Fossil Basket Clam (Eocene)
Corbula (Anapteris) regalis Palmer & Harris, 1919
Family Corbulidae (Basket Clams)
In March 1919, Katherine van Winkle Palmer wrote that after a lapse of 20 years, she was returning to a study of eastern American Tertiary fossils. In so doing, she found “accumulated in our laboratory several little lots of fossils, odds and ends, so to speak, that will scarcely fit into the general systematics studies here being undertaken, for some time to come.” So she and coauthor Gilbert Harris [these two would become the first two directors of PRI in subsequent years] described them.
The species: This is Corbula (Anapteris) regalis Palmer & Harris, 1919, a member of the bivalve family Corbulidae, whose members also survive today. It is a syntype (one of several original specimens from which the species was described), originally part of the Cornell University paleontology collection. A figure of another specimen, viewed from the interior, shows the most important characteristic of this species, and of its subgenus Anapteris, which was also described as new in this monograph. This feature is a wing or flare on the anterior dorsal part of the shell (missing at the upper left corner of the specimen in the photograph). This and other sculptural features are usually stabilizing mechanisms in bivalves, allowing the clam to secure itself more firmly within the sand. This is a small specimen, only 17 millimeters (slightly more than one-half inch) long in the photograph. This is the left valve of the bivalve, which at the time of description was the only valve known. Corbulids are “inequivalve,” that is one valve is larger than the other, and often differently sculptured — this left valve was the smaller of the two valves.
The collection: Corbula regalis is from the St. Maurice Horizon of the Eocene Epoch, 40-50 million years old. It was collected from Newcastle or Piping Tree, near Mechanicsville, Virginia, during the first Ianthina Expedition in 1897. This expedition was apparently one of several annual geological expeditions undertaken from the private launch Ianthina (named after a pelagic snail) by Cornell University.
Evolution on the Half Shell...
The Assembling the Tree of Life: Bivalvia project (BivAToL) is a part of the Assembling the Tree of Life initiative, a large research effort sponsored by the National Science Foundation. Its goal is to reconstruct the evolutionary origins of all living things.
Jetsam & Flotsam
Some of the BivATOL team met in early May at the Mote Marine Laboratory’s Tropical Research Station at Summerland Key, FL for a combined collecting trip and coding workshop. Both activities are essential to our project’s goal of determining the phylogenetic relationships among the bivalve families.
After collection, many of the species’ visible and molecular characteristics must be compared and “coded,” after which the phylogenetic computer analyses will be run to produce the final “tree” from which a hypothesis of relationships can be made. Below is an example of a portion of such a phylogenetic tree. Families that are on nearby branches are more closely related to each other than those further away.