Lecture 11 Flashcards
What is Tetrapoda?
A superclass
When did Tetrapoda arise?
During the Devonian period
What kind of organisms did Tetrapods arise from?
Lungfish-like Sarcopterygians
Name a few Sarcopterygians
Coelocanths, lungfishes, tetrapodamorph fishes & tetrapods
Describe Osteolepiforms
Cylindrical-like bodies, big heads and thick scales
Name some of the features that Osteolepiforms shared with tetrapods
Paired crescentic vertebrae and labrynthine teeth
What was one feature that was different between tetrapods and osteolepiforms?
Their ribs extended dorsally
What is a possible sister group to tetrapods?
Elpistostegalids
Elpistostegalids are more derived for shallow water life true or false?
True
What did elpistostegalids lose?
Unpaired dorsal and anal fins, their tail was also reduced
Name the two organisms that were the earliest known tetrapods until recently
Acanthostega & Ichthyostega
What was the recent discovery in regards to tetrapods?
Tiktaalik/Inuktituk fresh water fish seen in the shallows
In what period was Tiktaalik/Inuktituk around?
The Devonian period
Why was Tiktaalik significant time-wise?
It was 20 my older than acanthostega and ichthyosteag
Structurally, why was Tiktaalik significant?
Loss of bony operculum, ribs large & overlapping and forelimbs could bend in the middle
What did the loss of the operculum mean for tiktaalik?
It could raise its head up and snap up prey
What did large and overlapping ribs mean for tiktaalik?
Its body could be supported for being partially out of the water
What is the evidence for the aquatic life of acanthostega and ichthyostega?
Groove on the ventral side of the ceratobranchials to accommodate gill arteries, suggesting internal gills
What does polydactyl mean?
More than five toes
What digit number was variable across lineages?
Digit 5
What Hox gene clusters were responsible for digit development?
There are four gene clusters, HOXA-HOXD
When were the earliest known tetrapod tracks found?
Tetrapod trackways were found 18 my before the earliest known tetrapod fossils
Where were the tetrapod tracks found?
In the intertidal zone
What does the discovery of tetrapod tracks in the intertidal zone tell us?
That tetrapods and elpistostegalids overlapped for >10 my
Explain what was found in regards to movement in Icthyostega and current tetrapods
Icthyostega had limited ability to twist its main limb bones so couldn’t use ‘normal’ quadrupedal gaits. Couldn’t have made tetrapod tracks
Describe the classic theory of how tetrapods moved onto land
They moved from pond to pond before they dried out, although unsure as to how this would lead to being on land
What is another theory to describe how tetrapods moved onto land (juveniles)?
Juveniles congregated into shallow ponds to avoid predation and then fed on land
Describe the theory on how juvenile dispersal helped dispersal onto land
They were smaller and more able to cope with life on land with things like support, respiration & locomotion
What anatomical changes could be seen as adaptions to life on land?
Digits (support), ankles & wrists (articulation), pelvic girdle to vertebral column (predatory lunge in water) & distinct head (lifting to breathe)
When did the radiation of nonamniotic Palaeozoic tetrapods occur?
Late Devonian to early Cretacious period
Describe the habitat of the early Palaeozoic period
High sea & CO2 levels, greenhouse effect, hot and dry, few plants
Describe the habitat of the late Ordovician period
Glaciation, cooled some areas, invasion of land by aquatic plants
Describe the habitat of the Devonian period
Spread of plants affecting soils & climate change, cooling, soil development, increased weathering of rocks lead to trapped CO2 & high O2
Describe the development of the environment in the late Devonian period
Extensive vegetation & stabilised banks enabled a variety of microhabitats. Detrital inputs & wetlands vegetation provided a trophic base for complex food webs. 1st insects
Give a brief description of the role of oxygen levels
Low oxygen in mid Devonian favoured lung breathers & high oxygen/low co2 levels late Devonian/carboniferous period favoured insects
What were the main groups of Palaeozoic period
Stem tetrapods, Batrachomorphs, Reptilomorphs & Lepospondyls
What period is known as the major period of diversification?
The Palaeozoic
What are labyrinthodonts?
Stem tetrapods with deeply folded structure of enamel and dentine layers in the teeth
Give an example of stem tetrapods
Acanthostega and Ichthyostega
What is a Hynerpeton?
Had characteristics of tetrapods like shoulder girdle
What are stem amphibians?
Two main groups of Palaeozoic non-amniotic tetrapods, stem amphibians and stem amniotes
What is a temnospondyli?
Chubby short lookin crocodile thang
What is a large monophyletic group?
Amniotes
