Day 26: What can we learn from the fossil record?

What level of detail can we see in fossils preserved in amber?

We can do CT scans to see an extreme level of detail (such as in a fossil mite)

How do we know that the Cambian explosion was an explosion?

We infer it by comparing pre- and end-Cambrian Faunas 544mya - Ediacaran Fauna: sponges, jellyfish, comb jellies 520-515mya - Burgess Shale: arthropods (including trilobites), segmented worms, molluscs, vertebrates (hagfish and lamprey)

What types of organisms were found in the mesozoic

clams, snails, crabs, sharks, bony fishes

Uniformitarianism and importance

(James Hutton c. 1700) - geological processes taking place now operated similarly in the past Importance: By measuring rates of present geological processes, Geologists infer large-scale time-horizon for formation of various geological features on Earth

What are some explanations for the Cambrian explosion (3)?

1. "Explosion" was a morphological response over a short-time period to a longer-term genetic change? (Bromham et al 1998; Smith 1999) 2. Great changes in feeding ecology also helped to drive morphological diversity? Ediacaran: sessile, filter feeders Burgess Shale: benthic and pelagic predators, filter feeders, grazers, scavengers, detritivores A big increase in predation could have driven diversity in behaviors and morphology. 3. Changes in environment? Rising oxygen concentrations due to increase in photosynthetic organisms More oxygen would allow for larger organisms such as predators, which would in turn create more niches and coevolutionary arms races.

What are some examples of fossilized behaviors? (5)

1. A birthing Ichthyosaur = evidence of live birth 2. Predation: Pterosaur bones in velociraptor gut = raptors might have been scavengers since it is pretty unlike that they hunt flying prey. 3. Parental Care: fossil from China shows 34 juveniles in similar posture with one adult, indicating that parental care evolved before the split between crocodiles and modern birds 4. Culture: evolution of brain size in Homo genus can be linked to the evolution of culture 5. Developmental programs: molting arthropod from 505 mya (Cambrian) in real time.

Critical evolutionary transitional forms (3)

1. Archaeopteryx: dinosaurs to birds; birds evolved from/are theropod dinosaurs with feathers 2. Panderichthys (385 mya): crocodile-shaped and looks like a fish; fish-tetrapod transitional form. 3. Tiktaalik (365 mya): more tetrapod-like than Panderichthys in its breathing and feeding apparatus, but with similar locomotory adaptations.

What are some strengths of the fossil record? (3)/unique value of fossils to evolution

1. Deep time (radiometric dating can reveal a fossil's age) 2. Reveals common ancestors and evolutionary transitions 3. Identify major evolutionary events in history of life *for 2, this is great because it allows us to test Darwin's predictions by anticipating the discovery of transitional forms.

Evolutionary novelties that arose in the Cambrian explosion (8)

1. Diploblasts and Triploblasts (i.e. tissue types) 2. Coeloms (providing space for internal organs, support for hydrostatic skeletons, improved swimming and crawling) 3. Gastrulation (rearrangement of embryonic cells that allows tissue specialization) 4. Segmented body plans 5. Shells 6. External skeletons 7. Appendages 8. Notochord

What are some other weaknesses in the fossil record (not in class) (3)?

1. Gaps in the record 2. Only have phenotype to work on 3. One certain kinds of phenotypes are preserved (very few soft tissues)

What are some biases in the fossil record? (4/5)

1. Geographical: wet and anaerobic habitats 2. Taxonomic: most fossils are marine (80%), yet most extant taxa are not marine (10%). Almost 70% of animals lack hard structure that are easily fossilized. Flowers are really important, but very rarely get preserved. 3. Temporal = "pull of the present": fossils are lost when Earth's crust is recycled (subduction). Old rocks are rarer than new rocks. 4. Collector's bias: paleontologists are more interested in certain taxa (skulls rather than full skeletons; t-rex rather than small herbivores) 5. Morphospecies concept application: sexually dimorphic species could be classified as two separate species (same with species that have adults and juveniles that look very different). Cryptic species very likely to go undetected. <- this is more a bias in the species concepts.

What are some nearly-found fossils that show some lineages are much older than we thought.

1. Jawless fish around 530 mya. This means chordates are a lot older than we thought 2. Proterozoic blastomeres (1000-600 mya): bilateria originated 50 million years before the Cambrian.

How do we know the time period in which certain organisms were found?

1. Preserved specimens - the fossil record 2. Fossils are embedded in rock - geological timescales - and we can date rock.

