GEOL 240 The Dinosaurs: Introduction

GEOL 240 The Dinosaurs:Introduction

Summary

What is a fossil?The science of taphonomyHow it works

What is a Fossil

(from Latin fossilium "that which is dug up") are the physical remains of past life and its activities preserved in the rock record.

The only physical evidence of ancient organisms. Only direct data for knowledge of past life

Paleontology, the study of ancient life and their remains (fossils).

Vertebrate Paleontology, the study of ancient backboned animals, including dinosaurs

Isolated bones and teeth Skeletons, in varying degrees of completeness Footprints and trackways Skin impressions and Feathers Mineralized soft tissue (muscles, intestines,

possible heart) Eggs (some with embryos) and nests Coprolites (fossilized feces) T

race

Bod

y

Types of Dinosaur Fossils

Types of Trace Fossils

Fossilized Skin impresion

Mummification

The Process of Fossilization

taphos = “burial” + nomous = “law” The study of how fossils are formed.

The scope of taphonomic research can be conveniently summarized as:

The manner and cause of death of organisms Processes of decay and decomposition Transportation of fossils or potential fossils Burial of remains Diagenesis (conversion into rock) of remains

Taphonomy

The Importance Of Bones

The Data:

Discovering The Bones

Uncovering The Bones

Removing the Bones

carrying bones out of the desert

documenting bones in Big Bend

Some bones require cranes and trucks to move them

Collections area and bones

carefully removing fossils

from large blocks of rock.

Windows to the Prep Lab let you watch preparators work.

Preparing The Bones

Curating The Bones

(Source: http://www.mwc.mus.co.us/dinosaurs)

Aligning sauropod vertebrae

Measuring sauropod limb bones

Reconstructed dinosaur skeletons on display at

the Smithsonian Museum

Reconstructing The Skeletons

Developing The Story

Artist’s idea of how the Cretaceous might have looked.

Bones from the Big Bend site were deposited in “an ancient riverbed.”

Life-sized reconstruction of T. rex’s left hind leg with

foot skeleton.

Plant/Animal Fossils

Sandstone slab with more than 520 fresh-water herring from Green River Fm.

Petrified trees are also found at the dig site.

Turtle fossil from Green River Fm.

Tracks

This theropod track is in the Morrison Formation (Jurassic) of eastern Utah. Notice the greater depth of the track in the toe region, which suggests a horizontal posture for the dinosaur while it was walking.

Iguanodont track, left, compared to a meat-

eating dinosaur track.

Trackway with 2 sets of prints: Iguanadon and Megolasaurus.(Source: http://www.stone.uk.com/dinos/)

Teethmarks

Tyrannosaurus rex skull. One can see there is considerable “bite potential” in these large carnivorous teeth.

The end of this limb bone from Apatosaurus has parallel toothmarks on it. The spacing of the tooth marks, as well as the individual marks themselves, help to identify what dinosaur was feeding on this apatosaur.

Gastroliths

These could be gastroliths (dinosaur gizzard stones used in some birds to aid in grinding up food), or they could be just polished stones. One of the major criteria for suspecting gastroliths in this case is that these specimens were found in Mesozoic rocks that were known to contain dinosaurs. In a few cases a pile of similar stones has been found within the ribcage of a dinosaur. That is a more serious criterion.

Coprolites

This coprolite on the left has been attributed to Tyrannosaurus and is half a meter long. The one on the right is ascribed to a hadrosaur…whether they are correctly attributed or even correctly designated is just a guess

Eggs & Nests

One of the more spectacular dinosaur fossil finds of recent years was of a Late Cretaceous specimen of Oviraptor that was found in a sitting position directly overa nest. This find, a wonderful combination of trace fossils and a body fossil, represents one of the most compelling pieces of evidence for brooding behavior in dinosaurs. It could, of course be explained otherwise. This fossil find is currently on display at the American Museum of Natural History in New York and was illustrated in a National Geographic article.

Skin

This model at Dinosaur Valley provides an idea of how

dinosaurs might have looked.

A natural cast of the skin of a hadrosaurian dinosaur, preserved in sandstone. The skin had a pebbled structure and appears to have been devoid of scales.

Artistic Rendition

“The World of Dinosaurs” Commemorative Stamps

Sketch of Allosaurus

Animated Models

Full-sized Tyrannosarus rex head, purchased from the Dynamation company which makes robotic dinosaurs. The skin, and the color, of course, are an artistic and scientific guess.

Fully robotic Allosaurus Fragilis created for the McKinley Museum of Science and History in Ohio. Cut-away shows inner workings of pneumatic system.

