Chondrichthyes: cartilaginous fish Flashcards
when did they come about? main features - endoskeleton, teeth, etc?
- Early Silurian (approx. 440 Mya) to recent
- Cartilaginous endoskeleton
- Skull lacks suture in living forms
- Teeth usually not fused to jaws and replaced serially - replaced when lost
- Vertebrata made up of cartilaginous endoskeleton!!!!!!!!!
- Lung and swim bladder absent - more primitive, unlike the bony fish which have both
main groups?
• Two main groups:
○ Elasmobranchs
§ Sharks, skates, rays
○ Holocephalans
brain protection?
○ Brain is protected with a brain case made of cartilage - but it lacks suture (cracks/joints)
• Suture is important for birth - the suture allows for some compression - easier delivery with less complications. Without suture it is difficult and dangerous to deliver a baby. HOWEVER, the cartilage of the fishes is soft enough to compress.
when did elasmobranchs come about? features?
• Early Devonian (approx. 416 Mya) to recent
• 5-7 gill openings
• Palatoquadrate not fused to cranium !!
• Evolution - 3 distinct radiations (spreading):
○ Devonian - 416 mya
○ Carboniferous to Cretaceous- 354-65 mya
○ Triassic (206 mya) to modern day
○ Gaps in dates - gaps in knowledge, we do not know if one gave rise to another directly
describe the 1st radiation of elasmobranchs.
• Devonian (1st) radiation - Cladoselache
• Cladoselache - best known genus
• Well preserved fossils
1. Long streamlined body (no armor)
describe mouth and teeth of 1st radiation elasmo
○
4. Terminal mouth
5. Teeth
• Primarily 3 cusps - good for tearing flesh - could be predators
• Composed of dentine and enamel with pulp cavity -strong protected teeth
• Replacement teeth - ie teeth whorls
• Function of teeth whorls:
○ Alleviates broken/worn teeth
○ Allows a new predatory niche to be exploited
○ Easily replaced
other features of 1st elasmobranch - notochord, scales, claspers?
- Notochord in adult with cartilaginous neural arches- protective casing - more advanced/derived trait
- Tooth-like scales limited to fins/eyes/mouth
- Lacked claspers - cannot transfer semen to individuals of the other sex
- Good fossil remains/record
describe 2nd radiation of elasmobranch - when did it come about + what adaptive edge?
• Carboniferous (2nd) radiation - Hybodus
• Carboniferious to cretaceous - 354 mya - 66 mya
• Hyobus - best known genus
○ Triassic (251 mya) to late cretaceous (66 mya)
• Fossil remains
• Changes in feeding and locomotion happened
• Radiation during formation of pangea
○ More competition
○ Adaptive edge being generalist - able to feed on plants as well as prey
general 2nd radiation teeth
- Heterodont dentition
• Anterior teeth for flesh- cusps
• Posterior teeth - broader, flatter teeth - wasn’t present in 1st radiation
• Generalist, predators
what features (3) did hyobus (2nd) share with cladoselache (1st)
- Terminal mouth, multicusped teeth
- Ampistylic jaw
- Unrestricted notochords
- Not a direct line between two groups - might have been an intermediate group between them
- Second flourished in Mesozoic (245-65mya)
describe 3rd radiation - when did it begin? modern forms by?
rd radiation began in triassic (approx 245 mya)
• Modern forms by Jurassic (~201 mya)
• Elasmobranch evolution spans over 450 mil. yrs; last
100 mil. yrs show little change
• Filter feeders to predators
3rd radiation jaw and dentition. mouth?
