Phylogenetics Background Info continued and Craniates 1 2
Phylogenetics, Background Info (continued) and Craniates
1. 2. 3. 4. 5. Discussion of article Next article Additional Reading Schedule Changes Lecture material
Cladistic Classification / Phylogenetic systematics • The science of evolutionary grouping based on shared derived characteristics • The naming of organisms based on these groups – – – 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 • In combination: 1. Notochord • • • 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 • • Extension of the body caudal to the anus Increases the length of the body associated with locomotion
4. Endostyle • • 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 • • Filter feeding Respiratory
Characteristics and Phylogenetic Relationships of Chordates • Tunicates – – 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 – – – 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 – – 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 3. Endocrine system is complex 1. Neural crest 2. Neurogenic placodes 4. Gut 1. Muscularization 2. Nervous System 1. Above 2. Braincase (skeletal) 3. Complex sense organs 4. Cranial nerves 5. Tripartite brain 2. Regionalization 3. Differentiated organs 5. Cardiovascular 1. Gills 2. Heart 3. Hemoglobin
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