Meek studied several specimens of the animal preserved in gray phosphatic concretions found at the base of the Waverly Group near Danville, Kentucky, which include the holotype and seven paratypes.
[1] In 1897, Prussian-born American zoologist Arnold Edward Ortmann analysed an additional 27 fossils representing 18 individuals, which he determined to belong to the same species named by Meek.
[2] Further analysis by American paleontologist Harold Kelly Brooks in 1962 found that the aforementioned fossils show clear features of mantis shrimps, and that the species represented by these remains is unrelated to Crangopsis, thus the genus Archaeocaris was revalidated.
[3] While this species was initially known from only one specimen, additional fossils of A. graffhami would later be found in the upper Pilot Shale on Bactrian Mountain of the Pahranagat Range, Nevada, and described in 1979 by American paleontologist Frederick Schram.
It is fused to the frontmost thoracic segments and covers them entirely, while wing-like projections extend from the side of the carapace to the border of the thorax and abdomen.
Conical spikes are present on the propodus (penultimate segment), opposing the sharp dactylus to form a set of grasping claws.
The bottom margins of the sclerites (hardened plates) on each abdominal segment is straight and horizontal, aside from a small upwards curvature at the front.
These were first noticed by Brooks (1962), who recognized Archaeocaris to be an early mantis shrimp and placed it in the family Perimecturidae, believing it was a close relative of Perimecturus.
This family is monotypic, with Archaeocaris as its type and only genus, and is placed within Palaeostomatopodea (which is still used in a paraphyletic sense for the convenience of referring to the evolutionary grade).
Archaeocaris vermiformis Archaeocaris graffhami †Bairdops elegans Perimecturus parki Perimecturus rapax †Bairdops beargulchensis †Daidal pattoni †Daidal schoellmanni †Daidal acanthocercus Gorgonophontes fraiponti Gorgonophontes peleron †Chabardella spinosa †Tyrannophontes theridion †Tyrannophontes gigantion †Triassosculda ahyongi †Tyrannosculda laurae †Pseudosculda laevis †Archaeosculda phoenicia †Sculda pennata †Sculda syriaca †Ursquilla yehoachi †Lysiosquilla nkporoensis †Nodosculda fisherorum Squilla mantis
Unlike other known mantis shrimps of the Paleozoic (which lived in shallow marine or brackish-freshwater environments), both species of Archaeocaris are believed to have inhabited deep water in open seas.
The deposits in which this species is found has also preserved fossils of brachiopods (such as Lingula, Productus and Spirifer), bivalves (such as Aviculopecten, Palaeoneilo and Schizodus), bryozoans (such as Fenestella), conulariids (such as Conularia) and crustaceans (such as Palaeopalaemon and Ceratiocaris).
[4][12] The species A. graffhami has a wider chronological range, with the geologically oldest specimens originating from the upper Pilot Shale of Nevada and dating back to the earliest Kinderhookian (around 358.9 million years ago) of the Tournaisian stage.
[13] In addition, the type specimen of A. graffhami was collected from the Caney Shale in Oklahoma, a younger site which dates to the late Viséan stage (latest Meramecian or earliest Chesteran stages in the North American regional series, as recently as 330.9 million years ago), making it the youngest known record of the genus.