What on Earth Was Herrerasaurus?

dinosaurs were incredibly diverse and fascinating animals and the early evolution of this group of organisms is understandably the subject of a great deal of study working out how these creatures came to dominate the Mesozoic world and evolved to fill such an enormous range of niches has many implications for understanding macroevolution in general and so focusing on the early radiation of the amazing dinosaur lineage is highly important one dinosaur in particular has allowed a remarkable glimpse into the early evolution of the group while also being situated in the center of a fascinating debate herrerasaurus ishigwalastensis is a dinosaur that lived at the very start of the late Triassic period and ever since its Discovery has been shrouded in mystery as well as controversy The evolutionary relationships of herrerasaurus have been intensely debated over the years with all sorts of different positions proposed for this animal was this creature a theropod related to the giant carnivores of the Mesozoic was it an early sauropodomorph an ancestral lineage that the largest land animals to ever have existed was it an entirely unique Branch from a dinosaur Army tree or was it even a dinosaur at all all these ideas have been proposed at one time or another but in recent years it seems to have become a bit clearer what herrerasaurus really was so let's explore this fascinating prehistoric animal herrerasaurus was first uncovered in late Triassic aged rocks in Argentina rocks that actually turned out to be a very significant formation the ishigwalasto formation the story of the discovery of the first fossils from this dinosaur is actually pretty interesting with some quite impressive remains being found and then later overlooked for quite some time two expeditions to Northwestern Argentina were led by legendary American paleontologist Alfred Roma of Harvard won in 1958 and another in 1964-1965. Roma was already 64 years old during this first expedition and then 70 at the time of the second one and it was during the 1958 Expedition that the first remains of herrerasaurus were found a beautiful skull and some Associated post-cranial material were uncovered in blocks but then Upon returning back to Harvard once the Expedition had finished the fossils were unfortunately impounded at the port in Buenos Aires for two years only getting back to Harvard University in 1960. once they were back however no one studied them for quite some time and so it wasn't realized what these truly were until the early 2010s after it had become clear that the ishigwalasto formation was a very promising place to find fossils with not only dinosaurs coming out of this place but also very early dinosaur relatives other kinds of bizarre reptiles and a variety of synapsids Argentine paleontologists Osvaldo reig and Jose Bonaparte launched a series of expeditions to ishikwalasto between 1959 and 1964. it was during the 1961 Expedition that the back half of the body of a fascinating new animal was uncovered after a local Rancher named Victorino Herrera led the team to the place where he had found the bones after extracting the fossils it was then two years later the reek published a description of them naming them as a new genus and species reek named the dinosaur after the discoverer as well as the formation in which it was found and so herrerasaurus ishiguelistensis was revealed to the world at first reek considered herrerasaurus to be a carnosaurian theropod but there were some features of the skeletal Anatomy that led other paleontologists to disagree and resulted in a multi-decade-long debate over the true identity of this animal now to fully understand the significance of herrerasaurus and the many years of conflict over his placement it's important to be familiar with the basic main groupings of dinosaurs dinosaurs are generally agreed to be split into two main lineages although this has in recent years come into question as we'll see later but for now there are the soroskian dinosaurs including the theropods such as T-Rex and the long-necked sauropodomorphs and then the ornithischian dinosaurs including animals such as triceratops and kylosaurus Iguanodon and many many others paleontologist Alec Walker in 1964 in a paper investigating the relationships of the carnosaurian dinosaurs thought that herrerasaurus should be classified as a kind of early sauropodomorph saying that it was most similar to platysaurus type dinosaurs this would have meant that it would be classified within the now outdated group prosoropoda now known as the non-sauropod sauropodomorphs and basically meaning that herrerasaurus would actually represent an ancestral lineage to the famous long-necked sauropod dinosaurs instead of being an early branch of the theropods this classification was again supported by Alfred Roma in 1966 in the Third Edition of his iconic textbook vertebra paleontology where he said the herrerasaurus might be a member of the platius soraday family in the 14th part of the