Geminiraptor

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Geminiraptor
Temporal range: Early Cretaceous, 130–125 Ma
Geminiraptor.png
The holotype maxilla in multiple views
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Troodontidae
Genus: Geminiraptor
Senter et al., 2010
Species:
G. suarezarum
Binomial name
Geminiraptor suarezarum
Senter et al., 2010

Geminiraptor is a genus of troodontid theropod dinosaur that lived during the Early Cretaceous period in what is now Utah, North America. Geminiraptor was a small, ground-dwelling bipedal carnivorous paravian. The type species of Geminiraptor is G. suarezarum.[1]

Disovery and naming

The holotype and only known specimen of Geminiraptor is CEUM 7319, a maxilla recovered from the lower Yellow Cat Member of the Cedar Mountain Formation, dating to at least the early Barremian stage (about 130 million years ago). Geminiraptor was named by Phil Senter, James I. Kirkland, John Bird and Jeff A. Bartlett in 2010. The specific name refers to Drs. Celina and Marina Suarez, the twin geologists who discovered the Suarez site. The generic name is from the Latin geminae (“twins,” in honor of the Suarez sisters) and raptor ("seizer").[1]

Description

Hypothetical life restoration

The maxilla is long and low, with the process above the antorbital fenestra being horizontal, similar to other advanced troodontids. However, some features of the maxilla are more similar to the condition in basal troodontids such as Sinovenator. These include the presence of a promaxillary fenestra which is visible in lateral view, a narrow promaxillary strut (the bar of bone between the maxillary and promaxillary fenestrae), and a narrow interfenestral strut (the bar of bone between the maxillary and antorbital fenestrae).[1]

Geminiraptor is uniquely characterized by the presence of a large pneumatic chamber which expands the maxilla into a triangular shape in cross section, with the base formed by a bony shelf lingual to the teeth. Nine alveoli are preserved, although since both the anterior and caudal tips of the maxilla are missing, certainly more were present. By comparing Geminiraptor's maxilla to that of other troodontids, it was inferred that at least three more teeth were present in the missing anterior part of the maxilla and at least seven in the missing caudal area, for a total of at least nineteen teeth in the maxilla. The alveoli are characteristically square-shaped and separated by small walls of bone, a feature only known in Sinovenator among other troodontids.[1]

The paleontologist Thomas R. Holtz Jr. has estimated its weight around 2.27–9.1 kg (5.0–20.1 lb) and a possible length of 1.5 m (4.9 ft).[2] Although still a rather small dinosaur, Geminiraptor is larger than most other Early Cretaceous troodontids, with its maxillary proportions more similar to those of Late Cretaceous genera.[1]

Classification

Comparison of the maxilla of Geminiraptor to those of other paravians

Geminiraptor is considered a troodontid, a classification supported due to its large number of small teeth. The phylogenetic analysis conducted by its describers placed it in a clade with derived troodontids due to the oblong shape of its maxillary fenestra. Due to the large amount of missing data for the genus, its position within the family is not completely certain, and Geminiraptor may instead be a close relative of Sinovenator due to each of them having interdental bone walls, unlike all other known troodontids.[1]

Below is the proposed placement for Geminiraptor conducted by Senter et al. 2010:[1]

Deinonychosauria

Anchiornis

Troodontidae

Sinovenator

Geminiraptor

Mei

Byronosaurus

Sinornithoides

Sinusonasus

Saurornithoides

Zanabazar

Troodon

Paleoecology

Geminiraptor and contemporaneous fauna from the Yellow Cat and Poison Strip Members of the Cedar Mountain Formation (Geminiraptor in dark, pale purple; next to Utahraptor)

Geminiraptor was the first report of a troodontid in the Early Cretaceous of North America, proving their existence. It lived in the Yellow Cat Member of the Cedar Mountain Formation[1] about 130-125 million years ago.[2] The environments were semiarid areas with floodplain prairies, riverine forests, and open woodlands.[3] It has been also interpreted that there was a waterlogged bog-like environment.[4]