1. Hyostylic jaw suspension • Mandibular arch attaches to braincase • primarily through hyomandibula • Provides lateral mobility • Ventral mouth 2. Heteromorphic dentition • Upper stouter and recurved, serrated • Lower straighter and pointed
3rd muscles and notochord
- Scapulocoracoid cartilage
• Attaches right and left pectoral girdle
• Muscles help protrude upper jaw, moves mouth out
• Feeding action
○ Grab prey (lower jaw)
○ Protrude upper over prey- cartilaginous centra replace notochord
• Disks remain and act as shock absorbers
• Increases flexibility (S-shaped undulation) acting like a series of ball and socket joins
- cartilaginous centra replace notochord
scales, liver, tail 3rd
- Placoid scales
• Primitive and homologous to teeth
• Reduce turbulence
• New scales added during growth- Large oil filed liver
• Contains an oil named squalene
• Up to 25% body weight
• Provides buoyancy
• Alter buoyancy by altering liver oil content (lighter vs heavier)
• Oil varies by lifestyle and habitat
• First time we see a need for the organism to go upward - Heterocercal tail
• Once though designed to provide lift - swift and change depths
• But faster swimming species would then rise
• Now we know that most buoyancy comes from oil in the liver, so the tail is actually for navigating/propelling upwards - these complement each other
- Large oil filed liver
3rd lateral line system, ampullae of lorenzini, chemoreception
- Lateral line system
• Loaded with sensory cells/nervous tissues
• Made of interconnected surface pores and canals
• Functional unit: neuromast organ
○ Detect pressure and vibration changes - changes in the environment (act as mechanoreceptors)- Ampullae of lorenzini
• Detect electrical fields ie prey, conspecifics, enemies etc. - communication
• Evolved from hair cells of lateral line - have the sensory ability to detect electrical changes - Chemoreception
• Exceptional olfactory system - detect blood at 1 ppm
Can perceive long range chemical stimuli
- Ampullae of lorenzini
3rd visionsummary
- Vision
• Well developed
• Adapted for low-light intensities with (two advantages):
○ Numerous rod cells
§ Main pigment: rhodopsin
§ Do not differentiate color
○ Tapedum lucidum
§ Reflective layer in choroid behind retina
§ Impregnated with crystals of guanine
§ Adaptive for vision in nocturnal and deep oceanic species
3rd sensory system uses
- Sensory system summary - hunting strategy
• Larger brains vs other fish - can strategize
• Use sensory modes in hunting
○ Olfaction and mechanoreception
○ Vision
Electroreception: used in final stages of attack
3rd mating practices. claspers?
• Reproduction
○ Courtship and mating behavior
§ Wrapping, side swimming
§ Use of jaws - immobilize the other participant
□ Males with longer teeth
□ Females have reinforced skin - organ is not damaged by the mating process
□ Biting believed to stimulate females
○ Claspers - male
§ Intromittent organ for internal fertilization
§ Have internal skeleton
§ Flexed perpendicular and inserted in cloaca
§ Adjacent siphon sac functions to pump seminal fluid in via groove
○ Females: nidamental glands at anterior end of oviducts- secrete proteinaceous egg shell
describe oviparous
• Oviparous
○ Females lay eggs which hatch afterward
○ Large egg and case with yolk
○ O2 and inorganics diffuse in from the water
does not have to depend on nutrients from the mother - depends on yol
describe ovoviviparous
• Lecithotrophic viviparity (ovoviviparous)
○ Internal development
○ Egg shells softer and thinner bc protected by the mother’s body
○ Most of embryo nourishment comes from yolk
describe matrotrophy
• Matrotrophy (viviparous) - live young
○ Internal fertilization
○ Oviduct supplies most of the energy to the developing embryos - rely on mom for most of the nutrients
○ Complex physiological attachment
§ Yolk sac placenta
§ Slender projections from the wall of oviduct produce milky secretions
§ Independent evolution in elasmobranchs
• Great white, sand tiger, hammerheads, lemon sharks
two lineages of modern sharks?
1. Squalomorphs • Primitive, no anal fin • Found in cold deep water • Megamouth, dogfish sharks, basking sharks 2. Galeomorphs • More advanced, anal fin • Dominant in warm, shallow waters • Nurse sharks, great white, hammerheads, whale sharks
describe batoidea. gills, fins? locomotion
(Skates & Rays)
• Arose in early triassic 245 mya
• Mostly benthic (bottom dwellers)
• Dorso-ventrally flattened
• Hypotremates = 5 pairs of ventrally located gills
• Feed on benthic invertebrates and planktons
• Enlarged pectoral fins
• Extended radial cartilage for further support
• Basal elements of pectoral girdle to skull
• Use rajiform locomotion = vertical fin undulation
batoidea - jaws, teeth, hunting?
• Protrusible jaws • Use powerful suction and fused plate-like teeth for prey capture and consumption • Durophagous = eat hard food • Dorsal eyes and spiracle ○ Mouth ventrally located so… § Water - spiracles - mouth - gill slits ○ Adaptations for benthic lifestyle • Electric discharges • Some species such as electric ray • From various modified muscle tissues
describe holocephalans
ratfishes and chimaeras • Mid devonian 385 MYA • rat-like tail and teeth • Deep watered - benthic • Cartilaginous skeleton • Notochord persists in adult Large, mobile pectoral fins
holocephalan features. which one is unique?
