 tonne size for this animal, however making it still inaccessible to Siats behind its thick armour, with its spines distinct of a Polacanthine Nodosaur.
• Animantarx ramaljonesi, quite a small Nodosaur, it shared many similarities with Ankylosaurs, sans tail club. At around 4 metres and one tonne, its armour may have protected it, but a smart carnivore could have flipped it to expose its vulnerable underbelly, or attacked weak spots.
• Cedarpelta bibleyhallorum, a large Ankylosaur, around 6 metres and 5 tonnes, would have been well guarded by its thick armour, and its deadly shin-breaking tail club
• An un-named Therizinosaur, comparable in morph and size to Falcarius, at around 4-5 metres and 400-600 kilograms, would have been a viable choice for Siats, if it could keep away from its deadly claws.
• An un-named Pachycephalosaur, similar to Stegoceras, would have been good prey for Siats, its small size negating its powerful head-butt.
• An un-named Neoceratopsine, alike to Protoceratops or Micropachycephalosaurus, would have been easy prey for Siats of any age.

Here's a video about Siats from its lead researcher, wherein Dr Zanno presents her new find on a podcast.

Overall, Siats meekerorum was a deadly, apex carnivore with the capacity to kill anything from a tiny Ornithiscian, to maybe a 20-tonne brachiosaur, and in the end, it's a total man-eater.

Thanks for reading this (really long) blog post about Siats, the next post here will be about the Syfy TV show The Expanse's fearful Martian flagship, the Donnager Class Battleship.





SOURCES
https://en.wikipedia.org/wiki/Cedar_Mountain_Formation
https://en.wikipedia.org/wiki/Siats
https://www.researchgate.net/publication/258422652_Medial_Cretaceous_vertebrates_from_the_Cedar_Mountain_Formation_Emery_County_The_Mussentuchit_local_fauna