Fish to Tetrapod Transition 11-7

11-7 lecture Cambrian explosion continued from 11-5 lecture Cambrian jellyfish from Wisconsin Fossil jellyfish that come from a quarry ? rocks are sandstones and they preserve an ancient beach On this rock there are trace fossils/impressions left by something and look kind of like ?dune buggy tracks? and nobody can figure out what they are Jellyfish are fossilized as impressions Think a bunch of jellyfish got stranded on the beach and tried to escape and made this round sort of impression on the beach when they do that The Cambrian explosion was followed by Ordovician radiation Ordovician radiation had a HUGE explosion in genera ? bigger than Cambrian explosion Most of phyla originated in the Cambrian and then within each phyla you have a lot of genera and families that came up/occurred in the Ordovician radiation Ordovician is when the ?taxa? of the Cambrian explosion get sort of filled out and show many different types of each ?taxa? or phyla from the Cambrian Ordovician marine life ? was an ocean over Wisconsin at this time ? huge diversity of marine life during this time (with trilobites, relatives of squid/octopi, coral, etc) What about life on land? Was NOTHING on land, at least close to nothing, just rocks, while the Cambrian explosion was happening in the ocean with all the diverse marine life Took a long time for life in the ocean to transition up to land Problems (for both animals and plants) in leaving the water: Support (lack of buoyancy) Water holds you up and a lot better (cushions you) better than land does Dessication Drying out Temperature extremes Greater on land than they are in the water ? more frozen and super hot environments than in the water Respiration Getting oxygen out of the air is different than getting it out of the water Air has no nutrients Animals got nutrients out of water column ? can?t just wander around on land with your mouth open like you can in the water to collect different nutrients floating in the water Selection driven by huge increase in available light! Main reason why animals were drawn up to the land Especially for plants seeking to go through process of photosynthesis First animals out of water and on land were mats of bacteria and algae Land plants evolved from green algae Earliest fossil land plants are Silurian Small and simple (no leaves, no roots, simply branching) Not very prone to becoming fossils ? may have come out a little earlier than we think, we just can?t see that b/c of lack of a lot of fossils for them Earliest land plants were ?non-vascular? (lacking tissues that conduct fluids) Mosses are non-vascular Trees and most plants today have a vascular system for conducting fluids from top of plant to bottom Many important adaptations of plants involve transport of water, nutrients, and sugars between specialized tissues Now plants have stems and leaves and other tissues that each have different purposes Leaves collect light ? where photosynthesis happens that creates sugars Goes down through stem and vascular system of the plant and into the ground and roots to supply sugars and nutrients Adaptations: xylem = improved piping system for upward flow of water and nutrients from roots Made of elongated dead cells arranged end to end Are perforated also so you can transport water up them Simplest living vascular plant lacks leaves and roots In the early Devonian landscape ? plants generally <1m ? relatively short and still hanging around by the water After the Cambrian and the Ordovician Wood is made from reinforced xylem tissue By the Late Devonian, plants evolved broad leaves and assumed tree sizes By this time, could have actually had forests on the planet ? things probably looked quite different in the different characteristics of the different plants, but basic structure of forest would probably have been fairly similar and simple (tall tree, medium trees, short trees, bushes, etc) Late Devonian oldest known seeds (prior to this, plants required water to reproduce) Various terrestrial arthropods from the Silurian on Earliest animals on the land (that we know about) were trigonotarbid (~400 Ma) ? look a lot like spiders but don?t have any web-spinning apparatus Evolution of vertebrates Vertebrate classes: several classes of fish, amphibians, reptiles, mammals, birds Amphibians, reptiles, mammals, and birds are all TETRAPODS (means four-legged) Early Cambrian jawless fishes Ex: modern lamprey ? not very changed from extremely primitive first organisms, are jawless as well Are some fossils of these of soft tissues and impressions in the rocks ? almost look like leaves but when looked at in a microscope, can identify them as a type of fish First JAWED fishes are Late Silurian Jaws are modified gill arches Origin of tetrapods First multi-cellular animals with skeletons ? Cambrian explosion, and jawless fishes came just before that in the Cambrian Tetrapods evolved from LOBE-FINNED FISHES Characterized by: several pairs of strong fins Lobe-finned fishes: Several pairs of strong fins, and active hunters in shallow water Locomotion: tail for propulsion, ventral fins against bottom What was impetus to get out of the water (fish)? Predators Drought Basking Lying out in the sun in order to speed up digestion ? digestion is a temperature driven process, and fish are cold-blooded, but wanted to process more food faster so basking is therefore a benefit Reproduction Fossil record contains MANY transitional forms from lobe-finned fishes to tetrapods Acanthostega is an early tetrapod Tetrapod features: Legs with feet and digits Ear Fish-like features: Limbs not weight-bearing Tail fin Gills Is one of several of transitional forms that we have that is one of the intermediate stages in all these different features (between fish and lizards for example)