Vertebrate History in Rocks Ch. 11.5

What are Fossils? A fossil is a hardened remains or other evidence of a living thing that existed a long time ago. Sometimes it is an imprint in a rock – like a footprint or outline of a leaf.

Some are remains of bones, shells, skeletons, or other parts of living things. Fossils are made when a chemical process takes place over time, during which an organism’s tissues are replaced by hard minerals.

Fossils are found most frequently in sedimentary rock. Sedimentary rock is made up of hardened layers of sediments (clay, sand, mud, silt, etc.)

Over a very long time, layers of sediments can be pressed and cemented together to form rock. As sedimentary rock forms, traces of living things that have been trapped in sediments are sometimes preserved.

1677 Robert Plot, the head of a museum in England, published a book that had an illustration of a huge fossilized thighbone. Plot thought that the bone belonged to a giant human, but it was probably the thighbone of a dinosaur.

1811 Sea Reptile Along the cliffs near Lyme Regis, England, a 12 year old Mary Anning discovered the fossilized remains of the giant sea reptile now called Ichthyosaurus. Mary became one of England’s first professional fossil collectors.

1822 Dinosaur Tooth In a quarry near Lewes, England, Mary Ann Mantell discovered a strange looking tooth embedded in stone. Her husband Gideon drew the picture of the tooth. The tooth belonged to the dinosaur Iguanodon.

1861 Bird Bones A worker in a stone quarry in Germany found Archaeopteryx, a feathered, birdlike animal that also had many reptile characteristics.

1902 Tyrannosaurus A tip from a local rancher set Barnum Brown, a fossil hunter, to a barren, rocky area near Jordan, Montana. There Brown found the first relatively complete skeleton of Tyrannosaurus rex.

1964 Deinonychus In Montana, paleontologist John Ostrom discovered the remains of a small dinosaur, Deinonychus. This dinosaur was probably a predator that could move rapidly. This fossil led scientists to hypothesize that dinosaurs may have been endotherms.

1991 Dinosaur Eggs in China Digging beneath the ground, a farmer on Green Dragon Mountain in China uncovered what may the the largest nest of fossil dinosaur eggs ever found

Interpretation of Fossils A Paleontologist is a scientist that studies extinct organisms, examines fossils structure and makes comparisons to present-day organisms. By studying fossils, paleontologists can infer how animals changed over time.

One important piece of information that paleontologists can learn from a fossil is its approximate age.

A Fossil’s Age One method for estimating a fossil’s age takes advantage of the process in which sediments form. Older fossils are on the bottom, newer ones are on the top. However, sometimes rock layers can become tilted or even turned upside down by things like earthquakes.

Carbon Dating Another way to age fossils would be to use radioactive chemical elements. We know exactly how long they take to decompose, so we just look to see how much is left, compare it to a chart, and determine its age.

Using Fossils Paleontologists have used fossils to determine a likely pattern of how vertebrates changed over time. You can see in figure 27 from your book (pg. 399) that the pattern of vertebrate evolution looks like a branching tree.

Fossils show that the first vertebrates to live on Earth were fishes. Fishes first appeared on Earth about 530 million years ago. Amphibians came next, then reptiles, and then mammals and birds.