Pterotheca attenuata

Pterotheca attenuata Temporal range: Early Ordovician – Late Ordovician,
Pterotheca attenuata from the Milwaukee Public Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Subphylum:	Conchifera
Class:	Monoplacophora Odhner, 1940
Binomial name
Pterotheca attenuata (Ulrich, 1895)

Pterotheca attenuata is a fossil from the Ordovician upper Midwestern United States. It has been variously classified as a monoplacophoran, bellerophont, or some other gastropod. It lived in shallow marine waters and is a part of the Decorah Shale and Platteville Limestone fossil communities. It is often misclassified in museum collections because of its unusual morphology and therefore documentation of its range and abundance is poor.

Preservation and morphology

File:Pterotheca attenuata painting.jpg

Pterotheca attenuata life restoration

The shell is composed of two slightly concave sub-triangular layers that connect along the anterior most side. The dorsal layer has a ridge that extends perpendicularly from the rest of shell along the median plane. The underside of the ventral most layer is effaced and smooth, but the top of the ventral layer and the bottom of the dorsal layer both show a slight medial ridge.

P. attenuata is most often preserved in fine grained sedimentary rock like shale and limestone, but its range likely extends outside of these facies. The shell is often found broken and the two layers separated. P. attenuata's unusual shape and the fragmentary nature of many of its fossils are both causes of its frequent misclassification.