Wednesday 10/11/21 - Dinosaurs of the World Part 8/Finale; North America (Laramidia)
T.rex vs Triceratops, RJ Palmer
When someone asks you to name a dinosaur off the top of your head, most often you're going to say one that was first discovered in Western North America. Due to the United States of America's influence worldwide in most things, it's no surprise that North American Dinosaurs became popular around the world too. Scientifically, Western North America was also favoured for Fossilisation.
As mentioned in the previous blogpost about Appalachia, North America was split into two major sections by the Western Interior Seaway. Stretching from Alberta Canada to California USA, was the other subcontinent Laramidia. For much of the Cretaceous period, large regions of Laramidia were seasonal floodplains. Periods of flooding interspersed with periods of desertification meant that dinosaur remains were often covered in deep sand or deep mud very quickly. I won't go deep into the science, but it meant that lots of skeletons were preserved, undisturbed, very well.
Whereas some dinosaur species can be known from a handful of bones from a single specimen, arguably the most well known dinosaur, Tyrannosaurus rex, is known from more than 40 specimens. So not only are West North American Dinosaurs well known, but also well studied. Today we're gonna send out my Dinosaurs of the World series with a bang with everyone's favourite Dinosaurs.
Dilophosaurus, SpinoJP (Deviantart)
Dilophosaurus was an Early Jurassic Theropod from Western USA. It's fossils were originally found in Navajo County Arizona, with the help of Native Americans of the Navajo nation. The species name, wetherilli, honours the Navojo councillor who helped the dig team in not only this fossil site, but others too, John Wetherill. At the time of it's initial scientific description (1954), this dinosaur was known as Megalosaurus wetherilli, lumped in with many other theropods in that wastebasket taxon (read more Dinosaur Name Changes). Ten years later in 1964, another more complete skeleton was found, this time with the signature double crest. In 1970, it decided that this was a theropod unique enough to get its own genus: Dilophosaurus, meaning "two crested lizard".
Despite being one of the earlier dinosaurs, Dilophosaurus was large for its time, almost 2m tall and 7m long, about as large and heavy as a grizzly bear. I really hope it doesn't need clarifying, but Dilophosaurus had no evidence of a foldable neck frill, Jurassic Park made a lot of liberties with that dinosaur, including by making it smaller than its real adult appearance, strangely. It was the apex predator of its age and was likely the largest land animal of Early Jurassic North America.
Stegosaurus, Kaek McBeardy (ArtStation)
Stegosaurus was a large Stegosaurid Thyreophoran from the Late Jurassic. The first specimen was found in Colorado USA, but Stegosaurus and its relatives have also been found in Portugal, which was connected to North America at the time. Stegosaurus is most well known for its dual row of angular plates lining its back from its neck to the middle of its tail, but this condition is fairly unusual for its family. Other well known Stegosaurs like Miragaia or Kentrosaurus had plates only toward the front of the body, and long spines over most of the back. The plates were initially reconstructed as laying flat over the top of the dinosaur, and it was named Stegosaurus, meaning "roof lizard", but the reconstruction was of course changed later.
Stegosaurus is a very easily identified and unique dinosaur for its various features. It had one of the smallest head/brain to body size ratios of any dinosaur, and some early palaeontologists theorised it may have needed a second brain halfway down the body to even function, but this idea has of course been abandoned. It's back plates have been theorised to have a variety of potential roles, including sexual display, thermoregulation, and defence against predators, and those are not mutually exclusive either. The true defence capabilities of Stegosaurus was in its fan of tail spikes, the Thagomizer, which it would have swung violently at predators. Fun fact, the Thagomizer was actually a joke term made up by newspaper comic The Far Side, but Palaeontologists liked the name so much it became official terminology.
Edmontosaurus, Raphtor (Deviantart)
Edmontosaurus was a large Hadrosaur Ornithopod from Late Cretaceous North America. The genus Edmontosaurus has absorbed and let go of various Hadrosaur species in the past, including Trachodon and Anatotian. The first specimen to be called Edmontosaurus came from Alberta Canada, but the earliest fossil found to be currently attributed to Edmontosaurus was a dinosaur originally called Claosaurus from Wyoming USA. The genus name Edmontosaurus means "Lizard from Edmonton", and the type species, E. regalis, means "regal/king sized", since Edmontosaurus was one of the largest Hadrosaur species. It was 3m tall at the hip, and could've reached lengths of 12-13m.
One of the earlier found specimens of Edmontosaurus was the first "dinosaur mummy"; a corpse so well preserved that we can see the skin and muscles of the dinosaur stretched over the skeleton. This Edmontosaurus mummy preserves some details previously unknown about Hadrosaurs, including a horny beak over the front of the mouth, and front legs that formed a hoof-like structures for effective long distance quadrupedal travel. It did have a head crest, but it was not as large or elaborate as other North American Hadrosaurs.
