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Fossilized Footprints Lead Scientists Down a Prehistoric Path

journal.pone.0103255.g008_rotaWhether tromping alone or running in a pack, all prehistoric creatures got around somehow. Paleontologists can use fossilized bones to learn more about what dinosaurs ate, what they looked like, and even how they might have moved, but bones are only part of the “rocky” story. We can study fossils of all shapes, sizes, and sources to piece together missing information about how these creatures moved, interacted, and lived. Trace fossils, which include fossilized impressions like footprints and belly drag marks left in the ground, can tell us a surprising amount about how animals of the past lived and moved. They are more common than you might think, but typically aren’t studied as often as fossilized bones. PLOS ONE recently published two separate studies where authors used trace fossils to provide insight on tyrannosaurs social life and the slow and slithering movements of an ancient temnospondyl, bringing two prehistoric creatures to ‘life.’

Walking Buddiesjournal.pone.0103613.g002

Many tyrannosaur bones have been collected and documented, but few scientists have studied their footprints. In a new PLOS ONE study, researchers found three 75 million-year-old three-toed tyrannosaurid footprint with claw marks tracks heading southeast within an 8.5 meter-wide corridor in British Columbia, Canada (shown in the image above). Scientists took molds and measurements of the prints (shown in the image below) to understand the track-makers’ behavior. Scientists aren’t sure exactly which species of tyrannosaur made the prints, but similarities in depth and preservation of the tracks indicate that these three trackways were made by dinosaurs walking alongside journal.pone.0103613.g007each other in the same direction at a normal pace, around 8.50 kilometers per hour.

These trackways add to previous research about tyrannasaurid social behavior and locomotion, but the authors acknowledge that there is the possibility, although unlikely, that three dinosaurs could have passed through the same spot separately within a short period of time. Either way, the tracks make up the first record of the walking gait of tyrannosaurids and provide insight about how they moved across Western Canada.

Mysterious Slithering

A 200 million-year-old mysterious trackway, called Episcopopus ventrosus, in southern Africa may have been made by a dinosaur, or maybe by an early ancestor of the crocodile. Researchers that mapped, cast, and laser-scanned the best-preserved part of the journal.pone.0103255.g003Episcopopus ventrosus trackway found that the track belongs to a primitive amphibian-like animal from one of the earliest groups of limbed vertebrates, temnospondyls. The author’s estimate the track-maker was 3.5 meters long and dragged the hind portion of its body along a wet sand bar on the bank of a river bend, using only the claw-less tips of its digits (pictured above).

The movements were likely made by a large-headed, slithering, and slow-moving amphibian-like animal. Researchers usually use hind-limb-driven salamanders as a model for temnospondyl locomotion, but this discovery is causing researchers to re-examine their use of salamander models for this front-limb-driven temnospondyl.

Socializing and Slithering

From signs of dinosaurs moving in packs to amphibian-like animals slithering across river banks, trace fossils can support what we already know about prehistoric creatures, but they can also shake up the assumptions we’ve made, and in the case of the tetrapod, potentially change the way we study them. Fossilized bones may still be the better known field of study, but footprints and other trace fossils may help shape our understanding of patterns, reconstructing of past lives, and bringing of prehistoric animals back to “life.”

Citation: McCrea RT, Buckley LG, Farlow JO, Lockley MG, Currie PJ, et al. (2014) A ‘Terror of Tyrannosaurs’: The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae. PLoS ONE 9(7): e103613. doi:10.1371/journal.pone.0103613

Marsicano CA, Wilson JA, Smith RMH (2014) A Temnospondyl Trackway from the Early Mesozoic of Western Gondwana and Its Implications for Basal Tetrapod Locomotion. PLoS ONE 9(8): e103255. doi:10.1371/journal.pone.0103255

Images: All images are from the published manuscripts Figure 8, Figure 2, Figure 7, and Figure 3.

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