Tachiraptor ("thief of Táchira") is a genus of carnivorous theropod dinosaurs found in the early Jurassic period La Quinta Formation of Venezuela. It includes one species, Tachiraptor admirabilis, described from a fossilized tibia and ischium. They were small bipedal dinosaurs, with a deduced total body length of just over 1.5 m (4.9 ft). They were likely generalist predators, preying on smaller vertebrates like other dinosaurs or lizards.
Temporal range: Early Jurassic
|IVIC-P-2687, the holotype right tibia, and IVIC-P-2868, the referred left ischium|
Langer, Rincón, Ramezani, Solórzano, & Rauhut, 2014
Langer, Rincón, Ramezani, Solórzano, & Rauhut, 2014
Since the late 1980s in the Venezuelan state of Táchira, remains of dinosaurs have been uncovered at a road-cut between La Grita and Seboruco. Most of these belonged to a small herbivore that in 2014 was described as Laquintasaura. However, included in the discoveries were some theropod teeth, indicating a predator must have been present. In 2013, this was affirmed by the discovery of some theropod bones.
The description was based on two fossils, found in a layer of the La Quinta Formation dating from the Early Jurassic Hettangian stage. The region was once part of the equatorial belt of the ancient supercontinent of Pangaea. A maximum age of 200.72 ± 0.32 million years ago has been confidently established, but due to the limits of zircon radiometric dating, a precise minimum estimate is not known; the actual age could be considerably younger. Both fossils are from the same location, but assumed to represent two individuals. One of these was the holotype specimen, IVIC-P-2867. It consists of a nearly complete right tibia or shinbone. The second fossil was referred to Tachiraptor admirabilis on the assumption that only one species of neotheropod of such a size was present in the La Quinta Formation. It is specimen IVIC-P-2868, consisting of the damaged upper half of a left ischium, a bone of the pelvis.
The generic name was derived from that of the state of Táchira, where it was discovered, combined with the Latin word for thief, raptor. The specific name admirabilis was chosen in reference to the Admirable Campaign of 1813, conducted by Simón Bolívar, for which the type locality of La Grita was of strategic importance.
The authors established a number of distinguishing traits. One of these is a possible autapomorphy, a unique evolutionary innovation shown just by Tachiraptor. It pertains to the profile, seen from above, of the upper surface of the shinbone. Such surfaces generally have two projections, corners jutting out to behind, left and right. In Tachiraptor the outer projection, at the side of the fibula, has a rear edge making a sharp angle with the outer edge. This way a uniquely sharp point is formed which, uniquely also, extends further to behind than the inner projection at the opposite side.
Apart from the autapomorphy, a unique combination of, in themselves not unique, traits was also demonstrated. The bottom surface of the shinbone was, in its transverse width, about 1.5 times as wide as the longitudinal distance (measured from front to rear). In dinosaurs in general, the lower front of the shinbone is covered by the talus bone. A ridge on the front surface demarcates the upper limit of this area. In Tachiraptor this ridge ran obliquely at an angle of about 35° to the lower edge of the shinbone, covering a vertical distance of about a quarter to a third of the lower shinbone height. At its lower end, this ridge slightly curved upwards, being at this point close to the outer edge of the shinbone, at about a fifth of its transverse width. The shinbone extends to below in two bumps, left and right. When seen from the front, with Tachiraptor a line drawn between the bumps made an angle of 80° with the vertical axis of the bone.
The study describing Tachiraptor performed a cladistic analysis, establishing its probable evolutionary relationships (phylogeny) by computing an evolutionary tree assuming the least number of evolutionary changes. This analysis showed that Tachiraptor was a basal member of the Neotheropoda, the subgroup encompassing all but the earliest theropods. It thus was placed low in the evolutionary tree of the neotheropods. Tachiraptor was part of the stem leading to the Averostra, the group all theropods belong to from the Middle Jurassic onwards, including the birds. Being a sister species of the Averostra, it was described as a "stem-averostran". This made the discovery of Tachiraptor especially important, because before 2014, there were no unequivocal stem-averostrans known at all. Tachiraptor thus reduced their ghost lineage (an inferred though yet unproven line of descent) by twenty-five million years.
Tachiraptor also contributed to a greater knowledge of evolution by confirming that the equatorial zone of the supercontinent Pangea played an important role in the development of early dinosaurs, as already shown by the discovery of Laquintasaura.
The Anchisauria were a clade of sauropodomorph dinosaurs that lived during the Late Triassic and Early Jurassic. The name Anchisauria was first used by Galton and Upchurch in the second edition of The Dinosauria. Galton and Upchurch assigned two families of dinosaurs to the Anchisauria: the Anchisauridae and the Melanorosauridae. The more common prosauropods Plateosaurus and Massospondylus were placed in the sister clade Plateosauria.
However, recent research indicates that Anchisaurus is closer to sauropods than traditional prosauropods; thus, Anchisauria would also include Sauropoda.The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Dinosauriformes
Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.Haya griva
Haya is an extinct genus of basal neornithischian dinosaur known from Mongolia.Jeholosauridae
Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.La Quinta Formation
The La Quinta Formation is a Jurassic geologic formation which crops out in the Cordillera de Mérida and Serranía del Perijá of western Venezuela and northeastern Colombia. The formation is also present in the subsurface of the Cesar-Ranchería and Maracaibo Basins. At its type locality near La Grita, Táchira, it consists of a basal dacitic tuff followed by interlayered sandstones, tuffs, siltstones and rare limestones. Dinosaur remains including Laquintasaura, and Tachiraptor, are among the fossils that have been recovered from the formation.Fossil associations suggested that the La Quinta Formation was of Early to Middle Jurassic age, while a more recent estimate based on U–Pb zircon analysis demonstrates that the bonebed has a maximum depositional age of 200.91+0.55 Ma.Melanorosauridae
The Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder "Prosauropoda": the Anchisauridae, the Plateosauridae, the Thecodontosauridae, and the Melanorosauridae. Since then, these families have undergone numerous revisions. Galton and Upchurch (2004) considered Camelotia, Lessemsaurus, and Melanorosaurus members of the family Melanorosauridae. A more recent study by Yates (2007) indicates that the melanorosaurids were instead early sauropods.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Raeticodactylidae
Raeticodactylidae is a family of eudimorphodontoid eopterosaurian pterosaurs that lived in Switzerland during the Late Triassic. The family includes Caviramus, and the type genus Raeticodactylus, which are both known from the Kössen Formation, around 205 mya. Raeticodactylidae was first used in 2014 by Andres et al., as a group of all pterosaurs closer to Raeticodactylus than Eudimorphodon. The following phylogenetic analysis follows the topology of Andres et al. (2014).Riojasauridae
Riojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus. Sites containing Riojasauridae include the Lower Elliot Formation of Orange Free State, South Africa (where fossils of Eucnemesaurus have been found), and Ischigualasto, in La Rioja Province, Argentina ( where fossils of Riojasaurus have been recovered).Thescelosaurinae
Thescelosaurinae is a subfamily of ornithischian dinosaurs from the Early Cretaceous of Asia and the Late Cretaceous of North America.Unaysauridae
Unaysauridae is a family of basal sauropodomorphs from the Late Triassic of India and Brazil.Xixiposaurus
Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.Yueosaurus
Yueosaurus is an extinct genus of basal ornithopod dinosaur known from Zhejiang Province, China.