Episode 11 Field Guide: Trilobites from the Cincinnati Sea
Over 400 million years ago the oceans were teeming with life, but it didn’t look much like what you see at the aquarium or in Finding Nemo. Instead of colorful fish flitting through coral reefs, the ancient seas had giant, shelled squids darting past the icons of the early ocean: The Trilobites!
Journey back to the Late Ordovician sea with Dr. Brenda Hunda, Curator of Invertebrates at the Cincinnati Museum Center. Dr. Hunda has spent her career carefully documenting the changes in trilobites in the remarkable rocks near Cincinnati, Ohio. Trilobites were spectacularly diverse early arthropods (the group that includes crustaceous, insects, and arachnids) that adapted to the ever-changing seas, by swimming through the water, scooting along the ocean floor, and burrowing through the mud for their 300 million year reign. Our journey through the ancient Queen City features the musical talents of two great Cincinnati-area bands: The Cincinnati Dancing Pigs and Jake Speed and the Freddies! Take the plunge into invertebrate paleontology with Matt and Adam in this episode of Past Time!
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Click below to see images of our favorite invertebrates and to get oriented in ancient North America!
Quick links (More discussion and images after these definitions)
Trilobites – The stars of the early Paleozoic seas! These arthropods – relatives of crustaceous, insects, arachnids and the like – look like isopods (also called pill bugs, woodlice, sow bugs, or roly polys) but had a longer reign (300 million years!) and greater diversity. Some species were microscopic, and others were skateboard-sized!
Morphology – “The study of shape”. In this episode Dr. Hunda discusses the morphology of trilobites. In one study she connected the head shape of one species of trilobite to water depth in the ancient Cincinnatian seas.
Paleozoic Era – Meaning “Ancient Life”. It started around 540 million years ago with the Cambrian Period and ended around 250 million million years ago with the Permian Period. The end of the Paleozoic is marked by one of the largest mass extinctions to ever sweep through life, ushering in the Mesozoic Era (the “Age of Reptiles”).
Ordovician Period – The name for the time between 485 million years ago and 443 million years ago that follows the Cambrian Period. “The Great Ordovician Biodiversification Event” (GOBE!) marks this period of churning diversity. The biodiversity party came to a crashing halt with the End Ordovician Extinction, a biological collapse second only to the End-Permian.
Kope Formation – A group of beautifully preserved rock layers that can be found near Cincinnati, Ohio. Mostly shale and limestone, the blueish rocks of the Kope reach into Northwestern Kentucky and Southeastern Indiana and they have been a fossil hunting destination for generations. When the Kope was deposited, Cincinnati was the site of a shallow sea and was located much farther south in the tropics.
Venerable Cincinnati Invertebrates
Nautiloids – These tentacled creatures belong to the the phylum Mollusca, and are cephalopods, along with squids and octopuses. Nautiloids have tentacles sticking out of cone-like shells.
Eurypterids – Sometimes called “sea scorpions,” these extinct arachnids reached gargantuan sizes.
Brachiopods – A group of shelled animals that resemble clams but aren’t actually related. They are still around, but their diversity peak was in the Paleozoic.
Bryozoans – Also still living, but not the reef-building powerhouses they were during the Late Ordovician. These small animals form intricate structures by cementing their bodies to each other.
The Trilobite Expert
Our guest for this episode is Dr. Brenda Hunda, the Curator of Invertebrates at the Cincinnati Museum Center. Dr. Hunda is originally from Alberta, Canada which is Canadian dinosaur country much like Montana, Wyoming, and other western states are prime dinosaur country in the United States. She grew up thinking she wanted to study dinosaurs and mammals, but discovered the vast world of invertebrate paleontology when she was at the University of Alberta.
She wanted to ask questions about gradual changes through time. To answer them she needed large sample sizes, complete specimens, and regular rock deposition. She found it all in the world of trilobites! Her dissertation work brought her to the rocks around Cincinnati which are known by paleontologists around the world for the diverse sea preserved in shale and limestone. To understand Dr. Hunda’s questions and the fossils in Southwestern Ohio, we need to go back 450 million years…
The Soggy Ordovician
The Ordovician World was very different from the one we are familiar with in 2014. Cincinnati, Ohio was BELOW the Equator, and the Sahara Desert was almost at the South Pole!
Deep currents within the Earth’s mantle and core slowly rearrange the continents, in a process called Plate Tectonics. As continents collide, mountains are uplifted and new continents form. 450 million years ago, the continents were doing their slow dance with the Supercontinent Pangea still 200 million years in the future. Parts of Europe were slamming into the eastern edge of North America forming the Appalachian Mountains which soared higher than the Himalaya Mountains.
