Spinosauridae

Spinosauridae (meaning 'spined lizards') is a family of megalosauroidean theropod dinosaurs. The genus Spinosaurus, from which the family, subfamily, and tribe borrow their names, is the longest terrestrial predator known from the fossil record, and likely reached lengths of 15 m (49 ft). Most spinosaurids lived during the Cretaceous Period, with possible origins in the Late Jurassic, and fossils of them have been recovered worldwide, including in Africa, Europe, South America, Asia, and Australia, although none have been formally named from the latter continent. Spinosaur remains have generally been attributed to the Early to Mid Cretaceous, with the exception of the Ostafrikasaurus from the Late Jurassic. Spinosaurids were large bipedal carnivores with elongated, crocodile-like skulls lined with conical teeth bearing little to no serrations, and small crests on top of their heads. The teeth in the front end of their lower jaws fanned out into a spoon-shaped structure similar to a rosette, which gave the animal a characteristic look. Their shoulders were robust, prominent and bore stocky forelimbs with giant 'hooked' claws on the first finger of their hands. Many genera had unusually tall neural spines on their vertebrae, which supported sails or humps of skin or fat tissue. Direct fossil evidence and anatomical adaptations indicate that spinosaurids were at least partly piscivorous, with additional fossil finds indicating they also hunted pterosaurs and small to medium-sized dinosaurs. Osteological analyses have suggested a semiaquatic lifestyle for some members of this clade. Although reliable size and weight estimates for most taxa are hindered by the lack of good material, all known spinosaurids were large animals. The smallest, Irritator, was between 6 and 8 meters in length and 1 tonne (1.1 short tons) in weight. While Ichthyovenator, Baryonyx, and Suchomimus ranged from 7.5 to 11 meters long, and weighing between 1 and 5.2 tonnes (1.2 and 5.7 short tons). Spinosaurus was the largest, capable of reaching lengths of around 15 meters (49 ft) and weighing around 6.4–7.2 tonnes (7.1–7.9 short tons). This consistency in large body size among spinosaurids could have evolved as a byproduct of their preference for semiaquatic lifestyles, as without the need to compete with other large theropods for food, they would have been able to grow to tremendous lengths. Spinosaurid skull anatomy is similar in many respects to that of crocodilians. Spinosaurid skulls were long, low and narrow. As in other theropods, various fenestrae (openings) in the skull aided in reducing its weight. In spinosaurs however, the antorbital fenestrae were greatly reduced, akin to those of crocodilians. The tips of the premaxillae (frontmost snout bones) and dentaries (tooth bearing bones of the mandible) were expanded, forming what has been called a 'terminal rosette' of enlarged teeth. Behind this expansion, the upper and lower jaws were notched. The maxillae (main upper jaw bones) were long and formed a low branch under the nostrils that connected to the rear of the premaxillae. Spinosaurid teeth were subconical, with an oval to circular cross section and either absent or very fine serrations. Typically, their teeth were either straight or only slightly recurved front to back, and bore a varying number of flutes (ridges) running lengthwise across their tooth crowns. Lengthwise atop the skull ran a thin and shallow sagittal crest that was usually tallest near or above the eyes, either becoming shorter or disappearing entirely towards the front of the head. Spinosaurus's head crest was comb shaped and bore distinct vertical ridges, while those of Baryonyx and Suchomimus looked like small triangular bumps. Irritator's median crest stopped above the eyes in a bulbous, flattened shape. However, given that the upper surface of its holotype skull was damaged and the tip of its snout was missing, the complete shape of Irritator's crest is unknown. Angaturama (a possible synonym of Irritator) had an unusually tall crest on its premaxillae that nearly overhung the tip of the snout with a small protrusion. The nostrils were set far back on the skull, at least behind the teeth of the premaxillae, instead of at the front of the snout as in most theropods. Those of Baryonyx and Suchomimus were large and started between the first and fourth maxillary teeth, while Spinosaurus's nostrils were far smaller and more retracted. Irritator's nostrils were positioned similarly to those of Baryonyx and Suchomimus, and were between those of Spinosaurus and Suchomimus in size. Spinosaurids had long secondary palates, bony and rugose structures on the roof of their mouths that are also found in extant crocodilians, but not in most theropod dinosaurs. Oxalaia had a particularly wrinkled and elaborate secondary palate, while most spinosaurs had smoother ones. Spinosaurids had relatively large and well-built forelimbs, the radius (forearm bone) was stout and usually only half as long as the humerus (upper arm bone). Each manus (hand) wielded an enlarged, strongly recurved claw on the first digit (or 'thumb'), and were otherwise typical of tetanurans, bearing three digits. The coracoids were hook shaped. The hindlimbs were somewhat short and mostly conventional of other megalosauroid theropods. Spinosaurus however, had a particularly small pelvic (hip) region and hindlimbs proportional to body size.