Re: Avian evolution

On 7/11/24 10:19 PM, Volney wrote:

On 5/4/2024 6:09 AM, Pandora wrote:

Complexity of avian evolution revealed by family-level genomes
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Abstract
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Despite tremendous efforts in the past decades, relationships among main avian lineages remain heavily debated without a clear resolution. Discrepancies have been attributed to diversity of species sampled, phylogenetic method and the choice of genomic regions1,2,3. Here we address these issues by analysing the genomes of 363 bird species4 (218  taxonomic families, 92% of total). Using intergenic regions and coalescent methods, we present a well-supported tree but also a marked degree of discordance. The tree confirms that Neoaves experienced rapid radiation at or near the Cretaceous–Palaeogene boundary. Sufficient loci rather than extensive taxon sampling were more effective in resolving difficult nodes. Remaining recalcitrant nodes involve species that are a challenge to model due to either extreme DNA composition, variable substitution rates, incomplete lineage sorting or complex evolutionary events such as ancient hybridization. Assessment of the effects of different genomic partitions showed high heterogeneity across the genome. We discovered sharp increases in effective population size, substitution rates and relative brain size following the Cretaceous–Palaeogene extinction event, supporting the hypothesis that emerging ecological opportunities catalysed the diversification of modern birds. The resulting phylogenetic estimate offers fresh insights into the rapid radiation of modern birds and provides a taxon-rich backbone tree for future comparative studies.
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Open access:
https://www.nature.com/articles/s41586-024-07323-1

 I was thinking that since birds don't seem to have very much variation from the basic bird body plan, could it be possible that exactly one species survived the K-T event, and all modern birds are descended from it? When would the MRCA of all birds have lived? Older protobirds seem to have more variations not seen today. Some have teeth, some have claws on wings, long tails and/or 4 wings/feathered legs are also wings*.

Given phylogeny, there must be at some point one species ancestral to all modern birds. When that species lived is hard to be sure of. Molecular estimates range from around 120ma to 70ma or so. But it does appear that more than one bird species survived the K/T extinction. Just how many depends on how you time-calibrate the tree and on how you interpret a few Cretaceous fossils. But I'd say it's very unlikely for there to be a single surviving species.
A lot depends on just what Vegavis is. But it seems fairly certain that the paleognath, galloanserine, and neoavian lineages existed in the Late Cretaceous, at least.

(*) I have two bantam chickens with feathers on their legs and two of their claws on each foot. Could this be an old "4 wing" gene becoming reactivated? Or are chickens just more prehistoric? The bantams seem to fly a little better than non-bantam chickens, but that's probably just because they are very small. I haven't seen them try to flap their legs...

There is no "4-wing gene", just different expression patterns of the genes that make feathers. You're looking at some change in gene regulation, turning on genes in a particular place and time. There are plenty of other birds with feathers on their legs and/or toes. Ptarmigans, for example.