Life on Land 1. Timescales and routes onto land 2. Physiological challenges 3. Plants 4. Invertebrates 5. Vertebrate

1. Life on Land 1.Timescales and routes onto land 2. Physiological challenges 3. Plants 4. Invertebrates 5. Vertebrates

2. 1. Timescales and routes onto land Carboniferous Ordovician Devonian Devonian Carboniferous Most migration onto land was Palaeozoic. Major groups evolving entirely on land include insects, spiders and higher tetrapods.

3. 2. Physiological challenges 1. Homoiohydry Plants Animals Challenge Water Gas exchange Support Reproduction Internal hydrated environment - lignin xylem waxy cuticle stomata Stomata (CO2) Lignin, cutin (may have evolved from precursor molecules involved in UV protection). Spores, sporopollenin, internal fertilization Internal hydrated environment - waterproof cuticle, skin, modified excretion Diffusion eg spiders Lungs eg tetrapods (O2) Hard cuticle, arm/leg modifications Waterproof eggs Internal fertilization Or by living in cryptic or ephemeral habits, Or by being resistant to desiccation, eg. Some mites, mosses (poikilohydry)

4. 3a. Plants - early events Origin of vascular plants, eg. Rhynia. Tens of cm height, extensive cover. Silurian Turf of mosses (bryophytes) and liverworts - non-vascular plants a few cm in height. Origin of spores Ordovician Green scum near water. Bacteria and algae Limited surface stabilisation and humus buildup. Precambrian/ Cambrian

5. 3b. Plants - first forests Widespread,dense forests in a range of climatic bands and topographic niches. Large scale coal production. Rise of seed plants - gymnosperms eg Seed ferns, conifers, cycads Ice age?? Carboniferous Secondary wood by mid-Devonian. Deep root systems, soil development. Mainly seedless plants (eg ferns) Altered weathering/ CO2 Devonian Archaeopteris - a progymnosperm

6. 4. Invertebrates Crabs, woodlice, amphipods Mainly preadapted forms Post Palaeozoic migrations Slugs, snails, worms, scorpions May have needed leaf litter Main period of colonization Insects evolve Upper Palaeozoic forests Millepedes, spiders, other primitive arthropods Lower Palaeozoic turf

7. 5a. Vertebrates - family tree of tetrapods Turtles Diapsids Synapsids Modern amphibians Ichthyostega Ancestral reptile Lungfish Tetrapods Lobe finned fish (rhiphidistian) Lobe fin Tetrapod leg Ray finned fish

8. 5b. Timing of tetrapod evolution Carboniferous - reptile-like animals such as Westlothiana and real reptiles like this Hylonomus. True reptiles produce desiccation resistant eggs. Devonian - various tetrapods are known, most mainly swimmers, like this Ichthyostega. Relatives of these forms became truly terrestrial, but layed eggs in water. Silurian - Lobe-finned fishes swim using their fins. They were probably capable of limited locomotion on land, eg between drying pools