Lecture 28 Craniates

Question 1

what is clade craniata?

Answer 1

animals in chordata with a head

• skull of hard bone or cartilage
• origin of head allowed coordination of more complex movement and feeding behaviours
• marine, freshwater, terrestrial
• most are vertebrates

Question 2

what did ancestral chordates resemble?

Answer 2

lancelets

• same hox genes that organize vertebrate brain expressed in lancelet’s simple nerve cord tip
• genome sequencing suggests: genes associated with HEART AND THYROID COMMON TO ALL CHORDATES; genes assoc with transmission of nerve impulses UNIQUE TO VERTEBRATES

Question 3

what are the 5 derived characteristics of craniates?

Answer 3

1. two clusters of hox genes – non-craniates (lancelets and tunicates have

Question 4

what are the 5 derived characteristics of craniates?

Answer 4

1. two clusters of hox genes – non-craniates (lancelets and tunicates) have one cluster. Hox genes control the body plan of an embryo along the head-tail axis; determine the type of segment structures that will form
2. Neural crest. Collection of cells near the dorsal margins of closing neural tube in embryo. Give rise to a variety of structures, including some of the bones and cartilage of skull
3. endoskeleton and pronounced cephalization – brain encased in protective plates, endoskeleton is cartilage or bone, includes paired eyes and other sensory organs
4. circulatory system modified. closed circulatory systems, including a heart with at least two chambers, hemoglobin in RBC, supports higher metabolisms
5. embryonic pharyngeal clefts – develop into active organs –fxns associate with muscles and nerves – gill slits in aquatic species, parts of ear

Question 5

what is the origin of craniates?

Answer 5

• fossils from cambrian explosion document transition between non-craniate and craniate chordates
• in other cambrian rocks – fossils of more advanced chordates

Question 6

what are the basal craniates?

Answer 6

• extant classes that lack jaws
• hagfishes and lampreys - agnathans
• lack teeth and paired limbs (fins)
• extant agnathans look rather like eels - long flexible tubular bodies, no paired fins, paraphyletic group

Question 7

what are hagfishes?

Answer 7

agnathans - class myxini

• most basal group
• only known living animals that have a skull but no vertebral column
• cartilaginous cranium; no jaws
• ## well developed notochord: axial rod of cartilage

Question 8

what are hagfishes?

Answer 8

agnathans - class myxini

• most basal group
• only known living animals that have a skull but no vertebral column
• cartilaginous cranium; no jaws
• well developed notochord: axial rod of cartilage
• have a small brain, lensless eyespots, and tooth-like structures composed of keratin
• scavengers
• exude fibrous slime from body when attacked

Question 9

what is subphylum vertebrata?

Answer 9

• craniates that have a backbone/ vertebral column: chain of skeletal elements surrounding and protecting the nerve cord
• development of a complex nerve system
• replaces fxn of notochord
• provides increased rigidity
• provides attatchment for muscles and other skeletal elements
• became more efficient at capturing food and avoiding being eaten

Question 10

what are vertebrate synapomorphies?

Answer 10

1. vertebrae enclosing nerve cord
2. elaborate skull
3. fin rays, in the aquatic forms

Question 11

what are lampreys?

Answer 11

basal craniate, agnathan, class petromyzontida

• oldest living vertebrate
• cartilage skeleton
• notochord surrounded by a cartilaginous tube - paired dorsal spines from tube partially enclosed nerve cord
• primitive vertebral column
• eyes with lenses, no jaws or paired limbs
• look and behave like lancets (cephalochordates)
• suspension feeders
• ectoparasites of fish: clamp by funnel sucking mouth
• use sucker for upstream travels

Question 12

what are the origins of bone and teeth?

Answer 12

mineralization with calcium originated with vertebrate mouthpats

Question 13

what are conodonts?

Answer 13

• first vertebrates with mineralized skeletal elements in their mouth and pharynx
• fossilized dental elements are common in fossil record
• vertebrate endoskeleton became fully mineralized much later

Question 14

what are gnathostome vertebrates?

Answer 14

vertebrates that have jaws

Question 15

what are derived characteristics of vertebrates?

