Cambrian Explosion #41: Dinocaridida

Probably evolving from Siberion-like lobopodians, the dinocaridids were an “evolutionary grade” of panarthropods that were closely related to the ancestors of true arthropods. These animals were characterized by specialized front appendages on their heads and large swimming lobes along the sides of their segmented bodies, and their group included some of the most famous of the Cambrian “weird wonders”.

The earliest branches of the dinocaridids were the “gilled lobopodians”, which had lobopodian-like legs on their undersides and gills on the upper surfaces of their body lobes. The flap-like structures may have initially evolved just to provide a larger surface area for respiration, but they were quickly co-opted for swimming purposes and opened up a whole new range of ecological opportunities to the ancestral dinocaridids.

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Weird Heads Month #26: Curious Cambrian Creatures

During the Cambrian explosion, a time full of incredibly weird-looking evolutionary experiments, Opabinia regalis was one of the weirdest of all – so ridiculous, in fact, that when its anatomy was first revealed at a presentation the audience laughed.

Known from the mid-Cambrian Burgess Shale fossil deposits in Canada, this bizarre creature lived around 508 million years ago and had a body measuring just 4-7cm long (~1.5-2.75″).

It had five stalked eyes on its head, and a long flexible proboscis that resembled a vacuum cleaner hose ending in a pincer-like grasping structure. Its mouth was located on the bottom of its head, behind the base of its proboscis, and the opening pointed backwards forming a U-bend in its digestive tract.

The rest of its segmented body had overlapping swimming lobes and a tail fan, and small triangular structures that may have been legs on its underside.

It was probably a bottom-feeding predator or a detritvore, swimming along above the seafloor using its proboscis to snatch up small soft prey or organic material and passing it up to its mouth. 

It also seems to have been a fairly rare member of the Burgess Shale ecosystem, with less than 50 specimens known from the thousands of fossils found there.

For a while Opabinia was thought to represent a completely new phylum, but after further discoveries of similar animals like Anomalocaris it’s now considered to be a “stem-arthropod”, a close evolutionary cousin to modern insects, arachnids, myriapods, and crustaceans. Its exact relationships with other stem-arthropods are still being debated, however, and some studies suggest its closest living relatives may actually be tardigrades.