The upper, Emsian part of the formation contains a quite different fish assemblage, consisting of placoderms--petalichthyid Wijdeaspis, buchnosteids, large arthrodires, e.
Hibernaspididae), cephalaspids, large arthrodires and sarcopterygians, show that the lowermost part of the Razvedochnyj Fm is exposed.
In these arthrodires the anterior edge of the skull is turned down and nasal openings are faced forwards.
A transverse pitline, not known in other arthrodires, joins the centres of the PrO plates.
Arthrodires have commonly four sclerotic plates, e.
However, some characters of Eukaia: small postorbital plate and the suborbital plate, firmly fused to the skull roof, and a very large nuchal plate, which is considerably longer than the paranuchals and has a strongly convex posterior margin, separate the new genus from this group and indicate its relationship with other arthrodires.
He said that their work earlier this year suggests the reproductive structure in the dominant group of placoderms, called arthrodires
, was similar to present day sharks.
These are represented by species of arthrodires Coccosteus, Watsonosteus and Plourdosteus and antiarchs Asterolepis and Bothriolepis.
Noteworthy is the absence of the characteristic Middle Devonian arthrodires Homostius and Heterostius (Mark-Kurik & Nemliher 2003).
Kartalaspis and other Early Devonian arthrodires and their stratigraphical significance.
However, a closer inspection by Long and research team revealed they were the tiny bones of unborn fish from two adult species of arthrodires
(Incisoscutum ritchiei) - the biggest and most diverse placoderm group.