Loxommatidae

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The Baphetids or Loxommatids were large labyrinthodont predators of the Late Carboniferous period (Namurian through Westphalian) of Europe. Fragmentary remains from the Early Carboniferous of Canada have been tentatively assigned to the group.

Not only are they included among the very early Labyrinthodonts, but they were also among the first of the Carboniferous fossil tetrapods to be found and were originally described in 1850 by William Dawson. They are known mainly from skulls; very little skeletal material has been found. But even from this quite a lot can be deduced.

Palaeobiology

The presence of lateral lines and the long rows of needle-like teeth show that most were fish-eaters. Their development were likely amphibian, though no larval fossils are known. Their best-known characteristic was a curious, keyhole-shaped orbit formed by excavation of the lacrimal and prefrontal bones in front of the eye. It has been suggested that this space accommodated a salt gland or some kind of electrosensory organ.[1] Perhaps the better hypothesis is that the space allowed room for the contraction of an enlarged pterygoideus muscle. In that case, this skull modification would represent an early form of skull fenestration for jaw muscles.

The skull is shallow. Unlike the better-known embolomeres, the baphetid cheek and skull roof are sutured together. There is a strongly embayed spiracular ("otic") notch, but the stapes is distally broad, which seems to rule out a sensitive hearing apparatus. The palate is closed -- a primitive character, but very different from the temnospondyls. The coronoids bear no teeth or denticles, while the dentary has a double tooth row.

Since the taxon is based almost exclusively on skulls, the body is very poorly known. It is often said that the body was crocodile-like, but this appears to be largely supposition.

It is not clear whether all of the genera assigned to this group are really closely related. The traditional four genera of baphetids (Loxomma, Baphetes, Megalocephalus, and Spathicephalus) have recently been supplemented by Eucritta, a somewhat different form. It has also been suggested that Crassigyrinus may be closely related.

Relationships

Baphetids have been previously considered primitive temnospondyls and more recently batrachosaurs (reptile-like amphibia). It is likely, however, that they represent one more of a number of early Carboniferous tetrapodomorph radiations. Computer-assisted phylogenetic analyses of a data matrix using characteristics of most of the major groups of terrestrial vertebrates place the Baphetids close to the ancestry of amniotes.

With the reinterpretation of Ichthyostega and its relatives as aquatic forms, baphetids are good candidates for the spot of first tetrapodomorph group to actually spend substantial time on land. If so, baphetids may be a rather important taxon.

References

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