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Biodiversity 4: The Chordates

4 of 4 of my Biodiversity unit. Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet. Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke.

Andrew Huff

on 12 August 2016

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Transcript of Biodiversity 4: The Chordates

Before We Begin
Big Questions
Make sure you can
Last Common Ancestor of the Chordate Phylum
Basal Craniates
Our understanding of life's diversity is constantly expanding.

This presentation reflects a very brief explanation of the relationships among living organisms.

The "branches of the tree" only represent general relationships, not time or abundance or anything else.

The purple arrows spotlight important evolutionary developments.
What makes a chordate?
What they are:
aka: tunicates, lancelets
spinal cord*, no brain, no bones.
aka: Hagfish, Lampreys
no jaws.
aka: Sharks, Skates & Rays
Jaws (pun intended),
Cartillagenous skeleton
aka: "Fish"
Calcified skeleton
2 major divisions
aka: frogs, salamanders, & caecillians
3 chambered heart
part of lifecycle is aquatic, part is terrestrial
aka: lizards, snakes, crocodillians, turtles, tuatars
Totally terrestrial*
3 chambered heart
aka: "Avian Reptiles", "Birds"
adapted for flight*
aka: you, your dog, your cat
live birth*
nurse young with milk
The Characteristics of a Chordate:
Who's a Chordate?
Every animals with a backbone.
Your pets.
The animals you eat.
Where's your post-anal tail?

Where are your pharyngeal slits?
* at some point in the lifecycle, at least
Not all chordates are vertebrates!
Tunicates have a notochord, and a dorsal nerve cord in their larval form.

They are lost during maturation.
The lancelet has all features of a chordate throughout its life cycle...

...but it doesn't have a spinal column.
Why are they important?
Chordates that have a head containing sensory organs, brain and a skull
Haikouella: a fossil chordate with a brain, but no skull
The hagfish is the most basal living craniate.

It has a cartillagenous skull, but no vertebra
Lamprey's have a series of cartillagenous projections that grow from their notochord to surround their dorsal nerve chord.
What they are:
Chordates that have a developed head AND a spinal column of vertebra.
Most living vertebrates have jaws (gnathostomes).
Why are they important?
A conodant: a very common, ancient, jawless vertebrate
Jawless vertebrates were common through the Devonian (360 mya). 2 examples.
Agnathans: "No Jaw"
Dunkleosteus: an early gnathostome (up to 30 feet long)
Hypothetical Evolutionary Path for Jaws
There is no difference in Hox gene expression at the anterior end of lancelet and vertebrate embryos (what does that mean?)
The Neural Crest is a craniate-only region of the embryo
Chondricthyans have jaws!
Fins are common in gnathostome fish
Rays are bottom feeders & suspension feeders
Actinopterygii: "Ray Finned Fish"
Sarcopterygii: "Lobe Finned Fish"
More than 27,000 living species
Some examples:
3 major linneages:
Coelocanths: 1 living species
Lungfish: 6 living species
Tetrapods: All terrestrial chordates
A fossil sarcopterygian: 420 mya
A Coelocanth: Thought to have gone extinct 75 mya, until a dead one was caught by local fishermen off of South America in 1938
What they are:
Why are they important?
Gnathostomes that have limbs.
Tiktaalik: A fossil "fishapod"
Fossil progression showing limb evolution
"Both Ways of Life"
The lifecycle of a frog shows it's "Dual life"
What they are:
Tetrapods that have an amniotic egg with a watertight shell and extraembryonic membranes
Why are they important?
shell: protection
amnion: shock-absorber
full of amniotic fluid
chorion: gas exchange
allantois: metabolic waste
yolk sac: nutrients
The Amniotic Egg:
The 5 living lineages of
non-avian reptiles
Phylogeny of reptiles and their descendant taxa
*with apologies to crocodillians, marine iguanas, & sea snakes
*with apologies to penguins & rattites
Some of the flight adaptations of the avian wing
The Kiwi Bird (native to New Zealand) is adorable...
But it's egg laying is intense!
What They Are:
Amniotes that are able to regulate their own internal body temperature.
Due to the evolution of a 4-chambered heart.
Endothermy has evolved convergently in Aves and Mammals (why?)
Why are they important?
The mammalian heart
*with apologies to monotremes
Mammals evolved from the extinct synapsid group of reptiles
There are 3 major groups of mammals.
Most are eutherian ("placental")
Monotremes are a group of mammals that lay eggs.

This is a Short-beaked Echidna
Marsupials are a group of mammals which have young that develop in a pouch external to the body.

They are almost entirely found in Australia (why?)
Convergence among marsupial and placental mammals
The non-human apes:
The hominin lineage (post-chimp split)
Ardipithecus ramidus
~4.4 mya.
Small (50 kg)
Somewhat bipedal
Small brain (300-450 cc)
Australopithecus & Bipedalism
Genus Australopithecus
~4-1 mya.
Chimp sized
Variable brain size depending on species (380cc - 530 cc)
Homo ergaster
Genus Homo (pre-sapiens)
~2.4 mya - 30kya.
Human size
Somewhat bipedal
Bigger brain (600-1250 cc)
Homo sapiens skull (200kya - now)
Biggest Brain: 1,300 cc (on avg.)
Art seems to be a hallmark of humans...
How is the chordate phylum organized?

What are the characteristics of chordates that are used to classify them?

Where do humans fit within the larger context of life's diversity?
0.5 m
(vertebra & Jaws)
Some Birds!
Primate Phylogeny
Identify members of all the groups that were discussed in this presentation if given information about their characteristics.

Explain why the particular example organisms shown in this presentation belong in particular groups

Identify the characteristics most useful for classifying members of each group discussed in this presentation

Explain the evolutionary trends demonstrated in the chordates

Explain the advantages and tradeoffs of the strategies and adaptations that were discussed in this presentation.

Explain why the phylogeny discussed in this presentation is hypothetical and subject to continuing revision.

Discuss the evolution of the hominid lineage, and the evolutionary trends that have led to the evolution of modern Homo sapiens.
...and know how to use them...
In Summation...
...and a song!
Full transcript