Dentition and the evolution of teeth Romundina is currently understood to be the first placoderm to develop primitive tooth-like structures. Originally,
teeth were thought to arise following
Placodermi but prior to crown
Gnathostomata; however, recent research suggests that teeth may have arisen in derived placoderms such as
Romundina. There is currently much debate surrounding whether these tooth-like structures as well as the gnathal plates they sit on can be seen as the true primitive condition of Gnathostome dentition. Some researchers see the tooth-like structures of extensions of a primitive crushing plate, which is common in Placoderms. These primitive tooth-like structures lie on supragnathal plates and have a multi-cuspid appearance suggesting some degree of tooth-to-tooth
occlusion occurred. Additionally, synchrotron radiation
X-ray tomographic microscopy reveals that these tooth-like tubercle structures likely consist of a
dentine based core and an
enameloid cap common to many extant fish groups; however, they lack internal vascularization. The most prominent of these "bridge" features is the positioning of the nasal capsule dorsally between the eyes, a feature only present in early to mid Placoderms.
Romundina has been shown to unambiguously have a
jaw, however the
cranial anatomy and proportions of the brain are more closely aligned with those of jawless
vertebrates. The entirety of
Romundina was likely covered in irregularly shaped dermal scales, which is a characteristic unlike the more symmetrical scales that appear on Gnathostomes. Additionally,
Romundina likely had a vascular spine which grew posteriorly and proximally from the cranial side of the spine just posterior of the head. This spine likely played a heavily defensive role and grew similarly to how scales grow in Gnathostomes. Furthermore, this defensive spine is made up of semidentine odontodes, dermal bone, and perichondral bone suggesting that it is derived from dermal plates.
Diet and behavioral characteristics Romundina were small Placoderms and therefore had to rely on heavily armored skull and anterior sections of their body to fend off larger fish present at the same time. Corals and other shallow water organisms were also found alongside
Romundina in the same formation on Prince of Wales Island suggesting that they too lived in relatively shallow water. Their small size is also consistent with a shallow water habitat. Research suggests that
Romundina also ate mostly invertebrates such as crustaceans and worms. ''Romundina's
large crushing tooth-like structures as well as the large gnathal plates would appear to be useful in eating organisms with hard shells such as crustaceans. Romundina
likely did not migrate or swim long distances as all known specimens have been found in a relatively small range of area in Prince of Wales Island. This lack of geographical range also suggests that Romundina'' only lived in a highly specialized ecosystem. Overall, relatively little research has been done on the
Paleobiology. == Discovery and classification ==