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FOSSIL STINGRAYS FROM GREEN RIVER FORMATION FOR SALE
What Are The Stingrays?
Myliobatiformes is the order that includes all true stingrays, of which there are about 185 living species with global distribution. The Myliobatiformes are notable for their disc shapes and long whiptails. They swim with a grace that is reminiscent of underwater gliding. Their tails, contain one or two lengths that are barbed and may be serrated or venomous, known as stingers. Most stingray fossils preserve teeth plates, barbs, and scutes. That being said, there are two localities that produce complete, articulated stingray fossils: Monte Bolca in Italy, which contains fossils from the Tethys Sea, and the Fossil Butte Member of the Green River Formation of Wyoming. Both formations are dated to the Eocene, between 55 and 43 million years ago.
A modern-day stingray, which probably looked pretty similar to the Green River Formation rays.
Stingrays had and currently maintain a near global range, excluding Antarctica and Northern Europe. One thing they all have in common is that they live in shallow water at the very bottom, skimming, burrowing, or scrounging in the substrate. Of the near 200 living species of stingrays, all but a select family inhabit marine or brackish habitats. One family inhabits rivers in South America, as well as a relative that calls southeast Asian rivers home. But no living freshwater stingrays inhabit lakes. This absence of lake-dwelling stingrays and the lack of phylogenetic evidence have led paleontologists to conclude that the Green River Formation stingrays are the last of their families and are believed to have no living relatives.
Like sharks, stingrays have no bones, so placing a definitive date on the rise of stingrays is rather difficult. Conservative efforts place the modern stingray lineage 60 million years ago in the late Paleocene. That being said, there are remnants from a common shark/stingray ancestor that date to the Lower Jurassic, 200 million years ago. Most of the clues we have into the lifestyles of prehistoric rays come from the astoundingly well-preserved fossils from the Green River Formation. The Green River Formation (freshwater lake, early to middle Eocene) and Monte Bolca (isolated lagoon, early Eocene) stingrays are excellent examples of the specialization of the order since their estimated emergence 5 -10 million years prior in the Paleocene.
The majority of stingray fossils are found in the nearshore beds of the Green River Formation. This finding is to be expected for two reasons. The first is that it is congruent with the habits of modern rays, and the second is that the bottom of the lake at mid-depths was anoxic and inhospitable to bottom-dwelling species.
Stingrays from Monte Bolca lived in a very different environment than those in the Green River Formation. Monte Bolca in the Eocene was a warm, shallow lagoon that was protected from the rest of the Tethys sea by a large coral reef. The diversity of life within the Tethys Sea is quite distinct from a freshwater lake.
What Did The Stingrays Eat, And What Ate Them?
Spending most of their time hunkered down in the sand and silt at the bottom of the water they inhabit has distinct advantages for getting a specific range of crunchy foods. When living on the bottom, you eat other things that live on the bottom, like shrimp, crayfish, and bivalves. Eocene rays, like modern rays, have crushing plates for teeth that help them crunch through and grind up the rigid exoskeletons and shells of their food sources.
Identifying Features
Eocene stingrays look very similar to modern stingrays; a flat, disc-like body; eyes on the top of the head; and a long, tapering stinger. Both of the stingray species coming out of the Green River Formation follow this same basic body plan, though there are a couple of minor differences that are worth noting. The more common of these stingrays is H. radians, which was more petite than Asterotrygon and had a longer, more flexible stinger. Heliobatis fossils are typically found with the stinger bent at fairly extreme angles with multiple kinks. These rays have been found between 3 and 36 inches long, and average about 16 inches.
Fossil Stingray (Heliobatis) From Warfield Quarry near Kemmerer, Wyoming.
The team that discovered A. maloneyi accurately dubbed it the Eocene Fat-tailed stingray for a glaringly obvious reason–-it had a fat tail. The stinger is shorter and significantly thicker at the base than that of Heliobatis rays. In addition to being shorter and fatter, Asterotrygon stingers were also covered in overlapping hooked scutes. Outside of these differences, the two Green River Formation rays are visually very similar. However, Asterotrygon is estimated to be somewhere around 40 times rarer than Heliobatis, so if encountering a ray from this location you are likely looking at an individual from the genus Heliobatis.
Reproduction
Much can be inferred about the growth stages of the Eocene rays of the Green River Formation because of the clarity of detail in their fossils. There is a good record of stingrays from this location found with embryos in their abdomens and ejected fetuses near their mothers. These instances lead paleontologists to posit that the Green River Formation rays gave live birth.