incredibly useful Handbook of paleo herpetology series published in 1970 and focusing on the soreskian dinosaurs herrerasaurus was once again said to be a pro-sauropod 1970 also saw the naming and description of storicasaurus Price eye a late Triassic animal found in Brazil that was recognized to be very similar in many aspects to herrerasaurus the lower jaw many vertebrae the hip bones and parts of the Hinds limbs were found of this animal and it was enough for several paleontologists to realize that it could be a key taxon in figuring out the placement of herrerasaurus indeed in 1973 storicosaurus and herrerasaurus were then placed in a new family together named Herrera soride this paper disagreed with the assignment of these animals to the sauropodomorph dinosaurs however that was also cautious about placing them as theropods suggesting that maybe a whole new infra order of theropods needed to be created in order to classify these dinosaurs but then just as it seemed as though another animal could actually be classified as a close relative of herrerasaurus another study published in 1977 assigned to ricosaurus to its own family storica soraday and claimed that Herrera soraday only contained herrerasaurus itself while also saying that both these families could only be classified as being in an uncertain position within soreskians skipping forwards to 1987 a paper was published describing a new specimen of storicosaurus that added some new anatomical data used by the paleontologists to reassess its relationships to herrerasaurus and other dinosaurs the result of this though was to find that storicosaurus and herrerasaurus were neither theropods Norse oropodomorphs or indeed soreskians at all and that they also weren't close relatives to each other instead they were positioned as successive sister groups leading up to the branch where the soristian and onotheskin dinosaurs diverged but not for long because then in 1992 Argentine paleontologist Fernando novas found more anatomical characteristics of the skeletons that suggested storicosaurus and herrerasaurus were actually very closely related to each other and the Herrera soride family could actually include both these animals after all novice did agree that Herrera swords were basal to both ornithisians and sorriskians though and diverged before these other two lineages split off from their common ancestor however back in 1988 a joint Argentine American expedition including Fernando novas and well-known American paleontologist Paul cerino had actually returned to the ishigwalasto formation in order to find more fossils of these important Triassic animals and had managed to recover some beautiful new specimens of herrerasaurus including an almost complete skull and neck as well as a second specimen that preserved most of the body this discovery was reported in a paper published in 1992 by Serena novas in which they described a lot of the anatomy of the parts of this animal that hadn't been able to be studied until this point in this study based on the newly recognized skeletal traits of this new material Sereno and novas argued that herrerasaurus could actually be placed within the theropods representing a very archaic lineage of these dinosaurs that split off very early on in the evolution of the group in 1993 Sereno and colleagues then named and described the Triassic dinosaur ear Raptor also from the ishiguelasto formation in this paper Sereno again argued for a Herrera sword of Fenty with the theropods while also classifying ear Raptor as an even more basically positioned theropod Eoraptor is now of course generally considered to be a sauropodomorph instead though there's still some disagreement in recent works and it's a whole other story that could be covered by itself 1993 also saw the publication of a review paper that investigated all the different definitions of dinosaurs as a whole that existed at this time this work criticized the classification of ear Raptor done by Sereno and his colleagues disagreeing with Herrera swords as theropods and arguing that Herrera Sora day should not be included as true dinosaurs instead sitting just outside this grouping under this classification scheme the definition of Dinosauria would include just saurus gear and ornithis gear and as such exclude more basal groups novas then published another study in 1994 that supported the inclusion of Herrera swords within Dinosauria once again with many characters Founders supporting a sureskin Affinity he also found many shared characteristics with the theropods in particular and in 99 6 published a paper in which he performed a large-scale analysis of dinosaur relationships again finding support for Herrera swords as theropods the debate about the position of Herrera swords continued into the 21st century and while studies published in 2003 and 2004 supported the inclusion of herrerasaurus as a theropod other researchers favored the classification of the dinosaur in a more basal position as an early soroskian then in 2009 another very