Cristatusaurus

***Cristatusaurus*** (meaning "crested lizard") is a genus of theropod dinosaur that lived during the Early Cretaceous Period of what is now Niger, 112 million years ago. It was a baryonychine member of the Spinosauridae, a group of large bipedal carnivores with well-built forelimbs and elongated, crocodile-like skulls. The type species ***Cristatusaurus lapparenti*** was named in 1998 by scientists Philippe Taquet and Dale Russell, on the basis of jaw bones and some vertebrae. Two claw fossils were also later assigned to *Cristatusaurus*. *Cristatusaurus* is known from the Albian to Aptian Elrhaz Formation, where it would have coexisted with sauropod and iguanodontian dinosaurs, other theropods, and various crocodylomorphs.

Originally proposed to be an indeterminate species of *Baryonyx*, the identity of *Cristatusaurus* has been subject to debate, in part due to the fragmentary nature of its fossils. Some argue that it is probably the same dinosaur as *Suchomimus,* which has also been found in Niger, in the same sediment layers. In that case the genus *Cristatusaurus* would have priority, since it was named two months earlier. Others have concluded, however, that *Cristatusaurus* is a *nomen dubium*, considering it indistinguishable from both *Suchomimus* and *Baryonyx*. Some distinctions between the fossils of *Cristatusaurus* and *Suchomimus* have been pointed out, but it is uncertain whether these differences separate the two genera or if they are due to ontogeny (changes in an organism during growth). A recent study differentiated *Cristatusaurus* from *Suchomimus* and assigned as a valid spinosaurid genus, placed the theropod just outside Baryonychinae.

## Description

In 2012, American vertebrate paleontologist Thomas R. Holtz Jr. tentatively estimated *Cristatusaurus* at around 10 m (33 ft) in length and weighing between 1 to 4 tonnes (1.1 to 4.4 short tons). The holotype premaxillae are 115 mm (4.5 in) long and 55 mm (2.2 in) tall. The other known set of premaxillae (specimen MNHN GDF 365) are larger at 185 mm (7.3 in) long and 95 mm (3.7 in) tall. The holotype's smaller size, smoother surface, and lack of co-ossified (fused) sutures all indicate that it belongs to a juvenile individual; while MNHN GDF 365 probably represents an adult.

The tip of *Cristatusaurus*'s premaxilla was short and expanded, while the rear end was narrowed near the suture with the maxilla; this rosette-like snout shape was characteristic of spinosaurids. The front of the upper jaw was concave on the bottom, shaped to interlock with what would have been the convex and also enlarged tip of the mandible's dentary bone. A thin sagittal crest ran lengthwise on top of the premaxillae, a condition present in *Baryonyx* and *Suchomimus*, and very prominent in *Angaturama* (a possible synonym of *Irritator*). Like all spinosaurids, *Cristatusaurus*'s external nares (bony nostrils) were positioned further back on the skull that in typical theropods. Two bony processes extended across the underside of the snout, in a convex structure that formed the animal's secondary palate. This condition is observed in all extant crocodilians, but not in most theropod dinosaurs; however, it was a common trait among spinosaurids.

*Cristatusaurus*'s dental alveoli (tooth sockets) were closely spaced, those in the maxilla and dentary were flattened somewhat sideways; while the ones in the premaxillae were large and mostly circular, with the frontmost alveoli being the largest. Partial tooth crowns preserved in some alveoli show that the teeth were finely serrated, with flutes (lengthwise ridges) on their lingual (inward-facing side of teeth) surface. Both premaxilla specimens had seven alveoli on each side, the same number as in *Suchomimus*, *Angaturama*, *Oxalaia*, and the *Spinosaurus maroccanus* specimen.

One of the dorsal vertebrae (MNHN GDF 358) measured 13.5 cm (5.3 in) in centrum length, which is equal to the largest known vertebrae of *Spinosaurus maroccanus*. The preserved base of one of *Cristatusaurus*'s vertebral neural spines (MNHN GDF 359) was 15 mm (0.59 in) thick in comparison to the 25 mm (0.98 in) measurement seen in an equivalent *Spinosaurus* vertebra, indicating that *Cristatusaurus*'s neural spines were probably not as tall as those of *Spinosaurus*. Of the two manual unguals (claws) referred to *Cristatusaurus*, one was equivalent in size to those found for *Suchomimus* and *Baryonyx*, while the other was about 25 to 30 percent smaller. As a spinosaur, it would have wielded these claws with three-fingered hands carried by robust arms.

## *Cristatusaurus* in The Amazing Dinosaur Adventure

A family of *Cristatusaurus* from *The Lonely Journey*