http://www.bbc.co.uk/nature/28563682
Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, scientists have revealed.
Theropods shrunk 12 times from 163kg to 0.8kg before becoming modern birds.
The researchers found theropods were the only dinosaurs to get continuously smaller.
Their skeletons also changed four times faster than other dinosaurs, helping them to survive.
They found that the dinosaur group directly related to birds shrank rapidly from about 200 million years ago.
It showed a decrease in body mass of 162.2kg (25st 7lb) from the largest average body size to Archaeopteryx, the earliest known bird.
These bird ancestors also evolved new adaptations, including feathers, wishbones and wings, four times faster than other dinosaurs.
Shrinking and new bird-like traits jointly influenced the transition of dinosaurs to birds, researchers say.
The researchers concluded that the evolution of the branch of dinosaurs leading to birds was more innovative than other dinosaur lineages.
http://blogs.scientificamerican.com/tetrapod-zoology/2014/07/31/50-million-years-of-shrinking-theropod-dinosaurs/
| Because our results allow us to map the appearance dates of lineages onto the phylogeny, we can see that evolutionary rates across part of the lineage leading to birds occurred much faster than expected compared to the rest of the tree – up to four times faster, in fact (Lee et al. 2014a). This seemingly explains why several groups of tetanuran theropods – allosauroids, tyrannosauroids, compsognathids and others – appear near-simultaneously in the fossil record: it seems that the time intervals between their originations really were very short. Why evolution was occurring so rapidly in these animals remains, of course, an unknown. |
The study itself:
Abstract:
http://www.sciencemag.org/content/345/6196/562
Full study:
http://www.researchgate.net/publication/264386153_Sustained_miniaturization_and_anatomical_innovation_in_the_dinosaurian_ancestors_of_birds
The study Supplementary Material:
https://www.academia.edu/7832790/Lee_M.S.Y._Cau_A._Naish_D._Dyke_G.J._2014._Sustained_miniaturization_and_anatomical_innovation_in_the_dinosaurian_ancestors_of_birds._Science_345_562-566_NOTE_SM_below_has_hi-res_figures_which_were_pixellated_on_the_Science_SM_pdf_
Also see here:
http://pterosaurnet.blogspot.ca/2014/03/body-size-and-forelimb-length.html
Comparison with the Cambrian Explosion
https://www.academia.edu/4371818/Lee_M.S.Y._Soubrier_J._and_Edgecombe_G.D._2013._Rates_of_phenotypic_and_genomic_evolution_during_the_Cambrian_Explosion._Current_Biology_23_1889-1895_4_files_-_main_text_2_SI_files_Commentary_
The near-simultaneous appearance of most modern animal body plans (phyla) ~530 million years ago during the Cambrian explosion is strong evidence for a brief interval of rapid phenotypic and genetic innovation, yet the exact speed and nature of this grand adaptive radiation remain debated [1–12]. Crucially, rates of morphological evolution in the past (i.e., in ancestral lineages) can be inferred from phenotypic differences among living organisms—just as molecular evolutionary rates in ancestral lineages can be inferred from genetic divergences [13]. We here employed Bayesian [14] and maximum likelihood [15] phylogenetic clock methods on an extensive anatomical[16]and genomic[17] data set for arthropods, the most diverse phylum in the Cambrian and today. Assuming an Ediacaran origin for arthropods, phenotypic evolution was ~4 times faster, and molecular evolution ~5.5 times faster, during the Cambrian explosion compared to all subsequent parts of the Phanerozoic. These rapid evolutionary rates are robust to assumptions about the precise age of arthropods. Surprisingly,these fast early rates do not change substantially even if the radiation of arthropods is compressed entirely into the Cambrian (~542 mega-annum [Ma]) or telescoped into the Cryogenian (~650 Ma). The fastest inferred rates are still consistent with evolution by natural selection and with data from living organisms, potentially resolving ‘‘Darwin’s dilemma.’’ However, evolution during the Cambrian explosion was unusual (compared to the subsequent Phanerozoic) in that fast rates were present across many lineages.This means that the dino to bird theory is right up there with the Cambrian Explosion in terms of it being very unusual.
