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Saturday, February 20, 2016

Plecerias Hesternus, Petrified Forest National Park, Holbrook, Arizona


A Plecerias hesturnus in the Petrified Forest National Park visitor center in Holbrook, Arizona, seems to lunge right at you, whether to bite you or lick you is uncertain.
Plecerias hesternus looks like a big, happy dog lunging in for a slobber. To me, anyway. Described as “mammal-like,” Mr. P. hesternus’ kin got up to about 11.5 ft. long (3.5 m) and weighed up to about 2,200 lbs. (1,000 kg). They were aquatic herbivores, and paleontologists think their ecological niche was similar to a modern hippopotamus.
Drawing of P. hesternus compared to human in size
Credit Dr. Jeff Martz/NPS

Placerius hesternus is just one of many dinosaurs found at Petrified Forest National Park. There are other kinds of Triassic fossils found there, too: crayfish, ancient crocodile-like creatures, ferns, giant amphibians, and more. There are archaeological sites as well, not to mention that the painted desert is just gorgeous.

Of course, the park is justly famous for it’s petrified wood. But I was intrigued to learn that the “forest” isn’t really an ancient forest. According to the little movie I watched at the southern visitor center, the logs fell into a river or rivers during flooding. They wound up in a swamp downstream, got waterlogged, and sank to the bottom. There, muck, clay, sand, and volcanic ash covered and preserved them (kind of like how the Chinese make century eggs). Over time, the cellular structures were replaced by various kinds of crystals formed from minerals in the groundwater.

Oh, you were expecting photos of the petrified wood, maybe? Sure, I’ve got them in spades. Sign up below for my trip letters, and I’ll share some with you. I’ll also share a photo of the wash where I left a milkweed seed ball in Liz’s honor.



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Here’s a video with more about Petrified Forest National Park’s dinosaurs.