Parasaurolophus, PrehistoryByLiam (Deviantart)
Parasaurolophus was a medium sized Hadrosaur Ornithopod from Late Cretaceous North America. It was first discovered in Alberta Canada, but has since had posible species found from Montana, New Mexico, and Utah USA, and a newer specimen from Heilongjiang, China. The Parasaurolophus genus is known from a diverse assemblage of species of various crest sizes and shapes. P. walkeri, the most well known species has an almost straight head crest, while P. cyrtocriastus had a shorter crescent shaped crest. Parasaurolophus means "near crested lizard", and was initially compared to another Hadrosaur with a smaller crest called Saurolophus.
Several specimens have well preserved the inner workings of the head crest, which seemed to have a system of air pockets and tubes. Palaeontologists have interpreted the crest as being used to amplify sounds, producing a loud trumpet-like call that could be heard over a long distance. It may have also helped with sexual display and differentiating genders. Adult Parasaurolophus would've been 7-9m long and around 2.5m tall.
Ankylosaurus magniventrus
Ankylosaurus, Daniel Eskridge
Ankylosaurus was an Ankylosaurid Thyreophoran from Late Cretaceous North America. It was first found in Montana USA, but has also been found in Alberta Canada. It was the largest dinosaur of the Ankylosaur Clade, and also the namesake. Our current understanding of Ankylosaurus' life appearance has come from various specimens and related species, building up small details at a time. The genus name, Ankylosaurus, means "fused lizard", and its species name, magniventrus, means "great belly", both details known even from the first Ankylosaurus remains.
Ankylosaurus had a heavily armoured back covered in bone bumps called osteoderms, as well as just thickened skin in general. Unlike the Nodosauridae family of Ankylosaurs, (such as the Australian Minmi, see Part 1), dinosaurs in the Ankylosauridae family (I know, it's a little confusing) had thick tail clubs they would use for self defence against predators. Ankylosaurus was 8m long and 1.7 m tall, and the tail club itself was more than twice the size of a human skull.
Troodon is a dubious genus of Paravian Theropod from the Late Cretaceous. The first remains potentially attributed to Troodon were teeth found in Montana USA, but the first substantial remains were found from Alberta Canada. Since the first remains were very undiagnostic, that is, they told little about what the rest of the dinosaur looked like, Troodon was a very unspecific genus for a while, first as a Lizard, then a Pachycephalosaur, then later as a Theropod. The biggest problem is that the Alberta theropod skeleton may not in fact be the same species those Montana teeth came from. So even though current skeletal remains assigned to Troodon give us a clear idea of what the dinosaur looked like, the genus itself may not technically be valid.
The name Troodon means "Wounding Teeth", and I recently learned it is supposed to be pronounced "troh-wuh-don" and not "true-don". The dinosaur we known as Troodon was a small meat eating paravian. It shared a lot of body features with raptors, like a slim body, small jagged teeth, and a sickle toe claw. But it was more closely related to birds than most dinosaurs. Troodon is perhaps most well known for having the largest brain to body size ratio of any dinosaurs, smarter than most reptiles, but dumber than most birds. Troodon was supposedly 90cm tall and 2.5m long.
"Brontosaurus is Back", Tuomas Koivurinne
Brontosaurus was a Diplodocid Sauropod from Late Jurassic North America. The first remains assigned to the genus came from Wyoming USA. Brontosaurus means "Thunder Lizard" and is one of the first names that come up when you think of iconic Dinosaurs. Dinosaur fans who have not kept up with all of the literature may think that Brontosaurus got the "Pluto treatment": that through technicalities, its title was not valid. But things have changed again in Brontosaurus's favour recently.
So to clarify what I'm on about, during a period of early Palaeontology called the bone wars, two Sauropods were described, called Apatosaurus (1877) and Brontosaurus (1879). Neither had fully complete skeletons, so their full appearance was based partially on related dinosaurs like Camarasaurus and Diplodocus. Given that the bone wars consisted of naming as many new species as they could, it was initially glossed over that Brontosaurus and Apatosaurus could be the same animal, but during the 1990s, when a lot of dinosaur genera were cleaned up, many palaeontologists agreed that Brontosaurus and Apatosaurus were the same species, and since Apatosaurus was the older title, Brontosaurus was no longer a valid genus name.
Recently, in 2015, an extensive study of the Diplodocid group determined that the material assigned to Apatosaurus and Brontosaurus were different enough to be different species again. Although not all palaeontologists are fully on board with this decision yet, many are happy to say that Brontosaurus is a "real" Dinosaur again.
