Category Archives: Fossils

Underwater: fossils, drowned history, pipelines.

Fossils appear, blinking in the sun, uncovered by the annual winter draw-down of water in Percy Priest Lake in middle Tennessee. These fossils were creatures of shallow tropical seas, out of place now, stranded on a cold shore next to oaks and cedar trees.

Actinoceras. A mollusc that swam in the open water. Its shape is like an uncoiled Nautilus.

Actinoceras. A mollusc that swam in the open water. Its shape is like an uncoiled Nautilus.

A honeycomb coral (Favosites). The coral animals lived inside closely packed columns of calcium carbonate. Like modern corals, these were reef-building animals.

A honeycomb coral (Favosites?). The coral animals lived inside closely packed columns of calcium carbonate. Like modern corals, these were reef-building animals.

This stack is, I think, the remains of a stromatolite, a layered community of bacteria and bacteria-like cells.

This stack is, I think, the remains of a stromatolite, a layered community of bacteria and bacteria-like cells.

The presence of these species in a decidedly untropical locale hints at the back-story. The waaaay-back-story. A pink bull’s eye sits in the middle of the geologic map of Tennessee. Unfortunately the rocks don’t conform to the geologists’ color codings. Cream or gray limestone is wan in comparison. These rocks date from the Ordovician, ~450 million years old, deposited when what is now Tennessee sat closer to the equator, a bathwater sea under a tropical sun. The good times couldn’t last, though. As more sediment arrived and the Earth’s drunken crust staggered northward, the Ordovician deposits got buried.

But burial was not forever. A cross-section reveals the peculiar history of this area. The pink, Ordovician rocks are older than those that ring them and were pushed to the surface by the upward poke of the Earth goddess into the crust, a gesture powered by the collision of continental plates. Because the Ordovician rocks are made from highly erodible limestone, the center of this dome wore away and now sits lower than its surroundings. A dome turned into a bowl. Hence the improved gas mileage as you drive into central Tennessee and the labored engine when you depart.

Reefs are not the only remnants of life hidden under the lake’s waters. People forced by the US government onto the Trail of Tears (1838-1839) came through the old town of Jefferson. Then, in the 1960s, when the Army Corps of Engineers built the dam and filled the lake, they drowned roads, fields, and communities. As one former resident of old Jefferson recalled, the area “was the center of business for this end of the county. There wasn’t no Smyrna then.”

The Cherokees were forcibly bent to the will of the government. The Tennessee landowners in the path of the lake had no choice. History now repeats itself: today the Corps announced its intention to impose the desires of Andrew Jackson’s replacement on the Standing Rock Sioux Tribe, to forego environmental review, and waive its own policies. Soon, liquid fossils will flow through the pipeline. Expect water levels to rise.

 

 

 

 

 

Florissant fossils

One of the many pleasures of my visit to Yale last month was a visit to the collections of the Yale Peabody Museum. Among its treasures, the museum holds many of the fossils that were collected in the early 1900s from Florissant, Colorado.

The Florissant site is famous for its beautifully preserved plant and insect fossils, remains of the flora and fauna of the late Eocene, about 34 million years ago. In those good ol’ days, the climate was warmer and wetter, so a rich temperate forest grew in what is now a mix of dry, open grassland and ponderosa pine (replete with modern mammals, as I learned during my visit to the site last summer).

Most of the fossils are preserved in the finely laminate shale. Some of these laminae represent one year’s deposition: a layer of diatoms from the summer, overlain with ashy clay in the winter. These are interspersed with coarser material from rivers and landslides.

Division of Paleobotany, YPM 30074. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.

Division of Paleobotany, YPM 30074. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved. The whole section depicted here is about 5 mm deep.

Many of the animals from the Florissant fossil beds look familiar to us, an indication of the continuity of taxa and their ecological roles across tens of millions of years.

Tethneus twenhofeli (orb-weaving spider). Collected by W. H. Twenhofel, date unknown. Described by A. Petrunkevitch, 1922. (Division of Invertebrate Paleontology, YPM 25588. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.)

Tethneus twenhofeli (orb-weaving spider). Collected by W. H. Twenhofel, date unknown. Described by A. Petrunkevitch, 1922. (Division of Invertebrate Paleontology, YPM 25588. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.)

Cranefly. Collected by J. T. Gregory, 1953. (Division of Invertebrate Paleontology, YPM 50208. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.)

Cranefly. Collected by J. T. Gregory, 1953. (Division of Invertebrate Paleontology, YPM 50208. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.)

The flora likewise contains many familiar taxa — redwoods, poplars, pines, hickories — but it also contains some enigmatic extinct species. One such puzzle is Fagopsis longifolia, a tree that may belong to the Fagaceae. If this interpretation is correct, Fagopsis is  kin to the modern oaks and beeches.

The following remarkable fossil shows Fagopsis with attached leaves and a fluffy ball of staminate inflorescences (i.e, the “male flowers,” bearing the stamens that produce pollen).

Fagopsis longifolia. Division of Paleobotany, YPM 30249. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.

Fagopsis longifolia. Division of Paleobotany, YPM 30249. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.

The separate pistillate inflorescence (the “female flower”) is also beautifully preserved.

Fagopsis longifolia. Division of Paleobotany, YPM 30121. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.

Fagopsis longifolia. Division of Paleobotany, YPM 30121. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.

Here is a close-up of the same specimen, showing the details of the long styles.

Fagopsis longifolia. Division of Paleobotany, YPM 30121. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.

Fagopsis longifolia. Division of Paleobotany, YPM 30121. Copyright 2014, Peabody Museum of Natural History, Yale University, New Haven, CT. All rights reserved.

The most comprehensive treatment of the Fagopsis is Manchester and Crane‘s analysis of the leaves, flowers, fruits, and pollen of the species. It was therefore a privilege to examine the fossils with Peter Crane and to learn that the species still presents something of a puzzle, not fitting neatly into any modern group.

My thanks to Peter Crane, Shusheng Hu, Susan Butts, Derek Briggs, and Rick Prum for their welcome and assistance at the Museum. If you’re in New Haven, I strongly recommend a visit to the museum.