Episode 85 is all about Carnotaurus, a large theropod with thick horns above its eyes.

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In this episode, we discuss:

• The dinosaur of the day: Carnotaurus
• Name means “meat eating bull” due to it’s bull-like horns
• Large theropod that lived in the Late Cretaceous, in what is now South America
• Type species is Carnotaurus sastrei
• Species name is in honor of Angel Sastre, the owner of the ranch were the skeleton was found (skeleton found on ranch named “Pocho Sastre”)
• Skeleton was found in 1984
• Jose Bonaparte found Carnotaurus in 1984, as part of one of the expeditions in the project “Jurassic and Cretaceous Terrestrial Vertebrates of South America” (sponsored by the National Geographic Society that started in 1976)
• Skeleton was of an adult, and skull and muzzle were crushed in fossilization
• It took a long time to prepare the skeleton, since it was in very hard rock (hematite); Jose Bonaparte wrote a note naming Carnotaurus in 1985 describing the skull and a more complete description was written in 1990
• Part of Abelisauridae (group of large theropods)
• Closest relatives are probably either Aucasaurus or Majungasaurus
• Other animals found near Carnotaurus include turtiels, snakes, crocodiles, mammals
• Bipedal, about 26-30 ft (8-9m) long and weighing about 1.3-2.1 tons
• Small forelimbs and long, slender hindlimbs
• Forelimbs were proportionally shorter than other carnivores, even T-rex (forearm was 1/4 the size of the upper arm)
• Hand had 4 digits, but only the two middle ones had finger bones; the fingers were fused, immobile and probably didn’t have claws; the 4th digit was a split-like metacarpal that may have been some sort of spur
• A study in 2009 found that abelisaurids had vestigal arms (had reduced nerve fibers like in modern emus and kiwis, which have vestigial forelimbs)
• If Carnotaurus kept evolving, descendants may have lost its arms
• Had thick horns above its eyes (not seen on other carnivores)
• Very specialized (horns and neck)
• Had a deep skull and muscular neck
• Had a straight neck, instead of an s-curved neck like other theropods, and was wide towards the base
• Possible it used its head like a hatchet (along with thick, long neck) and teeth struck the prey multiple times to take it down
• May have fought using horns and neck and either pushing their skulls together, or ramming heads and using horns as shock absorbers
• Bone horns on the brow were 5.9 in (15 cm) long (probably keratin made them longer)
• Horns may have been used for fighting, display, or killing prey
• Horns may have protected eyes in fights, or been used in fights the way rams use horns (in 1998 Gerardo Mazzetta and team found that Carnotaurus‘ neck was strong enough to absorb the force of two Carnotaurus‘ butting heads at a speed of 5.7 m/s each
• Gerardo Mazzetta also said the horns could have hurt or killed small prey
• Some studies found that instead of head blows Carnotaurus‘ pushed slowly against each other with their skulls, so the horns could help prevent brain damage (horns were flat on the upper side and top of the skull had strongly fused bones)
• In 2009 Fernando Novas said the short skull may have helped them move their heads more quickly, and the strong neck and rigidity and strength of their spinal columns could help when butting heads
• Skull is 23.5 in (59.6 cm) long and proportionately short and deep
• Broad snout, and nasal bones had small holes and spikes
• Had small eyes and some degree of binocular vision
• Eyes set facing slightly forwards
• May have been able to hunt sauropods, though some scientists think it ate small animals
• Could bite quickly, but didn’t have a strong bite (also good for small prey)
• Long, slender teeth, with a shallow, weak lower jaw
• Skull and lower jaw was flexible, like modern snakes, so could swallow small animals whole, and teeth pointed upwards to keep the animal from escaping its jaws.
• But may have also been able to hunt large dinosaurs, since the skull could withstand the force of biting larger prey
• In 2005, Francois Therrien and colleagues found that Carnotaurus had a bite force 2x a modern American alligator and was similar to Komodo dragons, which have jaws that are better for slashing and weakening large prey, so Carnotaurus may have ambushed and killed large animals
• Robert Bakker said in 1998 that Carnotaurus probably ate sauropods, since it’s short snout and small teeth and strong back of the skull had also evolved, independently, in Allosaurus
• Good runner
• Could sprint, though probably not quite as fast as ornithomimids
• Person and Currie published a study in 2011, where they studied 50 species of carnivorous dinosaurs, all different sizes, and found that Carnotaurus was the 9th fastest dinosaur, because of its muscles in the tail
• Unclear exactly how fast Carnotaurus could have run
• Carnotaurus was probably fast, because it had caudal ribs in a “V” shape in the tail vertebrae, which meant it had room to have a larger caudofemoralis muscle than other theropods (most important muscle for locomotion and may have weighed up to about 300 pounds or 140 kg). However, other muscles that help with tail movement and stability (longissimus and spinalis muscle) were smaller, which meant it would have had a hard time making tight turns because the hip and tail had to turn at the same time, unlike other theropods
• Caudofemoralis is a pair of large muscles on the sides of the tails
• Tail had two caudal ribs (crescent-shaped flanges on the sides of the tail bones); all about 15% of its body weight
• Carnotsaurus fossils had skin impressions that showed a mosaic of polygonal, small scales (5mm in diameter) with large bumps on the sides of Carnotaurus, but probably no feathers
• Skin impressions found on the lower jaw, front of the neck, shoulder, and rib cage, and tail. There were patches of skin impressions on the right side of the skull too, but it wasn’t clear what they were when the skull was prepared, so they were accidentally destroyed (though scientists still found that the pattern on the left and right sides of the skull was different)
• Head had a different pattern compared to the body
• Had large, knob-like bumps on the side of the neck, back, and tail, in irregular rows
• Bumps were larger towards the top of Carnotaurus (probably were clusters of scutes, as seen on hadrosaurids); may have helped protect its sides when fighting either other Carnotaurus‘ or other theropods (similar to what iguanas have, which helps protect them in fights)
• No evidence of feathers
• Holotype is on display at the Argentine Museum of Natural Sciences
• Can see a life-sized sculpture at the Natural History Museum in LA (made by Stephen and Sylvia Czerkas, museum ordered it in the mid-1980s, and is one of the first theropod replicas to show skin accurately
• In The Lost World by Michael Crichton, there are Carnotaurus‘ that can camouflage, and the characters scare them away with flashlights
• Abelisauridae means “Abel’s lizards”
• Clade of ceratosaurian theropods that lived in the Jurassic and Cretaceous in Gondwana (Africa, South America, India, and Madagascar)
• Jose Bonaparte and Fernando Novas named Abelisauridae in 1985, when they described Abelisaurus (named after Roberto Abel, who discovered Abelisaurus)
• Bipedal and carnivorous
• Had short hindlimbs and ornamentation on the skull bones
• Skulls were generally tall and shallow
• Four digits on the hand
• Abelsaurids are also part of the group ceratosaurs (Limusaurus and Ceratosaurus ahd short arms in the Jurassic, like abelisaurids)
• Fun fact: Almost 200 birds have been driven to extinction since the year 1500. Some were driven to extinction by humans hunting like the dodo, moa, & elephant bird. But even more have gone extinct due to species introduced by humans. According to Birdlife.org: “In the last 500 years, species like rats, cats and mice have driven more than 70 bird species to extinction. They remain one of the greatest threats to our natural world.”Therefore after the Chicxulub impactor the greatest threat to dinosaurs is probably humans and our introduction of invasive species to new habitats.

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