Biota - Lifeforms

A wide variety of vertebrates swam in the Jurassic sea. Cartilaginous and bony fish were abundant, while large fish and marine reptiles were also common. Large fish and marine reptiles were also common; the largest bony ichthyosaurs and Jurassic pliosaurs are among the largest carnivorous reptiles ever discovered.

Mollusks dominated marine ecosystems, both as water column swimmers and seafloor dwellers. The detailed suture lines on ammonite shells make them easily identifiable, and their abundance and rapid evolution make them useful as indicator fossils for rock correlation and sequence maps. Ammonites are therefore an important tool for breaking the Jurassic into finer time intervals and developing relative time scales.

Large marine reptiles were abundant in Jurassic seas. Pisiform ichthyosaurs had an intelligent body shape similar to modern fast-swimming fish, large eye sockets and were probably the largest of vertebrates.

Insects are the most abundant terrestrial invertebrates in Jurassic fossils. The discovery of honeybees in the Jurassic also suggests that angiosperms were present early on or that honeybees initially adapted to other strategies.

According to their skeletal characteristics, dinosaurs can be divided into two groups: saurischians, related to lizards, and ornithischians, related to birds. The pubic bone of saurischians was anteriorly oriented, while the pubic bone of ornithischians was a posteriorly oriented appendage.

Other reptiles, including turtles, were present throughout the Jurassic, and modern lizard forms appeared in the Late Jurassic. The number of amphibians present during the Triassic declined dramatically during the Jurassic, and more modern forms evolved, including the first frogs with the skeleton we see today.