Incisoscutum

Incisoscutum
Temporal range: Late Devonian: Frasnian, 382.7–372.2 Ma
Incisoscutum specimen WAM 03.3.28
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: †Placodermi
Order: †Arthrodira
Suborder: †Brachythoraci
Clade: †Eubrachythoraci
Clade: †Coccosteomorphi
Superfamily: †Incisoscutoidea
Family: †Incisoscutidae
Genus: †Incisoscutum
Dennis & Miles, 1981
Species
  • Incisoscutum ritchiei Dennis & Miles, 1981 (type)
  • Incisoscutum sarahae (Long, 1994)
Synonyms
  • Gogosteus sarahae (Long, 1994)

Incisoscutum is an extinct genus of arthrodire placoderm from the Early Frasnian Gogo Reef, from Late Devonian Australia. The genus contains two species I. ritchiei,[1] named after Alex Ritchie, a palaeoichthyologist and senior fellow of the Australian Museum, and I. sarahae, named after Sarah Long, daughter of its discoverer and describer, John A. Long.

The genus is important in the study of early vertebrates as well-preserved fossilized embryos have been found in female specimens[2] and ossified pelvic claspers found in males.[3] This shows that viviparity and internal fertilization was common amongst these primitive jawed vertebrates, which are outside the crown group Gnathostomata.

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.[4]

  1. ^ Kim Dennis; R.S. Miles (1981). "A pachyosteomorph arthrodire from Gogo, Western Australia". Zoological Journal of the Linnean Society. 73 (3): 213–258. doi:10.1111/j.1096-3642.1981.tb01594.x.
  2. ^ John Long; Kate Trinajstic; Zerina Johanson (2009). "Devonian arthrodire embryos and the origin of internal fertilization in vertebrates". Nature. 457 (7233): 1124–1127. Bibcode:2009Natur.457.1124L. doi:10.1038/nature07732. PMID 19242474. S2CID 205215898.
  3. ^ Per Ahlberg; Kate Trinajstic; Zerina Johanson; John Long (2009). "Pelvic claspers confirm chondrichthyan-like internal fertilisation in arthrodires". Nature. 460 (7257): 888–889. Bibcode:2009Natur.460..888A. doi:10.1038/nature08176. PMID 19597477. S2CID 205217467.
  4. ^ Trinajstic, Kate (1995). "The role of heterochrony in the evolution of eubrachythoracid arthrodires with special reference to Compagopiscis croucheri and Incisoscutum ritchei from the Late Devonian Gogo Formation, Western Australia". Geobios. 28 (Suppl. 2): 125–128. Bibcode:1995Geobi..28..125T. doi:10.1016/S0016-6995(95)80099-9.