I just read (and then re-read!) the Field et al. 2018 Current Biology paper that this Cosmos Magazine cited and found the six species claim nowhere in the original paper. Help me out here-- are there any data supporting that flashy headline or was it just a sloppy science journalist who overinterpreted the results?
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I donāt really see where the 6 came fromā¦ the Field et al. paper wasnāt really about determining how many species crossed the K-Pg boundary. They based their analyses on two bird phylogenies that existed at the time. One of them, Prum et al 2015 āA comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencingā estimated about six extant lineages that existed before or just after the K-Pg boundary (Palaeognaths, Galloanserae, Strisores, Columbaves, Gruiformes, and a group including all other birds) so Iām guessing thatās where the six comes from.
But to claim that 6 species survived the extinction assumes:
- that the Prum et al. phylogeny (or whichever the reporter was referring to) was correct, and accurately determined which lineages pre-date the K-Pg boundary (in reality the timing of bird diversification is far from settled and very difficult to date accurately, other phylogenies show many more lineages predating the K-Pg)
- that all the species that survived the K-Pg extinction went on to produce successful lineages that survived to this day. In reality there were certainly many birds at that time whose lineages went extinct later, and so we donāt know about them.
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It may be an over-interpretation, ālineagesā is probably a better term. Regardless, it was a very small number with low initial diversity that made it through the extinction event.
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Iām a big fan of Punctuated Equilibrium! It has a philosophical consistency that appeals to me. Iāve been thinking about starlings and house sparrows over the years. Both are introduced to North America (albeit a short time ago in geological terms), and both have spread widely. As far as I know they are morphologically the same as when they were introduced. Has there been any work done to compare their genome to those found in Eurasia?
And another question - what does K-Pg stand for? Iāve always read K-T, but I donāt keep up on changes.
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Agreed. The easiest way Iāve discovered for getting people to understand the relationships a little better are using their own family relationships. Many people hear āclosest relativeā and think āMomā. And since this is as far they got, t-rex must be a chickenās āmomā or great, great, great, lot-of greats, grandma. I tell them to think about a cousin instead. Their moms and grand parents may be gone leaving that cousin as their āclosest relativeā. Systematics works similarly. And lousy record keeping means that we might be able to figure out whoās more closely related to who but we may never figure out who that great grandma actually was.
A few people have nodded like this explanation opened up a small glimmer of understanding.
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A picture is worth a thousand wordsā¦
https://evolution.berkeley.edu/evolibrary/article/evograms_06
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The Tertiary is no longer accepted as a bona fide period and has been replaced by the Paleogene and Neogene, so K-Pa now stands for the same boundary that K-T used to refer to. Itās like a geological version of a taxonomic synonymy-- once paleontologists realized the ātype specimensā werenāt actually representative of a global change (mullosks from all over the world didnāt line up in the same time periods) they had to make new definitions of the geologic periods, and the new system didnāt have a place for the Tertiary. Thereās a brief explanation at Wiki: https://en.wikipedia.org/wiki/Tertiary
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Thank you!
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Absolutely, there has been some work sequencing a portion of the genome of starlings in North America, a good reference is āEnvironmental correlates of genetic variation in the invasive European starling in North Americaā by Hofmeister et al. 2021. That study found that the starlings are relatively homogenous across the whole continent (likeā¦ extremely low differentiation), but a few parts of the genome show tentative signs of adaptation to different climates (temperature & precipitation). There hasnāt been enough time for very many new mutations to accumulate, but given a few hundred thousand years the North American starlings might become their own species.
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Thank you!
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You have to have some criteria for assessing relationships, and when it comes to nuance, particularly of extinct species or cryptic species, genetics is about as nuanced as you can get.
Behavior is often considered as well in extant species.
What would you propose people use instead of genetics, taxonomy, and behavior?
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Wait ā the modern-day Order Gruiformes had already formed by then?
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I wouldnāt feel comfortable making any confident statements since the relationships of the deep branches and their timing is still a bit unresolved in birds, but so far thatās what the data suggests - for example the Prum et al. 2015 phylogeny puts the divergence of Gruiformes from their sister group at about 66.5 MYA. They might not have looked like what we would recognize as Gruiformes today since the different Gruiform groups like rails, cranes, sunbittern etc didnāt separate from each other until a bit later.
