Vertebrate Evolution Flashcards
Evolution of vertebrates
- Evolution of the fish
- transition to land: the non-amniote tetrapods
- Invasion of the land
- Amphibians
- Reptiles
Evolution of the vertebrates
- Certain Invertebrates, called……… share characteristics with the vertebrates
Chordates
Evolution of the vertebrates
Distinguised by 5 principle features at some time in their lives
- Dorsal hollow nerve cord
- Notochord
- Pharyngeal slits
- Muscular Post-anal tail
- Endostyle
- Muscle arranged in segmented blocks (myomeres)
Do we still retain these chordate characteristics?
- yes!
Dorsal holloe nerve chord=
Spinal chord
Remmnants of ……….. become our intervertebral discs which act as cushion between our vertebrae
notochord
Pharnygeal gills slits
remnants= our Eustachean tubes
Post anal tail
Only in early development
Endostyle
Transformed into thyroid gland
Which group of invertebrates rise to vertebrates?
- shared derivided characteristics
- All vertebrates deuterostones; vertebrates evolve from deuterostomes
- chordates characteristics
- duplication of hox genes
- Presence of neural crest tissue
Cephalochordates (lancelets, Amphioxus)
- Have all traits
- feed likeife-style similar to some primitive fish
- juveniles and adults- free-swimming- resemble easly fishes- lack brain and cranium
Evolutionarfy development: the first vertebrates: Jawless fishes
- The agnatha or jawless fishes- oldest vertebrates500MYA
- Evolution of tripartate brain and a cranium
- 3 pairs of sense organs in head(eyes, nostrils, inner ear)
- Tail fin (caudal fin) and dorsal fins evolve first
- lack paired fins (on sides)
Evolution of jaws from gill arches
- jawed vertebrates evolved- 410mya
- jaws evolved from cartilaginous gill arches
- each gill arch has an overlying gill sllit
- Agnathans have more gills arches than do gnathostomes
- some arches lost
- 2 moved forward
- 1 becomes the bones in the jaw
- over half of all vertebrates are jawed fishes
Fist jaed fishes: 1 Placoderms
new characteristics (synapomorphies)
- JAWS
- paired fins: pectoral (shoulder) fins pelvic (hip) fins
- no true teeth (bony protuberence in jaw)
- lack internal bony skeleton but had dermal bone in head
- top predators, got to 30
- Fist appeared in silurian extinct end of devonian
Then the 2 other groups of gnathostomes evolved
Placodermi
All extinxt: jaws, no true teeth
Then the 2 other groups of gnathostomes evolved
Chondrichthyes
internal cartilaginous skeleton; sharks
Then the 2 other groups of gnathostomes evolved
Osteichthyes
internal bony skeleton
A. Ray-finned (Actinopterygii)
B. Lobed-fonned (Sarcopterygii)
Jawed fishes (Gnathostomes)
2. Chondrichthyes: (Sharks, skates & Rays)
- Firs appeared 450MYA
- internal cartilaginous skeleton (craqnium & vertebrae)
- External gills slits (water enters mouth flows over gills exits thrpugh gills slit)
- Gill arches with gills
- Jaws & paired fins (plesiomorphies)
- 5-7 gills arches:
- Initial reduction in gills arch # with evolution of jaws, but reduced firther druing shark evolution.
Chondrichthyes: First. true teeth
- First true teeth
- Identified by their tooth structure
- Dentine encoated with enameloid
- Replaced frequently * sitontopofjaws
- tooth whorls
- programmedtoothloss
– teeth are always new and sharp - sharks become top predators
Gnathostome (jawed vertebrates)
3.Osteichthyes (Bony Fish): united by presence of endochondral bone
These 2 groups are separated by the structures that support the fins
A. Actinopterygii: Ray-finned
The fin is supported by thin
cartilaginous fin rays (see arrow)
~30,000 species, most fish are this type
B.Sarcopterygii:Lobed-finned
The fin is support bone in the fin, few of these still extant
A. First: Actinopterygii
- (Ray- finned Bony fishes) dominate the waters today-ecologically Important
- bony fish evolved at same time as sharks, but adopted a heavier internal skeleton made of bone
- strong base for muscles
- Modern bony fish have highly mobile fins, thin scales, and symmetrical tail
– Differ from sharks in having a bony operculum which covers gills instead of numerous gill slits
– During evolution they lightened the external protection (heavy bony scales) and became faster swimmers.
