The Big Dinosaur Podcast

Episode 279 is all about Heterodontosaurus, a dinosaur with tusks and a beak.

We also interview Alida Bailleul, Postdoctoral Research Fellow at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP). Her research focuses on microscopic structure of dinosaur bone and tissue. Follow her work at www.ivpp-avianevolution.com

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In this episode, we discuss:

News:

• The best sauropod find from Switzerland finally has its own genus—Amanzia source
• Learn about dinosaurs while social distancing bit.ly/dinodistancing source
• Bring Dinosaurs into your home with a new AR App source

The dinosaur of the day: Heterodontosaurus

• Heterodontosaurid ornithischian that lived in the Early Jurassic in what is now South Africa
• Small dinosaur, between about 3 ft 10 in (1.18 m) to 5 ft 9 in (1.75 m) long and weighed between 4.4 to 22 lb (2 to 10 kg)
• Estimates based on the holotype and a second specimen
• Second specimen was much larger than the holotype (22 lb / 10 kg and up to 5 ft 9 in or 1.75 m long, compared to about 4 lb pr 1.8 kg and 3 ft 10 in or 1.18 m long). Not clear why there was such a big difference in size, but could show individual variation or sexual dimorphism
• Heterodontisauridae have some of the smallest dinosaurs, like Fruitadens (about 26 to 30 in or 65 to 75 cm long)
• Had a short body with a long tail
• Probably bipedal
• Probably a fast runner
• Had long, robust forelimbs that were about 70% as long as the hindlimbs
• Had strong arms, originally thought to be quadrupedal but now thought Heterodontosaurus used its arms for digging up roots and opening insect nests
• Hands somewhat resembled early theropods, like Eoraptor and Herrerasaurus
• Had five fingers on each hand that were long
• Had large hands, and it used the five fingers for grasping
• First three fingers had large claws
• Fourth and fifth fingers were possibly vestigial
• Two of its fingers were opposable, so it could pick things up with one hand
• Had long, slender hind limbs, and four toes on each foot
• The first toe on the foot (hallux) didn’t touch the ground
• Bones in the toes were claw-like, not hoof-like (more advanced ornithischians were more hoof-like)
• No ossified tendons in the tail, so was probably flexible
• Has been depicted as having long, filamentous integuments from its neck to tail (looks bristly), based on a description of fellow heterodontosaurid Tianyulong, described in 2009, which had those structures
• Had an S-shaped neck
• Had a small, elongated, narrow, triangular skull
• Had large eye openings
• Probably herbivorous, or maybe omnivorous
• Had a horny beak that covered the front jaws
• Had three types of teeth: small, incisor-like teeth, long canine-like tusks, and chisel-like/molar-like cheek teeth
• No teeth in the beak part
• Premaxilla (tip of the upper jaw) had three teeth on each side. First two teeth were small, and cone-shaped (incisors) and partially covered by the upper beak, and the third tooth on each side was a canine-like tusk
• First two teeth in the lower jaw were canine-like tusks, and bigger than the ones in the upper jaw
• Had 11 chisel-like cheek teeth on each side, for crushing and grinding, after a gap after the canine-like teeth. Middle cheek teeth were the largest, and they decreased in size. Had long roots, and a heavy enamel coat (good for wear)
• Cheek teeth have uniform wear and tear, so they formed at the same time. No evidence of newly erupted teeth
• Probably moved its jaw back and forth
• Thulborn suggested that Heterodontosaurus needed to replace its teeth regularly, because it ate tough vegetation. It may have done that with aestivation (like hiberation but in summer), when it wouldn’t need to eat. May have worked, since it lived in a desert-like habitat with hot, dry seasons with little food
• Hopson questioned this in 1980 and found wear patterns on the teeth that showed vertical and lateral, not back and forth movements. Also found variables in tooth wear, which showed continuous teeth replacement, though he did say X-rays of the most complete specimen didn’t show any unerupted replacement teeth
• Hopson rejected the aestivation idea due to lack of evidence
• Butler and others in 2006 CT scanned a juvenile Heterodontosaurus skull and found no replacement teeth. But they argued there must have been tooth replacement because the juvenile had the same tooth morphology as adults, and the teeth would have changed if the tooth grew continuously. They concluded Heterodontosaurus had sporadic tooth replacement
• In 2011, Norman and others described the upper jaw of another specimen, and found unerupted replacement teeth. Sereno in 2012 described a juvenile with unerupted replacement teeth
• But in 2012, Sereno said Heterodontosaurus had some features in its skull and teeth that showed an herbivorous diet (the beak with the cheek teeth for cutting vegetation, and the cheeks to keep food in its mouth while chewing, the enlarged jaw muscles, and position of the jaw joint so the bite would be evenly spread. Probably ate tough vegetation
