Polymorphitidae is a family of Early Jurassic

ammonoid Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefi ...

cephalopods that contribute to the Eoderoceratoidea. Two subfamilies, the Polymorphtinae and Tropidoceratinae, are included. Polymorphitid

ammonites Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttle ...

produced typically evolute shells, which are more compressed than in most members of the superfamily. Many possess ventral chevrons and/or a fastigate venter resembling a gable roof, which in some develops into a true keel on the outer whorls. The Polymorphtinae is the larger and more diverse subfamily of the two. their shells have venters (outer rims) that may be smooth or ribbed, or have a median row of beading or serrations. The Tropidoceratinae, referred to as the Acanthopleuroceratinae in the

Treatise A treatise is a formal and systematic written discourse on some subject, generally longer and treating it in greater depth than an essay, and more concerned with investigating or exposing the principles of the subject and its conclusions." Treat ...

L 1957, instead have a venter with a keel.

References

* W. Arkell ''et al.'', 1957. Mesozoic Ammonoidea, ''Treatise on Invertebrate Paleontology, Part L''. Geological Society of America and University of Kansas Press.
family Polymorphitidae
Eoderoceratoidea Ammonitida families Early Jurassic first appearances Early Jurassic extinctions {{ammonitina-stub