Stephen Meyer indicates that the major pulse of the Cambrian explosion started 530 million years ago and lasted 5 million years (Darwin’s Doubt, Fig. 3.8, p. 72). In his chart of phyla making their first appearance in the fossil record (Fig. 2.5, p. 32), Kinorhyncha is listed in the box among other phyla that “do not appear in the fossil record.”
Well, as Casey Luskin reported yesterday, now he can move it up into the Cambrian slot. The first fossil of these creatures has now been documented in China. That shifts the counter from 21 to 22 phyla appearing in the Cambrian — and not only in the overall 53-million-year period, but right near the start of the major pulse of the Cambrian explosion.
What does Kinorhynchus look like? Study the picture from Virginia Tech. It’s half the size of a grain of rice, but don’t be deceived by its small stature. It has a digestive system with a mouth, teeth, salivary glands, pharynx, esophagus, anus, and digestive glands. It has multiple body segments, spines, a nervous system with sense organs, and muscles for locomotion, as its name implies: “moving snout” or, as commonly known, “mud dragon.” Scientists call them kinos (“movers”) for short.
Discoveries of fossil specimens made in 2013 and 2014 have now been published in Nature‘s new open-access journal Scientific Reports. The authors clearly want to stuff this creature into a Darwinian phylogeny, but facts are stubborn things.
Kinorhynchs are unique among living cycloneuralians in having a segmented body with repeated cuticular plates, longitudinal muscles, dorsoventral muscles, and ganglia. Molecular clock estimates suggest that kinorhynchs may have diverged in the Ediacaran Period. Remarkably, no kinorhynch fossils have been discovered, in sharp contrast to priapulids and loriciferans that are represented by numerous Cambrian fossils. Here we describe several early Cambrian (~535 million years old) kinorhynch-like fossils, including the new species Eokinorhynchus rarus and two unnamed but related forms. E. rarus has characteristic scalidophoran features, including an introvert with pentaradially arranged hollow scalids. Its trunk bears at least 20 annuli each consisting of numerous small rectangular plates, and is armored with five pairs of large and bilaterally placed sclerites. Its trunk annuli are reminiscent of the epidermis segments of kinorhynchs. A phylogenetic analysis resolves E. rarus as a stem-group kinorhynch. Thus, the fossil record confirms that all three scalidophoran phyla diverged no later than the Cambrian Period.
It doesn’t really matter if this fossil appeared 535 million years ago, because whenever it was buried, it was already a complex animal very similar to modern kinos. The authors use ~535 Ma, indicating lack of precise dating. The press release says “more than 530 million years” three times. Even 535 Ma is still well within the Cambrian period that is thought to have begun 543 Ma (Meyer, p. 72).
Calling the fossil a “stem-group kinorhynch” or “kinorhynch-like” is wishful thinking. If anything, it is more complex than living kinos, having more body segments and sophisticated, well-organized body armor. Here’s a partial description of the fossil:
Worm-like animal composed of a head, a neck region, and a trunk. Head consists of an introvert with pentaradially arranged hollow scalids and a pharynx with octaradially arranged teeth. Neck region covered with 5 circlets of neck scalids. Trunk has at least 20 annuli and each annulus is covered with a circlet of tightly sutured small plates and armored with spinose sclerites. Five pairs of large spinose sclerites are bilaterally arranged and a single large spinose sclerite is midventrally located. Two pairs of caudal spines are located slightly ventral to the terminal anus.
Judging from the pictures, it has a well-structured body plan with five-fold symmetry and articulated plates, nothing like an Ediacaran animal. Any differences to modern kinos are so minor as to be academic, not phylogenetic. The authors admit that they can’t be sure if the specimens represent juveniles or mature adults; that might account for differences with modern kinos. Their “Phylogenetic Analysis” section states, “caveats should be noted, because future discoveries may reveal completely preserved adult specimens that could affect the character coding of E. rarus adopted here.”
This fossil now forces evolutionists to see three scalidophoran (“spine-bearing”) phyla exploding onto the Cambrian fossil record together, creating another opportunity to wave their hands and invoke “convergent evolution”:
If E. rarus and other Cambrian fossils are confirmed as stem-group kinorhynchs, then all three scalidophoran phyla must have diverged in the early Cambrian or earlier, and a Cambrian fossil record of kinorhynchs can offer fresh paleontological insights into the convergent evolution of segmentation in ecdysozoans [cuticle-shedding animals].
Something else is exciting about this discovery, as Luskin also notes. Remember the “small shelly fossils” that evolutionists have proposed as possible ancestors of the Cambrian animals? (cf. Debating Darwin’s Doubt, Chapter 13, and this ID the Future podcast). The authors suggest that those small shelly fossils may, in fact, be the remains of armor shed by scalidophorans during their regular molting periods.
Although priapulid-like fossils such as Circocosmia and Tabelliscolex also have sclerites, their sclerites are plate-like structures that are bilaterally arranged in longitudinal rows along a large number of annuli. On the other hand, the large sclerites of E. rarus and Form I are remarkably similar to disarticulated sclerites described as Paracarinachites spinus, which may be different from the type material of P. spinus. Similarly, the small plates in Form II resemble disarticulated sclerites described as Kaiyangites novoli. Thus, it is possible that these small shelly fossils may represent disarticulated sclerites of kinorhynch-like animals, although it is important to bear in mind that different animals may bear similar sclerites and the same animal may have several different types of sclerites….
If the small shelly fossils are molted sclerites of kinorhynchs, then they are products of advanced animals with complex body systems — not primitive ancestors leading up to the explosion.
The low resolution and low support are largely due to the large amount of missing data in the data matrix (i.e., many characters describing extant taxa are not preserved in fossil taxa). Nonetheless, the paleontological data and phylogenetic interpretation presented here invite further exploration of the phosphatization taphonomic window and careful re-examination of small shelly fossils (e.g., Paracarinachites spinus and Kaiyangites novoli) in search of Cambrian kinorhynchs.
It’s time to take another look at the small shellies. Maybe they are cast-offs of complex animals. That would require a major re-interpretation, further advancing the explosiveness of the Cambrian explosion.
And so Meyer’s challenge receives additional support as another phylum joins the Cambrian. The authors do their best to put a comforting spin on their find: “The new fossils have the potential to illuminate the Cambrian evolution of scalidophorans and kinorhynchs.” More to the point, they have the potential to illuminate the fossil record in the light of intelligent design.
Image credit: Eokinorhynchus rarus reconstruction, Dinghua Yang, via Nanjing Institute of Geology and Paleontology.