August 31 , 2016

by Lance Nixon

They are a party of explorers going up the Missouri River but also stepping back in time, for somewhere near the mouth of the White River – probably in what is now Gregory County of South Dakota – they find themselves standing on the floor of an ancient seabed.

And the creature they find there is at least as fearsome as the white bears they have been hearing about. The journals of Lewis and Clark make note of it on Sept. 10, 1804:

“Passed the lower point of an island covered with red cedar, situated in a bend on the L.S. This island is about 2 miles in length. Below this on a hill on the L.S. we found the backbone of a fish, 45 feet long, tapering to the tail. Some teeth, &c. Those joints were separated, and all petrified.”

But it’s clear, without any doubt, that it is a mosasaur that a trapper discovers near the Big Bend of the Missouri some three decades later, because that one – after being displayed in the garden of an Indian agent in St. Louis and subsequently purchased by a German prince – survives.

What is becoming apparent to people in the 19th century is that the area now known as South Dakota is home to a rich variety of fossils. The mosasaurs that roamed the shallow seas in the Cretaceous Period are only the start.

Menagerie of ancient animals confined in stone

That is why, on May 31, 1843, the renowned wildlife painter and naturalist, John James Audubon, stopping in Fort Pierre on his journey up the Missouri River to paint the mammals of North America, muses wistfully in his journal about the distant headwaters of the Teton, or Bad River.

“We are about one and a half miles above the Teton River, or, as it is now called, the Little Missouri, a swift and tortuous stream that finds its source about 250 miles from its union with this great river, in what are called the Badlands of Teton River, where it seems, from what we hear, that the country has been at one period greatly convulsed, and is filled with fossil remains.”

Audubon’s geography is inexact on the distance and the river involved, but in the crucial point he is exactly right – the Badlands of South Dakota, mostly along the White River, is still the world’s richest area for some kinds of fossils.

In that same year that Audubon is writing, 1843, part of a fossilized jawbone of an ancient mammal now known as a titanothere is taken from the Badlands to St. Louis as a curiosity, where Dr. Hiram Prout studies it and publishes a paper about it in 1846.

The National Park Service dates the scientific community’s interest in the fossils of the Badlands from that paper. The region’s impact on the relatively young discipline of paleontology is clearly visible in the fact that by 1854, when paleontologists counted a total of 84 different species of prehistoric animals that had been found in North America, 77 of them were known from the White River Badlands. To this day, no other place on earth is known to be as rich in fossils of Oligocene mammals.

Best place in the country for hunting dead animals

But South Dakota has much older fossils from the two great ages of dinosaurs; and marine fossils from that last great age of dinosaurs when oceans covered the central part of the state.

“For a paleontologist like myself, South Dakota is an absolute dream to work in,” says assistant professor Darrin Pagnac, curator of vertebrate paleontology at the South Dakota School of Mines & Technology in Rapid City. “We have fossils that span almost the entire evolutionary history of what we call multicellular organisms – organisms that are not single-celled. Our oldest fossils date back to as far back as around a little over 500 million years ago and we have a comparatively complete record right up until the end of the last ice age and even further. So it’s just an amazing place to work.”

That would put the first signs of life in South Dakota in what’s called the Cambrian Period. But there are also tantalizing clues, if no clear proof, of earlier life in South Dakota, from what is called the Precambrian Period.

“I had some stuff that I thought was Precambrian fossil stuff, but I could never convince the paleontologists,” said Jack Redden, a retired geologist from the South Dakota School of Mines & Technology. “There’s little doubt in places that life had begun back then. The problem with the Precambrian here is that all of the Black Hills has been metamorphosed.”

Because those rocks have been transformed by heat and pressure, traces of life, if there were any, may have been distorted or erased. But what remains from the Cambrian Period on in South Dakota is a long record. A lot of other places have a rich fossil history but far more constrained to specific time periods, Pagnac said.

“It’s difficult to go anywhere else in North America and see the level of diversity that we have in South Dakota. It’s really amazing. In comparison Montana has wonderful fossil resources, but they’re primarily Cretaceous. Nebraska has fantastic fossil resources but they’re primarily Eocene, Oligocene, Miocene.

“That’s one of the reasons I love working here so much, because I get to see such an amazing variety of fossils. I get a phone call from our volunteers down in the museum saying, ‘Someone has a fossil they want to show you.’ I can expect anything – absolutely anything. And I love that.”

Pete Larson, one of the owners of the Black Hills Institute of Geological Research Inc., agrees.

“South Dakota is extremely rich, especially western South Dakota. South Dakota and Wyoming are two of the richest states in the union for fossils. Wyoming matches South Dakota for richness,” Larson said. “Montana in a different way is also pretty rich. The nice thing about South Dakota is in a very short period of time you can literally go through all the ages. In Wyoming things are a little more scattered.”

Four great zones for fossils

Though fossils can show up from any area of the state, Pagnac singled out at least four major zones that have attracted paleontologists over the years, starting with the fossils that first attracted the attention of Lewis and Clark.

Marine Cretaceous: “What you’re finding near Pierre is from what’s called the Pierre Shale. Those are those very black rocks with little yellow stringers, we call them, little yellow beds of volcanic ash, basically,” Pagnac said.

The formation is rich in fossils of sea life.

“Certainly by Pierre you’re going to be getting these Cretaceous marine organisms that existed probably around 75 to 80 million years ago. These include a lot of the things you see in our museum, the long-necked plesiosaurs that we always say looked like the Loch Ness monster, or what that’s supposed to be, the swimming mosasaurs, which are basically a fully aquatic variety of lizards like Komodo dragons. They are very closely related to those animals, and in lieu of legs, they just evolved flippers and a big strong tail. They share ancestors with Komodo dragons.”

