Channels, Spring 2018

Channels • 2018 • Volume 2 • Number 2 Page 71 Kangaroos, while the lightness and strength of the great femur and tibia are altogether appropriate to great powers of leaping. (Cope, 1868) Leidy and Cope’s claim of a semi-erect posture of their dinosaurs spread across the pond to Europe, and the four-legged Megalosaurus and Iguanodon eventually gained the same semi- erect stance. This idea of a semi-erect posture for Iguanodon was further supported by the work of Louis Dollo. Dollo’s upright posture was based on a comparison of anatomical characteristics with birds of the class palaeognathae (flightless birds). The strongest basis for his argument came from a fossil trackway found within the same strata as Iguanodon . The animal that left the tracks walked bipedally. To test his hypothesis, he placed the middle digit of an Iguanodon foot into a cast of the fossil tracks, and found that it was a perfect fit. Dollo concluded that the footprints belonged to Iguanodon , and that it did not use its tail as a prop like a kangaroo. Instead, the tail dragged along the ground, “and the impression [from the tail] thus formed was certainly very weak because it has not been preserved. (Dollo, 1883)” Dinosaurs took to their feet becoming less like kangaroos, and more like their tail dragging cousins reptiles (Figure 3). The Start of a Crisis: John Ostrom Questions the Paradigm Most paleontologists at the time still viewed dinosaurs as cold-blooded lizards in need of tropical climates to thrive. Because of their large size they were considered to be sluggish, dim-witted, and probably swamp-dwelling in the case of many herbivorous dinosaurs. This was primarily due to Owen’s creation of the dinosaurian clade within reptilia. His idea that dinosaurs were “terrible lizards” kept them from being seen as anything more than just massive reptiles. This would continue to be the consensus for more than a century. Then in 1960’s, John Ostrom began to “drain the swamps of dinosaurs.” He began with hadrosaurs, which were thought to be snorkeling creatures with a crocodile-like tail that would feed on the abundance of aquatic vegetation. Ostrom used the locations where hadrosaur fossils were found. Most other dinosaur fossils were found in deposits interpreted to be coastal plains with swamps and meandering streams. He found that the fossil flora within hadrosaurian-bearing strata was more consistent with conifer forests than vast swamps with aquatic vegetation. He also noticed that hadrosaurs had an amazing tooth structure and tooth battery. Teeth were constantly being replaced and grinding patterns on the teeth suggested that these animals were eating fibrous materials. Ostrom also found an unfamiliar paper that described the gut contents of a “mummified” hadrosaur Anatosaurus (now Edmontosaurus annectens ). The contents, “revealed the abundant presence of conifer needles…and twigs, seeds, and fruits of other land plants. (Ostrom, 1964)” He also pointed out the ossified tendons that occur in the dorsal and caudal portions would reinforce the tail too much. The tendons would not allow for smooth movement like a crocodile’s tail, and in fact, they would restrict its movement. Hadrosaurs became terrestrial creatures, and the lugging around of their bulky tails was envisioned as off the ground. Dinosaurs were slowly changing from lethargic swamp-residing beasts to being more active, but they were still considered cold-blooded lizards.