February 21, 2022 | Jerry Bergman

No Evidence for the Evolution of Crab Eyes

This crab eye was complete,
well-developed and functional,
with soft tissue preserved.

 

by Jerry Bergman, PhD

Scientists have discovered a new kind of fossil crab with huge eyes that was probably a free-swimming predator. Found in mid-Cretaceous strata Darwin-dated at 95 million years old, the perplexing creature has been named Callichimaera perplexa. Its swimming habit is especially unusual because modern adult crabs “scuttle across the floors of silent seas, hardly reliant on small eyes as they scavenge or graze.”[1]

Artistic rendition of the extinct crab Callichimaera perplexa depicting the crab swimming after a male comma shrimp, Eobodotria muisca (Cumacea). Notice the gigantic eyes. Illustration courtesy of Masato Hattori.

The new crab possessed a combination of anatomical features so strange it is called the “platypus of crabs,” so bizarre that it has forced a redefinition of what is a crab.[2] The headline of a study published in the journal Cell indicates how surprising this creature was: “The remarkable visual system of a Cretaceous crab.”[3] The authors believe that “True crabs (Brachyura) are one of the few groups of arthropods to evolve several types of compound eyes” but, they acknowledge, they currently have no evidence of its supposed evolution. For this reason, the researchers admitted, with regard to the compound eyes of these extinct crabs, that

the origins and early evolution of which are obscure…. the origins and evolution of their visual systems remain poorly constrained…. Although the ocular anatomy is preserved in exquisite detail in several specimens of C. perplexa and demonstrates the unique visual system in this crab, it does not reveal the origin and evolution of the many types of compound eyes found in extant crabs.”[4]

Soft Tissue Preserved

The researchers from Yale University retrieved an abundance of hard evidence of this organism’s eyes. They found “detailed preservation of large compound eyes and soft tissues such as the optic lobe of C. perplexa, together with information on eye morphology and growth rates” which, they said, “permits a comparison with data on a diversity of extant crabs and shows that it was an active visual swimmer.”[5] From this clear evidence of “internal optic neuropils and external corneal elements” of the eyes of C. perplexa, the researchers believe this extinct crab

is the first known post-Paleozoic arthropod to preserve both…. the eyes and carapace, allowing for the calculation of the optical growth rate. C. perplexa shows the fastest optical growth rate compared with a sample of 14 species of extant brachyurans. The growth series of C. perplexa, in combination with the calculation of the interommatidial angle and eye parameter, demonstrates that it was a highly visual predator that inhabited well-lit environments.[6]

As more and more examples of evidence for soft tissue preservation are uncovered, evolutionists will no longer have the excuse of ‘lack of evidence’ for evolution due to the claim that soft tissue does not preserve in the fossil record. So far, the soft-tissue evidence that has been discovered, including that of C. perplexa, shows stasis – the absence of evolution. This supports the creation model.

High Quality Vision

Another drawing of Callichimaera perplexa, the “platypus of crabs.” This drawing more accurately shows the comparative enormity of the eyes. Image credit: Elissa Martin, Yale Peabody Museum of Natural History.

Also notice that even though the researches have made a determination of the quality of the image that the C. perplexa eyes produce from the evidence, in the end they had to assume the high quality of the image the eyes produced. The reason is because they had no direct evidence based on a working eye. They rejected the idea that the eye was still evolving and C. perplexa was at the stage of evolution where the image was still very poor. They rejected this view because they recognized that, to successfully survive in its poorly lit marine environment, it must have had excellent vision.

Evolution requires progress from the simple eye spot to the complex vertebrate eye, a process driven by natural selection. Thus, each step in this evolution would have to be an improvement, and the earlier steps would, therefore, have had comparatively inferior eyesight. Their conclusion:

Image-forming compound eyes are such a valuable adaptation that similar visual systems have evolved independently across crustaceans. But if different compound eye types have evolved independently multiple times, how useful are eye structures and ommatidia morphology for resolving phylogenetic relationships? Crabs are ideal study organisms to explore these questions because they have a good fossil record extending back into the Jurassic, they possess a great variety of optical designs, and details of eye form can be compared between extant and fossil groups.[7]

More research will no doubt ensue on this creature because of the “discovery of hundreds of exceptionally well-preserved specimens from rock formations in Colombia and the United States.”[8] My supposition is this fossil trove will confirm stasis. So far, the discoveries have provided no evidence of evolution. This means that no evidence of their evolution currently exists.

Summary

Although “Tracing the evolution of photoreceptor genes and eye morphology across a robust crab tree could be an informative first step to reconstructing the evolutionary history of vision across this iconic group [of crabs],” the fact is, the “evolutionary history of apposition and superposition eyes is still poorly understood.”[9] The reason it is poorly understood is because out of the millions of fossils so far unearthed, including both hard and soft tissue, no documented evidence of evolution is seen.

References

[1] Elbeon, Asher, This Ancient Crab Had Unusually Huge Eyes, The New York Times, 23 January 2022.

[2] Shelton, Jim, Meet Callichimaera perplexa, the platypus of crabs,” Yale News, 24 April 2019.

[3] Jenkins, Kelsey M., et al., 2022. The remarkable visual system of a Cretaceous crab, iScience, Cell Press, 21 Jan 2022.

[4] Jenkins, et al., 2022.

[5] Jenkins, et al., 2022.

[6] Jenkins, et al., 2022.

[7] Luque, Javier, et al., Evolution of crab eye structures and the utility of ommatidia morphology in resolving phylogeny, bioRxiv, posted 7 October 2019.

[8] Shelton, 2019.

[9] Luque, et al., 2019.


Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,300 publications in 12 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,500 college libraries in 27 countries. So far over 80,000 copies of the 40 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.

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Categories: Fossils, Marine Biology

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