Lecture 3 – Mammalian Diversity: Mesozoic Mammals & Monotremes Luo et al., (2002). Node labeled 1...
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Transcript of Lecture 3 – Mammalian Diversity: Mesozoic Mammals & Monotremes Luo et al., (2002). Node labeled 1...
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Lecture 3 – Mammalian Diversity: Mesozoic Mammals & Monotremes
Luo et al., (2002).
Node labeled 1 indicates our (stable) clade-based definition of Mammalia.
This is the commonly used crown-clade definition.
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Luo et al., (2002).
We’ll look first at the Morganucodontids.From the latest Triassic and early Jurassic.
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Best 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 sockets
Primitive limb girdles.
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Best know from the genus Morganucodon.
Dentary was greatly expanded.
Articular was small and still present.
The angular was on mandible
Cheek teeth had three cusps
Alternate-site chewing.
Insectivorous.
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Luo et al., (2002).
We’ll next look at the Triconodonts.
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Triconodonts
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.
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Triconodonts
About a meter long, and probably was carnivorous.
Repenomamus.
Hu et al., 2005, Science, 433:139
Derived pectoral girdle & ancestral pelvic girdle.
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Multituberculates
“Rodents of the Mesozoic”
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Multituberculates
Diverse and persistent group• Dates from upper Jurassic, spans Cretaceous-Tertiary, coextisted with
modern mammals• Mouse-sized to marmot-sized
Named for unique dentition• Chisel-like incisors• Large diastema• Complex, grinding molars (source of name)
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Multituberculates
There’s good evidence that at lest some of the multituberculates were arboreal.
Their diversification coincides with the early Cretaceous diversification of flowering plants (angiosperms).
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Paraphyletic- used informally
• Mid Jurassic
• Earliest bifunctional teeth - single cheek tooth with grinding and shearing function.
• Tribosphenic molars, ( primitive tooth type for living mammals)
“Pantotheres”
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Bishops, Ausktribosphenos
Mesozoic Mammals: Recent discoveries
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Bishops, Ausktribosphenos
Actually related to Monotremes, implying a dual origin for bifunctional teeth.
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195 MYA
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Hadrocodium
This pushes the date for the origin of mammals back.
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Z-X Luo et al. Nature 476, 442-445 (2011) doi:10.1038/nature10291
Juramaia sinensis
The oldest eutherian (placental mammal) ~ 160 MYA
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Just in last few years, more diversity has been discovered among Mesozoic mammals.
Luo (2007. Nature, 450:1011)
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Monotremes – 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)
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Monotremes – Mosaic of primitive and derived characters.
Primitive Characters
Cloaca
Skull characters - possess pre- and post frontal bones.- no auditory bulla- lacrimal bones absent
Pectoral girdle
Epipubic bones.
Cervical ribs.
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Monotremes – Mosaic of primitive and derived characters.
Primitive Characters
-Reproductive 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, and young lap milk from tufts of fur rather than suckling.
- male lacks a scrotum, and testes remain in the abdominal cavity.
- males lack seminal vessicles
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Monotremes – Mosaic of primitive and derived characters.
Derived Characters
Venom
Leathery bill or beak.
Raspy pads instead of teeth (as adults).
Electroreceptors in bill of platypuses
Echidnas have spines.
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Order Monotremata, Family Tachyglossidae
Tachyglossus - short-beaked echidna
Zaglossus - long-beaked echidna
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Order Monotremata, Family OrnithorhynchidaeOrnithorhynchus - platypus