opisthotics are also known in Tarjadia, and form the paraoccipital processes, two projections for the attachments of muscles that horizontally rotate the skull. These processes form notches that may be tympanic fossae, grooves towards the eardrums. Vertebrae The vertebrae of Tarjadia have centra, or central bodies, that are about as long as they are high. The centra have concave ventral surfaces and depressed lateral surfaces. The neural spines that project upward from the centra are laterally compressed, but have distal portions that expand into a flattened table with a groove on its upper surface. Above the flat tables of the neural arches lie the paramedian osteoderms, which also form a flat surface. Thick transverse processes on some vertebrae suggest that they make up the sacrum, the area of the spine that attaches to the pelvis. The six vertebrae known from Tarjadia probably represent the posterior dorsals, sacrals, and first caudals, comprising the end of the back vertebrae and the beginning of the tail vertebrae. Classification Comparisons between Tarjadia and other Triassic archosaurs and archosauriforms were made in its initial 1998 description. The archosauriforms Doswellia and Euparkeria, as well as the archosauriform family Proterochampsidae, all have heavy armor over the dorsal vertebrae and existed around the same time as Tarjadia. Proterochampsids do not have ornamented osteoderms like Tarjadia, nor do they have two rows of osteoderms on either side of the back (most proterochampsids, with the exception of Cerritosaurus and Chanaresuchus, have only a single row on either side). While Euparkeria has a pair of osteoderms overlying each vertebra, similar to the condition seen in Tarjadia, its osteoderms aren't ornamented. Ornamented paired osteoderms are seen as derived conditions in Doswellia and crurotarsan archosaurs. Some studies have not considered Tarjadia to be a close relative of Doswellia because of differences in the structure of the vertebrae. Moreover, Tarjadia possesses a prefrontal bone in the skull which is absent in Doswellia. Among crurotarsans, vertebrae that are each overlain by a single row of pitted, paired osteoderms as in Tarjadia are seen in aetosaurs, phytosaurs, and Crocodylomorpha. Tarjadia has been distinguished from aetosaurs by its apparent lack of an anterior articular lamina (a depressed region along the front of each osteoderm), and clear differences in the skull tables. Tarjadia differs from sphenosuchians and proterosuchians, the two main Triassic crocodylomorph groups, in that its osteoderms lack any clear structures on the anterior edges of the