Invertebrates Eggs laid by invertebrate animals are known from the fossil record. Among these are eggs laid by ancient
cephalopods. Eggs laid by
ammonoids are the best known cephalopod egg fossils. The best preserved fossil ammonite eggs were preserved in the
Jurassic Kimmeridge Clay of
England. Nevertheless, the
fossil record of cephalopod eggs is scant since their soft, gelatinous eggs decompose quickly and have little chance to fossilize. Another major group of Mesozoic cephalopods, the
belemnoids, have no documented eggs in the fossil record whatsoever, although this may be because scientists have not properly searched for them rather than an actual absence from the fossil record.
Fishes and amphibians Fossil fish eggs have an extensive
record going at least as far back as the
Devonian and spanning into the
Cenozoic era. The eggs of many different fish
taxa have contributed to this record, including
lobe-finned fish,
placoderms, and
sharks. Occasionally eggs are preserved still within the mother's body, or associated with fossil
embryos. Some fossil eggs possibly laid by fish cannot be confidently distinguished from those laid by
amphibians. Several fossilized fish or amphibian eggs have been classified as ichnogenera, including
Mazonova,
Archaeoovulus,
Chimaerotheca,
Fayolia, and
Vetacapsula.
Reptiles The fossil record of reptile eggs goes back at least as far as the
Early Permian. However, since the earliest reptile eggs probably had soft shells with little
preservation potential, reptilian eggs may go back significantly farther than their fossil record. Many ancient reptile groups are known from egg fossils including
crocodilians,
dinosaurs, and turtles. and plesiosaurs are known to have given live birth and are therefore not anticipated to have left behind egg fossils.
Dinosaur eggs are among the most well known kind of fossil reptile eggs. ==Classification==