Horseshoe crabs are survivors by anyone’s measure; they have carried on their lives virtually unchanged, according to the standard evolutionary timeline, for 450 million years. This not only points to incredible stasis against alleged forces of evolution; it also means they have survived at least three global extinctions that evolutionary biologists and geologists say wiped out most other species. Not only that, the world has changed drastically since they allegedly evolved from who-knows-what arthropod ancestors – perhaps trilobites, that appeared in the Cambrian Explosion without ancestors. But the numerous, successful trilobites did not survive the global extinctions. Given these contradictory facts, how can the horseshoe crab possibly be an exhibit for evolution? A recent article shows how.
Horseshoe crabs are not crabs; they are arthropods, similar in some ways to scorpions. The UK Natural History Museum gave facts and fancies about these amazing, complex animals on the verge of a BBC News special TV program about them:
At the end of the article comes the evolutionary exhibit. Richard Fortey does his best to explain why an unevolved creature is really evidence for evolution:
For every hyped-up demonstration of evolution in action the media announces with gusto, there are setbacks that often do not get the splashy headlines. Here are three recent examples.
Treehopper evolution wasn’t: Recently a “spectacular” announcement that some bugs called treehoppers had evolved a new functional appendage has been found false. “Evidence for a spectacular evolutionary novelty was recently reported,” wrote nine scientists in PLoS ONE,1 claiming that the treehopper bugs evolved their odd-looking “helmet” as new thoracic appendages. Those evolutionists, publishing in Nature,2 were not at all modest in their pronouncement: “Here we show that the treehopper (Membracidae) ‘helmet’ is actually an appendage, a wing serial homologue on the first thoracic segment. This innovation in the insect body plan is an unprecedented situation in 250 Myr of insect evolution.”
Wrong, the new team reports. It’s not a novelty, but a common and widely-distributed feature among hemiptera (true bugs) – just an invagination of tissue, not a distinct limb. The new paper not only corrects the error but criticizes the evolutionists who proposed the wrong idea, telling them basically they should have consulted the insect experts (entomologists) before hopping to a Darwin-tree conclusion. “The treehopper pronotal wing hypothesis yields examples of misinterpretation that could have been avoided through updated best practices in phenotype knowledge representation and the broader development of anatomical references,” they said.
Wish Ida known: Remember Ida, the extinct lemur that briefly made a splash in the science headlines as being a possible human ancestor? (5/19/2009, 3/03/2010). The discoverer even paid homage to Darwin by naming it Darwinius masillae, and it became the star of a TV documentary. Live Science reported this month that new evidence is casting doubt on it having anything to do with the human line. Another similar lemur fossil from Wyoming shows a grooming claw characteristic of mammals on other branches of the assumed evolutionary line of primates. “After examining the data, both with and without information about the grooming claw,” therefore, “it appeared both these ancient primates were more closely related to lemurs than to monkeys, apes and humans.”
(Radar note: Ida was yet another Phil Gingerich special. Guess he is the modern-day Haeckel? Not that there are not many candidates!)
Darwin wouldn’t like this: Biologists can’t conjure up gradualism out of the data. Charles Darwin’s theory depended on the slow accumulation of gradual changes over long periods of time. In Current Biology last month,3 Douglas Erwin tried hard to put a happy face on the ugly problem of “punctuated equilibria” that causes mismatches between molecular methods of tracing the unfolding tree of evolution, and the fossil record that shows stasis and explosive diversification. Factoring in the ad hoc method of “rate heterogeneity” (something like artist Salvador Dali’s stretchy clocks in The Persistence of Memory) still doesn’t get the data in sync.
Erwin recalled the long-standing “tension between microevolutionists and macroevolutionists” – the former looking for processes they can tweak in the lab, the latter looking at the fossils. It’s a tension that has lasted for over a century. Even though Erwin grinned like a hungry flashlight salesman that “Several recent papers now shed new light on macroevolutionary processes,” his light was lacking batteries in the body of his Dispatch.
First, the darkness: “The discrepancy between plots of the diversity of taxa through time as inferred from molecular phylogenies and those based on counts documented by the fossil record has long been troubling,” he said, “largely because molecular phylogenies appear to underestimate the frequency of extinction.” In hopes of mitigating the damage, he presented three recent papers. One team of evolutionists found additional ways to tweak their models to get a better fit, particularly with dolphins and whales. But the next subtitle states, “Punctuations Are Not Passé.” The second study, this one more extensive, covering 40 species from fish to mammals, was not so gradual: “Their analysis supports a model of rare bursts of extensive evolutionary change in a sea of shorter-term fluctuations.” At the end of the section, Erwin lists three possible explanations for this:
1. Mikó I , Friedrich F , Yoder MJ , Hines HM , Deitz LL , et al. 2012 On Dorsal Prothoracic Appendages in Treehoppers (Hemiptera: Membracidae) and the Nature of Morphological Evidence. PLoS ONE 7(1): e30137. doi:10.1371/journal.pone.0030137.
2. Prud’homme et al., “Body plan innovation in treehoppers through the evolution of an extra wing-like appendage,” Nature 473 (05 May 2011), pp. 83–86, doi:10.1038/nature09977.
3. Douglas H. Erwin, “Macroevolution: Dynamics of Diversity,” Current Biology, Volume 21, Issue 24, R1000-R1001, 20 December 2011, 10.1016/j.cub.2011.11.007.
