Lecture 3 - Friday, August 29, 2008.1. Finish lampreys and fossil forms of jawless fishes2. Evolution of jaws and paired fins3. Other Fossil Fishes4. Distinguishing characters of Chondrichthyes & Osteichthyes

a. explanation traits (fin rays, scales, claspers, teeth in rows)5. Other characters of Chondrichthyes (show shark video)6. Distinguishing Characters of Elasmobranchii & Holocephali

Myxini

formes

Petrom

yzon

tiform

es

Chondri

chthy

es

Osteich

thyes

Gnathostomata

We are going out in the field next Tuesday. Please meet at the Shelford Vivarium. Corner of Healey & Wright Street. We will leave at 1pm.

Be there or be square.

I will send out an e-mail next Monday/Tuesday morning to remind all of you.

Petromyzontiformes – Lampreys

(Lampetra fluviatilis)

Lamprey Distribution

Eggs hatch in 12-14 days

Am

moc oe te s ta ge

Parasitic Lamprey life cycle

Eggs hatch in 12-14 days

Am

moc oe te s ta ge

Free living species metamorph into adults and immediatelyreturn to spawning site to mate and then die

Nonparasitic Lamprey life cycle

Chestnut Lamprey (Ichthyomyzon castaneus)

European Brook Lamprey (Lampetra planeri)

lamprey video1

lamprey video2

funny lamprey video

Sea Lamprey, Petromyzon marinus

• Anadromous species native to both sides of the North Atlantic

• Large parasitic species (up to 3’), can kill up to 40 lbs. of prey in lifetime

• Classic example of the deleterious effects of an exotic species initiated by man-made habitat alterations

• But also one of the few examples of successful control of exotic species

Sea Lamprey, Petromyzon marinus

First reported in 1890but may be native

Sea Lamprey, Petromyzon marinus

First reported in 1890but may be native

Niagara Falls served as barrier to dispersal

Welland Canal was built to allow ships to getaround Niagara Falls

Sea Lamprey, Petromyzon marinus

First reported in 1890but may be native

Niagara Falls served as barrier to dispersal

19211936

1946

Sea Lamprey, Petromyzon marinusControl measures

•Physical barriers to spawning streams

•Releasing sterilized males

•Application of a lampricide (TFM) - poured into streams known to harbor ammocoetes, specific to ammocoetes

Sea Lamprey, Petromyzon marinus

Ostracoderm from Ordovician(450 MYA)

Maisey, J. G. 1996. Discovering fossil fishes. HenryHolt and Co., New York.

Ostracoderms

paraphyletic group (actually two groups)• No jaws • The first vertebrates- cartilaginous internal skeleton• Bony exoskeleton armor-1st true bone (dermal) • First ones were small (< 15 cm)• No paired fins• Bottom dwellers• Lots of Diverse forms

?

Where did the jaws come from?

Many different arrangementsevolved in different groups.

Placoderms - many families, very abundant- armored fishes with jaws that had paired fins- probably first jawed vertebrate

Nuchal joint = ‘craniovertebral joint’

- could open their mouths VERY wideto eat prey

Acanthodii - “Spiny sharks”

- thought to be sister group to Osteichthyes

- important for “folded fin theory”

- also appeared early & were abundant

Order and Abundance

Jawless fishes came first.

BUT placoderms, Acanthodians, & Sharks & Co. show up at a very similar time.Makes it difficult to work out ancestor - descendant relationships.

Chondrichthyes synapomorphies

1. Pelvic claspers • Derived from the margin of the pelvic fin

Mating Sharks Video 1

Mating Sharks Video 2

Cool Shark Videos to Checkout

Chondrichthyes synapomorphies

Teeth not fused to jaws

• Replaced serially in whorls

Chondrichthyes synapomorphies

3. Skull (chondrocranium) lacks sutures

Elasmoid

GanoidPlacoid

Cosmoid9

bonedentindentinee

enamel

heterocercal abbreviate

d heterocercal

homocercal

isocercal

8

Bull Shark with heterocercal tail

Major living gnathostome lineages

Subclass HolocephaliRatfishes, rabbitfishes, or chimeras

Order Chimaeriformes (58 species)

Subclass HolocephaliRatfishes, rabbitfishes, or chimeras

Subclass Holocephali

• lacking gill slits - a single gill covering over 4 gill openings

• Upper jaw fused to cranium

• skin is naked in adults

• Some males have cephalic claspers in addition to pelvic ones

Differ from sharks and rays by:

Order Chimaeriformes

Ecology, Life History

• Reproduction, oviparous (egg-laying), internal fertilization

• Benthic, deep sea (80 to 2600 m), around the world

• Nocturnal

• Feed mainly on benthic invertebrates

Review Questions1. Which structures did jaws evolve from? Which structures did paired fins evolve from? What is the importance of Acanthodii in relationship to the “folded fin theory”? Why is the evolution of jaws considered to be a major innovation of vertebrates? What were the ecological consequences of the evolution of jaws? What were the ecological consequences of the evolution of paired fins?

2. Who were the placoderms and what advantages did they have over the Ostracoderms? What two traits did they lack that might have placed them at a disadvantage in terms of feeding?

3. To what extent does the fossil record give us a complete picture of the history of the evolution of fishes? What are some of the difficulties of working with fossils? Did you read pages 175-176?

4. On page 194, your book shows a picture of skin thickness of male and female blue sharks. Which sex has thicker skin? What is the proposed reason for this?

5. Draw out the phylogenetic tree for Myxiniformes, Petromyzontiformes, Chondrichthyes, and Osteichthyes. Indicate which groups are Gnathostomata. Draw the synapomorphies onto the branches of the tree. Describe lepidotrichia vs. ceratotrichia, claspers, and placoid scales. Also list the type of skeleton, presence/absence of swimbladder or lungs, solid cranium, and teeth replaced as rows.

Review Questions (Cont’d.)

6. What traits distinguish the Elasmobranchii from the Holocephali? Who are the Holocephali? Where do they live? How do they reproduce? How many species are there?