Wooster’s Fossil of the Week: a siliquariid gastropod (Eocene of Alabama)

December 25th, 2011

It is hard to believe that this twisty tube is a snail, but it is. Tenagodus vitis (Conrad, 1835) is the scientific name for this worm-like gastropod from the Claiborne Sand (Eocene) of Alabama. It was originally named by Conrad as Siliquaria vitis, a name still commonly used even though it was made a junior synonym by CoBabe and Allmon (1994).

This kind of gastropod with its awkward shell clearly didn’t crawl around. It was a sessile benthic epifaunal filter-feeder, meaning that it lived stationary on the seafloor filtering organic material from the water. Some of these sessile snails twisted their tubes around each other and formed a kind of gastropod reef.
The twisty part of Tenagodus vitis shows its true snaily nature.
The related Siliquaria anguina. (From Cooke et al., 1895, Cambridge Natural History, volume 3, Fig. 153.)
The discoverer of Tenagodus vitis was Timothy Abbott Conrad (1803-1877). He was a conchologist (one who studies shells) and paleontologist in New York and New Jersey, and he was a paleontological consultant during the early days of the Smithsonian Institution.

References:

CoBabe E.A. and Allmon, W.D. 1994. Effects of sampling on paleoecologic and taphonomic analyses in high-diversity fossil accumulations: an example from the Eocene Gosport Sand, Alabama. Lethaia 27: 167-178.

Conrad, T.A. 1835. Fossil shells of the Tertiary formations of North America, illustrated by figures drawn on stone by T.A.Conrad. vol. 1, no. 3, p. 29-56, pl. 15-18 (pp. 77-110, pl. 15-18 in 1893 reprint by G.D. Harris [with pl. 19-20 not included in original by Conrad], reprinted 1963 by the Paleontological Research Institution, Ithaca, NY).

Wooster’s Fossils of the Week: Nummulitid foraminiferans (Eocene of the United Arab Emirates)

July 3rd, 2011

The Great Pyramids of Egypt are made primarily of a yellowish limestone. About 40% of that limestone is made of the fossil type pictured above. These are foraminiferans (single-celled organisms with shells) that lived by the countless billions during the Eocene (56 to 34 million years ago) in the Tethys Ocean. They are called Nummulites from the Latin nummulus, which means “little coin”. They have the honor of having been first described by the 5th Century BCE Greek historian Herodotus, who noticed them in the Pyramid stones. (He thought, by the way, that they were fossilized lentils.)

(From R.A. Lydekker (1894), Life and Rocks.)

If you slice a nummulitid test (what we call a foraminiferan shell) like a bagel, the inside is revealed to be a long spiral. The single-celled organism built the shell by progressively adding to this spiral, making the largest foraminiferan tests ever known, some over 15 cm in diameter. (Most foraminiferans have tests about the size of a pinhead.)

I collected our Wooster Nummulites during fieldwork with my colleague Paul Taylor near Al Ain in the United Arab Emirates. I thought at the time that I was picking up two species: a small one and a significantly larger one. I later learned that these are two versions of the same species. Nummulites reproduced alternately sexually and then asexually. This alternation of generations is seen today in many living foraminiferans, and we see an analogue in some plants like ferns.

Nummulitids are the stars of a strange story in paleontology. A British zoologist who was at the time assistant keeper of invertebrates at the British Museum (Natural History) wrote a book (The Nummulosphere, 1912) and a series of papers with the astonishing thesis that all rocks were actually made of foraminiferan tests — all rocks! Even basalt, granite and meteorites are organic in origin. The late Stephen Jay Gould told the tale of Randolph Kirkpatrick (1863-1950) memorably in his compilation of essays The Panda’s Thumb (Norton, 1980). Kirkpatrick’s work is well worth reading for his incredible arguments. (Lava, for example, is melted “siliceous nummulitic rock” recycled back to the surface.) The tortured logic to show the remains of Nummulites tests in igneous rocks is oddly entertaining.

“Fig. A [Plate XXI]. Section of rotten trachyte [a volcanic rock] permeated with sulphur from interior of upper crater of Tenerife, x 4.5. The coils of a much-blasted nummulite in perpendicular section are visible to the trained vision.”

 

The Messel Fossil Pit: A world-class experience

August 13th, 2010

FRANKFURT, GERMANY–Last year at this time I had the privilege of visiting the Middle Cambrian Burgess Shale on an expedition led by my friend Matthew James of Sonoma State University in California. It was an extraordinary opportunity to visit one of the most important fossil sites in history. Today our IBA field trip had a tour of another UN World Heritage fossil locality: the Messel Pit near Darmstadt, Germany. These Eocene oil shales were formed under very unusual conditions. They are maar deposits formed in a volcanic crater. Catastrophic releases of poisonous gases, the hypothesis goes, occasionally killed the surrounding fauna, causing many to tumble into the anoxic lake to be preserved in amazing detail. This is the home of Ida (Darwinius masillae), the controversial primate fossil now in Oslo (which I also saw last summer).

Our field party was taken down into the center of the maar to an excavation site run by the Senckenberg Museum in Frankfurt. There we watched a team of paleontologists excavate blocks of the shale and examine them for fossils.

Paleontologists extracting large blocks of Messel oil shale to examine for fossils.

Close-up of the Messel Shale. It contains about 40% water in outcrop, and so dries quickly in the sun. Fossils must be kept wet until preserved by various chemicals.

One of the paleontologists splitting Messel Shale with a large knife. The waste pile of examined pieces is behind her. Note the spray bottle of water beside her chair. The fossils must be kept from drying out until they are preserved.

Bits of an Eocene bird found in the Messel Shale while we were visiting.

An artesian well in the center of the Messel structure made when geologists drilled over 400 meters into the shales below. Yes, the tradition is to drink a glass of the water! (And I did.)

An outcrop of the Messel Oil Shale near the eastern side of the pit.

With this memorable paleontological experience our International Bryozoology Association field trip ended. I am grateful to Priska Schäfer of Kiel University for the fantastic (and complicated) organization and leadership. My teaching and research has been greatly enhanced, and I made wonderful new friends as well.

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