LECTURE 5 Paleozoic Era SilurianDevonian Periods 439 mya

LECTURE 5: Paleozoic Era Silurian/Devonian Periods (439 mya- 360 mya)

What Index Fossil appears at the Beginning of the Silurian? • Parakidograptus acuminatus – Extinct group: graptolite (hemichordate)

What Significant Events Happened during the Silurian and Devonian? • Life emerged from the water and colonized the land. – Plants (green algae evolved into bryophytes, then tracheophytes) and animals (insects) KEY DEVELOPMENTS: – The development of vascular plants, pollen and seeds • provided plants with a way to reproduce and survive on dry land, creating new habitats – The development of jaws • allowed fishes and other emerging vertebrates to catch larger prey – The development of tetrapods— • limbed animals—would pave the way for animals that could walk on land

Why did Plants Move onto Land? • The ozone layer shielded life like water once did – Gave protection from the sun’s harmful radiation. Only water had provided this protection before • Soils had formed that could nourish plant life – Bacteria, algae, and fungi had gained an early foothold on land, secreting organic acids that broke rock down into its mineral elements. Nutrient-rich soils formed as these organisms died and their decaying matter combined with the minerals. – The next Plants to evolve were vascular plants

What Adaptations are Required for Land Plants? • Stand Upright (no support form water) • Tolerate UV radiation • Tolerate Climate Changes • Be able to acquire nutrients from substrate other than water • Produce gametes (seeds) that can move in the air

How did Plants Evolve? 1. Green Algae 2. Bryophytes (430 mya) • • • Non- vascular Moist areas Mosses/liverworts (spores) 3. Seedless Tracheophytes (420 mya) • • Vascular Ferns, horsetails 4. Seed Producing Tracheophytes (365 mya)(Gymnosperms)

First land plants (Bryophytes)likely similar to extant leafy liverworts…….

What is the Oldest Fossil Plants? • Cooksonia – 428 mya – Bryophyte – Small, few cm long – No leaves, roots horizontal stems with hairs connecting to soil

What was a Trimerophyte? • Trimerophyte (seedless vascular plant) – stems with branches Pertica quadrifaria • these leafless plants are early relatives of every seed-bearing plant, fern, and horsetail living today

• By the end of the Devonian: – Extensive forests (club moss and horse tail ancestors) with tall trees (Seedless Tracheophytes. Lycophytes) – These plants later were out competed by seed plants and nearly all have gone extinct

Why did Jaws Evolve? • The vertebrate jaw can be traced back to 440 mya • Most jawless fishes went extinct, but jawed fishes became the ancestors for most modern fishes today. • Jaws evolved from gill arches (Gnathostomes- jawed Fish) – From Jawless fish (Agnathas) • Helped fish catch food – Jaws allow mouths to open wide and catch larger prey – Jaws with teeth can bite, crush, and chew. • Protected by bony, overlapping plates, Placoderms were among the first fishes with jaws

Placoderm fish armored head Dunkleosteus terrelli Devonian (417 -354 million years ago) Cleveland, Ohio Stretching up to twenty feet long and sporting powerful jaws (no teeth) equipped with tooth-like plates, Dunkleosteus was one of the world’s first large vertebrate predators.

FISH GROUP KEY FEATURE Jawless Fish (agnathas) 500 mya - no jaws - no paired fins - gave rise to placoderms, cartilaginous and bony fish Placoderms – First Jawed Fish (Gnathostome) 439 mya -Jaws without teeth - Armored fish -Paired fins Cartilaginous (Chondrichthyes) 395 mya - cartilage skeletons - no swim bladder - no lungs - internal fertilization Bony (Osteichthyes) Actinopterygians (ray-finned) Sarcopterygians (lobe-finned) - gills - lungs - swim bladder - some developed fleshy lobe fins (gave rise to amphibians)

When did Tetrapods Evolve? • Fish were the first animals to develop “feet” about 370 mya – Sarcopterygian fishes had muscular lobes at the bases of their paired fins. Within these lobes were large bones, one of which connected the rest of the fin bones to the body, like toes on a foot – Their fins were made for walking. Over time, some Sarcopterygian fishes may have begun using their muscular, lobed fins to "walk" in shallow, swampy waters, pushing their way through dense plant growth – Tetrapods branched out to include many familiar animals. From one type of Sarcopterygian fish evolved the first tetrapods: • vertebrates with four paired limbs and digits (fingers and toes)

What is a Coelacanth? • "living fossil" – only lobe-finned fish in existence • Evolved about 360 mya • paired lobe fins that extend away from its body like legs and move in an alternating pattern, like a trotting horse

What is the Evidence for Tetrapod Evolution? • Homologous Structures – The front fins of certain sarcopterygian fishes and the front limbs of tetrapods share the same bones: humerus, ulna, and radius. – The hind fins of certain sarcopterygian fishes and the hind limbs of tetrapods share the same bones: femur, tibia, and fibula. • Sarcopterygian fins are paddle-like, while tetrapod limbs have digits (fingers and toes) that grip the ground

Eusthenopteron: "Fish with Legs" (Transition to tetrapod)

Panderichthys (“Fish with Fingers”)

Tiktaalik- 375 mya • Extinct Sarcopterygian • They may have begun using their muscular, lobed fins to "walk" in shallow, swampy waters, pushing their way through dense plant growth • Eventually they would move from shallow waters to land

Acanthostega- 365 mya • First Fish with Digits (8 of them) on each limb • Probably Stayed in shallow waters – Limbs could not support weight

Ichthyostega – 360 mya • First 4 -legged land animal- Amphibian – Stayed near water

What were the Characteristics of Early Tetrapods? • It lived in the water and had a long, fishy tail • But its feet had 8 digits (more than any living tetrapod has today)

What Happened at the End of the Devonian Period (360 mya)? • Mass Extinction #2 • Continental Movement – Continents had moved over the South Pole – Because of the pole’s yearround cold climate, snowfall accumulated on the continents, forming glaciers • The climate became too cold for many species • With much of Earth’s water frozen into glaciers, sea levels dropped. Lower sea levels would have robbed life of their habitat in the shallower oceans.

Who was Impacted by the Mass Extinction? • Up to 70% of all marine species may have died out – Reefs, and the life they supported, were devastated – Many species of corals, brachiopods, trilobites, and mollusks disappeared – The armored fishes—placoderms and ostracoderms—were completely wiped out

Sea Levels and Temp vs. Time