Episode 50 is all about Hesperosaurus, one of many oldest stegosaurs from the Morrison Formation.
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On this episode, we talk about:
- The dinosaur of the day: Hesperosaurus
- Identify means “western lizard”
- Lived within the Jurassic
- Fossils first present in 1985, in Wyoming
- Patrick McSherry, a fossil hunter, discovered the fossils on a ranch in Wyoming. However he had some hassle digging up the bones as a result of laborious rock, so he bought assist from Ronald G. Mjos and Jeff Parker from Western Paleontological Laboratories. In addition they labored with Dee Corridor, a paleontologist from Brigham Younger College
- At first they thought the bones had been Stegosaurus, however Clifford Miles, who ready the fossils, discovered they had been a brand new species
- Kind species is Hesperosaurus mjosi, named in 2001
- Kind species described in 2001 by Kenneth Carpenter, Clifford Miles, and Karen Cloward
- Named “western” as a result of it was discovered within the western United States. Named “mjosi” to honor Ronald Mjos, who additionally had a forged made, which you’ll be able to see within the Denver Museum of Pure Historical past
- In 2001, the holotype was the oldest recognized stegosaur in America
- Holotype included an almost full cranium, and a lot of the physique (13 neck vertebrae, 13 again vertebrae, 3 sacrals, 44 tail vertebrae, neck ribs, dorsal ribs, chevrons, left shoulder blade, pelvis, ossified tendons, and 10 neck and again plates (shaped in 2 rows)
- Based mostly on healed fractures, the holotype was an outdated Hesperosaurus particular person
- A part of the stegosaur household, however one of many older stegosaurs within the Morrison Formation
- Shut relative of Stegosaurus, and like Stegosaurus it had two rows (most likely alternating) of plates on its again and 4 spikes on its tail (thagomizers, informally)
- Informally the tail spikes are referred to as thagomizers, after a Gary Larson “Far Aspect” cartoon was printed in 1982 exhibiting cavemen calling the spikes thagomizers (line was “Now this finish is named the thagomizer…after the late Thag Simmons”)
- Plates weren’t as tall as Stegosaurus, however probably longer
- Cranium was deeper than Stegosaurus
- Kenneth Carpenter initially stated Hesperosaurus was a basal stegosaur. However in 2008, Susannah Maidment and colleagues printed a research that confirmed it was a derived kind, and an in depth relative of Stegosaurus and Wuerhosaurus. They stated it ought to be thought of to be a species of Stegosaurus (Stegosaurus mjosi as an alternative of Hesperosaurus mjosi); and renamed Wuerhosaurus to Stegosaurus homheni. However this controversial and never everybody agrees (Carpenter and Christiansen each individually rejected this in 2010, saying Hesperosaurus was completely different sufficient to be its personal genus)
- Carpenter disagreed as a result of he thought that the kind species of Stegosaurus, Stegosaurus armatus, as a result of he thought of Stegosaurus armatus to be a nomen dubium, and rejected lumping all Stegosaurus fossils from North America into one species. He additionally thought that S. stenops was a separate species and in contrast Hesperosaurus to S. stenops. Variations he discovered embrace Hesperosaurus having a big antorbital fenestra, a brief and deep maxilla, 13 neck vertebrae as an alternative of 10, 13 dorsal (again) vertebrae as an alternative of 17, and oval formed plates as an alternative of triangular plates
- Revealed descriptions of Hesperosaurus fluctuate although, attributable to completely different interpretations. Plate form might differ attributable to erosion, the completely different numbers of vertebrae could also be attributable to whether or not a number of the vertebrae ought to be a part of the neck or again
- In 2012 an histological research discovered that Hesperosaurus osteoderms had been the identical as these in Stegosaurus (CAT-scans confirmed the plates having skinny, dense outer partitions, with spongy bone inside, and the spikes had thicker partitions and spongy interiors with a single giant blood vessel)
- In 2010, a research on the smooth seen elements of the “Victoria” specimen discovered the primary proof {that a} stegosaur had a horn sheath on the plates, which can imply the plates had been used for protection (because the horn sheath would have strengthened the plate and given it sharp chopping edges); additionally reinforces the show principle as a result of the sheath elevated the plates’ seen floor, and sheaths are often brightly coloured
