Lecture 28 Craniates Flashcards
1
Q
what is clade craniata?
A
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
2
Q
what did ancestral chordates resemble?
A
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
3
Q
what are the 5 derived characteristics of craniates?
A
- two clusters of hox genes – non-craniates (lancelets and tunicates have
4
Q
what are the 5 derived characteristics of craniates?
A
- 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
- 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
- endoskeleton and pronounced cephalization – brain encased in protective plates, endoskeleton is cartilage or bone, includes paired eyes and other sensory organs
- circulatory system modified. closed circulatory systems, including a heart with at least two chambers, hemoglobin in RBC, supports higher metabolisms
- embryonic pharyngeal clefts – develop into active organs –fxns associate with muscles and nerves – gill slits in aquatic species, parts of ear
5
Q
what is the origin of craniates?
A
- fossils from cambrian explosion document transition between non-craniate and craniate chordates
- in other cambrian rocks – fossils of more advanced chordates
6
Q
what are the basal craniates?
A
- 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
7
Q
what are hagfishes?
A
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
8
Q
what are hagfishes?
A
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
9
Q
what is subphylum vertebrata?
A
- 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
10
Q
what are vertebrate synapomorphies?
A
- vertebrae enclosing nerve cord
- elaborate skull
- fin rays, in the aquatic forms
11
Q
what are lampreys?
A
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
12
Q
what are the origins of bone and teeth?
A
mineralization with calcium originated with vertebrate mouthpats
13
Q
what are conodonts?
A
- 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
14
Q
what are gnathostome vertebrates?
A
vertebrates that have jaws
15
Q
what are derived characteristics of vertebrates?
A
- 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
16
Q
what are derived characteristics of vertebrates?
A
- 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
17
Q
where did jaws come from?
A
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
18
Q
what were the earliest fossil gnathostomes?
A
armoured vertebrates called placoderms
19
Q
what are the three lineages of jawed vertebrates alive today?
A
- chondrichthyans
- ray finned fishes
- lobe fins
20
Q
what is class chondrichthyes?
A
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
21
Q
what are sharks?
A
- 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
22
Q
what is shark reproduction?
A
- copulation
- males have pelvic fins modified as claspers, hold female and help to guide sperm
- fertilized internally but embryos can develop in different ways
23
Q
what is oviparous?
A
eggs hatch outside mother’s body
24
Q
what is ovoviviparous?
A
embryo develops within uterus and nourished by egg yolk
25
Q
what is viviparous?
A
embryo develops within uterus and nourished through a yolk sac
26
Q
what is class chondrichthyes?
A
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
27
Q
what are sharks?
A
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
28
Q
what is shark reproduction?
A
- 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
29
Q
what is viviparous?
A
embryo develops within uterus and nourished through a yolk sac placenta from mother’s blood
30
Q
what are rays and skates?
A
chondrichthyes
similar to sharks
- swim by flapping pectoral fins
- dorso-ventrally flattened
- flat platelike teeth for grinding prey
