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The new framework for understanding placental mammal evolution.
Abstract: An unprecedented level of confidence has recently crystallized around a new hypothesis of how living placental mammals share a pattern of common descent. The major groups are afrotheres (e.g., aardvarks, elephants), xenarthrans (e.g., anteaters, sloths), laurasiatheres (e.g., horses, shrews), and euarchontoglires (e.g., humans, rodents). Compared with previous hypotheses this tree is remarkably stable; however, some uncertainty persists about the location of the placental root, and (for example) the position of bats within laurasiatheres, of sea cows and aardvarks within afrotheres, and of dermopterans within euarchontoglires. A variety of names for sub-clades within the new placental mammal tree have been proposed, not all of which follow conventions regarding priority and stability. More importantly, the new phylogenetic framework enables the formulation of new hypotheses and testing thereof, for example regarding the possible developmental dichotomy that seems to distinguish members of the newly identified southern and northern radiations of living placental mammals.
Publication Date: 2009-07-08 PubMed ID: 19582725DOI: 10.1002/bies.200900053Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- Non-U.S. Gov't
- Review
Summary
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The research article presents a new theoretical framework for understanding the evolutionary relationships among living placental mammals, highlighting a more stable tree of descent compared to previous hypotheses. Still, certain areas of uncertainty persist, including the origin of the placental root and the exact positioning of some species within their major groups.
Evolving Understanding of Placental Mammal Evolution
In the body of the paper, the authors discuss the development and strengthening of a new hypothesis regarding the common descent patterns among living placental mammals, which includes species like elephants, horses, humans, and many others. These mammals are categorized into four major groups:
- Afrotheres: This group includes aardvarks, elephants, and sea cows.
- Xenarthrans: This group consists of anteaters and sloths.
- Laurasiatheres: This group encompasses horses, shrews, and potentially bats.
- Euarchontoglires: This group includes humans, rodents, and possibly dermopterans.
Compared to previous hypotheses, the researchers found this tree of descent to be remarkably more stable.
Uncertainties in the New Framework
Despite the promise shown by this new hypothesis, the authors acknowledged there remain uncertainties. These included determining the location of the placental root—the point from which all placental mammals evolved. The exact positions of sea cows and aardvarks within afrotheres, bats within laurasiatheres, and dermopterans within euarchontoglires were also areas of uncertainty.
Implications of the New Phylogenetic Framework
The authors not only proposed a new rubric for understanding the nomenclature used within the phylogenetic tree but also appreciated the potential of this new framework in enabling the formulation and testing of new hypotheses. For instance, this framework could explore the developmental dichotomy that appears to differentiate members of the newly identified southern and northern radiations of living placental mammals.
In conclusion, this research presented an evolved understanding of placental mammal evolution, acknowledging the existing uncertainties, and pointing towards new directions for further study.
Cite This Article
APA
Asher RJ, Bennett N, Lehmann T.
(2009).
The new framework for understanding placental mammal evolution.
Bioessays, 31(8), 853-864.
https://doi.org/10.1002/bies.200900053 Publication
Researcher Affiliations
- Department of Zoology, University of Cambridge, Downing St., Cambridge CB23EJ, UK. r.asher@zoo.cam.ac.uk
MeSH Terms
- Animals
- Biological Evolution
- Dentition
- Female
- Mammals / classification
- Mammals / physiology
- Phylogeny
- Placenta / physiology
- Pregnancy
- Spine / pathology
Citations
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