Chordates, Chordate Evolution, and Vertebrate Story

(Lesson 2, 3 and 4)

Phylum Chordata = Chordates (Taxa)

Urochordates, Cephalochordates, and Vertebrates

Cephalochordates

Lancelets - 6-7cm, filter feeders

Urochordates

Sea Squirts/Tunicate - Larval chordate characteristics, keep pharyngeal slits

Vertebrates

Everything else - Very diverse

Notochord

Not a spinal cord, hydrostatic organ, elastic rod, flexes laterally, does not collapse

Pharyngeal Pouches

Endostyle

glandular groove on floor of pharynx, filter feeding, homology with thyroid

Thyroid

arises from floor of the pharynx, T3/T4, Calcitonin

Dorsal Nerve Cord

Formed by invagination

• Embryonic process

• Surface ectoderm thickens into neural plate

• Folds/rolls inward from the surface to create a tube

Postanal Tail

Extension of the chordate locomotor apparatus

Agnathans and provide examples

Agnathans are jawless vertebrates, including lampreys and hagfish.

What are the two main groups of Gnathostomes?

Chondrichthyes (sharks, rays, chimaeras) and Osteichthyes (bony fish).

What are the two subclasses of Osteichthyes?

Actinopterygii (ray-finned fishes) and Sarcopterygii (lobe-finned fishes).

What are the characteristics of Palaeonisciformes?

Living members include paddlefish, sturgeon, and bichirs; they have ganoid scales.

What are the characteristics of Neopterygii?

They have smaller scales for increased flexibility and include species like bass, perch, and trout.

What is the function of the swim bladder in fish?

It helps with buoyancy control.

What are the two types of swim bladders?

Physoclistous (derived, more prone to barotrauma) and Physotomous (primitive, allows gulping air).

What adaptations do lungfish have?

Lobed fins, a prominent notochord, paired lungs, and alternating fin movement.

What is Tiktaalik roseae and why is it significant?

A transitional fossil showing features between fish and tetrapods, such as robust pectoral fins.

Lissamphibia (Examples and characteristics)

Includes salamanders, frogs, toads, and caecilians; they often have paired lungs and lack scales.

Types of Lissamphibia

Anurans, Urodela, Apoda

Anurans

Frogs and Toads, tympanum present and prominent

Paired limbs

No tail in adults

Urodela

Salamanders, Paired limbs

• Lungs reduced or absent

• Long tail

Apoda

Caecilians

Wormlike burrowers

• No limbs (or girdles)

• Reduced eyes

What are the two main lines of Amniotes?

Sauropsida (birds and reptiles) and Synapsida (mammals).

What are the four primary skull types in amniotes?

Based on temporal fenestra and arches: Synapsid (mammals) and Diapsid (birds and reptiles), with turtles being Anapsid.

What are the key characteristics of mammals?

Hair, mammary glands, non-nucleated red blood cells, and a single jawbone (dentary).

What are the three groups of mammals?

Monotremes (egg-laying), Metatherians (marsupials), and Eutherians (placental mammals).

What are some examples of mammal diversity?

Cetaceans (whales), Sirenia (manatees), Chiroptera (bats), and Primates.

What is the significance of surface area in biological functions?

Surface area affects heat loss, fluid absorption, respiration, and metabolism.

What are the three primary germ layers in organogenesis?

Ectoderm, Endoderm, and Mesoderm.

What are the four tissue types found in adults?

Epithelial, connective, muscle, and nervous tissue.

What is the role of the ectoderm in development?

It forms the epidermis and nervous tissue.

What is the role of the endoderm in development?

It forms the digestive and respiratory linings, including organs like the liver and pancreas.

What is the role of the mesoderm in development?

It forms skeletal muscles, circulatory components, kidneys, and connective tissue.

Cranium

Protection for evolving sensory structures

• Bone/Cartilage

• Cranial portion of neural tube

Neural Crest Cells

Stem cells located at the side of the neural tube after neurulation that migrate throughout embryo and give rise to a range of cell types

Epidermal (ectodermal) placodes

Localized thickenings of ectoderm just

lateral to neural plate border that give rise

to cells that make up many of the sensory

components in the vertebrate head

Steps in Vertebrate Development

1) “Prevertebrate"

2) Agnathan

3) Gnathostome

Prevertebrate

Transition from solely ciliary feeding

Muscular pump → increased feeding and respiration efficiency → increased size

Agnathans (General ans examples)

Jawless fish - Hagfish and Lampreys

Hagfish

Slime predator defense, Two pairs of tooth-like rasps on top of “tongue, Adult hagfish: no true vertebrae

Lampreys

Vertebrae are cartilaginous, many are parasitic

Gnathostomes

Development of jaws from rostral pharyngeal arches, Paired pectoral fins, paired pelvic fins

3 divisions of Gnathostomes

Placoderms, Chondrichthyes, and Teleostomi

Placoderms

Extinct species, 380–360 million years ago

Chondrichthyes

Chimera, no scales, fused upper jaw to brain case

No swim bladder - Oily livers

Vertebral column- cartilage with some calcium

2 types of Teleostomi

Acanthodii and Osteichthyes

Acanthodii

EXTINCT

Osteichthyes

Characteristics:

• Persistent presence of bone

• Development of swim bladder (vs. oily liver)

• Operculum is bony (vs. skin)

2 types of Osteichthyes

Actinopterygii and Sarcopterygii

Actinopterygii

Ray-finned fishes

Sarcopterygii

Fleshy-finned fishes /lobe-finned fishes