1Lecture 3 – Mammalian Diversity: Mesozoic Mammals & Monotremes Luo et al., (2002).This is the commonly used crown-clade definition.Node labeled 1 indicates our (stable) clade-based definition of Mammalia.
2Luo et al., (2002).We’ll look first at the Morganucodontids.From the latest Triassic and early Jurassic.
3Best know from the genus Morganucodon. Small – The skull length was around 3 cm and total length around 10 cm.Skull had large nasal cavity. Respiratory turbinates probably present.Well-developed inner ear region.Very large eye socketsPrimitive limb girdles.
4Best know from the genus Morganucodon. Cheek teeth had three cuspsDentary was greatly expanded.Articular was small and still present.Alternate-site chewing.The angular was on mandibleInsectivorous.
5Luo et al., (2002).We’ll next look at the Triconodonts.
6Triconodonts Teeth similar to Morganucodontids but cusps are linearized.Mammalian pectoral girdle.Pelvic girdle is still ancestral.Had a very sprawling posture.Great example of mosaic evolution.
7Triconodonts Repenomamus. About a meter long, and probably was carnivorous.Derived pectoral girdle & ancestral pelvic girdle.Hu et al., 2005, Science, 433:139
9Multituberculates Diverse and persistent group Dates from upper Jurassic, spans Cretaceous-Tertiary, coextisted with modern mammalsMouse-sized to marmot-sizedNamed for unique dentitionChisel-like incisorsLarge diastemaComplex, grinding molars (source of name)
10flowering plants (angiosperms). MultituberculatesThere’s good evidence that at lest some of the multituberculates were arboreal.Their diversification coincides with the early Cretaceous diversification offlowering plants (angiosperms).
11“Pantotheres” Paraphyletic- used informally Mid Jurassic Earliest bifunctional teeth - single cheek tooth with grinding and shearing function.Tribosphenic molars, ( primitive tooth type for living mammals)
15HadrocodiumThis pushes the date for the origin of mammals back.
16Juramaia sinensis The oldest eutherian (placental mammal) ~ 160 MYA Z-X Luo et al. Nature 476, (2011) doi: /nature10291
17Just in last few years, more diversity has been discovered among Mesozoic mammals. Luo (2007. Nature, 450:1011)
18Monotremes – egg-laying mammals. Order - Monotremata: ‘One hole’Cloaca (sewer) - single opening for unrinary, digestive, & reproductive tracts.Earliest fossils from Cretaceous (>120 MYA, record poor, but increasing)
19Monotremes – Mosaic of primitive and derived characters. Primitive CharactersCloacaSkull characters - possess pre- and post frontal bones.- no auditory bulla- lacrimal bones absentPectoral girdleEpipubic bones.Cervical ribs.
20Monotremes – Mosaic of primitive and derived characters. Primitive CharactersReproductive characters- oviparous- eggs have huge amount of yolk relative to therians- eggs are shelled - have a shell gland- mammary glands have separate openings, no nipple, andyoung lap milk from tufts of fur rather than suckling.- male lacks a scrotum, and testes remain in the abdominal cavity.- males lack seminal vessicles
21Monotremes – Mosaic of primitive and derived characters. Leathery bill or beak.VenomRaspy pads instead of teeth (as adults).Electroreceptors in bill of platypusesEchidnas have spines.