They were interpreted as the result of placoderm
fish dragging or pushing off the sediment.
The blades, called gnathal plates, looked so peculiar that most scientists thought that the three-part jaw originated in an early bony fish and that placoderms
were just a side branch in the vertebrate family tree.
Matt Friedman, a paleobiologist at Oxford University, said: "If you look at just the top of the skull and the body, it looks like a placoderm
The limestone middle part (up to 10 cm) is rich in cephalopods and arthrodire placoderms
were also the first vertebrates to have jaws, but they still had no teeth, which appeared in later fish.
were also some of the first vertebrates to have necks separating their heads and shoulder bones, allowing the fish to move their heads independently of the rest of their bodies.
of the Voskresenskoye locality might have entered a separate community of their own from the tetrapod one of the Andreyevka-2 locality and have been stenohaline, possibly depending on a food type missing from the latter.
The genus Guerichosteus, which had previously been known from the Emsian of Poland (Holy Cross Mountains, placoderm
sandstone, Rhinopteraspis cornubica Zone), is also found in the Lower Eifelian of Estonia.
such as the gigantic Dunkleosteus and lobe-finned fishes-similar to the modern lungfish-dominated the waters, while ray-finned fishes, sharks and tetrapods were in the minority, according to Maureen Kearney, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research, along with NSF's Division of Earth Sciences.
Histologic studies of placoderms
and fossil elasmobranchs.
Long said that the claspers were used by the ancient fish, an extinct class of armoured fish called placoderms
, to grip inside the female while they were mating.
They are represented by undetermined placoderms
, acanthodians and sarcopterygians (Fig.