What fossils can tell us about the evolution of viviparity and placentation.
Abstract: Recently a fossil of one of the earliest jawed fishes was found with a fetal skeleton and the remains of a cord. It was from the Devonian period and takes the history of vertebrate placentation back to 380 million years ago. This and later fossil evidence for viviparity in marine reptiles and early mammals is reviewed. Of particular interest are the fossils of horses as they document that a reproductive strategy with a single precocial newborn was evolved early on. In one instance there is sufficient representation of soft tissue to imply that early horses had a diffuse placenta, much as had been predicted by phylogenetic analyses of placentation.
Publication Date: 2008-09-06 PubMed ID: 18774606DOI: 10.1016/j.placenta.2008.07.012Google Scholar: Lookup
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Summary
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The research paper discusses a fossil discovery that sheds light on the evolution of viviparity (live birth) and placentation in vertebrates, revealing this process could have begun as far back as 380 million years ago.
Background
- The study is centered around a significant fossil discovery – a preserved fetal skeleton and cord within an ancient jawed fish dating back to the Devonian period.
- This fossil marks the earliest known evidence of vertebrate placentation, significantly extending the ancestry of this characteristic back to 380 million years ago.
Fossil Evidence for Viviparity
- The research offers a review of fossil evidence related to viviparity, which represents the condition where young are born alive rather than being hatched from eggs.
- Specifically, it highlights fossil proof of viviparity present in marine reptiles and early mammals, marking a significant evolutionary advance.
Evolutionary implications of Horse Fossils
- The fossils of horses provide essential insight into early viviparity. It was shown that horses, from an early stage, had adopted a reproductive strategy that favored a single, well-developed newborn, also known as being precocial.
- This indicates a significant early shift from a strategy of producing numerous underdeveloped offspring (which is common among reptiles and fishes) towards producing fewer, more mature newborns – a strategy predominantly seen in mammals today.
Early Placentation in Horses
- In one particular instance of a preserved horse fossil, the preserved soft tissues hint towards the existence of a diffuse placenta.
- This supports predictions made by previous phylogenetic analyses of placentation, which suggested that diffuse placentas were present in earliest horses.
Conclusion
- The research concludes by asserting that these fossils increase our understanding of the evolutionary trajectory of viviparity and placentation. In essence, they show the reproductive strategies have evolved over an even longer period than previously thought.
Cite This Article
APA
Carter AM.
(2008).
What fossils can tell us about the evolution of viviparity and placentation.
Placenta, 29(11), 930-931.
https://doi.org/10.1016/j.placenta.2008.07.012 Publication
Researcher Affiliations
- Department of Physiology and Pharmacology, University of Southern Denmark, J. B. Winsloewvej 21, Third Floor, DK-5000 Odense, Denmark. acarter@health.sdu.dk
MeSH Terms
- Animals
- Biological Evolution
- Female
- Fossils
- Mammals
- Placenta
- Viviparity, Nonmammalian
Citations
This article has been cited 2 times.- Laird MK, McShea H, McAllan BM, Murphy CR, Thompson MB. Uterine remodelling during pregnancy and pseudopregnancy in the brushtail possum (Trichosurus vulpecula; Phalangeridae).. J Anat 2017 Jul;231(1):84-94.
- Franzen JL, Aurich C, Habersetzer J. Description of a Well Preserved Fetus of the European Eocene Equoid Eurohippus messelensis.. PLoS One 2015;10(10):e0137985.
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