There is quite a bit of buzz this week about Matthew Barron and colleagues report on a new classification of dinosaurs .
The researchers amassed a very large dataset of dinosaur fossils, the largest and most comprehensive known collection. The data include specimens from 74 taxa which were scored on 457 traits. (While Dinosaurian in comparison to earlier studies, in this age of Big Data this dataset is still pretty puny. As the press reports noted, it took years to round up the data by hand, and five minutes to run the program.)
The resulting family tree is considerably different from text book consensus up to now. As it should be. The overthrown classifications were based on small datasets and quite a few untested assumptions and intuitions. Since the new analysis doesn’t include these assumptions, the results are different.
Of course, this sort of analysis needs to be taken carefully. This dataset is big enough and broad enough that it is worth taking seriously, but we still need to remember the limitations of the method.
First of all, the data are based mainly on skeletal remains, which are only a partial picture of the animals in question. We know only too well that skeletal analysis can mislead.
In addition, this kind of analysis can be quite sensitive to the exact sample used. Adding or omitting some traits, or additional fossils could rearrange the results, possibly quite a bit. This means that future contributions might well produce different results.
The researchers point out some aspects of the classification that seem to add face validity to the results. In this tree, the earliest taxa seem to be small and omnivorous, which makes sense. Gigantic size and specialized diets would seem to be evolved from more moderate sized and general animals.
One conclusion that is particularly interesting is that in this taxonomy, “the supinated, grasping hands seen in some early taxa are interpreted as the primitive dino- saurian condition.” (p. 505) In other words, early dinosaurs had grasping front pawa. As they say, this might have been a key evolutionary advantage, and might also have been a precursor to development of bipedalism.
- Matthew G. Baron, David B. Norman, and Paul M. Barrett, A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature, 543 (7646):501-506, 03/23/print 2017. http://dx.doi.org/10.1038/nature21700