If youāre interested in looking at the bird phylogeny you can see it without a paywall here: https://www.researchgate.net/publication/282651425_A_comprehensive_phylogeny_of_birds_Aves_using_targeted_next-generation_DNA_sequencing
(Keep in mind this is from 6 years ago so the consensus about some of the branches has changed since then)
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And?..
Did you read that report?
First off, it doesnāt have anything to with the issue of species classification or anything else related to that, it has specifically to do with health.
Setting that rather major issue aside, it doesnāt propose or even hint at a change to using genetics to sort out potential health issues, it raises the issue of diet, exercise, etc (eg. behaviors, something already included in the previous comment about species classification criteria), and the role of the environment (something at the foundation of the principle of evolution via natural selection). The report is about how these factors influence gene expression, which is part of the sub-field of epigenetics.
Gene expression and epigenetics are very much part of the field of genetics, so that report is coming out in favor of what we are already doing, just calling attention to some of the more difficult to parse nuances in the field.
Very little of anything in that report is relevant to the issue of long extinct species and which ones survived as we canāt look at epigenetics and gene expression of those long vanished species, or of the ancestors to extant species, and we already look very closely at the environments these organisms lived and at what can interpret from the fossil record of their behaviors.
Not only is that reference not proposing using anything different to aid in classification, itās not really relevant as the things it does mention are already a major part of what we already look at in the zoological and paleontological sciences. So much so that they are specific sub-fields that people have been specializing in for a long time.
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You mean, doing exactly what people do in the present day? And what people are limited to when looking at long extinct organisms?
Just because we have added genetic analysis to our toolkit in modern times doesnāt mean that weāve abandoned useful and relevant older methods. In fact, those have been refined and added too as well.
Looking at the convergence of homologous structures from the macro scale (eg, wings, beaks, wrist joints, eyes, etc) down to the micro level (eg. different genes that wind up leading to similar traits in different organisms via different pathways, or different pathways to the same function in a single species, such as lactose tolerance in humans which as evolved multiple times and is more evidence for convergent evolution* ) is still a fundamental aspect of modern evolutionary and biological sciences studies.
Thatās quite literally suggesting that people do exactly what they are already doing.
- *Gerbault, et al 2011 Evolution of lactase persistence: an example of human niche construction
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Boy, the Opisthocomus (Hoatzin) branch spit off a long time ago. not surprising considering how weird they are, but thatās an impressive amount of time for a narrow branch to survive.
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Well, Iām not sure exactly what you mean by that, but as a geneticist studying bird evolution I would have to object 
If you mean that we still have a poor understanding of what many genes do and how specific mutations affect phenotype, then I would agree, but I think that is a reason to motivate more research, not avoid genetics.
I went into this field because I want to understand how birds evolve and how different species arise. Genetics allows you to answer questions that would be guesswork - or at least much more difficult - with any other methods, for example:
- Do the morphological differences between Population A and Population B reflect a single genetic difference, or many accumulated differences? Is it variation within a single species, or are they reproductively isolated?
- How often does Population A successfully interbreed with Population B in the wild?
- Do hybrids between Population A and Population B have less fitness than their parents?
- Did two species with the same trait evolve that trait convergently, or was it homologous? Did convergent evolution use the same mechanism, or different mechanisms to make the same trait in different species?
- Does species A look a bit more like species C because they hybridized, or is it convergence?
- How long ago did Species A and Species B divergence from each other, and what biogeographical events could have caused it?
Evolutionary genetics is a very different field than taxonomy, although genetics can inform taxonomic decisions.
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Well, you say modern science is doing it wrong, that genetic studies are going in parallel universe where no other methods exist, so they canāt collaborate, and old times were better, you should prove your point, not by just saying āyou have to read it to understand meā.
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I think youāll find that we have read the resources you, and others, have mentioned, and thatās in part why we have had those responses.
Iād suggest that an approach that is more modern and inclusive than one from the 18th century, one that includes and uses many of the very things you are suggesting that need to be considered, is the more powerful and appropriate tool to use when attempting to parse out challenging relationships between species and branches of life.
There are a lot of good and accessible resources out there that can be used to gain a bit more understanding of modern approaches to studies of evolution and taxonomy. Perhaps a bit more familiarity with some of them might be useful?
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