What is "incisoscutum"

Incisoscutum is a genus of arthrodire placoderm from the Late Frasnian Gogo Reef, from Late Devonian Australia. The genus contains two species I. ritchiei, named after Dr. Alex Ritchie, a palaeoichthyologist and senior fellow of the Australian Museum, and I. sarahae, named after Sarah Long, daughter of its discoverer and describer, Dr. John A. Long.

The genus is important in the study of early vertebrates as well-preserved fossilised embryos have been found in female specimens and ossified pelvic claspers found in males. This shows that viviparity and internal fertilisation was common amongst these primitive jawed vertebrates, which are outside the crown group Gnathostoma.

In a study of fossil remains, comparison of the ontogeny of fourteen dermal plates from Compagopiscis croucheri and the more derived species Incisoscutum ritchiei suggested that lengthwise growth occurs earlier in the ontogeny than growth in width, and that dissociated allometric heterochrony has been an important mechanism in the evolution of the arthrodires, which include placoderms. These same fossil specimens also show that Incisoscutum was a predator, as muscle fibres from the tails of other placoderms have been found in the stomach regions.