Larson added that South Dakota is also among the places where Archelon, the largest sea turtle ever known, has been found.

“If you want to look for fossils in the Marine Upper Cretaceous, South Dakota’s the place to come,” Larson said.

In fact, Redden adds, the Pierre Shale formation in which those fossils are found, though it extends from Canada to New Mexico in the Great Plains, is named for Fort Pierre, since it was there that the formation was easily exposed and could be easily studied. Geologists first described it almost exactly 150 years ago, in 1862.

Cretaceous terrestrial: The counterpart of what is happening in the oceans around Pierre in the Cretaceous Period is what is happening on dry land.

For example, the Hell Creek Formation – named for a site in Montana but extending into the Dakotas and Wyoming – is rich in fossils.

“The Hell Creek Formation has the end of the age of dinosaurs,” Larson said. “It has the Tyrannosaurus rex and the various food groups for the Tyrannosaurus rex. If you want to look at the very end of the age of dinosaurs, this is the place to come. Then the asteroid came and left lots of job openings which mammals filled.”

That Hell Creek Formation includes the corner of South Dakota that bumps up against Wyoming, Montana and North Dakota.

“You’re going to be finding those dinosaurs up in the northwest part of the state,” Pagnac said. “And the reason they’re limited to up in the northwest part of the state is that this is the part of the state that wasn’t covered by this ocean. You can at one point trace the boundary of this inland sea where we find the plesiosaurs, the mosasaurs, you can sort of trace that boundary up along the northwest edge of the state, and once you hit, say, Harding County, that’s where you’re going to get those dinosaurs that lived at the very end of the age of dinosaurs, Tyrannosaurus, Triceratops, lots of what we call duck-billed dinosaurs, or hadrosaurs, and armored dinosaurs called Ankylosaurus – big club-tailed dinosaurs – and dome-skulled dinosaurs, Pachycephalosaurus. Those are very, very common up in the northwest part of the state.”

New finds from this part of South Dakota continue to add to what is known about dinosaurs, or in some cases, simply to raise new questions.

For example, Christopher Ott and Pete Larson described a new kind of horned dinosaur in 2010 from the Hell Creek Formation in northwest South Dakota that they named “Tatankaceratops,” blending the Lakota word for ‘bison,’ ‘tatanka,’ with a Latin root to come up with a name meaning “bison horn face.’ They date it to 65.5 million years ago.

“We named it in honor of the Lakota people,” Larson said.

But scientists since the discovery have discussed the possibility that it might not be a new species, but perhaps a juvenile Triceratops, or perhaps a deformed one. It might also be a dwarf species of Triceratops, some believe.

Jurassic: Part of what gives South Dakota its amazing diversity of fossils, Pagnac said, is the uplift of the Black Hills that brings to light rocks much older than those of the Cretaceous Period.

“Here in the Black Hills in a small ring around the edge of the Hills, we have sediments that contain much older dinosaurs as well. These are dinosaurs from the end of the Jurassic Period and these are going to be about 150 million years old. This is a whole suite of different dinosaurs but ones that are very familiar to everyone. These are the long-necked, plant-eating sauropod dinosaurs, the ones that got utterly immense, things like Apatosaurus, Diplodocus, Barosaurus, Camarasaurus.”

But for a past generation of people who learned about Brontosaurus, console yourselves … that name is gone.

“It turned out that two different researchers named the same animal, and we figure that out, the one that was named first gets the name, and so Apatosaurus stuck,” Pagnac said. “It’s too bad – Brontosaurus is kind of a cooler name: ‘Thunder lizard.’”

Some of the Jurassic formations in South Dakota also yield some other famous characters from prehistory.

“That’s also where we get Stegosaurus, the big plated dinosaur with spikes, and the big carnivorous dinosaur at that time would have been Allosaurus,” Pagnac said.

Badlands mammals: The other really big source of fossils in South Dakota, Pagnac said, is the Badlands region.

“The Badlands preserve fossil mammals that lived from around 35 to maybe 20 million years ago. These include all kinds of really fantastic animals, things like brontotheres that were elephant-sized animals related to rhinos. They had a big slingshot-shaped horn on their nose. Lots of camels, animals called oreodonts that are really difficult to describe, and carnivorous animals. There were small saber-toothed cats at that time. Large animals called hyenadonts that were wolf-like, even bear-like carnivores.”

Eastern South Dakota: Pagnac said fossils can turn up from other parts of the state, but not as readily.

“The reason we find so many more marine fossils around Pierre and not so many in the eastern part of the state doesn’t necessarily have to do with the lack of rocks over in the eastern part of the state. The Pierre formation is still over there in the eastern part of the state,” Pagnac said.

The problem is that the glaciers bulldozed their way across eastern South Dakota in the last ice age. Since the Missouri River marks the western edge of where the last ice sheet reached, East River is entirely covered in glacial sediment. The fossil-bearing rocks are there, but buried.

“In order to get at those fossils, you would either have to drill through this glacial sediment, or in certain specific areas such as down along the Missouri River on the Nebraska-South Dakota border, the rivers will cut deep enough to begin to expose these rocks.”

And in that glacial sediment itself, east of the Missouri, the fossils are not as old.

“You will find fossils in these glacial sediments, but these are some of the youngest fossils we find – lots of mammoth remains, lots of bison remains, even on occasion some very large camel and horse remains. Of course these are animals that were around during the last ice age,” Pagnac said.