In the Ordovician, most of North America was flooded. There weren’t any glaciers – which lock up water and drop sea levels – until the very end of the Ordovician. Most of North America was under waster and Cincinnati, not too far from the Appalachian coast, was a shallow tropical sea.
Today, shallow seas are the most diverse ecosystems on the planet. In shallow seas, light can penetrate to the ocean floor and reefs, large organic mounds, can build up making homes for hundreds of species. On a planet with a lot of shallow seas, there were a lot of opportunities for life to take off. And it did.
The period before the Ordovician is called the Cambrian Period. The Cambrian is a period that kicks off a couple of big units of time. It’s the beginning of the Paleozoic Era (meaning “Ancient Life”, also called the “Age of Fishes”), and the Phanerozoic Eon (meaning “Visible Life”. We’re still living in the Phanerozoic Eon).
The reason it initiates so many geological clocks is because the Cambrian is when life first gets diverse. Before the Cambrian, life was mostly single-celled organisms, with a few mysterious experiments with many cells. But during the Cambrian, the evolutionary story of multicellular life set the ground rules. Most phyla date back to the Cambrian including the phylum Chordata (humans and all other vertebrates belong here), phylum Arthropoda (the stars of this episode belong here), phylum Mollusca (squids, snails, clams and friends), and on and on.
But in the Ordovician all these phyla (the plural of “phylum”) became diverse. The Tree of Life evolved its trunk and limbs in the Cambrian, and in the Ordovician the limbs grew branches. One phylum that really started to sprout early were the arthropods, especially the trilobites.
Trilobites (meaning “three lobed”) are arthropods (meaning “jointed feet”) because, like other arthropods, they have exoskeletons, segmented body plans, and segmented limbs. Their fossil record begins early on in the Cambrian and they radiate quickly in the Cambrian and on into the Ordovician. The basic trilobite body plan had the cephalon (head plate) on one end with sophisticated compound eyes followed by several segments that lead to a tail. Many species could tuck their tail against the head, protecting the underside of the animal like an armadillo or a pill bug.
Some species of trilobite, like Agnostus pisiformis, were microscopic, while others, like Isotelus rex, made it up to 2.3 feet long (70 cm)! Some species deviated from the basic plan, sprouting pronged forks like Walliserops and eye stalks like Neoasaphus. Erbenochile erbeni, a Moroccan trilobite was covered in spikes and had visors over its column-like eyes! You gotta put exclamation points after this stuff!
Today, paleontologists like Dr. Hunda have named over 20,000 species of trilobites. We only have 10,000 species of birds today and 6,000 species of mammals. Those 20,000 species are spread over the 300 million year reign of the trilobites, so there are certainly still trilobites left to discover! In the middle of this crazy diversity, Dr. Hunda hunkered down to understand the evolutionary story told by one species found in the Late Ordovician…
This video features Dr. Brenda Hunda explaining some of the Ordovician collections she curates. This video was produced by the Cincinnati Museum Center.
Flexicalymene is pretty nice
One of the sections of rock that drew Dr. Hunda’s attention was the Kope Formation, an Upper Ordovician expanse of rock that was deposited, one layer at a time, while the Cincinnati area was a shallow, tropical sea. The site of the Kope formation was a geological sweet spot for preserving abundant trilobites: It was far enough from the beach to ensure every storm didn’t rip up newly deposited layers and fossils, but close enough to the beach to be a well-lit for Ordovician reefs to build up. Each layer chronicles changes in the sea on the century, or even decade-level, and each layer contains the remains of – literally – tons of animals.
Exploring the formation, which runs for miles across Ohio, Indiana, and Kentucky, Dr. Hunda was able to walk through the Kope as the rocks got closer to the ancient shore, or she could walk out to sea along where the water would have been deeper. With an experienced crew, Dr. Hunda spent hundreds of hours in the field, collecting thousands of specimens of Flexicalymene granulosa, a common trilobite in the Kope formation. She carefully documented each discovery, then took them back to the lab where she could prepare the fossils, photograph them, and use special computer programs to place points on the fossils. The computer programs helped her summarize all the small changes she observed on the faces of her specimens.
Dr. Hunda then tied the shape of a specimen’s head to the spot where it was found. Her analysis showed subtle variations in subgroups of F. granulosa with specific head shapes liked to track water depth and water temperatures through time. These subtle shape changes are the fuel of evolutionary change and speciation, but during the Late Ordovician of Cincinnati, there wasn’t a whole lot of change to adapt to and the trilobites happily tracked their preferred environments. But that all changed at the end of the Ordovician…
Winter is Coming
The End-Ordovician extinction was devastating to the biodiversity that had built up over tens of millions of years. As much as 85% of species went extinct in the second largest calamity to affect life on Earth. It’s difficult to understand an event that occurred 440 million years ago, but rocks from Africa show massive glaciers were building up on the large southern continent of Gondwana. The ice sheets dropped global sea levels, draining the shallow seas – like the one over Cincinnati – leaving only deep oceans for life to swim through. Deep oceans don’t harbor the kind of diversity supported by shallow, well-lit seas.
