An unusual Turritella gastropod about 50 million years old from the west coast of the United States

Turritella gastropods are very common shallow-marine fossils. Their geologic time range is from the Cretaceous to modern-day. Their shells are long and narrow, with spiral sculpture (ribs), although some species can have small nodes on the spirals.

During my years as a paleontologist, I have collected many Turritella. One of my favorite subspecies is Turritella meganosensis protumescens (approximately 51 million years old = early Eocene), because it is very unusual in having, at least on the adult part of the shell, only one very thick, spiral rib.

Turritella meganosensis protumescens Merriam and Turner, 1937,

Ventura Co., southern California;

 height of largest specimen 2 1/4 in. (57 mm)

This subspecies of turritellid gastropod has been found in only a few places, and most are in California (two areas in Ventura County and one in Riverside County). It has also been found, however, in southwestern Oregon.

Specimens of this gastropod are associated commonly with coarse-grained sediments (including pebbles), which were deposited in nearshore, high-energy ancient environments. Apparently, the thick shell of T. m. protumescens with its wide spiral rib on the upper part of each whorl was well adapted for these turbulent waters.

Turritella meganosensis protumescens Merriam and Turner, 1937,

Ventura County, southern California;

 height of specimen 2.5 in. (62 mm).

The specimen shown immediately above is the largest specimen I have collected of this turritellid. The early part of its shell is weathered, and, therefore, does not show the spiral ribs that are normally present there.