3 Early Mammal Like reptiles

Question 1

3.5 Early mammal-like reptiles

LO:

Answer 1

Mammal-like reptiles of the

Palaeozoic

The Palaeozoic world

• Continental geography
• Climate
• Ecology
• Extinctions

Life on land

• The first tetrapods
• Amniotes

Early predecessors of mammals

• The Pelycosaurs
• Therapsids

Question 2

What is the Palaeozoic Climate characterized by?

What did ice sheets cover much of? for what periods?

Where were vertebrates restricted to?

What did continental coalescence lead to?

Answer 2

• Much of the Palaeozoic characterised by

fluctuating ice sheets affecting global

temperatures and sea level.

• Ice sheets covered much of Gondwana in the

mid-Carboniferous until the mid-Permian. This

caused wide variation in regional climate.

• Vertebrates restricted to the equatorial

regions.

• Continental coalescence increased land mass, altered ocean currents and influenced climate.

Question 3

What was the first land animal?

What as the first amphibian? When did it appear? Give an example

Answer 3

Lobe-finned fish (Crossopterigians) thought to be the predecessors of land tetrapods

The first amphibians appeared during the Devonian, about 350 mya. These were like BIG newts/salamanders – eg Ichthyostega (Late Devonian, Greenland) – well known fossil, it was one of the first tetrapods described

Question 4

The first tetrapods (“amphibians”) 363 Mya

Where were they commonly found?

As well as ichthyostega another well known fossil is acanthostega

What drove them onto land?

Answer 4

Commonly found in Greenland

Acanthostega

• Spent most its time in water
• Had a gills, and a lateral spine modifications were evident, in water spine doesn’t need to be adapted for gravity

Exploiting niches: food

Question 5

The first tetrapods (“amphibians”)

What was the significant find in 2006 that pre-dates the first tetrapods by 12 million years?

Answer 5

A highly significant find in 2006 was Tiktaalik roseae, better known as the “fishapod,” a 375 million year old fossil fish that pre-dates the first tetrapods by 12 million years

Question 6

Early tetrapod radiations

What are the three main groups that are recognised?

Answer 6

• Three main groups are classically recognised:

1. Temnospondyls (larger forms, e.g. Eryops)
2. Leptospondyli (smaller forms)
3. Lissamphibia (contains extant amphibians) – contains descendants that are living amphibians

Question 7

Adaptations for life on land

A range of physiological and physical adaptations have to occur whilst maintaing functional continuity.

List the physiological changes that need to occur for life on land

List the physical changes for life on land

Answer 7

Physiological

Sensory (olfaction replaces lateral line) – needs to be replaced by something more appropriate

Respiration – needs to change from gills to breathing … moist skin / proper lung based respiration
Water balance – internal water balance
Reproduction – major chain

Early amphibian like tetrapods – were tied to water – eggs were lay in water

Physical

Increased support of body (spine)
Limb joints and limb girdles – need modification
Digits – we go from having many digits to having just five, why five? No simple answer to that
Skin/scales
Reproduction

Question 8

Tetrapod vertebral morphology