Travis Ingram Flashcards
Order of periods?
“Camels Often Sit Down Carefully, Perhaps Their Joints Creak Painfully, Quite Early”
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Triassic
Jurassic
Cretaceous
Paleogene (early Cenozoic)
Quaternary (Cenozoic)
When were the 5 extinctions and what went extinct?
Ordovician Extinction (440 million years ago):
Mainly affected marine species
About 85% of marine species were lost
Late Devonian Extinction (360 million years ago):
About 75% of species were lost
Affected both marine and terrestrial life
Permian Extinction (“The Great Dying”) (250 million years ago):
Most severe extinction event
96% of marine species and 70% of terrestrial vertebrate species were lost
Triassic Extinction (200 million years ago):
About 76-80% of species were lost
Affected both marine and terrestrial life
Cretaceous (K-T) Extinction (65 million years ago):
75-76% of all species were lost
Most famously, non-avian dinosaurs went extinct
Affected a wide range of species across marine and terrestrial environments
Cambrian
Began around 550mya
Explosion - More trophic roles and niches similar to today, relatively rapid (40my) origin of most modern phyla. Sparked by Environment stimulus hypothesis - rising O2 levels in seawater causes by increased photosynthesis due to Ediacaran Fauna and carbon sequestration made increased size and metabolic rate permitted which made evolution of mobile predators and new selection pressures.
So recognisable body plans with hard parts appear including:
-Segmented bodies
-Shells/Exoskeletons
-Complex eyes
-Notocord
-Bilateral symmetry
-Larger size
Diversity of body plans have been stable since here so even if rewinded it is likely body plans would always be like this!!!!!!!!
Some vertebrate fossils towards the end
Ordovian
Began around 500mya
First unmistakable fish fossils without jaws. Jaws appeared towards the end and start of silurian.
Ostracoderms (non-monophyletic group)
- jawless filter feeders with paired fins
- well-developed brain and prominent dermal skull bone
Rise of Fish: The first true vertebrates continued to evolve, with jawed fish possibly appearing late in the period.
Silurian
Began around 450mya.
Ostracoderms diversified during this time and so did the evolution of jaws.
Devonian
Began around 400 mya
“Age of Fishes”
Diversification of:
- placoderms e.g. Dunklesteus (Dominant in Devonian, extinct at end)
- Acanthodii (spiny sharks), lineage of true sharks, skates, rays and therefore survived into Permian)
- cartilaginous fishes (lineage of true sharks, skates, rays and therefore survived into Permian- ray-finned fishes)
- Ray-finned fishes, Highly successful - almost 50% of vertebrate species today
- lobe-finned fishes - evolved into Tetrapods (transition to land) in late Devonian due to adaptations to hydrologic variability:
- desiccation resistance
- ability to breathe air
Carboniferous (Mississippian and Pennsylvanian)
Began around 350mya
Amniotic egg evolved after in the late Devonian tetrapods had evolved. This made amenities fully terrestrial and many new ecological niches opened up for use.
Anapsids (no hole behind eye socket in skull) gave ride to synapsids and diapsids because the fenestrae allowed stronger muscle attachment between lower jaw and skull.
Reptiliia origanated in the Carboniferous but diverged during the Permian
Permian
Around 300mya
In the early permian synapsids evolved into dominant terrestrial vertebrates like the pelycosaur (not a dinosaur), amphibians not dominant now.
In the late Permian Therapsids were dominant.
Reptilia diverged in the Permian:
Two main lineages diverged
1. Lepidosaurs
- ancestors of lizards, snakes & tuatara
2. Archosaurs
- ancestors of crocodiles, dinosaurs, birds & probably turtles
PERMIAN EXTINCTION ‘The great dying’ 250mya
Primary cause likely massive eruption
of the Siberian Traps
→climate change
→acidification
→anoxia
→toxicity
Possible bolide impact
as trigger for eruption
Triassic (Mesozoic)
Began around 250mya
Aftermath of the great dying.
Amphibia - temnospondyls remain dominant semiaquatic predators
Synapsida - most therapsid groups declining,
cynodonts are the group that give rise to first mammals around the end of the triassic
Reptilia:
- pseudosuchians (crocodile relatives)
- first pterosaurs (First flying vertebrates) and ichthyosaurs
- first dinosaurs - didn’t diversify until jurassic
Jurassic + Cretaceous (Mesozoic)
Three major dinosaur clades:
- Sauropodomorpha
- Theropoda
- Ornithischia = Almost all herbivorous (evolution of scales, frills, armour, and other adornments) (Stegosaurs, Triceratops)
- Some reptiles (diapsids) went back to being marine (secondarily aquatic lifestyle) and still diversifying
- In the Jurassic the first Avialiae evolved (powered flight), preadaptations allowed this because they didn’t have as many independent steps to allow this. Archaeopteryx - first known bird (~150 m.y.a)
Most mammals were small nocturnal omnivores
or insectivores at the end of the Mesozoic.
