Structural Extremes in a Cretaceous Dinosaur

Abstract

Fossils of the Early Cretaceous dinosaur, Nigersaurus taqueti, document for the first time the cranial anatomy of a rebbachisaurid sauropod. Its extreme adaptations for herbivory at ground-level challenge current hypotheses regarding feeding function and feeding strategy among diplodocoids, the larger clade of sauropods that includes Nigersaurus. We used high resolution computed tomography, stereolithography, and standard molding and casting techniques to reassemble the extremely fragile skull. Computed tomography also allowed us to render the first endocast for a sauropod preserving portions of the olfactory bulbs, cerebrum and inner ear, the latter permitting us to establish habitual head posture. To elucidate evidence of tooth wear and tooth replacement rate, we used photographic-casting techniques and crown thin sections, respectively. To reconstruct its 9-meter postcranial skeleton, we combined and size-adjusted multiple partial skeletons. Finally, we used maximum parsimony algorithms on character data to obtain the best estimate of phylogenetic relationships among diplodocoid sauropods. Nigersaurus taqueti shows extreme adaptations for a dinosaurian herbivore including a skull of extremely light construction, tooth batteries located at the distal end of the jaws, tooth replacement as fast as one per month, an expanded muzzle that faces directly toward the ground, and hollow presacral vertebral centra with more air sac space than bone by volume. A cranial endocast provides the first reasonably complete view of a sauropod brain including its small olfactory bulbs and cerebrum. Skeletal and dental evidence suggests that Nigersaurus was a ground-level herbivore that gathered and sliced relatively soft vegetation, the culmination of a low-browsing feeding strategy first established among diplodocoids during the Jurassic.

A new sauropod dinosaur from the Early Cretaceous of Tunisia with extreme avian-like pneumatization

“…Tataouinea shows closest affinities with the Iberian Demandasaurus than with other African 13 or South American taxa [23][24][25] . Accordingly, a European lineage of nigersaurines results bracketed by North African taxa; the latter clade is part of a mainly Gondwanan radiation.…”

“…A robust hyposphenal ridge is present ventral to the postzygapophyses, as in Demandasaurus. All neural spines are posterodorsally directed, with the anteriormost scimitar-shaped (as in Cathartesaura and Zapalasaurus 23 ) and the posterior straight (as in Limaysaurus and Nigersaurus 13,24 ). The anterior half of both ilia were found in articulation with the sacrum.…”

“…Diverse vertebrate faunas are known from calcareous platforms, islands and xeric coastal plains, often inhabited by endemic forms. Although the fossil record from these deposits consists mostly of incomplete specimens, diagnostic elements document unique characters interpreted as a reflection of special adaptations to exceptional combinations of ecological and climatic factors 2,7,[12][13][14] .…”

Mesozoic dinosaurs from Brazil and their biogeographic implications

“…2, 4b) (Upchurch et al 2004, Wilson 2005. Several isolated specimens have been regarded as Rebbachisauridae (Medeiros and Schultz 2001, Medeiros et al 2007), a group with an abundant record in Aptian-Coniacian deposits of Argentina and North Africa (Upchurch et al 2004, Gallina andApesteguía, 2005), but also from older strata of Europe (Sereno and Wilson 2005, Sereno et al 2007, Mannion 2009) and possibly South Africa (Figs. 2, 4b) (Canudo and Salgado 2003).…”

Inner ear anatomy is a proxy for deducing auditory capability and behaviour in reptiles and birds

“…Modern mCT imaging avoids these problems by providing reconstructions accurate to several micrometres of the internal space of the inner ear in intact specimens (e.g. Witmer et al 2003Domínguez Alonso et al 2004;Sanders & Smith 2005;Sampson & Witmer 2007;Sereno et al 2007;Witmer & Ridgley 2008;Milner & Walsh 2009), thus representing the maximal dimensions of the original soft tissue. However, the ECD encloses soft-tissue structures other than the basilar papilla (e.g.…”