Summary of Nature Article 06277 Essay

1031 Words Nov 14th, 2012 5 Pages
Temporal evolution: is early mammal evolution best characterized by major long branches reaching deep into the Mesozoic and by the long evolutionary fuse that delayed diversification within long branches? short-lived branches with a short evolutionary fuse before diversification?

.Ecological diversification: is lineage splitting of early mammals decoupled from, or correlated with ecological diversification?

.Morphological transformation: are originations of key mammalian characters singular evolutionary events, or iterative convergences despite their complexity?

Temporal pattern of early mammal evolution
The evolution of early mammals occurred in successive diversifications or episodes of quick splitting of relatively short-lived
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The hypothesis of the decoupling of phyletic divergence from ecological diversifications rests on the assumption that the major Mesozoic mammal groups lacked ecological specializations, other than generalized habits. This assumption is now falsified by discoveries of several new Mesozoic mammals with convergences to highly specialized extant mammals.

Fossorial behaviour was documented by taphonomic evidence or some premammaliaform cynodonts, but only recently did the fossorial skeletal specializations (such as scratch digging) become known for mammaliaform lineages.

The hypertrophied digging-limb features and the unique columnar and enamel-less teeth were developed in the Late Jurassic Fruitafossor 150 million years (Myr) ago, 100 Myr before a similar character complex evolved convergently in armadillos and aardvarks, among placentals.

New skeletal fossils suggest that some (although not all) Mesozoic eutherians and metatherians and their near kin also developed such adaptations(climb on uneven terrain) , as shown by the elongate intermediate phalanges and convex profiles of manual and pedal distal phalanges, and in the tarsus, among other skeletal features.

They unveiled a new picture in which ecological diversification is not unique to the Early Cenozoic mammalian radiation, and that many dead-end Mesozoic mammal clades

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