Lecture 8: Ornithischia- Stegosaurs and Ankylosaurs

Question 1

What are the main features?

Answer 1

Pelvis similar to birds pelvis. Process of pubis has rotated backward to lie close to and parallel with the Ischium. Opisthopubic condition.

Question 2

What are other shared features?

Answer 2

An additional bone, the predentary, joining the front of the lower jaws. A narrow bone, the palpebral, crossing the outside of the eye socket, possibly mobile and connected with the upper eye lid. A toothless and rough front tip of snout. Ossified (bony) tendons above the sacral region for stiffening the backbone at the pelvis.

Question 3

What were the basal ornithischia?

Answer 3

Triassic ornithischian fossils are extremely rare compared to triassic saurischians. Pisanosaurus (argentina), Eocursor (south africa). No definitve record of ornithischians in north america.

Question 4

Describe the Heterodontosauridae?

Answer 4

it was the most basal major radiation of ornithischia. Late triassic or early jurassic to early cretaceous; lived on most continents. Examples: heterodontosaurus, tianyulong, fruitadens. Small bodied bipeds with canine like front teeth and chewing back teeth.

Question 5

Describe the lesothosaurus (basal ornithischia)

Answer 5

is close to the base of the clade Genasauria, which contains the majority of ornithischians. Long limbed small herbivore. From lesotho, southern Africa. Early jurassic

Question 6

What is the thyreophora?

Answer 6

Thyreo- shield- phora- “bearer”. jugal (cheek bone) with broad processes behind the eye. Parallel rows of dermal armour scutes on the back of the body.

Question 7

What are the basal thyreophora?

Answer 7

Scutellosaurus: early jurassic, arizona
Emausaurus: early jurassic,germany
Scelidosaurus: early jurassic, Engalnd. Replaced by their stegosaurus and ankylosaur descendants in the middle jurassic (scelido. may acutally be the most basal ankylosaur

Question 8

Describe Stegosauria

Answer 8

(stego-roof and sauros-lizard) Osteoderms: row of bones that can develop into spines and plates along the back and tail. Parascapular spines over the shoulder blade in some species.

Question 9

Describe other features of the stegasauria

Answer 9

Quadrupedal limb posture. Long, thin small head (small brains!) Simple teeth-herbivores, short and massive forelimbs. long and columanr hindlimbs, broad hooves, 3-9 m in length, 300-1500 kg

Question 10

Stegasauria capacity for survival

Answer 10

worldwide distribution, origin in the middle jurassic, by late jurassic about 10 species, down to as few 2 in early cretaceous, Evolution over a large time span

Question 11

Describe the history of discovery of stegasaurs

Answer 11

Early discoveries in england in 1870’s. Great Dinosaur rush at como bluff by marsh and cope, upper jurassic morrison formation: stegosaurus. The Spiny kentrosaurus (kentro-prickly) disovered in eastern africa, 1910s. Recent discoveries in china and portugal.

Question 12

Describe the Paleobiology of the stegasauria

Answer 12

Footprints are uncommon. Gait- not built for great speeds. Large and strong hindlegs (stride) short forelimbs (shorter stride). Cadence: hindlegs and forelimbs work at the same rate. Hindlegs surpass the forelimbs.

Question 13

Consequences of body build

Answer 13

Slow walk, temporarily bipedal by lifting up forelimbs. speeds of 6-7 km/hour are estimated

Question 14

Food mechanisms of stegasauria

Answer 14

Jaws are covered with rhamphotheca as seen in modern turtles and birds. Sharp edged allowing stripping foliage from plants. small chewing teeth, weak chewing muscles.

Question 15

Stegosaurus level of feeding?

Answer 15

Body position suggest low feeding on underbrush. Centre of gravity is more back due to very strong hind legs. Bakker suggested standing on hind legs. Long flexible tail acted as 3rdleg. Modern analogue to this is a kangaroo

Question 16

Describe the stegasaurs brains!

Answer 16

Brain has to be smaller than the brain case.To measure brain size, paint case with latex and pull out through foramen magnum (opening for spinal cord) normally brain size grows with body size. Stegosaurs have an uncomplicated range of behaviors.

