Lecture 9: Pachycephalosauria

Question 1

What does Pachycephalosauria mean?

Answer 1

Pachy means thick, kephale means head and Saurus means lizard

Question 2

Describe the Fossil record/discovery

Answer 2

Rudimentary fossil record. 1850’s stenopelix found in lower cretaceous of Germany but skull was lacming and its position in marginocephalia is still uncertain (possibly ceratopsian) First cranial fragments found in western US by Leidy and Marsh in late 1800s, but not properly identified

Question 3

Who discovered the first pachy. dome? Where did he find it? what did he name it?

Answer 3

lawrence lambe discovered it in Alberta, named Stegoceras in 1902.

Question 4

Who described the first and only reasonably complete stegoceras in 1924?

Answer 4

CM Gilmore. it had skull and partial skeleton, 2 m in length, short forelimbs, long hindlimbs and ornamented skull.

Question 5

In 1943 what part of the Pachycephhlosaurus was found?

Answer 5

Skull, it was 65cm in length, with solid dome 20m thick, snout studded with large densely packed bumps. Animal estimated up to 8m long

Question 6

In 1970s-80’s where was a large number of specimens found?

Answer 6

China & Mongolia. there was naming of new genera, homalocephale, prenocephale, tylocephale, wannanosaurus, goyocephale.

Question 7

What did the homalocephale skull look like?

Answer 7

Flat skull but thick headed (a juvenille character?)

Question 8

Describe the recent discovery (2006) of the dracorex

Answer 8

Latest cretaceous, found in south Dakota. Very spiky but domeless skull, resembles a dragon. Controversial taxon: juvenille?

Question 9

Dome characteristics are helpful for ____________ taxa

Answer 9

Distinguishing

Question 10

What was preservation like?

Answer 10

Overrepresentation of skulls due to its sturdiness. over a dozen pachycephalosaurian species, many based only on skulls/domes. All in northern hemisphere. Late cretaceous. Long gap bw evolutionary divergence from other marginocrphalians and their first definite appearance in the fossil record.

Question 11

What are the characteristic features of the pachycephalosaurus?

Answer 11

Mainly from cranial region, thickened skull roof, modified cheek region, shortening of floor of braincase, expansion of the back and skull, strongly ornamented external skull surface, short forelimbs, reduction of pubic bone (it does not contribute to the hipjoint) special features on back and tail.

Question 12

Species division based on skull roof

Answer 12

Pachycephalosauridae: rounded skull roof
Homalocephalidae: flattened skull roof (their phylogenetic relationship is debated: flat skull roof of homalocephalids can also indicate immaturity)

Question 13

distribution of pachycephalosauria

Answer 13

Found exclusively in Northern hemisphere (laurasia). Origin might be in central and eastern Asia where most were found. Arctic migration to north america. Alaskacephale found on North slope of Alaska

Question 14

What was the preservation like in North America?

Answer 14

mainly skull caps found in river and lake sediments, Skeletons are widely missing- perhaps No suitable habitats with fossilization potential

Question 15

Why isn’t transport over long distances hypothesized anymore?

Answer 15

recent analysis of wear on skull caps does not support this

Question 16

Fossil abundance

Answer 16

a total of 575 specimens of pachycephalosaurids are known, almost three quarters of those are from the campanian belly river group in Alberta.

Question 17

Preservation in Asia

Answer 17

More complete specimens, desert conditions, small streams, there is little evidence for transport

Question 18

Desribe their eating habits

Answer 18

They were herbivores, browsing not far from the ground, front jaw carries simple peg like gripping teeth, further back are cheek teeth with small triangular crowns with coarse serration, cutting and puncturing plant leaves and fruits.

Question 19

Why is their ribcage broad?

Answer 19

Leaves room for a large gut

Question 20

What is their social behaviour like?

Answer 20

Head butting (like rams) scars on smooth outer surface of skulls, inner structure: network of bony columns perpendicular to surface. support against stress

Question 21

Features that support behaviour

Answer 21

Strong neck muscles, dampening hurtful rotation or dislocation, vertebrae spliced together in a tongue and groove fashion, ridgidity to back preventing lateral rotaion

Question 22

Sexual dimorphism

Answer 22

Specimens in the same area and during same time: sympatric specimens. Comparisons between dome size and braincase size. Accelerated growth of dome size and thickness: males? smaller domes: females?
Dimorphism of domes has been suggested for pachycephalosaurs but not confirmed.