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Episode 354: Spinosaurus and Allosaurus debates proceed

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    Episode 354 is all about Pisanosaurus, a small Triassic herbivore that’s both an ornithischian or a non-dinosaur dinosauromorph.

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    On this episode, we talk about:

    Information:

    • A fantastic twitter thread by Brian Engh continues the dialogue about how probably Allosaurus was to be a scavenger supply

    • The Spinosaurus swimming debate continues with a brand new paper about its attainable aquatic diversifications supply
    • isotopes from titanosaur eggshells assist present their nesting behaviors supply
    • The world’s largest identified Triceratops skeleton, “Massive John” goes up for public sale in France in October supply

    • The Pacifico Yokohama conference middle in Japan has a dinosaur show Referred to as DinoScience: The Dinosaurs of Laramidia supply
    • Whirinaki Whare Taonga in New Zealand has the exhibit Dinosaur rEvolution: Secrets and techniques of Survival supply
    • A Flintstones spinoff that includes Pebbles and Bamm-Bamm known as Yabba Dabba Dinosaurs is coming to HBO Max on September 30 supply

    • Colin Trevorrow says that Jurassic World: Dominion will discover the query, “If dinosaurs lived amongst us, would you be secure?” supply
    • The brand new sport Jurassic World Evolution 2 will likely be launched on November 9 supply

    The dinosaur of the day: Pisanosaurus

    • Primitive dinosauriform that lived within the Triassic in what’s now La Rioja, Argentina (Ischigualasto Formation)
    • Ongoing debate about whether or not or not it’s a dinosaur
    • Small, calmly constructed, most likely bipedal

    • Had a small head, lengthy legs (most likely a quick runner)
    • Herbivorous
    • Estimated to be 3.3 ft (1 m) lengthy

    • Estimated to weigh between 5 to twenty lb (2.3 to 9.1 kg)
    • Discovered a partial skeleton in 1962
    • Fossils discovered by José Bonaparte, Rafael Herbst, and the preparators Martin Vince and Galileo Scaglia

    • Features a partial cranium with elements of the precise jaw and tooth, cervical vertebrae, dorsal vertebrae, rib and rib fragments, elements of the pelvis, femora, tibia, fibula, elements of the toes, and extra
    • Holotype is fairly incomplete, and plenty of fragments
    • Described in 1967 by Rodolfo Casamiquela

    • Sort species is Pisanosaurus mertii
    • Genus title means “Pisano’s lizard” and is in honor of the paleontologist Juan Arnaldo Pisano
    • Species title is in honor of the naturalist Carlos Merti

    • Initially regarded as a “very primitive ornithopod, with all most likely represents an advert hoc household”
    • Casamiquela mentioned it was a shock of a dinosaur, particularly “in mild of the paucity of stays of representatives of the Ornithischia all through the complete geologic column in South America”
    • Casamiquela named a brand new household, Pisanosauridae, however that title is now not used

    • Has been reclassified many occasions, as a heterdontosaurid, fabrosaurid, hypsilophodont, the earliest identified ornithischian, and a silesaurid (a clade of dinosauriforms and the sister group to dinosaurs)
    • Principally due to incomplete fossils
    • Orientation of the pubis is unclear. Some reconstructions have it ahead pointing (like in saurischians)

    • In 1976 José Bonaparte redescribed Pisanosaurus and mentioned it had some distinct characters, such because the hip-joint being open, and the metacarpals within the hand being lengthy
    • In 1991 and 2012 Sereno instructed Pisanosaurus was a chimera, and that the cranium fragments, pelvis, and distal hind limb may very well be from one particular person, however the remaining belonged to a different taxon, primarily based on the proportions not resembling the identical form or dimension of comparable bones in heterodontosaurids, and he mentioned there wasn’t a lot justification for the affiliation of the bones and impressions
    • In 2004 Norman and others instructed the cranium bones had been ornithischian, and the postcrania was just like bones of a non-dinosaur

    • In 2007, Irmis and others mentioned the fossils “can’t be thought to be a chimaera primarily based merely on character incongruence between totally different areas of the physique”
    • In 2009, Novas accepted it being one particular person. Bonaparte, in 1976, included a sketch of the fossils the way in which he discovered them within the discipline, which exhibits it belongs to 1 particular person
    • In 2017, Federico Agnolin and Sebastián Rozadilla wrote a paper in regards to the phylogenetic reassessment of Pisanosaurus, and agreed the fossils had been all from one particular person

    • Authors redescribed a number of the options of Pisanosaurus
    • Wrote in regards to the fragmentary skeleton, together with partial jaws, dorsal vertebrae, 4 fragmentary vertebrae in an unsure place within the column (regarded as caudal vertebrae, however later redescription discovered it to be cervical vertebrae, after which later regarded as one thing else (unsure what), impression of a part of the pelvis and sacrum, partial hind limb, a left scapular blade (that was misplaced), a most likely metacarpal III and impressions of some metacarpals (additionally misplaced)
    • Talked about Pisanosaurus being described from an incomplete, poorly preserved skeleton (makes it onerous to explain, and so they mentioned elements of the outline was tentative due to this), and a latest description of the clade Silesauridae has having tooth like ornithischians

    • Prompt Pisanosaurus was a part of Silesauridae, the non-dinosaurian dinosauriform, primarily based on the tooth being related (diminished denticles, in addition to tooth fused to the maxilla and dentary bone), and different similarities, similar to sacral ribs between two sacral vertebrae
    • Regarded as an ornithischian primarily due to its tooth and teeth-bearing bones
    • “Nonetheless, it’s value noting that archosaurs, apart from ornithischians, exhibiting such a specialised dentition had been unknown earlier than the early 2000s”

