Review, 1st 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)

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 Amphibians— Vertebrates Invade the Land

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 Oldest Amphibians

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 Rapid Adaptive Radiation

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

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 Transition from Water to Land

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 Evolution of the Reptiles — the Land is Conquered

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 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 –no longer had to return to the water as part of their reproductive cycle Able to Colonize All Parts of the Land

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

Evolutionary relationship among the Paleozoic reptiles Paleozoic Reptile Evolution

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

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

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

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 Therapsid Characteristics

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

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 Summary

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 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 Earliest Land Plant 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

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

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

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

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 Evolution of Seeds

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 Gymnosperms

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 Late Carboniferous and Permian Floras

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

An important non-swamp dweller was Glossopteris, the famous plant so abundant in Gondwana (a seed fern) –Great resource for paleobiogeographers Glossopteris oss1.htm