Cenozoic - Tertiary (Paleogene, Eocene, Oligocene)
“Age of Mammals” (and birds) (and percomorph fish)
After the K-T extinction, ecological opportunity allowed
diversification into many new niches.
More species became active during the day.
Theropoda survived the K-T and diversified as the dominant flying clade - Birds.
Flying mammals remained largely nocturnal.
Evolution of flight diversified.
Ray-finned fish had been successful since the Devonian, but the ‘percomorphs’ underwent spectacular diversification in the Cenozoic.
Secondarily evolution of aquatic lifestyle by terrestrial vertebrates (more on land predators now so opposite to when Tetrapods evolved terrestrial lifestyle to avoid predators, evolutionary arms race)
While not reaching the size of the largest dinosaurs, some mammals and birds became massive compared to most modern species, filling the niches of larger dinosaurs who went extinct, some have roughly the same ecological analogues.
Primates diverged from mammals soon after the K-T extinction, likely because of filling other niches higher up.
Jaws
Appeared in the late Ordovician (450mya)
Key innovation that lead to diversification of feeding behaviour and lead to specialised feeding strategies. Also lead to the later innovation - pharyngeal jaws that lead to further diversification.
Evolutionary origin of jaws = Homologous to some of the anterior gill arches.
Macroevolution
Large evolutionary change usually in morphology that occurs over a long period of time.
Red Queen Hypothesis
Biotic factors (from other living organisms) are most important, especially coevolution with predators,
competitors and parasites/pathogens
Court Jester Hypothesis
abiotic factors are most important, including ‘chaotic’ events such as bolide impacts, and changes in the climate
What 3 forms were involved in the transition to land in the late Devonian how did this happen?
Eusthenopteron - clearly a fish - Mid Devonian (~385 m.y.a.)
Tiktaalik roseae (~375 m.y.a.) - transitional form
Ichthyostega (and Acanthostega ) - clearly tetrapods
Late Devonian (~365 m.y.a.)
Evolution of Tetrapod Legs:
Fins become legs - shift in structure of the limb likely
via regulatory changes in hox gene expression.
Increasingly adapted to support weight rather than
to move through water.
Describe early tetrapods and how they became fully terrestrial and when this happened?
Amphibians - Late Devonian
- “double life” (reproduction & larval stages require water)
- Acanthostega & Ichthyostega (~365 m.y.a.)
- likely primarily aquatic with ability to drag self on land
Then in the carboniferous (320mya) KEY INNOVATION of amniotic egg evolved. The amniotic egg allowed
tetrapods to become truly terrestrial and use habitats far from water bodies ecological opportunity provided by diversification of vascular plants and insects
→new niches in Carboniferous forest
What did anapsid give rise to?
synapsid and diapsid reptiles
What did synapsids give rise to?
Therapsids and eventually mammals
What did diapsids give rise to?
Birds, dinosaurs, retilia
What diversity did Ornithischia evolve to have and when?
- In the Jurassic after the Triassic extinction event
- Almost all herbivorous
- Evolution of scales, frills, armour, and other adornments
- Ancestrally bipedality (from the Triassic), at least 3 reversions to quadripedality in the jurassic and cretaceous, Clades achieved quadrupedality via distinct changes in musculature and kinematics
- Stegosaurs, Triceratops
What diversity did Sauropodomorpha evolve to have?
- Herbivorous quadrupeds - include the largest ever
terrestrial animals - Replacement with ever-larger clades through the Mesozoic, by the time the Cretaceous came there were only a few very large types and they were gone after the cretaceous
- Not really diversification just directional evolution bigger
What diversity did Theropoda evolve to have?
- Bipedal, hollow-boned, mostly carnivorous
- First bipedal top predators, would lead to Red Queen Hypothesis occurring
- Spinosaurs - secondarily aquatic lifestyle
- Feathers widespread among Theropoda
- Arm reduction in several large predatory lineages
(possibly a developmental constraint due to large head size) - Evolved wings at least twice - only one had true flight (powered flight) - all the previous adaptations were why they could fly but weren’t with the purpose of flying at that time
Archaeopteryx - How did this become the first known retile transition form to bird?
