Tachiraptor
| Tachiraptor Temporal range:Early Jurassic,Hettangian
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|---|---|
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| IVIC-P-2687, theholotyperighttibia,and IVIC-P-2868, the referred leftischium | |
Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Neotheropoda |
| Genus: | †Tachiraptor Langer, Rincón, Ramezani, Solórzano, & Rauhut, 2014 |
| Species: | †T. admirabilis
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| Binomial name | |
| †Tachiraptor admirabilis Langer, Rincón, Ramezani, Solórzano, & Rauhut, 2014
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Tachiraptor( "thief ofTáchira") is agenusof carnivoroustheropoddinosaursfound in the earlyJurassicperiodLa Quinta FormationofVenezuela.It includes onespecies,Tachiraptor admirabilis,described from a fossilizedtibiaandischium.They were smallbipedaldinosaurs, with a deduced total body length of just over 1.5 m (4.9 ft).[1]They were likelygeneralistpredators,preying on smallervertebrateslike other dinosaurs or lizards.[2][3]
Discovery
[edit]
Since the late 1980s in the Venezuelan state ofTáchira,remains of dinosaurs have been uncovered at a road-cut betweenLa GritaandSeboruco.Most of these belonged to a smallherbivorethat in 2014 was described asLaquintasaura.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.[1]
In 2014, thetype speciesTachiraptor admirabiliswas named and described byMax Cardoso Langer,Ascanio D. Rincón, Jahandar Ramezani, Andrés Solórzano andOliver Rauhut.[1]
The description was based on two fossils, found in a layer of theLa Quinta Formationdating from theEarly JurassicHettangianstage.[1]The region was once part of theequatorial beltof the ancientsupercontinentofPangaea.[3]A maximum age of 200.72 ± 0.32million years agohas been confidently established, but due to the limits ofzirconradiometric 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 theholotypespecimen, IVIC-P-2867. It consists of a nearly complete righttibiaor shinbone. The second fossil was referred toTachiraptor admirabilison the assumption that only one species ofneotheropodof such a size was present in the La Quinta Formation. It is specimen IVIC-P-2868, consisting of the damaged upper half of a leftischium,a bone of the pelvis.[1]
Etymology
[edit]The generic name was derived from that of the state of Táchira, where it was discovered, combined with theLatinword for thief,raptor.Thespecific nameadmirabiliswas chosen in reference to theAdmirable Campaignof 1813, conducted bySimón Bolívar,for which thetype localityofLa Gritawas of strategic importance.[1]
Description
[edit]Tachiraptorwas a small bipedal predator. The shinbone has a length of about 25 cm (9.8 in); from this, the total body length of the animal has been deduced at just over 1.5 m (4.9 ft).[1][4]
The authors established a number of distinguishing traits. One of these is a possibleautapomorphy,a unique evolutionary innovation shown just byTachiraptor.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. InTachiraptorthe outer projection, at the side of thefibula,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.[1]
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 thetalus bone.A ridge on the front surface demarcates the upper limit of this area. InTachiraptorthis 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, withTachiraptora line drawn between the bumps made an angle of 80° with the vertical axis of the bone.[1]
Phylogeny
[edit]The study describingTachiraptorperformed acladisticanalysis, establishing its probable evolutionary relationships (phylogeny) by computing an evolutionary tree assuming the fewest evolutionary changes. This analysis showed thatTachiraptorwas a basal member of theNeotheropoda,the subgroup encompassing all but the earliest theropods. It thus was placed low in the evolutionary tree of the neotheropods.Tachiraptorwas part of the stem leading to theAverostra,the group all theropods belong to from theMiddle Jurassiconwards, including the birds. Being asister speciesof the Averostra, it was described as a "stem-averostran". This made the discovery ofTachiraptorespecially important, because before 2014, there were no unequivocal stem-averostrans known at all.Tachiraptorthus reduced theirghost lineage(an inferred though yet unproven line of descent) by twenty-five million years.[1]
Tachiraptoralso 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 ofLaquintasaura.[1]
Paleoenvironment
[edit]Tachiraptorhails from the La Quinta Formation of northern South America, in what is now Colombia and Venezuela, and was found in the Venezuelan part of the formation. The La Quinta environment is interpreted as a tropical lowland forest. Its location and time suggests eusauropods reached a broad distribution before the breakup ofPangaeaand the Toarcian faunal turnover.[5]Other dinosaurs from this formation include the eusauropodPerijasaurus,from Colombia, and the ornithischianLaquintasaura,from Venezuela.
References
[edit]- ^abcdefghijkLanger, Max C.; Rincón, Ascanio D.; Ramezani, Jahandar; Solórzano, Andrés; Rauhut, Oliver W.M. (8 October 2014)."New dinosaur (Theropoda,stem-Averostra) from the earliest Jurassic of the La Quinta formation, Venezuelan Andes ".Royal Society Open Science.1(2).Royal Society:140–184.Bibcode:2014RSOS....140184L.doi:10.1098/rsos.140184.PMC4448901.PMID26064540.
- ^Hannah Osborne (9 October 2014)."Dinosaur Species Discovered:Tachiraptor admirabiliswas T-Rex's Tiny Ancestor from Venezuela ".International Business Times.Retrieved8 December2014.
- ^abCharles Q. Choi (7 October 2014)."Newfound South American Predator Snacked on Little Dinosaurs".LiveScience.Retrieved8 December2014.
- ^Sid Perkins (7 October 2014)."New meat-eating dinosaur lived in the wake of a mass extinction".Science News.Retrieved8 December2014.
- ^Rincón, Aldo F.; Raad Pájaro, Daniel A.; Jiménez Velandia, Harold F.; Ezcurra, Martín D.; Wilson Mantilla, Jeffrey A. (2022)."A sauropod from the Lower Jurassic La Quinta Formation (Dept. Cesar, Colombia) and the initial diversification of eusauropods at low latitudes".Journal of Vertebrate Paleontology.42(1): e2077112.Bibcode:2022JVPal..42E7112R.doi:10.1080/02724634.2021.2077112.S2CID251501541.
