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New Dinosaur (Theropoda, stem-Averostra) From the Earliest Jurassic of the La Quinta Formation, Venezuelan Andes

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New Dinosaur (Theropoda, stem-Averostra) From the Earliest Jurassic of the La Quinta Formation, Venezuelan Andes

Max C Langer et al. R Soc Open Sci.

Erratum in

Abstract

Dinosaur skeletal remains are almost unknown from northern South America. One of the few exceptions comes from a small outcrop in the northernmost extension of the Andes, along the western border of Venezuela, where strata of the La Quinta Formation have yielded the ornithischian Laquintasaura venezuelae and other dinosaur remains. Here, we report isolated bones (ischium and tibia) of a small new theropod, Tachiraptor admirabilis gen. et sp. nov., which differs from all previously known members of the group by an unique suite of features of its tibial articulations. Comparative/phylogenetic studies place the new form as the sister taxon to Averostra, a theropod group that is known primarily from the Middle Jurassic onwards. A new U-Pb zircon date (isotope dilution thermal-ionization mass spectrometry; ID-TIMS method) from the bone bed matrix suggests an earliest Jurassic maximum age for the La Quinta Formation. A dispersal-vicariance analysis suggests that such a stratigraphic gap is more likely to be filled by new records from north and central Pangaea than from southern areas. Indeed, our data show that the sampled summer-wet equatorial belt, which yielded the new taxon, played a pivotal role in theropod evolution across the Triassic-Jurassic boundary.

Keywords: Averostra; Dinosauria; Early Jurassic; U–Pb geochronology.

Figures

Figure 1.
Figure 1.
Maps of (a) Venezuela within northern South and Central America, (b) Táchira State within Venezuela and (c) La Grita area indicating the location of the type locality of Tachiraptor admirabilis (black arrow). Dash-dotted lines denote main roads; thin dotted lines, paved secondary roads.
Figure 2.
Figure 2.
Date distribution plot of analysed zircons of this study. Bar heights are proportional to 2σ analytical uncertainty of individual analyses; solid bars are analyses used in age calculation. Horizontal lines signify calculated sample dates and the width of the shaded band represents internal uncertainty in weighted mean at a 95% confidence level. Arrow points to additional analysis plotting outside the diagram. Reported date incorporates external sources of uncertainty. See the electronic supplementary material, table S1 for complete analytical data and text for details of date uncertainties.
Figure 3.
Figure 3.
Tachiraptor admirabilis gen et sp. nov. Holotype right tibia (IVIC-P-2867) in (a) lateral (proximal portion), (b) proximal, (c) lateral, (d) distal and (e) cranial (distal portion) views. Referred left ischium (IVIC-P-2868) in (f) lateral view. Abbreviations: ab, astragalar buttress; cc, cnemial crest; ai, cranial emargination; cn, caudal notch; fc, fibular condyle; fcr, fibular crest; ia, iliac articulation; in, intercondylar notch; it, incisura tibialis; keg, ‘knee extensor groove’; lg, longitudinal groove; lk, lateral kink; mc, medial condyle; om, outer malleolus; op, obturator plate; pp, pubic peduncle; pvr, ‘postero-ventral ridge’; rd, ridge; tn, tibial notch; vr, ventral ridge.
Figure 4.
Figure 4.
Strict consensus of the 1107 MPTs recovered with the inclusion of Tachiraptor admirabilis into the dataset of Xu et al. [12]. Branch colours represent extension of ghost lineages in millions of years (red, less than 15; purple, 15–35; blue, more than 35). Taxon bar lengths correspond to their chronologic distribution/uncertainty (based on various sources). Bar colours match those of the index Middle Jurassic palaeomap [70] and correspond to the provenance of Triassic/Jurassic theropods from the defined palaeobiogeographic provinces (SG, South Gondwana; EA, Euramerica; TU, Transurals; EB, Equatorial Belt) at the time of their occurrences.

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