Scientists make tracks on dinosaur claw function
Paleontologists at the Cleveland Museum of Natural History and Dickinson Museum Center (North Dakota) have just published new research describing the behavior of sauropod dinosaurs, the largest animals to ever walk the earth. Sauropods, like the museum's own Haplocanthosaurus, are famous for their size, but it is their unusual feet that caught the interest of researchers.
Several competing hypotheses, or scientific questions, have been proposed. One, the "substrate grip" hypothesis, proposed that the overlapping claws would have been employed in slippery, muddy environments like river banks or lakeshores, providing traction and prevent miring. Another, the "scratch digging" hypothesis, suggested that the claws would have formed an effective scraper, like a garden hoe, and would have been utilized for excavating nests. Both hypotheses were plausible, until scientists looked at a new line of evidence.
The eureka moment for the research group came when they considered alternative ways to test their hypothesis. "Prior studies have tried to answer this question by examining the bones of sauropod feet, but no one looked at the tracks those feet left," said Hall. Trackways are the fossilized impressions left by an animal's feet after it walked through soft, wet sediment like mud or silt. "We studied over 30 tracks, all of which preserve the morphology of the foot and position of the claws while these animals were walking in muddy substrates. In some cases, impressions of the skin and scales from the bottoms of the feet are visible."
Hall and his coauthors Ashley Hall (also of the Cleveland Museum of Natural History), and Dr. Denver W. Fowler (Dickinson Museum Center, North Dakota), reached out to researchers across the world for images of well-preserved sauropod tracks, and received a wealth of data and photographs from Texas, to Morocco, to Portugal.
The fossil tracks showed that sauropods did not utilize their unique claw flexing arrangement while walking in deep, wet mud, meaning they did not use them to help 'grip' while walking in muddy areas. Instead, the toes were either carried in a neutral position or extended outwards, which was unexpected. The study concludes it is more likely that the claws of sauropods were an adaptation for excavating nests, a behavior corroborated by comparison with similarly shaped claws used by some species of tortoises for digging, and fossil evidence of trench-like nests in which sauropod eggs have been discovered.
Fowler added "surely the most exciting thing about dinosaurs is understanding how they lived; our new study takes us one step closer."
Photos courtesy of Cleveland Museum of Natural History.
Source: Cleveland Museum of Natural History [November 30, 2016]