Take a look at what you can find in a pay-to-dig site near Delta, Utah.
Wheeler shale in the House Range of Western Utah is one of the best places to hunt for trilobites in North America. Fortunately, the place has a commercial quarry near a little town called Delta and today we will present a bunch of trilobites discovered there by our fellow fossil hunters: Mike and his family, who graciously offered us their finds for filming. Let's start with this wonderful example of a trilobite resembling those from the genus Asaphiscus. The trilobite is large, almost 2 inches long, and the preservation is remarkable. 500 million years have passed, but the fossil looks like the animal that just crawled out of the mud. The Wheeler shale was described by a scientist with the last name Meek in 1870. He also discovered and named a bunch of local trilobite species based on the specimens collected by expeditions carried out as part of US Geographical and Geological surveys in 1860s and early 1870s. When you touch the dark-gray rock, it feels like a soap bar - very soft and smooth without any polishing whatsoever.
Another rock has trilobites of 2 different species, Asaphiscus wheeleri and Elrathia kingi. Asaphiscus has massive pygidium with many segments fused together at the rear end.
Sometimes, you can find a primitive trilobites, like Olenellus, that do not have pygidium (a rear part of trilobite body) with fused plates. Another sign of early trilobites is the absence of rupture lines to separate cheeks from the cephalon during the molting. The line is called cranial suture and clearly present in Elrathia species to the point that many Elrathia exoskeletons simply lack “cheeks”. These cheeks are called librigena, while the frontal part, which usually stays attached to the rest of the exoskeleton, is called fixigena. Almost all fossilized trilobites are molted exoskeletons, as you probably already know. The chemical composition of the trilobite exoskeletons, by the way, is indicative of changes in ocean chemistry when calcium phosphate-based shells were slowly giving a way to shells built from calcium carbonate. At the time of the trilobite appearance in Early Cambrian period, the concentration of oxygen in the marine environment started to reach levels that enable the formation of calcite crystals. Remember, the calcite is calcium salt containing 3 atoms of oxygen and one atom of carbon. Thanks to relentless cyanobacteria generating oxygen in the process of photosynthesis during billions of years, the oxygen-based chemistry was starting to play out. In the case of trilobites, it was all about calcite. Shrimp and crabs build their exoskeletons from a protein called chitin. Trilobites combined chitin with calcite, which made their armor harder and more prone to fossilization. This is why trilobites are over- represented in the fossil records while other more soft-bodied animals are rare. Moreover, trilobites, as borrowing and actively moving animals, were disrupting the ecology of the sea beds, which previously were dominated by microbial mats. Trilobites and other burrowing Cambrian creatures destroyed the mats thereby causing extinction of the species that depended on them. The deposits comprising the Wheeler shale were formed in the Cambrian period along the shores of the continent called Laurentia. A significant chunk of that ancient continent is now North America, although at that time it was closer to equator. Shallow-water reefs developed near the shores of Laurentia but Wheeler shale was formed from sediments accumulating beyond the reefs in deeper waters. They often contain material delivered to the ocean depths during periodic massive landslides, possibly by storms as well. The remains of the animals that were quickly buried under very fine sediment sometimes had a good chance to be preserved as fossils with very fine details, allowing scientists to have a glimpse to a prehistoric life long gone. So, if you are to visit the locality, watch out because you can potentially find such rarities as soft-bodied creatures, for instance Hallucigenia, Naraoia or Wiwaxia.
Common fossils in this location are very tiny, eyeless trilobites, which you would easily recognize. This is a perfect example of such a trilobite belonging to genus Itagnostus and until recently known as Peronopsis. These trilobites were only a few millimeters long and had a tail segment approximately the same size as the head segment (cephalon). Instead of rolling they folded in half and, perhaps, this type of movement helped them to get around and possibly escape from predators. One can assume that they were swimming most of the time and catching minute particles of food before they reached the sea bottom. Good luck in fossil hunting, stay curious and see you next time.
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Негізгі бет Үй жануарлары мен аңдар Trilobites of Wheeler Shale
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