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Researchers: Mammals’ “arms” backdated 100 million years; predate dinosaurs

Denyse O'Leary
March 19, 2019
Intelligent Design, stasis
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A variety of bones from early mammal relatives/ (c) Jacqueline Lungmus, Field Museum

From ScienceDaily:

Bats fly, whales swim, gibbons swing from tree to tree, horses gallop, and humans swipe on their phones — the different habitats and lifestyles of mammals rely on our unique forelimbs. No other group of vertebrate animals has evolved so many different kinds of arms: in contrast, all birds have wings, and pretty much all lizards walk on all fours. Our forelimbs are a big part of what makes mammals special, and in a new study in the Proceedings of the National Academy of Sciences, scientists have discovered that our early relatives started evolving diverse forelimbs 270 million years ago — a good 30 million years before the earliest dinosaurs existed.

“Aside from fur, diverse forelimb shape is one of the most iconic characteristics of mammals,” says the paper’s lead author Jacqueline Lungmus, a research assistant at Chicago’s Field Museum and a doctoral candidate at the University of Chicago. “We were trying to understand where that comes from, if it’s a recent trait or if this has been something special about the group of animals that we belong to from the beginning.” …

Lungmus and Angielczyk found that a wide variety of different forelimb shapes evolved within the therapsids 270 million years ago. “The therapsids are the first synapsids to increase the variability of their forelimbs — this study dramatically pushes that trait back in time,” says Lungmus. Prior to this study, the earliest that paleontologists had been able to definitively trace back mammals’ diverse forelimbs was 160 million years ago. With Lungmus and Angielczyk’s work, that’s been pushed back by more than a hundred million years. Paper. (open access) – Jacqueline K. Lungmus, Kenneth D. Angielczyk. Antiquity of forelimb ecomorphological diversity in the mammalian stem lineage (Synapsida). Proceedings of the National Academy of Sciences, 2019; 201802543 DOI: 10.1073/pnas.1802543116 More.

So many good ideas seem to have got started quite early and been around nearly forever. One wonders if flexible forelimbs got started quickly too…

See also: “Super-Ancient Mobile Organisms” Push Mobile Life Back To 2.1 Billion Years Ago

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Stasis: Life goes on but evolution does not happen

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Comments
“scientists have discovered that our early relatives started evolving diverse forelimbs 270 million years ago — a good 30 million years before the earliest dinosaurs existed.” Did they discover how the developmental processes of the different varieties evolved? Here’s a tip: The Choreography of Fertilization Coticchio G., Brambillasca F. Coticchio G., Albertini D., De Santis L. (eds) Oogenesis. 2013. Springer, London. DOI: 10.1007/978-0-85729-826-3_20
At fertilization, a continuum is established between the final phases of oogenesis and the formation of a new individual. In mammals, the two processes are overlapped. The fertilizing spermatozoon represents the paternal contribution to zygote constitution and at the same time the trigger for the completion of meiosis. Oocytes can mimic fertilization, being able to recapitulate autonomously many of the events of early embryonic development. However, without the sperm contribution development to term cannot occur. The sperm, in fact, carries not only the paternal chromosomes, but also cytoskeletal elements and biochemical cues that are essential to complement and regulate the oocyte cellular legacy. Therefore, oocyte-sperm fusion creates a unique cellular machinery whose regulation in time and space influences the long term destiny of the ensuing embryo.
Embryonic development: how cell choreography shapes animals
Just as the collective movements of many dancers are needed to perform the choreography in a ballet, the collective behavior of many cells is required to perform the movements that shape our bodies during embryogenesis. Amazingly, the complex shapes and patterns of many animals come from a spherical, single cell embryo.
OLV
perhaps the earliest known evidence of mammals predates the earliest known dinos, by a relatively small margin, it does not mean they did not both start out at the same time, or dinos a literal partial day prior as we hold based on the Moshe Emes series and framework for understanding science. Pearlman
Brother Bogart:
Are reptile forelimbs any less diverse that mammal forelimbs?
Yes. The shoulder joint of mammals allows for many variations on the same theme. The shoulder joint of lizards and reptiles is much more restrictive as to what it can support for a limb. ET
Quoted text: “scientists have discovered that our early relatives started evolving diverse forelimbs 270 million years ago — a good 30 million years before the earliest dinosaurs existed.” Did they discover how that happened? Or just observed the variety? Do they show how the developmental processes of the different varieties came to be? OLV
Are reptile forelimbs any less diverse that mammal forelimbs? Brother Brian

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