Sunday, 31 December 2000
About two dozen families of eurypterids “sea scorpions” are known from the fossil record. Although these ancient predators have a superficial similarity, including a defensive needle-like spike or telson at their tail end, they are not true scorpions.
They are an extinct group of arthropods related to spiders, ticks, mites and other extant creepy crawlies.
Eurypterids hunted fish in the muddy bottoms of warm shallow seas before moving on to hunting grounds in fresh and brackish water during the latter part of their reign.
They declined in numbers and diversity until becoming extinct during the Permian–Triassic extinction event (or sometime shortly before) 251.9 million years ago.
As to the oldest and youngest of the order, we can look to the Stylonurina. Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from deposits primarily in Europe and North America, but also in Siberia.
Compared to the suborder, Eurypterina, the stylonurines were comparatively rare and retained their posterior prosomal appendages for walking. Despite their rarity, the stylonurines have the longest temporal range of the two suborders. The suborder contains some of the oldest known eurypterids, such as Brachyopterus, from the Middle Ordovician as well as the youngest known eurypterids, from the Late Permian.
They remained rare throughout the Ordovician and Silurian, though the radiation of the mycteropoids (a group of large sweep-feeding forms) in the Late Devonian and Carboniferous is the last major radiation of the eurypterids before their extinction in the Permian.
Saturday, 30 December 2000
Hoploscaphites nebrescensis is an upper Maastrichtian species and index fossil. It marks the top of ammonite zonation for the Western Interior.
It has been recorded from Fox Hills Formation in North and South Dakota as well as the Pierre Shale in southeastern South Dakota and northeastern Nebraska.
It is unknown from Montana, Wyoming, and Colorado due to the deposition of coeval terrestrial units. It has possibly been recorded in glacial deposits in Saskatchewan and northern North Dakota, but that is hearsay. Outside the Western Interior, this species has been found in Maryland and possibly Texas in the Discoscaphites Conrad zone. Collection of the deeply awesome (and enviable) José Juárez Ruiz.