- However thermoregulation would have been tougher, because the horn sheath supplies one other insulating layer and it has a easy floor, however fashionable cattle and geese use horns and beaks to assist settle down, even with their horn sheaths
- A number of fairly full skeletons of Hesperosaurus have been discovered
- Since 1995 Hans Jacob Siber, a Swiss paleontogist, excavated stegosaur specimens in Wyoming. As of 2001, 3 different Hesperosaurus specimens have been discovered there (at first they had been regarded as Stegosaurus): “Moritz” (present in 1995, a partial skeleton) “Victoria” (additionally present in 1995, not reclassified till 2010 by Nicolai Christiansen, and has pores and skin and horn sheath impressions in addition to a largely full cranium); “Lilly” (present in 2002 and named after the sisters Nicola and Rabea Lillich who volunteered to assist excavate); all three are actually a part of the Aathal Dinosaur Museum assortment in Switzerland
- Not all 3 Swiss specimens have but been formally described
- Nicolai Christensen and Emanuel Tschopp described “Victoria” (discovered within the Howe-Stephens quarry, the place different smooth tissue impressions have been discovered)
- When Victoria died, she was partially buried, after which utterly buried by a second stream of sediment, preserving parts on her proper facet
- Had sufficient smooth tissue impressions to point out it had a honeycomb scale sample on its pores and skin (additionally seen in hadrosaurs and one different stegosaur, from Asia, Gigantspinosaurus)
- Scale sample will not be uniform, however is completely different relying on a part of the physique (bigger, domed scaled are surrounded by smaller ones on its again)
- Concluded there is a plate/horn sheath primarily based on it having a easy plate with shallow grooves (although not 100% confirmed)
- In 2015, extra Hesperosaurus specimens had been discovered (a minimum of 5 in Montana)
- The specimens present in 2015 confirmed that Hesperosaurus (generally known as Stegosaurus mjosi) confirmed sexual dimorphism. Evan Thomas Saitta printed a research that confirmed there have been two varieties of plates
- The paper, “Proof for sexual dimorphism within the plated dinosaur Stegosaurus mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Higher Jurassic) of Western USA,” was printed April 22 in PLoS ONE
- Specimens discovered with two varieties of plates (giant and spherical v. tall and spiky) weren’t completely different species however completely different gender
- Evan Saitta, lead writer stated the big vast plates had been most likely from males (for show), and the tall spiky ones had been from females (used as deterrents)
- They had been discovered collectively, which exhibits they most likely co-existed, and the plates had comparable development rings (so the dinosaurs had been across the similar age, and it’s not that the plates modified with age)
- Hesperosaurus was 20-23 ft (6-7 m) lengthy and 2-3 tons
- Quick, vast head
- Had 20 maxillary enamel on head facet (fewer than Steogsaurus), although comparable (however bigger)
- In 2007 Peter Malcolm Galton wrote that Hesperosaurus enamel had been completely different, attributable to having tough vertical ridges on the higher a part of the crown, and weakly developed advantageous grooves on the tooth floor
- Herbivore, most likely ate moss, cycads, conifers, ferns, horsetails
- Stegosaurs had been first round in Asia within the center to late Jurassic, after which migrated to North America a couple of million years later
- Predators included Ceratosaurus and Allosaurus
Some assume Hesperosaurus is extra intently associated to Dacentrurus (a stegosaur from Europe) as an alternative of Stegosaurus - Stegosauridae is a household that lived within the Jurassic and Cretaceous
- They’ve rows of osteoderms (plates) and thagomizers on their tails
- Might have been used for show, protection, and/or thermoregulation
- Gradual, as a result of their entrance legs had been shorter than rear legs, however giant and highly effective
- Two subfamilies: Dacentrurinae and Stegosaurinae
- Stegosaurinae are usually bigger (earliest one is Lexovisaurus from England)
- Dacentrurinae have lengthy again spines and necks
- Dacentrurinae contains Dacentrurus and stegosaurs extra intently associated to Dacentrurus than Stegosaurus, akin to Hesperosaurus and Miragaia
- Enjoyable Truth: The quickest animal to ever reside is technically a dinosaur: the peregrine falcon, which reaches high speeds of 240 mph.