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I Know Dino Podcast: Hesperosaurus

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    Episode 50 is all about Hesperosaurus, one of many oldest stegosaurs from the Morrison Formation.

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    On this episode, we focus on:

    • The dinosaur of the day:  Hesperosaurus
    • Title 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 bother digging up the bones because of the exhausting rock, so he acquired assist from Ronald G. Mjos and Jeff Parker from Western Paleontological Laboratories. Additionally they labored with Dee Corridor, a paleontologist from Brigham Younger College

    • At first they thought the bones have been Stegosaurus, however Clifford Miles, who ready the fossils, discovered they have 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 many 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 (fashioned 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    • Based mostly on healed fractures, the holotype was an outdated Hesperosaurus particular person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 revealed in 1982 exhibiting cavemen calling the spikes thagomizers (line was “Now this finish is known as the thagomizer…after the late Thag Simmons”)
    • Plates weren’t as tall as Stegosaurus, however presumably longer
    • Cranium was deeper than Stegosaurus

    • Kenneth Carpenter initially stated Hesperosaurus was a basal stegosaur. However in 2008, Susannah Maidment and colleagues revealed a examine that confirmed it was a derived type, and a detailed relative of Stegosaurus and Wuerhosaurus. They stated it must 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
    • Printed descriptions of Hesperosaurus range although, as a result of completely different interpretations. Plate form could differ as a result of erosion, the completely different numbers of vertebrae could also be as a result of whether or not among the vertebrae must be a part of the neck or again

    • In 2012 an histological examine discovered that Hesperosaurus osteoderms have 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 examine on the tender seen components of the “Victoria” specimen discovered the primary proof {that a} stegosaur had a horn sheath on the plates, which can imply the plates have been used for protection (for the reason that horn sheath would have strengthened the plate and given it sharp slicing edges); additionally reinforces the show idea as a result of the sheath elevated the plates’ seen floor, and sheaths are normally brightly coloured
    • However thermoregulation would have been harder, for the reason that horn sheath offers one other insulating layer and it has a clean floor, however trendy cattle and geese use horns and beaks to assist quiet 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 have 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 principally 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 tender tissue impressions have been discovered)
    • When Victoria died, she was partially buried, after which fully buried by a second movement of sediment, preserving components on her proper aspect
    • Had sufficient tender 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 clean plate with shallow grooves (although not 100% confirmed)
    • In 2015, extra Hesperosaurus specimens have been discovered (a minimum of 5 in Montana)

    • The specimens present in 2015 confirmed that Hesperosaurus (typically known as Stegosaurus mjosi) confirmed sexual dimorphism. Evan Thomas Saitta revealed a examine that confirmed there have been two kinds 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 revealed April 22 in PLoS ONE
    • Specimens discovered with two kinds 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 have been most likely from males (for show), and the tall spiky ones have been from females (used as deterrents)
    • They have been discovered collectively, which reveals they most likely co-existed, and the plates had comparable progress rings (so the dinosaurs have been across the identical age, and it’s not that the plates modified with age)
    • Hesperosaurus was 20-23 ft (6-7 m) lengthy and 2-3 tons

    • Brief, vast head
    • Had 20 maxillary enamel on head aspect (fewer than Steogsaurus), although comparable (however bigger)
    • In 2007 Peter Malcolm Galton wrote that Hesperosaurus enamel have been completely different, as a result of having tough vertical ridges on the higher a part of the crown, and weakly developed nice grooves on the tooth floor

    • Herbivore, most likely ate moss, cycads, conifers, ferns, horsetails
    • Stegosaurs have been first round in Asia within the center to late Jurassic, after which migrated to North America just a few 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 have 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 consists of Dacentrurus and stegosaurs extra intently associated to Dacentrurus than Stegosaurus, similar to Hesperosaurus and Miragaia
    • Enjoyable Truth: The quickest animal to ever stay is technically a dinosaur: the peregrine falcon, which reaches prime speeds of 240 mph.



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