AP Bio-Biodiversity: The Chordates

Last Common Ancestor of the Chordate Phylum

Big Questions

Make sure you can

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?

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.

Chordates

In Summation...

Before We Begin

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 blue arrows spotlight important evolutionary developments.

Reptiles

aka: lizards, snakes, crocodillians, turtles, tuatars

Characteristics:

• Totally terrestrial*
• 3 chambered heart

Non-Vertebrate

Chordates

aka: tunicates, lancelets

Characteristics:

• spinal cord*, no brain, no bones.

* at some point in the life cycle, at least

The 5 living lineages of

non-avian reptiles

*with apologies to crocodillians, marine iguanas, & sea snakes

Not all chordates are vertebrates!

Phylogeny of reptiles and their descendant taxa

Chondricthyans

Amphibians

The lancelet has all features of a chordate throughout its life cycle...

...but it doesn't have a spinal column.

aka: Sharks, Skates & Rays

Characteristics:

• Jaws (pun intended),
• Cartillagenous skeleton

aka: frogs, salamanders, & caecillians

Characteristics:

• 3 chambered heart
• part of lifecycle is aquatic, part is terrestrial

"Both Ways of Life"

Tunicates have a notochord, and a dorsal nerve cord in their larval form.

They are lost during maturation.

Chondricthyans have jaws!

Fins are common in gnathostome fish

The lifecycle of a frog shows it's "Dual life"

...and know how to use them...

Aves

aka: "Avian Reptiles", "Birds"

Characteristics:

• feathers
• adapted for flight*

Rays are bottom feeders & suspension feeders

*with apologies to penguins & rattites

Some Birds!

Basal Craniates

aka: Hagfish, Lampreys

Characteristics:

• no jaws.

Archeopteryx

Osteichthyes

The Kiwi Bird (native to New Zealand) is adorable...

Haikouella: a fossil chordate with a brain, but no skull

aka: "Fish"

Characteristics:

• Calcified skeleton
• 2 major divisions

The hagfish is the most basal living craniate.

It has a cartilaginous skull, but no vertebra

Sarcopterygii: "Lobe Finned Fish"

Actinopterygii: "Ray Finned Fish"

3 major linneages:

• Coelocanths: 1 living species
• Lungfish: 6 living species
• Tetrapods: All terrestrial chordates

More than 27,000 living species

But it's egg laying is intense!

Some of the flight adaptations of the avian wing

Some examples:

A Coelocanth: Thought to have gone extinct 75 mya, until a dead one was caught by local fishermen off of South America in 1938

Lamprey's have a series of cartilaginous projections that grow from their notochord to surround their dorsal nerve chord.

Endotherms!

What They Are:

A fossil sarcopterygian: 420 mya

Agnathans: "No Jaw"

• 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?)

The mammalian heart

Why are they important?

Amniotes!

What they are:

Mammals

Tetrapods that have an amniotic egg with a watertight shell and extraembryonic membranes

The Amniotic Egg:

aka: you, your dog, your cat

Characteristics:

• hair
• live birth*
• nurse young with milk

embryo

amnion: shock-absorber

full of amniotic fluid

shell: protection

chorion: gas exchange

*with apologies to monotremes

yolk sac: nutrients

allantois: metabolic waste

Mammals evolved from the extinct synapsid group of reptiles

Why are they important?

There are 3 major groups of mammals.

Primate Phylogeny

The non-human apes:

Tetrapods

What they are:

Monkeys

Gnathostomes that have limbs.

Most are eutherian ("placental")

Fossil progression showing limb evolution

Monotremes are a group of mammals that lay eggs.

This is a Short-beaked Echidna

Prosimians

The hominin lineage (post-chimp split)

Convergence among marsupial and placental mammals

Homo sapiens skull (200kya - now)

Australopithecus & Bipedalism

Homo ergaster

Ardipithecus ramidus

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?)

Biggest Brain: 1,300 cc (on avg.)

Tiktaalik: A fossil "fishapod"

Genus Australopithecus

~4-1 mya.

• Chimp sized
• Bipedal
• Variable brain size depending on species (380cc - 530 cc)

77kya

"lucy"

Art seems to be a hallmark of humans...

Why are they important?

1889

~4.4 mya.

• Small (50 kg)
• Somewhat bipedal
• Small brain (300-450 cc)

Genus Homo (pre-sapiens)

~2.4 mya - 30kya.

Human size

• Somewhat bipedal
• Bigger brain (600-1250 cc)

Vertebrates!

What makes a chordate?

What they are:

The Characteristics of a Chordate:

Chordates that have a developed head AND a spinal column of vertebra.

Most living vertebrates have jaws (gnathostomes).

0.5 m

Jawless vertebrates were common through the Devonian (360 mya). 2 examples.

Where's your post-anal tail?

Where are your pharyngeal slits?

Dunkleosteus: an early gnathostome (up to 30 feet long)

A conodant: a very common, ancient, jawless vertebrate

Hypothetical Evolutionary Path for Jaws

Craniates!

Who's a Chordate?

Why are they important?

What they are:

(vertebra & Jaws)

Chordates that have a head containing sensory organs, brain and a skull

• Every animals with a backbone.
• Your pets.
• The animals you eat.
• You

The Neural Crest is a craniate-only region of the embryo

There is no difference in Hox gene expression at the anterior end of lancelet and vertebrate embryos (what does that mean?)

Why are they important?