- first known bird (~150 m.y.a)
Ancestral reptilian features: - teeth inserted into jaws
- long bony tail
- scales on head and legs
- clawed fingers on forelimbs
Birdlike features: - asymmetric flight feathers
- clavicles fused into ‘wishbone’
How did the evolution of flight in vertebrates diversify during the Cenozoic?
Convergence began to occur a lot more.
Convergent features
- flapping
- increased aerobic capacity
- light/hollow bones)
Non-convergent features
- elongation of different
homologous limb bones
- use of hindlimbs in bats
- use of skin vs. feathers
Non powered gliding also continue to evolve.
How and when was the evolution of aquatic lifestyle by terrestrial vertebrates (returning the the sea)?
Happened in the early cenozoic filling newly available niches, what already had closest traits would be able to fill these niches quicker.
Good fossil record - series of transitional forms
Pakicetus (~55 m.y.a.)
- likely amphibious fish eater
- cetacean-like inner ear (for underwater hearing)
- four functional legs
- flexible neck
- long tail
Then secondary evolution of aquatic lifestyle by terrestrial vertebrates.
Convergence for efficient sustained swimming at top speed:
- fusiform body shape
(streamlined, slightly larger in front)
- power from caudal (rear) fin
- endothermic (at least somewhat)
Nonconvergent:
- dolphins flex dorso-ventrally while
most reptiles & fish flex laterally
Explain point 1 of the essay with examples from each period (Survival of Extinction Events)
Survival of Extinction Events
Certain animals would likely survive major extinction events due to specific adaptations and characteristics that have proven advantageous in the face of catastrophic changes. For example, small mammals survived the K/T extinction that wiped out the dinosaurs because of their ability to burrow underground, their diverse diets, and their capacity to enter low-energy states1. These traits would likely confer similar survival advantages in a “replay” scenario, leading to the persistence of comparable animal groups.
Examples:
Paleozoic: During the end-Permian extinction (252 million years ago), small burrowing animals like the mammal-like reptile Lystrosaurus survived due to their ability to shelter underground1.
Mesozoic: In the K-T extinction (66 million years ago), small mammals survived by utilizing underground burrows and having diverse diets that included insects and aquatic plants1.
Cenozoic: During the Pleistocene extinctions, smaller and more adaptable mammals like rodents and bats survived while larger mammals went extinct.
Explain point 2 of the essay with examples from each period (Evolutionary Trajectories and Niche Filling)
Evolutionary Trajectories and Niche Filling:
Animals existing up to the chosen starting point would already possess evolutionary traits that predispose them to fill specific ecological niches. The principle of convergent evolution suggests that similar environmental pressures would lead to the development of analogous adaptations, even in unrelated species. This phenomenon would likely result in the emergence of comparable animal forms and functions, as organisms evolve to exploit available resources and adapt to similar ecological challenges.
Examples:
Paleozoic: The evolution of lobe-finned fishes into early tetrapods like Tiktaalik, filling the niche of shallow water predators and eventually leading to land vertebrates.
Mesozoic: The evolution of theropod dinosaurs into birds, filling aerial niches previously occupied by pterosaurs.
Cenozoic: The evolution of cetaceans from land mammals, filling niches left vacant by marine reptiles after the K-T extinction.
Explain point 3 of the essay with examples from each period (Environmental and Physical Constraints)
Environmental and Physical Constraints
The fundamental laws of physics, chemistry, and the relatively stable environmental conditions on Earth would impose similar constraints and opportunities on evolving life forms. These constraints would likely lead to the development of comparable body plans, physiological processes, and ecological strategies across different evolutionary scenarios. For instance:
Hydrodynamics would favor streamlined bodies for aquatic animals.
Gravity would influence the evolution of skeletal structures and locomotion methods.
The properties of light would drive the development of similar visual systems.
Atmospheric composition would influence respiratory adaptations.
These consistent physical and environmental factors would channel evolution along similar paths, resulting in animal diversity that is broadly recognizable, even if specific species differ in details.
Examples:
Paleozoic: The development of similar body plans in trilobites across different lineages due to constraints imposed by their marine environment and exoskeleton structure.
Mesozoic: The convergent evolution of streamlined body shapes in ichthyosaurs (reptiles) and modern dolphins (mammals) due to hydrodynamic constraints of aquatic life.
Cenozoic: The repeated evolution of saber-tooth morphologies in different mammalian lineages (e.g., saber-tooth cats, marsupial thylacosmilids) in response to similar predatory niches.
