Zimmer has a summary of the latest discoveries in the evolution of the baleen whales. It’s beautiful stuff, with the lineage showing their origin from toothed whales, through a phase where they had both teeth and baleen, to their current condition lacking teeth and having only baleen.
Phosphatized pre-Cambrian embryos are cool. It’s amazing that they’ve been preserved at all, and they are spectacularly gorgeous. We can learn about the evolution of development from their superficial appearance, but what we really want to do is poke around their interiors and analyze them cell by cell, something that has been hard to do without destroying them in the process. Until now.
A report in Nature (and a too short mention on a researcher’s web page) describes the application of synchrotron X-ray tomographic microscopy (SRXTM) to these fossilized embryos to resolve their internal structure. It’s a powerful tool, and it’s generating some beautiful images.
You may recall that Martin Brazeau was going to spend July doing fieldwork—well, he’s back, and is going to be telling us about his exciting month in a Canadian cow pasture, if ever you wanted to hear a first-hand account of paleontological research.
Muton has some splendid photos of fossil spiders.
Yunnanozoans and Xidazoon…there are some very pretty early Cambrian critters on display at Sinanthropus.
A new report in this week’s Nature clears up a mystery about an enigmatic fossil from the Cambrian. This small creature has been pegged as everything from a chordate to a polychaete, but a detailed analysis has determined that it has a key feature, a radula, that places it firmly in the molluscan lineage. It was a kind of small Cambrian slug that crawled over matted sheets of algae and bacteria, scraping away a meal.
Here I am, in the upper midwest, and I still haven’t made it to the Field Museum in Chicago—Chicago is just far enough away that I can’t quite make the trip, and it’s close enough that it doesn’t sound at all exotic. I just have to rely on other people’s accounts. (I’ve also noticed that Megatherium is a spectacular specimen.)
Lindsay makes a factual error: Minnesota does not have a state fossil. We had a bill introduced almost 20 years ago to make Castoroides ohioensis, a 6-foot long, 250 pound giant beaver, our state fossil…but some people objected to the fact that it’s named after Ohio, and I suspect there might have been some concern about the beaver jokes.
We do have a list of potential nominees. I’m rooting for Endoceras proteiforme, myself—a giant nautiloid would be perfect!
Two short articles in this week’s Science link the orb-weaving spiders back to a common ancestor in the Early Cretaceous, with both physical and molecular evidence. What we have is a 110-million-year-old piece of amber that preserves a piece of an orb web and some captured prey, and a new comparative study of spider silk proteins that ties together the two orb-weaving lineages, the Araneoidea and the Deinopoidea, and dates their last common ancestor to 136 million years ago.
Araneoids and Deinopoids build similar looking webs—a radial frame supporting a sticky spiral—but they differ in how they trap prey. Deinopoids spin dry fibers that they fluff into threads that adhere electrostatically to small insects; Araneoids secrete glue onto the the strand, which takes less work (no fluffing), and is much more strongly adhesive. The differences are enough to make one question whether there was a single origin of orb weavers, or whether the two groups independently stumbled on the same efficient form of architecture.
The diagram above shows the early cleavages of the embryo of the scaphopod mollusc, Dentalium. You may notice a few peculiarities: the first cleavage is asymmetric, producing a cell called AB and a larger sister cell, CD. Before the second division, CD makes a large bulge, called a polar lobe, and it almost looks like it’s a three-cell stage—this is called a trefoil embryo, and can look a bit like Mickey Mouse. The second division produces an A, a B, a C, and a D cell, and there’s that polar lobe, about as large as the regular cells, so that it now resembles a 5-cell embryo. What’s going on in these animals?