early possible therabod was named and described Tower halai from the late Triassic of New Mexico and in the study herrerasaurus was again found to be a theropod but actually in a more basal position than ear Raptor 2010 then saw the publication of yet another early saurus skin dinosaur chromogi Soros also from the ishikwalasto formation classified as a sauropodomorph the phylogenetic analysis performed in this paper actually once again found Herrera swords to be base alsooriskians not included within the theropods then later in 2010 another new species of Herrera sword was named San Juan Soros again from the ishikwalasto formation in this paper adding the new anatomical characteristics obtained from the new dinosaur to the phylogenetic analysis done in the study Herrera swords were again found to be placed at the base of soroscure outside of the more derived grouping called yusaurus gear then we moved to 2011 when to no one's surprise yet another early dinosaur from the ishikwalasto formation was named and described another basal theropod called eodromeos Serena was again involved in this paper and once again the researchers favored the positioning of Herrera swords as true theropods rather than basal soreskians in 2014 there was then a study re-examining a kind of middle Triassic dinosaur reform called luisukus in which another phylogenetic analysis placed Herrera swords as outside theropods but in an unresolved position among the theropods and sauropodomorphs this brings us up to the 2017 paper that completely shook up the dinosaur family tree especially when it came to the herrerasaurus this paper proposed a new classification scheme for the dinosaurs putting theropods and ornithiskins together in a new grouping called ornithoskeleta while Herrera swords and sauropodomorphs were found to be most closely related to one another and remained as members of soroscure in 2019 the world then welcomed another new genus and species of herrerasaurid the new taxon nathovorax Cabrio which is known from a particularly nice and complete articulated skeleton Unearthed in southern Brazil the completeness of the skeleton allowed paleontologists to gain much more insight into Herrera sword Anatomy especially because the endocranial cavity was preserved within the brain case and so by micro CT scanning the specimen the shape of the brain that would once have been present here was able to be examined interestingly nathophorax also showed that Herrera swords were positioned in the ecological roles that would later be taken over by medium to large body-sized theropods being the original dinosaurs to occupy these carnivorous niches napovorax also added more anatomical details that allowed a more complete phylogenetic analysis and within dinosaurs as a whole Herrera swords were once again found to be placed as early diverging soristians instead of theropods and that just about brings us up to today though I'm sure more studies are bound to be on the way which will again change details of their evolutionary relationships so as you can see the history of research on this dinosaur has been an absolute mess with all sorts of different ideas floated around at one time or another and that's not even mentioning the other taxa that were described which are now considered to be synonyms of herrerasaurus the generoskisaurus named in 1963 and francoisaurus named in 1986 which are now both considered to just be other examples of herrerasaurus however herrerasaurus should really be classified there's no denying that this is a fascinating and unique dinosaur indeed The Peculiar anatomy of part of a skeleton are the reason that it's caused such confusion among paleontologists and also why it's such a key taxon in figuring out the early evolution of this iconic group of animals herrerasaurus is known from some pretty complete remains thanks to the many expeditions to ishikwalasto they've recovered a lot of this dinosaur skeleton and a series of papers published by Sereno and novas in the early 90s detailed much of the anatomy herrerasaurus has a very interesting skull with it being described as lacking nearly all of the specializations of later dinosaurs it was quite narrow and low with a rather rectangular side profile and the configuration and shapes of the skull openings between the orbits and nostrils are unique in this animal with one of the openings actually being a feature usually only found in more derived theropods a particularly notable feature of the herrerasaurus skull is the presence of a well-developed joint Midway along the lower jaw known as an intramandibular joint that would have enabled the mandible to flex and for the front half to rotate down about 15 degrees compared to the back half Sereno and novas made the comparison of such a feature to some Modern anguomorph lizards which use such a flexible lower jaw and catching life prey so perhaps herrerasaurus engaged in similar Behavior the hands of herrerasaurus were also probably employed in the catching and subduing of prey items possessing