What is a fossil?• A fossil is the preserved remains of a once-living organism.How are fossils formed?• Fossils are formed when animals or plants are buried in sedimentary rock.• You should remember how sedimentary rock is formed and how to identify which layers are the oldest and which are youngest.
Plants and animals buriedhere might become fossils.
If sediment covers a dead organism before the it has time to rot, the organism’s body may become fossils fossilized.As many, many years pass, new types ofsediment are deposited on top of the originalsediment containing the fossil and the layers ofsediment change to rock. As a result, thefossils are finally buried under layers of rock.
Based on what you already know about howsedimentary is formed, you should be able to tellwhich fossils in this picture are older or younger. The youngest fossils would be found in the a. top layers of rock b. the middle rock layers c. the bottom Natural Resources Canada layers of rock
There are four types of fossils:MoldsCastsTrace fossilsWhole or part of an organism that hasbeen preserved
1. A mold forms when: a. an organism diesand is buried in sediment such as sand, silt orclay b. the sediment changes to rock and theorganism’s body decomposes leaving animprint or mold in the rock. Molds can be seenif the rock is broken open.Present day scallop Mold of a scallop in clay Mold of scallop in rock
2. A cast forms when an organism dies and isburied in sediment. Its body rots leaving a“hole” in the shape of its body. Water withminerals fills up the hole. When the waterevaporates, a copy of the original structure oforganism is formed as a rock.Picture of present day snail Picture of fossilized snail Bob Hermann//Cochise College. R.Weller/Cochise College.
Ammonite mold Ammonitec astMolds and casts are often found together.
Trace fossils include leaf prints, burrows,coprolites (feces or poop), trails,footprints.Trace fossils of an animal tellsomething about its movement andbehavior.Trace fossils are not an imprint of thehard part of an animal’s body.
4. Whole or a part of a body is preservedIn rare instances an entire organism orits skeleton is preserved because theorganism gets trapped in a substancethat protects its body from decaying.Examples are:
A spider trapped in tree sap. The tree saphardened into amber, preserving the wholespider. Wikimedia Commons
A sabretooth cat skeleton found in LaBrea Tar Pits in California. The tiger fellinto the tar and got “stuck”. His skeletonwas preserved by the tar. Wikimedia Commons
Sometimes, a whole organism can be preserved if it is frozen very quickly. Photo: Francis Latreille/National Geographic40,000 year old frozen baby mammoth found in Siberia
What do fossils tell us?• Fossils give clues about organisms that lived long ago.• They also provide evidence about how Earth’s surface has changed over time.• Fossils help scientists understand what past environments may have been like.
In the next few slides you will see fossilsfound either in or near Fort Worth. Theytell us: •what organisms lived here millions of years ago. •about the environment of this area at that time. •and help us see how things have changed over time.
Looking at these organisms, you canconclude they once lived:a. in a forest c. in a grasslandb. In an ocean d. in a desertYes, you could conclude that they oncelived in an ocean.So what must have been here in Fort Worthat that time (100 million years ago)?Yes, at one time, very long ago, this areawas covered by a shallow sea.
The North American continent during late Cretaceous time.The Western Interior Sea covered most ofthe Midwest from the present Gulf ofMexico to the Arctic.
Wikipedia CommonsWestern Interior Seaway during the mid-Cretaceous, about 100 million years ago.
100 million years ago Central Texas was a shallow seaAs the sea receded, Central Texas rose above sea level.
The next pageshowsdinosaurfootprintsfound in thePaluxy Riverbed inDinosaur StatePark, GlenRose, TX veryclose to FortWorth.
Dinosaur tracks made113 million years ago in thePaluxy River bed near GlenRose, TX.
Paleontologists who examined the three-toed printsidentified Acrocanthosaurus as the likely trackmaker.Other dinosaurs had also left their footprints here.Sauropod tracks likely made by Paluxysaurus, aherbivore, appear as huge potholes—sometimesthree feet long—pit the rocky bottom of the riverbed. Acrocanthosaurus Paluxysaurus,
Based on what scientists know about dinosaurs,what can we conclude about the climate at GlenRose 113 million years ago and the kinds of plantsthat grew during this time?
AProtohadrosdinosaur skull wasfound in FlowerMound, Texasin 1994.The Protohadroslived 98 millionyears ago.A Protohadro dinosaur belongs to theHadrosaurs family, the formal name ofduck-billed dinosaurs.
Above is a artist’s painting of what a Protohadrosmight have looked like and the habitat thatscientists believe it lived in.
A cast of its Dinosaur remains of a Tenontosaurusdossiwere foot found in 1998 by a nine year old boy on a ranch just west of Fort Worth near Weatherford. This dinosaur lived 110 million years ago.A cast of skull and teeth in rock. A cast of a foot. An artist’s picture of what a Tenontosaurus dossi might have looked like..
From these finding what can weconclude about the environmentand climate of the region aroundFort Worth 98--110 million yearsago?
To conclude, let’s review a few thingswe have learned.Fossils area. always made of rockb. an artist’s painting of animals thatlived long agoc. the remains of plants and animalsthat lived long agod. dishes that people used wholived long ago
Fossils give us information abouta. organisms that lived long agob. the climate and environments of the pastc. how the earth has changed over timed. all of the above
Fossils are usuallyfound ina. soilb. sedimentary rockc. igneous rock from volcanoesd. the interior of the Earth
The fossils in layer C are theAB a. the youngestC b. the oldest c. the same age as the fossils in layer A
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