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Amargasaurus cazaui, from Argentina's late Jurassic period, may be familiar to some of you who played the latest generation of the Pokemon games. Amaura and Aurorus were based off of this species of sauropod, which carries twin rows of spikes down its neck. It was formerly thought that these spikes supported sails of skin, but analyses have shown that if that was the case, Amargasaurus' sails would have rendered its neck inflexible, making it unlikely. Instead, they were probably free spines, and would have served the sauropod well both for display and also for intimidation and defense. One paleontologist has even suggested that the spikes, which were probably covered in a thick sheath of keratin, could have been used as a sound display. The Amargasaurus could shake its neck and cause the spikes to rattle against each other, creating a clacking sound not unlike a very large set of bamboo chimes.
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Magyarosaurus dacus is a sauropod from a heavily-forested island that is now part of modern-day Romania. As we see today in many island animals, the restricted size of the terrain led to a reduced size in its inhabitants, including these pygmy sauropods, no taller than today's horses and weighing a mere one ton. Magyarosaurus, like its close relatives around the world at the time, had an armor-plated back. Underneath its skin were osteoderms - large bony scutes that formed in rows. In addition to being armor, these osteoderms could be dissolved from the inside and made hollow, the calcium forming them recycled to become eggshells during the breeding season.
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An exposed slab of late Jurassic mudstone north of Moab, Utah reveals a unique scene of a potential interaction between a few dinosaurs. A large sauropod, possibly a Camarasaurus, turns mid-stride, apparently reacting to a smaller theropod running nearby. A few yards away, an Allosaurus leaves the site with an irregular stride, possibly the result of a limp. Was this a site where an adult Allosaurus and a juvenile tried to tackle a Camarasaurus and were driven off after a conflict? Or was the smaller theropod running past after something else that caused the Camarasaurus to turn and watch it warily as it ran by? There's no way for us to know what the order of these events were, or what even the exact event was, but it lends nicely to some interesting speculation.

Below, photos of the trackway from my visit this morning. )

I will be home tomorrow, so soon we will be back to my regular level of detail in these drawings, or so I hope!
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Last week, a paper was published in PLOS Biology by a team of Oxford scientists who, based on skeletal measurements, calculated the masses of 426 species of dinosaur. The largest, Argentinosaurus, was a massive sauropod weighing in at roughly 90 tons, while the smallest they measured was Qiliania, an Enantiornithine bird that weighed 15 grams, making the weight of the largest dinosaur 6 million times the weight of the smallest non-extant known species (the smallest-ever dinosaur known is the Bee Hummingbird of Cuba which weighs 2 grams). It's suspected that size played a large role (no pun intended) in the survival of the maniraptorans past the mass extinction 65 million years ago, as the smallest dinosaurs may have been able to avoid the worst effects of the asteroid impact by being more generalist, requiring fewer resources, and/or being able to exploit niches not available to larger species.

Update: today (5/16/14) a team of paleontologists in Argentina announced they've found a new sauropod species that may be even bigger than Argentinosaurus, and estimate its weight at 100 tons. Should be interesting to see what comes of this new discovery.

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Lauren Helton

September 2014

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