Siats
Named after Siats, a man-eating monster from the mythology of the Ute people of Utah, near where the fossil was found.
Siats is an extinct genus of large theropod dinosaurs known from the Late Cretaceous Cedar Mountain Formation (Mussentuchit Member) of Utah, United States. The genus contains a single species, Siats meekerorum. It was initially classified as a megaraptoran, a clade of large theropods with controversial relationships. Alternative positions within the Neovenatoridae, Allosauroidea, and Tyrannosauroidea have also been proposed.
Under dispute
Siats was originally described as a megaraptoran within Neovenatoridae (Allosauroidea). Its position has since been contentious: it has been recovered as a tyrannosauroid, as a non-megaraptoran neovenatorid, and as a coelurosaur of uncertain placement, and Jones (2026) tentatively retains it in Neovenatoridae. The recent allosauroid analysis of Kellermann and colleagues (2025) recovers it firmly within Megaraptora, where it is placed; its position relative to Megaraptoridae is unresolved, so it is left in Megaraptora incertae sedis.
Diagnosis
- Craniocaudally expanded centrodiapophyseal laminae lacking well-developed infradiapophyseal fossae on proximal caudals
- Transversely flattened, axially concave ventral surface yielding subtriangular cross-section on distal caudal vertebrae
- Transversely concave acetabular rim of iliac pubic peduncle
- Truncated lateral brevis shelf with notched caudal end
- Abbreviated, transversely broad neural spines on dorsal vertebrae (height ~50% maximum centrum height)
Species
Siats meekerorum Zanno & Makovicky, 2013
Type species
Named for geologist John Caldwell Meeker and the Meeker family, in recognition of their support of paleontological research.
- Holotype
- FMNH PR 2716 , Field Museum of Natural History
- Material
- Partial postcranial skeleton of immature individual including axial column, pelvic girdle, hind limb
- Horizon
- Mussentuchit Member, Cedar Mountain Formation, Cenomanian, Late Cretaceous , 100.5–93.9 million years ago
- Locality
- Emery County, Utah, United States
References
- Zanno, L. E.; Makovicky, P. J. (2013). Neovenatorid theropods are apex predators in the Late Cretaceous of North America. Nature Communications 4(1). Springer Science and Business Media LLC. doi:10.1038/ncomms3827 zanno2013a
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Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.
Source of the body length, mass, and hip height estimates.
jones2026c -
Kellermann, M.; Cuesta, E.; Rauhut, O. W. M. (2025). Re-evaluation of the Bahariya Formation carcharodontosaurid (Dinosauria: Theropoda) and its implications for allosauroid phylogeny. PLOS ONE 20(1): e0311096. Public Library of Science (PLoS). doi:10.1371/journal.pone.0311096
Allosauroid re-evaluation recovering Siats firmly within Megaraptora.
kellermann2025a