GEOL 240 The Dinosaurs: Introduction
Jan 12, 2016
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…