Episode 457: Beyond Bones: Dinosaur Soft Tissues. Dinosaur bones are some of the most famous fossils. But dinosaur skin, feathers, blood vessels, tendons, and even organs have been found in the fossil record.

Here are a couple recent papers describing how and where soft tissue preserves:

• Researchers found the most common chemical mechanisms for soft tissue preservation source
• How minerals in the Burgess Shale contributed to some of the best soft tissue preservation found anywhere in the world source

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The dinosaur of the day: Chilesaurus

• Dinosaur that lived in the Late Jurassic (~150 mya) in what is now Chile (Toqui Formation)
• Looked like other early dinosaurs, walked on two legs, had a long tail, long(ish) neck, and long body (think of Massospondylus or Eodromaeus)
• Estimated to be about 10.5 ft (3.2 m) long
• Has been called a platypus dinosaur
• Had a combination of features seen in theropods, ornithischians, and sauropodomorphs
• Had a theropod-like body
• Not that great of a runner (based on features in the shinbone, and having a broad foot with a weight-bearing first toe)
• Had stout limb bones, like sauropodomorphs
• Had strong arms, with a large first claw similar to basal sauropodomorphs
• Had grasping hands
• Had three short, thick fingers with two claws
• Herbivorous
• Had “spatula-shaped” teeth or leaf shaped teeth
• Had ornithischian-like (bird-like) hips. Had a backward facing pubic bone, which would give it room for a large gut (good for plant eaters)
• Had a slender neck
• Had a proportionally small head
• Had a rounded skull
• Probably had a beak
• Type species is Chilesaurus diegosuarezi
• Named in 2015 by Fernando Novas and others
• Fossils found in 2004 by Diego Suárez, a then 7-year-old who with his geologist parents Manuel Suárez and Rita de la Cruz and his sister Macarena were hiking (he found a vertebra and a rib)
• Genus name means “Chile lizard”
• Genus name refers to Chile
• Species name is in honor of Diego
• More fossils reported in 2008, thought to be “the first significant remains of carnivorous dinosaurs” in Chile (from the Jurassic)—previously known from isolated teeth from the Late Cretaceous
• Holotype is an articulate, pretty complete skeleton of a juvenile (missing feet and most of the tail)
• Four other partial skeletons and additional bones of juveniles and adults found
• Holotype is about 50% the length of the largest individual found (about 5.2 ft or 1.6 m long)
• First complete dinosaur found that lived in the Jurassic in what is now Chile
• Novas and others said that “Chilesaurus is a unique dinosaur lineage known only from southern South America, suggesting an outstanding case of endemism among otherwise relatively cosmopolitan worldwide Jurassic dinosaur faunas”
• Originally thought to be a tetanuran theropod (clade that includes megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans)
• In 2017, Matthew Baron and Paul Barrett found Chilesaurus to be the “earliest diverging member of Ornithischia”, and Chilesaurus was an early ornithischian after splitting from Ornithoscelida
• Baron and Barrett proposed Chilesaurus was a missing link between carnivores and early herbivores
• Ornithoscelida groups together ornithischians and theropods
• Ornithoscelida not really talked about anymore, and seems the latest is more that silesaurs evolved into ornithischians
• Not sure what to consider it (maybe still ornithischian?)
• Had some interesting features that upended what paleontologists thought when it came to when certain features evolved
• Did not have a predentary bone (bone at the tip of the bottom jaw), which had previously been thought to be a fundamental feature of ornithischians
• Didn’t have teeth in the front of its snout, and had support for a beak, which may mean ornithischians were already adapted to an omnivore or herbivorous diet before they had a predentary bone
• Did have a backward facing pubis
• Possible the pubis position is related to it being an herbivore, and related to dinosaurs evolving longer, more complex digestive tracts
• Sauropodomorphs did not have the backward pubis, “which may have condemned them to quadrupedality as any expansion of the gut anterior to the hips would have resulted in an anterior shift to the centre of mass” according to Baron and Barrett
• In 2017 Nicolas Chimento and others studied the forelimb posture of Chilesaurus
• All the skeletons found were preserved in a way that looks like the resting posture of Mei long and other dinosaurs that look to be resting, like Sinornithoides and Albinykus
• Arms are flexed toward the body and hands facing backwards
• But hindlimbs are extended out
• Seems the Chilesaurus individuals were buried quickly and fossilized in a life position while eating or resting (probably not sleeping)
• In advanced theropods, has been suggested that the resting posture of the arms is related to soft tissue structures like the propatagium (largest skinfold of the wing)
• Chilesaurus’ flexed arm may indirectly indicate it had propatagium, an important feature for flying
• Not saying Chilesaurus could fly, but may have had features early on linked later to flying
• Other animals that lived around the same time and place include sauropods like diplodocids and titanosaurs, and crocodyliforms

Fun Fact:

Three paleoartists influenced decades of how dinosaurs were depicted in comics and other media.

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