Description: This 50 million year old, Eocene-Era fossil fish comes from one of the world's famous Laggerstatten, the Green River Formation in Wyoming. A small portion of the fish fossils from Green River exhibit such fine preservation. The significant extent of soft-tissue preservation that makes the site famous is evident in this specimen.

This is an exquisite, museum quality female Stingray specimen known as Heliobatis radians (Order: Rajiformes; Family: Dasyatidae), at once a rare and highly sought species, and the only species of ray from this formation. The preservation is superb and the preparation is the best there is. Note in the pictures the details in the barbs and the thorn-like spines of the tail. This one is known to be a female due to the absence of claspers used by the male in mating. Heliobatis is highly sought not only for the rarity, but because a specimen such as this makes for an awesome display.

Rays belong to the Chondrichtyes, as do the sharks. All have an inner skeleton made of cartilage. Since cartilage comprises more organic material (collagen and elastic tissues) than bone, it decays more rapidly. As a result, fossils of cartilaginous fishes generally are rare. It is accompoanied by a 93 mm long Knioghtia eocaena in the lower corner, making for a wonderful contrast between one of the most rare and most common fish found in Green River deposits.

About the Green River Formation: There are numerous locations worldwide that are noted for wondrous preservation of bony fishes, and the Green River formation that covers some 25,000 square miles of SW Wyoming, west Colorado and east Utah is one of the premier examples. The formation is one of the largest lacustrine sedimentary accumulations in the world, and spans the period from 40 to 50 million years ago during the Eocene Epoch.

During the Eocene, based on the fossil record, the region was sub-tropical to temperate. Some 60 vertebrate taxa have been described from the formation, including crocodiles, boa constrictors, and birds, as well as abundant invertebrates and plants. The unusually excellent preservation of the Green River fish fossils is usually attributed to a combination of two factors: 1) a cold period during the Eocene that would have caused dead fish to sink faster due to a less inflated swim bladder; and 2) the great depth of the lakes and the consequent anoxic conditions that would have often prevented scavengers from disturbing the carcasses.