(Source: www.panix.com/~spoerri)

Famous Dinosaurs

(Source: www.tbssuperstation.com)

(Source: www.dinosaur.org/Gertie6.htm)

Godzilla

Gertie

Dino

Barney & Company

Jurassic Park

Dinosaur Myths

Dinosaurs represent failure & extinction. Dinosaurs and humans. Dinosaurs were either all hot-blooded or all cold-blooded. The word dinosaur means “terrible-lizard”. Whatever you read in the latest “dinosaur book” must be true. Dinosaurs all died at the same time. Mammals arose after the dinosaurs, and helped drive the

dinosaurs into extinction by eating dinosaur eggs. An asteroid (or comet) killed the dinosaurs. All big reptiles from the prehistoric past [“Monsters”] are

dinosaurs. Archaeologists dig up dinosaurs.

Because fossils are preserved in rock, need to understand basics of geology.

  Rocks (naturally occurring cohesive solids

comprised of one or more minerals or mineraloids) are generated in one of three primary manners (basis of rock classification):

•Igneous •Metamorphic •Sedimentary

Quick Course in Geology

Rock Types

IGNEOUS SEDIMENTARY METAMORPHIC

Igneous RocksIgneous Rocks

Igneous rocks form when moltenrock (magma) originating from deep within the Earth solidifies forming distinct crystals of different minerals.

The chemical composition of the magma and its cooling rate determine

the final igneous rock type.

Intrusive

(within the Earth)

Extrusive (erupts to surface)

Igneous rocks start out as molten rock

Metamorphic RocksMetamorphic Rocks

Metamorphic rocks are rocks that have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form.

Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. BUT THEY ARE NOT MELTED DURING THE METAMORPHIC PROCESS

Metamorphic Rocks

Sedimentary RocksSedimentary Rocks

Sedimentary rocks are formed from pre-existing rocks (sediment) and/or pieces of once-living organisms. They form from deposits that accumulate on the Earth’s surface as a result of transport and settling of sediment which then becomes compacted to form rock layers.

Clastic Sediment

Formed of fragments of weathered rocks or ash/dust - Sand, clay, & boulders are examples.

Clastic sedimentary rocks are named according to the sizes of the particles.

Clast = Greek for “fragment” or “piece”

Clastic Sediment

Formed of fragments of weathered rocks or shells - Sand, clay, boulders and shell fragments are examples.

Clastic sedimentary rocks are named according to the sizes of the particles.

Conglomerate Sandstone Siltstone Shale (clay)

Clastic Sedimentary Rocks

Chemical Sedimentary Rocks

“Chemical” sedimentary rocks are often assumed to have formed by chemical chemical precipitationprecipitation. The process is visualized as beginning with water traveling over or through rock, dissolving some of the minerals and carrying them away from their source. Eventually these minerals are thought to have precipitated when the water evaporates away or when the water becomes over-saturated. Other origins appear to be probable.

Examples: “Evaporites”

Gypsum (CaSO4 • 2H2O) and Halite (NaCl)

Gypsum is sometimes formed by the evaporation of seawaterrich in calcium - it forms after limestone and before halite

Biologic Sedimentary Rocks

Biologic sedimentary rocks form from once-living organisms. They may form from accumulated carbon-rich plant material (coal) or from deposits of animal shells.

Limestone & dolomite are often composed in part or in whole of the shells and other hard body parts of marine organisms such as clams, coral, oysters, and microscopic organisms like diatoms that have been transported and deposited as sediment, then hardened into rock

Biologic Sedimentary Rocks

The Rock Cycle

Sedimentary Environments

Uniformitarian assumptionMarine - Ocean/SeaNon-marine (or terrestrial)

fluvial lacustrine eolian deltaic

Beach Environment

Deltaic - where fluvial meets lacustrine or marine

Fluvial - Rivers and Streams

Flood Plains

Lacustrine - Lake

Eolian - wind blown

“Fluvial” RocksRiver ChannelSandstoneConglomerateSiltstoneFloodplainSandstone, SiltstoneClay

Flood Plains

Conglomerate > 2 mm

Rounded Particles Angular Particles (Breccia)

Sandstone 2mm - 1/16 mm

Today sandstone can form on beaches

Siltstone 1/16 mm - 1/256 mm

Siltstone can accumulate at lower energy levels

Clay < 1/256 mm in diameter

Shale - fissile (i.e. breaks into sheets) Claystone – massive not fissile

Shale and claystone require either lower energy levels or mass transport

Geologic Time

Relative Time verses “Absolute Time”

“Absolute Time” is based on radiometric dating (using radioactive decay to determine the exact age of a sample)

Relative Time is based on establishing the relative order of events without knowing the duration of each event or the amount of time lapsed between events

1. Principle of Original Horizontality 2. Principle of Superposition

Relative TimeRelative Time

Principle of Cross-Cutting Relationships

A < B < C

Law of Included Fragments (Inclusions)

Principle of original continuity

Other Concepts

Unconformity

Represents an interruption in the deposition of sediment - no material is deposited and possibly some rock layers may have been eroded