Major events/periods in evolution to know (5)

1. Solar: 4500 mya; formation of earth 2. Archaean: 3900 mya; origin of life 3. Paleoproterozoic: 2500; origin of Eukaryotes and sex 3. Cambrian: 543 mya; explosion (molluscs, annelids, arthropods, echinoderms) 4. Cretaceous: 65 mya; extinction of dinosaurs and ammonites

4 major ways to generate a fossil (include a few examples)

1.Compression/impression: organism is buried in sediment before it decomposes. The pressure of the sediment forms and impression. This usually happens in water or very windy habitats. Only the outer structure is preserved - and can often be distorted. You can see a lot of detail such as the stomata of a leaf. 2. Permineralized: organisms are buried in sediment and dissolved minerals precipitate in cells. This mostly happens in water or in very windy habitats. It can preserve fine details, including internal structure These are the classic fossils that you would see on display in museums such as t. rex skulls or petrified wood. 3. Casts and Molds: organism decays (or dissolves) after being buried in sediment. Molds are formed from unfilled spaces while casts form when new materials fill the space and harden into rock. Again, this will happen predominately in wet environments. Molds and casts can preserve external and internal surfaces. 4. Unaltered remains: when weathering, scavenging, and decomposition are minor such as in peat bogs, permafrost, tar pits, and amber This is very rare. So the record of such preservation is extremely patchy. This can preserve almost all parts of the body. Examples are butter and human skin preserved for 1000s of years in peat bogs, large mammals such as mammoths, and many insects and plants in amber

What is the craziest/most direct way we have been able to study fossil species?

A fruiting plant Silene stenophylla "regenerated" from permafrost (-7°C) specimens that were 32,000 years old Used maternal, immature fruit tissue found in a fossil squirrel burrow This makes for early easy comparison with current species and is also a great way to get ancient DNA easily.

Result of Cambrian explosion/why it is an explosion

Almost all extant phyla originated in a 40 million year period in the Cambrian. It ranks as one of the greatest events in the history of the Earth

What was the major evolutionary event that we focused on?

Cambrian Explosion (540mya)

What is the importance of the transitional forms we discussed?

Every one was predicted by paleontologists (test of evolutionary principles)

What types of organisms were found in the Cambrian?

Explosion (general): molluscs, annelids, arthropods, and echinoderms) Specifics: Sponges, Coelenterates (corals, jellyfish, etc.), Trilobita, inarticulata/brachiopods, eocrinoidea, monoplacophora, vertebrates (hagfish and lamprey)

What are some other biases in other fields?

Fields are very focused on particular systems or areas: Molecular genetics: E. coli, Neurospora crassa Developmental genetics: Drosophila, Arabidopsis thaliana Behavior: Birds and mammals Ecology: North American and European uplands

What was a remarkable fossil find allowed us to look at the evolution of developmental processes?

Fossilized blastomeres of some form of worm-like animal. We find them in different stages of development.

What was a surprising anthropology find in the fossil record?

Homo floriensis: "Hobbit" (3 feet tall) from Indonesian island of Flores Descendent of Homo erectus (not on direct lineage to Homo sapiens) Most recent specimen aged at 13,000 years old Therefore, co-existed with modern humans for perhaps 100,000 years!

Plot formation of earth, origin of life, origin of sex, Cambrian explosion, and origin of man

Humans = last 8 minutes of last day of class

Does the molecular evidence suggest that the Cambrian explosion was indeed an explosion?

Molecular clock data (combined with phylogenetic analysis) indicates that many of the 'Cambrian' fauna originated some 1200-800mya (Runnegar 1982; Wray et al 1996) *Cambrian explosion = 540. This produced great controversy and suggested that there are older fossils. Some recent finds indicate that some lineages may be even older!

What types of organims were found in the Paleozoic?

Polychaete worms, crinoids, ostracods, brachiopods

Who gets fossilized? (3 sup, 2 direct answers)

Probability of fossilization affected by specimen durability, burial, and lack of oxygen Therefore organisms from particular habitats and show particular behaviors are more likely to be fossilized Habitats: river deltas, swamps (commonly anaerobic), beaches, sea floor Behaviors: burying (e.g. clams), shedding of structures (e.g. leaves, pollen, exoskeletons)

Critical technique for investigating deep time?

Radiometric dating Rock contain radioactive isotopes Radioactive decay (change from 'parent' to 'daughter' state) is constant and not affected by the environment Rate of decay can be measured (in a mass spectrometer) Therefore, ratio of parent to daughter isotopes can be used to infer rock age

Examples of radiometric dating techniques

Rubidium-strontium has a half-life of 47 billion years Carbon-14 has a half-life of 5,730 years

What is Paleontology?

The scientific study of life in the geologic past, especially through the study of animal and plant fossils. It answers questions that other areas of evolutionary biology cannot.

Hutton's big idea

Uniformitarianism

How did we figure out what color microraptor was? What type of fossil was it?

We used nanoscale analysis to reveal coloration and iridescence since melanosomes that produce different colors have different morphologies. It turns out 130 myr old Microraptor had dark iridescent plumage and "ornamental" tail feathers (Li et al 2012) Microraptor was an example of permineralization.

Fossil

any trace left by an organism