Vertebrate Zoology - 02 Evolution Complete

Linnaeus Belief of Species

Believed species were fixed and unchangeable.

Understanding of evolution requires three parts:

• Fact of evolution

• Course of evolution

• Mechanism of evolution

Jean-Baptiste de LaMa

French naturalist and later professor at National Natural History Museum in Paris

Philosophie Zoologique (1809) argued all 3 aspects of evolution:

1. Species changed over time

2. Organisms started simple, became more “perfect”

3. Evolution by inheritance of acquired characteristics

LaMarckian evolution

Inheritance affected by use or disuse; Confuses physiology with genetics

Charles Darwin

• Voyages on HMS Beagle, describes much biodiversity in South America, islands

• Develops theory of evolution by natural selection, sits on it for decades

• Prompted to publish when ARW discovers the same mechanism.

Alfred Russel Wallace

• 4 years younger than Darwin

• Poorer background, spent most of career in field

• Greatly admired Darwin, sent him his theory for his opinion

• ARW also remembered as “father of biogeography”.

Three basic parts of evolution by natural selection:

1. Inheritable variation under nature

2. Differential survival and reproduction

3. Time (generations)

Origin of Species (Darwin 1859)

• (With 6 editions) Presented an “abstract” of Darwin’s case

• Evidence largely from biogeography, natural history, some paleontology and geology, and analogy with artificial breeding of animals by humans.

Two serious scientific criticisms of Darwin and Wallace’s ideas at the time:

• Time: ages of fossils, the Earth unknown then; unclear if the world was old enough for such a slow process

• Inheritance: No one knew how traits were passed from parent to offspring, and the hypotheses they did have were wrong.

The modern estimate of the age of the Earth is…

4.54 + 0.05 billion year

Pangenesis

A version of blending, wherein every part of the body contributed to gametes.

(Gregor Mendel) Particulate Inheritance

Transmission of alleles or discrete units of genes.

Order of Evolution Takes a Long Time

• Life appeared around 4.3-3.8 billion years ago.

• Eukaryotes appear by 1.8 billion years ago

• Animals appear around 650 Mya

• Vertebrates appear ~518 Mya

• Mammals appear ~225 Mya

• Primates ~66 Mya

• Humans ~300,000 years ago.

Calendar of Evolution takes a long time.

Archaea

Have a nucleus

Amorphea (aka: Unikonta)

One flagellum developed

Opisthokonta

Evolved from protistan ancestors

Multicellular

Evolved independently

Bikonta

A group that includes plants.

Holomycota

Includes Fungi

(Group) Bilateria

Left and right side possessing bilateral symetry

Protostomia

First mouth (only one opening)

Deuterostomia

Two openings (butt and mouth chordata)

Gnathostomata

Jaws

Osteichthyes

Bones

Sarcopterygii

Two bones in limbs

Tetrapoda

Possesses four legs (Example: Amphibia)

Amniota

Generates amniotic fluid for reproduction (Reptile; birds)

Sauropsida

Group that includes “Reptiles” and birds

Synapsida

Group that includes no hole in the back of the skull

The first vertebrate ancestors appear in _______ period ~518 Ma; Resembled modern-day Cephalochordata (lancelets): marine filter feeders without jaws or bones

Cambrian period

What is a chordate?

• Notochord (cartiligous cord for structure)

• Dorsal, hollow nerve cord

• Postanal tail

What is a vertebrate?

Segmented vertebral column (fully or partially replaces notochord)

• Multi-chambered heart

• Inner ear with semicircular canals

• Brain with >=3 sections (Cranium with brain)

• Discrete sense organs

• Nostrils (defines clade Olfactores)

• Gut with digestive organs

Cambrian World

• 538-486 Million years ago

• Most of the land was in southern hemispher

• No known land, few animals (arthropods)

• Cambrian Explosion: modern animal phyla first appear in fossil record 538-525 (approx. Mya)

• Chordates and vertebrates appear

Ordivician period

• 486-443 Million years ago

• Highest sea levels of Paleozoic

• Molluscs and arthropods dominate the oceans

• First terrestrial plants appear

• Jawed fishes may have appeared in late Ordovican

• Ended in mass extinction (2nd worst in history)

Silurian Period

443-419 Mya

• Jawed fish appear (3 lineages); jawless fish decline

• Vascular plants appear on land; arthropods dominate land (Myriapoda, Arachnida, Hexapoda)

• Drastic climate fluctuations

• Sarcopterygii appear late

Devonian Period

• 419-358 Mya

• “Age of Fishes”-placoderms, first sharks, much greater diversity than Silurian

• Fish à tetrapod transition in one lineage of freshwater rhipidistians (Sarcopterygii)

• Land plants dominate terrestrial ecosystems, no large herbivores yet

Carboniferous Period

• 358-298 Mya

• Terrestrial vertebrates become more established

• Age of Amphibians” – high diversity of early amphibians, esp. labyrinthodonts

• Amniotes appear and diversify into sauropsid and synapsid lineages

• Many global coal beds laid down during this period

• Pangea begins to assemble

Permian Period

298-251 Mya

Synapsid amniotes were dominant for most of Permian

Pelycosaurs, later therapsids and cynodonts were apex predators

Archosauromorphs appeared

The “Great Dying: Permian-Triassic mass extinction, 81% of marine and 70% of terrestrial species.

Triassic period

• 251-201 Mya

• Dinosaurs appear, but won’t get big until Jurassic

• Therapsids, dicynodonts, pseudosuchians remain dominant land fauna

• Crown group Lissamphibia, Teleost first appear and diversify

• Atlantic Ocean begins to form

• Most land still part of Pangea

Jurassic Period

201-143 Mya

Dinosaurs become dominant land animals in all ecosystems

First crown mammals evolve

Birds evolve within theropod dinosaurs

Conifers, gingkos, cycads form forests

Climate 5-10 °C warmer than now, no ice caps, 4x higher CO₂

Cretaceous period

• 143-66 Mya

• Crown birds, angiosperms, appear.

• Crown mammals and multituberculates diversify

• Dinosaur diversity and size peak

• Ends with Cretaceous-Paleogene (KT) extinction 66 Mya – asteroid strike near Yucatan peninsula

Palogene Period

• 66-23 Mya

• Consists of Paleocene, Eocene, and Oligocene epochs

• Rapid diversification of mammals and birds following extinction of non-avian dinosaurs…most modern orders appear

• Grasslands begin to proliferate

Neogene period

• 23-2.6 Mya

• Consists of Miocene and Pliocene

• Mammals and birds continue radiating

• Continents in essentially modern positions

• First Homo appear near end of period

Quarternary Period

• 2.6 Mya – present

• Pleistocene and Holocene epochs

• Some claim new “Anthropocene” epoch has started, but this is controversial and not widely accepted

• Repeated ice ages in Pleistocene drove evolution of Pleistocene megafauna

• Pleistocene megafauna driven to extinction by climate change and humans

• Modern humans evolve about 300,000 years ago (Pleistocene)