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
Comments on the Late Devonian placoderms
from the Holy Cross Mountains (Poland).
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.
Ces eurypteides deouverts anteieurement proviennent d'un aflleurement dam la pattie ouest de la Formation de Campbelhon et on croit que l'espece a frequente un milieu du delta cotier, de pair avec un assemblage riche en vertebres, qui a compris des cephalaspides, des placodermes
, des acanthodiens et des requins.
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.
Long explained that that limbs and genitals developed via the same developmental pathways, so fossils showing the oldest evidence of pelvic fins (the placoderms
) also showing the oldest expression of sexual organs (claspers) might not be such a coincidence.
Overall, this outcrop is famous for an abundant association of vertebrate remains: psammosteids (Mark-Kurik 1968, 1995; Obruchev & Mark-Kurik 1965), placoderms
(Karatajute-Talimaa 1963), sarcopterygians (Vorobyeva 1977), chondrichthyans (Marss et al.
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.