Though there can be no doubt
whatever as to the occurrence of genuine Reptiles in deposits of
unquestionable Permian age, there is still uncertainty as to the
precise number of types which may have existed at this period.
This uncertainty arises partly from the difficulty of deciding
in all cases, whether a given bone be truely Labyrinthodont or
Reptilian, but more especially from the confusion which exists at
present between the Permian and the overlying Triassic deposits.
Thus there are various deposits in different regions which have
yielded the remains of Reptiles, and which cannot in the meanwhile
be definitely referred either to the Permian series or to the
Trias by clear stratigraphical or palaeontological evidence. All
that can be done in such cases is to be guided by the characters
of the Reptiles themselves, and to judge by their affinities to
remains from known Triassic or Permian rocks to which of these
formations the beds containing them should be referred; but it
is obvious that this method of procedure is seriously liable
to lead to error. In accordance, however, with this, the only
available mode of determination in some cases, the remains of
_Thecodontosaurus_ and _Palaeosaurus_ discovered in the dolomitic
conglomerates near Bristol will be considered as Triassic, thus
leaving _Protorosaurus_[20] as the principal and most important
representative of the Permian Reptiles.
Pages:
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311