Jun. 5th, 2014

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Didn't quite have time to finish last night, so here it is this morning. This is Edmontosaurus annectens, one of the best-known dinosaurs in existence. On top of having found hundreds of very complete skeletons of adults and juveniles, we have a few very complete mummies as well, which have allowed us to know the skin texture (loose and scaly, with round tuberculous scales more like a gila monster than a snake), and diet (lots of seeds, conifers and gymnosperms, based on gut contents and isotope ratios in the teeth). We have skeletons that show signs of scar tissue, damaged vertebrae and hips, and tooth marks, showing that they were preyed upon by large tyrranosaurs, as well as skeletons that show bone damage from other ailments such as cancer. Skeletons have been found from Alaska to Colorado, a huge range for any dinosaur, and some have suggested they may have been migratory like today's caribou, heading south to avoid the arctic winters. Their front toes were even developed into hoof-like structures, with the hard-scaled skin fully enclosing flattened toe bones. And they definitely lived in herds, some of which may have numbered thousands of Edmontosaurs.

Despite everything we do know, we're still finding out new information about this and other Edmotosaurus species. At the end of 2013, one specimen was discovered that preserved impressions of soft tissue around the head, which revealed for the first time that Edmontosaurus had a fleshy rooster-like comb on top of its head - something we never could have seen from skeletons alone. Just one more reminder of how little we know, even when it comes to a species we think we know so much about.
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Pterodaustro guinazui is a Cretaceous pterosaur from South America. A filter-feeder, it possessed thousands of small teeth on its lower jaw that functioned similarly to baleen in today's whales, allowing it to sift through shallow water and mud to find krill, crustaceans, small clams, and other aquatic foods. This is one of the best-known pterosaurs, with every growth stage from egg to adult known from hundreds of fossils. This is the only pterosaur that swallowed stones like some of today's birds do, likely to help grind down the shells of their prey. They also were likely nocturnal, based on similarities between the scleral rings - the bone scaffolding for the eye in many reptiles and birds - of this species and nocturnal birds today.

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Lauren Helton

September 2014

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