Lepidotes

Lepidotes (from λεπιδωτός, 'covered with scales') (previously known as Lepidotus) is an extinct genus of Mesozoic ray-finned fish. It has long been considered a wastebasket taxon, characterised by "general features, such as thick rhomboid scales and, for most of the species, by semi-tritorial or strongly with dozens of species assigned to it. Fossils attributed to Lepidotes have been found in Jurassic and Cretaceous rocks worldwide. It has been argued that Lepidotes should be restricted to species closely related to the type species L. gigas, which are only known from the Early Jurassic of Western and Central Europe, with most other species being not closely related, with other species transferred to new genera such as Scheenstia. Lepidotes belongs to Ginglymodi, a clade of fish whose only living representatives are the gars (Lepisosteidae). The type species L. gigas and close relatives are thought to be members of the family Lepidotidae, part of the order Lepisosteiformes within Ginglymodi, with other species occupying various other positions within Ginglymodi.

Description
Inhabiting both freshwater lakes and shallow seas, Lepidotes was typically about 30 cm long. The body was covered with thick, enamelled scales.

Lepidotes was one of the earliest fish in which the upper jawbones were no longer attached to the jugal bone. This allowed the jaws to be stretched into a 'tube' so that the fish could suck in prey from a greater distance than in previous species. This system is still seen in some modern fish, such as carp.

Lepidotes scales are ovular in shape, and are 18.5 mm long and 3 mm thick at the thickest point. The scales are smooth and shiny on the external surface, with only a few small depressions scattered toward the centre that are shaped like punctures.

Stomach contents of Lepidotes from the Early Jurassic of Germany have found remains of crustacean cuticles, and it is suggested that they fed on relatively soft-bodied prey, which was grasped with the slender marginal teeth, before being crushed by the rounded palatal teeth.

Distinguishing characteristics
Many characteristics were identified by Woodward in 1895, and they are listed below:


 * a fusiform trunk only moderately compressed;
 * the fact that the marginal teeth are compressed;
 * the presence of stouter inner teeth that are smooth;
 * ossified ribs;
 * very large fin-fulera on all fins;
 * that all paired fins are small;
 * short and deep dorsal and anal fins;
 * very robust, smooth or feebly oriented scales;
 * flank scales that are not much deeper than wide;
 * scales ventrally nearly as deep as broad;
 * and the presence of inconspicuous dorsal and ventral ridge-scales.

Taxonomy
Currently valid species after.

L. gigas
The type species of the genus, it is known from the Early Jurassic (Toarcian) of Germany.

L. elvensis
L. elvensis was described by Ducrotay de Blainville in 1818. It is known from an almost complete specimen housed in the Paris Museum of Natural History. The specimen measures up to 75 cm long. The specimen is from the Upper Lias, in Bavaria. The specimens P. 7406, P. 7407, P. 7408, P. 2014, P. 2054, P. 3529a, P. 3529b, 18992, 18993/94 19662, 32421, and 32422 have all been assigned to this species. The external bones of this species are smooth, but some have sparsely-placed coarse tuberculations (protuberances). The frontal bone is more than twice the length of the parietal in the specimens. It also has a comparatively narrow marginal symphysis (articulation). Other specimens are known from France.

L. semiserratus
This species was named by Agassiz in 1837 and is known from some incomplete remains. It has been classified as closely related to L. elvensis. It is more elongate than L. elvensis, being four times as long as tall. It also has more sharply angulated sutures between its parietals, and the parietals are also proportionally longer. It is known from the specimens P. 1127, P. 7409, P. 2012, P. 2012a, P. 3527, P. 3528, P. 3528a, P. 5213, P. 5228, P. 6394, P. 7410, and 35556, all from the Upper Lias of Yorkshire, England

L. buelowianus
Known from the Early Jurassic of (Toarcian) Germany.

Reassigned species
"Lepidotes" latifrons from the Middle-Late Jurassic of England has been reassigned to the genus Isanichthys. Many other European species from the Late Jurassic-Early Cretaceous have been reassigned to Scheenstia.