Distribution of chondrichthyans
in the Lower and Middle Devonian of Belarus (stratigraphic chart after Kruchek et al.
The oldest chondrichthyan
from the Early Devonian period.
Number of species by genera of Mexican chondrichthyans
Dulvy NK, Forrest RE (2010) Life histories, population dynamics, and extinction risks in Chondrichthyans
In: Descriptions of New Australian Chondrichthyans
In spite of the evolutionary and economic importance of chondrichthyans
, there are a scarce number of investigations with regards to the ovary structure and they have been conducted mainly in species from intensive fishing zones (Pratt, 1988; Hamlett et al.
There are over 1,000 species of Chondrichthyans
(cartilaginous fish) including Elasmobranches: the sharks (c.
Some specific areas examined include phylogenetic relationships among the major lineages of modern Elasmobranchs, reproductive evolution of chondrichthyans
, reproduction in fisheries science, the Elasmobranch ovary, the testis and spermatogenesis, and alkaline glands and Clasper glands of batoids.
Silurian and Lower Devonian thelodonts and putative chondrichthyans
from the Canadian Arctic Archipelago (Cornwallis, Baillie-Hamilton, Devon, and Prince of Wales islands).
are represented by ray teeth and spines.
Some modern chondrichthyans
with molariform or pavement-like dentitions, such as horn sharks (Heterdontiformes), bonnethead sharks (Sphyrna tiburo), some rays (Mylobatidae), and chimeras (Holocephali), are durophageous (Dean, 1906; Smith, 1942; Cappetta, 1987; Wilga and Motta, 2000).
We were permitted to examine a private collection of some 20 teeth of chondrichthyans
taken in gray Finis Shale some 20 kilometers from where the spine was found, but whether any of these might have come from fish like Physonemus we cannot say.
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.
As a consequence, palaeontological studies of disarticulated remains of chondrichthyans
have focused on teeth and very little attention has been paid to scales.
Sharks are classified as chondrichthyans
(cartilaginous fishes), one of the most diverse and oldest taxa of vertebrates.