LECTURE 6 – NON-MAMMALIAN SYNAPSIDABE AWARE OF THE CHARACTERISTICS OF AMNIOTES (AND WHICH TAXA ARE AMNIOTES)? WHAT IS THE SYNAPSID TYPE OF TEMPORAL FENESTRATION AND HOW DOES IT COMPARE TO ANAPSIDS AND DIAPSIDS? We know thisThree different conditions:Anapsid condition No fenestraEarly amniotes and turtlesSynapsid condition Single fenestra behind orbitSynapsids (mammals and mammal-like reptiles)Diapsid conditionTwo fenestrae behind orbitLepidosaurs (tuataras, lizards and snakes) and archosaurs (crocodiles, dinosaurs and birds)WHO DOES THE SYNAPSID CLADE INCLUDE? (WHICH 2 GROUPS?) 1- Nonmammalian synapsids, or “mammal-like reptiles” (extinct)2- Mammals-Monotremata – platypus, spiny anteaters-Marsupialia - marsupials-Eutheria – placentalsSynapsida includes all amniotes descended from a common ancestor with the synapsid type of temporal fenestrationWHO ARE THE NONMAMMALIAN SYNAPSIDS? (WHICH 3 GROUPS?) 1-Pelycosaurs (pelycosauria)2-non-cynodont therapsids3-cynodont therapsids (cynodontia)BE AWARE OF THE GEOLOGIC TIME SCALE (ERAS, PERIODS, ETC., MAJOR EVENTS)WHEN DID THE SYNAPSIDS BEGIN TO RADIATE? Synapsids first amniotes to radiate in terrestrial habitatsPaleozoic – late carboniferousPermian – synapsids were the most abundant terrestrial vertebratesTriassic – top carnivoresHad 1st radiation (pelycosaurs) & a significant portion of their 2nd radiation (therapsids) in the Paleozoic before the radiations of the diapsids we already covered. The 3rd radiation of the synapsid lineage (mammals) did not reach its peak until the cenozoic era.Through the late Paleozoic & early Mesozoic the synapsid lineage was becoming increasingly mammal like & mammals & dinosuars both appears on the scebe in the late Triassic period.3 groups of extant mammals – monotremes, marsupials, & placentals-have evolved by the late Mesozoic era, accompanied by several groups of mammals that are now extinct.WERE THE PELYCOSAURS MONOPHYLETIC? NopeGeneralized amniotes-most were generalized carnivoresWERE THE NON-CYNODONT THERAPSIDS MONOPHYLETIC? yes?WHEN DID THE THERAPSIDS APPEAR AND HOW DID THEY INTERACT WITH THE PELYCOSAURS? Appeared in the Middle/Late PermianOften called advanced mammal-like reptilesHerbivorous & carnivorousPossibly replaved the Pelycosuars in later Permian. Hypothesis fits with knowledge of global climates and vegetational zones in the Permian & with where we find fossils of these synapsids.-Includes Non-cynodont therapsids and cynodont [Non-cynodont split from cynodont because therapsids aren’t monophyletic and cynodonts were more closely related to humans/mammals]*cynodont therapsids – mammalian ancestorsnoncynodont therapsidsKNOW AN EXAMPLE OF A PELYCOSAUR (MAMMAL LIKE REPTILES) AND A LITTLE BIT ABOUT ITS BIOLOGY includes sailbacks such as dimetrodonNotable traits –--complexity of dentition-arched palate-lower jaw flangePelycosaurs-best known – dimetrodon – sailback (sphenacodont) – large, carnivorous forms with large sharp teeth. An enlarged caninelike tooth in the maxillary bone is a key feature linking sphenacodonts to more derived synapsidsAdditonal derived features – arched palate ( first step toward the development of a separation of the mouth & nasal passages seen in some therapsids[First non-mammalian synapsids, large carnivores, could rip prey apart, “sail back” used for temperature regulation and display purposes, ectotherm, tooth variety (dentition) (multiple cusps on teeth), arched palate (separation of mouth and nasal passage)]MANY OF THE TRENDS WE SEE IN NON-MAMMALIAN SYNAPSIDS ARE FOR WHAT 2 MAJOR PURPOSES? increase metabolism – endothermy. Skull & skeletal changesinsulation – hairrespiration rate – nasal turbinate bonesKNOW THE 11 TRENDS IN NON-MAMMALIAN SYNAPSIDA (NOT JUST THE LIST, KNOW WHAT EACH MEANS)1) size of temporal fenestra – more jaw muscles-implies more food eaten per day.--small opening in pelycosaurs becomes an increasingly larger opening in more derived theraspids--- This ^ plus an increasing tendency to enclose the braincase w/ dermal bone results in a distinct temporal fossa for the origin of a larger volume of jaw musculature2) Condition of the lower temporal bar –a bar of bone bowed out from the skull in the region of the orbit indicates the presence of a masseter muscle, originating from this bony bar & inserting on the lower jaw, again suggesting more effective food processing. - The temporal bar originally lay very close to the upper border of the lower jaw, leaving no room for muscle insertion on the outside of the lower jaw. - In cynodonts and mammals the bar is bowed outward forming the zygomatic arch and indicating the presence of a masseter muscle.3) Lower jaw and jaw joint – Changes reflect the increased compromise between food processing and hearing in synapsids. – The lower jaw in Pelycosaurs resembles amniote condition. Tooth bearing portion, the dentary, takes up only about half of the jaw. – By the level of cynodonts, the dentary has greatly expanded and the postdentary bones have been reduced in size. – In mammals, the dentary forms a new jaw joint with the skull3- Teeth – greater specialization of the dentition reflects an increased emphasis on food processing. - Teeth of pelycosaurs are homodont – same size & shape, no evidence of regionalization n of function- In more derived synapsids the teeth become increasingly heterodont although the actual mastication with precise occlusion of the cheek teeth is a mammalian feature. Mammals have reduced the number of tooth replacements to two (diphyodonty) have the postcanine teeth further differentiated into premolars(replaced) & molars (not replaced) & have the lower teeth set closer togetherthan the uppers) Mammals also have double rooted molars and prismatic enamel on their teeth. 5) Development of a bony secondary plate – A secondary palate seperates the nasal passages from the mouth & allows breathing and eating at the same time. – It also reinforces the skull against stresses from increased amounts of food processing. – No bony secondary palate is apparent in pelycosaurs. – An incipient, incomplete secondary palate is present in some noncynodonts and in mammals (dicynodont therapsids evolved a bonysecondary palate convergently). – A ridge inside of the nasal passage suggesting the presence of nasal turbinates is found in cynodonts & therocephalians. – Mammals have merged the originally