S is for Stigmaria
From the Carboniferous
Life in the USA is not normal. It feels pointless and trivial to be talking about small looks at the fascinating natural world when the country is being dismantled. But these posts will continue, as a statement of resistance. I hope you continue to enjoy and learn from them. Stand Up For Science!
The name Stigmaria sounds like a nice scientific name for a fossil, but it’s not really specific to a particular genus or species. It’s a form taxon – the name for a group of fossils that has a distinctive form and/or function but may exist across multiple species. In this case, stigmaria is the name for fossil roots of various big trees and other plants that lived in the Carboniferous coal swamps of the US about 325 to 300 million years ago. Coal – carbon – is the origin of the name Carboniferous.
The two examples in the top photo are probably from Indiana, from the Pennsylvanian (Upper Carboniferous) Period.
Two of the most common genera of coal-forest trees, Sigillaria and Lepidodendron, can both have roots like this. In the photo you can see the nodes on the sides that probably represent the attachment points for rootlets that helped anchor the trees in place; they’re similar in that role to the hairs and branches you sometimes find on carrots.
Sigillaria and Lepidodendron are really lycopods, giant clubmosses that reached 40 meters in height. Lycopods are among the earliest land plants known on earth (Silurian, about 428 million years ago) and they survive to the present day in about 1,200 species of clubmosses and their relatives that reproduce by spores. Sigillaria, Lepidodendron, and others are the main constituents of the coal in Pennsylvania and the Midwest, but they (and the swamps in which they thrived) were extinct by the end of the Pennsylvanian Period about 299 million years ago because of a change to a regionally cooler and drier climate.
The word stigmaria comes from Greek stigma, “a mark made by a pointed instrument, a dot.” The word is also related to “stick”. Lycopod is from Greek for wolf foot, for the claw shape of the root systems, and Lepidodendron means scale tree for the symmetrical scars on the trees where branches and leaves were attached.
One does not build the coal beds and 80,000 feet of perpendicular Old Red Sandstone in a brief time – no, it took twenty million years. In the first place, a coal bed is a slow and troublesome and tiresome thing to construct. You have to grow prodigious forests of tree-ferns and reeds and calamites and such things in a marshy region; then you have to sink them under out of sight and let them rot; then you have to turn the streams on them, so as to bury them under several feet of sediment, and the sediment must have time to harden and turn to rock; next you must grow another forest on top, then sink it and put on another layer of sediment and harden it; then more forest and more rock, layer upon layer, three miles deep -- ah, indeed it is a sickening slow job to build a coal-measure and do it right! —Mark Twain, 1903.
Enjoyed both text and graphics -- relished the Twain quote!