Question 17

Describe stegosaurus behavior

Answer 17

No known nests, no known eggs, sexual dimorphism (number of sacral ribs, shape of the femur)

Question 18

The roles of spines and plates

Answer 18

Were they purely defense? not attached to underlyign neural spine of the vertebrae, but embedded in the skin. Put down and raised for defense? always up for thermoregulation, evenly grooved with lines and honeycomb structures. Surrounding blood vessels helping to cool and absorb solar energy. Plates are in double row and staggered.

Question 19

Describe the phylogeny

Answer 19

The early ones had spines, serving for defense, later ones had plates. Vascular serving for thermoregulation.

Question 20

What was the cluster of long spikes on the tail of a stegosaurus nicknamed?

Answer 20

The thagomizer, it was a defensive weapon

Question 21

Name the Modern examples of Ankylosaurs?

Answer 21

Armadillo, turtles and certain bugs. Armour almost totally protected animal.

Question 22

Describe the evolution of ankylosaurs

Answer 22

First definitive ankylosaurs in middle jurassic, fossils are rare. Some late jurassic and early cretaceous species may form a clade of early ankylosaurs, polacanthidae. Great increase in diversity towards the end of the early cretaceous, derived families ankylosauridae and nodosauridae, lasted until the end of the cretaceous.

Question 23

Size of ankylosaurs

Answer 23

Moderate size, mostly up to 5 m in length, short legs

Question 24

History of research

Answer 24

Hylaeosaurus discovered in England by Mantell in 1830s.One of the first dinosaurs named, and one of the original three members of Owen’s Dinosauria. Nodosaurus from Wyoming named by Marsh. Not recognized as their own group distinct from the stegosaurs until the 1920s.

Question 25

Name the important fossil localities for ankylosaurs

Answer 25

Alberta Badlands, Mongolia, also present in southern Gondwana (Australia and Antartica)

Question 26

Is there an incomplete fossil record for ankylosaurs?

Answer 26

Yes, plate arrangement on neck back and tail is based on only a few specimens. Good fossils from China and Mongolia. Asian fossils often found in upright position: rapid burial, possibly in sandstorms

Question 27

Describe their habitat (ankylosaurs)

Answer 27

Skeletons in North America hace been found near marine settings or in marine sediments. Terrestial, but near the sea

Question 28

What position are fossils typically found in?

Answer 28

North american specimens commonly found upside down, due to heavy armour turning animal around prior to settling.

Question 29

What distinctive feature did ankylosaurs have?

Answer 29

A Terminal club- Distal vertebrae fused together to form handle, Osteoderms fused to vertebrae to form knob. Nodosauridae had no tail club.

Question 30

Food and eating habits?

Answer 30

Head is carried close to the ground. Theory of eating bugs not widely accepted. Herbivores due to tooth and break shape.

Question 31

Describe ankylosaur mouth parts

Answer 31

Shape of the beak varies: scooped shaped (selecting plants) Round shaped (indiscriminate feeding). Teeth not closely packed, wear and tear can be seen in fossil teeth.

Question 32

Did they have a long tongue? (ank.)

Answer 32

it is Suggested by bones in the throat supporting the tongue

Question 33

What did ankylosaurs secondary palate allow them to do?

Answer 33

to chew and breathe at the same time

Question 34

Did they have deep cheek pouches? (ank.)

Answer 34

Identified by teeth deeply inset

Question 35

Describe their digestion (ankylosaurus)

Answer 35

Deep rib cages: hosting an expanded abdominal region & possibly had fermentation compartments like horses, rhinos and cattle

Question 36

what was their movement like? (ank.)

Answer 36

Large weight so slow movement. Trackways suggest a speed of 3 km/hour. also suggested by limb and body posture.

Question 37

Their brain and Behavior (ank.)

Answer 37

Small brains. Slow animal, but well protected from predators. Plates over the eyes, usually solitary specimens, but a group of juvenile pinacosaurus was found (fortress in the mesoizoic landscape.