Miscellany: gaps in evolution cause discontinuity (General)

by David Turell , Thursday, September 15, 2022, 22:18 (588 days ago) @ David Turell

Look at the amazing complex development in 380-million-year-old fish:

https://www.scientificamerican.com/article/the-oldest-3-d-heart-from-our-vertebrate-anc...

"The two-chambered organs, which date back about 380 million years, are preserved within remarkable three-dimensional fossils of ancient, armored fish called placoderms, which were the first vertebrates to develop jaws more than 400 million years ago. These jawed fish represent an evolutionary leap toward the body plan present in most animals with a backbone today—including humans. The fossils reveal that it didn’t take long for evolution to land on this basic body plan: At this point in evolutionary history, the S-shaped heart in the placoderms was already well separated from the other organs, lodged near the newly evolved jaw. The heart’s separation from the abdominal organs is still seen today.

"The fish fossils also contain livers and intestines, as well as stomachs that are so beautifully preserved that the folds of their lining are still visible. The organs are the oldest preserved in three dimensions in any jawed vertebrate.

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"For 380-million-year-old organs, the structures didn’t look so alien from modern anatomy. The intestines were spiraled like a cinnamon bun, and the stomach had a muscular layer and a layer of glands, indicating that the fish used digestive juices. The two-lobed liver was large and probably helped keep the fish buoyant, much like shark livers do today, Ahlberg says. The heart had two chambers, similar to the hearts of jawless vertebrates such as lampreys, but the chambers were stacked so that the atrium was toward the animal’s back and the ventricle was toward its chest. That’s a shift from the arrangement seen in older jawless vertebrates, where the chambers are oriented side by side, says Maldanis, who was part of a Brazilian team that reported the first-ever fossilized vertebrate heart in 2016. (my bold)

Comment: look at what appeared so quickly. Early fish vertebrates of two types were in the Cambrian. Of course, organs cannot be seen, but must assumed to be present back then. The Ediacarans had nothing like this complexity. Only design fits.