Originally published in: Ordovician News, 13: 58-59. S. John's 1996.
Vaclav Petr1 - Petr Kacha2
We have recently completed a preliminary study on the interesting possibility of frequent occurrence of camouflage and mimicry among Barrandian Ordovician trilobites. Curiously, to date, most of the articles on fossil camouflage and mimicry have been concentrating on finding colours or colour patterns in the fossil record. Other characteristics of camouflage and mimicry (including those best observable in the fossil record, i.e. morphological ones) do not play an important role in the palaeontological research. While it is generally accepted that there are many examples of similarities in the fossil record resulting from close relationship (i.e. because of common ancestry), there has been less enthusiasm for the notion that two similar species at the same place and time were related as a 'model' and its 'mimic' or that they were camouflaged in the same manner. It is possible that many examples of species diversity in the fossil record and even the so-called 'ecophenotypic' variations in a single fossil species have resulted from camouflage!
Palaeontologists have traditionally searched only for the
distinction of 'environmental' from 'genetic' variations but ancient animals did
not live in a sort of "abiological laboratory" environment. We have found, for
example, that specimens of trilobites coming from fine-grained sediments bear
dense, soft granulation on their carapaces (in extremely fine-grained sediments
the carapax may be smooth), while those from coarse-grained ones are provided
with large granules scattered on the outer surface of the exoskeletons. Such
interesting correlations are found in many other Barrandian trilobites,
including several common species such as the Ordovician dalmanitid
Dalmanitina socialis (Barrande). Tha fact that the more ontogenetically
younger trilobite individuals have coarser and more sparse granules on their
exoskeleton indicates relatively stable diameter of the granules and points to a
close connection of the granulation with the grain size of substrate. There are
possibilities of many types of camouflage and mimicry in trilobites and several
ones have been discussed previously by Lamont (1967, 1969). Unfortunately, the
conclusions of the latter author have been typically ignored and never followed
in the works of other specialists.