Jawed Fishes (Gnathostomes)
In both Chondrichthyes and Osteichthyes The circulation is a simple loop from heart to gills to body and back
B. Lobed-finned Bony Fishes (Sarcopterygians) less abundant today but are important evolutionarily
Evolved ~ 390 mya. Abundant in Devonian
* Fleshy fins supported by bone
* 3 Lineages:
– Coelacanths (a) thought to be extinct 65mya but found off Madagascar and Indonesia !
– Lungfishes (b) Extant in Africa, S. Am Australia
– Tetrapodomorph fish (c) All extinct
Sarcopterygian (lobed-finned) Fish
concentra group 3.Tetrapodomorph Fishes
Only the Tetrapodomorph fish had characteristics that would be important on land:
1. Bones in fins homologous to tetrapod limbs
2. And Lungs
3. And nostrils that opened into mouth (internal nares) so they could breath through nostrils and air would enter the lung
4. And teeth like early amphibians
Traits associated with the transition:
- Simplification of cranium
- Fewer vertebrae
- More pronounced pelvic girdle
Early Tetrapods Evolve ~ 370 MYA
But what were earliest non- amniote tetrapods like?
* First vertebrates to walk on land. Why come out of water?
* Larger than extant amphibians
* Spent much time in water
– Caudal fin, lateral line, scales – Needed water for reproduction
* Called non-amniote tetrapods because did not have many of the characteristics that unite modern amphibians (we will do these later)
Major Steps in Vertebrate Evolution
Chordate to Vertebrate
– Tripartatebrain&cranium,Aganthans: Hagfish
– Start of vertebral column, Aganthans: Lampreys,
Major Steps in Vertebrate Evolution
Evolution of Jaws & Paired Fins
– AgnathantoGnathostome,Placoderms
Major Steps in Vertebrate Evolution
Evolution of true teeth
– Chondrichthyes
Major Steps in Vertebrate Evolution
Presence of endochondrial bone & internal bony skeleton
– Osteichthyes(Actinopterygii&Sarcopterygii).
Pectoral fins supported by bones homologous to tetrapod limbs
- Sarcopterygian tetrapodomorphs (Eusthenopteron,Tiktaalik)
Legs with multiple digits (non-amniote tetrapods)
Acanthostega,Ichthyostega
Now evolution of the modern amphibians
Lissamphibia
Then evolution of Amniotes with
Amniotic Egg
Then Sauropsid
Synapsid split
Later Non-amniote Tetrapods
- Began to inhabit dry uplands during early Permian period (280-248 mya). Large size and body covered with scales indicate skin was not used as respiratory system
- By (248 mya) therapsid (reptiles) ousted amphibians from their niche on land
- By (213 mya),, most aquatic
- only two groups from Jurassic (213-144 mya)
Anura - frogs and toads Caudata - salamanders
and newts
Amphibian Habitats
- Reinvasionoflandby modern amphibians in Tertiary period (65-2 mya)
- BUT…tiedtowater for reproduction
- Butliveinawide variety of habitats:
– Tropics, temperate forest, deserts
– Even in places where is it below freezing in winter (NE, Canada)
Amphibian habitats
Adaptations :
1 . Legs to support weight
2. Lung to extract oxygen
3. 3.But need way to prevent
body desiccation
4. Reproduction in water to
prevent egg desiccation
5. Redesigned heart to drive
new respiratory system
Three clades of modern amphibians (Lissamphibia)
- Anurans (“no tail”) frogs and toads ~6,000 species
- Caudata (“tailed”) Salamanders and newts
~600 species - Apoda (“no feet’) Caecilians
~200 species
Characteristics of Lissamphibia
Legs (secondarily lost in Apoda)
* Eggs not amniotic - must be kept moist
*Lungs (secondarily lost in some);pulmonary circulation, partially divided heart, all ectothermic
New derived characteristics (synapomorphies):
Skin: No scales, Water permeable
* Use for respiration (cutaneous respiration) but must be kept moist (behavior, wax)
* Many have poison glands in skin
* Unique teeth
* Unique rods in retina
– Metamorphosis between larval and adult stage * Most spend part of life in water part on land =amphi
– Carnivorous at some point in their lives
Modern Lissamphibia: 1. Anura
Anura - amphibians without tails
Frogs smooth skin, long legs
* Toads bumpy skin. Adapted to dry
environments
– Highly modified skeleton with urostyle
– most live in or near water, and return to water to reproduce; eggs lack amniotic membrane/shell
* eggs fertilized externally and hatch into tadpoles
* Tadpoles undergo metamorphosis
Lissamphibia: 2. Caudata
Urodela (Caudata) - salamanders
- Few inches to >1’
- Elongated bodies, long tails, and sooth, moist skin
- May be terrrestrial but most have aquatic larval stage then metamorphosis
–fertilization is usually internal. Males release spermatophore which is
picked up by female
Lissamphibia 2. Caudata (tailed-ones, salamanders)
- Maybeterrestrialor aquatic.
