Read Online Dinosaurs Without Bones by Anthony J. Martin - Free Book Online Page A
Authors: Anthony J. Martin
Ads: Link
fossil record (Late Triassic) to their very end (Late Cretaceous). Something noteworthy about these sauropod trackways found thus far, though, is that nearly all show these massive animals walked on emergent surfaces, such as along coastlines, lakeshores, or river floodplains.
Still, paleontologists wondered: What if dinosaurs other than hadrosaurs or sauropods went for a swim? How would we know from looking at their bones? For example, even the most skilled anatomists would be hard pressed to demonstrate from an elephant’s skeleton that these multi-ton animals are capable of swimming long distances. Yet Indian elephants ( Elephas maximus ) canswim as far as 25 miles (40 km), a feat far better than most humans are capable of. In fact, elephant swimming abilities show one of the probable ways mammoths dispersed to islands during the Pleistocene Epoch, where some isolated populations lasted until only about 4,000 years ago. (These elephants also became much smaller after generations of living on these islands, leading to the oxymoronic condition of becoming “dwarf mammoths.” But that’s another story.)
Just in case you were wondering whether trace fossils might come to the rescue again to solve this dinosaurian mystery, you would be right (again). First, as early as 1980, a paleontologist interpreted swim tracks from Early Jurassic rocks of Connecticut as made by theropods, and provided a fine argument as to how such dinosaurs would have made these tracks while partially buoyed by water. More than twenty years later, in 2001, paleontologists working in separate studies and places (Wyoming and the U.K.) interpreted Middle Jurassic tracks as possible dinosaur swim tracks. Soon after that (2006), hundreds of much better examples were discovered and documented by Andrew Milner in Early Jurassic rocks of southwestern Utah at and near the St. George site that also has the dinosaur-sitting traces mentioned earlier. The next year (2007), dinosaur swim tracks were again interpreted from long linear marks on an expansive surface of Early Cretaceous rock in Spain. In 2013, yet more dinosaur swim tracks were reported from another Early Cretaceous site in Queensland, Australia. Suddenly, dinosaurs seemed to be swimming everywhere.
How would you know whether a dinosaur was swimming by looking at its tracks? Well, for one thing, you wouldn’t know it at all unless its feet touched the bottom of the water body it crossed. If the water were too deep, buoyancy would have kept dinosaur bodies—along with their feet—above any sediment surface that would have recorded their tracks. But through a combination of legs long enough to reach the bottom and water shallow enough to allow this, they would have made tracks.
Why should a dinosaur swim at all? Or as an actor might ask, what was their motivation? Getting from one place to another is alikely reason, instead of walking around a shallow lake or stream, or the old “to get to the other side” answer. Yet another argument relates to their attraction to aquatic environments as great sources of food. For theropods, this might have been fish, but other aquatic animals also might have served as tasty treats. For hadrosaurs and sauropods, though, which were (as far as we know) all herbivores, this is not such a good explanation. Not surprisingly, recreational purposes have never been suggested for swimming dinosaurs, but who knows whether an occasional dip might have also relieved any dinosaurs suffering from skin parasites or a hot day in the Mesozoic.
The Not-So-Secret Social Lives of Dinosaurs
Tracks also tell us about dinosaur social lives, and thanks to these trace fossils we are confident that many dinosaur species moved together as herds, packs, flocks, congresses, murders, or whatever group name seems appropriate. Assemblages of dinosaur bones composed of many individuals but only representing one species also support this idea, and we now take for granted that the stereotype of
Still, paleontologists wondered: What if dinosaurs other than hadrosaurs or sauropods went for a swim? How would we know from looking at their bones? For example, even the most skilled anatomists would be hard pressed to demonstrate from an elephant’s skeleton that these multi-ton animals are capable of swimming long distances. Yet Indian elephants ( Elephas maximus ) canswim as far as 25 miles (40 km), a feat far better than most humans are capable of. In fact, elephant swimming abilities show one of the probable ways mammoths dispersed to islands during the Pleistocene Epoch, where some isolated populations lasted until only about 4,000 years ago. (These elephants also became much smaller after generations of living on these islands, leading to the oxymoronic condition of becoming “dwarf mammoths.” But that’s another story.)
Just in case you were wondering whether trace fossils might come to the rescue again to solve this dinosaurian mystery, you would be right (again). First, as early as 1980, a paleontologist interpreted swim tracks from Early Jurassic rocks of Connecticut as made by theropods, and provided a fine argument as to how such dinosaurs would have made these tracks while partially buoyed by water. More than twenty years later, in 2001, paleontologists working in separate studies and places (Wyoming and the U.K.) interpreted Middle Jurassic tracks as possible dinosaur swim tracks. Soon after that (2006), hundreds of much better examples were discovered and documented by Andrew Milner in Early Jurassic rocks of southwestern Utah at and near the St. George site that also has the dinosaur-sitting traces mentioned earlier. The next year (2007), dinosaur swim tracks were again interpreted from long linear marks on an expansive surface of Early Cretaceous rock in Spain. In 2013, yet more dinosaur swim tracks were reported from another Early Cretaceous site in Queensland, Australia. Suddenly, dinosaurs seemed to be swimming everywhere.
How would you know whether a dinosaur was swimming by looking at its tracks? Well, for one thing, you wouldn’t know it at all unless its feet touched the bottom of the water body it crossed. If the water were too deep, buoyancy would have kept dinosaur bodies—along with their feet—above any sediment surface that would have recorded their tracks. But through a combination of legs long enough to reach the bottom and water shallow enough to allow this, they would have made tracks.
Why should a dinosaur swim at all? Or as an actor might ask, what was their motivation? Getting from one place to another is alikely reason, instead of walking around a shallow lake or stream, or the old “to get to the other side” answer. Yet another argument relates to their attraction to aquatic environments as great sources of food. For theropods, this might have been fish, but other aquatic animals also might have served as tasty treats. For hadrosaurs and sauropods, though, which were (as far as we know) all herbivores, this is not such a good explanation. Not surprisingly, recreational purposes have never been suggested for swimming dinosaurs, but who knows whether an occasional dip might have also relieved any dinosaurs suffering from skin parasites or a hot day in the Mesozoic.
The Not-So-Secret Social Lives of Dinosaurs
Tracks also tell us about dinosaur social lives, and thanks to these trace fossils we are confident that many dinosaur species moved together as herds, packs, flocks, congresses, murders, or whatever group name seems appropriate. Assemblages of dinosaur bones composed of many individuals but only representing one species also support this idea, and we now take for granted that the stereotype of
Similar Books
