Natures wonders: slimy hagfish; Bechly on early vertebrates (Introduction)

by David Turell , Saturday, March 16, 2024, 16:51 (250 days ago) @ David Turell

The messy state of understanding the origin of vertebrates:

https://evolutionnews.org/2024/03/fossil-friday-hagfish-and-lampreys-overturn-establish...

"Hagfish or slime eel are a poorly known group of very primitive jawless marine vertebrates, which lack a vertebral column and lens eyes, but possess a remarkable strategy to escape predators: they can tie themselves in a knot and work through a slippery slime cover that is quickly produced by their skin glands. This slime contains packets of tightly coiled keratin fibres that expand explosively 10,000 times in less than half a second, which is certainly a marvel of biotechnological engineering...For a long time the poor state of knowledge on hagfish embryology represented a significant obstacle for evolutionary biologists, but finally new data “revealed that some apparently primitive morphological traits can be regarded as artifacts deriving mainly from fixation conditions.” Oops!

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"Just a few years ago a seminal study by Miyashita et al. (2021) described new fossil evidence that complete overturned previous well-established views on the phylogeny and evolution of vertebrates (also see Miyashita 2021a, 2021b). This traditional view was based on the striking similarity between invertebrate lancelets (Branchiostoma or Amphioxus) and lamprey ammocoete larvae, which are both functionally blind, eel-like filter-feeders that burrow in sand. The obvious assumption was that this represents the ancestral condition for vertebrates, which was modified in adult cyclostomes into a sucking mouth disk with spikes and modified in gnathostomes into biting jaws. Another implicit assumption is that the filter feeding larvae would be only retained in lampreys, but secondarily reduced in the evolution of hagfish and gnathostomes. This was the textbook scenario that generations of biology students, including myself, learned at university. Miyashita (2021a) admitted that “once fortified with historical inertia, just-so stories are difficult to interrogate. In this case any ammocoete-driven narrative hinges on one prediction: ammocoetes must extend deep into the vertebrate tree. Though seemingly straightforward, this prediction is hard to test.'“(my bold)

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The most recent study by Marlétaz et al. (2024) rather dated the cyclostome-gnathostome split in the Early Cambrian, thus right within the main pulse of the Cambrian Explosion.

As we have seen, hagfish and lampreys present various challenges to mainstream evolutionary biology. Their fossil record as well as their incongruent pattern of anatomical similarities is better explained by intelligent design. This is especially true for the very unique and highly complex feeding apparatus of cyclostomes or the hagfish slime glands, which represent a genuine marvel of engineering.

Comment: Hagfish and lampreys are our origin as the first vertebrates back in the Cambrian. What I have skipped over is Bechly's minute analysis of the battle in the current fossil literature as illustrated in the paragraph with my bold. How critical Bechly is pf his fellow paleontologists is shown in this snippet:

"Thus, the most parsimonious interpretation of the Cyp26A1 evidence would rather favor cyclostome paraphyly, while the other gene families were ambiguous or not informative. That the authors still endorse cyclostome monophyly in spite of their own conflicting data, without even bothering to discuss the issue, shows how much theory and consensus thinking trump data in evolutionary biology nowadays." (my bold)

And this:

"The incongruence goes even further: jawless and jawed vertebrates are sister groups and both possess hemoglobin as an oxygen transport protein. This would suggest that hagfish, lampreys, and gnathostomes inherited this trait from their common craniate ancestor. However, the study by Hoffman et al. (2010) found that that hemoglobin was independently invented in both lineages by cooption of paralogous genes. The press release says “that red-blooded vertebrates evolved twice” (University of Nebraska-Lincoln 2010). The authors concluded that “this example of convergent evolution of protein function provides an impressive demonstration of the ability of natural selection to cobble together complex design solutions by tinkering with different variations of the same basic protein scaffold.” God forbid to consider the obvious alternative of intelligent design." (my bold)

Published to calm down dhw. This explains who Bechly is.