Casineria was a tetrapod which lived 340 million years ago in the Mississippian period. Casineria was very small (15 centimeters long), but its skeleton was more advanced than the primitive tetrapods, and it was more closely related to amniotes than to amphibians. Casineria may have been one of the very first true amniotes, a group which consists of synapsids and sauropsids, and it pushes back the origin of amniote lineages much farther than was previously realized. Casineria, phylogenetically, is placed by paleontologists as a basal ("primitive") member of the group Amniota, though it may lie just outside the group, as a basal member of Amniota sensu lato. Like most primitive amniotes, this creature was an insectivore, and it may have laid eggs on land. This earliest amniote had five fingers on each hand.

Discovery

In 1992, an amateur fossil collector spotted the remnants of this four-legged creature on the shore of Cheese Bay, Scotland. For the next five years, work on the fossil languished at the National Museums of Scotland in Edinburgh while researchers focused on other projects. Around 1997, work began to expose the remanider of the fossil from the surrounding matrix. the work revealed that the animal probably lived in an environment much drier than previously understood. The findings were first reported in the April 8, 1999 edition of Nature.

In the early Carboniferous period before the appearance of Casineria, vertebrates were aquatic. Casineria and its relatives were the first vertebrates to live and reproduce on land.

Notes

References

• Richard Monastersky, "Out of the Swamps: How early vertebrates established a foothold—with all 10 toes—on land", The Weekly Newsmagazine of Science, Volume 155, Number 21 (May 22, 1999)