Paleontology Studying The Fossil Record

Phylogeny The evolutionary history of a species or a group of species over geologic time The evolutionary history of a species or a group of species over geologic time

Phylogeny is backed by the fossil record. The fossil record refers to the order in which fossils appear within layers of rock that mark the passing of geologic time. Which layer do you think is the oldest? The Fossil Record and Geologic Time

When rocks are in layers it is usually a sign that the rocks are sedimentary rocks. Sedimentary rocks are the richest source of fossils.

The Fossil Record and Geologic Time Specific conditions are needed for fossilization. Only a tiny percentage of living things became fossils.

Organic substances in dead organisms typically decay rapidly. Organic substances in dead organisms typically decay rapidly. Parts that are rich in minerals (e.g., teeth, bones) may become fossils by permineralization. Permineralization occurs after burial, as the empty spaces within an organism’s hard parts (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater and the minerals precipitate from the groundwater, thus occupying the empty spaces. Types of Fossils - Permineralization

In some cases the original remains of the organism have been completely dissolved or otherwise destroyed. When all that is left is an organism- shaped hole in the rock, it is called an external mold. If this hole is later filled with other minerals, it is a cast. An internal mold is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail. Types of Fossils – Casts and Molds External Mold Cast

Trace fossils are the remains of trackways, burrows, eggs and eggshells, nests, droppings and other types of impressions. Fossilized droppings, called coprolites, can give insight into the feeding behavior of animals and can therefore be of great importance. Types of Fossils – Trace Fossils Tracks Coprolites

Fossil resin (colloquially called amber) is a natural polymer found in many types of strata throughout the world, even the Arctic. Types of Fossils – Fossil Resin The oldest fossil resin dates to the Triassic, though most dates to the Tertiary.

What kind of fossil is each of these?

Paleontologists use many methods to date fossils. Relative dating Fossils near the surface are relatively recent, while those that are deeper are relatively older. Geologists have established a geologic time scale that reflects a consistent sequence of historical periods. Those periods are grouped into four eras: Precambrian, Paleozoic, Mesozoic, and Cenozoic.

Absolute dating – age is given in years, instead of relative terms (before/after, early/late). Radiometric dating is the measurement of radioactive isotopes found in fossils and rocks, to determine age. The half-life of an isotope is the number of years it takes for 50% of the original sample to decay.

The fossil record is substantial, but does not provide a complete evolutionary history. The fossil record usually tells us about abundant, widespread organisms with hard shells or skeletons.

Phylogeny has a biogeographic basis in continental drift. Moving continents isolate populations, allowing for evolution to occur. 250 million years ago all continents were connected as Pangaea. Pangaea “broke” apart about 180 million years ago.

Mass Extinctions Mass extinctions often changed the complexion of entire ecosystems and food webs resulting in species, genera, families and even higher taxa dying out.

Geological Timeline

Precambrian 4, mya The Precambrian is an informal name for the supereon comprising the eons of the geologic timescale that came before the current Phanerozoic eon. First single-celled organisms, simple plants, and invertebrate animals: algae, bacteria, jellyfish, flagellates, amoebas, worms, sponges 4, mya (millions of years ago) Stromatolites

Cambrian Period mya First trilobites, forams, brachiopods, nautiloids, clams, snails, crustaceans, crinoids, gastropods, corals, protozoans Stromatolites The Age of Trilobites

Cambrian Period mya The diversification of lifeforms was relatively rapid during this period, and is termed the Cambrian explosion. Stromatolites Complex organisms became gradually more common in the millions of years immediately preceding the Cambrian, but it wasn't until this period that mineralized - hence readily fossilized - organisms became common. Most of the continents resembled deserts spanning from horizon to horizon.

Ordovician Period mya First starfish, sea urchins, blastoids, eurypterids, bryozoa, scaphopods, jawless fish, echinoids. The Age of Cephalopods

Silurian Period mya First land plants, ferns, sharks, boney fish, water scorpions. An eurypterid, a prehistoric sea scorpion The Age of Coral

Devonian Period mya First insects, tetrapods, ammonites, placoderms. Early tetrapods Acanthostega (foreground) and Ichthyostega. The Age of Fishes

Carboniferous Period Mississippian Epoch mya First reptiles, spiders, amphibians. Crinoid meadow in a shallow sea The Age of Crinoids Why is it called the Carboniferous Period? Hint: There was no fungi to decompose the dead trees.

Carboniferous Period Pennsylvanian Epoch mya First conifers, synapsids Dragonfly: 75 centimeter wingspan The Age of Plants and Giant Insects

Permian Period mya Heyday of synapsids, including pelycosaurs Early The Age of Amphibians

Permian Extinction mya The Permian–Triassic (P–Tr) extinction event, informally known as the Great Dying, was an extinction event that occurred about 250 million years ago, forming the boundary between the Permian and Triassic geologic periods.

Permian Extinction mya It was the Earth's most severe extinction event, with up to 96 percent of all marine species and 70 percent of terrestrial vertebrate species becoming extinct; it is the only known mass extinction of insects. 57% of all families and 83% of all genera were killed off. Because so much biodiversity was lost, the recovery of life on earth took significantly longer (10 to 50 million years) than after other extinction events. This event has been described as the "mother of all mass extinctions".

Permian Extinction mya There are several proposed mechanisms for the extinctions; An earlier peak was likely due to gradualistic environmental change such as sea-level change, anoxia, increasing aridity, and a shift in ocean circulation driven by climate change. The later peak was probably due to a catastrophic event(s) such as impact events, increased volcanism, or sudden release of methane hydrates from the sea floor

Triassic Period mya First turtles, cycads, lizards, dinosaurs, mammals The Age of Dinosaurs (1)

Jurassic Period mya First squids, frogs, birds, salamanders The Age of Dinosaurs (2)

Cretaceous Period mya First flowering plants, snakes, modern fish, rise and fall of toothed birds, heyday of dinosaurs The Age of Dinosaurs (3)

The K-T Extinction 65.5 mya The Cretaceous–Tertiary extinction event was a large-scale mass extinction of animal and plant species in a geologically short period of time. Widely known as the K–T extinction event, it is associated with a geological signature known as the K–T boundary, usually a thin band of sedimentation found in various parts of the world.

Scientists theorize that the K–T extinctions were caused by one or more catastrophic events, such as massive asteroid impacts (like the Chicxulub impact), or increased volcanic activity. 85% of all species died in the K-T extinction. The K-T Extinction 65.5 mya

Several impact craters and massive volcanic activity, such as that in the Deccan traps, have been dated to the approximate time of the extinction event. These geological events may have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology. The K-T Extinction 65.5 mya Iridium is extremely rare in normal rock but common in asteroids. K-T boundary layer

Tertiary Period mya Diversification of mammals, first marine and large terrestrial animals, horses, whales, monkeys, first grasses, apes, anthropoids, first hominids. The Age of Mammals

Quaternary Period 1.8 mya to present Mammoths, mastodons, Neanderthals, first modern human beings (Homo sapiens) The Age of Mammals