- Olfaction – form of chemosensation mediated by receptor cells to respond to the presence of chemicals w/ specific traitso --Receptor cells responsible for the sense of smell are located in the OlFacTory EpiTHelIum All vertebrates but lampreys have a pair of olfactory organs that house the Olfactory Epithelium (lamprey singular)o -In Fishes – water (containing chemicals) enters through the InCuRrent nostril – passes over the Olfactory Epithelium – Exits through the Excurrent nostril ----In fishes – olfact organs not connected to mouth or throat(independent)- Nasal ways dif in tetrapods – Have noses that open to world through a singe pair of external nostrils  Open to throat through a pair of Internal NostriLS called CHONAE (choana sing.)I. Tetrapod Olfaction-Olfactory receptors associated w/ mouth & throat – pass air over olfactory epithelium every breath-receptors can be very sensitive------amongst extant mammlas have most sensitive---due partly to presence of thin scrolls of bones called TURBINATES -Turbinates highly developed in mammals – significantly increase the surface area available for olfactory epitheliumII. Vomeronasal Organ/ Jacobsons organa. In anterior roof of mouthb. Well developed in snakes & in some mammalsi. Flehman Behavior in ungulates ( where the head is lifted high & the upper lip is curled) – likely a way of inhaling pheromones into the vomeronasal organ3 MAJOR TETRAPOD LINEAGES Batrachomorphao Stem Tetrapodso Lissamphibiao Temnospodyls Lepospondyli Reptilomorphao Amniotes Synapsids- Anthracosaurs- Mammals- Mammal Like reptiles Parareptiles- Turtles- Stem Parareptiles Eureptileso Stem Eureptiles- Diapsidso Lepidosaurso Turtles?o ArchosaursTetrapod origins in LATE DEVONION PD (360 mya) @ same time began transition from water to land (based on fossil record)Lepospondyli1. Diverse tetrapods – semi-aqua & terrestrial forms2. Many body forms some similar to extant - suggest similar ecologies & life hisotries3. Relation to other tetrapods uncleara. 5 GROUPS OF LEPOSPONDYLI ****i. NECTRIDIAii. Microsauriaiii. Aistopodaiv. Adelogyrinidaev. LysorophiaNectridian Lepospondyls1. bad devel. Limbs – prob aquatic2. *DiploCAUluS – well known lepos. From NA3. up to 1 m in length4. ** boomerang shaped headThe Batrachomorpha-Aq, semi aq & terr. Forms--MID CORBONIFEROUS PERIOD 340 mya*Reduced # of digits on the forelimbs ---- 4 vs. 5 as in other crown group tetsTwo Groups1. Temnospondylia. Extinctb. Paraphyletic – some gave rise to amphibians nowc. Large (>2 m) – prob look & act like crocodlies 2. Lissamphibia a. some extant – Anurans, Salamanders, CaeciliansThe Reptilomorpha1) Third major lineage of tetrapodaa) Origins in Early carboniferousb) Majority of extant tetra’sSensory systems – water vs air-lateral line system good watr bad air b/c water is denser than air-Electroreception – better in water b/c it conducts electricity-Air better for vision & hearing-Chemical senses (Olfactory) work better in air than waterHow did the Choanae evolve? Posterior nostril migrated from its external to internal position over evolutionary time Critics – This would involve migrating across a field of teeth in the upper jaw & is unlikely – no fossil intermediates found for support of hypothesisKenIchThys – 395 myo Osteolepiform fish