Chordate Phylogeny
description
Transcript of Chordate Phylogeny
Phylogeny (cont.)
5 Classes (before tetrapods)1. Agnatha
Jawless fish; hagfish and lampreys
2. Chrondrichthes Sharks, skates and rays3. Osteichthes Bony fish4. Actinopterygii Ray- finned fish5. Sarcopterygii Lobe-finned fish
Sea Squirt
Amphioxus
Lamprey
Hagfish
Chordate Origins
Chordates developed during the Cambrian period, around 560 Ma
Evolutionary issueThere is a poor fossil record for the origin of chordates, since they were most likely soft-bodied creatures
Primitive chordates (like the sea squirt) are studied closely, along with Hemichordates, to try and piece together their origins
Chordate characteristics:
1. Dorsal, hollow nerve cord2. Notochord
Chordate Basics
3. Pharyngeal slits4. Post-anal tail
Embryonic
Development
1. Egg becomes fertilized, then divides repeatedly (cleavage)
2. Cells arranged into a round, hollow ball (called a blastula) with a fluid filled cavity (called the coelom)
3. One side of the ball indents and grows inward (gastrulation) until an opening is formed (called the blastopore)
4. Indentation continues until it breaks through the wall on the other side, creating a second opening
The notochord forms out of the mesoderm • made up of a hard, fibrous material
The dorsal, hollow nerve cord is derived from the ectoderm (through ‘invagination’)• eventually forms the brain and spinal
cord
The Pharyngeal slits develop after the mouth and pharynx form, creating holes or slits into the pharynx• may become gills for respiration• used to filter food or eject water while
eating
The post-anal tail is created when the body elongates
Embryonic Dev. (cont.)
Considered to be “primitive” chordates (“proto” means first)
Larvae are generally planktonic, while adults may be sessile, benthic or they may burrow into the substrate
May be solitary or colonial, and feed by means of cilia and mucus
Male and female gonads are either found in a single individual (monoecious) or in separate individuals (dioecious)
Protochordata Includes subphylums:• Hemichordata• Urochordata
(tunicates)• Cephalochordates
Thought to be an intermediate group of species between the echinoderms and the chordates
• Acorn Worm• Pterobranch• Graptolites (extinct)
Has pharyngeal slits and a dorsal nerve cord (may not be hollow). However, they do not appear to have a notochord (merely a stomochord) and have no post-anal tail
Hemichordata
Acorn Worms(Enteropneusts - Hemichordata)
• # Species: 75-80• Evolved: 500-540 Ma• Size: can reach over 1 meter• Nutrition: Filter feeders or normal ingestion• Lifestyle: Planktonic larvae, burrowing adults• Support: Stomochord• Musculature: Circular or longitudinal orientation• Non-segmented muscles
• Reproduction: Dioecious or segmentation• Chordate Characteristics: Pharyngeal slits and dorsal nerve cord
Pterobranch(Hemichordata)
• # Species: about 20• Evolved: 500-435 Ma• Size: can reach 1 mm• Nutrition: Filter feeders (ciliated tentacles)• Lifestyle: Planktonic larvae & sessile, colonial adults• Support: Stomochord and rigid, tube housing• Musculature: Circular or longitudinal orientation• Non-segmented muscles
• Reproduction: Dioecious or asexual• Chordate Characteristics: Pharyngeal slits and dorsal nerve cord
Graptolites EXTINCT(Graptolithina - Hemichordata )
•# Species: thought to be hundreds•Evolution: 490-545 Ma (extinct 298-354 Ma)•Lifestyle: Colonial and sessile or benthic
These were tiny, tubular creatures, which when fossilized may resemble a saw blade.
Subphylum
Urochordata
Over 20,000 species - thought to be the oldest living
chordates
Includes:•Tunicates (aka Sea Squirts; Ascidiacea)•Larvacea•Thaliacea
Tunicates (Sea Squirt)(Ascidiacea - Subphylum Urochordata)• # Species: about 2,000• Evolved: 540 Ma• Size: (small)• Nutrition: Filter feeders (complex straining apparatus); eat mostly plankton• Lifestyle: Planktonic larvae & sessile adults• Support: Notochord and tunic• Musculature: •Reproduction: hermaphroditic or asexual
Larvacea and Thaliacea(Subphylum Urochordata)
• Larvacea look more like tunicates during adulthood• Thaliacea retain their tadpole-like body plan from larval state to their plankton-like adulthood (benthic)• Some are sexual and others are asexual, skipping the larval state altogether• May live solitary or colonial lives
Subphylum
Cephalochordata
About 25 species
This is the first group of chordates to retain all 4 traits into adulthood
Includes:•Lancelets (or Amphioxus)
Lancelets (Amphioxus)(Subphylum Cephalochordata)
• # Species: about 20• Evolved: 520 Ma• Size: up to 2 inches• Nutrition: Filter feeders - plankton and algae• Lifestyle: Burrowing adults• Support: Notochord (extends all the way to snout)
• Musculature: Segmented (myotomes)•Reproduction: Dioecious
Evolution of
Vertebrates Debate
DNA confirms neither of these diagrams are
feasible
Why? Larval Development basis Pharyngeal slit development basis
Class Craniata
The evolution of heads!
The evolution of the head (or skull) occurred around the same time that vertebrates evolved.
All species in the Subphylum Vertebrata convert their notochord into a backbone (except for the hagfish)
Subphylum Vertebrata
The notochord is now converted to vertebral plates.
With the inclusion of a head (or skull), species developed a brain, eyes and more complex nervous systems (the nerve cord becomes the spinal cord).
Includes:• Hagfish• Lampreys•Cartilaginous, lobe-finned and bony fish
Hagfish(Subphylum Vertebrata)
• # Species: about 72• Evolved: 330 Ma• Size: about 30 inches• Nutrition: Parasitic or scavengers; eat mainly worms or dead creatures• Lifestyle: Live in the muddy bottom of the ocean
There is no known larval state• Support: Notochord •Reproduction: Dioecious (has both male and female gonads, but not hermaphroditic)
Lampreys(Subphylum Vertebrata and Craniata)
• # Species: approx. 3• Evolved: approx. 330 Ma• Size: 5-40 inches• Nutrition: Filter feeders as larvae & parasitic adults (feeds on the blood of prey)• Lifestyle: Burrowing larvae & free swimming adults• Support: Cartilaginous skeleton•Reproduction: Dioecious (has both male and female gonads, but not hermaphroditic)