.
.
.
/ˌneɪθoʊstoʊˈmɑːtə/
.
(“gnathostomata” are the ‘jawed vertebrates’)
(the term derives from ‘Greek’: γνάθος (gnathos) “jaw” + στόμα (stoma) “mouth”)
(‘Gnathostome’ diversity comprises roughly 60,000 species, which accounts for 99% of all living ‘vertebrates’)
(in addition to ‘opposing jaws’, living ‘gnathostomes’ also have ‘teeth’, ‘paired appendages’, and a horizontal semicircular canal of the ‘inner ear’, along with physiological and cellular anatomical characters such as the ‘myelin sheathes’ of ‘neurons’)
(another is an adaptive ‘immune system’ that uses V(D)J recombination to create ‘antigen recognition sites’, rather than using genetic recombination in the ‘variable lymphocyte receptor gene’)
(it is now assumed that ‘Gnathostomata’ evolved from ancestors that already possessed a pair of both ‘pectoral’ and ‘pelvic’ fins)
(in addition to this, some ‘placoderms’ were also shown to have a third pair of ‘paired appendages’, that in males had been modified to ‘claspers’ and ‘basal plates’ in females, a pattern not seen in any other ‘vertebrate group’)
(the ‘Osteostraci’ are generally considered the sister taxon of ‘Gnathostomata’)
(it is believed that the jaws evolved from ‘anterior gill support arches’ that had acquired a new role, being modified to pump water over the ‘gills’ by opening and closing the ‘mouth’ more effectively – the ‘buccal pump mechanism’)
(the mouth could then grow bigger and wider, making it possible to capture larger prey)
(this close and open mechanism would, with time, become stronger and tougher, being transformed into real ‘jaws’)
(newer research suggests that a branch of ‘Placoderms’ was most likely the ancestor of present-day ‘gnathostomes’)
(a 419-million-year-old fossil of a ‘placoderm’ named Entelognathus had a bony skeleton and anatomical details associated with cartilaginous and bony fish, demonstrating that the absence of a bony skeleton in ‘Chondrichthyes’ is a derived trait)
(the fossil findings of primitive bony fishes such as Guiyu oneiros and Psarolepis, which lived contemporaneously with Entelognathus and had ‘pelvic girdles’ more in common with ‘placoderms’ than with other ‘bony fish’, show that it was a relative rather than a direct ancestor of the extant ‘gnathostomes’)
(it also indicates that ‘spiny sharks’ and ‘Chondrichthyes’ represent a single sister group to the ‘bony fishes’)
(fossil findings of juvenile ‘placoderms’, which had ‘true teeth’ that grew on the surface of the ‘jawbone’ and had no roots, making it impossible to replace or regrow as they broke or wore down as they grew older, proves the common ancestor of all ‘gnathostomes’ had teeth and place the origin of teeth along with, or soon after, the evolution of ‘jaws’)
(late ordovician-aged microfossils of what have been identified as scales of either acanthodians or “shark-like fishes”, may mark Gnathostomata’s first appearance in the ‘fossil record’)
.
*undeniably unambiguous ‘gnathostome’ fossils, mostly of primitive ‘acanthodians’, begin appearing by the early ‘silurian’, and become abundant by the start of the ‘devonian’*
.
.
.
.
.
.
💕💝💖💓🖤💙🖤💙🖤💙🖤❤️💚💛🧡❣️💞💔💘❣️🧡💛💚❤️🖤💜🖤💙🖤💙🖤💗💖💝💘
.
.
*🌈✨ *TABLE OF CONTENTS* ✨🌷*
.
.
🔥🔥🔥🔥🔥🔥*we won the war* 🔥🔥🔥🔥🔥🔥