Mammals Cont.

1. Mammals Cont.

2. Amniote Lineages croc dino + bird liz. snake • Synapsida • earliest split; gave rise to mammals • earliest synapsids were not mammals • Testudinomorpha • next split; turtles • Diapsida • includes all other currently living amniote groups tuatara Test. Synapsida

3. Mammalian Origins • More than one synapsid lineage • Mammals only surviving lineage • Over time, ancestral synapsid lineage developed mammalian traits

4. Non-mammalian Synapsids • Synapsids among the first amniotes • First and second synapsid radiations included both carnivorous and herbivorous species • how do we know this? • Fairly large • 10 – 200 kg • some up to 1000 kg • Extinct lineages include • pelycosaurs • therapsids • Permian mass extinction • cynodonts (a therapsid lineage) survived and radiated • gave rise to mammals Dimetrodon Moschops

5. Evolutionary Trends Cynodonts to Earliest True Mammals • Decreasing body size • early cynodonts were dog-sized • rabbit-sized • earliest true mammals were size of shrews • Increased brain size • Increased respiratory efficiency • Increased efficiency of locomotion • flexion of vertebral column • limbs under body From BBC website

6. Evolutionary Trends Cynodonts to Earliest True Mammals • Increased feeding efficiency • skull evolved larger fenestra to accommodate larger jaw muscles • heterodonty • different teeth, different functions • specialized teeth such as molars • gripping • tearing • chewing • Endothermy and higher metabolic rates Morganucodon – the earliest known mammal – 210 mya

7. Deciding When Mammals Became Mammals - Teeth • Why teeth? • mammary glands, fur define mammals • don’t fossilize well • Note precise occlusion – the way teeth fit together • Note specialization of teeth

8. Deciding When Mammals Became Mammals - Teeth • The Hypothesis • mammals get two sets of teeth – milk teeth and adult teeth • precise occlusion is required for feeding specializations of mammals • chewing • biting • etc. • precise occlusion is only possible with adult teeth • therefore, young need some way to gain nourishment before adult teeth arrive • lactation • monotreme model for simple lactation

9. The last major radiation • Synapsid • Therapsid • Cynodont • mammal • Small insectivores • led to all modern mammal groups • Occurred around 65 mya • why is this date important?

10. Selected Orders of WV Mammals • Marsupiala – ex. oppossums • Insectivora – ex. shrews • Chiroptera - bats • Lagomorpha – ex. rabbits • Rodentia – ex. mice • Carnivora – ex. raccoon • Artiodactyla – ex. deer

11. Marsupiala • Marsupium (abdominal pouch) of females • most, but not all marsupials have a marsupium • echidnas (Monotremata) also have a pouch Virginia Opossum

12. Marsupiala • Marsupials are best distinguished from Eutherians by their reproductive mode • small amount of energy invested in young prior to birth • litter weighs less than 1% of mother’s body mass • some rodent litters weigh 50% of mother’s body mass • Virginia Opossum young are about the size of a bee when born • marsupials invest much more in lactation than do eutherians

13. Virginia Opossum • Omnivore. Items include: • insects, lizards, mice, snails, earthworms, fruits, nuts, seeds, grasses, carrion • Prehensile (grasping) tail can be used to hold objects, hang from limbs • Often feigns death when escape is impossible Prehensile Tail Response to a perceived threat

14. Insectivora • Very diverse order • six families • includes shrews, moles, hedgehogs, tenrecs, and others • Thought to possess primitive characters common to the earliest mammals • Unlike most mammal orders, there is no character or key set of characters that distinguishes Insectivora Short-tailed Shrew Eastern Mole

15. Insectivora • General (but not diagnostic) characters include • small to medium-sized • pentadactyl (five digits) • pointed snouts • small pinnae (external ears) • eyes small or absent Hedgehog Yellow-streaked Tenrec

16. Shrews: Body Size and Metabolism • Often associated with moist areas due to high respiratory water loss - size related • High metabolic rate associated with short life spans - ave = 1 yr • Too small to hibernate or migrate • Must forage throughout the year, exposing to extremes in weather • Daily food intake may exceed body weight

17. Chiroptera • Nearly global in distribution - areas in red • Second only to rodents in number of species - about 920 • Based on feeding, reproduction, behavior, and morphology, bats are the most specialized mammalian order • Only mammals to evolve true powered flight • Sizes span almost 3 orders of magnitude (10X) from 2 g (a penny weighs about 3 g) to 1600 g • Most species are insectivorous, but others are carnivorous, nectivorous, frugivorous, or sanguinivorous

18. Order Lagomorpha • Hares, rabbits, and pikas - about 80 sp. • Were once classified as rodents, but now considered a separate order Black-tailed Hare American Pika

19. Order Lagomorpha • Peg teeth are diagnostic • second pair of incisors immediately behind rodent-like first incisors

20. Coprophagy in Lagomorphs • Ingestion of feces to aid in nutrient absorption, especially B vitamins, and enhance energy assimilation • Minimal amount of fiber is processed when plant material first ingested due to rapid passage rate of food through gut • Lagomorphs produce two types of feces • moist, mucus-covered which are eaten directly from anal opening • hard, round feces which are passed normally • Rabbits typically practice coprophagy twice daily • Also practiced by many rodents and shrews

21. Order Rodentia • By far the most speciose mammalian order • 2016 sp. • 43 % of all mammal sp. • Worldwide distribution • native everywhere except Antarctica, New Zealand, and some oceanic islands • Most species are small, weighing 20 - 100 g, but capybaras can reach 50 kg (ca 110 lb) Capybara White-footed Mouse

22. Order Rodentia • Teeth are diagnostic • single pair of upper, lower incisors • diastema between incisors and molars/premolars • no canine teeth • Rodent incisors are rootless, growing constantly • Incisors become sharp as a result of gnawing • anterior portion of incisor has enamel, which is hard • posterior doesn’t • differential wear

23. Rats and birds on oceanic islands • Rats not native to most oceanic islands • Island bird species are often “naïve” • Polynesian, Norway, and Black Rats introduced as a result of human activity • Introduced rats have caused bird extinctions on at least 26 islands • eat eggs, nestlings • ground-nesting birds especially vulnerable • may also compete for food resources • Some islands, such as Fiji, have experienced rat introductions without consequent bird extinctions • already had native rats

24. Order Carnivora • Relatively small order - about 271 sp., but great diversity among species • Most species eat meat • more digestible than vegetation • harder to locate, capture, kill • Many of world’s most highly endangered sp. are members of Carnivora. Why? • Economics • Perceived danger • Slow reproduction • Contaminants • Food chain consequences

25. Order Carvivora • Carnassial (cutting, shearing) teeth • Well-developed, elongated canine teeth • Jaw musculature usually strong, well-developed for crushing Carnassial teeth of Gray Wolf Saber-toothed Cat