What is Scipionyx?

Scipionyx samniticus (Dal Sasso and Signore 1998; Dal Sasso and Maganuco 2011; SBA-SA 163760; 46.1cm; Early Cretaceous; Figs. 1,2) was originally considered a hatchling compsognathid, like Compsognathus. Here, in the large reptile tree (LRT, 1211 taxa; Fig. 3) it is a late-surviving member of an Early Jurassic radiation that produced SpinosaurusDeinocheirus and their kin, with basal taxa close to Proceratosaurus (Fig. 2). The short rostrum and large orbit indicate a juvenile status, perhaps only a few days old. Internal organs were preserved along with the bones, but no outer integument was preserved. The feet and long tail are conjectural. The vertebrae of the back are not pneumatised. This taxon provides some clues to the post-crania of Proceratosaurus.

Figure 1. Scipionyx skull and overall. The tail and feet are restored.

Figure 1. Scipionyx skull and overall. The tail and feet are restored.

Long considered a compsognathid
Scipionyx, nests at the base of its clade, as several other compsognathids nest in the LRT. Thus, various compsognathids gave rise to most theropods, including giant killers and tiny flyers. The Scipionyx clade includes a series of long-snouted taxa culminating with Deinocheirus and Spinosaurus. Proceratosaurus (Fig. 2) is a close relative from the Middle Jurassic known from a partial skull.

Figure 2. The hatchling Early Cretaceous Scipionyx compared to the adult Middle Jurassic Proceratosaurus. Scipionyx provides clues to the post-crania of Proceratosaurus, while Proceratosaurus provides clues to the adult skull shape of Scipionyx.

Figure 2. The hatchling Early Cretaceous Scipionyx compared to the adult Middle Jurassic Proceratosaurus. Scipionyx provides clues to the post-crania of Proceratosaurus, while Proceratosaurus provides clues to the adult skull shape of Scipionyx.

The Scipionyx clade
(Fig. 3) originated in the Early Jurassic. Several members continued into the Late Cretaceous. Others did not. One trait, among several, this trade seems to hold in common, and originating with Scipionyx, is a nuchal crest created by a rise in the posterior rim of the parietal. This deepens the bone surrounding the upper temporal fenestra for greater anchors of jaw adductors.

Figure 3. The Scipionyx clade includes Allosaurus, Deinocheirus, Spinosaurus and other larger theropods.

Figure 3. The Scipionyx clade includes Allosaurus, Deinocheirus, Spinosaurus and other larger theropods.

References
Dal Sasso C and Signore M 1998. Exceptional soft tissue preservation in a theropod dinosaur from Italy. Nature, 392: 383–387.
Dal Sasso C and Maganuco S 2011. Scipionyx samniticus (Theropoda: Compsognathidae) from the Lower Cretaceous of Italy — Osteology, ontogenetic assessment, phylogeny, soft tissue anatomy, taphonomy and palaeobiology, Memorie della Società Italiana de Scienze Naturali e del Museo Civico di Storia Naturale di Milano XXXVII(I): 1-281

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