Another Complex Cambrian Animal Fossil Found in Greenland - Evolution News & Views

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Another Complex Cambrian Animal Fossil Found in Greenland

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A video clip at Nature News shows a newly discovered Cambrian animal, announced in Nature. It's similar in form to the apex predator Anomalocaris, but without the grasping claws. Instead, it has rows of bristles that reminded the discoverers of fine structures on filter feeders like shrimp, whale sharks and baleen whales. For this reason, the team from the University of Bristol are calling the animal, dubbed Tamisiocaris borealis, a "gentle giant" that grazed the Cambrian seas as a swimming filter feeder, sweeping up the abundant small prey that proliferated in the Cambrian explosion.

From seven partial frontal appendages and a head shield collected in early Cambrian strata in northern Greenland, they estimate the creature grew to 70 cm (about 28 inches). New Scientist reproduces a short animation of the feeding mechanism on this "blue whale of the Cambrian," believed to have tucked its catch into its mouth using the curled appendages.

That's the facts. Now, the implications.

This is another complex animal that appears in the Cambrian explosion. No transitional forms or primitive ancestors are described; it's just "there," in Greenland rocks, already playing its role in its ecological niche. According to the University of Bristol, Jakob Vinther and his team are fully aware that the Cambrian explosion was a time "in which all the major animal groups and complex ecosystems suddenly appeared." (Emphasis added.) Notice that the explosion included "complex ecosystems," not just dozens of new body plans. The abstract of the paper emphasizes that fact, saying, "Cambrian pelagic ecosystems seem to have been more modern than previously believed."

That word modern shows up several times in the paper. They compared T. borealis with "modern suspension feeders" and found it fulfilling a similar role in the Cambrian ecosystem:

On the basis of the morphologies seen in modern animals, a suspension-feeding anomalocarid would be predicted to have evolved a setal mesh, with large appendages bearing long, flexible setae to increase capture area, with close, regular setal spacing. This is indeed the morphology observed in Tamisiocaris.

(That's baloney about evolution "predicting" this. A student of ecology, studying an unfamiliar ecosystem, could predict that a creature with certain traits would be found filling a niche, without reference to how it originated.)

Their final use of the word modern is instructive. They note that (contrary to earlier beliefs) hierarchical levels of filter feeders were at work in Cambrian seas:

Other pelagic predators known from Lagerst├Ątten [strata with exquisite preservation of fossils] elsewhere would also have fed on mesozooplankton, including ctenophores, cnidarians, chaetognaths and pelagic arthropods.... The Cambrian pelagic food web was therefore highly complex, containing multiple trophic levels, including pelagic predators and multiple tiers of suspension feeders. This underscores the remarkable speed with which a modern food chain was assembled during the Cambrian explosion.

Let's take stock of the predicament evolutionists are in with this new fossil. Another unique anomalocarid ("weird shrimp") appears suddenly in the early Cambrian, along with Anomalocaris, trilobites, sponges, worms and all the other unprecedented body plans. "Before then, most life forms were bacteria or microbial mats," Live Science says.) The Cambrian animals suddenly appear, all interacting in a complex food web, with multiple tiers of predators and scavengers. Moreover, the ecosystem of complex phyla "assembled" with "remarkable speed."

Faced with this dilemma, WWDD? (What would Darwin do?) We know the answer from long experience: simply assert that they "evolved." Use other euphemisms as necessary, for variety: they developed, they appeared, they assembled. Not surprisingly, the news release refers to the explosion as "the highly productive Cambrian period" for evolution. Unguided processes were going gangbusters!

See here, will you?

The animals lived 520 million years ago during the Early Cambrian, a period known as the 'Cambrian Explosion' in which all the major animal groups and complex ecosystems suddenly appeared. Tamisiocaris belongs to a group of animals called anomalocarids, a type of early arthropod that included the largest and some of the most iconic animals of the Cambrian period. They swam using flaps down either side of the body and had large appendages in front of their mouths that they most likely used to capture larger prey, such as trilobites.

However, the newly discovered fossils show that those predators also evolved into suspension feeders, their grasping appendages morphing into a filtering apparatus that could be swept like a net through the water, trapping small crustaceans and other organisms as small as half a millimetre in size.

The evolutionary trend that led from large, apex predators to gentle, suspension-feeding giants during the highly productive Cambrian period is one that has also taken place several other times throughout Earth's history, according to lead author Dr Jakob Vinther, a lecturer in macroevolution at the University of Bristol.

Dr Vinther said: "These primitive arthropods were, ecologically speaking, the sharks and whales of the Cambrian era. In both sharks and whales, some species evolved into suspension feeders and became gigantic, slow-moving animals that in turn fed on the smallest animals in the water."

Don't you understand? Species evolved. Phyla evolved. Stop worrying so much. Suspension feeders were needed, so the cook in the kitchen hollers, "Coming right up!" He serves fresh Tamisiocarus on a rock. "Enjoy!"

Since Darwin can survive one explosion, how about this neat trick: the Anomalocarid explosion within the Cambrian explosion:

Tamisiocaris is one of many recent discoveries of remarkably diverse anomalocarids found in rocks aged 520 to 480 million years old. "We once thought that anomalocarids were a weird, failed experiment," said co-author Dr Nicholas Longrich at the University of Bath. "Now we're finding that they pulled off a major evolutionary explosion, doing everything from acting as top predators to feeding on tiny plankton."

Reporters know the trick just as well, asserting in their articles that this "evolved" here, that "evolved" there (e.g., Live Science asserts as fact, "during the Cambrian hard exoskeletons, jointed limbs, compound eyes and antennae evolved").

If you think that's a clever way to handle anomalies, check this out. At the end of the paper, the discoverers turn their fossil into a divining rod on the predictability of evolution:

Finally, the discovery of a suspension-feeding anomalocarid has implications for debates concerning the predictability of evolution, or lack thereof. One view holds that evolution is ultimately unpredictable [reference given here to Stephen Jay Gould's book Wonderful Life]. The notable convergence between Tamisiocaris and extant suspension feeders, however, suggests that although different groups occupy ecological niches at different times, the number of viable niches and viable strategies for exploiting them are limited. Furthermore, the derivation of the suspension-feeding Tamisiocaris from a large apex predator parallels the evolution of suspension-feeding pachycormid fish, sharks and whales. In each case, suspension feeders evolved from nektonic macropredators. This suggests that evolution is canalized not only in terms of outcomes, but in terms of trajectories. The result is that independent evolutionary experiments by animals as different as anomalocarids, fish and whales have converged on broadly similar outcomes.

Ignore that book over there. That's religion. We're talking about science!

Image credit: Dr Jakob Vinther, University of Bristol.


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