Rising sea levels flooded
many of the continental interiors during the Jurassic, creating warm,
shallow-water environments where marine animals and plants could thrive.
These regions saw an increase in diversity of microscopic phytoplankton
such as coccolithophores, dinoflagellates,
and foraminiferans. Reef ecosystems
continued to flourish, thanks to many species of corals
and sponges. Among these sessile (stationary) organisms
lived gastropods (snails), along with the now-rarer
crinoids. In the waters
above swam predatory cephalopods such as ammonoids
and belemnites. Sharks and
bony fishes remained common and shared the seas with
plesiosaurs, and other marine reptiles. The first
true marine crocodiles had appeared, alongside the
first true teleost fishes (which today are the most
diverse vertebrates on Earth).
Fresh-water environments were home to many invertebrates, amphibians,
turtles, and crocodilians, as in the Triassic. On land, herbivorous
insects diversified, and we see the first examples
of many modern forms such as leaf hoppers, snakeflies, and wasps.
One extinct group, the Kalligrammatidae, a group related
to lacewings, possessed large, conspicuous wings with big “eyespots.”
These insects, with their fluid-feeding mouthparts, probably were
ecologic analogs to modern butterflies. Beetles—the
most diverse group of organisms on Earth today—began their diversification
during the Jurassic as well. Some modern groups of beetles had evolved
by this time and fed on conifers, cycads, and ferns just as their
descendents do today. Flies, beetles and caddisflies diversified in
aquatic habitats, feeding in a variety of ways including filtering,
collecting and shredding detritus, eating living plants, and preying
on other aquatic organisms.
Sphenodontians and the first lizards
may have preyed upon many kinds of adult and larval insects. All these
animals lived in terrestrial environments with abundant gymnosperm
trees, but flowering plants were still absent. The understory plants
included ferns, horsetails, and
but grasses (a type of flowering plant), had not yet evolved.