Life on land

We're pretty sure that life began in the oceans, and that the major milestones we looked at in the first lecture of this course occurred in water. Thus life on land represents a series of invasions of this new habitat from marine and/or freshwater organisms. This series of videos provides an overview of how and when this has occurred.

Introductory video

Summary

Today, based on your feedback we have six shorter videos as opposed to four slightly longer ones. Total running time remains similar – thanks for those of you that took the time to feedback that more, short videos is preferable, it was a pleasure to incorporate this (sorry that it was only possible to include it by the last lecture – this was the first I could because lectures were recorded in advance). We'll finish off the content in zoom, as in recent weeks. The lineup today is:

  • Terrestrial ecosystems – Section 10.1.
  • Adaptations to life on land – Section 10.2.
  • Precambrian life on land – Section 10.3.
  • Plants move onto land – Section 10.4.
  • Arthropods move onto land – 10.5.
  • Vertebrates move onto land – 10.6.
  • Life on land since the Mesozoic – Zoom.

10.1 – Terrestrial ecosystems

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Summary

  • For our puproses, we may want to consider freshwater ecosystems as terrestrial as well as dry land.
  • Multicellular eukaryotes moved onto land during the phanerozoic. Today we'll be looking at some major groups, in the order they made it onto land, namely:
    • Plants!
    • Arthropods!
    • Vertebrates!
  • There is a great diversity of life on land – potentially because there are so many niches in land environments.

So, we're thinking about land animals. Obviously, there is no better way to get thinking about them than doing a quiz!






10.2 – Adaptations to life on land

Air is different to water, in many ways. Just as we cannot breathe underwater, aquatic animals struggle to breathe air. Dealing with this change in respiration is just one of a suite of adaptations to life on land. We look at these adaptations in the next video.

Summary

Amongst the suite of adaptations to life on land across eukaryote groups, we see changes allowing organisms to:

  • Minimise water loss
  • Deal with increased gravity / lack of bouyancy
  • Present damage from UV light
  • Reproduce in the absence of water
  • Breathe air

10.3 – Precambrian life on land

Many books will tell you that all life on land originates in the last 500 million years. But that isn't strictly true.

Summary

  • There hasn't always been land exposed to the air. We believe this probably appeared by 3.2 Ga, and was definitely present by 2.5 Ga
  • We have evidence for life on periodically exposed bacterial mats from 1.0 Ga (Torridonian rocks, NW Scotland)
  • And in lacustrine/fluvial ecosystems at around the same time (Nonesuch Shale, Mi/Wi USA)

10.4 – Plants move onto land

The first macroscopic organisms on land (that we know of) were plants (FWIW, I suspect fungi were around on land at this time too). Lets learn about the early fossil record of plants!

Summary

  • The earliest evidence for complex plant life on land is found in the form of spores in the Ordovician
  • Land plants started as small, non-vascular things like mosses
  • Vascular plants followed soon afterwards, during the Early Silurian
  • The oldest widely accepted land-plant body fossil is the ~425 Ma genus Cooksonia

10.5 – Arthropods move onto land

Arthropods may have been on land with – or even before (ask me in zoom...) – the first plants. But we pick them up in the fossil record shortly after Cooksonia.

Summary

  • Myriapods (the group including millipedes and centipedes) and arachnids were on land by the Silurian
  • Many of the problems we have working out the tree of life of the arthropods are down to convergent evolution based on living on land
  • Our insights into early life on land are very much defined by a few important lagerstätte
  • Forest ecosystems appear by 380 Ma; rooting systems then radically change continental sedimentary systems

10.6 – And vertebrates move onto land

Late to the life on land game, coming in almost last of major groups, are the vertebrates!

Summary

  • Vertebrates moved on to land in the Devonian between 385 and 375 Ma, evolving within the lungfish
  • The split between true amphibians (Lissamphibia: frogs, caecilians and salamanders) and amniotes (mammals and sauropsids, the latter being reptiles + birds) may have occurred in the Late Devonian
  • Certainly, the first amniotes – small- to medium-sized insectivores – were around in the Carboniferous coal forests
  • The insects (the first animals to fly) had also taken to the skies by this point

Bonus stuff!

You made it! Well done for surviving semester one of the academic year 2020-2021.

Want to learn more about human evolution?

We are very lucky at the University of Manchester to have a world expert in human evolution working with us – Dr Marta Pina Miguel. Dr Pina Miguel is a Marie Skłodowska-Curie Fellow in the University, an Associate Researcher at the ICP Miquel Crusafont (Spain), and a world expert in the evolution of the primate postcranium and the origin of the positional behaviors observed in living apes and humans.

She has kindly put together a short overview for everyone sitting EART22101 on the evolution of bipedalism! You can find this bonus (and exclusive!) content below:

This is the end

And that, right there, brings us to the end of the last website for EART22101 Evolution and Palaeobiology. Thanks ever so much for your engagement throughout: I hope you have enjoyed the course. I have certainly enjoyed writing and delivering it!

Happy christmas. Russell & Rob hope you have a great break.

The bReakfast Club closing scene