The diverse fauna that lived alongside Geminiraptor included other Theropods: Utahraptor, Yurgovuchia, Nedcolbertia, Falcarius and Martharaptor; Ornithischians: Iguanacolossus, Hippodraco, Planicoxa, Cedrorestes and Gastonia; Sauropods: Cedarosaurus, Venenosaurus, Mierasaurus and Moabosaurus.[3][5][6][7] Non-dinosaur animals were present as well, including Turtles: Glyptops, Naomichelys and Trinitichelys; the Rhynchocephalian Toxolophosaurus; Goniopholidids[7][5] and the Early Mammal Cifelliodon.[8]

Additional contemporaneous paleofauna was recovered from the Early Cretaceous of the Cedar Mountain Formation, but the majority of them are indeterminate and/or unnamed: UMNH VP 21752 (an indeterminate Velociraptorine represented by a left pelvis and possibly a radius) and UMNH VP 20209 (indeterminate Eudromaeosaur represented by a caudal vertebra and fragmented tail).[9]. A large, sail-backed Iguanodont is represented with large vertebrae and fragmentary remains.[10] A Neochoristodere was unearthed from the Yellow Cat Member, represented by a left femur[11], plus an isolated Mesoeucrocodylian skull that measures 20 cm (7.9 in).[5]

See also

References

  1. ^ a b c d e f g h Senter, P.; Kirkland, J. I.; Bird, J.; Bartlett, J. A. (2010). "A New Troodontid Theropod Dinosaur from the Lower Cretaceous of Utah". PLoS ONE. 5 (12): e14329. doi:10.1371/journal.pone.0014329. PMC 3002269. PMID 21179513.
  2. ^ a b Holtz, T. R.; Rey, L. V. (2007). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House. Supplementary Information 2012 Weight Information
  3. ^ a b Paul, Gregory S. (2016). The Princeton Field Guide to Dinosaurs (2nd Edition). Princeton, New Jersey: Princeton University Press. pp. 151, 163, 229, 252, 314, 319, 326, 327. ISBN 9780691167664.
  4. ^ Royo-Torres, R.; Upchurch, P.; Kirkland, J.I.; DeBlieux, D.D.; Foster, J.R.; Cobos, A.; Alcalá, L. (2017). "Descendants of the Jurassic turiasaurs from Iberia found refuge in the Early Cretaceous of western USA". Scientific Reports. 7 (1): 14311. doi:10.1038/s41598-017-14677-2. PMC 5662694. PMID 29085006.
  5. ^ a b c Kirkland, J.I. (December 1, 2016). "The Lower Cretaceous in East-Central Utah—The Cedar Mountain Formation and its Bounding Strata". Geology of the Intermoutain West. 3: 1–130.
  6. ^ Weishampel, D. B.; Dodson, P.; Osmolska, H. (2007). The Dinosauria, Second Edition. University of California Press. p. 554.
  7. ^ a b Kirkland, J. I.; Cifelli, R.; Britt, B. B.; Burge, D. L.; Decourten, F. L.; Eaton, J. G.; Parrish, J. M. (1999). "Distribution of Vertebrate Faunas In the Cedar Mountain Formation, East-Central Utah". Vertebrate Paleontology in Utah: 201–218.
  8. ^ Huttenlocker, A.; Grossnickle, D. M.; Kirkland, J. I.; Schultz, J. A.; Luo, Z. X. (2018). "Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana". Nature. 558 (7708). doi:10.1038/s41586-018-0126-y. ISSN 1476-4687.
  9. ^ Senter, P.; Kirkland, J. I.; Deblieux, D. D.; Madsen, S.; Toth, N. (2012). Dodson, Peter (ed.). "New Dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the Evolution of the Dromaeosaurid Tail". PLoS ONE. 7 (5): e36790. doi:10.1371/journal.pone.0036790. PMC 3352940. PMID 22615813.
  10. ^ Scheetz, R. A.; Britt, B. B.; Higgerson, J. (2010). "A large, tall-spined iguanodontid dinosaur from the Early Cretaceous (Early Albian) basal Cedar Mountain Formation of Utah". Journal of Vertebrate Paleontology. 30: 158A.
  11. ^ Britt, B. B.; Scheetz, R. D.; Brinkman, D. B.; Eberth, D. A. (2006). "A Barremian neochoristodere from the Cedar Mountain Formation, Utah, U.S.A." (PDF). Journal of Vertebrate Paleontology. 26 (4): 1005–1008. doi:10.1671/0272-4634(2006)26[1005:ABNFTC]2.0.CO;2.