Choropterygida

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Taxobox

Choropterygida were a group of kinetoramphidans distinguished by their lack of propulsory fins. The earliest choropterygidan fossils are known from scales and vertebrae from the early Devonian of Ukraine and Germany. As one of the first offshoots of the Kinetoramphida, they were a short-lived but successful clade throughout the Devonian up until their decline and then extinction in the early Carboniferous. Choropterygidans were the primary vertebrate predators among reef environments for a great deal of their history.

Characteristics[edit | edit source]

Choropterygidans lacked lateral fins along their bodies, and overall had more elongated bodies than other early gnathostomes. As with other kinetoramphidans, they were capable of a great deal of cranial kinesis, but less than osteotelans. Choropterygidan skulls were stocky and powerful; the jaws typically narrowed significantly upon passing the joint, but still bore thick and sturdy bone walls. Their vertebrae were typically tall and slender by kinetoramphidan standards.

Evolution and extinction[edit | edit source]

The earliest known choropterygidan was discovered in terminal Pragian beds of Ukraine. It is represented by a sequence of five vertebrae; this specimen is not currently considered complete enough to be given its own genus. Said vertebrae completely lack the strain marks seen on osteotelans with fins. The lack of those markings imply this may be the first choropterygidan. However, with the lack of more definitive material, its affinities can't be definitively stated. Much more complete choropterygidan remains are found in the Hunsrück Slate of Germany, dating to the early Emsian (approx. 400 million years ago). Several taxa seem to be present from this formation in the genus Schuppig, all of which are known from crushed skeletons and soft tissue. These are the first members of a family (Schuppigidae) that became ubiquitous during the Devonian. Specimens of Schuppig feature long, thin skulls with a high degree of cranial kinesis, long and narrow teeth, and a long, finless body covered in smooth scales.

Schuppigids continued to thrive, especially in coastal and reef environments. Larger choropterygidans also appeared, such as the pelagic bone-crushing Pistricidae and enigmatic, possibly bathypelagic family Scotoplasmidae. Other taxa are known from scanty remains, or those that cannot be referred to any other families. One such oddball is Carcharophis from the Famennian of Antarctica; it was a large macropredator of a sort otherwise unseen in choropterygidans. At this time, the majority of large or unspecialized macropredators were eurypterids, cephalopods, mitrichthyeans or osteotelans; this was a rare exception.

After flourishing throughout the Devonian, choropterygidans were dealt a terrible blow by the Hangenberg event. Along with other reef-dwelling organisms, schuppigids went extinct, as did pistricids. Scotoplasmid fossils are known from the Carboniferous in low numbers, but no fossils are known from later than the Serpukhovian.