Dinosaurs Test 3

Susannah Maidment

Believes that Jakapli is a ceratopsian, not a basal thyreophoran

• a lot of work on stegosaurs and other ornithischians

Victoria Arbour

A lot of work on ankylosaurs and other ornithischians (Zuul, Ziapelta)

Peter Dodson

Studied lambeosaurines from N. America (1970s)

• many species had been named

• Dodson recognized that much of the variation between these ‘species’ actually reflected changes through growth (ontogeny)

Holly Woodward

Testing of Nanotyrannus hypothesis using histology

Maiasaura growth series

O.C. Marsh

Bone Wars

• Triceratops

• Stegosauria

Thyreophorans

“Shield bearers”

• stegosaurs, ankylosaurs

Marginocephalians

“Shelf heads”

• pachycephalosaurs, ceratopsians

Ornithopods

“Bird foot”

• hadrosaurs, iguanodonts, others

Feathers in Ornithischians

• tianyulong

• psittacosaurus

Yinlong

“Hidden dragon”

• one of the earliest known ceratopsians

• HAS A ROSTRAL BONE

Aquilops

• N. America

• small

• earliest known ceratopsian from North America

  • Montana

Chasmosaurines

“Long Frills”

• long BROW horns

• shorter NASAL horn

• Late Cretaceous, North America

TRICERATOPS

Centrosaurines

“Short Frills”

• short BROW horns

• longer NASAL horns

• often have SPIKES ON FRILL

• Late Cretaceous, N. America & Asia

CENTROSAURUS

Genasauria

Thyreophora + Cerapoda

Cerapoda

Marginocephalia + Ornithopoda

• Cerapods have ASYMMETRICAL TEETH with enamel on ONE side (dental batteries)

Saurolophine

Ornithopods

• no elaborate head crest

Maiasaura, Edmontosaurus

Ontogeny

The development of an organism; changes through growth

Nanotyrannus

Late Cretaceous

N. America

Small tyrannosaur discovered in Hell Creek

• more teeth in jaw than T. rex

• ROBERT BAKKER

Ootaxonomy

eggs

Osteogenetic cell

stem cell

Osteoblast

forms bone matrix

Osteocyte

maintains bone tissue

Osteoclast

resorbs bone

LAG

Line of Arrested Growth

• indicator of ~annual growth slowing/stoppage

Physiology

the study of various integrated functions of an animal

Metabolism

the chemical reactions and pathways an organism uses to obtain energy and put it to work

• an aspect of physiology

Endotherm

organism that regulates its temperature INTERNALLY

• humans

Ectotherm

organism that uses EXTERNAL sources to regulate its temperature

Poikilotherm

organism whose core temperature FLUCTUATES

Homeotherm

organism whose core temperature remains constant

Predator/Prey Ratios

• Bakker proposed these ratios were consistent with ENDOTHERMY

  • endothermy is much more costly in terms of energy use than ectothermy

  • ectothermic predators require less food than endotherms

    • different predator/prey ratios

  • dinosaur predator/prey ratios more similar to that of mammals (endotherms)

PROBLEMS:

• assumes all death due to predation

• based on museum collections (may be biased towards rare or well preserved fossils)

Respiratory turbinates

Mucus covered surfaces of turbinates pull moisture out of the air before it leaves the nose, conserving water

• apparent absence of turbinates in non-avian dinosaurs suggested that they may NOT have been endothermic

  • however, some dinosaurs have very complex nasal passages (Ankylosaurs, pachycephalosaurs)

• turbinates may also be related to smell & cooling the brain

Histology

• can be examined to explore metabolism

• heavily remodeled bone

  • lots of nutrient supply

Mesozoic plants

Gymnosperms (non-flowering seed plants): tough and toxic, resist herbivory

Angiosperms (FLOWERING plants): flowers, fruits, replacement growth with browsing, work with and encourage herbivory

Late Triassic: Important new vertebrates

• first frogs and turtles

• first pterosaurs

• first mammals

Endemism

Development in relative isolation leading to distinctness

• a region populated by distinct faunas unique to it has high endemism

LOW endemism during Triassic and early Jurassic (Pangaea)

Mesozoic Takeaways

1. Two biggest extinctions frame the Mesozoic (Great Dying, K/Pg)

2. Triassic is unusual… has old groups, Triassic groups, and new groups established which persist through Mesozoic

3. Dinosaurs dominate terrestrial environments from Late Triassic until the end of the Cretaceous (~165 Ma)

4. Pterosaurs and various marine reptiles through Mesozoic too

5. Modern groups (mammals, frogs, lizards, birds, snakes) all present through much of Mesozoic

6. Birds have longer history with non-avian dinosaurs (85 Ma) than without (66 Ma)

7. First mammals appear about the same time as first dinosaurs! (Triassic Period)

8. Plants (flora) show similar pattern; archaic groups in Triassic, continually modernize through Mesozoic. Angiosperms in early Cretaceous.

9. Pangea breaks up (Gondwana & Laurasia) and continents move towards modern position

10. Climate warm and equable. High sea levels throughout

Five Largest Extinctions (Oldest-Youngest)

1. Ordovician-Silurian (450-440 Ma)

   1. Two events, 85% of all species became extinct

2. Late Devonian (375-360 Ma)

   1. 70% of all species became extinct. Evidence for a series of extinction pulses

3. Permian-Triassic (252 Ma): The Great Dying

   1. 90% of all species became extinct; recovery of vertebrates took 30 Ma

4. Triassic-Jurassic (201 Ma)

   1. about 70% of all species became extinct

5. Cretaceous-Paleogene (66 Ma)

   1. about 70% of all species became extinct

K/Pg Asteroid Impact Hypothesis

• proposed in 1980

  • Helen Michel, Frank Asaro, Walter Alvarez, Luis Alvarez

• abnormal abundance of iridium in K/Pg marine clay in Italy

• iridium anomaly now found worldwide in marine and terrestrial record

• hypothesize 6-mile wide bolide (impacting body) struck Earth w/ catastrophic consequences

Found associated with K/Pg boundary

Shocked Quartz: quartz placed under such pressure that the crystal lattice becomes compressed and disoriented; “impact metamorphism”

Microtektites: small, droplet-shaped blobs of silica-rich glass thought to have crystallized from the impact ejecta

Chixulub Crater

Yucatan Penninsula, Mexico

• 180 km in diameter

• evidence of tsunami deposit in Texas

  • Chicxulub site situated to produce such an event

• evidence indicate low-angle, directional impact

The Hell Creek Formation

One of the few terrestrial sections in the world that cross the K/Pg boundary

• deposited ~68-66 mya

Dinosaur/Mammal species

>10,000 species of dinosaurs alive today

~6,500 species of mammals

Which one of the following is NOT one of the three major groups of ornithischian dinosaurs?

Sauropods

This pachycephalosaur may actually be a juvenile Pachycephalosaurus

Dracorex

Ornithischians or ‘bird-hipped’ dinosaurs INCLUDES modern birds

FALSE