Vernanimalcula
One of the claims of Creationists is that the animals found in the Cambrian period (543-490 million years ago) have no predecessors. From Pathlights:
The lowest strata containing fossils is the Cambrian. (Below that is the Precambrian, with no fossils other than an occasional algae.) Called the “Cambrian explosion” by scientists, it is a sudden appearance of billions of fossils of over a thousand different life forms. Yet they are all distinct species, with nothing leading up to them. Every major life group (phyla) has been found in the Cambrian strata. …
No life below the Cambrian. Below the Cambrian, in the Precambrian, essentially nothing living is to be found.
While this statement was false (there were plenty of fossils such as the Precambrian Ediacaran fauna and even older bacteria), the relatively sudden appearance of complex animals in the Cambrian has always provided the Creationists a certain amount of grist for their mills.
Here’s a little guy, Vernanimalcula, found in China in 2004, who shows otherwise. The name, Vern-animal-cula, means simply “small Spring animal.”
There’s a piece of jargon I must introduce here: “bilaterian,” i.e. an animal with bilateral symmetry - a defined front-&-back, and a defined top-&-bottom, and a defined left-and-right. When most of us think of animals, we probably think of bilaterians: vertebrates, insects, molluscs, etc.. Single-celled animals, sponges, jellyfish, corals, all those simpler animals, are not.
What is special about the Cambrian is the relatively sudden appearance of bilaterians, and a rather impressive variety of them. (Although there were no dinosaurs, birds, or reptiles in the Cambrian, as this other, even more moronic, Creationist site claims. There was no life on land for another hundred million years. One of the challenges of doing these pieces is trying to avoid getting bogged down in the vast amount of lies and nonsense on Creationist sites.)
From Science Magazine, July 2004: Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian
Ten specimens of a small (<180 micrometers) animal displaying clear bilaterian features have been recovered from the Doushantuo Formation, China, dating from 40 to 55 million years before the Cambrian. Seen in sections, this animal (Vernanimalcula guizhouena) had paired coeloms extending the length of the gut; paired external pits that could be sense organs; bilateral, anterior-posterior organization; a ventrally directed anterior mouth with thick walled pharynx; and a triploblastic structure. These fossils provide the first evidence confirming the phylogenetic inference that Bilateria arose well before the Cambrian.
Scientific American published this more general article on Vernanimalcula in August, 2005.
Here are pictures. Keep in mind how small Vernanimalcula was, less than 1/4 of a millimeter. If you click and look at the full size picture, the individual cells of its body are visible. So are the surface pits, which the authors speculate are sensory organs; these are consistent with predictions of how the first eyes evolved.
Fig. 1. Images of three different, fairly well preserved specimens of the bilaterally organized fossil animal Vernanimalcula guizhouena. Left panels show digitally recorded, transmitted light images of sections about 50 _m thick, which had been ground from larger rock samples, mounted on slides, and viewed through a light microscope. Right panels show color-coded representations of the images on the left. These were prepared by digital image overlay. Yellow, external ectodermal layer; ochre, coelomic mesodermal layer; red, surface pits; mauve, pharynx; light tan, endodermal wall of gut; gray-green, lumen of mouth; dark gray, paired coelomic cavities; lighter gray, lumen of gut; brown, “gland-like” structures, with central lumen (B); light green, mineral inclusions (C). The scale bar represents 40 _m in (A), 55 _m in (B), and 46 _m in (C). (A) Holotype specimen, X00305, slightly tilted, almost complete ventral level coronal section, passing through the ventrally located mouth. (B) Coronal section of second specimen, X08981, passing through dorsal wall of pharynx and displaying complete A-P length of digestive tract, including posterior end [not visible in (A)]. (C) Tilted coronal section of third specimen, X10475, possibly slightly squashed, passing through dorsal wall of pharynx and through the dorsal wall of the gut.
“Vern” may not look like much, but he’s packing a whole lot of important stuff, the genetic tools needed for even more complicated animals. Here’s another quote from the Science article:
The morphology of Vernanimalcula demonstrates that the evolutionary appearance of developmental programs required to generate a multilayered bilaterian body plan preceded the entrainment of the growth programs required for macroscopic body size. Furthermore, the organization of these fossils, taken together with their provenance, indicates that the genetic tool kit and pattern formation mechanisms required for bilaterian development had already evolved by Doushantuo times, long before the Cambrian. Therefore, the diversification of body plans in the Early Cambrian followed from the varied deployment of these mechanisms once conditions permitted, not from their sudden appearance at or just before the Cambrian boundary.
There is another, especially satisfying, part of the Vernanimalcula story. It was predicted. One of the hallmarks of science is that it is predictive, not in the sense of fortune-telling, but in the sense of predicting, for example, what we should find in the fossil record. In the past decades, scientists looking at the divergence of genes concluded that bilaterians diverged from simpler animals long before the Cambrian. (Here’s a 2003 study.) Exactly how long has been (and still is) has been the subject of some debate. But there was no getting around the molecular biology and its prediction: bilaterians pre-dated the Cambrian … by a lot. Thanks to the extraordinarily well-preserved phosphate rocks of the Doushantou Formation in China, Vernanimalcula was there, waiting to be discovered.
Click on the thumbnails of Fig 2) for details of the internal structure, and Fig. 3) for a 3-D reconstruction.
Fig. 2. Close-up images of prominent anatomical features of Vernanimalcula guizhouena. The scale bar represents 18 _m in (A), 32 _m in (B), 24 _m in (C), and 28 _m in (D). SO, sensory organ, i.e., external pit; LU, lumen; PH, pharynx; MO, mouth; CO, coelomic lumen; CW, mesodermal coelomic wall; GU, gut. (A) Detail of collared mouth, multilayered pharynx, and one anterior surface pit. In this image, which is from the holotype specimen (Fig. 1A), the floor of the pit can be seen to be composed of a specialized concave layer. Note the coelomic wall, which here as elsewhere in these specimens has a thickness of about 5 to 6 _m. (B) Mouth of a fourth specimen, Q3105, displaying collared mouth and pharynx, ventral view. (C) Lumen of pharynx from a fifth specimen, X10419, secondarily encrusted but revealing morphology of opening of pharynx into gut similar to that seen in the specimens shown in Fig. 1. (D) Close-up of spaced external pits, interpreted as possible sensory organs, from the same specimen as shown in Fig. 1B [compare (A)].
Fig. 3. Three-dimensional reconstruction of Vernanimalcula. The model was constructed with FormZ, version 4.0, a software from Auto-Des- Sys Inc. (Columbus, OH), and with proportions derived from the holotype specimen in Fig. 1A. (A) and (B) display computed external views of the reconstruction, (C) to (F) the computed sections. (A) Perspective view indicating planes of section shown in (C) to (F), as indicated by the colored dots. (B) Dorsal view. (C) Perfect coronal section. (D) Slightly tilted coronal section similar to the image shown in Fig. 1A. (E) Transverse section. (F) Sagittal section. (C to F) Yellow, ectoderm; ochre, coelomic mesoderm; light tan, endoderm.
There is a lot more fascinating information on Vernanimalcula in the Science magazine link.
RINO Sightings for the week