The near-simultaneity and the much faster rates of evolution required by the dino to bird theory are VERY UNUSUAL. As unusual as the Cambrian Explosion.
Also:
http://www.evolutionnews.org/2013/09/how_to_solve_th076861.html
http://www.uncommondescent.com/intelligent-design/darwins-dilemma-remains-unresolved-what-lees-paper-didnt-discuss/
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ReplyDeleteThere is an oddity in the way the authors put it.
They see that several groups of tetanuran theropods – allosauroids, tyrannosauroids, compsognathids and others – appear near-simultaneously in the fossil record.
What they should then say is that the evolutionary rates must have been up to four times faster, for the dino to bird theory to be correct.
Instead they say that the four times faster rate seemingly "explains" why several groups of tetanuran theropods – allosauroids, tyrannosauroids, compsognathids and others – appear near-simultaneously.
That way of putting it is obviously false. The faster rate does not "explain" it.
In fact, they give NO explanation. Because they have no explanation.
The way they put it is a very subtle form of begging the question.
As is often the case, subtle question begging is hard to see at first.
And then as if to double down they say:
"Why evolution was occurring so rapidly in these animals remains, of course, an unknown".
But in fact, they do not know that evolution was occurring rapidly in these animals. That is a conclusion they came to based on the near simultaneity and their belief in the dino to bird theory.
They have no independent evidence that evolution was occurring rapidly. But they put it as if the four times faster rate was a fact.
Here is the honest straightforward way it should be put:
The evolutionary rates must have been up to four times faster, for the dino to bird theory to be correct.
When put that way, our thought would logically be:
"Hmm. Then maybe the dino to bird theory is not correct".
It is interesting that S8 (Data Set 1) and S9 (Data Set 2) do not show a decrease in size.
ReplyDeletehttps://www.academia.edu/7832790/Lee_M.S.Y._Cau_A._Naish_D._Dyke_G.J._2014._Sustained_miniaturization_and_anatomical_innovation_in_the_dinosaurian_ancestors_of_birds._Science_345_562-566_NOTE_SM_below_has_hi-res_figures_which_were_pixellated_on_the_Science_SM_pdf_
They are "based on parsimony (cladistic) analysis".
So there is an oddity.
Decreases only appear when they use a particular method. And that method includes stratigraphic information.
BUT the stratigraphic information is based on ghost lineages of up to tens of millions of years
http://www.researchgate.net/publication/264386153_Sustained_miniaturization_and_anatomical_innovation_in_the_dinosaurian_ancestors_of_birds
ReplyDeleteSee Figure 3.
Notice the red line connecting the compsognathid branch and the ornithomimosaur branch.
This is an indication that they are not similar.
Of course one is a dinosaur and the other is a secondarily flightless member of paraves, so that is exactly what one would expect.
http://www.evolutionnews.org/2013/06/erwin_valentine_cambrian_explosion073671.html
ReplyDeleteWhat is great about the Lee et al study is it dramatically shows what the dino to bird THEORY really requires. It requires "sustained miniaturization" and a series of "4 times faster evolution" which is effectively impossible.
ReplyDeleteConsequently the theory itself is effectively impossible.
Keep in mind that it is a THEORY. But it cannot be correct, as the Lee et al study shows.
An interim step that the dino to bird theorists could adopt is to accept that the so-called "non-paraves maniraptors" are not transitional between dinosaurs and birds, but rather secondarily flightless members of Paraves.
But that is jumping from the frying pan into the fire.
In that case it will not require a "sustained miniaturization" nor a series of "4 times faster evolutions".
It will require ONE enormous leap!
Everyone knows this and that is why they keep pretending that the so-called "non-paraves maniraptors" are transitional between dinosaurs and birds - in spite of the ghost lineages up to tens of millions of years.
But Lee et al have blown that pretense completely out of the water.