ZOOL 403 Lecture Notes - Lecture 3: Monotreme, Skull, Synapsid
21 Jan 2020
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Learning objectives: explain why primitive/derived is not equivalent to less/more evolved, understand the large groupings of synapsida and where monotremata falls within. Evolutionary orientation (phylogeny 2: key feature of synapsids: lower temporal fenestra in skull present, mammaliaformes: dentary-squamosal jaw articulation. Jd pmb: diphyodont dentition, prismatic enamel, double-rooted molars, dorsoventral flexion of backbone, mammalia: includes monotremes, loss of quadrate-articular jaw point, acquisition of enclosed middle ear (independently in monotremes. Evolution orientation: and therians): thrinaxodon= quadrate-articular joint only, probainognathus= both quadrate-articular and dentary-squamosal joints, morganucodon= quadrate and articular much reduced, opossum= only dentary-squamosal joint. Evolution orientation: order monotremeta involves 2 families, name them, family ornithorynchidae (web: also called platypus). Involves ornithorynchus anatinus: family tachyoglossidae, genus tachyoglossus, genus zaglossus (includes 2 extinct species, genus megalibwilia (dotted line; i am assuming they extinct) Evolution orientation: platypus is a size of small cat: ornithorynchus anatinus very small then comes tachyoglossus aculeatus. Key characters of monotremata: pectoral girdle, venom/foot spine, thermoregulation, reproduction.
