Posted by ricardo marcenaro | Posted in Fossils - Fosiles: Avitelmessus grapsoideus - Links to more Fossils | Posted on 13:31
Subphylum Crustacea, Class Malacostraca, Order Decapoda
Geological Time: Eocene
Size: Crab fossil is 21.3 cm (8 ½”) in width by 10.5 cm (4 ¼”) in length
Fossil Site: Peedee Formation, North Carolina
Description: Avitelmessus grapsoideus is one of the best-known fossil crabs in the world, but rarely if ever found in this condition! Most specimens are of relatively poor quality, with little detail, and are best known from the Ripley formation. This particular specimen is from the same formation as the type specimen described by Rathbun early in the century, the PeeDee formation of North Carolina. At a whopping 67 million years old, this specimen was found in a small quarry alongside numerous other cretaceous fauna including remains of large reptiles, actual dinosaurs, ammonites, and echinoids. Virtually the entire coastal ecosystem was represented.
Specimens of this quality are extremely rare with only a few existing in private or public collections. Of those few, this is one of, if not, the single, best this writer has ever seen (very hard matrix- this is a superior preparation). Our ace preparator, Rod Bartlett of B.C. Canada invested 60 hours of meticulous air abrasion into this masterpiece. Many partial specimens from the now lost site (currently a bass stocked lake) were used in several recent publications describing primary and secondary sexual characteristics and other features of this species almost never seen preserved even in much much younger species such as those famous specimens from Italy (usually composites, incidentally- not so this ancient specimen)
Covered "head to toe" in spikes, spines, and pustules, this specimen looks as if it could get up and walk off of the matrix. Specimens like this are likely never to be seen again, and this specimen would enhance any collection, public or private. In fact, museums around the globe are clambering for one of these to add to their collections (though enough information has been gather from partial specimens to make this one of the better understood fossil families in history!) In life, like crabs of now, those spines and bumps served as anchor points for sponges, algae’s and the like to help in the camouflage of this unique animal. One can imagine it was probably not very appetizing to swallow with the longer spines as well (although, clearly bitten partial specimens were uncovered during the existence of the quarry.)
Interestingly, the species is known to have ten legs, of course, but the rear most legs are almost never found intact on any specimen from anywhere- it is assumed they are extremely reduced relative to the remaining legs- a feature of this crab’s family, the dakotacancridae.
This crab was preserved in what we have found must have been a catastrophic burial (e.g., localized underwater slide or hurricane event.) All the fossils found are found in relatively very shallow lenses in the Peedee of North Carolina, and a very small arial range.
Very definitely an "investor" grade fossil. If we didn't happen to be in possession of another of the three known of this quality in our private collections, there is no way this would be made.
Avitelmessus was described in 1923 by Mary J. Rathbun, who assigned it to the family Atelecyclidae. Martin Glaessner re-assigned it to the family Dakoticancridae in 1960.
The shell of Avitelmessus was about 2.25 inches (5.7 cm) in length and was nearly ovular in shape, with a "rounded outline". The upper surface was marked by "broad, shallow grooves" which formed two attached diamond-like shapes, with the larger one closer to the front. "Subsidiary" grooves came in contact with both sides of the larger diamond. The "fairly blunt" anterior edge of the carapace possessed a small, central rostrum, with orbits on either side. The front legs were modified to become chelipeds, with pincers formed by an upper finger, which was movable, and a lower finger, which was stationary (an extension of the previous leg segment). All limbs were covered by "fine granules". At least one specimen with "color markings" (considered rare among fossil crabs) has been discovered. The colors are described as "a medium background, dark spots and blotches, and light lines".
Fossils - Fosiles: Avitelmessus grapsoideus - Links to more Fossils
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