HOW IMPORTANT WAS THE MESOZOIC FOR MAMMAL DIVERSIFICATION? 2/3rds of mammalian history occurred in the MesozoicGeographical continuity of Pangea in the late Paleozoic and early Mesozoic eras allowed tetrapods to migrates freely – evenglobal distributionBy Late Mesozoic – pangea no longer connected – spread/separation resulted in isolation of tetrapods and limited possibility for migration. So, they became progressively different on different continents. *******breakup of pangea – continental drift2 major geographic groups-laurasia-gondwanaEnd of the Mesozoic-small mammals-dinosaurs-hair-endothermy-nocturnalMesozoic era periodsCretaceous period– extinction of dinosaurs– first primates– first flowering plantsJurassic period- First birds- Dinosaurs diversityTriassic period- first mammals- first dinosaurs? WHAT ELSE WAS DIVERSIFYING AT THIS TIME? Late Triassic – shift in vegetational communities especially in gondwana where the floras were replaced by conifers. Floral turnover matched by faunal turnover – many animals extinct, and dinosaurs & mammals made a first appearance at this time, as well as other modern groups such as sphenodontids (lizard sister group), turtles & crocodiles. Extinct groups such as pterosaurs (flying reptiles) also appeared + marine reptileslike ichthyosaurs & plesiosaurs.WHAT WERE THE 2 MAJOR PERIODS OF MAMMALIAN DIVERSIFICATION (WHEN DID DIVERSIFICATION TAKE PLACE)? 2 major radiations1 – juassic/cretaceous2 – cretaceous-multitubercultates-first therians-terrestrial ecosystemBE ABLE TO NAME ONE OF THE OLDEST MAMMALS AND KNOW WHEN IT LIVED. Early Jurassic – morganucodon (also known as eozostrodon) from wales.* --had 3 main molar cusps in a more or less straight line<primitive tribosphenic molars--had a characteristic anatomy of the nasolacrimal duct, possibly associated with the new harderian gland (associated w/ eye secretes oily substance that travels down thenasolacrimial duct to the nose where it can be wiped off with paws – preen fur to repel water)----anatomy present in morganucodon but absent in cynodontsMegazostrodon from south Africa, and sinocodon from china. Asomewhat older possible mammal is adelobasileus known onlyfrom an isolated braincase from the late Triassic of texasWHAT WAS THE SIZE OF THE FIRST MAMMALS? Earliest mammals very small (shrew sized) smaller than cynodonts (rat sized)WHAT 2 CHARACTERS ABOUT TEETH ARE CHARACTERISTIC OF MAMMALS (VERSUS NON-MAMMALS)? -diphyodonty detectable in the fossil record-precise occlusion (mastication)-sideways movement of jaws-durableWHAT IS AN IMPORTANT SKULL CHARACTERISTIC THAT DEFINES MAMMALS? Dentary-squamosal jaw articulation Derived skull features allowing for enlargement of the brain & inner ear areaWHAT 2 NON-SKELETAL CHARACTERISTICS DEFINE MAMMALS? Hair & lactationUNDERSTAND HOW THE EVOLUTION OF LACTATION, DIPHYODONTY, AND SUCKLING OCCURRED AND ARE IMPORTANT IN MAMMALIAN EVOLUTIONARY HISTORY2 QUESTIONS ASKED – FIRST, WHEN DID PROVIDING THE YOUNG WITH MILK ORIGINATE AND DID IT COINCIDE WITH THE POINT THAT WE CONSIDER AS THE CYNODONT MAMMAL TRANSITION? SECOND, HOW DID MILK AND THE MAMMARY GLAND ITSELF EVOLVE? Lactation likely appeared with the origin of mammalsMammary glands evolved from glands associated w/ hair folliclesWhen did suckling evolve? – tied in to hard secondary palateArgued that precise occlusion & diphyodonty indicate the presence of lactation in early mammals. Precise occlusion would not work with the polyphyodont condition because only a fully erupted tooth occludes properly with its counterpoint inthe other half of the jaw – thus diphyodonty must have preceded precise occlusion in evolution. However an animal could reduce its number of sets of teeth only if it was fed mily during its early life. If the newborn were fed only on liquid food, the jaw could grow while it had no need of teeth and permanent teeth could erupt near adult sized jaw. Thus, if an animal has precise occlusion & diphyodonty it must first have developed lactation-suggestion for lactation evolution – sebaceous glands (type of glands associated with hair (prob had primitive ability to secrete small quantities of organic materials)) originally secreted pheromones signaling the offspring to recognize their mother & to stay with her.*cynodonts would not have been able to suckleSuckling ability – unique mammalian featureMammals form fleshy seals against the bony hard palate with the tongue & with the epiglottis, effectively isolation thefunctions of breathing & swallowing. Use seals to suckyle nipple while breathing through the nose.Adults have lost the more posterior seal that allows this action b/c larynx shifts more ventrally in early childhoodFacial muscles are another characteristic feature of mammals absent in other vertebrates. Probably first evolved in the context of mobile lips & cheeks that enable the young to suckle.The facial muscles are thought to be homologous with the neck constrictor muscles (constrictor colli, also called sphincter colli) of other amniotes b/c both types of muscles are innervated by the facial nerve. This muscle aids in the transport of food down the esophagus & with the mammalian mode of swallowing a discrete bolus of food, this muscle could be coopted for a diff function. Evidence that the acquisition of facial muscles may have occurred somewhat differently in various mammal lineages b/c monotremes extend a diff portion of the constrictor colli onto the face during development than do therians. WHAT ARE THE 2 MAJOR FUNCTIONS OF MILK? BE ABLE TO ELABORATE ON BOTH FUNCTIONS 1. Immunity – milk contains proteins that are related to lysozyme enzymes that attack bacteria & had been propsed that the original use of milk might have been for protection of the eggs in a nest of microorganisms. New molecular evidence suggests that mammary gland & milk production arose as part of the immune system & that milk was especially involved in controlling inflammatory response.2. Nutritional – once a secretion of this type ^ (immune system stuff) any evolution to a more nutrition milk was just an added benefit – not primary purposeWHAT ARE THE EVOLUTIONARY ADVANTAGES OF LACTATION? 1. production of offspring is no longer seasonal – separated from seasonal food supply. Unlike birds which lay eggs only where food is(spring/summer), mammals can store food as fat & convert it to milk at a later date.2. not