The Vertebrate Story

Introduction

• Innovations
• vertebral column
• head
• Origin of vertebrates
• prevertebrate ciliary pump
• agnathan muscular pump
• gnathostome jaws
• Vertebrate classification

Morphological Concepts:

Homology: two or more features that share a common ancestor, i.e., a bird’s wing and a mole’s arm

Analogy: features with a similar function, i.e., the wings of bats and bees

Homoplasy: features that look alike, dolphin and turtle flippers

Each of these three concepts are separate contributors to animal design

• Dolphins and bats live very different lives but there are a number of fundamental likenesses that they share because of their common ancestry (i.e., hair, mammary glands, skeletal structures)
• Dolphins and ichthyosaurs belong to very different vertebrate ancestries but share certain likenesses (flippers and streamlined bodies) to meet the common hydrodynamics designs of living in marine waters

1. Similar function in similar habitat may produce convergence of form (analogy),

2. Common ancestry can carry shared and similar structure (homology), and

3. Sometimes these collectively can result in similarity of appearances (homoplasy).

Biological Function: refers to the action or property of a part as it functions in the organism

Biological Role: refers to how the part is used in the environment during the course of the animal’s life

To determine function, we need to use physiological and anatomical studies, as well as use tools such as electromyograms, X-rays, etc.

To determine biological roles, we need to observe the animal in the real world and see how it operates ---- ecomorphology.

Preadaptation: this means that a structure or behavior has the necessary form and function before the role arises. This does not mean that the trait arises in anticipation of some future role.

All chordates share the following four characteristics at some point in their development:

• pharyngeal gill slits - a series of openings that connect the inside of the throat to the outside of the "neck". These are often, but not always, used as gills.

• dorsal hollow nerve cord - a bundle of nerve fibers which runs down the "back". It connects the brain with the lateral muscles and other organs.

• notochord - cartilaginous rod running underneath, and supporting, the nerve cord.

• post-anal tail - an extension of the body past the anal opening

What is a Vertebrate?

It has all of the chordate characters plus:

• In lampreys (top), the vertebral elements are only the basidorsal (red) and the interdorsals (blue).
• In the gnathostomes, there are in addition ventral elements, the basiventrals (purple) and interventrals (orange), and the notochord may calcify into centra (pink).

Origin of Vertebrates:

1. emergence of the chordate body plan

2. origin of bone

3. origin of paired sensory structures

Origin of Gnathostomes:

1. origin of jaws

2. origin of teeth

3. origin of paired fins

4. origin of swim bladder in osteichthyes

Origin of Tetrapods:

1. origin of limbs in amphibians

2. origin of the amniotic egg

2. Two pairs of jointed locomotor appendages, which can include fins (pectoral and anal/dorsal fins, as well as the forelimbs and hindlimbs)

3. Outer covering of protective cellular skin, which can be modified into special structures such as scales, hair, and feathers

4. Metamerism found in skeletal, muscular and nervous system. This includes ribs, vertebrae, muscles, and ganglia/peripheral nerves

5. Well-developed coelom or body cavity completely lined with epithelium (cellular tissue of mesodermal origin) that may be divided into 2 to 4 compartments

6. Well-developed internal skeleton of cartilage and/or bone, separated into axial skeleton (skull, vertebrae, ribs, sternum) and appendicular skeleton (girdles and appendages)

7. Highly developed brain enclosed by skull and nerve cord enclosed by vertebrae - these provide advanced neural structures that are highly protected from damage

8. Well-developed sense organs (eyes, ears, nostrils) located on the head (cephalization)

9. Respiratory system, including either gills or lungs, located closely to the pharynx or throat

10. Closed circulatory system with ventral heart and median dorsal artery

11. Genital and excretory systems closely related, utilizing common ducts and pathways

12. Digestive tracts with two major digestive glands (liver and pancreas) that secrete into it
 

SUBPHYLUM: Vertebrata

            Class: Myxini

    Superclass AGNATHA

            Class:
                Conodontia*
                Pteraspidomorphi*
                Cephalospidomorphi

