Anatomy of Juravenator Starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany

N. Jb. Geol. Paläont. Abh. 258/3, 257–296 Article Stuttgart, December 2010

Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany

Luis M. Chiappe, Los Angeles and Ursula B. Göhlich, Vienna With 26 figures

CHIAPPE, L. M. & GÖHLICH, U. B. (2011): Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany. – N. Jb. Geol. Paläont. Abh., 258: 257–296; Stuttgart.

Abstract: We provide a detailed study of the morphology of the holotype of Juravenator starki from the Late Jurassic of the Solnhofen area of southern Germany. The incompletely ossified surface of multiple bones and lack of se veral skeletal fusions indicate that Juravenator starki is based on an immature specimen. Nonetheless, numerous unique mor phologies and bone proportions distinguish this taxon from Compsognathus longipes, the only previously named non-avian theropod dinosaur from the Late Jurassic of the Solnhofen Archipelago. Yet, its skeletal anatomy is most similar to that of Compsognathus and other theropods that have often been regarded as closely related to the latter – sometimes within a monophyletic Compsognathidae. Juravenator is characterized by having a small size (~ 0.75-meter-long in the holotype) with fe w maxillary teeth, lack of a premaxillar y-maxillary diastema, an antorbital fenestra subequal in length to orbit, an elongate scapula that is narrowest at its neck, a propor tionally short humerus and high and abr uptly tapered manual cla ws, and bo w- like zygapophysial articulations in the mid-caudal v ertebrae. Portions of the epider mis preserved mainly along the tail provide the only glimpse of the mor phology of the skin of basal coelurosaurs, and structures newly revealed under UV light hint at the possibility of f ilamentous integumentary structures – akin to those interpreted as proto-feathers in other basal coelurosaurs – also covering the body of this dinosaur. The discovery of Juravenator has provided evidence of morphologies – from details of the skull to the epider mis – that are poorl y known in other theropods inter preted as at or near the base of Coelurosauria, and thus contributes signif icantly to our understanding of the evolutionary history of this clade. The exquisitely preserved holotipic skeleton adds significantly to the meager record of small-bodied Late Jurassic theropods.

Key words: Juravenator, Theropoda, anatomy, taphonomy, preservation, Jurassic, Solnhofen Lime- stones.

1. Introduction the evolutionary debate of the 19th century (DESMOND 1982; OSTROM 1978; CHIAPPE 2007), the rather un - Small non-avian theropods of Late Jurassic age are specialized morphology of “compsognathids” (Comp- rare worldwide (WEISHAMPEL et al. 2004). Onl y a sognathus and a series of alle ged Late Jurassic-Early handful of them e xist in Europe and until recentl y, Cretaceous relatives – CURRIE & CHEN 2001; HOLTZ these dinosaurs were best represented b y two incom- et al. 2004; H WANG et al. 2004; N AISH et al. 2004; J I plete skeletons of Compsognathus longipes (WAGNER et al. 2007b; G ISHLICK & GAUTHIER 2007) has com- 1861). Despite the historical signif icance of Comp - plicated interpretations of this g roup’s monophyly. In sognathus, the discovery of which played a key role in this paper, “compsognathids” are used without an y