Transcript Phylogenetics

Phylogenetics, Background
Info (continued) and Craniates
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Discussion of article
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Additional Reading
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Lecture material
Cladistic Classification /
Phylogenetic systematics
• The science of evolutionary grouping based on
shared derived characteristics
• The naming of organisms based on these groups
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Plesiomorphy:
Synapomorphy:
Autapomorphy:
Monophyly:
Paraphyly:
Polyphyly:
M
N
A
B
spizit
C
Cladogram
Branch
Node
Internode
Root
OTU
Ingroup
Outgroup
Autapomorphy
Plesiomorphy
Synapomorphy
The five synapomorphies of the
Chordates
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In combination:
1. Notochord
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Hydroskeleton
Liquid-filled cells encased in a fibrous CT sheath
Allows for lateral undulation
2. Dorsal-hollow CNS (cf. paired structures of annelids
and arthropods)
3. Post-anal tail
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Extension of the body caudal to the anus
Increases the length of the body associated with
locomotion
4. Endostyle
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Longitudinal groove in the floor of the pharynx
Lined with glandular cells
Bind iodine in matrix (homologous to thyroid gland)
Transports food to esophagus
5. Pharyngeal slits
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Filter feeding
Respiratory
Characteristics and Phylogenetic
Relationships of Chordates
• Tunicates
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2000 species
Mostly Ascidians (sessile adults)
Hermaphroditic
In larvae – locomotion
– Notochord absorbed in the adult
– Tubular nerve cord
» Ependyma only
» Integrates locomotion
» Retained to some degree in adult
– Eyespot, balancing organ
– Cerebral vesicle becomes a ganglion in adult
Tunicate Adult
Tunicate larvae
Cf. vertebrate
• Cephalochordates
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45 species, mostly Branchiostomata (Amphioxus)
World-wide distribution
Motile
Short, post-anal tails
Distinct anterior end
• Not well developed head
– Notochord extends entire length of body
– Dioeceous
The Parade of the Craniates
• 50,000 known living species
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Plus extinctions since 500 MYA
Mostly marine
Hagfish + Vertebrata
Clearly exhibit all 5 chordate synapomorphies
• Some only in the embryonic stages
• Thyroid gland in all craniate adults
– Paired, cephalized sensory organs
• Nose, lateral eyes, ears
– Major organ systems
“Cephalized”
Why the concentration of
paired sensory organs here?
Major synapomorphies of the
Craniates
1. Developmental
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Neural crest
Neurogenic
placodes
2. Nervous System
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Above
Braincase (skeletal)
Complex sense
organs
Cranial nerves
Tripartite brain
3. Endocrine system is
complex
4. Gut
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Muscularization
Regionalization
Differentiated organs
5. Cardiovascular
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Gills
Heart
Hemoglobin