Answer 15

• opposing jaws
• mineralization of skeleton
• 2 pairs of appendages (extinct agnathans - 1 pair, extant agnathans - no paired fins)
• genome duplication, including duplication of hox genes (4 clusters)
• enlarged forebrain – enhanced smell and vision

Question 16

what are derived characteristics of vertebrates?

Answer 16

• opposing jaws
• mineralization of skeleton
• 2 pairs of appendages (extinct agnathans - 1 pair, extant agnathans - no paired fins)
• genome duplication, including duplication of hox genes (4 clusters)
• enlarged forebrain – enhanced smell and vision

Question 17

where did jaws come from?

Answer 17

skeletal supports of pharyngeal slits

• modification of 2 pairs of skeletal rods that had supported anterior pharyngeal slits - modified to pump water over the gills by opening and closing the mouth more effectively
• the mouth could then grow bigger and wider – capture more prey
• posterior slits became specialized for gas exchange

Question 18

what were the earliest fossil gnathostomes?

Answer 18

armoured vertebrates called placoderms

Question 19

what are the three lineages of jawed vertebrates alive today?

Answer 19

• chondrichthyans
• ray finned fishes
• lobe fins

Question 20

what is class chondrichthyes?

Answer 20

sharks, rays, etc

• cartilaginous fishes - cartilage endoskeleton; not a primitive character state – derived from ancestors with bony skeletons
• have bony teeth
• development of most vertebrates: skeleton is first cartilaginous and then becomes ossified; mineralization of cartilage by CaPO3 – chondrichthyans skip this

Question 21

what are sharks?

Answer 21

• streamlined bodes and swift swimmers - propulsion from tial, pectoral fins for lift
• NO SWIM BLADDER - buoyancy from storing oil in liver - sink while swimming, must use muscles to gulp water to aerate gill
• short digestive tract with ridge called spiral valve to increase digestive surface area
• CLOACA
• rough skin - dermal placoid scales with spines, reduce drag, quieter
• scales homologous with teeth
• continuously shed and replace teeth
• acute sense of sight and smell
• detect electrical field
• detect vibrations in water via lateral line

Question 22

what is shark reproduction?

Answer 22

• copulation
• males have pelvic fins modified as claspers, hold female and help to guide sperm
• fertilized internally but embryos can develop in different ways

Question 23

what is oviparous?

Answer 23

eggs hatch outside mother’s body

Question 24

what is ovoviviparous?

Answer 24

embryo develops within uterus and nourished by egg yolk

Question 25

what is viviparous?

Answer 25

embryo develops within uterus and nourished through a yolk sac

Question 26

what is class chondrichthyes?

Answer 26

sharks, rays, etc - cartilaginous fishes - cartilage endoskeleton; not a primitive character state -- derived from ancestors with bony skeletons - have bony teeth - development of most vertebrates: skeleton is first cartilaginous and then becomes ossified; mineralization of cartilage by CaPO3 -- chondrichthyans skip this

Question 27

what are sharks?

Answer 27

chondrichthyes - streamlined bodes and swift swimmers - propulsion from tial, pectoral fins for lift - NO SWIM BLADDER - buoyancy from storing oil in liver - sink while swimming, must use muscles to gulp water to aerate gill - short digestive tract with ridge called spiral valve to increase digestive surface area - CLOACA - rough skin - dermal placoid scales with spines, reduce drag, quieter - scales homologous with teeth - continuously shed and replace teeth - acute sense of sight and smell - detect electrical field - detect vibrations in water via lateral line

Question 28

what is shark reproduction?

Answer 28

- copulation - males have pelvic fins modified as claspers, hold female and help to guide sperm - fertilized internally but embryos can develop in different ways - protected in a leathery egg case

Question 29

what is viviparous?

Answer 29

embryo develops within uterus and nourished through a yolk sac placenta from mother's blood

Question 30

what are rays and skates?

Answer 30

chondrichthyes similar to sharks - swim by flapping pectoral fins - dorso-ventrally flattened - flat platelike teeth for grinding prey