Despite marine invertebrate extinctions at the turn of the Triassic and still more turmoil in the Jurassic, mollusks and other groups had recovered and diversified by the Middle Jurassic. Many modern marine invertebrates—including scallops, oysters, and other bivalves burrowing in seabeds—evolved at this time. Although they’d faced near-elimination in the end-Permian mass extinction, crinoids, sea urchins, sea stars, and other echinoderms now proliferated. Further evolutionary “experimentation” occurred among crustaceans and cephalopods. This mural shows a floating community of crimson crinoids suspended from a log covered with bivalves, surrounded by darting squid and ammonites.

The squidlike Acanthoteuthis speciosa sported an ink sac and 10 tentacles with tiny hooks. Its relatives, the belemnites, had bullet-shaped shell ends, now commonly found as fossils.

Whether large or small, like those of Promicroceras planicosta, ammonoid shells contained gas-filled chambers for flotation.

Horseshoe crabs—little changed since their first appearance in the fossil record—still have shield-shaped carapaces. This Jurassic species is Mesolimulus walchi.

A well-preserved prawn, Aeger armatus, lies in limestone formed in an ancient lagoon.