Tag Archives: Formations

SuperCroc at Sternberg

The Sternberg Natural History Museum at Fort Hays State University is featuring a new exhibit, The Science of SuperCroc from now until August 5.

The star of the show is the African crocodilian species Sarcosuchus whose remains have been found in the modern Sahara, in the Elrhaz Formation. This Early Cretaceous (~112 million years ago) crocodile had a long, slender snout with a prominent down-turn or hook at the tip. When fully mature it is estimated to have been between 37-40 feet in length, and weighed as much as 17,000 pounds.

The largest living crocodile is the saltwater croc, and the largest confirmed individual was just over 20 feet in length and weighed a mere 2,600 pounds.

Restoration of Sarcosuchus, the SuperCroc

Sarcosuchus had its eyes placed high upon its skull suggesting that it spent most of its time submerged in the water. Like so many other things in paleontology, the question of what Sarcosuchus may have eaten is not agreed upon by researchers. Some suggested that the size of Sarcosuchus and its overhanging upper jaw made it able to wrestle large prey items, even massive long-necked sauropod dinosaurs. Others point to the slenderness of the muzzle and it not looking stout enough to withstand the forces that would be required to bring down large prey. There were plenty of lobe-finned fish in Sarcosuchus’s environment. I see a fish-eater in this skull myself.

Also on display with the large croc is Suchomimus, a theropod dinosaur whose remains have been found in the same geological formation as Sarcosuchus. Suchomimus, whose name means crocodile mimic, was a forty-foot long beast which also had a long slender muzzle. Its forelimbs were armed with very long sickle-curved claws. This animal is thought to have eaten fish and probably other sorts of meat, but its skull also does not appear equipped for biting and holding very large struggling prey.

SuperCroc Sarcosuchus skeleton at Sternberg Museum

The presence of both of these animals, and many others found with them, show that the Sahara area of today was a lush, swampy habitat in the Early Cretaceous. The effect of climate change and plate movements over millions of years can turn a wet verdant habitat into a harsh, dry desert. My how times change.

Go see SuperCroc at the Sternberg Museum if you have a chance.

Niobrara Chalk

One of the most famous formations is the Niobrara Chalk. This formation is exposed in northwest Kansas and southern Nebraska. Formations are sometimes divided into members, subsections of the formation based upon its rock type. The Niobrara Chalk has two members: the lower Fort Hays Limestone and the upper Smoky Hill Chalk. It is the Smoky Hill Chalk which is best known for its fossils.

The sediments that comprise the Niobrara Chalk were deposited in the Western Interior basin during the Late Cretaceous. At that time sea levels rose and the interior of North America was inundated by a shallow sea, the Western Interior Sea. The sea cut North America in half by spreading from the Gulf of Mexico to the Canadian Arctic. Volcanoes to the west, in what is now Utah and Nevada, spewed ash into the sea and sediments eroded from mountains along the western coast were washed into the sea by rivers. What is today Kansas was much closer to the eastern shore of the sea, a low alluvial plain, also gently washing sediment into the sea basin.

Block diagram of the Western Interior Sea

Image from Hattin, 1982.

The upper member, the Smoky Hill, was deposited from 87 to 82 million years ago, so it preserves a five million year window into the past. Elsewhere we discussed that the Cretaceous sea had a wealth of planktonic organisms. Many of those organisms had calcium carbonate-based shells and body parts, which furnished a steady supply of material to sink to the sea floor. The consistent supply of sediment, both from land and sea, and conditions at the sea floor allowed for the excellent preservation of animals. Those that died and sank to the bottom were rapidly covered by the rain of sediment and entombed until today.

And the diversity of organisms preserved is amazing. In almost every museum with fossils that I have been in, I recognize fossils from Kansas. Giant marine reptiles (mosasaurs and plesiosaurs), flying reptiles (pterosaurs), great toothy fishes, large turtles, and toothed diving birds have all been found. Each of these groups has a very interesting story to share, and we will explore many of them here. An extensive website on fossils from the Niobrara Chalk can be found at OceansofKansas.com.

