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Ecology & Evolutionary Biology

lec 3 eeb388 9/27/2012 11:54:00 AM Synapsid Evolution and the origin of Mammals  Oldest mammals/synapsids are known from the Pennsylvanian 318- 319 MYA (Cenozoic for mammals), Paleozoic for synapsids aka ancestors of mammals may even originate before that  Skull fenestration: o Anapsid : no temporal openings o Most amniotes come from: o Synapsid: 1 temporal openings (mammals evolve from this)  Temporal fossae in mammals is the reminent of this  Between 3 bones: post orbital(this fuses in most extant), squamosal, jugal o Diapsid : 2 openings Synapsid:  Oldest: pelycpsara: extinct at the peranian  More derived and more mammal like: thorapsids @ the pernian  During the Triassic most thorapsids  True mammals in Jurassic Pelycosauria  Family ophiacodontidae o Large skulled predators includes oldest know synapsid arcaothryris from nova scotia o All pelycosaurs went extinct before the end of the Permian  Family eothyridae o Small lightly build carnivores with small maxilla but large canines  Family caseidae o Herbivorous o Very small gead among largest pelycosaurs  Family varanopsidae o Also small agile predators  Family edaphosauridae o Herbivorous o Small head characteristic dorsal snail supported by elongate neural spines  Family sphenacodontidae o Large head with large maxillary canines 1 o Many with elongate neural spines such as dimetron o Sister to Soft tissue characters difficult to say where they came form cuz they decompose Therapsida  Mmammal characteristics shared with all therpasieds o Enlargments of temporal fenestrrae o Anteroventrally sloping occiput o Reduction of palatal teeth o ** look at pics  Biarmosuchia o Most pelycosaur like of therapsides o Carnivorous o Extinctt at end of Permian  Dinocephalia o Large bodied o Large group o Carnivorious omnivorouous and herbivorous o Head ornamentation possibly used for competition  Dicynodontia o Large herbivores o Retained large canines o Not extinct until end of Triassic  Gorgonopsia o Large carnivores top predators of end Permian o Extinct at the end of the Permian  Therocephalia o Medium large carnivores o Sister group to cynodonts o May have possed vibrissae(whiskers) and or hair o Extinct I early Triassic  Cyondontia o Includes mammals o First appeared in late Permian o Probably possessed hair and laid eggs 2 o Most weasel to dog sized carnivores with some herbivorous lineages o Mammals thought to evolved form one of several small bodied probably endothermic Triassic forms o Best known non-mammalian cynodont is thrinaxodon  Features thrinaxodon shares with mammals  Multicupsid teeth  Differentiated teeth  14/i3  saggital crest  strongly bowed zygomatic arch  extensive secondary palate  double occipal condyle  thoracic **see pics  reflective laminal is very c shaped
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