The Cambrian Explosion (the abrupt appearance of animal phyla in the earliest fossil layers bearing multicellular body plans) remains unmuffled. Known by Darwin as a problem for his theory, it has become more problematic to his followers over time. There are now many more Cambrian fossils than Darwin knew of, and they continue the pattern: sudden appearance of complex animals, complete with legs, digestive systems, eyes, and nervous systems. Discoveries of Precambrian fossils have not helped: the ones that are more than microbial appear to be mere colonies of cells with no relationship to animals. Here are more discoveries that fit this pattern.
Burgess shale tulip animals: A new species of filter-feeding marine animal that resembles a tulip has been found on Mt. Stephen in British Columbia, Canada, site of the internationally famous Burgess Shale fossil bed. Pictures of the fossils and an artist reconstruction can be found on PhysOrg. Named Siphusauctum gregarium, the animal is about 8” high and lived in colonies. The Burgess Shale is dated Middle Cambrian, but the existence of this fully-formed animal, complete with gut, foot anchor and pump to drive water through its “unusual filter-feeding system” implies a very short fuse between the Precambrian and its abrupt appearance.
Crustaceans with modern aspect: Like lobster? Think of the complexity of this animal with eyes, antennae, claws, legs, mouth parts equipped with mandibles, and internal organ systems, including a digestive tract and sexual organs. Crustaceans are a highly diverse group of arthropods that include lobsters, crayfish, and crabs. Among the crustacean subphylum are the branchiopods (which includes the fairy shrimp and water flea), ostracods (small shelled crustaceans; see diagram of complex internal organs on the Lake Biwa Museum site), and copepods (“oar-foot” swimmers; see Smithsonian for description).
At another site in western Canada called the Deadwood Formation, a trio of scientists from Cambridge, Hawaii and Canada found exquisitely-preserved crustaceans “of surprisingly modern aspect” in mudstone, a type of rock that was thought to form very slowly (12/14/2007). The abstract of their paper in PNAS says it best:1
Previous “cryptic” fossils hinted at the presence of crustaceans in the Early Cambrian, but now, the new discovery shows them alive and well in the Middle Cambrian: “the Deadwood fossils provide crucial phylogenetic and ecologic datapoints for charting a major Cambrian radiation of crustaceans.” The Deadwood Formation extends from western Canada to the Black Hills of South Dakota, they noted.
After showing an array of beautifully detailed fossils and discussing them, the authors concluded that their discovery pushes back the date of branchiopods 80–100 million years (Lower Devonian to Middle Cambrian), ostracods 70 million, and copepods 190–210 million years. They did their best to maintain their evolutionary belief, pointing to differences between the fossil forms and modern or later fossil forms, for example, “In any case, they offer clear potential for reconciling the Orsten forms with adults and larger bodied relatives for a new, high-definition narrative of early mandibulate evolution.” Nevertheless, these fossils show “direct evidence for sophisticated particle-handling” and represent “the acme of Cambrian differentiation within appendages,” they said.
It’s hard to see evolution in the picture of “early origination and subsequent conservation in crustacean form and function” these fossils illustrate, especially when the fossil copepods are larger than modern ones. To reconcile that with evolution, they postulated that the presence of fish with predatory eyes would drive crustacean size down. Maybe they forgot that the Chinese found fish fossils in the early Cambrian (8/21/2002, 1/30/2003), but that seems the least of their worries. The complex body parts represented in these fossils begs for explanation how a gradual, unguided Darwinian process would lead to such high levels of functional complexity in short order, abruptly, with no fossil pathway evident, much earlier than expected.
Up periscope! Sea spider eyes: Did you know there are spiders at the bottom of the sea? A paper in PLoS ONE talked about them.2 They are called pycnogonids, and they have unusual eyes on stalks that look like periscopes. The authors of the paper did not find Cambrian fossils of sea spiders. Instead, they tried to infer their evolutionary origins, and placed them in the Cambrian as the oldest arthropods. “Recently it was suggested that arthropod eyes originated from simple ocelli similar to larval eyes,” they said. “Hence, pycnogonid eyes would be one of the early offshoots among the wealth of more sophisticated arthropod eyes.”
Putting puzzle pieces together in some kind of evolutionary arrangement, though, seems the least of their worries. They found that these eyes had nerves from the stalks down to the brains of these eight-legged creatures. How eyes popped into existence suddenly in the earliest layers bearing animal fossils is the “elephant in the room” that most evolutionists dodge. They ended with an “if-then” statement of doubtful premise: “If arthropod eyes originated from simple ocelli similar to larval eyes, pycnogonid eyes could be one of their early offshoots, which date back at least 500 Myr to the Cambrian, and be older than the appearance of distinct lateral and median eyes.” Notice that they are not saying sea spiders have “simple” ocelli (light-sensitive organs, as in dragonflies; see 8/13/2004), just that they were a later offshoot of a presumed ancestor, “if” arthropod eyes “originated” by evolution.
1. Harvey, Vélez and Butterfield, “Exceptionally preserved crustaceans from western Canada reveal a cryptic Cambrian radiation,” PNAS, Published online January 17, 2012, doi: 10.1073/pnas.1115244109.
2. Lehmann T , Heß M , Melzer RR , 2012 Wiring a Periscope – Ocelli, Retinula Axons, Visual Neuropils and the Ancestrality of Sea Spiders. PLoS ONE 7(1): e30474. doi:10.1371/journal.pone.0030474.