page_title: Spinosauridae
section_title: Postcranial skeleton
hierarchical_section_title: Spinosauridae / Description / Postcranial skeleton
caption_attribution_description: English: Comparison of reconstructed sails of spinosaurid dinosaurs; clockwise from top left: Irritator, Spinosaurus, Suchomimus, and Ichthyovenator.
context_page_description: Spinosauridae is a family of theropod dinosaurs comprising up to thirteen known genera. They came into prominence during the Cretaceous period, with possible origins in the Middle or Late Jurassic. Spinosaurid fossils have been recovered worldwide, including Africa, Europe, South America, Asia, and possibly Australia. Their remains have generally been attributed to the Early to Mid Cretaceous, with the exception of the earliest named genus, Ostafrikasaurus from the Late Jurassic.
  Spinosaurids were large bipedal carnivores. Their crocodilian-like skulls were long, low and narrow, bearing conical teeth with reduced or absent serrations. The tips of their upper and lower jaws fanned out into a spoon-shaped structure similar to a rosette, behind which there was a notch in the upper jaw that the expanded tip of the lower jaw fit into. The nostrils of spinosaurids were retracted to a position further back on the head than in most other theropods, and they had bony crests on their heads along the midline of their skulls. Their robust shoulders wielded stocky forelimbs, with three-fingered hands that bore an enlarged claw on the first digit.
context_section_description: The coracoid bones of the shoulders in spinosaurids were robust and hook shaped. The arms were relatively large and well-built; the radius (long bone of the forearm) was stout and usually only half as long as the humerus (upper arm bone). Spinosaurid hands had three fingers, typically of tetanurans, and wielded an enlarged ungual on the first finger (or "thumb"), which formed the bony core of a keratin claw. In genera like Baryonyx and Suchomimus, the phalanges (finger bones) were of conventional length for large theropods, and bore hook-shaped, strongly curved hand claws. Based on fragmentary material from the forelimbs of Spinosaurus, it appears to have had longer, more gracile hands and straighter claws than other spinosaurids. 
  The hindlimbs of Suchomimus and Baryonyx were somewhat short and mostly conventional of other megalosauroid theropods. Ichthyovenator's hip region was reduced, having the shortest pubis (pubic bone) and ischium (lower and rearmost hip bone) in proportion to the illium (main hip bone) of any other known theropod. Spinosaurus had an even smaller pelvis and hindlimbs in proportion to its body size; its legs composed just over 25 percent of the total body length. Substantially complete spinosaurid foot remains are only known from Spinosaurus. Unlike most theropods—which walk on three toes, with the hallux (first toe) being reduced and elevated off the ground—Spinosaurus walked on four functional toes, with an enlarged hallux that came in contact with the ground. The unguals of its feet, in contrast with the deeper, smaller and recurved unguals of other theropods, were shallow, long, large in relation to the foot, and had flat bottoms. Based on comparisons with those of modern shorebirds, it is possible that Spinosaurus's feet were webbed.
  The upwards projecting neural spines of spinosaurid vertebrae (backbones) were very tall, more so than in most theropods. In life, these spines would have been covered in skin or fat tissue and formed a sail down the animal's back, a condition that has also been observed in some carcharodontosaurid and ornithopod dinosaurs. The eponymous neural spines of Spinosaurus were extremely tall, measuring over 1 m (3 ft 3 in) in height on some of the dorsal (back) vertebrae. Suchomimus had a lower, ridge-like sail across the majority of its back, hip, and tail region. Baryonyx showed a reduced sail, with a few of the rearmost vertebral spines being somewhat elongated. Ichthyovenator had a sinusoidal (wave-like) sail that was separated in two over the hips, with the upper ends of some neural spines being broad and fan-shaped. A neural spine from the holotype of Vallibonavenatrix shows a similar morphology to those of Ichthyovenator, indicating the presence of a sail in this genus as well. One partial skeleton possibly referable to Angaturama also had elongated neural spines on its hip region. The presence of a sail in fragmentary taxa like Sigilmassasaurus is unknown. In members of the subfamily Spinosaurinae, like Ichthyovenator and Spinosaurus, the neural spines of the caudal (tail) vertebrae were tall and reclined, accompanied by also elongated chevrons—long, thin bones that form the underside of the tail. This was most pronounced in Spinosaurus, in which the spines and chevrons formed a large paddle-like structure, deepening the tail significantly along most of its length.
caption: Reconstructed neural spine sails of four spinosaurids; clockwise from top left: Spinosaurus, Irritator, Ichthyovenator, and Suchomimus.
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