lecture 3 – mammalian diversity: mesozoic mammals & monotremes

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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. Luo et al., (2002). We’ll look first at the Morganucodontids . - PowerPoint PPT Presentation

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Slide 1

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.

Luo et al. (2002).

Well look first at the Morganucodontids.

From the latest Triassic and early Jurassic.

Morganucodontids

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 were present.

Well-developed inner ear region.

Very large eye sockets

Primitive limb girdles.

Best known 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-side chewing.

Insectivorous.

Luo et al. (2002).

Well next look at the Triconodonts.

Triconodonts

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.

Triconodonts

About a meter long, and probably was carnivorous.

Repenomamus.

Hu et al. (2005, Science, 433:139.).

Derived pectoral girdle & ancestral pelvic girdle.

Multituberculates

Rodents of the Mesozoic

Multituberculates

Multituberculates

Diverse and persistent group

Date 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)

Multituberculates

Theres good evidence that at lest some of the multituberculates were arboreal.

Their diversification coincides with the early Cretaceous diversification of

flowering plants (angiosperms).

Theres controversy in the literature, but they probably retained the ancestral

sprawling posture (Keilan-Jaworowska & Hurum 2006).

Retained primitive pectoral and pelvic girdles.

Mesozoic Mammals: Other discoveries

Early Cretaceous (~115 MYA) Have Eutheria-like tribosphenic molars.

Ausktribosphenos

Bishops

Bishops, Ausktribosphenos

Actually related to Monotremes, implying a dual origin for bifunctional teeth.

195 MYA

Three ear ossicles.

Hadrocodium

13

Hadrocodium

This pushes the date for the origin of mammals back.

Morganucodontids

Triconodonts

Multituberculates

Luo et al. Nature 476, 442-445 (2011) doi:10.1038/nature10291

Juramaia sinensis

The oldest eutherian (placental mammal) ~ 160 MYA

In last several years, more diversity has been discovered among Mesozoic mammals.

Luo (2007. Nature, 450:1011)

Monotremes egg-laying mammals.

Cloaca (sewer) - single opening for unrinary, digestive, & reproductive tracts.

Order - Monotremata: One hole

Earliest fossils from Cretaceous (>120 MYA, record poor, but increasing)

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.

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

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.

Order Monotremata, Family Tachyglossidae

Tachyglossus - short-beaked echidna

Zaglossus - long-beaked echidna

21

Order Monotremata, Family Ornithorhynchidae

Ornithorhynchus - platypus

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