SPIRORHAPHE: DECODING THE SPIRALS OF AN ENIGMATIC GRAPHOGLYPTID TRACE FOSSIL THROUGH GEOLOGIC TIME

Graphoglyptids are morphometrically intricate trace fossils that are formed as open burrow systems that are frequently preserved in deep sea deposits as casts on the base of turbidite beds. Graphoglyptids are found in many sizes and shapes, including meandering (Cosmorhaphe), net-like mesh (Paleodictyon), and spiraling (Spirorhaphe).

There are several spiraling graphoglyptid ichnogenera, which include Spirorhaphe, Spirodesmos, Spirophycus, and Macaronichnus. However, they are behaviorally or morphologically different enough from one another to warrant unique ichnogenera. Spirorhaphe has been recognized as a trace fossil since the late 1800’s, nevertheless, the behavioral purpose of Spirorhaphe has much been debated over the years. It has been referred to as a fodinichnion (deposit feeding trace), agrichnion (farming trace), or an irretichnion (trapping trace).

Within the ichnogenus Spirorhaphe, there are three ichnospecies currently recognized. S. involuta is known from the Ordovician, but this sample is a single occurrence with the next earliest specimen known from the Late Cretaceous, when the number of known occurrences explodes. S. azteca is a rare ichnospecies and is identified in only a couple of localities, including the Early Permian of New Mexico and the Eocene of Mexico. S. graeca is also a rare ichnospecies of Spirorhaphe with one of the only known occurrences being the illustrated example in Seilacher’s (1977) description from the Eocene Pindos Flysch of Greece.

The large gap in time between the initial occurrence of S. involuta in the Ordovician and the later occurrences starting in the Late Cretaceous indicates that the producer of the Ordovician trace fossil was likely not the same as the producer of the much younger trace fossils. This leads to the question of what the trace maker was doing in both time periods in order to produce a nearly identical trace. A related question is what happened in the Late Cretaceous to allow an explosion of different graphoglyptid morphologies to suddenly emerge in the deep marine environment. An evaluation of Spirorhaphe morphological variations helps us understand the paleoecologic and paleoclimatic changes that spurred an expansion of graphoglyptid niches at this critical time in geologic history.