10.1 Palaeogeography During Pangea & Plate Tectonics

What did Alfred Wegener notice, then suggest?

Noticed that the eastern coastline of South America & the western coastline of Africa looked like two connectable puzzle pieces

Fossils of ancient animals (unlikely able to swim across ocean) were found in both & there were several geological formations that seemingly had twins in the other

Suggested that the continents had once been connected → had since drifted apart (but he didn’t know how this had occurred)

The Crust

The outermost layer of the earth → continents & ocean basins

Is considered a thin layer → 5-25km deep

The Mantle

Layer below the crust

Considered in terms of the upper portion and the lower portion

The Lithosphere

(2)

Consists of the crust & the solid upper portion of the mantle → is rigid

Composes of many discrete pieces (or plates) that fit together

The Asthenosphere

The lower portion of the mantle

Is a viscous solid → slowly flowing, shape may be deformed under the uneven weight of the lithosphere → the intense heat & pressure cause the fluid behaviour

The Inner & Outer Core

Located below the mantle → primarily composes of iron & nickel

Outer core → molten liquid

Inner core → a solid ball w temp approx. the same as the surface of the sun

The —A— of the inner layers of the earth creates convection currents in the —B—.

Lower portions of the —B— slowly heat causing them to —C—, & then slowly cool causing them to —D—.

Pieces of the —E— are affected by these currents.

A → extreme heat of the inner layers

B → currents in the asthenosphere

C → heat causing them to expand & rise upwards

D → cool causing them to sink

E → plates/pieces of the lithosphere are affected by these currents

Plate Tectonics

The movement of the lithosphere

Provided an explanation for the drifting continents theorized by Wegner

Mechanism of Plate Tectonics

(progress through an ~4 step cycle)

1) The asthenosphere currents pull along the undersurfaces of the pieces → causes them to slowly move

2) The cool crust is more solid & dense than the layers below → causes lithosphere plates to slowly sink & to melt into the lower layers gradually along one of the edges of a plate

3) As one edge sinks → a small gap is created along the opp edge through which molten rock can escape

4) This rock then cools & solidifies → thus adding its own mass to the edge

Two Ways Plate Tectonics Has Been Verified

1) The discovery of mid-ocean ridges → revealed plate edges where new crust was being formed & show that rock on either side of the ridges have been slowly drifting apart

2) Advanced global positioning satellites tracking systems can detect the ongoing movements of the continents

As plates move, they can come into conflict & collide → what does this causes?

(3)

At the boundary where two plates collide → tremendous pressure builds

Often sites of sudden pressure releases → volcanoes & earthquakes

Gradual pressure releases can slowly build mountain ranges

What was the state of the world’s continents & oceans during the Triassic?

Pangea → single supercontinent

Panthalassa → single super-ocean

What effect did Pangea have on the diversity of dinos worldwide during the Triassic & the beginning of the Jurassic?

Single unbroken land mass → the first dinos could spread across the entire plant, w no major sea barriers

Thus late Triassic & early Jurassic dinos all across the world are fairly similar

Dinos During Pangea:

Sauropods Compared to Prosauropods

Sauropods surpassed prosauropods → both in abundance & body size

Characteristics of Diplodocids (4)

Were sauropods w extremely long necks (even compared to other sauropods)

Front legs were much shorter than their hind legs

The skull is elongated → has simple peg-like teeth that are positions only at the front of the mouth (not on the sides) → good for cropping off leaves/tender growth

Characteristics of Macronarians

(4)

Compared to diplodocids → have more robust bodies & their front legs are not notably shorter (some the front are longer)

Still have the long necks characteristic of sauropods

Has a shorter snout & their teeth are individual & line the entire jaw → mouth of a powerful muncher

What niche do diplodocids & macronarians share? How do they niche partition?

Both fill the ecological niche of high browsers

Diplodocids → adapted to reach high & prune off the most delectable Jurassic foliage

Macronarians → were less picky eaters, could crunch much harder, even woody vegetation → could eat what the diplodocids left behind

Ecological Niche

An animal’s role in the ecosystem; how it survives in that ecosystem

Niche Partitioning

When similar animals avoid direct competition for food resources by exploiting diff ecological niches

Thyreophorans

+ example

A group of ornithischians w body armor

Includes Stegosaurus

Allosauroids

(3)

Was a large theropod dino w vertebrae that interlock more rigidly → spines held stiffer

Legs were proportionally longer → suggests that they were faster than megalosaurids or ceratosaurids (other large predators)

Was among the most successful predators of the Late Jurassic

Characteristics of Coelurosaurs

(4)

Group of theropods w a long series of sacral vertebrae, narrow hands, and tails w back halves that are skinny, stiff, and lightweight

Birds arose from this group