We refer to what Agassiz calls prophetic
and synthetic types; for which the former name may suffice, as the
difference between the two is evanescent.
"It has been noticed," writes our great zoologist, "that certain types,
which are frequently prominent among the representatives of past ages,
combine in their structure peculiarities which at later periods are
only observed separately in different, distinct types. Sauroid fishes
before reptiles, Pterodactyles before birds, Ichthyosauri before
dolphins, etc. There are entire families, of nearly every class of
animals, which in the state of their perfect development exemplify such
prophetic relations.
The sauroid fishes of the past geological ages are an example of this
kind These fishes which preceded the appearance of reptiles present a
combination of ichthyic and reptilian characters not to be found in the
true members of this class, which form its bulk at present. The
Pterodactyles, which preceded the class of birds, and the Ichthyosauri,
which preceded the Cetacea, are other examples of such prophetic
types."--(Agassiz, "Contributions, Essay on Classification," p. 117.)
Now, these reptile-like fishes, of which gar-pikes are the living
representatives, though of earlier appearance, are admittedly of higher
rank than common fishes.
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