Antiarchs (
Placoderm fishes) from the Devonian Aztec Siltstone, Southern Victoria Land, Antarctica.
2003), disarticulated cephalaspids,
placoderms and acanthodians, and both articulated and disarticulated eurypterids (Miller 2007a).
More than 100 million years before dinosaurs walked the Earth,
placoderms thrived.
It was assumed
placoderms died out and a different group evolved into bony fish.
The limestone middle part (up to 10 cm) is rich in cephalopods and arthrodire
placoderms. According to the detailed analysis of Janiszewska et al.
Scientists were excited by its mUG SHOT: mix of traits from
placoderms - an extinct armoured fish - and bony fish, which gave rise to all modern fish that have jaws and skeletons made of bone.
Called
placoderms, these extinct animals were among the earliest vertebrates with jaws.
"We could then make comparisons with the embryology of living vertebrates, thus demonstrating that
placoderms possessed teeth," he explained.
These previously discovered eurypterids are from the western exposure of the Campbellton Formation and are believed to have inhabited a coastal deltaic setting, along with a rich vertebrate assemblage that included cephalaspids,
placoderms, acanthodians, and sharks.
The Andreyevka-2 community including antiarch
placoderms, acanthodians, chondrichthyans and osteichthyans, as well as tetrapods, has been discussed on repeated occasions by the first author of this paper (Lebedev 1986, 1992, 2013; Lebedev et al.
Furthermore, the analysis demonstrated that all of these early members of the modern gnathostomes are clearly separated from what now appear to be the most primitive vertebrates with jaws: a collection of armored fishes called
placoderms.
sp.;
placoderms Actinolepis tuberculata Agassiz, Homostius sp., Byssacanthus dilatatus (Eichwald); acanthodians Archae-acanthus quadrisulcatus Kade, Diplacanthus kleesmentae Valiukevicius, Acanthodes?
"Our finds show that these extinct armored fishes, the
placoderms, had intimate copulation with males inserting claspers (a structure that is part of the pelvic fin) inside the female to deposit sperm," Long said.
