Study in <em>Nature</em> Finds Teeth Evolved More or Less Simultaneously with Jaws - Evolution News & Views

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Study in Nature Finds Teeth Evolved More or Less Simultaneously with Jaws


Teeth present several evolutionary enigmas. Back in March, ENV noted a report in Nature, "On the difficulty of increasing dental complexity," that seemed to confirm the argument of Mike Behe and other ID advocates: unguided evolution has an easy time breaking things, so that their functionality is degraded, but a much harder time building up new functionality. In the study, Harjunmaa et al. studied dental mutants. We said here at the time:

Their hypothesis is tremendously significant and its publication represents a genuine breakthrough. The authors argue that known dental mutants (in mammals) invariably show a decrease in complexity, losses of structure, etc. What is never observed, however, are increases in complexity (e.g., novel cusps).
As a dentist's son, I found that insight particularly satisfying. Now a thoughtful reader, Malcolm, points out another report in Nature, this one seeking to solve the mystery of where teeth come from in the first place ("Development of teeth and jaws in the earliest jawed vertebrates"). Of teeth, the research team of R├╝cklin et al. observes:
[T]heir evolutionary origins are much debated. Placoderms comprise an extinct sister clade or grade to the clade containing chondrichthyans and osteichthyans, and although they clearly possess jaws, previous studies have suggested that they lack teeth, that they possess convergently evolved tooth-like structures or that they possess true teeth. Here we use synchrotron radiation X-ray tomographic microscopy (SRXTM)13 of a developmental series of Compagopiscis croucheri (Arthrodira) to show that placoderm jaws are composed of distinct cartilages and gnathal ossifications in both jaws, and a dermal element in the lower jaw. The gnathal ossification is a composite of distinct teeth that developed in succession, polarized along three distinct vectors, comparable to tooth families. The teeth are composed of dentine and bone, and show a distinct pulp cavity that is infilled centripetally as development proceeds. This pattern is repeated in other placoderms, but differs from the structure and development of tooth-like structures in the postbranchial lamina and dermal skeleton of Compagopiscis and other placoderms. We interpret this evidence to indicate that Compagopiscis and other arthrodires possessed teeth, but that tooth and jaw development was not developmentally or structurally integrated in placoderms.
Translation? Science Daily summarizes:
It takes both teeth and jaws to make a pretty smile, but the evolutionary origins of these parts of our anatomy have only just been discovered, thanks to a particle accelerator and a long dead fish.

All living jawed vertebrates (animals with backbones, such as humans) have teeth, but it has long been thought that the first jawed vertebrates lacked pearly gnashers, instead capturing prey with gruesome scissor-like jaw-bones.

However new research, led by the University of Bristol and published October 17 in Nature, shows that these earliest jawed vertebrates possessed teeth too indicating that teeth evolved along with, or soon after, the evolution of jaws.

Using advanced 3D microscopy, the team reconstructed the jaws of Compagopiscis, a placoderm or primitive armored jawed fish. It turns out the beast had teeth after all, so jaws and teeth emerged more or less together in evolutionary history.
Professor Philip Donoghue of the University of Bristol's School of Earth Sciences said: "This is solid evidence for the presence of teeth in these first jawed vertebrates and solves the debate on the origin of teeth."
Malcolm smartly notices:
So the solution for how teeth evolved is that they didn't! They were always there. Cool, I think I've just solved how everything evolved -- it was always there. Or did I miss something?
No, I don't think you did.

Image credit: opacity/Flickr.