1. Vertebrate Evolution

2. Vertebrate Evolution Steps
Vertebral column
Jaws, paired appendages (fins), bony skeletons
Lungs
Legs
Amniotic Egg

4. Hagfishes Agnathans: hagfishes and lampreys
eel-like in shape
an ancient vertebrate lineage that predates the origin of paired fins, teeth, and bones hardened by mineralization (ossification).
Hagfishes are the most primitive living “vertebrates”
cartilage skeleton
lack vertebrae: have
a strong flexible
rod of cartilage which
extends the length of the
body

5. 1. Vertebrate Column
Lampreys: notochord persists as the main axial skeleton, but pairs of cartilaginous projections extend dorsally, partially enclosing the nerve cord with what might be a vestige of an early stage vertebral column.

6. 2. Jaws, paired appendages, and bones!
The gnathostomes, have true jaws and also two sets of paired appendages.
In “fishes” these paired appendages function in swimming.
In tetrapods, the appendages are modified as legs to support movements on land.

7. More on jaws and fins…
Jaws and paired fins were major evolutionary breakthroughs.
Expression of some of the Hox genes may determine whether sets of paired appendages develop in the embryo
Jaws, with the help of teeth, enable the animal to grip food items firmly and slice them up – eat new types of food.
Paired fins, along with the tail, enable fishes to maneuver accurately while swimming.
With these adaptations, many fish species were active predators, allowing for the diversification of both lifestyles and nutrient sources.

8. Where did the jaws come from?
Vertebrate jaws evolved by modification of the skeletal rods that have previously supported the anterior pharyngeal slits.
The remaining gill slits remained as the site of respiration.

9. Bones!
Nearly all bony fishes have an ossified endoskeleton with a hard matrix of calcium phosphate.
Bony fishes are the most numerous group of vertebrates, both in individuals and in species (about 30,000 species).

10. 3. Lungs…
During the Devonian period, a diversity of plants and arthropods already lived on land
trees and other large vegetation were transforming terrestrial ecosystems
terrestrial habitats created new living conditions and food for fishes living near the water’s edge
A diversity of fishes resembling modern lobe-fins and lungfishes evolved.

11. What’s a lungfish?! Three genera of live today
Live in stagnant ponds and swamps.
Can gulp air into lungs to provide oxygen, but also have gills
When ponds shrink during the dry season, some lungfishes can burrow into the mud and aestivate.
Probably the ancestor of amphibians

12. 4. Legs…transition to land
The fossil record chronicles the transition to land over a 50-million-year period from 400 to 350 million years ago.
fossils of Acanthostega not only have the bony support of gills but also the same basic skeletal elements as the walking legs of amphibians, reptiles, and mammals.

13. Tetrapods continued…
Tetrapod: A vertebrate possessing two pairs of limbs, such as amphibians, reptiles, birds and mammals.
Legs were used underwater first…
In shallow water, leg-like appendages were probably better equipment crawling through the dense vegetation
Amphibians used these leg-like appendages to walk on land
benefited from abundant food and relatively little competition

15. Tetrapod Evolution

16. 5. Amniotic Egg
The amniote clade consists of the mammals, the birds, and the vertebrates commonly called reptiles, including turtles, lizards, snakes, and crocodiles.
The evolution of amniotes from an amphibian ancestor involved many adaptations for terrestrial living including
the amniotic egg
waterproof skin
increasing use of the rib cage to ventilate the lungs

17. The incredible egg!
Among tetrapods, most amphibians lay eggs in water or an otherwise moist environment.
The other terrestrial tetrapods are amniotes, producing shelled, water-retaining eggs which allow these organisms to complete their life cycles entirely on land.
While most modern mammals do not lay eggs, they retain many of other key features of the amniotic mode of reproduction.

19. Homework: Vertebrate Diversity Notes
Directions: Use pages to take notes on the key characteristics and unique evolutionary adaptations of each of these groups:
Chondrichthyes
Osteichthyes
Amphibia
Modern Reptiles
Birds
Mammals (Monotremes, marsupials, and eutherian mammals)