The Big Dinosaur Podcast

Episode 25 is all about Allosaurus, one of the best known carnivores.

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In this episode, we discuss:

News:

• A new study found that it’s possible to tell the gender of a Stegosaurus based on its plates, according to PLOS ONE and NBC News
• A new dinosaur called Chilesaurus Diegosuarezi was found in Chile, according to The Guardian,  Nature, and Tico Times. Chilesaurus is related to T. rex, but was an herbivore
• Another new dinosaur called Yi Qi was discovered in China. Yi had bat-like wings, according to Nature, National Geographic,  and Smithsonian
• Paleontologist Rich McCrea is looking to raise $190,000 to help research and promote a large dinosaur track site in British Columbia, according to CBC News
• A new site in Bolivia has the most dinosaur footprints in the world, and it’s on a limestone wall, according to Fox and MSN (see MSN for great pictures)
• For $2 million, you can own your own Triceratops skull, according to 10tv
• Want to know the difference between T-rex in real life versus the movies? Check out InfoBarrel
• Most of Jurassic World’s dinosaurs are played by people, as puppets, according to GEEK
• The astroid that killed dinosaurs may have triggered the volcanic activity that also killed them, according to CBS News
• Secaucus Field Station in NJ is closing down at the end of this year, to make way for a new school, according to NJ 101.5
• A new movie called Cowboys v. Dinosaurs came out May 19, straight to HD, according to Huffington Post

The dinosaur of the day: Allosaurus, whose name means “different reptile”

