Episode 35 is all about Acrocanthosaurus, a carnivore with a high spine, somewhat similar to Spinosaurus
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In this episode, we discuss:
- The dinosaur of the day: Acrocanthosaurus, whose name means “high spined lizard” (and is also the antagonist in the novel Raptor Red
- Theropod that lived in North America during the early Cretaceous
- Fossils found in Oklahoma, Texas, Wyoming (teeth found in Maryland)
- Only one species, Acrocanthosaurus atokensis
- J. Willis Stovall and Wann Langston Jr. named the species in 1950
- First fossils discivered in the early 1940s. Holotype and paratype are partial skeletons and skulls from the Antlers Formation in Oklahoma
- Acrocanthosaurus atokensis is named after Atoka Countyin Oklahoma, where the holotype was found
- Another partial skeleton found in 2012 in the Cloverly Formation (a juvenile), Wyoming; may have been the only theropod in the Cloverly Formation
- Tooth found in southern AZ, possibly Acrocanthosaurus
- 1990s two more complete specimens were described (from Texas, a partial skeleton without a skull; from OK found by Cephis Hall and Sid Love, an even more complete skeleton nicknamed “Fran”–the largest and only known one with a complete skull and forelimb)
- After finding a few pieces of Acrocanthosaurus, Cephis Hall and Sid Love got permission to dig for the dinosaur (land was owned by Weyerhaeuser, a timber and building materials company) from Weyerhaeuser’s regional timberlands manager (said they had no interest in paleontological findings); but once they found out how valuable it was (after 3-4 years excavation) they contested ownership and it went court; first time two amateurs successfully excavated major dinosaur quarry by themselves without financial or logistical support from a university or commercial fossil company
- North Carolina Museum Acrocanthosaurus was in a court battle (then a “mysterious donor gave millions of dollars to the museum to purchase the set of fossils for display”; more in Russell Ferrell’s book, Acrocanthosaurus: Bones of Contention
- Acrocanthosaurus skeleton of NC took 3 years to excavate (1983-6) from amateur collectors Cephis Hall and Sid Love; Black Hills Institute cleaned and prepared the bones; because of this find, scientists realized Acrocanthosaurus was related to Allosaurus and Carcharodontosaurus
- Bones of NC Acrocanthosaurus were jet black from minerals in the sediment; had a punctured shoulder blade and several healed broken ribs
- Black Hills Institute said it was one of the most difficult preparations (due to moss and pyrite on the bones, which released acids when removed, so the bones had to be prepared in vaccum boxes or the preparors had to use respirators)–added many extra hours to the preparation
- Can see an Acrocanthosaurus (54% of actual skeleton, not replica) in the N.C. Museum of Sciences
- Sometimes called “Acro” for short. Museum of Natural Sciences in North Carolina nicknamed it “Terror of the South”
- Possible Acrocanthosaurus footprints in the Glen Rose Formation of central Texas (though it’s unclear for sure); however, it’s close to the Antlers and Twin Mountains formations and is from a similar time period, during which the only theropod known from around then at that place was Acrocanthosaurus
- Glen Rose tracks were found in 1938. AMNH paleontologist Roland T. Bird studied them. One footprint seemed to skip a step (overlapping footprint with sauropod), so he thought that meant the predator latched onto prey with teeth and missed a step (though the gait of the prey didn’t change, so seems unlikely the sauropod would just continue on its merry way at that point)
- Bird excavated the trackway in 1940 (half of it now in American Museum of Natural History (AMNH), in New York behind the Apatosaurus, other half in Texas Memorial Museum in Austin)
- Track at the AMNH shows heropod prints on top of sauropod tracks (suggests it stalked the sauropod herd, since its print came after the sauropod’s); but it’s unclear when these tracks were made–they could have been made as a group, or the dinosaurs could have just happened to go that route but at different times)
- David Thomas, artist, and James Farlow, paleontologist, reconstructed the trackway (predator followed the sauropod very closely, made the same turns, probably interacted; also right before the theropod skipped a step the sauropod left a drag mark, so maybe it was attacked and faltere or it “threw its weight to avoid being bitten); not sure it was an attack, just know there’s a missing track; but they think the theropod stalked the sauropod and may have tried to attack. However, trackways are fragile ( the trackway at the Texas Memorial Museum has deteriorated since on display)
