Plate Tectonics 100 Year Anniversary

This year marks the centennial anniversary of the theory of plate tectonics with the publication of  “The Origin of Continents and Oceans” by German explorer and geophysicist Alfred Wegener, now a true legend. His data-driven hypothesis and analyses were highly criticized and discounted by entrenched mindsets, and mostly forgotten until the 1960s. The fossil record, generally, and trilobites, particularly played a pivotal role in mapping drfting, collisions and breakups of continents across geologic time. How the theory all came together is summarized in a 2013 Nature paper:  Naomi Oreskes, Nature 501, 27–29; 2013.

The two trilobites above are, respectively, Dicranurus hamatus elegantus, from the Haragan Formation, Coal County, Oklahoma, and Dicranurus monstrosus, from the Laatchana Formation deposits near Alnif, Morocco. Both fossil sites are dated to the lower Devonian period about 400 million years ago. Their resemblance is nothing short of remarkable, despite now separated by the Atlantic Ocean and more than 4000 miles. The similarity is because the Morocco of today was in the continental shelf of Gondwana during the Devonian, and Oklahoma was in the continental shelf of Euramerica (also called Laurussia), separated by the Paleotethys Sea (as shown here); these landmasses were drifting together as the supercontinent Pangaea was forming. The fossil sites were thus proximal and at comparable latitudes, suggesting they shared the same marine environments. The comparable species likely share common ancestry and occupy the same or closely related genera. Are they the same species – could they interbreed? Who knows, at a minimal, they share a very close common ancestor. What a difference a century made for Alfred Wegener.

Still not convinced about plat tectonics? There are many examples of DEvonian trilobite commonality between Morocco and Oklahoma among diverse trilobite orders: Lichida; Phacopida; Proetida; and Corynexochida. Maybe I’ll pst those here another day. Of course, some folks will never be convinced, think the Earth is but 10,000 years old, that humans and dinosaurs co-existed, and all that rubbish – well, denial is not just a river in Egypt.

For ‪#‎FossilFriday‬, an amazing spiny trilobite (Dicranurus) from 375 million-year-old (Devonian) rocks of Oklahoma, and now part of the Denver Museum of Nature & Science collection.

Back when North America was underwater, these “cockroaches of the sea” scurried and swam across the seafloor, chomping mud and worms for a living!

Chosen by Museum Curator James W Hagadorn.

The Twin head-tail, Dicranurus (1977)

Phylum : Arthropoda
Class : Trilobita
Order : Lichida
Family : Odontopleuridae
Genus : Dicranurus
Species : D. hamatus, D. elegans, D. monstrosus

  • Devonian
  • 2 cm long (size)
  • Morocco and Oklahoma (map)

Dicranurus was a genus of Lower Devonian lichid trilobites that lived in a shallow sea that lay between Euramerica and Gondwana, corresponding to modern-day Oklahoma and Morocco, respectively. As such, their fossils are found in Oklahoma and Morocco.

Their bodies averaged about 1-inch or so, in length, though their large spines made them at least 2 inches in length. It is speculated that such tremendous spines hampered the ability of predators, such as arthrodire placoderms, to attack them, as well as to help prevent them from sinking into the soft mud of their environment. Dicranurus trilobites are distinguished from other lichids by the pair of large, curled, horn-like spines that emanate from behind the glabellum. The genus name refers to these distinctive horns, in fact.

It’s time for a “strange” #TrilobiteTuesday! Trilobites survived for over a quarter of a billion years–plenty of time for them to develop into the more than 25,000 species so-far recognized by science. But amid that mind-boggling variety of trilo-types there exist a number of species that are so unusual, so strange, so out-and-out bizarre that they deserve special mention. These are creatures so alien in appearance that few observers would believe that such out-of-this-world life forms could actually exist. But they did, and they were among the first rulers of the earth’s seas. Imagine the likes of the aptly-named Dicranurus monstrosus with two monstrous “horns” sweeping back from the top of its cephalon. Strange, indeed! Explore more trilobites.

Yin & Yang.  Two species of Dicranurus trilobites, the tan one on the left being Dicranurus elegans from the Haragan Formation of Oklahoma and the black one on the right being Dicranurus monstrousus from Morocco.  

They both lived at close to the same time and in fact during the shallow seas which are now exposed in Oklahoma and Morocco were very close to each other.  

Both of these beautiful specimens can be found at FossilEra.com

Dicranurus is a rare trilobite in the Haragan Formation with only a few complete specimens being found at the Black Cat Mountain Quarry in a year, but one this nice only comes along once every several years. This magnificent example was collected a decade ago and prepared by Bob Carroll. I haven’t seen a specimen this nice come out of the quarry in several years. It’s huge for the species at 3.05" long, laid out perfectly prone with no disarticulation which is typical with these trilobites.  Recently added for sale at FossilEra.com

It’s ‪Trilobite Tuesday‬! The Museum’s permanent trilobite exhibit can be found in the Grand Gallery, near the famed Great Canoe. In the case are specimens covering time periods from Cambrian through Carboniferous–nearly 280 million years of earth history. 

Featured in the display are a Cambrian-age Olenoides from Canada, an assortment of Ordovician-age Asaphids from Russia, a Silurian-age Arctinurus from New York and a Devonian-age Drotops from Morocco. The exhibit also presents a detailed view of the multi-lensed compound eyes of trilobites and discusses the theory of Plate Tectonics by presenting nearly identical Dicranurus specimens from both Morocco and Oklahoma.

Ready for more trilobites?