Bonnerichthys

In modern oceans, the very largest organisms specialize in filter feeding, or living on the very small plankton in the water. (Read more about the filter feeding niche). Up until now, it has appeared to researcher that during the Age of Dinosaurs, when the oceans were dominated by large, toothy reptiles, there were no marine animals specializing in the niche of large-bodied filter feeding, despite ample evidence that the oceans were rich in planktonic resources.

However, this niche was in fact filled during the Mesozoic as demonstrated in a recent paper in the journal Science (Friedman et al., 2010). Turns out that several species of fish did specialize in filter feeding, and they too grew quite large. Most of the specimens were already sitting in drawers in museums, having been misunderstood for many years, until Friedman and his colleagues re-evaluated them.

For example, one species has been known for over 100 years—having been named by E. D. Cope in 1873 as ‘Portheus’ gladius from a specimen collected from the Niobrara Chalk formation in western Kansas. The Niobrara Chalk was deposited during the Late Cretaceous period (see a geologic time scale). The species has a long and complex taxonomic history, mostly of interest to professionals, but it does clearly show that many scientists reviewed the fossil material and scratched their heads in wonder about this strange set of fossils.

Friedman and his colleagues have finally put the pieces together, and it fills in much about the history of life in the oceans. They have created a new genus in which to place the species, so now it is known as Bonnerichthys gladius. The genus was named for the Kansas fossil-collecting family that collected the most complete specimen found to date.

Bonnerichthys would have been about 20 to 25 feet in length with a huge, gaping mouth. You can see an artist’s reconstruction of Bonnerichthys at Oceans of Kansas. And you can listen to an interview with Matt Friedman at NPR.

This discovery opens up a whole new understanding of the paleoecology of the Mesozoic oceans, and shows that filter feeding was utilized for at least 100 million years longer as a major life strategy than previously recognized.

FRIEDMAN, M., K. SHIMADA, L. MARTIN, M. J. EVERHART, J. LISTON, A. MALTESE, AND M. TRIEBOLD. 2010. 100-million-year dynasty of giant planktivorous bony fishes in the Mesozoic seas. Science, 327:990-993.

Formations

The crust of the Earth is composed of a complex mix of rock types formed in specific depositional environments. Most of your everyday experience occurs in erosional environments, places where the surface of the Earth is being eroded away by physical or chemical processes. Rocks underfoot are being broken up then transported as sediments to other areas. The Grand Canyon is a good example of a river cutting through the layers of rock, exposing those layers, and transporting the rock away—piece by piece.

A cross section model of the Grand Canyon showing the rock layers and how they are broken into recognized formations.

Where is that material going? It is transported to places where it is deposited, depositional environments, where the sediments accumulate. Given enough time and protection from further weathering, those newly deposited sediments can become the sedimentary rocks of the future. The deposition of sediment occurs in a wide variety of environments such as in oceans, rivers, ponds and the like.

If we look at the rocks on the surface of the Earth today, we can see differences in their color, texture, composition, and so on. We see layering as one rock type gives way to another. Geologists map these layers to trace out the history of the Earth, as each change in rock type represents a change in the environment that created it. So each outcropping of rock represents a time machine of sorts, transporting us back to the primeval environment of that spot.

A geologic formation is a formal unit, technically called a lithostratographic unit. That fancy word simply means that rocks are grouped by similar lithology, or rock type. For example, during the Late Cretaceous the last inland sea across the mid-continent of North America (a specific environment) deposited thick accumulations of chalk and shale. Today, we can lump specific sections of that collection of rock (lithology) into a single formation and call it the Niobrara Formation.

Each formation is described and named in a specific, formal way. There are rules that geologists should follow in designating specific formations (North American Commission on Stratigraphic Nomenclature, 2005). For example, each formation should have a type section designed. This type section is not unlike a type specimen mentioned in another post: it represents the standard for that formation to help others understand how it is unique.

In future posts we will explore more aspects of formations.

NORTH AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE. 2005. North American Stratigraphic Code. American Association of Petroleum Geologists Bulletin, 89(11):1547-1591.

