Here’s an appropriate post for Darwin Day: a new discovery of some very old fossils.
You remember the Burgess Shale fauna, right? The whole story, although it’s since been revised, is given in Steve Gould’s excellent book Wonderful Life (1989). Discovered by Charles Wolcott in the Canadian Rockies in 1909, the site’s shale-preserved fossils were largely neglected until students Simon Conway Morris and Derek Briggs analyzed them decades later. They’re from the Cambrian, a bit more than 500 million years ago.
The first analysis suggested that they belonged to many groups (perhaps phyla) no longer living, suggesting that there had been a luxuriant explosion of life that was subsequently pruned away by extinction. The assemblage also contained a fossil chordate, Pikaia gracilens, perhaps a relative of our ancestors, although it wasn’t a vertebrate:
The diversity of weird, un-placeable fossils led to the message of Gould’s book: had the “tape of life” been rewound, and had extinction not removed most of the Burgess Shale fauna, life today might have descended from those creatures and would be very different from what we see on Earth today. Gould’s message was one of contingency: evolution is unpredictable because of the vagaries of the environment. (Of course, while I see evolution as unpredictable by humans, I see it largely as deterministic, since environmental perturbations must themselves obey the laws of physics. Evolution is only non-deterministic insofar as mutations might be the result of completely indeterministic processes involving quantum-level events.)
At any rate, a closer examination of the fauna by Briggs and Conway Morris showed that most of the anomalous beasts were actually members of extant groups, like arthropods, annelids, and sponges, so the fauna really wasn’t as much of an outlier as Gould suggested. That somewhat overturned his idea that the types of life on Earth today were purely the result of contingencies.
Nevertheless, there are still animals in the original Burgess fauna that defy identification; one of them is the bizarre Opabinia regalis, which looks like a shrimp with a vacuum-cleaner hose attached to its head. Here’s a specimen from the nice Smithsonian site on the Burgess shale (first link in this post):
Another weird one was the six-foot predator Anomalocaris canadensis (the genus name means “abnormal shrimp”) a large predator that may be closely related to ancient arthropods. Here’s a reconstruction and a fossil of its two forelimbs:
Later comparable fauna, also remarkably well preserved, were found in the Chengjiang biota of Yunnan, China, a series of Cambrian shale fossils about 525 million years old. They’re notable for containing what may be the first known jawless fish (“agnath,” a group that comprised the ancestral vertebrates), Myllokunmingia. Here’s a fossil of that species and then a reconstruction (it’s somewhat speculative; we don’t know whether it had eyes). Myllokunmingia was about 1.1 inches (2.8 cm) long:
Which brings me to the point of this post: a new paper in Nature Communications by Jean-Bernard Caron et al. It describes a site 50 km from the Burgess Shale site (and not too far from where I’m speaking in Kamloops this spring), that, like the original Walcott site, contains a remarkable array of wonderfully-preserved invertebrate (and one chordate) species, 22% of which are new to science. It also contains many fossils known from the Chengjiana fauna, showing that some species had a broad distribution.
The specimens haven’t yet been worked up and many aren’t yet identified as to group, but some are known as identical species from other places. When the new ones are identified, however, we may see some severe revision of the early history of life.
The paper is not much more than a description of the site (called “Marble Canyon”) and a brief description of the fauna, with some pictures, so I’ll show both. A nice article in the Globe and Mail (be sure to watch the one-minute video showing the beautiful location) gives some of these photos; my captions are lifted that article:
The fossil bed was discovered in 2012, in a section of Kootenay National Park in British Columbia that cannot be accessed by trails. Although the team is not sharing the site’s precise location – to protect it from pillaging by would-be fossil hunters – Dr. Caron said it was near a scenic feature called Marble Canyon.
“It’s on the side of a mountain like any other mountain,” said Alex Kolesch, a manager with Parks Canada. “To be able to discern what’s there, you would really need to know what you’re looking for.”
The team first stumbled upon the site while looking for exposed sections of rock similar to that found in the Burgess Shale. One evening, they came to a place where it seemed that fossils were littering the ground. Upon closer inspection, they realized it was no fluke, but the eroding edge of a significant deposit that previous expeditions had missed. Within days, there were pulling out high-quality specimens of ancient marine life in stunning numbers.
First the site and some excavations:
The animals. If you think you know your groups, guess which phyla these belong to. The paper, which unfortunately is not free, gives some answers. For example, the third photo below shows a new species of arthropod:
Here are two pictures from the Nature Communications paper. The first shows another chordate, Metaspriggina, which has remarkable preservation of the internal organs, including the heart and liver, and, especially, the eyes (“ey” in figure), so we know that eyes had already evolved by this time. The scale bar is 5 mm long (0.2 inches):
And here is something I didn’t know about, a “bivalved arthropod,” apparently with some kind of bivalve-like shell. This one is new to science and not yet named; the scale line is 10 mm (0.4 inches), so you can see that these specimens are small:
The fossils include the first preserved neural tissue from any specimen of this period, but its meaning awaits further analysis.
Happy Darwin Day: one of your ancestors might be in the pictures above!
h/t: Diana MacPherson
Caron, J.-B., R. R. Gaines, C. Aria, M. G. Mángano, and M. Streng. 2014. A new phyllopod bed-like assemblage from the Burgess Shale of the Canadian Rockies. Nature 2014/02/11/online