- Mostreturntowater to reproduce.
- The “Big Night”
– Migrate to vernal pools during first rainfall > 50o F in Spring
– Metamorphosis more subtle
Lissamphibia 3. Apoda
Apoda - highly specialized group of tropical burrowing amphibians
– legless, but have jaws and teeth
– internal fertilization
– vivparous, many ways of providing nutrition to young
Amniote key adaptation: the amniotic egg
Shelledeggorinternalgestation.
* Removedneedformoistenvironmentforreproduction.
* chorion - outermost membrane * amnion - encases embryo
* yolk sac - surrounds yolk (food)
* allantois - surrounds was
Amniotes-Invaders of the Land: Reptiles, Birds & Mammals
New Characteristics:
–dry skin with SCALES prevents water loss but can’t use skin to take up water or gas
–thoracic breathing (better way to ventilate lungs) allows higher rate of aerobic metabolism
–amniotic egg
* Internal fertilization
Characters of amniotes that minimize water loss
- Amniotic eggs
- Oviparous amniotes lay shelled eggs — mineralized
portion is impermeable; water moves only through
pores - Viviparous amniotes — the eggs develop in the
mother’s uterus.
- Dry Skin
- Reptiles have keratinous scales.
- Birds have feathers made of keratin
- Mammals have keratin in skin
- Consequences: Prevents water loss but also water uptake. Skin can no longer be used for respiration
Uric acid precipitates and doesn’t
hurt developing embryo in egg
Respiration in Amniotes
Amniotes expand their rib cages by muscular contraction and take air into lungs via negative pressure breathing. Amphibians can’t do this (they force air into lung).
This “thoracic breathing” s a better way to ventilate lungs
- Allows higher rate of aerobic metabolism
- Doesn’t require moist skin
- Allows better control of water and ion balance, and body temperature than aquatic gills
- Later improvement in mammals with evolution of the muscular diaphragm
Evolution of the Amniotes
- We will do the Synapsid lineage first, then return to it in next lecture with the Mammals
- Then we will do the Sauropsid lineage:
– Anapsid turtles
– Diapsid - Archosaurs (Crocodiles, Dinosaurs to Birds) * Lepidosaurs (Lizards and Snakes)
Amniotes are classified using the SKULL TYPE
Look for holes IN ADDITION to eye socket (Orbit) and nasal openings (Nares)
Synapsid: 1 extra hole on each side Mammalian lineage
Anapsid: no extra holes (other than orbit or nares) Turtle lineage
Diapsid : 2 extra holes on each side Crocodiles, Dinosaurs & Birds Tuatara’s
Modern Reptiles (Squamates)
Synapsid Lineage
A. Pelycosaur
- Sail for thermoregulation (ectotherms)
- Strong jaws first land vertebrates to kill organisms their own size
- Large (200Kg)
- Dominant for 50my but replaced by next group by 250 mya
Synapsid Lineage
– B. Therapsids
(Mammal-like reptiles)
– speeding up metabolism
* Fur?Probably endothermic
* Dominant for 20 my
* gave rise to mammals
* Extinct by 170 mya
Synapsid Lineage
- About 170 mya Therapsids gave rise to mammals
- Early mammals were small
- The predominant reptiles were large diapsids Dinosaurs
- After the extinction of the dinosaurs 65 mya mammals become more abundant and radiate into a variety of niches
