View/Open - American Museum of Natural History

142 Buletin American Museum of Natural History
[Vol. LIX
This reasoning tends to support, to some extent, the customary
union of the smaller non-branchiosaurian amphibians in one group;
but such common features as they may possess are few.
The line of thought used above gives, of course, too simple a picture
and neglects the many complexities possible in the ontogeny of vertebrae.
ENVIRONMENT OF THE LINTON AMPHIBIANS
Case (1917) has discussed the environmental conditions surrounding
the Linton fauna, but it may be of interest to review the situation in
the light of a better understanding of the amphibian forms concerned.
Vegetable material must, of course, have been the ultimate source of food
supply, but none of the amphibians was adapted to this sort of diet.
Water-living invertebrates were presumably numerous, although their
remains are exceedingly rare, owing (as Case suggests) to an intense
competition for food in the small remnant of a once large pool in which
the Linton fish and amphibians presumably met their death. Fish were
abundant, especially several species of small palmoniscids, which appear
to have been invertebrate feeders, as were presumably the moderately
abundant ccelacanths and the comparatively rare dipnoans.
Upon the invertebrates must have fed not only most of the fish
fauna, but the smaller amphibians, such as Cocytinus, Saurbopleura and
most of the branchiosaurs, while forms of somewhat larger size (as
Ctenerpeton and aistopods) may have varied this diet by devouring the
smaller pa]aeoniscids.
Among the larger forms, whose diet very probably consisted exclusively
of other vertebrates, are to be included the pleuracanths,
fresh-water shark-like types of considerable size, whose remains are
abundant in the Linton cannel (it is interesting to note that no certain
remains of osteolepid crossopterygians have been discovered in this
locality).' The numerous palaeoniscids probably formed the staple food
of these larger fish, but it is likely that small amphibians may have played
a part in their diet.
Of presumably similar habits were the larger amphibians, Colosteus,
and the labyrinthodonts, fish-eaters for the most part, but preying also
on their smaller amphibian relatives.
COMPARISON WITH OTHER FAUNAS
If faunas of simliar type be sought abroad, it is obvious that the
closest comparison is with the Jarrow (Ireland) Coal Measures fauna,
'Newberry has described several species of " Rhizodus," all but one based on teeth which are probably
those of labyrinthodonts; the remaining one appears to be founded on a lung-fish plate.