Researchers have determined that comb jellies came before sponges by analyzing the appearance and placement of genes throughout the branches of life:
For the last decade, zoologists have been battling over the question, "What was the oldest branch of the animal family tree?" Was it the sponges, as they had long thought, or was it a distinctly different set of creatures, the delicate marine predators called comb jellies? The answer to this question could have a major impact on scientists' thinking about how the nervous system, digestive tract, and other basic organs in modern animals evolved.
Now, a team of evolutionary biologists from Vanderbilt University and the University of Wisconsin-Madison have devised a new approach designed specifically to settle contentious phylogenetic tree-of-life issues like this. The new approach comes down squarely on the side of comb jellies.
The method and its application to this and 17 other controversial phylogenetic relationships were published online April 10 by the journal Nature Ecology & Evolution. The article is titled "Resolution of contentious relationships in phylogenomic studies can be driven by one or a handful of genes."
Contentious relationships in phylogenomic studies can be driven by a handful of genes (DOI: 10.1038/s41559-017-0126) (DX)
Phylogenomic studies have resolved countless branches of the tree of life, but remain strongly contradictory on certain, contentious relationships. Here, we use a maximum likelihood framework to quantify the distribution of phylogenetic signal among genes and sites for 17 contentious branches and 6 well-established control branches in plant, animal and fungal phylogenomic data matrices. We find that resolution in some of these 17 branches rests on a single gene or a few sites, and that removal of a single gene in concatenation analyses or a single site from every gene in coalescence-based analyses diminishes support and can alter the inferred topology. These results suggest that tiny subsets of very large data matrices drive the resolution of specific internodes, providing a dissection of the distribution of support and observed incongruence in phylogenomic analyses. We submit that quantifying the distribution of phylogenetic signal in phylogenomic data is essential for evaluating whether branches, especially contentious ones, are truly resolved. Finally, we offer one detailed example of such an evaluation for the controversy regarding the earliest-branching metazoan phylum, for which examination of the distributions of gene-wise and site-wise phylogenetic signal across eight data matrices consistently supports ctenophores as the sister group to all other metazoans.
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Fossils discovered by UNSW scientists in 3.48 billion year old hot spring deposits in the Pilbara region of Western Australia have pushed back by 580 million years the earliest known existence of microbial life on land. Previously, the world's oldest evidence for microbial life on land came from 2.7- 2.9 billion-year-old deposits in South Africa containing organic matter-rich ancient soils.
"Our exciting findings don't just extend back the record of life living in hot springs by 3 billion years, they indicate that life was inhabiting the land much earlier than previously thought, by up to about 580 million years," says study first author, UNSW PhD candidate, Tara Djokic. "This may have implications for an origin of life in freshwater hot springs on land, rather than the more widely discussed idea that life developed in the ocean and adapted to land later."
Scientists are considering two hypotheses regarding the origin of life. Either that it began in deep sea hydrothermal vents, or alternatively that it began on land in a version of Charles Darwin's "warm little pond". "The discovery of potential biological signatures in these ancient hot springs in Western Australia provides a geological perspective that may lend weight to a land-based origin of life," says Ms Djokic.
Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits (open, DOI: 10.1038/ncomms15263) (DX)
Previously:
3.7 Billion-Year-Old Fossil Found
Oldest Evidence of Life on Earth Found in 3.77-4.28 Billion Year Old Fossils
Researchers Use Genetic Analysis to Determine That Comb Jellies Were the Earliest Animals
(Score: 2) by bzipitidoo on Sunday April 16 2017, @03:32AM (2 children)
Seems a chicken and egg problem. I would have thought a herbivorous animal would have been first to evolve, and predators could only evolve after there was something to prey on.
Or am I totally off base, and these early animals cannot so easily and neatly be fitted into herbivore, carnivore, and omnivore categories?
(Score: 2) by takyon on Sunday April 16 2017, @03:43AM
Microbes are *like* little animals eating each other. That seems like the base level of life. Comb jellies [wikipedia.org] may be older than plants [wikipedia.org] as we know them.
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(Score: 1) by khallow on Sunday April 16 2017, @03:56AM
(Score: 0) by Anonymous Coward on Sunday April 16 2017, @04:18AM
Researchers have determined that comb jellies came before sponges
Was expecting an article on the development of sexual reproduction.