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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 • • Neural crest Neurogenic placodes 2. Nervous System • • • • • Above Braincase (skeletal) Complex sense organs Cranial nerves Tripartite brain 3. Endocrine system is complex 4. Gut • • • Muscularization Regionalization Differentiated organs 5. Cardiovascular • • • Gills Heart Hemoglobin