• Hear more about chewing and jaw muscles of herbivorous dinosaurs, check out our interview with Ali
• https://iknowdino.com/Yamaceratops-episode-205/
• Since Heterodontosaurus was so basal, it may help show the shift from early carnivorous dinosaurs to being herbivorous
• Laura Porro in 2008 said “It’s likely that all dinosaurs evolved from carnivorous ancestors. Since Heterodontosaurs are among the earliest dinosaurs adapted to eating plants, they may represent a transition phase between meat-eating ancestors and more sophisticated, fully-herbivorous descendants.”
• Not many juveniles have been found, so not much known about how it changed as it grew, but eye sockets seem to have gotten smaller as it grew up, and the snout became longer and had more teeth
• Types of teeth were the same, so juveniles and adults probably had similar diets
• Thulborn in 1974 thought that there was sexual dimorphism with tusks (males had tusks, females did not), but tusks were found in a juvenile skull, so wouldn’t be something that develops later for mating. Also, most skulls found have tusks
• Originally tusks were thought to be used for defense or display, and that Heterodontosaurus was herbivorous. But now, thought that Heterodontosaurus may have been omnivorous and used tusks for killing prey occasionally (to go with the claws). Going after prey would be an advantage in the dry season when there was less vegetation
• A 2016 study found that Heterodontosaurus may have used its tusks by grazing against the lower beak while it was cropping vegetation
• Heterodontosauridae is one of the most primitive/basal groups of ornithischian dinosaurs
• Heterodontosaurids mostly found in southern Africa, but have also been found in Eurasia and the Americas
• Type and only species: Heterodontosaurus tucki
• Genus name means “different toothed lizard” and refers to its teeth, which were unusual (and all different, or heterodont)
• Species name in honor of George C. Tuck, managing director of the Austin Motor Company of South Africa, who supported the expedition
• Holotype found during a British and South African expedition between 1961-1962, on a mountain at an altitude of about 6,200 ft (1,890 m)
• Described and named in 1962 based on a skull, by Alfred Crompton and Alan Charig (skull was nearly complete and slightly crushed)
• Holotype skull was crushed but nearly complete (postcranial remains that belonged to the skull not found until 2011)
• Holotype is now at the Iziko South African Museum
• Only described the front part of the skull and lower jaw when they named Heterodontosaurus, and said the description was preliminary
• Very few early ornithischians were known at the time
• Hard to prepare the specimen, because it was covered in a thin, hard, rusty layer containing haematite that could only be removed using a diamond saw, which damaged the specimen
• Second specimen found in 1966 in the Eliot Formation, about 5,807 ft (1,770) m above sea level, on Krommespruit Mountain. Included the skull and skeleton, articulated
• Second specimen described in 1976 by Albert Santa Luca, Crompton, and Charig
• Forelimbs had been discussed in an article by Peter Galton and Bob Bakker in 1974, and helped establish that Dinosauria was a monophyletic natural group (many scientists at the time thought Saurichia and Ornithischia were not directly related)
• Other specimens have been found, including one in 2005 in a streambed near Grahamstown in Eastern Cape Province of South Africa, which is the most complete individual found so far, but was too hard to remove because of the rocks around it. So it was scanned at the European Synchrotron Radiation Facility in 2016. They took 5 days to scan, and found it was a juvenile
• Richard Thulborn suggested Heterodontosaurus was a junior synonym to Lycorhinus in 1970. Lycorhinus was named in 1924, and was also found in South Africa. He reclassified Heterodontosaurus tucki to Lycorhinus tucki, and said it was a distinct species because of small differences in the teeth and where it was found
• Thulborn also named a third species of Lycorhinus, Lycorhinus consors. Though Galton in 1973 disagreed with the synonymization. Charig and Crompton agreed in 1974 that Heterodontosaurus and Lycorhinus were in the same family, but thought they were still separate genera, especially since the holotype of Lycorhinus angustidens (the type specimen) was so fragmentary and not well preserved so it was hard to compare against. James Hopson eventually looked at the holotype of Lycorhinus and said Heterodontosaurus was its own genera in 1975. He also changed Lycorhinus consors to be Abrictosaurus consors
• Other dinosaurs that lived in the same time and place included Lesothosaurus, Massospondylus, and the theropod Meapnosaurus, as well as other heterodontosaurids such as Lycorhinus, Abrictosaurus, and Pegomastax. Other animals included amphibians, turtles, and crocodylomorphs

Fun Fact: Modern dinosaurs (birds) have a higher body temperature than humans.

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