The putative euthycarcinoid or aglaspid track maker of the Krukowski quarry (a 2003 discovery) and possibly the earliest animal life on land in the fossil record

For more than a decade the Blackberry Hill Site has yielded a diverse ichnofauna and medusoid fossils that represent an ancient biota that may provide the earliest evidence of life venturing ashore during the Upper Cambrian. While Climactichnites, Protichnites, Diplichnites are found in multiple horizons, this sandstone flagstone A large, 5-inch specimen of putative euthycarcinoidquarry has yielded no animal fossils with hard parts except for rumors of some hyoliths that has as yet not been confirmed. In 2003, however, a desiccation layer between sandstone yielded arthropod cast body fossils of the putative maker of many of the trackways in the quarry. We will need to wait for the publication to have a name, but the animal's morphology has affinity to both the Euthycarcinoid and the Aglaspid groups, which were both multi-legged, telson-bearing creatures.


EuthycarcinoidThe euthycarcinoids are poorly understood and highly enigmatic arthropods that have at various times been assigned to nearly all major clades of Arthropoda. Vaccari (2004) notes that recent work has supported a placement with crustaceans or a myriapod-hexapod assemblage, a basal position in the Euarthropoda, or a placement in Hexapoda or a hexapod stem group. The near future may better define the elusive euthycarcinoids, as phylogenetic studies unveil the genes involved in arthropod evolution (Schram, 2001).The euthycarcinoids are known from 13 species from Upper Ordovician or Lower Silurian-Middle Triassic from Western Australia, Europe (e.g., the Rhynie chert) and the Mazon Creek in Illinois. In all cases the depositional characteristics suggests freshwater or brackish water environments. Recently, Vaccari (2004) described Apankura machu from a 38 mm holotype coming from late Cambrian of Argentina that occurs along with footprints and tail-drag trackways conspicuously similar to those of Protichnites from the Krukowski quarry. This finding pushes back the groups origin by some 50 million years. Since the Krukowski quarry is probably an older Cambrian assemblage, the Krukowski ichnofauna be the earliest arthropod fossils in the fossil record that are associated with land-based footprints. The trackways in the formation strengthen the theory that similar traces of subaerial origin from Cambro-Ordovician such as the Cambrian Krukowski quarry and the Ordovician Kingston formation in Ontario, Canada (MacNaughton, 2002) were made by euthycarcinoids. I am also struck that this arthropod has similarities to Fuxianhuia protensa, a basal arthropod from the Chengjiang Lagerstatte of China.


Aglaspid from middle Cambrian of UtahSimilarly, the Aglaspids remain enigmatic arthropods. Once placed with chelicerates, most workers now consider them incertae sedis, as the early arthropod phylogeny remains a highly confounded arena. The enigmatic group of early arthropods are possibly closely related to trilobites, and possibly link the trilobites with the Chelicerata. Hoxie (2005) has proposed aglaspids as among the key candidates for Protichnites trackmakers. Aglaspid fossils are found in many Cambrian and Ordovician fossil sites throughout the world. These arthropds had eight to twelve pairs of appendages, and a wide range of sizes from an inch long to nearly a foot. It is almost certain that the aglaspids did not live on land, but perhaps came ashore to mate and lay eggs, as horseshoe crabs do today. Or they may have been escaping 1 inch long specimenpredators that by the late Cambrian consisted of some scary creatures such as anomolacaris. Or, perhaps microbial mats along the shoreline provided an abundant and easy food source. Regardless, it was a paramount event for life on earth when thethe first attempts at land colonization were made. Morphologically, aglaspids appear similar to the modern-day pill bug (or rolly polly), except, like some trilobites, often had a prominent cephalon and tail appendage or telson. Their legs, designed for strolling the seafloor, probably would not have enabled arthropod mass mortalitymuch speed during land locomotion.

The Krukowski quarry ichnofossils are often distinguished by ripples and fine layering in the sandstone that are characteristic of wind-blown sand compacted over millennia, rather than underwater sediments. Recently discovered in the Krukowski quarry are ichnofossils coincident with raindrop impressions, further evidence of a subaerially exposed environment where the aquatic inhabitants of this Cambrian shoreline were venturing ashore. The Krokowski quarry footprints in the sand may thus represent the earliest fossil evidence in arthropod terrestrialization.

Also see: Ichnofossil Nomenclature


Krukowski Quarry Ichnofossils for Sale