    Superclass GNATHOSTOMATA

        a) Grade Pisces

            Class:
                Placodermi*
                Acanthodia*
                Chondrichthyes
                Sarcopterygii
                Actinopterygii

        b) Grade Tetrapoda

            Class:
                Amphibia
                Reptilia
                Aves
                Mammalia

SUBPHYLUM: Urochordata (tunicates or sea squirts)

SUBPHYLUM: Cephalochordata (Branchiostoma)

SUBPHYLUM: Craniata

(Myxini plus Vertebrata)

Myxini - hagfishes

Cepahlospidomorphi - lampreys
- about 50 species still living
- 360+ million year fossil record
- 2 independent lineages
- lampreys are FW and oceanic animals
- parasitic and non-parasitic forms (latter only live as an adult long enough to reproduce)

Chondrichthyes (chondro = cartilage + ichthyes = fish)
2 subclasses with about 800 living species
- Elasmobranchii - sharks, skates and rays (5-7 pairs of gill arches)
- Holocephali - ratfish and chimeras
(4 pairs of gill arches, single external opening)

Elasmobranchs are subdivided into:
1. sharks (superorder Selachimorpha - 340 species)
2. skates and rays (superorder Batidoidimorpha - 425 species)
some give birth to live young, some are filter feeders

Holocephalens have a smooth epidermis, no ribs, large eyes, upper jaw
fused to the braincase and a long flexible tail (30 species)
- these fish are mollusk feeders and have broad grinding teeth (ratfish)

Sarcopterygii ("lobe-finned")
2 living subclasses
Porolepimorpha and Dipnoi (lungfishes - 6 species)
Coelacanthimorpha (extinct except for the Coelacanth)

Actinopterygii ("ray-finned" fishes) (20,000+ species)
2 living subclasses
Chondrostei (sturgeons and bichirs)
Neopterygii (all teleosts)

Amphibia - amphibians = amphi + bios ("double life")
2 subclasses
Labrynthodontia (extinct)
Lepospondylia
The latter group has about 3000 species.
3 orders
    Urodela (Caudata) - salamanders (tailed)
    Salientia (Anura) - frogs/toads (tail-less)
    Gymnophiona (Apoda) - caecilians (foot-less)

Reptilia (currently ~6,000 species)
4 subclasses
Anapsida - turtles
Parapsida - extinct aquatic dinosaurs
Synapsida - extinct dinosaurs ==> mammals
Diapsida - extinct dinosaurs, crocodiles, existing lizards and snakes ==> birds

Aves -- feathered reptiles ???
25 orders with 8600 species

2 subclasses
Archaeornithes (extinct)
Neornithes (modern)

- at least 2 reptilian characters they retain are their amniotic eggs and the scales on their legs
- almost every component of a bird’s anatomy is geared for flight
- hollow, honeycombed bones (2 m wingspan frigate bird weighs 4 oz)
- also get a reduction in some organs for example only one ovary
- excellent vision, very adaptable beak
- modified digestive system (no teeth, gizzard instead)
- very efficient respiratory system
- large brains, complex behavior

Archaeopteryx lithographica - primitive bird with reptilian characters often considered a hoax

• claws
• teeth
• pelvic bones
• no keeled sternum

Chordates ---

pharyngeal gill slits

dorsal hollow nerve cord

notochord

post-anal tail

• vertebral development
• additional modifications within classes for aquatic and terrestrial existence

What was it like on land?

Warm and humid

Lots of vegetation:
    scale trees
    horsetails

Lots of invertebrates
    insects
    arachnids

fossorial - burrowing

cursorial - running

arboreal - in trees

aerial — flying or gliding

saltatorial - hopping

Heterodont dentition - many types of teeth

Homodont dentition - one type of tooth