Geological Contemporaniety and Persistent Types of Life | Page 9

are three, the Cystidea, Blastoidea, and
Edrioasterida, among the Echinoderms; and two, the Trilobita and
Eurypterida, among the Crustacea; making altogether five for the great
sub-kingdom of Annulosa. Among Vertebrates there is no ordinally
distinct fossil fish: there is only one extinct order of Amphibia--the
Labyrinthodonts; but there are at least four distinct orders of Reptilia,

viz. the Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria, and
perhaps another or two. There is no known extinct order of Birds, and
no certainly known extinct order of Mammals, the ordinal distinctness
of the "Toxodontia" being doubtful.
The objection that broad statements of this kind, after all, rest largely
on negative evidence is obvious, but it has less force than may at first
be supposed; for, as might be expected from the circumstances of the
case, we possess more abundant positive evidence regarding Fishes and
marine Mollusks than respecting any other forms of animal life; and yet
these offer us, through the whole range of geological time, no species
ordinally distinct from those now living; while the far less numerous
class of Echinoderms presents three; and the Crustacea two, such orders,
though none of these come down later than the Paleozoic age. Lastly,
the Reptilia present the extraordinary and exceptional phenomenon of
as many extinct as existing orders, if not more; the four mentioned
maintaining their existence from the Lias to the Chalk inclusive.
Some years ago one of your Secretaries pointed out another kind of
positive paleontologic evidence tending towards the same
conclusion--afforded by the existence of what he termed "persistent
types" of vegetable and of animal life.* He stated, on the authority of
Dr. Hooker, that there are Carboniferous plants which appear to be
generically identical with some now living; that the cone of the Oolitic
'Araucaria' is hardly distinguishable from that of an existing species;
that a true 'Pinus' appears in the Purbecks, and a 'Juglans' in the Chalk;
while, from the Bagshot Sands, a 'Banksia', the wood of which is not
distinguishable from that of species now living in Australia, had been
obtained.
[footnote] *See the abstract of a Lecture "On the Persistent Types of
Animal Life," in the 'Notices of the Meetings of the Royal Institution of
Great Britain'.--June 3, 1859, vol. iii. p. 151.
Turning to the animal kingdom, he affirmed the tabulate corals of the
Silurian rocks to be wonderfully like those which now exist; while even
the families of the Aporosa were all represented in the older Mesozoic
rocks.
Among the Molluska similar facts were adduced. Let it be borne in
mind that 'Avicula', 'Mytails', 'Chiton', 'Natica', 'Patella', 'Trochus',
'Discina', 'Orbicula', 'Lingula', 'Rhynchonella', and 'Nautilus', all of

which are existing 'genera', are given without a doubt as Silurian in the
last edition of 'Siluria'; while the highest forms of the highest
Cephalopods are represented in the Lias by a genus, 'Belemnoteuthis',
which presents the closest relation to the existing 'Loligo'.
The two highest groups of the Annulosa, the Insecta and the Arachnida,
are represented in the Coal, either by existing genera, or by forms
differing from existing genera in quite minor peculiarities.
Turning to the Vertebrata, the only Paleozoic Elasmobranch Fish of
which we have any complete knowledge is the Devonian and
Carboniferous 'Pleuracanthus', which differs no more from existing
Sharks than these do from one another.
Again, vast as is the number of undoubtedly Ganoid fossil Fishes, and
great as is their range in time, a large mass of evidence has recently
been adduced to show that almost all those respecting which we
possess sufficient information, are referable to the same sub-ordinal
groups as the existing 'Lepidosteus', 'Polypterus', and Sturgeon; and
that a singular relation obtains between the older and the younger
Fishes; the former, the Devonian Ganoids, being almost all members of
the same sub-order as 'Polypterus', while the Mesozoic Ganoids are
almost all similarly allied to 'Lepidosteus'.*
[footnote] *"Memoirs of the Geological Survey of the United
Kingdom.--Decade x. Preliminary Essay upon the Systematic
Arrangement of the Fishes of the Devonian Epoch."
Again, what can be more remarkable than the singular constancy of
structure preserved throughout a vast period of time by the family of
the Pycnodonts and by that of the true Coelacanths; the former
persisting, with but insignificant modifications, from the Carboniferous
to the Tertiary rocks, inclusive; the latter existing, with still less change,
from the Carboniferous rocks to the Chalk, inclusive?
Among Reptiles, the highest living group, that of the Crocodilia, is
represented, at the early part of the Mesozoic epoch, by species
identical in the essential characters of their organization with those now
living, and differing from the latter only in such matters as the form of
the articular facets of the vertebral centra, in the extent to which the
nasal passages are separated from the cavity of the mouth by bone, and
in