long and recurved claws on digits one to three that indicate they were probably effective at grasping study of the arms and pectoral girdle of the dinosaur shows that the three Claude digits would have converged upon flexion ideal for grasping or raking at objects and various muscle attachment points on the arm bones support this idea herrerasaurus does actually possess five digits however the fourth and fifth fingers are very reduced and they did not have claws on their ends another of the Mysteries surrounding herrerasaurus concerns the number of hip vertebrae that are possessed although more advanced or derived sorriskian dinosaurs generally had at least three vertebrae incorporated into the fused sacrum herrerasaurus appears to only have two this is a very basal condition among dinosaurs and was one of the main features that led many researchers to consider it as a very primitive soroskian or even outside Dinosauria however others such as Serena or novas argued that this just indicates that the sore skins and ornithiskins must have independently evolved to incorporate more than two vertebrae into the sacrum as they support herrerasaurus's position as a theropod so we've looked at all the different positions that herrerasaurus has been placed in as well as some of the anatomical features that make this animal so intriguing but what about the environment in which it lived the ishic Wallace of formation has been absolutely invaluable in elucidating some of the Mysteries shrouding the early diversification of the dinosaurs and this locality was also home to a whole variety of other amazing organisms exposed today within a 50 kilometer Long Valley in Northwest Argentina this formation represents an environment that was once a floodplain with evidence of ancient Rivers as well as indications that various volcanic eruptions occurred here resulting in Ash layers within the formation dating to between 232 and 225 million years old other inhabitants of the ishicolas formation include various early dinosaurs such as the previously mentioned ear Raptor chromogi Soros eodromeus and San Juan Soros as well as another basal sauropodomorph called panphagia named in 2009 all sorts of arcosauromorph reptiles lived in this environment too including the massive sorosuchus which was likely the top predator of ishiguel asto synapsids were prevalent here too animals related to the ancestors of mammals with a great diversity in size ranging from absolutely tiny forms all the way up to the massive disinodons named ishikwalastia temna spondals relatives of modern amphibians are also well documented from their formation as is a range of plant life herrerasaurus is therefore an intriguing member of the dinosaur lineage with some unique quirks of its Anatomy that's made it an absolute nightmare for paleontologists to classify but its position as an early diverging member of the dinosaur lineage makes the study of this animal imperative to understanding how this group of animals came to dominate the terrestrial ecosystems of the Mesozoic world well I really hope you enjoyed learning about this remarkable mysterious dinosaur and the history of how it sent paleontologists absolutely mad thank you for also continuing to support the channel and the content we're making especially the new longer form videos we're creating which I'd recommend going and checking out if you haven't already in this new series that we're trying out I along with two of my friends and fellow paleontology students at University with me discuss the latest in paleontological news explore various Topics in more detail than we would in our usual videos and have much more discussion about them and talk about our own research on the prehistoric animals we're studying for our University work we're also planning to film a lot of our fossil hunting trips as well as our visits to various museums and sites of paleontological interest and we've also got some plans to interview paleontologists about their work the first episode is already up and although it's a little rough around the edges it's been very fun to experiment with this new format and we're very open to any suggestions and feedback that you're able to provide we really want to include as much audience participation as we can too and we'll be doing some votes as to what topics we should cover now next or places we should visit so please do come and join in we've also got a very fun and much improved second episode on the way very soon so be sure to catch that anyway thank you for watching and thank you especially to our patrons including our dinosaur tier supporters Amanda Von nordeck archieanthus Clara Middleton Daniel Ingraham drove 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Channel: Ben G Thomas

Views: 194,125

Keywords: Biology, Science, Paleontology, Palaeontology, Dinosaurs, Animals, Nature, Wildlife, Ben, Thomas, Prehistory, Anatomy, Fossil, Bones, News, 7Daysofscience, Days, of

Id: uYnKONIwzKc

Length: 18min 36sec (1116 seconds)

Published: Tue Nov 29 2022