Triceratops feat dead T.rex, RJ Palmer
Triceratops was a large Chasmosaurine Ceratopsian from Late Cretaceous North America. The first remains that became attributed to Triceratops were found in Colorado USA, and those were a pair of brow horns. Originally those horns were thought to belong to a species of large American Bison, but once more of the skull was recovered, it was compared to the earlier described dinosaur, Ceratops. It was given the genus name Triceratops, which means "three-horned face". Over time, more than half a dozen species were named, but as of the late 2000's, there are two valid species, T. horridus ("rugose/rough"), and T. prorsus ("straight"). Pictured above is Triceratops horridus, distinguished by strongly recurved brow horns; T. prorsus had comparatively straight brow horns.
Triceratops was perhaps the largest Ceratopsian (horn faced dinosaur), reaching 3m tall at the hip and 9m long. It's brow horns could be up to 1m long, and it had a frill of bone around the base of its neck about 1m across. Although this neck frill is one of Triceratops's most defining traits, most other dinosaurs in its family, the Chasmosaurs, had proportionately larger frills. The purpose of this intimidating head ornamentation was almost certainly for defence against predators, but may have served in courtship displays too. As often depicted in paleomedia, Triceratops would have been hunted by Tyrannosaurus rex, but it was far from a one sided fight. Triceratops was the most dangerous dinosaur for a Tyrannosaurus in its environment.
Tyrannosaurus rex, RJ Palmer
Tyrannosaurus rex was a large Tyrannosaur Theropod from Late Cretaceous North America. During the 1800s, several species of similar theropod were named, including Manospondylus and Dynamosaurus, but were eventually dissolved into Tyrannosaurus. The first remains to be assigned to Tyrannosaurus were found in Montana USA, but it has subsequently been found in Colorado, North and South Dakota, and Wyoming. As mentioned in previous posts in this series, Tyrannosaurus was among the largest of all meat eating dinosaurs. Giganotosaurus was around the same size or larger, and Spinosaurus was shorter but longer, but Tyrannosaurus was most likely the heaviest, as it was very powerfully built. It was 12-13m long, around 4 tall, and estimated to weigh 8-10 tonnes as an adult.
Tyrannosaurus was a very impressive dinosaur beyond just its size. Unlike other large theropods which had many short jagged teeth, Tyrannosaurus had fewer, but larger dagger like teeth, the largest of which being 30cm (1 foot) long. It had the strongest bite force of any terrestrial animal ever, able to break bones, even the skulls of Triceratops. T.rex also had fantastic binocular vision, comparable to today's birds of prey. Some have pointed these adaptations to signs of a scavenging lifestyle, but most palaeontologists these days think Tyrannosaurus both actively hunted, and opportunistically scavenged, like any carnivore would. I've previously written about this topic, The Dinosaur Scavenger Debate.
The life appearance of Tyrannosaurus rex has been under constant change since its initial description. First it was a slow moving, completely upright biped, with a posture like a kangaroo, but later it was reconstructed with a more horizontal gait. More recently, the debate has been on the skin covering of Tyrannosaurus. Tyrannosaurus comes from a group of theropods called the Coelurosaurs, which includes Dromeosaurs, Ornithomimosaurs, and all living birds. Heavy feathering is ancestral to this group, but many Tyrannosaurs were too large to need a full covering of feathers. Elephants are hairless because a large body size retains heat better and they live in a hot environment, and so perhaps Tyrannosaurus, which lived in a relatively hot and humid climate, would've had bare skin too. The current take is that a young Tyrannosaurus would've had close to a full coat of feathers, but as they got older, they lost a lot of their feathers and became essentially bare.
Tyrannosaurus means "tyrant lizard" and it's species name, rex, means "king". Tyrannosaurus rex is very well known from its full binomial name, while most dinosaurs are just known from their genus name, but as this series has hopefully communicated, all dinosaurs have two part names. As do all living things. Triceratops horridus, Velociraptor mongoliensis, Homo sapiens etc. But Tyrannosaurus rex is a very cool and catchy name, so it's nice that it caught on.
And that was the last episode in my series, Dinosaurs of the World. The aim of the series and the reason why the likes of Tyrannosaurus and Triceratops came last, was to demonstrate the wide diversity of Dinosaurs from across the globe, not just North America. Palaeontology is a global discipline taking on the minds of dinosaur fans everywhere.
The Ancient Continent of Laramidia may have been the home of many of the most popular dinosaurs known, but exciting dinosaurs have been found from Australia to Africa, from Asia to South America, and many many places in-between. If you've been reading all other entries in this series, thankyou for taking the time to consume the ramblings of an amateur Palaeontology enthusiast. If this was the first of this series you've read, there are 7 other blogposts about dinosaurs from all across the world, and I hope you take the time to read them all. Have a good one guys.
Part 1: Australia and Antarctica
Part 4: Madagascar and India
Part 7: North America (Appalachia)