• Allosaurus got its name “different lizard” because its vertebrae was different from other dinosaurs
• May be more than 3 species, others may include Allosaurus amplexus, atrox, europaeus, jimmadseni, maximus, and tendagurensis (but there is a lot of variation between some and very little between others so not everyone accepts these are all species)
• There are only three widely accepted Allosaurus species: fragilis, maximus, and jimmadseni
• 8 species of Allosaurus have been proposed over a 30-year timespan, so unclear how many species there actually are
• A. fragilis is the most common Allosaurus species (at least 60 specimens)
• Many dinosaurs have been mistakenly classified as either Allosaurs or part of the allosauridae family
• Part of the reason for the confusion is Marsh’s holotype Allosaurus was incomplete, and even though Edward Cope found a well preserved Allosaurus specimen two years after Marsh, later Allosaurus discoveries were compared to the incomplete skeleton
• Othniel Charles Marsh formally named Allosaurus fragilis in 1877, based on better material found in Garden Park, CO
• Allosaurus was one of the earliest dinosaur discoveries
• Allosaurus was discovered during the Bone Wars, and some Allosaurus specimens were classified as different species
• First pretty complete skeleton of Allosaurus was found in 1883 in Colorado by rancher M.P. Felch
• H.F. Hubbell found a more complete Allosaurus skeleton in 1879, but it wasn’t examined until 1903, after he died (one of the most complete theropod skeletons)
• Ferdinand Vanpeer Hayden first described Allosaurus in 1869, as having a petrified horse hoof (found near Granby, CO); the hoof was actually a tail bone, which Joseph Leidy classified to the genus Antrodemus
• Allosaurus fossils from all ages have been found (eggs through adult)
• May have used arms to grip prey as it attacked
• Had larger arms than most theropods, which means it probably used arms regularly, though scientists are not sure how
• The length of its forelimbs were 35% the length of hindlimbs (as an adult)
• Hands had three digits
• Had sharp claws up to 6 inches long
• Had inner dewclaw
• 2 Allosaurus species in Dinosaur National Monument: jimmadsen and fragilis
• Allosaurus jimmadsen is more rare; the two have different skeletal details
• Only one half of the jimmadseni skull has been found so far, but it was separated along the midline (the left half); it’s the most complete Allosaurus, and even has the wishbone in place
• The skull was found one year after the body, because of equipment that can detect radiation in bone (jimmadseni)
• At Dinosaur National Monument, the Allosaurus fragilis skeleton has bone of the best preserved skulls (which is rare because it has thin bone and can be easily crushed)
• Allosaurus fragilis had teeth up to 3 inches long and grew to 30 feet in length; it’s one of the largest predators in the Morrison Formation
• Had a disproportionately large skull, like other large theropods
• Weighed 3 tons
• Had a big head, with bony ridges (like blunted horns)over the eyes covered in a keratin sheath (that may have been to attract mates)
• Allosaurus had serrated teeth to cut through flesh
• It had binocular vision but was limited to twenty degrees (so would have to see prey directly in front of it, otherwise if the prey turned quickly Allosaurus would only be able to use one eye to see the prey and would not have depth perception (Allosaurus could turn its head, but timing would matter in an attack)
• Had a low attachment point on the skull, according to a 2013 biomechanical study by Eric Snively and colleagues. Means it could make quick, forceful vertical movements with its skull, similar to falcons (grip prey with skull and feet, then pull up to remove flesh; could move head and neck quickly and with a lot of control)
• Probably lost teeth easily during feeding and quickly replaced them (lower and upper jaw had 14-17 teeth, bones at the tip of the snout (premaxilla) had 5 teeth)
• Allosaurus was bipedal, had a long tail to help counter balance its head with an S-curved neck
• Like other theropods, Allosaurus had bird like features, like a wishbone and air sacs in its neck vertebrae
• Had a brain similar to crocodiles, and had large olfactory bulbs but an underdeveloped area for assessing, which might mean that it only recognized a few smells, like for prey or its own kind
• High EQ (brain to body weight), highly intelligent compared to many dinosaurs of its time
• Could hear low frequency sounds
• Allosaurus had gastralia (hanging belly ribs that are thiner than upper ribs and support and protect internal organs, such as lungs; and they may have aided in breathing. They are not attached to backbone like our ribs, but are formed from the skin in the middle region of the body so they are referred to as “dermal bones”)
• Allosaurus matured to have shorter, muscular legs, probably to better protect it from injury when tackling larger prey
• Younger allosaurs had proportionately longer legs which would make them quicker and better adapted to catching small, quick prey. When they got older their legs got heavier and proportionately shorter which would make them a bit more durable but not as fast (probably more important to stay healthy than run as fast as possible once adult sized)
• May not have been very fast, due to having short arms that could not help break their fall. Dr. Bruce Rothschild, from the Arthritis Center of Northeast OH, found evidence in 1998 of 14 fractured ribs in an Allosaurus that it probably got from falling (bellyflops while running); reported in New Scientist
• An x-ray analysis of Allosaurus found that its ribs had cracked and healed. Allosaurus could handle many injuries from running
• Since Allosaurus was smaller and lighter than T-rex, could probably run faster than T-rex
• May run up to 21 mph, (2007 study in journal Proceedings of the Royal Society B
• Allosaurus fossils have been found in Montana, Wyoming, South Dakota, Colorado, Oklahoma, New Mexico, and Utah
• Allosaurus is the official state fossil of Utah
• About 75% of all carnivorous dinosaurs found in Morrison Formation are Allosaurus
