Mammals Flashcards
Features
- synapsid - 1 hole, modified to be combined with the orbit
- 1st group of amniotes to radiate widely in terrestrial
- split from sauropsids very early
- dinosaurs extinct, after mammals begin to increase - likely due to changes in vegetation, flowering and insects etc. diversity
Those that gave rise to the mammals
- Pelycosaurs - basal/early amniotes
- Therapsids - more derived
- Cynodonts gave rise to the mammals
General trends on way to mammals
•limbs from outside to underneath •feet reduced in size - nimble •pelvic girdle becomes reduced in size •don't have ribs on lumber vertebrae •temporal fenestra changing in size -all suggest move towards endothermy and more active
Changes in the skull from non-mammalian synapsid to mammalian
•teeth from homodont to heterodont, large canines etc.
•articulation of the jaw on top changed
-dentary (jaw bone) becomes prominent bone in lower jaw, 1 bone rather than many
•bones previously in jaw become smaller and pushed back - incorporated into middle ear
-more powerful jaw = compromise between hearing and eating, eventually housing sound in different structure
•zygomatic arch more developed (cheek bone)
-increased musculature in jaw
-needed food? endothermic…
Limb orientation changes
•more underneath body
•body undulations = conflict between muscles for movement and breathing
-true in lizards and early amniotes
•mammals have separated the two - thorax kept firm
•also have diaphragm, muscles to help ribs expand and contract = ventilation
•fast-moving animals aided in ventilation
Early mammals
•small and insectivorous •egg laying •nocturnal and solitary (likely) •eyes geared up for low light conditions - nocturnal -lots of rods in retina -not very good at colour vision •likely to have strong infant/mother bond •large olfactory bulbs •endothermy •lactation and suckling •hair of keratin = insulation -whiskers important
precise occlusion evolution
most mammals - diphyodonty
•precise occlusion - top fit into bottom = grinding surface improved
-not possible in polyphydonty
-diphyodonty must have evolved before precise occlusion
•lower jaw narrower than upper
Diphyodonty evolution
- animals were fed milk early in life - don’t need permanent teeth till later on
- lactation must have evolved first - before diphyodonty and precise occlusion
Lactation evolution
•milk produced by mammary glands
•related to apocrine glands - associated with hairs
•mammarys originally secreting organic substances - like aggregating hormones (what apocrine did)
•milk produced to protect eggs from dessicaiton
•milk had antimicrobial properties
-selective advantage to feed on milk - evolving into nutritious secretion
Evolutionary advantages of lactation
•don’t need to breed at seasonal food supply peaks
•mother not dependent on paternal care
•viviparity less strenuous as don’t need to produce young that is well-developed
-can develop normally outside of body (extreme in marsupials)
Suckling
- suckling unique to mammals - due to tight seals in pharynx
- seals applied due to tongue and soft palette found at back of mouth - fluid can be controlled
- seal behind one at back of mouth seen in young but lost later on - gets less well-developed
- seals used in feeding in baleen whales
Facial muscle development
- homologous with those of the neck region in reptiles
- reptiles tend to swallow food whole - well-developed neck muscles
- mammals chew food more - due to precise occlusion
- allows complicated facial expressions
Marsupial reproduction
- pouch/marsupium in 50% spp
- paired vaginae transport system
- birth in pseduovaginal canal
- 2 uteri and simple placenta
- altricial young
- M have bipartite penes - splits in 2
Primates
- retention of clavicle (collar bone)
- shoulder joint permits limb movement in all directions - elbow joint allows rotations of forearm
- 5 digits on all limbs
- usually 1 young per pregnancy
- reduced snout
- reduced no. of teeth
- claw modified into flattened nails
- large brain
Strepsirrhini
tarsiers and prosimians •small, nocturnal and can have long snout •skull - unfused symphysis and front -lack of postorbital closure •long rostrum •postorbital bar and temporal fossa •no plate separating orbits from temporal fossa •distributed across Africa and SE Asia (lemurs Madagascar)
