Field of Science

The Origin and Early Radiation of Dinosaurs

Finally this is out, although presently only as an accepted manuscript in Earth Science Reviews.  I was one of the reviewers for this paper and felt that it constitutes a very well written overview of early dinosaur work to the present, including many of the recent cool finds from the Chinle Formation of course.  I was reviewing this manuscript last year about the time another early dinosaur review paper came out by Max Langer and colleagues (not sure why this paper is so delayed) and feel that these papers are nice complements to each other.

[Note: after writing this I noticed that Brusatte et al. added a similarily worded paragraph to the end of the introduction.  I also noticed that they use the word "compliment" when they mean "complement".  See the difference here ;)].

Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and M. A. Norell. 2010. The origin and early radiation of dinosaurs. Earth Science Reviews. Early online. doi: 10.1016/j.earscirev.2010.04.001

Abstract - Dinosaurs were remarkably successful during the Mesozoic and one subgroup, birds, remain an important component of modern ecosystems. Although the extinction of non-avian dinosaurs at the end of the Cretaceous has been the subject of intense debate, comparatively little attention has been given to the origin and early evolution of dinosaurs during the Late Triassic and Early Jurassic, one of the most important evolutionary radiations in earth history. Our understanding of this keystone event has dramatically changed over the past 25 years, thanks to an influx of new fossil discoveries, reinterpretations of long-ignored specimens, and quantitative macroevolutionary analyses that synthesize anatomical and geological data. Here we provide an overview of the first 50 million years of dinosaur history, with a focus on the large-scale patterns that characterize the ascent of dinosaurs from a small, almost marginal group of reptiles in the Late Triassic to the pre-eminent terrestrial vertebrates of the Jurassic and Cretaceous. We provide both a biological and geological background for early dinosaur history. Dinosaurs are deeply nested among the archosaurian reptiles, diagnosed by only a small number of characters, and are subdivided into a number of major lineages. The first unequivocal dinosaurs are known from the late Carnian of South America, but the presence of their sister group in the Middle Triassic implies that dinosaurs possibly originated much earlier. The three major dinosaur lineages, theropods, sauropodomorphs, and ornithischians, are all known from the Triassic, when continents were joined into the supercontinent Pangaea and global climates were hot and arid. Although many researchers have long suggested that dinosaurs outcompeted other reptile groups during the Triassic, we argue that the ascent of dinosaurs was more of a matter of contingency and opportunism. Dinosaurs were overshadowed in most Late Triassic ecosystems by crocodile-line archosaurs and showed no signs of outcompeting their rivals. Instead, the rise of dinosaurs was a two-stage process, as dinosaurs expanded in taxonomic diversity, morphological disparity, and absolute faunal abundance only after the extinction of most crocodile-line reptiles and other groups.

9 comments:

  1. It is indeed a cracking paper - I will definitely be keeping it handy. The only issue I had was the conflation between contingency and chance. As Gould stressed in Wonderful Life, the two are related but not the same (Michael Shermer has also addressed the point in an essay here - http://www.stephenjaygould.org/library/shermer_contingency.html)

    Despite that quibble, though, I loved it, and I definitely appreciated the willingness of the authors to consider the macroevolutionary implications of what they had covered.

    ReplyDelete
  2. This comment has been removed by the author.

    ReplyDelete
  3. Yes, I agree completely. We are talking about contingency, and I think this comes across clearly in our discussion (at least I hope). We only use the word 'chance' at one point in the manuscript. This was meant to convey that what we mean by contingency--clearly the better term--has often been considered as "chance" in the literature on dinosaur origins,. This comes across as a bit confusing, though, and we'll try to change it in the proofs. In any case, as Randy says, we do not argue that the rise of dinosaurs was a chance event, but rather that it was contingent on various unpredictable events in earth history.

    Steve Brusatte

    ReplyDelete
  4. Thanks for the updates/comments about the "chance" issue. I understood the thrust of the argument, and I most certainly agree about the evolution of dinosaurs being contingent upon unpredictable events (most prominently mass extinctions), just the line "The tension between selection and contingency (chance)..." on page 66 of 163 in the accepted manuscript version set off a red flag in my mind.

    Like I said, though, that is a nitpick on what is otherwise a great review.

    ReplyDelete
  5. Check out the first line in the link below. This is how I'm used to seeing the word "contingency" used as well. I didn't realize it was controversial.

    http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRT-4M2X87W-7&_user=10&_coverDate=10%2F10%2F2006&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1326000992&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0d6f8905ac8888f29cbae8ed7abb23e8

    ReplyDelete
  6. The link didn't paste. The article I was trying to link is:
    Erwin, D.H. 2006. Evolutionary contingency. Current Biology 16:R825-R826 doi:10.1016/j.cub.2006.08.076

    The first line of the article reads: "What is contingency? Chance, in a word."

    ReplyDelete
  7. Bill - Thanks for the link to the paper.

    Most of the controversy had to do with the ongoing debate between Gould and Dennet/Dawkins/Conway Morris, but even though that has mostly died down I think there is still some confusion between the relationship between chance and contingency.

    The way I interpret Gould's point, chance does not equal contingency, but is just part of the larger historical explanation. Events in the history of life on earth (such as mass extinctions) may be the result of chance or are at the very least unpredictable, and this series of unpredictable states has a major influence on evolution. Gould presented this as a counterpoint to a law-like version of evolution that Conway Morris and others have promoted (i.e. run the "tape of life" again according to the same natural laws and you will get practically the same outcome). As defined by Gould himself in Wonderful Life, contingency is "an unpredictable sequence of antecedent states", so while chance does play a role in that I wouldn't say the two are equivalent, especially since antecedent states don't always have to be the result of chance events - exaptations, I would think, would also be a fine example of how a previous state influenced the evolution of a lineage. In such a case the reason why an organism possessed the characteristic would be understandable by contingency, as well, but it would not be directly attributable to chance.

    ReplyDelete
  8. I agree with Gould/Brian's interpretation of contingency. Contingent events in earth history are certainly not subject to chance alone, they are merely unpredictable. There are certainly good uniformitarian reasons why these events happen, whether it be ocean anoxia or a bolide impact. Just because an event is not predictable does not mean it is by "chance" or "random." A hurricane hitting New Orleans is certainly a contingent event (at least within the span of human lifetime), but no one would say it is chance (we understand very well why there is such a high hurricane risk in the Gulf Coast).

    ReplyDelete
  9. I have a project which is all about Dinosaurs, this blog really helps me gain more knowledge for my project. Hope to hear more like this article.

    ReplyDelete

Markup Key:
- <b>bold</b> = bold
- <i>italic</i> = italic
- <a href="http://www.fieldofscience.com/">FoS</a> = FoS