mesosaur
Concise Oxford English Dictionary © 2008 Oxford University Press:
mesosaur/ˈmɛsəsɔː/
▶noun an extinct small aquatic reptile of the early Permian period, with an elongated body and a long, narrow snout with numerous teeth.
– origin 1950s: mod. L., from Gk mesos ‘middle’ + sauros ‘lizard’.
'mesosaur' also found in these Oxford entries:

