Tiny shark lived with huge T.Rex SUE

SUE is one of the most complete and largest specimens of T.Rex we know of. Recently discovered small shark teeth tell a tale about the world she lived in.

Back in 1990, paleontologist Sue Hendrickson’s team had a flat tire after a dig, and while the team took care of the problem, she continued to inspect the area and found bones sticking out of a nearby hillside. These bones belonged to a female T.Rex that lived some 67 million years ago and was later named SUE after the woman who discovered her.

Wisely, scientists from the Field Museum in Chicago where SUE’s remains are on display today, held on to the rock she was found in. Sieving through this sediment, they discovered tooth fossils that belonged to a small shark and published about it in a new study. Peter Makovicky, the museum’s associate curator, answered our questions about the shark, and what it tells us about SUE.

T.Rex SUE at the Field Museum in Chicago. Courtesy of: J. Mier via Wikimedia.

ResearchGate: What made you look at the earth surrounding SUE?

Peter Makovicky: Bill Simpson, the Museum’s Collection Manager of Fossil Vertebrates, and leader of the team that prepared SUE, had the foresight to save the sediment that accumulated during the preparation process, the cleaning of the fossil.

About a decade later, Terry “Bucky” Gates joined my lab and began a project to screen the sediments to look for microvertebrate fossils – teeth, scales, and bones of small animals – to build a better picture of what lived in the environment with SUE. This involved suspending the sediment in water and then running the slurry through a set of connected sieves, each with a finer mesh than the preceding one. Once the sediment was screened and the sand and silt is washed away, the remaining concentrate needed to be carefully picked through.

One of the tiny fossilized teeth recovered from Galagadon, so named for the shape of its teeth, which resemble the spaceships in the video game Galaga. Credit: Terry Gates

This is where the hero of our story comes into the picture. Karen Nordquist, a steadfast Field Museum volunteer for three decades, the last half of which she has spent peering through a microscope meticulously picking tiny fossils out of screen-washed sediments, recovered two dozen tiny, millimeter sized teeth that turned out to be a new species of carpet shark

ResearchGate: What do the teeth look like?

Makovicky: The teeth are tiny – only a millimeter across. They have an unusual shape with three unequal points and a wide apron at the root perforated by small canal. Some of the teeth bear an uncanny resemblance to the spaceship in the 80's arcade game Galaga, which inspired the genus name.

ResearchGate: What did the shark look like? Is it comparable to sharks today? What’s changed?

Makovicky: Galagadon was a tiny shark between one and two feet long. Most carpet sharks, the group Galagadon belongs to, are bottom dwelling animals with camouflage patterning, blunt faces, and barbels by their mouth. It is very likely that is what our new species looked like.

An illustration showing what Galagadon would have looked like in life, swimming along the river floor. Credit: Velizar Simeonovski, Field Museum.

ResearchGate: What was the shark doing there?

Makovicky: All living carpet sharks are marine and most live in the Indopacific region. So, finding a carpet shark in the SUE quarry shows not only that ancient carpet sharks could live at least intermittently in fresh water habitats and that carpet sharks enjoyed a much wider distribution in the Mesozoic when warm, shallow seas covered parts of many continents. One possibility is that the teeth are small because they belong to a juvenile and that ancient carpet sharks may have used freshwater habitats as nurseries, but that is speculative. I doubt Galagadon spent its whole life in fresh water habitats, but the big take home message here is that the fossil record can show us how the distributions and physiology of lineages  have changed over Deep Time.

ResearchGate: What does the shark tell us about SUE and her habitat?

Makovicky: One previous idea about the SUE site was that it was an oxbow lake, i.e an isolated water body. The presence of sharks, which besides Galagadon, include two other species, indicate a connection to the Western Interior Seaway a hundred miles or so to the east.

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Featured image: Velizar Simeonovski, Field Museum