Happy Winds-day Piglet! Happy Winds-day Pooh! Today: Patterns in the Fossil Record – Review fossil formation Changes in the type and distribution of fossil species Similarities between fossils Body Structures and Patterns (in fossils)

There are many ways in which an organism can be fossilized One of these ways is shown in the next sequence of slides In principle, a fossil is formed when An organism dies Its body is buried in mud, or sand. The soft parts decay but some of the hard parts (skeleton, shells, seeds) are preserved The mud or sand eventually becomes rock and the hard parts of the organism are mineralised. When the rock is exposed as a result of earth movements or erosion, the fossil remains can be dug out and studied. 3 Fossil formation

Living fish A Dies Enclosed in sediment Hard parts fossilised Living fish B Dies Enclosed in sediment Hard parts fossilised Fish B becomes a fossil much later than fish A The sediment eventually becomes rock The deeper the rock layer, the older the fossil 4 Process of fossilisation

living fish sediment from river fish skeleton partly buried by sediment 5 Sedimentation

fish skeleton fossilised older sediment becomes rock more recent sediment collects 6 Layers of sediment

land raised above water level recent rock older rock 7 Earth’s crust movement

earth movements fracture rock fossilised skeleton exposed 8 Fractured rock

When rock strata become exposed, it can be assumed that, in most cases, the lowest layers are the oldest* This means that the fossils of organisms preserved in the lowest layers represent animals and plants that lived many millions of years ago rock strata of increasing age 9 Rock strata © Alan Richardson

This is a fossil of a fish which lived 40 million years ago 10 Fossil fish

The fossils present in any rock layer can show: What type of fossils lived during that time The number of each species (how widespread or abundant the species was) Lots of horse fossils means horses were abundant at that time If newer strata show different types or numbers of fossils we can infer that species have changed The next slide shows how this picture appears for vertebrate animals The width of each band represents the relative abundance of the organisms as judged by their fossil remains. For example, 100 million years ago there were many more species of reptiles than there are today Mammals do not appear at all in rocks older than about 3 million years 12 Vertebrate sequence

Relative number of species 400 million years ago fish amphibia reptiles birds mammals 100 million years ago 200 million years ago 300 million years ago o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o Possible lines of evolution 13 Vertebrate fossil record

Interpretation of the fossil record (1) In interpreting the fossil record, remember that: Every species that ever lived is NOT shown in the fossil record Not everything that lived during a time period gets fossilized. Many species that existed in the past didn’t die in areas that were likely to create a fossil Fossils only preserve the skeletons, shells and other parts resistant to decay 2 Fossils are found only if they are exposed by Earth movements or erosion 3 14 Interpretation (1)

Interpreting the fossil record (2) Despite its gaps, the fossil record does show that, over millions of years, Organisms became more numerous and more diverse, i.e. many more species came into existence 1 Organisms became more complex 2 Most fossils are of things that no longer exist, but, There are many basic similarities in the body structure of the fossils and similar organisms living today 3 There are a few fossils which show characteristics intermediate between major groups 4 15 Interpretation 2

Some Other Patterns… Fossils are found in more locations as we move toward more recent times Fossils are found in more varied environments – oceans to rivers/lakes to shores to dry land etc. Organization of the bodies of different species are similar –They share some anatomical features even though they may show up in fossils that are very far apart in time

Body Structures and Patterns Read and follow the instructions to answer the questions and complete the data tables Be able to define and give examples of: –Homologous structures –Analogous structures –Vestigial structures