• 4 gill openings (vs. 5-7 in elasmobranchs)
• Fleshy operculum covers gills (unique!!!)
• Lack spiracle - use nostrils to draw in water (new adaptation)
• Holostylic jaw suspension
○ Unmodified hyoid arch
○ Jaws with fused tooth plates !!
○ Lack teeth whorls, but teeth continuously grow
• Cephalic claspers in males
○ On head (unique!!)
○ Used to grasp the female
○ Not sperm transfer
○ Males also have pelvic claspers
• Few to no scales
• Some species with poisonous dorsal spine
• Oviparous
Young hatch as miniature adults
1st radiation pectoral and pelvic fins?
Pectoral/pelvic (paired fins): anchored by basal elements and radial cartilage - increased motility
• Dorsal (unpaired): anchored by basal/radial; spined- helps with defense
• Caudal: notochord (into upper lobe), radial cart (into lower lobe)
○ Lateral keels: stabilizers at base of caudal fin - balance
○ Higher motility and sensitivity
1st radiation jaw suspension !!!!!
- Jaw suspension - important!!!!
• Amphistylic jaw suspension - cranium is indirectly connected to the jaw
• Hyomandibula and palatoquadrate attach independently to chondrocranium
• Jaw attachment through two articulations:
○ Anteriorly connected to the cranium via a ligament
○ Posteriorly connected to the cranium by hyomandibula
2nd radiation pelvic and pectoral fins? tail? anal; fin?
- Pectoral and pelvic fins (paired):
• Plate like basals evolved so greater fin mobility
• Segmented radial cartilages shortened - motility increased, more force
• Formed ceratotrichia - fin support primarily made of keratin - increased strength and functioning of the fins(protein)
• Intrinsic fin muscles enhanced flexibility and mobility of fin- Heterocercal tail
• Stronger propulsion using tail twist mechanism - Anal fin
• First evolved in this group !!!!!!
• Required for stability - Dorsal fin spine improved -improved stability
- Claspers in all species- improved reproduction !!!!!!!!
Well-developed ribs - protect organs
- Heterocercal tail
batoidea (skates and rays) scales?
• Placoid scales
○ Mainly lacking = weight reduction and increased flexibility
○ Stingrays have stinger - modified placoid cells
1st radiation vs 3rd
1 Hyostylic jaws:
Upper jaw is not directly attached to cranium. Enlarged hyomandibula (upper bone of hyoid
apparatus) is the primary structure supporting the jaw. Allows increased motion in upper jaw,
adaptive during capture and holding of prey. Cladoselache had amphystylic jaws wherethe upper
jaw was firmly anchored to the skull.
#2 Ventral versus terminal mouth:
Ventral mouth reduces drag when capturing prey. A terminal mouth, as found in Cladoselache,
represents significant drag (water intake) when opened.
#3 Heteromorphic Teeth:
Different teeth on upper and lower jaw allowing increased food sources (prey) and niche
diversification. Teeth primarily 3 cusped (homodont) in Cladoselache.
#4 Cartilaginous centra replace the notochord:
Modern sharks have evolved concave depressions in opposable centra for increased support and
p. 7 of 7
flexibility. In turn, S-shaped undulations lead to faster swimming. Remnants of the notochord act
as shock absorbers. Cladoselache had axial support provided by the notochord and no complete
vertebrae, although it did have neural arches.
#5 Better developed sensory system:
With millions of years to evolve, modern sharks have an elaborate sensory system including such
structures as ampullae of Lorenzini and the lateral line system. These detect chemical, mechanical,
and magnetic stimuli. Vision is also enhanced in modern sharks. Although Cladoselache likely
possessed a sensory system, it was not as elaborate as that found in modern sharks.
1st elasmobranch summary?
- Summary
- Pelagic predators with light weight bodies
- Had sinusoidal motion
- took whole prey or slashed into pieces with teeth
- Similar to extant frilled shark (chlamydoselachus)
describe batoidea fins. locomotion?
• Enlarged pectoral fins
• Extended radial cartilage for further support
• Basal elements of pectoral girdle to skull
• Use rajiform locomotion = vertical fin undulation
•
describe 2 modern shark lineages
1. Squalomorphs • Primitive, no anal fin • Found in cold deep water • Megamouth, dogfish sharks, basking sharks 2. Galeomorphs • More advanced, anal fin • Dominant in warm, shallow waters Nurse sharks, great white, hammerheads, whale sharks
