#anomalocarids

Several years ago, C.M. Kosemen curated a book called All Your Yesterdays, in which paleoartists from around the Internet contributed their theories and depictions of extinct animal features and behavior that might not have been preserved in the fossil record.  (It’s a free download, for anyone interested.)

John Meszaros contributed to All Your Yesterdays with a speculative animal he called a “cetiocarid” - an anomalocarid relative that used specialized versions of the anomalocarid’s grasping arms to filter-feed plankton like a baleen whale.

In 1892, a fossil much like the one pictured above was discovered in Cambrian-era rocks in Canada by paleontologist Joseph Frederick Whiteaves.  Whiteaves believed he had found the fossilized tail of a crustacean, and named his discovery Anomalocaris - “strange shrimp”.

Later, the disk-shaped fossil pictured above was discovered, and interpreted by its discoverers as a jellyfish-like animal, dubbed Peytoia.  Specimens of Peytoia were often discovered in conjunction with the fossils of large, leaf-shaped objects, but it was assumed that they belonged to two different complete animals, which happened to share an environment and frequently became fossilized together as a result.  The leaf-shaped fossils were dubbed Laggania, and were theorized to have been sponges or echinoderms.

In 1979, paleontologists Derek Briggs and Harry Whittington realized that these animals were so frequently found in conjunction for a reason - they weren’t separate species at all, but body parts of the same animal.  As is paleontological custom, the first name took precedence, and Anomalocaris was revealed.

Anomalocaris was the largest animal of the Cambrian period, growing up to seven feet in length.  It was likely a powerful swimmer, using its twin rows of paddle-like lobes ("Laggania”) to hover through the water like a modern cuttlefish.  It swept up prey in its twin facial “arms” (the original Anomalocaris fossils), and crunched through their exoskeletons with its circular mouth (”Peytoia”).  It likely fed primarily on trilobites, as many fossil trilobites are preserve with round “bite marks” on their sides.

Truly the T. rex of the Cambrian, Anomalocaris has risen from relative obscurity following the revelation of its confusing anatomy, and has become one of the most well-known and popular Cambrian animals.  However, it wasn’t unique; it belongs to an entire family of strange shrimp, and many other Cambrian animals are likely their close relatives.

The name “Peytoia” was eventually given to another anomalocarid - this one much smaller than Anomalocaris, and likely a potential prey animal for its bigger, meaner relative.  Based on its softer mouth and paddle-lined facial arms, Peytoia was likely adapted to sweep up seafloor sediment and filter out food particles.

Amplectobelua, a Chinese species, had specialized prongs on its facial arms that formed almost pincer-like structures.  Some paleontologists theorize that it could use them to grab and hold prey.

Hurdia possessed a large, hollow structure on its head of uncertain purpose, and used a powerful swimming tail to move around, lacking any paddle-lobes.  Several other species of recently discovered anomalocarid, Aegirocassis and Stanleycaris, possess similar anatomies, possibly forming a sister group to “true” anomalocarids.

Tamisiocaris was adapted to filter-feed in a manner similar to a baleen whale, with massive fronds growing from its facial arms that could sweep up plankton and other microscopic prey.

Some relatives of the anomalocarids appear to possess walking legs, which hints at a close relationship between the anomalocarids and the ancestors of modern arthropods.  One such animal is Pambdelurion, a many-legged wormlike animal whose fuzzy facial arms were likely used for silt-filtering.  Another, Kerygmachela, was a blind creature that used its massively distended facial limbs to navigate by touch.

Opabinia might be a relative of the anomalocarids, but nobody really knows, because Opabinia is the weirdest animal in the history of the damn world.

Most shocking of all is Schinderhannes, an anomalocarid from the Devonian - some 100 million years after every other known species.  Its anatomy is much more streamlined, and raises even more questions as to the ancestry of modern arthropods.