The Earth Story

The biggest arthropod ever This phylum is a large one, including a wide diversity of creatures from crabs and spiders to insects, all based on the idea of a chitinous carapace and lots of wiggly legs. They have been around since the Cambrian, diversifying ever since. The Eurypterids (aka sea scorpions, from the Greek for wide wing) were an order of extinct ancestors of arachnids, and some of them were the biggest predatory bugs ever, reaching up to 2.5 metres long. They appeared in the Ordovician and thrived in warm shallow seas and lakes right up until the great dying at the end Permian mass extinction (460-248 million years back). They have been found on all the continents.

For #fossilfriday, meet the Fezouata Biota In 2010, a paper on the Fezouata formation in the Anti-Atlas Mountains of southeastern Morocco described the unit as a possible Lagerstätte – a location of exceptional fossil preservation including remnants of the soft parts of organisms. These are some of the discoveries in that unit.

A Final Journey Set In Stone

Something unfortunate happened to a horseshoe crab some 150 million years ago. A harsh storm washed it into a toxic lagoon, where it scrambled around and eventually died. What it left behind was remarkable - a perfectly fossilized story of its final, brief journey, capturing the longest, complete death track ever found.

The horseshoe crab, Mesolimulus walchi, was discovered in Solnhofen, Germany, along with many other beautifully fossilized animals. The soft carbonate mud preserved insects, sea jellies, and dinosaurs with great detail. M. walchi was likely a juvenile at the time of its death, measuring 12.7cm long by 6.9cm wide. The toxic lagoon that it was dropped into was highly salty and anoxic (no oxygen).

According to Dean Lomax of the Doncaster Museum & Art Gallery in the U.K. and Christopher Racay of the Wyoming Dinosaur Center, the disturbed surface at the beginning of its trail shows that the horseshoe crab sank to the bottom of the lagoon on its back and struggled to turn upright. It then began its mortichnia, meaning death track or last walk, meandering and making a few turns before becoming distressed. It then began to asphyxiate, leaving behind less uniform, deeper and more erratic imprints as it tried to escape. At the end of the 9.7 meter fossilized trail we find the complete specimen of the crab.

Lomax and Racay dismiss the hypothesis that it was dropped in the lagoon by a flying predator, such as a pterosaur, due to the lack of any predation marks. Lomax writes in the journal Ichnos, “Trackways and trace makers preserved together in the fossil record are rare and such specimens allow unique insights into behavior and ecology.” So our little arthropod friend did not die in vain: its story was set in stone and survived millions of years as one of the most amazing specimens of its kind.

~ SW

For more info: http://www.sci-news.com/paleontology/article00554.html (Original paywalled article) http://www.tandfonline.com/doi/abs/10.1080/10420940.2012.702704#preview

Photo credit: Ghedoghedo http://bit.ly/1udDEqt

·      bat_gal_bribriSo fast, I couldn't keep up. Jumping spiders are almost always on the move, actively hunting bugs rather than passively waiting at a web. These guys won't bite, unless they feel trapped. Even then, the bite is harmless. 🕷🕷🕷🕷🕷🕷 I love having these spiders around the house to rid my space from unwanted bugs. They're curious critters, so they may check you out, but will leave you alone. I once had one come up the side of the bed to watch me. When I had enough of its curiosity, I shooed it back down the bed, no harm to me or it.

Fossil crab