• Cleveland Lloyd Quarry in Utah has over 10,000 dinosaur bones, mostly of Allosaurus (and others like Stegosaurus and Ceratosaurus); having so many bones in one place may support the idea of hunting in packs
• Cleveland Lloyd Quarry may have had so many allosaurs because they were attracted to feed on disabled or dead allosaurs and sometimes were killed (may explain the high number of juvenile and subadults (often killed at feeding sites, like modern crocodiles and Komodo dragons)
• The predators outnumber the prey by a ratio of 3:1 in the Cleveland Lloyd Quarry, possibly because the herbivores were trapped in mud which attracted predators
• Lived on plains in North America in the late Jurassic
• Lived alongside Apatosaurus, Diplodocus, Camarasaurus, Stegosaurus and Camptosaurus
• Common predator
• Weaker bite than alligators, lions, and leopards, so Allosaurus may have used its skull as a hatchet (slam upper jaw onto prey then tear out flesh with teeth), according to 2001 study in Nature journal
• Probably was an active hunter
• Probably preyed on stegosaurs and iguanodonts
• One example found of an Allosaurus that got in a fight with a Stegosaurus. It died from a wound from a deep stab of a stegosaurus‘ tail to its pubis (Stegosaurus could jab like a sword, not swing side to side–no locking joints, more like a monkey’s tail). It probably penetrated the bone, and the wound was probably fatally infected
• In a 2005 paper in The Carnivorous Dinosaurs (Indiana University Press), wrote about an Allosaurus tail bone with a puncture wound from a Stegosaurus tail spike and a Stegosaurus neck bone with a bite mark from Allosaurus
• Also, found evidence of an Allosaurus bite mark on a Stegosaurus plate
• C.W. Gilmore described in 1914 three Stegosaurus tail spikes that broke, which may mean it had hit dinosaurs hard enough to break its spikes
• Allosaurus tooth marks found on an Apatosaurus vertebra, so evidence of Allosaurus attack
• Could open its jaws very wide (because it was double hinged), and may have grazed flesh (could have possibly attacked sauropods and eat part of it without killing it)
• Also shared area with Ceratosaurus and Torvosaurus (other theropods)
• It hunted by overpowering prey, and may have hunted in small groups
• May have hunted in packs, to take down large sauropods like Brachiosaurus (could not do it alone)
• Not much evidence of gregarious behavior, instead mostly antagonistic, injuries and bite wounds to skulls (establish dominance in a pack or settle territory disputes); may have been too aggressive to hunt in packs, also modern carnivores (lizards, crocodiles, birds) rarely work together and are often territorial and kill and cannabilize intruders, even of same species
• Allosaurus may have attacked its own kind, for rights to feed at a carcass, mating rights, or by a potential mate who didn’t want the attention
• May have hunted in packs wih “mobbing behavior” where it attacks a prey until the prey separates from the group and then wears the prey down, which collapses and then the predator moves in
• Juvenile allosaurus may have formed packs and avoided adults until they became adults themselves
• Allosaurus probably reached adult size at age 15 and lived up to age 28, according to 2006 study in the Journal of Morphology
• One famous Allosaur is Big Al, who lived a hard life (19 deformities from disease and injury, though most of them healed, but Al would not have been able to live to be old)
• In 1991, a joint team consisting of researchers from the Museum of the Rockies and the University of Wyoming Geological Museum found an Allosaurus fossil near Shell, Wyo. that was 95 percent intact — they dubbed it “Big Al.” In 1996, the same team discovered “Big Al Two,” the best-preserved Allosaurus skeleton to date.
• Big Al was discovered in 1991; 95% of a juvenile specimen that was 26 feet long (see BBC’s “Ballad of Big Al”)
• Big Al weighed more than 3.3 tons
• Big Al was discovered in Wyoming. Big Al had damage to ribs, toe bones and vertebra, and bone infection (Osteomyelitis–mircoogranisms infected the bone, which was damaged in a way that caused it to break, and which was attacked by the dinosaur’s immune system). The results were misshapen bones
• Big Al had an infection that probably lasted up to 6 months
• Later Big Al Two was excavated, and is the best preserved skeleton of its kind so far
• Young allosaurs probably stayed close to their nests until they got older or maybe had to leave to make room for new chicks (possibly so they wouldn’t attack the new babies out of jealousy)
• Seems to grow about 330 pounds per year
• May be more Allosaurus fossils than any other type of large theropod
• You can see the real Allosaurus fragilis skull at the Quarry Exhibit Hall in Dino National Monument
• Can also see Allosaurus fragilis at the Carnegie Museum of Natural History in Pittsburgh, PA
• Allosaurus is part of the allosauridae family, which is part of the group Carnosauria
• Marsh named the family in 1878, but the name was not really used intil the 1970s (instead Megalosauridae was the term more often used, but it became the “wastebasket taxon”)
• Before 1976, more publications referred to Allosaurus as Antrodemus, a species discovered by Josephy Leidy in 1870. But in 1920, Charles W. Gilmore found that Antrodemus‘ tail vertebra was the same as that of Allosaurus, and that Allosaurus should be changed to Antrodemus because it was named first. Then James Medsen published his monograph in 1976 and said the name Allosaurus should be used because Antrodemus was based on poor quality findings with not many diagnostic features or even any information on the geological formation where the one Antrodemus bone came from
• Madsen’s monograph has led to more studies on Allosaurus
• Allosaurids were medium to large size carnivorous dinosaurs
• Allosaurids were great hunters, and there were more of them than Megalousauridae and Ceratosauridae
• Most upper Jurassic and lower Cretaceous carnosaurs are somewhat closely related to Allosaurus
• Other allosaurids include Saurophagnax, and Epanterias (which may actually be an Allosaurus)

Fun Fact: The first flowering plants appeared in the Triassic period, along with the first flying vertebrates