The discovery in 1992 of fossilized Devonian tetrapod footprints – more than 365 million years old – has forced paleontologists to rethink – how and when animals emerged onto land GEOLOGY IS A YOUNG SCIENCE, CONSTANTLY EVOLVING WITH RICH NEW DISCOVERIES JUST WAITING FOR THE NEXT CLASS OF GRADUATE GEOLOGISTS TO “ROCK THE WORLD” Tetrapod Footprint Discovery

Tetrapod trackway – at Valentia Island, Ireland These fossilized footprints – which are more than 365 million years old – are evidence of one of the earliest four-legged animals on land Tetrapod Footprint Discovery

One of the striking parallels between plants and animals – is the fact that in passing from water to land, – both plants and animals had to solve the same basic problems For both groups, – reproduction was the major barrier With the evolution of the seed in plants and the amniote egg in animals, – this limitation was removed, and both groups were able to expand into all the terrestrial habitats Transition from Water to Land

A chordate (Phylum Chordata) is an animal that has, at least during part of its life cycle, – a notochord, – a dorsal hollow nerve cord, – and gill slits Vertebrates, which are animals with backbones, are simply a subphylum of chordates Vertebrate Evolution

The structure of the lancelet Amphioxus illustrates the three characteristics of a chordate: – a notochord, a dorsal hollow nerve cord, and gill slits Characteristics of Chordates

Yunnanozoon lividum is one of the oldest known chordates – Found in 525 MY old rocks in Yunnan province, China – 5 cm-long animal A Very Old Chordate

Sturgeon Fresh water fish Canada A prehistoric fish Has a notochord, No scales, plates instead Asymetrical tail

– a random mutation produced a duplicate set of genes – allowing the ancestral vertebrate animal to evolve entirely new body structures – that proved to be evolutionarily advantageous Not all scientists accept this hypothesis and the evolution of vertebrates is still hotly debated Hypothesis for Chordate Origin

Echinoderms and chordates – have similar – embryonic development In the arrangement of cells resulting from spiral cleavage, (a) at the left, – cells in successive rows are nested between each other In the arrangement of cells resulting from radial cleavage, (b) at the right, – cells in successive rows are directly above each other – This arrangement exists in both chordates and echinoderms Spiral Versus Radial Cleavage

A fragment of a plate from Anatolepis cf. A. heintzi from the Upper Cambrian marine Deadwood Formation of Wyoming Anatolepis is one of the oldest known fish – a primitive member of the class Agnatha (jawless fish) Fragment of Primitive Fish Fish appear in the late Cambrian

The oldest and most primitive of the class Agnatha are the ostracoderms – whose name means “bony skin” These are armored jawless fish that first evolved during the Late Cambrian – reached their zenith during the Silurian and Devonian – and then became extinct Ostracoderms — “Bony Skinned” Fish

ostracoderm An ostracoderm, an extinct jawless fish that existed from about 510 million to 350 million years ago. The name means "shell- skinned," and this fish was typically armored with scales and bony plates. Instead of vertebrae it had a rigid notochord. (Copyright 1995 by Grolier Electronic Publishing, Inc

Jawless Fish Modern: Lamprey “Living Fossil”

The evolution of jaws: advantage While their jawless ancestors – could only feed on detritus jawed fish – could chew food and become active predators – thus opening many new ecological niches Apparent modification of the first two or three anterior gill arches Evolution of Jaws

Many fish evolved during the Devonian Period including – the abundant acanthodians – placoderms, – ostracoderms, – and other fish groups, such as the cartilaginous and bony fish It is small wonder, then, that the Devonian is informally called the “Age of Fish” – because all major fish groups were present during this time period Devonian: Age of Fish

Devonian jawed fish – that evolved during the Late Silurian were the placoderms, whose name means “plate-skinned” Placoderms were heavily armored jawed fish – that lived in both freshwater and the ocean, – and like the acanthodians, – reached their peak of abundance and diversity during the Devonian Other Jawed Fish

