Robust time estimation reconciles views of the antiquity of placental mammals

Apr 18, 2007

Despite great progress over the past decade, the evolutionary history of placental mammals remains controversial. While a consensus is emerging on the topology of the evolutionary tree, although with occasional disagreement, divergence times remain uncertain.

The age of earlier nodes and in particular the root, remain especially uncertain in the absence of definitive placental fossils deeper into the Cretaceous. Both paleontological and morphological studies suggest that the radiation of placental orders and super orders occurred close to the Cretaceous–Tertiary (K–T) boundary about 65 million years ago (mya). In contrast, molecular studies have suggested markedly older origins for many superordinal groups and that some extant orders diversified before the K–T boundary.

However, this discrepancy may not be real, but rather appear because of the violation of implicit assumptions in the estimation procedures, such as abrupt acceleration of evolutionary rate entangled with gradual variation and large-scale convergent evolution in molecular level.

By their new robust procedure, Dr. Kitazoe and his collaborators identified a strong and short-term acceleration of mitochondrial genome along the lineage leading to Laurasiatheria. The revised time at the root of placental mammals was much younger than the preceding reports, 84 million years ago instead of around 122 million years ago.

As a result, the estimated distribution of molecular divergence times is broadly consistent with quantitative analysis of the North American fossil record and traditional morphological views. They emphasize the necessity to scrutinize the implicit assumptions adopted by the models of molecular evolution and to develop procedures which rely little on those assumptions.

Citation: Kitazoe Y, Kishino H, Waddell PJ, Nakajima N, Okabayashi T, et al (2007) Robust Time Estimation Reconciles Views of the Antiquity of Placental Mammals. PLoS ONE 2(4): e384. doi:10.1371/journal.pone.0000384

Source: Public Library of Science

Explore further: Dwindling wind may tip predator-prey balance

add to favorites email to friend print save as pdf

Related Stories

Tree rings and arroyos

38 minutes ago

A new GSA Bulletin study uses tree rings to document arroyo evolution along the lower Rio Puerco and Chaco Wash in northern New Mexico, USA. By determining burial dates in tree rings from salt cedar and wi ...

Montreal VR headset team turns to crowdfunding for Totem

42 minutes ago

A challenger in the virtual reality headset marketplace has launched a crowdfunding campaign to get the project off the ground. The headset is called Totem. The company behind Totem is Montreal-based Vrvana. ...

Recommended for you

Dwindling wind may tip predator-prey balance

15 hours ago

Bent and tossed by the wind, a field of soybean plants presents a challenge for an Asian lady beetle on the hunt for aphids. But what if the air—and the soybeans—were still?

Environmental pollutants make worms susceptible to cold

20 hours ago

Some pollutants are more harmful in a cold climate than in a hot, because they affect the temperature sensitivity of certain organisms. Now researchers from Danish universities have demonstrated how this ...

Research helps steer mites from bees

22 hours ago

A Simon Fraser University chemistry professor has found a way to sway mites from their damaging effects on bees that care and feed the all-important queen bee.

User comments : 0