Review 1 st Paleozoic Vertebrate lecture At one

Review, 1 st Paleozoic Vertebrate lecture • At one point in their lives, all chordates have: – – Notochord Dorsal hollow nerve cord Gill/phyrangeal slits Tail • First vertebrates were marine fish without jaws – Ostracoderms • Devonian = Age of Fish

Evolution in the Devonian • Evolution of jaws was a big deal – Extended ecological web/opened new ecological niches • Ray Finned Fish and Lobe Finned fish – Lobe fins -> lungfish, crossopterigians (both have protolungs) – Crossopterygians -> amphibians • First creatures on land were Arthropods (early Devonian)

Amphibians— Vertebrates Invade the Land • Although amphibians were the first vertebrates to live on land, they were not the first land-living organisms • Land plants, which probably evolved from green algae, first evolved during the Ordovician • Furthermore, insects, millipedes, spiders, and snails invaded the land before amphibians

Oldest Amphibians • The oldest amphibian fossils Ichthyostega – found in the Devonian of eastern Greenland – streamlined bodies, long tails, and fins – four legs, a strong backbone, a rib cage, and pelvic and pectoral girdle Precursor organism (Acanthostega) Was adapted to movement in Wet boggy environments

Rapid Adaptive Radiation • Like other groups that moved into previously unoccupied niches – amphibians underwent rapid adaptive radiation – became abundant during the Carboniferous and Early Permian • Little resemblance to modern amphibians • Much more diverse

Carboniferous Coal Swamp • Reconstruction of a Carboniferous coal swamp The serpentlike Dolichosoma Large labyrinthodont amphibian Eryops

Transition from Water to Land • In passing from water to land, plants and animals had to solve the same basic problem – the method of reproduction was the major barrier to expansion into the various terrestrial environments – required evolution of the seed in plants and the amniote egg in animals

Evolution of the Reptiles — the Land is Conquered • Amphibians limited in colonizing the land – had to return to water to lay their gelatinous eggs • Evolution of the amniote egg freed reptiles from this constraint http: //www. geoclassics. com/mesosour. htm

Amniote Egg • In an amniote egg – the embryo is surrounded by a liquid sac, the amnion cavity – provided with a food source (yolk sac) and waste sac • Its evolution freed reptiles to inhabit all parts of the land

Able to Colonize All Parts of the Land • In this way the emerging reptile is – in essence a miniature adult – bypassing the need for a larval stage in the water • The evolution of the amniote egg allowed vertebrates – to colonize all parts of the land – no longer had to return to the water as part of their reproductive cycle

One of the Oldest Known Reptiles • Reconstruction and skeleton of Hylonomus lyelli from the Pennsylvanian Period – Hylonomus lyelli was about 30 cm long

Paleozoic Reptile Evolution • Evolutionary relationship among the Paleozoic reptiles

Pelycosaurs (Finback Reptiles) • • Most pelycosaurs have a characteristic sail on their back Sail explanations: display, thermoregulation Odd: not closely related; neither had ‘sailed’ predecessor Adaptive escalation? The herbivore Edaphosaurus The carnivore Dimetrodon

Therapsids— Mammal-like Reptiles • The pelycosaurs became extinct during the Permian – and were succeeded by therapsids – that evolved from the carnivorous pelycosaur lineage – and rapidly diversified into • herbivorous • and carnivorous lineages

Therapsids • A Late Permian scene in southern Africa showing various therapsids – Many paleontologists think therapsids were endothermic – and may have had a covering of fur Moschops Dicynodon

Therapsid Characteristics • Therapsids were small- to medium-sized animals – displaying the beginnings of many mammalian features • Many paleontologists think therapsids were endothermic • or warm-blooded – enabling them to maintain a constant internal body temperature – allowing them to expand into a variety of habitats

How are we related to them anyway? • Relationships among Amniota are tracked via ‘fenestrae’, or openings in the head. • Fenestrae: – Make the head lighter – Anchor points for muscles

Fenestrae in the descendents of proterothyrids

Summary • Fish – First appeared in the Cambrian (jawless fish – first vertebrate) – Diversified in Devonian (Age of Fish) • Amphibians – First appeared in the Devonian – Evolved from lobe-finned fish • Reptiles – First appeared in Pennsylvanian – Did not need to return to water to reproduce

Plant Evolution • Evolution of photosynthesis: Archaean cyanobacteria • Genetic evidence suggests that plants evolved from green algae • No Cambrian explosion for plants – Many steps needed to move plants onto the land

Buoyancy and humidity • How to keep your guts wet in a dry world? – Cutin: exterior plant waxes protect from dessication • How to stay upright when you’re not buoyant in air? – Cellulose and lignin: rigid polymers that make cells strong • How to grow bigger than a few centimeters in a dry world? – Develop the ability to move fluids from soils to leaves

Earliest Land Plant • Earliest plants did not produce seeds • The sedimentary rocks in which these plant fossils are found – indicate that they lived in low, wet, marshy, freshwater environments • The earliest known fertile land plant was Cooksonia – seen in this fossil from the Upper Silurian of South Wales

Vascular plants – Vascular system: • network of tubes which distribute nutrients and remove wastes • Not clear if Cooksonia was truly vascular • First definitive vascular plant: ferns

Plant Evolution • Major events in the evolution of land plants – The Devonian Period was a time of rapid evolution for the land plants – the appearance of leaves – and emergence of seeds

Early Devonian Plants • Reconstruction of an Early Devonian landscape – showing some of the earliest land plants Protolepidodendron Dawsonites Bucheria

Early and Late Devonian Plants • Early Devonian – relatively small – low-growing – bog-dwelling types of plants • Late Devonian – tree-size plants up to 10 m tall Chaleuria cirrosa

Evolution of Seeds • The evolution of the seed during the Late Devonian – liberated land plants from their dependence on moist conditions – and allowed them to spread over all parts of the land • In the seed method of reproduction – the spores are not released to the environment – but are retained on the spore-bearing plant – where they grow into the male and female forms

Gymnosperms • In the case of the gymnosperms • or flowerless seed plants – male cone produces pollen – egg is contained in the female cone – After fertilization • seed develops into a mature, cone-bearing plant • Seed plants • like reptiles – were no longer restricted to wet areas – but were free to migrate into previously unoccupied dry environments

Late Carboniferous and Permian Floras • Rocks of the Pennsylvanian Period are the major source of the world's coal • The geologic and geographic conditions of the Pennsylvanian – ideal for the growth of seedless vascular plants – these coal swamps had a very diverse flora

Pennsylvanian Coal Swamp • Reconstruction of a Pennsylvanian coal swamp with its characteristic vegetation

Glossopteris • An important non-swamp dweller was Glossopteris, the famous plant so abundant in Gondwana (a seed fern) – Great resource for paleobiogeographers http: //www. lowcountrygeologic. com/plants/gl oss 1. htm