Noasauridae is an extinct family of theropod dinosaurs belonging to the group Ceratosauria. They were closely related to the short-armed abelisaurids, although most noasaurids had much more traditional body types generally similar to other theropods. Their heads, on the other hand, had unusual adaptations depending on the subfamily. 'Traditional' noasaurids, sometimes grouped in the subfamily Noasaurinae, had sharp teeth which splayed outwards from a downturned lower jaw. The most complete and well-known example of these kinds of noasaurids was Masiakasaurus knopfleri from Madagascar. Another group, Elaphrosaurinae, has also been placed within Noasauridae by some studies. Elaphrosaurines developed toothless jaws and herbivorous diets, at least as adults. The most complete and well known elaphrosaurine was Limusaurus inextricabilis. At least some noasaurids had pneumatised cervical vertebrae. Some are considered to have had cursorial habits. Noasauridae is defined as all theropods closer to Noasaurus than to Abelisaurus.
Description Noasauridae was a very diverse group, with the two most complete members, Masiakasaurus and Limusaurus, showing unusual features very different from each other. Masiakasaurus had an unusually downturned jaw, with long and sharply pointed spoon-shaped teeth. Some of these teeth were nearly horizontal in orientation. Limusaurus, on the other hand, was completely toothless as an adult and likely possessed a horny beak. This large disparity means that it is difficult to find any skull features shared by members of Noasauridae as a whole.
Noasaurids had longer arms than their relatives the abelisaurids, whose arms were tiny and diminished. Although by no means as large or specialized as the arms of advanced bird-like theropods, noasaurid arms were nevertheless capable of movement and use, possibly even for hunting in large-clawed genera such as Noasaurus. Some genera such as Limusaurus did have somewhat reduced arms and hands, but far from the extent that abelisaurids acquired. Noasaurids were also nimble and lightly built, with feet showing adaptations for running such as a long central foot bone (metatarsal III). Noasaurids varied in size, from the small Velocisaurus which was under 5 feet (1.5 meters) long, to much larger genera such as Elaphrosaurus and Deltadromeus, which were more than 20 feet (6.1 meters) in length. A collection of features which characterize noasaurids in particular has been compiled by Rauhut & Carrano (2016), who included controversial taxa such as Deltadromeus and the elaphrosaurines within Noasauridae. If these groups did not belong to Noasauridae as the study claims, then these similarities are examples of convergent evolution. Among the most prominent traits relate to the shoulder region. In this family, the long, upward-stretching scapula (shoulder blade) merges with the smaller and more compact coracoid (shoulder girdle), forming a fused shoulder bone known as a scapulocoracoid. While the presence of a scapulocoracoid is by no means unique to this family, noasaurids do have particularly large and wide scapulocoracoids, with a tall and semicircular coracoid region. The hooked rear edge of the coracoid region is also offset from the glenoid (shoulder socket) by a large U-shaped notch. The humerus (upper arm bone) was thin and straight, with a low and somewhat rounded humeral head (the portion which attached to the shoulder). In contrast, abelisaurids had a large and bulbous humeral head (although similarly rounded) while that of other theropods was flattened from front to back.
The leg is also somewhat characteristic in members of this family. The tibia (large innermost bone of the lower leg) was flattened from the front near the foot, although it was rounded further up the leg. As in other theropods, the femur (thigh bone) of a noasaurid had a ridge along the inner rear surface, known as a fourth trochanter. However, in noasaurines and elaphrosaurines (but not necessarily other genera such as Deltadromeus), this fourth trochanter was much smaller and lower than the enlarged crest-like structure present in the majority of basal theropods; only a few other groups of theropods (coelophysoids, coelurosaurs, and a few species of abelisaurids) also have reduced fourth trochanters. In addition, the two subfamilies have a metatarsal II (the foot bone connected to the innermost major toe) which was flattened from the side. Further reductions to this metatarsal were present in noasaurines (particularly Velocisaurus). In these genera as well as Deltadromeus, metatarsal IV (which connected to the outermost major toe) also became reduced in some respects. In all noasaurids, the mid caudals (vertebrae in the middle of the tail) had very low neural spines. The cervical (neck) vertebrae, on the other hand, were quite varied within this family. In noasaurines and a few other genera (such as Laevisuchus), the neural spines of vertebrae at the front of the neck were positioned towards the front part of their respective vertebrae. This is quite unusual compared to other theropods, which have neural spines roughly midway down their vertebrae. These genera also have long and spine-like epipophyses on the cervicals of most of the neck, although they diminish near the neck. Epipophyses are bony projections located above the postzygapophyses (joints on the rear edge of a vertebra connecting to the front edge of the following vertebra). Elaphrosaurines, on the other hand, have cervical epipophyses which are much more diminished or even absent in the case of Elaphrosaurus. Many noasaurids are only known from vertebrae, including both valid (Laevisuchus, Spinostropheus) and dubious (Composuchus, Jubbulpuria, Ornithomimoides, Coeluroides) genera.
Noasaurinae
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