    • Silesaurus opolensis was described in 2003, and researchers in 2005 and 2007 talked about how related dentition in Revueltosaurus, a pseudosuchian, and basal silesaurids present how the range of Triassic archosaurs with extremely derived “masticatory morphology” (how they chewed) remains to be not properly understood
    • Mentioned this implies herbivorous-like dentition was extra widespread than beforehand thought, and herbivory occurred greater than as soon as inside archosaurs
    • Pisanosaurus maxilla and dentary had about 15 tooth positions, identical as Silesaurus and heterodontosaurids

    • Enamel are very fragmented, weathered, and cracked, so onerous to know precise variety of tooth or what they regarded like
    • Dentary had characters thought-about to be ornithischian (initially described as having “barricade-like dentition”), however onerous to match them with silesaurids as a result of the printed specimens are incompletely preserved
    • Later descriptions discovered the tooth didn’t kind a barricade

    • Has some dental options in widespread with ornithischians, like non-recurved, low-crowned tooth (low-crowned tooth are like what individuals have), however can see these characters in “a number of Triassic herbivorous archosaur lineages, together with the pseudosuchian Revueltosaurus and silesaurids similar to Sacisaurus and Silesaurus”
    • Tentatively reconstructed the pelvis to be cup-shaped (“acetabular morphology”), which is totally different from ornithischians
    • Didn’t have options that made it apparent it was an ornithischian or perhaps a dinosaur, however did have some options just like different silesaurids

    • Agnolin and Rozadilla talked about how Pisanosaurus was regarded as a heterodontosaurid for some time, however heterodontosaurid tooth are totally different from Pisanosaurus
    • They discovered that Pisanosaurus is a “stem dinosaur”, most likely a part of Silesauridae, however might also belong to a “nonetheless poorly identified clade of stem dinosauriforms”
    • However concluded, primarily based on phylogenetic evaluation that Pisanosaurus shouldn’t be thought-about the oldest identified ornithischian, which the authors mentioned was according to a 2011 examine by Olsen and others that discovered ornithischian radiation occurred after the Triassic-Jurassic boundary

    • In 2017, Matthew Baron wrote “Pisanosaurus mertii and the Triassic ornithischian disaster: may phylogeny supply an answer?”
    • Wrote: “Right here I suggest that phylogeny may maintain the answer to this downside. I look at how another place for Ornithischia – nested both inside Theropoda or Sauropodomorpha – may very well be the rationale behind their later look and relative rarity within the Early Jurassic. An Early Jurassic origin of Ornithischia would pressure us to contemplate that the anatomical similarities between ornithischians and Early Jurassic taxa may not be convergences, and to broaden the present datasets of early dinosaurs to check these concepts.”
    • Julia Desojo and others in 2020 checked out fossils from the Late Triassic Ischigualasto Formation

    • Mentioned although three papers discovered Pisanosaurus to not be an ornithischian, the “ornithischian affinity of Pisanosaurus mertii was solely questioned on numerical phylogenetic grounds”
    • Checked out all of the earlier research and the specimen and located it to be extra prone to be an ornithischian than a silesaurid
    • Reviewed Pisanosaurus anatomical traits and located that the traits that arguably made it a silesaurid had been traits that had been plesiomorphic for dinosauriformes (an ancestral character) and was in different dinosauromorphs and early dinosaurs

    • Additionally discovered greater than 10 characters shared by Pisanosaurus and heterdontosaurids or different early ornithischians amongst early dinosauriforms
    • Discovered Pisanosaurus to be from about 229 million years in the past, and is the oldest identified ornithischian within the newest Carnian (within the Late Triassic)
    • Mentioned Pisanosaurus “fills the long-speculated ghost lineage between youthful members of that clade and the oldest identified saurischian dinosaurs at ca. 233 Ma.”

    • Additionally mentioned sooner or later there will likely be a quantitative evaluation of the phylogenetic relationships of Pisanosaurus (out of scope for his or her paper)
    • Müller and Garcia, in 2020 had one other speculation, that Pisanosaurus was a transitional taxon between silesaurids and ornithischians
    • Fernando Novas and others got here out with a evaluation of the fossil file of early dinosaurs from South American and its phylogenetic implications this yr (print model in October of this yr, 2021), printed in Journal of South American Earth Sciences

    • Wrote “The early evolution of dinosaurs was a posh course of that occurred within the context of a “crowded ecospace”” and likewise wrote “there is no such thing as a consensus about early dinosaur phylogeny, and our paper just isn’t the exception”
    • Did help the Ornithischia and Saurischia groupings, not Ornithoscelida
    • Studied a bunch of specimens, together with Pisanosaurus

    • Talked about some debate that silesaurids could also be included inside Ornithischia (simple to reinterpret tips on how to classify their characters, as a result of they’ve a excessive diploma of homoplasy (shared characters, not from a standard ancestor)
    • Concluded “there are presently main uncertainties regarding the phylogenetic relationships of Pisanosaurus”
    • One other case of want extra fossils to find out

    • If Pisanosaurus is taken into account to be an ornithischian, as a result of it’s the one one from the Triassic, it fills helps fill a 30 million yr hole (subsequent identified ornithischians had been from the Early Jurassic, like Eocursor and Lesothosaurus)
    • Fossils of Pisanosaurus are within the Colección de Paleontología de Vertebrados, Instituto Miguel Lillo in Argentina
    • Lived in a heat, humid local weather, with ferns, horsetails, and conifers

    • Different animals that lived across the identical time and place included Herrerasaurus, Eoraptor, Saurosuchus, Hyperodapedon (a beaked reptile), aetosaurs (spiny armored reptiles), and plenty of different herbivorous animals

    Enjoyable Truth:
    Vultures have distinctive diversifications to take care of the elevated pathogens of rotting meat, however even they gained’t eat meat that’s too outdated.

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