Episode 93 is all about Pachycephalosaurus, an ornithischian with a thick skull.

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In this episode, we discuss:

• The dinosaur of the day: Pachycephalosaurus
• Name means “thick headed lizard”
• Type species is Pachycephalosaurus wyomingensis
• Lived in the late Cretaceous in North America (Montana, South Dakota, Wyoming)
• Known from a skull with thick skull roofs (more complete fossils found after it was first described)
• Tylosteus, a dinosaur from western North America, is synonymous with Pachycephalosaurus
• First Pachycephalosaurus fossils may have been found in the early 1850s
• Donald Baird found a bone fragment in 1859 or 1860 in the Lance Formation in Montana. Joseph Leidy described it in 1872, but thought it was part of an armadillo-like animal or part of the dermal armor of a reptile. It was called Tylosteus. Then more than 100 years later Baird reexamined the bone and found it was part of the bone on th eback of the skull of Pachycephalosaurus
• Usually the name Tyolsteus would remain because it was named before Pachycephalosaurus, but Baird petitioned to use Pachycephalosaurus instead of Tylosteus in 1985 because the name Tylosteus hadn’t been used in more then 50 years, and was based on undiagnostic materials
• Charles Gilmore named Pachycephalosaurus wyomingensis in 1931, based on a partial skull found in the Lance Formation in Wyoming. Gilmore assigned it Troodon wyomingensis but Charles Sternberg corrected this in 1945
• Had teeth similar to Troodon, which is why it was classified as a Troodon
• Barnum Brown and Eric Maren Schlaikjer found more complete material and changed the name to Pachycephalosaurus in 1943. They named two species: grangeri (based on a skull from the Hell Creek Formation in Montana) and reinheimeri (based on a dome from the Lance Formation in South Dakota). As of 1983, these species are considered synonyms of Pachycephalosaurus wyomingensis
• Then Troodon‘s tooth was found to match Stenyonychosaurus, a theropod very different to pachycephalosaurids, so the new group was established, Pachycephalosauridae in 1974, instead of Troodontidae (Pachycephalosaurus was the next genus with seniority)
• This is because the oldest Pachycephalosaurus fossils were described in 1872
• Two Pachycephalosauria most closely related to Pachycephalosaurus are Dracorex and Stygimoloch, which may be junior forms of Pachycephalosaurus
• Stygimoloch was named in 1983, Dracorex in 2006
• Dracorex hogwartsia was named in 2006 in honor of Harry Potter
• In 2007, Jack Horner presented at the Society of Vertebrate Paleontology that Dracorex and Stygimoloch may have been juveniles Pachycephalosaurus instead (dome and horns are not well developed). Jack Horner and M.B. Goodwin published their findings in 2009. They said the Pachycephalosaurus lost its spikes and grew domes as it matured. More evidence of this from baby Pachycephalosaurus skulls described in 2016 by David Evans and Mark Goodwin from two bone beds in the Hell Creek Formation. They had knobs on their skulls, which shows they started off with knobs and then developed domes. Nick Longrich and colleagues published a study in 2010 that supported the idea that flat-skulled pachycephalosaurs were juveniles, PLOS One: Extreme Cranial Ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus by John R. Horner , Mark B. Goodwin. Published: October 27, 2009
• Found that Dracorex and Stygimoloch were juveniles of Pachycephalosaurus
• In 2006 Robert Sullivan said that the Tylosteus bone may be more like Dracorex than Pachycephalosaurus (though Dracorex may be a juvenile Pachycephalosaurus)
• Lived in the same time and area as T-rex
• Either herbivorous or omnivorous
• Unclear what they ate. They had small teeth that could not chew tough vegetation. Probably ate leaves, seeds, fruit, and insects
• Had sharp, serrated teeth, good for shredding plants
• Small teeth, with leaf-shaped crowns
• Had a pointed beak
• About 15 ft (4.5 m) long and weighed 990 lb (450 kg)
• Bipedal
• Had long hindlimbs and small forelimbs
• Had large eye sockets that faced forward, so had good vision and probably binocular vision
• Probably had a short, thick neck and a heavy, rigid tail
• Had an S or U curved neck
• Known as bone-headed or dome-headed dinosaurs
• Had a large, bony dome on the top of its skull (10 in, 25 cm thick). Back of the dome had bony knobs and the snout had short bony, blunt spikes that projected upwards
• Scientists at one point thought that Pachycephalosaurus heads were kneecaps (in the late 1800s) when not many dinosaur bones had been found
• Thick skull domes made scientists think Pachycephalosaurus fought each other by butting heads (disputed)
• Scientists used to think that Pachycephalosaurus were like bighorn sheep or musk oxen, except bipedal, and that males rammed their heads into each other
  Now there’s a debate. It’s thought the skull roof couldn’t have sustained the impact of ramming, and it wasn’t until recently scientists found evidence of scares or damage on the skulls
• The S or U shaped neck meant they couldn’t directly head butt
• They may have fought by flank butting instead, based on the fact that they were pretty wide (Sues proposed this theory in 1978, Ken Carpenter explained more in 1997)
• Goodwin and Horner did a study in 2004 that showed the bone structure of the dome is spongy inside (may have crumbled from too many blows to the head)
• PLOS One: Common Functional Correlates of Head-Strike Behavior in the Pachycephalosaur Stegoceras validum (Ornithischia, Dinosauria) and Combative Artiodactyls by Eric Snively , Jessica M. Theodor. Published: June 28, 2011
• CT scans of Pachycephalosaurs (Stegoceras and Prenocephale prenes) found they could withstand head to head impacts
• Joseph Peterson did CT scans of Pachycephalosaurus skull in 2012
• A study in 2012 showed cranial pathologies that probably happened from fighting. In 2013, Peterson et. al found that 22% of all domes in their study had cranial pathologies from osteomyelitis, an infection from trauma that leads to infection of bone tissue. Flat headed pachycephalosaurids did not have pathologies. This supports the idea that they fought intra species (adult males at least). Also, pachycephalosaurid domes are made of fibrolamellar bone, which has fibroblasts that help heal wounds. This strongly supports the idea that they butted heads
• Dome may have attracted mates
• Can see Pachycephalosaurus in Jurassic Park movies. In The Lost World it was portrayed as smaller (more like Stegoceras size)
• Pachycephalosaurus is one of the four dinosaurs you can play as in the game Saurian
• Pachy is also in ARK: Survival Evolved. Wild ones in the game are usually passive, but also charge and headbutt. Domesticated ones are good for battle (because of head butting), and it’s fast
• Part of the clade Pachycephalosauria (herbivorous ornithischians that lived in the Late Cretaceous in North America and Asia)
• Although Pachycephalosauria are bipedal, they are more closely related to ceratopsians than ornithopods
• Pachycephalosaurus is the largest known pachycephalosaurid
• Pachycephalosauria is a clade of ornithischians
• Name means thick headed lizards
• Lived in the late Cretaceous in North America and Asia
• Bipedal with thick skulls
• Fun fact: The book Articulating Dinosaurs by Brian Noble recounts the original T-rex mount in the AMNH which is in a Barney-like upright position and Noble quotes Henry Fairfield Osborn saying, “The upright figure is not well balanced and will be more effective with the feet closer together, the legs straighter and the body more erect. These reptiles have a series of strong abdominal ribs not shown in the models. The fourth position places the pelvis in an almost impossible position…” So in this case at least, they intentionally made the mount relatively unrealistic in order to make it look more impressive…

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