Past Time

Meet Alienochelys selloumi, a giant, snorkel-nosed turtle with powerful, shell-crushing plates in its massive beak! The distant relative of the largest turtle alive today, the leatherback sea turtle, Alienochelys swam the ancient ocean of North Africa at the very end of the Age of Dinosaurs (the Late Cretaceous). It was found in the same rocks as Ocepechelon, the whale turtle discussed in our first Quick Bite back in July. There were a lot of giant, goofy, snorkel-snouted turtles in Cretaceous Morocco! When Alienochelys' discovery was announced, another paper was published describing fossilized pigment molecules that showed many marine reptiles, including a 55 million-year-old leatherback sea turtle, were dark in color, an adaptation we see in many modern swimming vertebrates. It's time to pick a new-favorite fossil turtle with Past Time!

Little people! Giant reptiles! Towering elephants! Huge birds! It sounds like the stuff of literary and box-office gold, but this Middle-Earth-like world actually existed 17,000 years ago on Flores, an island near Indonesia. Homo floresiensis, or "The Hobbts", only stood three feet tall but they cast a huge shadow over the story of human evolution. In 2004 fossils of the small, big-footed hominins were discovered and they have challenged paleoanthropologists, like this episode's Dr. William Jungers, to reconsider many hypotheses of human origins including which species left the continent and how we're all related. Once thought to just be small versions of Homo erectus, the hobbits may have much more ancient ancestors, posing more questions for the fossil record to answer as the human story becomes even more complicated...and interesting!

Last episode we featured Lythronax, the oldest-known North American tyrannosaur and a close relative of Tyrannosaurus rex. But tyrannosaurs weren’t the only big carnivores to tromp through the Mesozoic of North America. Before the tyrant lizards were huge, there was another giant terrorizing the American West: Siats! Named for a Ute mythological giant, Siats was a bus-sized carnivore in the middle Cretaceous of Utah (99 million years ago). The giant had close relatives - the neoventors - on almost all the continents. This is a bit of a mystery because the continents were getting spread out by 99 million years, making it tough to explain how the neovenators conquered the world. In North America, this global dynasty replaced another family of giants: the carcharodontosaurs which included Acrocanthosaurus the top carnivore of the Early Cretaceous of Western and Eastern North America. The discovery of Siats shows different lineages of carnivorous dinosaurs could get really big and T. rex is just the last monarch to fill the giant carnivore niche in North America. It’s another toothy, terrifying tale on Past Time!

Tyrannosaurus rex is a dinosaur celebrity, a villain in most dinosaur movies and documentaries, but where did the massive beast come from? On November 6, 2013, a team of paleontologists including our expert in this episode, Dr. Randy Irmis from the University of Utah and the Natural History Museum of Utah, published two new skeletons of Tyrannosaurus’s close kin: Teratophoneus and Lythronax. The skeletons reveal Tyrannosauridae (T. rex’s family) was diverse 80 million years ago with different species living in different parts of Western North America. The new genus Lythronax is the oldest member of the Tyrannosauridae even though its anatomy closely resembles the last species of tyrannosaurid, T. rex. A massive sea divided Western North America, called Laramidia, from Eastern North America, called Appalachia. Laramidia was a long, skinny continent that ran from Alaska to Baja California. In general, in modern ecosystems, the larger the land-mass, the more species can live on it. Laramidia was one-tenth the size of the continent of North America, but it supported more species of large animals than the complete continent of North America today! Geologists, paleontologists, and ecologists aren’t sure how this was possible so they continue to search for new fossils and the origins of the North American ecosystem. New fossils, like Teratophoneus and Lythronax show us there are still more questions to answer using the fossil record! Sic semper tyrannis!

Fossils are the raw materials of paleontology, but if we want to know how an animal moved or ate, paleontologists, like Dr. Paul Gignac, need to study living animals, too. Dr. Gignac studies crocodylians, measuring their bite forces across species and as they grow up to figure out how the strongest bite in nature evolved. Using techniques drawn from mechanical engineering and physiology, Dr. Gignac discovered the relationship between body size and bite force in crocodiles, and developed equations to calculate those forces. Then he used these equations to calculate the bite forces of giant extinct crocodiles like Deinosuchus. He also studied the bite marks left by the sickle-clawed dinosaur Deinonychus to calculate dinosaur bite forces. There are so many questions to ask about extinct animals but there's also a lot left to learn about their living descendants! The lines between scientific disciplines get blurred and the questions just get more interesting in this episode of Past Time!