- Vertebrae with tall spines from the early Cretaceous were found in England, and in 1988 Gregory S. Paul said they were a second species of Acrocanthosaurus, called Acrocanthosaurus altispinax (later classified as a new genus, Becklespinax)
- When it was discovered, Acrocanthosaurus and many other big theropods were only known from partial skeletons, which led to a lot of reclassifying. Although first an Allosauridae, Acrocanthosaurus was for a while part of Megalosauridae (wastebasket taxon), and to some scientists it was thought of as a spinosaurid (because of the long spines–until the 1980s)
- Part of the superfamily Allosauroidea; originally part of the Allosauridae family but now most scientists classify it as part of the Carcharodontosauridae family
- In 2011, paleontologists Drew R. Eddy and Julia A. Clarke found in a study (comparing and contrasting anatomical features) that Acrocanthosaurus shared a common ancestor with Allosaurus, but belongs to the Carcharondontosaurus family
- Acrocanthosaurus was one of the largest theropods, at 11.5 m (38 ft) in length, and weighing up to 6.2 tonnes (6.8 short tons)
- Typical large theropod, but lived in early Cretaceous (millions of years before T-rex and Giganotosaurus)
- 4.5 ft (1.4 m) long skull
- Upper jaw had 19 curved, serrated teeth
- Like allosaurids, it had long, low ridges that ran on each side of its snout from the nostril to the eye
- Typical allosaurid skeleton (long heavy tail to counterbalance, short forelimbs, three clawed digits on each hand
- Probably not a fast runner, because it’s femur was longer than its tibia (opposite of small fast-running dinosaurs)
- Probably an apex predator, preyed on Sauropods, Ornithopods, and Ankylosaurs
- Feet had four digits each, and first digit was smaller than the rest and did not touch the ground
- Analysis of the forelimb found that it probably had a lot of cartilage in its joints (like living archosaurs), and when resting, the forelimbs would hang from the shoulders, elbows bent, claws facing inwards, humerus angled slightly backwards
- Could not swing its arm in a circle, but could swing it backwards; could not completely straighten out its arm or bend it much
- Could bend all digits backwards to nearly touch the wrist
- First digit of the hand had the biggest claw (permanently flexed)
- Because forelimbs could not swing very far forward (couldn’t scratch its own neck), probably used its mouth to hunt, but once it had prey in jaws, used its arms to hold the prey against its body and impale it with claws; may have also held prey in jaws while slashing into it with claws)
- 2005 scientists did a CT scan of a replica of Acrocanthosaurus cranial cavity and found it was most similar to Carcharodontosaurus and Giganotosaurus (fellow carcharondontosaurids)
- Brain was somewhat S-shaped (like a crocodile, more so than a bird); had large olfactory bulbs (good sense of smell)
- When resting, its head would have been looking downward towards the ground (from CT scan), 25 degrees downward
- Because Acrocanthosaurus was a large predator, it probably had a large range and lived in many different areas. Deinonychus also lived in the area, but was much smaller and not much competition
- Bipedal predator, with (notable) high neural spines (probably to support muscle over its neck, back and hips)
- 17-inch (43 cm) spines from its vertebrae on its back, neck and tail
- Tall neural spines were sometimes more than 2.5 times the height of the vertebrae they came out of (though Spinosaurus had much higher spines); unclear what the spines did (help with communication, store fat, control temperature)
- Spines may have also been used for visual display (sign of being healthy), or had different colors or markings
- If the hump was fat, Acrocanthosaurus would have to eat more (bigger the hump, more successful predator, good for attracting mates); or shows dominance because they’re a better hunter
- Twin Mountains and Antlers formations were large floodplains that drained into a shallow inland sea (in early Cretaceous), sea then expanded and became the Wester Interior Seaway (divided North America for most of the late Cretaceous)
- Acrocanthosaurus is the state dinosaur of Oklahoma, as of 2006, though it already had a state fossils (Saurophaganax, a carnivore)
- Theropod->Carnosaur->Carcharodontosauridae
- Carnosaurs lived in the Jurassic and Cretaceous, and is comprised of allosaurs and their close relatives (used to include a large array of theropods)
- Some of the largest ones are Giganotosaurus and Tyrannotitan, which are also some of the largest known predatory dinosaurs
- Carnosaurs have large eyes and narrow skulls
- Many carnosaurs were later classified as more primitive theropods (includes megalosaurids, spinosaurids, ceratosaurs)
- Fun Fact: Dinosaurs may have inspired dragon myths in China and Europe.
