Cambrian Explosion #54: Trilobita – Transform and Roll Up

Most trilobites were able to roll themselves up into a protective ball – a behavior known as enrollment or volvation – exposing just their heavily armored backs to attackers. They’re often found fossilized curled up like this, and rare preservation of soft tissues shows that they had a complex system of muscles to help them quickly achieve this pose while simultaneously tucking their antennae and all their limbs safely inside their enrolled shells.

Some species also developed sharp defensive spines and spikes that jutted out when they enrolled, making themselves even more daunting to potential predators in one of the earliest known examples of an evolutionary “arms race”.

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Cambrian Explosion #49: …Some Sort Of Euarthropod?

The major groups of the euarthropods are the chelicerates, mandibulates, and the extinct artiopodans, but there were some Cambrian species that still can’t be easily fitted in to any of those lineages.

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Cambrian Explosion Month #05: Phylum Cnidaria – Anthozoa

Cnidarians are a diverse group that includes modern corals, sea anemones, sea pens, jellyfish, hydra, and even some parasitic forms. They’re the closest relatives of bilaterians in the animal evolutionary tree, and their ancestry goes back at least 560 million years into the Ediacaran Period, with the polyp-like Haootia being one of the earliest definite cnidarian fossils – and molecular clock estimates suggest the group might have actually originated much much earlier than that, possibly as much as 740 million years ago.

The anthozoan lineage of cnidarians (corals, anemones, and sea pens) spend their adult lives as polyps attached to the seafloor, either solitary or colonial, and since many lineages have hard calcium carbonate skeletons their fossil record is generally much better than that of the soft-bodied medusozoan jellyfish.

While corals are major contributors to reef ecosystems in modern times, back during the Cambrian they were actually rather rare. The weird little archaeocyathan sponges were the main reef-builders in the early-to-mid Cambrian, and after their decline reefs were mainly formed by algae and other types of sponges.

But, sometimes, growing among these reefs were also some tiny Cambrian corals.

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Spectember #22: Land Dolphins 2 – The Beakening

And so we finish Spectember as we started… with ridiculous land dolphins!

Transcript for the text on the image under the cut:

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Spectember #19: Flightless Bats

(Giant Flightless Bats From The Future are bit of a specevo meme, so of course I had to include some this month.)

Transcript for the text on the image under the cut:

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