BISC 102 Lecture Notes - Lecture 3: Phylogenetic Tree, Theropoda, Monophyly

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Evidence for Change through Time:
● Fossils are one source: Traces of organism that lived in the past
Many different mode of preservation: Permineralization (petrifaction),
impressions, compressions, casts and moulds, tracks, original materials.
The many fossils that have been found and described in the scientific
literature make up the fossil record which spans geological time from 3.5
billion years ago to recent
Morphology, embryology, DNA similarities are also important sources of evidence
for evolutionary history of organisms (Phylogeny)
Biogeography/Endemism
Darwin was more interested in endemic mockingbirds than finches
Three distinct species are restricted to single islands in the Galapagos but are clearly
related to other species in the archipelago
Rare dispersal events between environment followed by evolution in relative
isolation on each island, leading to different populations on each
There are no fossils of mockingbirds here, so use other data to trace evolutionary
history:
Patterns: Although the mockingbirds are extremely similar, distinct species
are found on different islands
Recent data supports Darwin’s hypothesis that the Galapagos mockingbirds
share a common ancestor
Fossil Record:
Found, not missing “links”
Many transitional fossils have been discovered since Darwin’s time, clearly
intermediate in morphology between reptile/dinosaurs and modern birds
Whale fossils are another example: Also lungfish to terrestrial tetrapods (4-limbed
vertebrate) and many others have filled theoretical gaps in fossil record
Scientists expect many gaps to exist since the fossil record is incomplete for most
organisms (fossilization requires rare special conditions), but enough fossils
sequences have been discovered to confirm that evolution has occurred
Gaps will always remain in fossil record
Finding a new fossil that fills the gap can be interpreted as creating two new
gaps that need to be filled
The assumption that a complete series of fossils is needed to demonstrate
evolutionary change is unrealistic and unreasonable
Example: Birds are feathered and modified theropod dinosaurs
Fingers and claws in some living birds: But no teeth or elongate bony tail
● Hoatzin: Amazon nests flooded forest floor
Claws used to climb in vegetation before they can fly
Claws are lost in adult birds
Chicken wing 3 digits remain as vestiges of ancestral reptile fingers
Homologies
All vertebrate share a common skeletal structure: Based on structure of ancestral
tetrapods
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Document Summary

Fossils are one source: traces of organism that lived in the past. Many different mode of preservation: permineralization (petrifaction), impressions, compressions, casts and moulds, tracks, original materials. The many fossils that have been found and described in the scientific literature make up the fossil record which spans geological time from 3. 5 billion years ago to recent. Morphology, embryology, dna similarities are also important sources of evidence for evolutionary history of organisms (phylogeny) Darwin was more interested in endemic mockingbirds than finches. Three distinct species are restricted to single islands in the galapagos but are clearly related to other species in the archipelago. Rare dispersal events between environment followed by evolution in relative isolation on each island, leading to different populations on each. There are no fossils of mockingbirds here, so use other data to trace evolutionary history: Patterns: although the mockingbirds are extremely similar, distinct species.

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