Description and Classification

Tachiraptor admirabilis is currently the only known species within its genus. It was a relatively small, bipedal carnivore, estimated to be around 1.5 to 2 meters (approximately 5 to 6.5 feet) in length. Knowledge of Tachiraptor is based on limited fossil material, specifically a nearly complete right tibia (shinbone) and a partial left ischium (a pelvic bone). Despite the fragmentary nature of these remains, they possess unique characteristics that allow for its distinction.

Tachiraptor is classified as a member of Theropoda, the group of mostly carnivorous dinosaurs that includes iconic predators like Tyrannosaurus rex and Velociraptor. More specifically, it is considered a basal neotheropod, belonging to the clade Averostra. This places it within the lineage that gave rise to more advanced theropods such as ceratosaurs and tetanurans. Its exact position within early theropod evolution is still a subject of study, but it shares some features with other early Jurassic theropods like Dilophosaurus, though it is more derived than very primitive theropods from the Late Triassic like Coelophysis.

Distinguishing Features

The known bones of Tachiraptor exhibit several features that distinguish it from other early theropods:

• The tibia (shinbone) possesses a distinct, sharp flange on its posterolateral (back and outer side) surface that is notably expanded.
• There is a unique, semicircular scar on the tibia marking the attachment point for the M. femorotibialis externus (a thigh muscle). This scar is located unusually far from the cnemial crest (a projection at the top front of the tibia).
• The ischium (pelvic bone) has specific characteristics in its shape and articulations that contribute to its unique identification.

Paleoenvironment and Diet

Tachiraptor lived in what is now western Venezuela during the Hettangian stage of the Early Jurassic. The La Quinta Formation, where its fossils were found, represents a terrestrial environment characterized by river systems and floodplains. The climate at the time was likely warm, with distinct wet and dry seasons.

Tachiraptor shared this environment with another dinosaur, the small, early ornithischian Laquintasaura venezuelae, which was discovered in the same formation. It is highly probable that Tachiraptor, as a carnivore, preyed upon Laquintasaura. Its diet would have also included other small vertebrates present in its ecosystem, such as lizards or early mammal relatives. Its size suggests it was an agile hunter of smaller prey.

Significance and Ongoing Research

The discovery of Tachiraptor is highly significant for several reasons. It is one of the very few dinosaur genera formally named from Venezuela, greatly improving our understanding of dinosaur distribution in northern South America (part of the ancient supercontinent Gondwana). It provides crucial insights into the early diversification of theropods shortly after the major Triassic-Jurassic extinction event, a critical period in dinosaur evolution.

Tachiraptor helps to fill a geographical and temporal gap in the fossil record of early theropods. Ongoing research focuses on further analyzing the known fossil material and comparing it with other early theropods to better understand its evolutionary relationships. Paleontologists also hope that future expeditions to the La Quinta Formation will yield more complete remains of Tachiraptor and other contemporary fauna, which would provide a clearer picture of this Early Jurassic ecosystem in northern Gondwana and the role Tachiraptor played within it.