Recreation of a Devonian seafloor showing: Devonian Seafloor an ostracoderm (Hemicyclaspis) –a placoderm (Bothriolepis) an acanthodian (Parexus) a ray-finned fish (Cheirolepis)

A Late Devonian marine scene from the midcontinent of North America featuring the giant placoderm, Dunkleosteus Late Devonian Marine Scene

Geologic Ranges of Major Fish Groups

Cartilaginous fish, – class Chrondrichthyes, – represented today by sharks, rays, and skates, – first evolved during the Middle Devonian – and by the Late Devonian, – primitive marine sharks such as Cladoselache were quite abundant Cartilaginous Fish

Arrangement of fin bones for (a) a typical ray-finned fish (b) a lobe-finned fish – Muscles extend into the fin – allowing greater flexibility Ray-Finned and Lobe-Finned Fish

From a modest freshwater beginning during the Devonian, – ray-finned fish, which include most of the familiar fish such as trout, bass, perch, salmon, and tuna, – rapidly diversified to dominate the Mesozoic and Cenozoic seas Ray-Finned Fish Rapidly Diversify

Coelacanths are marine lobe-finned fish – that evolved during the Middle Devonian – and were thought to have gone extinct – at the end of the Cretaceous. In 1938, a fisherman caught a coelacanth – in the deep waters off Madagascar, – and several dozen more have been caught since then. Living Fossil: Coelacanths

Lungfish were fairly abundant during the Devonian, – but today only three freshwater genera exist, – one each in South America, Africa, and Australia Their present-day distribution presumably – reflects the Mesozoic breakup of Gondwana The “lung” is actually a modified swim bladder – that most fish use for buoyancy in swimming In lungfish, this structure absorbs oxygen, – allowing them to breathe air – when the lakes or streams in which they live become stagnant or dry up. Lungfish Fish

When the lakes become stagnant and dry up, – The lungfish burrow into the sediment to prevent dehydration – and breathe through their swim bladder – until the stream begins flowing or the lake fills with water When the water is well oxygenated, – however, lungfish rely upon gill respiration – Transitional form? Lungfish Respiration

The crossopterygians are an important group of lobe-finned fish because amphibians evolved from them Some species reaching over 2 m in length, – were the dominant freshwater predators during the Late Paleozoic. Amphibians Evolved from Crossopterygians

Rhipidistian Crossopterygian and Eusthenopteron

Similarities between the crossopterygian lobe- finned fish and the labyrinthodont amphibians Fish/Amphibian Comparison Their skeletons were similar

Comparison of the limb bones – of a crossopterygian (left) and an amphibian (right) Color identifies the bones that the two groups have in common Comparison of Limbs ulna radiushumerus

What structural problems existed for marine animals to move on to land? Water to Land Barriers Acanthostega – oldest tetrapod?

– desiccation – reproduction – the effects of gravity – stronger bones required – and the extraction of oxygen from the atmosphere by lungs rather than from water by gills Protection from predators – cover?

These problems were already partly solved by the crossopterygians – they already had a backbone and limbs – that could be used for walking – and lungs that could extract oxygen The oldest amphibian fossils are found – in the Upper Devonian Old Red Sandstone of eastern Greenland Problems Partly Solved

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 even snails invaded the land before amphibians Amphibians— Vertebrates Invade the Land

A Late Devonian Landscape in Eastern Greenland A Late Devonian Landscape The flora was diverse, –consisting of a variety of small and large seedless vascular plants Ichthyostega was an amphibian that grew to a length of about 1 m

Compare tetrapod to amphibian Oldest tetrapod Early amphibian

In 2006, an exciting discovery – of a m long – 374-million-year-old (Late Devonian) “fishapod” – was announced. Tiktaalik roseae (“large fish in a stream”) – was hailed as an intermediary – between lobe-finned fish like Panderichthys – and the earliest tetrapod, Acanthostega. Transition to Amphibians

