This is a trilobite with colour patterns of the species Eldredgeops rana rana from the Wanakah Shale of New York.
Fossils and especially trilobites with color pattern preservation are great exceptions and rarities. George C. Esker, 1968 discusses some finds of Phacops rana* with color markings, i.e. color patterns from the Devonian of New York. (*= Eldredgeops rana)
Esker speculates that the irregular but symmetrical dot patterns are related to the preservation of chromatophores. Such a color change physiology is known in recent crustaceans. However, these require a certain transparency or at least a high translucency of the carapace. McRoberts et al, 2013 state that these punctate patterns correspond to spherical structures within the inner laminate layer of the trilobite carapace. These appear to be made of transparent calcite.
However, located below the outer prismatic part of the shell. McRoberts et al therefore ruled out exoparasites and epibionts (i.e. fouling). Due to the symmetrical and non-random distribution of these color patterns, this hypothesis can be ruled out with a certain certainty.
Muscle attachment points or diagenesis can also be ruled out as an explanation. Although diagenesis and this conservation variations do have an impact on the visibility of these color patterns.
After all, the trilobite shell must not be remineralized to be able to preserve these primary details.
In the Schoenemann et al, 2014 paper, the authors tend not to follow McRoberts' interpretation of these spheres as translucent calcite windows for chromatophores. It is true that these spherical structures could also be detected. However, these were apparently not transparent either. But this could be a variation in the preservation
Color patterns in trilobites are actually very rarely preserved as in all kind of fossils. At least color patterns are also found in other trilobite orders.
At least the function as a camouflage pattern to optically disguise the body outline was probably given.
This approximately 40 mm long Eldredgeops shows these structures in an extraordinarily good state of preservation. In particular, the microstructures of the trilobite shell are very well preserved. In adittion offers this specimen a strong contrast of the patterns to the relative pale carapace.
Overall, this is a very interesting trilobite in a nice stretched preservation.
Esker GC. 1968 : Colour markings in Phacops and Greenops from the Devonian of New York.
McRoberts, Christopher & Hegna, Thomas & Burke, Jeri & Stice, Morgan & Mize, Steven & Martin, Markus. ,2013 : Original spotted patterns on Middle Devonian phacopid trilobites from western and central New York.
Schoenemann, Clarkson & Ryck, 2014 : Colour Patterns in Devonian Trilobites. 113- 117 in The Open Geology Journal, 2014, 8, 113-11 |
