unit 19

A person who studies fossils is a paleontologist. The word fossil comes from the Latin for “obtained by digging”.

A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. A body fossil is a fossil made from parts of an organism’s body.

A trace fossil contains no part of an organism's body but records the impact of an organism on its environment. A footprint is an example.

Fossils have been found on every continent, including Antarctica. Rivers, mountains, deserts, and badlands are all excellent locations because they have high levels of erosion, which exposes fossils in sedimentary rocks.

Fossils must be removed from the site where they are found so that they are not further eroded. Paleontologists use rock hammers, chisels, and other tools to carefully cut into the rock around the fossil.

A Lagerstätte is a deposit that exhibits extraordinary fossils with exceptional preservation. The Cambrian Burgess Shale Fossil Bed is one example.

A transitional fossil is any remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. Tiktaalik is an example.

Only a tiny percentage of living organisms were ever fossilized, and only a tiny percentage of those have been found.

For a body fossil to form, an organism must be buried in sediment quickly before it decomposes completely. Permineralization is the process in which empty spaces within an organism become filled with mineral-rich groundwater.

Most body fossils that we find were formed from already-mineralized parts of the body such as bones, shells, or exoskeletons.

In these specimens, even the soft tissues have been fossilized because the organism was quickly buried in an extremely anoxic low-oxygen environment.

If an organism dissolves completely, it leaves a void in the sediment called an impression fossil or external mold. If that void is filled with different minerals carried in groundwater, a cast is formed.

Compression fossils contain some of the original organic material, although the organic molecules have typically undergone chemical changes. Many are dark brown because they contain more stable carbon compounds.

A microfossil is a fossil that is less than 1 mm in size. Microfossils may be formed by single-celled organisms or parts of multicellular organisms such as spores.

A biosignature is any element, isotope, or molecule that provides scientific evidence of past or present life. Large amounts of oxygen and small amounts of methane are examples of atmospheric biosignatures.

ESA’s Rosalind Franklin rover is supposed to launch in 2028 to look for biosignatures on Mars. Other missions are planned to Titan and Europa.

A pseudofossil is an inorganic chemical process that can produce structures that look organic and can be mistaken for fossils. Manganese dendritic crystals are an example.

Amber is fossilized tree resin that often includes specimens of organisms that became trapped in the sticky liquid resin. The oldest amber dates to the Carboniferous, but most dates to the Cretaceous and later.

We have discovered arthropods such as insects and arachnids in amber and even parts of dinosaurs such as tails. However, it is not possible to recover dinosaur DNA from amber because the DNA molecules fragment and degrade too quickly and react with chemicals in the amber.

Tar pits are places where petroleum has seeped to the surface. The fossils recovered from them are relatively recent, typically dating to the Pleistocene.

Fossils recovered from ice and permafrost also date back only to the Pleistocene. Yes, DNA can sometimes be recovered because these mammals lived more recently and freezing slowed chemical decomposition.

X-ray computed tomography and scanning electron microscopy allow researchers to construct 3-dimensional models of structures and see fine details.

Scientists have learned that dinosaurs had more soft tissue such as muscle and fat, and more fuzz and feathers than previously thought. This was learned using techniques such as laser-stimulated fluorescence.

Dinosaurs were often brightly coloured and patterned. We know this from studying fossilized melanosomes.

Mary Schweitzer found red blood cells and collagen fibres in the fossilized leg bone of a Tyrannosaurus rex by demineralizing the bone in a weak acid.

Trace fossils consist mainly of tracks and burrows, but also include coprolites and marks left by feeding. They reveal animal behaviours because they show how animals moved, ate, and lived.

The name Maiasaura means “good mother dinosaur” because it was discovered with nests containing eggshells and young too old to be hatchlings. This was the first evidence that dinosaurs cared for their young.

A long-necked sea reptile found in Germany is important because it is the oldest one of its kind found there and helps scientists understand ancient ocean life when Earth’s oceans lost a lot of oxygen.