Spending time in Purgatoire

Giant Short-Faced Bear: a Northern California Original

In 1878, James D. Richardson explored Potter Creek Cave in Shasta County, California. He found the skull of a bear beneath several inches of cave dirt, and he sent the specimen to Edward D. Cope, who determined that it was the type specimen for a new species of American “cave bear” (Cope, 1879).

Reconstruction of the Giant Short-faced Bear, Arctodus

When a scientist studies an animal and determines that it is something new to science, they set up a name for it and designate a type specimen. The type specimen, or type, holds a special significance as the “name bearer” for the entire species, and subsequent investigations of that species make reference to the type. They are often kept in special collections within the museums that hold them, or at least given special protection over other specimens. For example, they often are not loaned out as other specimens in the museum collection might be, so there is less risk of damage. (For a description of geologic type sections, see formations).

All too often the type specimens of fossil species have been based on fragmentary material or poor descriptions, making a full understanding of the species more difficult. A famous example of this is the story of the dinosaur Apatosaurus.

Apatosaurus was named by Cope’s rival, O. C. Marsh (Marsh, 1877). Both Cope and Marsh were rushing to describe more fossil species than the other, and their famous rivalry led to shoddy work by both men on occasion. Marsh said the type specimen of Apatosaurus was a “nearly complete specimen in excellent preservation.” However, he only briefly described the vertebrae of this new animal in his haste to publish the new name.

Later, Marsh published the name Brontosaurus, with a few comments on the pelvis and vertebrae of that type (Marsh, 1879). Brontosaurus soon became widely known to the public, and to many, represented the quintessential dinosaur. However, by 1903 Elmer Riggs recognized that Apatosaurus and Brontosaurus were in fact the same species of dinosaur, and since Apatosaurus was named two years before Brontosaurus, that name had priority and was the name that should be used (Riggs, 1903). However, the old name Brontosaurus was in such popular usage that it took many decades for the public to catch on. Now, it seems that every young dinosaur buff knows of this name change and is comfortable with it.

Since the first Short-faced Bear fossil to be recognized in North America was from Northern California, the type specimen, and the name of the bear, Arctodus simus, will be forever linked to the region. This “American Cave Bear” is now known from over 100 localities from Alaska to Mexico, east coast to west (Richards et al., 1996). It was a wide-spread species of the late Pleistocene Ice Age.

What is perhaps most striking about this bear is its size. Arctodus is the largest mammalian carnivore ever discovered. It is larger than any of the modern bears, tigers, or lions by a significant degree. An estimate for the largest Arctodus found to date suggests that if the individual was “lean” it weighed from 1,300 to 1,400 pounds (Nelson and Madsen, 1983). In contrast, a male lion weighs about 450 pounds. (See How big was the GSFB?)

So this imposing carnivore of the Ice Age roamed across North America, and the North State can forever claim it as its own. A full skeletal mount of this beast can be seen in the new Gateway Science Museum at Chico State.

COPE, E. D. 1879. The cave bear of California. American Naturalist, 13:791.

MARSH, O. C. 1877. Notice of new dinosaurian reptiles from the Jurassic Formation. American Journal of Science, 14:514-516.

MARSH, O. C. 1879. Notice of new Jurassic reptiles. American Journal of Science, 18:501-505.

NELSON, M. E., AND J. H. MADSEN, JR. 1983. A giant short-faced bear (Arctodus simus) from the Pleistocene of northern Utah. Transactions of the Kansas Academy of Science, 86(1):1-9.

RICHARDS, R. L., C. S. CHURCHER, AND W. D. TURNBULL. 1996. Distribution and size variation in North American short-faced bears, Arctodus simus, p. 191-246. In K. M. Stewart and K. L. Seymour (eds.), Palaeoecology and Palaeoenvironments of Late Cenozoic Mammals: Tributes to the Career of C.S. Churcher. University of Toronto Press, Toronto.

RIGGS, E. S. 1903. Structure and relationships of opisthocoelian dinosaurs. Part
1: Apatosaurus Marsh. Field Columbian Museum, Geological Series, 2:165-196.

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