Semiaquatic adaptations in a giant predatory dinosaur

Abstract

We describe adaptations for a semiaquatic lifestyle in the dinosaur Spinosaurus aegyptiacus. These adaptations include retraction of the fleshy nostrils to a position near the mid-region of the skull and an elongate neck and trunk that shift the center of body mass anterior to the knee joint. Unlike terrestrial theropods, the pelvic girdle is downsized, the hindlimbs are short, and all of the limb bones are solid without an open medullary cavity, for buoyancy control in water. The short, robust femur with hypertrophied flexor attachment and the low, flat-bottomed pedal claws are consistent with aquatic foot-propelled locomotion. Surface striations and bone microstructure suggest that the dorsal "sail" may have been enveloped in skin that functioned primarily for display on land and in water.

Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy

“…In most basal theropods (e.g., coelophysoids, Torvosaurus, Spinosaurus, Allosaurus, Acrocanthosaurus; Rauhut, 2003;Ibrahim et al, 2014) the phalanx I.1 bears a transversely wide proximodorsal lip on phalanx 1 of digit I. Such a wide lip appears to be related with a transversely extended, deep, and well-defined extensor ligament pit on distal metacarpal I, a condition regarded as plesiomorphic among theropods (Sereno et al, 1993;Rauhut, 2003).…”

The evolution of ornithischian quadrupedality

“…a allometric coefficient, HAPW humerus anteroposterior width, HL humerus length, HMLW humerus mediolateral width, p probability that the allometric coefficient is equal to isometry, n sample size. Figure modified from feature to have arisen multiple times in Theropoda, but it has never appeared within this clade (recent controversial claims for quadrupedality in Spinosaurus notwithstanding: Ibrahim et al 2014). Large body size is correlated with quadrupedality in sauropods (e.g.…”

A reconstruction of the palaeoecology and environmental dynamics of the Bahariya Formation of Egypt

“…Bahariya went through 4 biozones (Tahoun et al 2013) named after the dominate taxa in each: zone 1 (Afropollis jardinus), zone 2 (Elaterosporites klaszii), zone 3 (Cretacaeiporites densimurus) & zone 4 (Trilobosporites laevigatus); the changes in flora correlating to changes in sea level and climate. These zones remain consistent across the western desert with some variation due to the localized environmental conditions; supporting the idea of a continual ecological province (Ibrahim et al 2014b), at least in North Eastern Gondwana.…”

“…While Sigilmassasaurus braviolis (Russell, 1996) is usually considered a junior synonym of Spinosaurus (Evers et al 2012;McFeeters et al 2013;Ibrahim et al 2014b), it now appears that S. braviolis may indeed be a valid taxa (Evers et al 2015).…”

“…Bahariya records a crucial period in Mesozoic history and with renewed interest in North African palaeofauna (Mannion & Barrett, 2013;Ibrahim et al 2014b), an understanding of Bahariya's fauna will be essential to help settle issues of taxonomy and ecology. Specimens from Bahariya are also known from partial skeletons as opposed to the Kem Kem beds where most are known from isolated and broken remains from various individuals (E. Läng personal communication, 2014).…”