The origin of the angiosperms (flowering plants) is an exciting field, blending evo-devo, fossil discoveries and phylogenetics. In order to understand it, we need to resolve relationships between all the seed plants, as well as identify the ancestor of the angiosperms, so that we can have an image of the transition between the non-flowering and the flowering plants and single out the evolutionary and ecological causes behind the flower’s success. Reviewing this topic, even in summary form, would require a post of its own, so I’ll just introduce this new paper. The researchers describe Leefructus mirus, a relatively derived flowering plant (a eudicot) from a ~122 Ma locality in China (which also yielded the two other oldest fossil flowers, Archaefructus and Hyrcantha). It is thus not the oldest record for flowering plants (to my knowledge, that goes back to ~125 Ma tricolpate pollens from North America). Butit is one of the oldest body fossils and thus is critical for our understanding of early flower evolution. Unfortunately, it is not all that basal – the authors place it on the stem of the Ranunculaceae (buttercups) and so provides more info for that taxon than it does for the angiosperms as a whole. However, its mere presence is evidence that the angiosperm diversification really was explosive, if such diversity was already present a few million years after their origin. Also, the fossil is very, very beautiful.
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2. Species Concepts
This week’s issue of the Comptes Rendus Palévol (Vol. 10, Iss. 2-3) is devoted to species concepts in palaeontology. This is one of my favourite topics, both from a philosophical and a biological point of view. It is critical enough to merit its own field of study, eidonomy. In palaeontology, it can be tough to demonstrate truly separate species without falling back on typological criteria, as many of the case studies in this issue demonstrate. I highly-recommend reading through these papers. For the general overviews if you don’t want the individual case studies, check out the papers by Dubois and Laffont et al.
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Field entomologists know how critical it is to choose the proper sampling technique. If you want to capture butterflies, you use a sweep net, not beating. If you want tree ants, a pitfall trap will not do you much good. But there are some methods designed to be general: the pitfall trap is the most common. It’s basically a hole in the ground with a container and a preservative. It can be baited to attract specific groups, but in general, the pitfall trap is the best way to get a general idea of the diversity of ground-dwlling arthropods (and, with some modifications, underground-dwlling arthropods!). That said, the success of a pitfall trap is quite variable: the size of the hole/container has an effect, the strength of the preservative, the location, etc. This paper shows quite concludively that the ‘classic’ pitfall trap, using a cup, is not as successful as a funnel trap, i.e. having a funnel that leads to the cup. The larger the funnel, the more successful. The reason is pretty simple: if you observe most arthropods going near a pitfall trap, they will casually peer inside. Some of the times they fall to their doom, other times they go willingly, sometimes they start falling and manage to correct themselves, and sometimes they just ignore the trap. With a funnel, they have significantly less chances, since it’s a gentle slope. The arthropod will think it’s just a small dip in the landscape, set foot on it and most likely slip down into the container. The larger the funnel, the larger the catchment area. So keep that in mind next time you go sampling (and also keep in mind the basic rule of entomological ethics: do not sample more than necessary!).
The 3465 Ma Apex Chert is well-known. In 1993, J. William Schopf, published a paper in Science claiming to have identified microfossils (pictured above) – this would have made them by far the oldest-known life forms. Of course, this was not simply accepted, but there were no serious challenges to the discovery and the fossils remained as classic examples of early life. It wasn’t until 2002, when Martin Brasier published a paper in Nature, that Schopf’s “evidence” (which really consisted of nothing more than drawings and pictures) led to a resurgence in the debate of whether these were real fossils or mere pseudofossils. Since then, Schopf and Brasier (and their respective allies) have traded blows. I personally sided with Brasier and co., but this position was based more on paranoia and past experience than scientific evidence. Well, now I can conclusively say that I was right all along! Hah! This paper does a chemical analysis on the “fossils” using sections thinner than ever before. What they found was that they are made completely out of iron. They show no optical or chemical evidence of having been once biogenic and then geochemically replaced by iron either: they are simply fractures that filled with haematite. No fossils to be found here, move right along. To summarise it in nice, bold letters for skimming readers: the Apex Chert “fossils” are just pseudofossils.
I touched the surface of the importance of biomineralisation in the Cambrian Radiation already. This paper is a review of that subject, but doesn’t focus on the Cambrian Radiation itself, but its direct precursor and beginnings. While in the Cambrian, the first large biomineralised animals appeared, the Ediacaran had numerous small biomineralised critters swimming around. This paper reviews these organisms and various aspects of their mineralisation, including the functional, physiological and ecological aspects. The result is that it becomes clear that the advent of biomineralisation led to increased feeding efficiency and protection from predation, as well as various lifestyle advantages, such as easier attachment to substrates. In all, it adds more support for the conclusion that the Cambrian Radiation was one primarily driven by ecology, not a special evolutionary process.