This “fishapod” has characteristics of both fish and tetrapods – It has gills and fish scales – but also a broad skull, eyes on top of its head, flexible neck and large ribcage – that could support its body on land or shallow water, and the beginning of a true tetapod forelimb Tiktaalik roseae

Diagram illustrating how Tiktaalik roseae is a transitional species between lobe-finned fish and tetrapods Tiktaalik roseae

Reconstruction of a Carboniferous coal swamp Carboniferous Coal Swamp

Amphibians were limited in colonizing the land – because they had to return to water to lay their gelatinous eggs The evolution of the amniote egg freed reptiles from this constraint In such an egg, the developing embryo – is surrounded by a liquid-filled sac, called the amnion – and provided with both a yolk, or food sac, – and an allantois, or waste sac Evolution of the Reptiles — the Land is Conquered

The amnion cavity – surrounds the embryo. The yolk sac – provides the food source while the allantois – serves as a waste sac The evolution of the amniote egg freed reptiles – to inhabit all parts of the land Amniote Egg

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 – because they no longer had to return – to the water as part of their reproductive cycle SUCCESS of reptiles is partly because – of their advanced method of reproduction – and their more advanced jaws and teeth, as well as their ability to move rapidly on land Colonization of All Parts of the Land

Evolutionary relationship among the Paleozoic reptiles Paleozoic Reptile Evolution

Most pelycosaurs have a characteristic sail on their back Pelycosaurs (Finback Reptiles) The carnivore Dimetrodon The herbivore Edaphosaurus

An interesting feature of the pelycosaurs is their sail – It was formed by vertebral spines that, – in life, were covered with skin The sail has been variously explained as – a type of sexual display, – a means of protection – and a display to look more ferocious – OR a thermo-regulatory device! ?? Pelycosaurs Sails

current consensus – sail served as thermoregulatory device, – raising the reptile's temperature by catching the sun's rays or cooling it by facing the wind Because pelycosaurs are considered to be the group from which therapsids evolved, and are more mammal like – it is interesting that they may have had some sort of body-temperature control Pelycosaurs Sail Function

A Late Permian scene in southern Africa showing various therapsids- 90% of reptiles Therapsids Dicynodon Moschops –Many paleontologists think therapsids were endothermic: warm-blooded –and may have had a covering of fur –as shown here

By the end of the Permian, – about 90% of all marine invertebrate species were extinct, – compared with more than two-thirds of all amphibians and reptiles Plants apparently did not experience – as great a turnover as animals did Count the losses at the end of the Permian…….

END HERE for TEST 3 December 2010

When plants made the transition from water to land, – they had to solve most of the same problems that animals did desiccation, support, and the effects of gravity Plants did so by evolving a variety of structural adaptations that were fundamental to the subsequent radiations Plant Evolution

The Devonian Period was a time of rapid evolution for land plants Major Events in the Evolution of Land Plants

The earliest land plants from the Middle to Late Ordovician – were probably small and bryophyte-like in their overall organization but not necessarily related to bryophytes The evolution of vascular tissue in plants was an important step – as it allowed for the transport of food and water The ancestor of terrestrial vascular plants – was probably some type of green algae While no fossil record of the transition – from green algae to terrestrial vascular plants exists, – comparison of their physiology reveals a strong link Earliest Land Plants

Besides the primary function – of transporting water and nutrients throughout a plant, – vascular tissue also provides – some support for the plant body Additional strength that acts to counteract gravity is derived – from the organic compounds lignin and cellulose, – which are found throughout a plant's walls Vascular Tissue Also Gives Strength

The earliest known fertile land plant was Cooksonia – seen in this fossil from the Upper Silurian of South Wales produced spores typical of vascular plants These plants probably lived in moist environments such as mud flats This specimen is 1.49 cm long Earliest Land Plant Late Silurian and Devonian and found in New York State