With habitats shrinking, many species went extinct. The ones that survived had to adapt to cooler global temperatures. When the glaciers melted, the continents were flooded with water low in oxygen and the deep oceans were practically stagnant. A second extinction swept through the Ordovician survivors. The species that survived this one-two extinction punch would have to slowly rebound in the next period: The Silurian.
Many species of trilobites managed to survive the Ordovician and live on into the Silurian, but they were an embattled group as fish with jaws became abundant and diverse. The elaborate spines and spikes of Devonian trilobites may be defensive features for warding off hungry fish. But it was a losing battle and trilobites continued a slow decline. By the end of the Permian Period, only one lineage of trilobites was still crawling through the seas. The Permian Period is the last period of the Paleozoic and it is marked by the only mass extinction larger than the end-Ordovician: The Permian-Triassic Extinction. An estimated 96% of marine species were wiped off the face of the Earth, among them the last trilobites.
“When the end of the world comes, I want to be in Cincinnati. It is always ten years behind the times.” – Attributed to Mark Twain
If you are interested in looking for your own Ordovician specimens in the Cincinnati area there are plenty of places to collect, including Caesar Creek State Park, East Fork State Park, and Trammel Fossil Park. For help with identification, check out this website, the book Fossils of Ohio edited by Rodney Feldmann (It’s a useful reference for fossils from Southeastern Indiana and Northwestern Kentucky, too) and don’t forget to visit Dr. Hunda at the Cincinnati Museum Center!
For this episode we are especially grateful to two Cincinnati-area bands that let us use their music to bring the sounds of the Queen City to the podcast. The first is the bluegrass “old timey folk band” Jake Speed and The Freddies. Check out their website for information on upcoming shows and download their music on iTunes. If you like a hot mandolin, witty lyrics with an edge, and a great voice, throw these guys in your ears (after listening to this episode of Past Time). In this episode we used samples from “Ohio River Waltz”, “First Street Fell”, and “Ohio River Blues”.
Our other musical guests were The Cincinnati Dancing Pigs, “Cincinnati’s premier jug band”! Here’s their website and music on iTunes. In this episode we sampled “Jug Band Music”, “Jug Band Blues”, “Stealin'”, and “Rag Mamma Rag.” Matt defies you to listen to them and not grin for a couple of hours.
If you’re in the Cincinnati area, especially in the Spring or Summer, check out their schedules and try to catch these guys live!
Sound effects in this episode were also sampled from www.freeSFX.co.uk, www.freesound.com, and GarageBand loops. “The Newport Blues” and “I’m Going to Cincinnati” by The Cincinnati Jug Band were sampled, but we were unable to establish copyright ownership related to these tracks. If you have information regarding who to contact for use of these historic recordings, please contact us.
A Sea Without Fish: Life in the Ordovician of the Cincinnati Region by Richard Arnold Davis and David L. Meyer. While slightly technical, this book is an approachable introduction to the life during the Ordovician Biodiversification Event. It also explores the history of paleontology in the Midwest.
Trilobite: Eyewitness to Evolution by Richard Fortey. A very accessible book that reveals trilobites in all their strange, diverse glory.
Annals of the Former World by John McPhee. A classic popular account of the geological history of North America, especially the rise of the Appalachian Mountains.
The Cambrian Explosion: The Construction of Animal Biodiversity by Douglas H. Erwin and James W. Valentine. A textbook that explores the roots of the Ordovician ecosystem and the meaning of the phrase “Cambrian Explosion” from the Burgess Shale of Canada to the rocks of the United Kingdom.
Webber, A.J. and B.R. Hunda (2007) Quantitatively comparing morphological trends to environment in the fossil record (Cincinnatian Series; Upper Ordovician). Evolution 61(6): 1455-1465.
Hunda, B.R., A. Thompson, A.J. Webber and N.C. Hughes (2008) Short-term, paleoenvironmentally-related morphological variation in the Ordovician trilobite Fleicalymene granulosa. In Advances in Trilobite Research eds. I. Rabano, R. Gonzalo, and D. Garcia-Bellido.
B.R. Hunda, N.C. Hughes, and K.W. Flessa (2006) Trilobite taphonomy and temporal resolution in the Mt. Orab Shale Bed (Upper Ordovician, Ohio, U.S.A). Palaios 21(1): 26-45.