A Late Cretaceous Turritella

WELCOME TO MY FIRST POST.

The reason for creating this first series of posts is to demonstrate one of the major uses of fossils: "to tell time." The following pictures show common fossil gastropods (snail seashells) belonging to genus Turritella that you might find on hikes in the mountains or to beach cliffs in the southern California area. Turritella is a group of species that look similar. Although there are many fossil species of Turritella in southern California, I selected eight common ones. The youngest species is still living but also has a fossil record.

The time interval in which each species lived will be shown on its accompanying time diagram. These eight species collectively span an interval of about 75 million years (from Late Cretaceous to Holocene). The Holocene includes recent time.

Fossil species are called "morpho-species" because they are determined solely by differences in morphology (size, shape, sculptural details). By studying the pictures, you will see that they are different from each other in the following possible ways (see labeled picture below): shell narrowness, number of spiral ribs (cords) on each whorl (one 360° turn), how strong the ribs are relative to each other, and whether or not nodes are present on any of the ribs. It is amazing to me how many variations of differences occur in just these few morphologic characteristics.

height 53.5 m

 Turritella chicoensis pescaderoensis Arnold, 1908

AGE RANGE: Late Cretaceous (late Campanian = about 75 million years ago).

GEOGRAPHIC RANGE: Northern California to northern Baja California, Mexico.

REMARKS: This species is abundant in the Santa Ana Mountains, Orange County, and in the Simi Hills, Ventura County.

In this and my subsequent posts, you will see that the genus and species names are always italicized (follows international protocol); also, the first letter of the genus name is always capitalized, but the
first letter of the species name is always lowercase.

The author who named the species and the year in which is was named should be included in the name of a species. The genus name can be abbreviated to just one letter (as in T. chicoensis pescaderoensis), if it is clear as to what the "T." means to the reader.


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