Principle of Fossil Succession

Requires evolutionary assumption of Standard Model for interpretation as biological succession. If this assumption is wrong, the interpretation must change drastically

Fossil Record

Correlation

Correlation

““Absolute Time”Absolute Time”Radioactive Decay

Electron Capture

the decay of beryllium-7 to form lithium-7

Uranium Decay

Half-life

The time required for one-half of the nuclei in a sample to decay

Geologic Time Scale

Divided into FOUR major time units: EONS - largest division - there are 4 eons ERAS – three – Paleozoic, Mesozoic,

Cenozoic PERIODS – seven (6 in other parts of

world) EPOCHS - smallest block of time only the

most recent era is divided into epochs

EONS

Hadean - 4.6 to 3.8 billion radiometric years ago Archean - 3.8 to 2.5 billion radiometric years ago Proterozoic - 2.5 Ba to 544 million radiometric

years ago Phanerozoic - 544 million radiometric years to now

Archean

Means “ancient”Rocks which appear to have formed on

the earth early in it’s history First evidence for life - one celled

organisms

Proterozoic

Meaning “revealed life”Remarkably, for the Standard Model,

modern continents have been stable since beginning of Proterozoic

the first rocks with apparent fossils of living organisms, mostly bacteria-like forms

Evidence for significant oxygen levels throughout.

Phanerozoic

Means “visible life”the most recent eondivided into three ERAS

Paleozoic “ancient life” Mesozoic “middle life” Cenozoic “recent life

Geologic Column

Outcrop in Nova Scotia, Canada of the McCoy Brook Formation (Lower Jurassic) in which a dinosaur skeleton was found (inset box)

An Example: How Geology Works

(Drawing of previous illustrating layering.)

Letters on right are: a, brown, “wind blown” sand; b, layering delineated by the boundaries of thin lava flows (basalt); c, angular blocks of basalt with a matrix of brown sandstone (interpreted as a fossil talus slope deposit).

How Geology Works:

Layering in sandstone (a) tilted - must have been more extensive.

PRINCIPLE OF ORIGINAL HORIZONTALITY Lava flow (b) broken up and abutting sandstone which drapes over it.

Sandstone must be younger than basalt. PRINCIPLE OF ORIGINAL CONTINUITY What was the environment that produced the sandstone? Dinosaur in sands which “look like” dune sands, in detail – could have been fossil dunes produced in a desert.What is the rubbly rock that looks like it is made of basalt boulders and sandstone (c)? Sands contain blocks of basalt looking similar to modern

talus cones – Could be fossil talus cones. PRINCIPLE OF UNIFORMITARIANISM

How Geology Works:

What of the animal itself? Turns out to be a prosauropod dinosaur,

probably Anchisaurus - known elsewhere in the world only in rocks of the Upper Triassic and Lower Jurassic of the Mesozoic -

PRINCIPLE OF BIOTIC SUCCESSION

How Geology Works:

Lava flow (brown and gray - North Mountain Basalt) above Triassic and Lower Jurassic strata, Five Islands Provincial Park, Nova Scotia

How Geology Works:

In the lava flow itself we could use K-AR dating scheme to find out the lava flow dates as 200,000,000 radiometric years - consistent with radiometric dates found elsewhere near the Triassic-Jurassic boundary (193-213 million radiometric years) APPLICATION OF RADIOMETRIC DATING

Just below that is a gray layer containing the fossil pollen of plants: this pollen compares well with the pollen in England and Germany in rocks which contain many marine fossils (including Psiloceras planorbis) correlating with the Lower Jurassic in the Jura mountains

PRINCIPLE OF BIOTIC SUCCESSION Below that are other gray rock layers without lava that contain

pollen of rather different composition comparable to what is found in the prosauropod beds themselves in the type Triassic rocks in Germany. PRINCIPLE OF BIOTIC SUCCESSION

How Geology Works:

Thus, we would conclude that the rocks deposited around the prosauropod bones are higher in the geological column than the lava flow and the Triassic-Jurassic transition -PRINCIPLE OF SUPERPOSITION

We might make other predictions of what we should find: other reptiles, no triassic types, other radiometric systems agreeing etc.

Test, TEST AGAIN, adjust.

How Geology Works:

We might also choose to interpret the data differently. Perhaps the dinosaurs were all living on the earth at the same time and they were transported in such a way that this particular species of dinosaur was buried with these specific kinds of plant and animal fossils everywhere in the world and that this occurred not millions of years ago but a few thousand years ago in a global flood.

If we chose to interpret the data this way, we would have to acknowledge that there were a lot of questions we did not know the answers to, and that our position was generated from our model.

That is fine, so long as we do not pretend that we have answers where we do not. “I don’t know, but I am trying to find out” is an acceptable answer in science.

How Geology Works:

Your Turn…