An interesting parallel can be seen between seedless vascular plants and amphibians When they made the transition from water to land, they both required a source of water in order to reproduce Amphibians gelatinous egg had to remain moist And Plants required water for the sperm to travel through – to reach the egg Parallel between Seedless Vascular Plants and Amphibians

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

The rocks of the Pennsylvanian Period Late Carboniferous – are the major source of the world's coal Coal results from – the alteration of plant remains – accumulating in low swampy areas The geologic and geographic conditions of the Pennsylvanian – were ideal for the growth of seedless vascular plants, – and consequently these coal swamps had a very diverse flora Late Carboniferous and Permian Floras

Reconstruction of a Pennsylvanian coal swamp – with its characteristic vegetation Pennsylvanian Coal Swamp Amphibian Eogyrinus

Living sphenopsids include the horsetail Equisetum Horsetail

Another important non-swamp dweller was Glossopteris, the famous plant so abundant in Gondwana, – whose distribution is cited as critical evidence that the continents have moved through time Glossopteris

White areas represent sequences of rocks Cratonic Sequences of North America that are separate d by large- scale uncon- formities shown in brown

During the Triassic Period Paleogeography of the World

Evaporites accumulated in shallow basins – as Pangaea broke apart during the Early Mesozoic – Water from the Tethys Sea flowed into the Central Atlantic Ocean Early Mesozoic Evaporites

Jurassic

During the Late Cretaceous Period Paleogeography of the World

The subsequent separation of South America and Africa – formed a narrow basin – where thick evaporite deposits – accumulated from the evaporation – of southern ocean waters Thick Evaporites from the Southern Ocean

Marine water flowed into the southern Atlantic Ocean from the south Thick Southern Ocean Evaporites

Late Cretaceous note the seaway in central US

The world's climates result from the complex interaction between – wind and ocean currents – and the location and topography of the continents In general, dry climates occur – on large landmasses – in areas remote from sources of moisture – and where barriers to moist air exist, – such as mountain ranges Wet climates occur – near large bodies of water – or where winds can carry moist air over land Ocean Currents and Continents

Widespread Triassic evaporites, red beds, and desert dunes: such as Zion National Park which began in the Jurassic – in the low and middle latitudes – of North and South America, Europe, and Africa – indicate dry climates in those regions, while coal deposits – are found mainly in the high latitudes, – indicating humid conditions These high-latitude coals are analogous to – today's Scottish peat bog – or Canadian muskeg Evaporites, Red Beds, Dunes, Coal

Newark and Hartford Basins form Widespread igneous intrusions Areas where Triassic fault-block basin deposits crop out in eastern North America

This sill was one of many that were intruded into the Newark sediments – during the Late Triassic rifting – that marked the separation – of North America from Africa Palisades Sill of the Hudson River

Reptile Tracks Reptile tracks in the Triassic Newark Group – were uncovered during the excavation – for a new state building in Hartford, Connecticut Because the tracks were so spectacular, – the building side was moved – and the excavation was designated as a state park

Mesozoic Cephalapods

White Cliffs of Dover, UK

Lived and died in clear warm seas that covered much of Britain around 70 to 100 million years ago. When they died, they fell to the bottom in a rain of fine white mud. As chalk formed from the mud, layers and lumps of hard, glassy flint also developed - prized by stone-age man for tools.

Latimeria – belongs to a group of fish once thought to have gone extinct at the end of the Mesozoic Era – A specimen was caught off the coast of East Africa in 1938 – Since then many more have been captured Living Fossil

Reptiles and Birds

All dinosaurs possess a number of shared characteristics, such as full and upright posture with limbs directly beneath their bodies yet differ enough for us to recognize two distinct orders, the Saurischia and Ornithischia A distinctive pelvic structure characterizes each order

Cladogram showing dinosaur relationships – showing pelvises of ornithischians and saurischians – Among the several subgroups of dinosaurs Dinosaur Cladogram theropods were carnivores and all others were herbivores