''Geminiraptor'' (meaning "twin seizer") is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

troodontid Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

that lived in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

. ''Geminiraptor'' was a small, ground-dwelling

bipedal Bipedalism is a form of terrestrial locomotion where an animal moves by means of its two rear (or lower) limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' ...

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

paravian Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the av ...

. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

of ''Geminiraptor'' is ''G. suarezarum''.

Discovery and naming

The holotype and only known specimen of Geminiraptor is CEUM 7319, a

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

recovered from the Lower Yellow Cat Member of the

Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid-Cretaceous. The formation was named for Cedar Mountain (Utah), Cedar Mountain in northern Emery Cou ...

, in

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

, dating from the early to late

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

stage (about 139 to 134 million years ago). The name refers to Drs. Marina and Celina Suarez, the twin geologists who discovered the Suarez site from which the fossil was recovered. ''G. suarezarum'' was named by Phil Senter, James I. Kirkland, John Bird and Jeff A. Bartlett in

2010 The year saw a multitude of natural and environmental disasters such as the 2010 Haiti earthquake, the Deepwater Horizon oil spill, and the 2010 Chile earthquake. The 2009 swine flu pandemic, swine flu pandemic which began the previous year ...

. The generic name, ''Geminiraptor'', is from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''geminae'' (“twins") and ''raptor'' ("seizer"). The specific name, ''suarezarum'', uses their last name ''Suarez''.

Description

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 ''Sinovenator'' (meaning "Chinese hunter") is a genus of troodontid dinosaur from China. It is from the early Cretaceous Period (geology), Period. Discovery and naming Two specimens of a troodontidae, troodontid were described in 2002 in paleo ...

''. 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). ''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 Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...

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. The

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Thomas R. Holtz Jr. has estimated its weight around and a possible length of .Supplementary Information 2012
/ref> Although still a rather small dinosaur, ''Geminiraptor'' is larger than most other

troodontids, with its maxillary proportions more similar to those of

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

genera.

Classification

''Geminiraptor'' is considered a

, a classification supported due to its large number of small teeth. The

phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

conducted by its describers placed it in a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

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. Below is the proposed placement for ''Geminiraptor'' conducted by Senter et al. 2010:

Paleoecology

Cedar Mountain Formation Yellow Cat Fauna

''Geminiraptor'' was the first report of a troodontid in the Early Cretaceous of North America, proving their existence. It lived in the Lower Yellow Cat Member of the

about 139-134 million years ago. The environments were semiarid areas with floodplain prairies, riverine forests, and open woodlands. It has been also interpreted that there was a waterlogged bog-like environment. Paleofauna that lived alongside ''Geminiraptor'' in the lower bed, included other

Theropods Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

: ''

Falcarius ''Falcarius'' (meaning "sickle cutter") is a genus of primitive therizinosaur dinosaur that lived during the Early Cretaceous period in what is now North America. Its remains were first collected in the Cedar Mountain Formation in 1999, with subs ...

'' and '' Yurgovuchia''. The

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...

Mierasaurus ''Mierasaurus'' is an extinct genus of sauropoda, sauropod dinosaur from the Early Cretaceous of Utah, United States. The taxon was first described and named in 2017 in paleontology, 2017 by Rafael Royo-Torres and colleagues, from a mostly compl ...

'', the large

iguanodontian Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively sm ...

'' Iguanacolossus'' and the turtle ''

Naomichelys ''Naomichelys'' is an extinct genus of helochelydrid stem turtle known from the Cretaceous (Aptian-Campanian) of North America. It is the only member of the family known to be native to North America. Distribution ''Naomichelys'' is known nume ...

'' are also found here. There are also indeterminate

Goniopholidid Goniopholididae is an extinct family of moderate-sized semi-aquatic neosuchian crocodyliformes. Their bodyplan and morphology are convergent on living crocodilians. They lived across Laurasia (Asia, Europe and North America) between the Middle J ...

crocodiles and an unnamed velociraptorine known from the Lower Yellow Cat.

References

{{Taxonbar, from=Q1936000 Troodontidae Dinosaur genera Valanginian dinosaurs Cedar Mountain Formation Fossil taxa described in 2010 Taxa named by James I. Kirkland Dinosaurs of the United States

Discovery and naming

Description

Classification

Paleoecology

See also

References