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Citation: Benson RBJ, Campione NE, Carrano MT, Mannion PD, Sullivan C, et al. (2014) Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biol 12(5): e1001853. doi:10.1371/journal.pbio.1001853

Citation: Benson RBJ, Campione NE, Carrano MT, Mannion PD, Sullivan C, et al. (2014) Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biol 12(5): e1001853. doi:10.1371/journal.pbio.1001853

Most of the time I’m focusing on population genetic time scales when I think of evolutionary change. That is, allele frequency shifts within a species level lineage, or narrower. Since this is amenable to experimental analysis obviously there are advantages. But sometimes I really wonder if I’m doing a disservice to myself not paying more attention to examinations of evolutionary change on the scale of tens of millions of years and across whole clades which might have thousands of species. A new paper in PLoS BIOLOGY, Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage
is very interesting. Here’s the author summary:

Animals display huge morphological and ecological diversity. One possible explanation of how this diversity evolved is the “niche filling” model of adaptive radiation—under which evolutionary rates are highest early in the evolution of a group, as lineages diversify to fill disparate ecological niches. We studied patterns of body size evolution in dinosaurs and birds to test this model, and to explore the links between modern day diversity and major extinct radiations. We found rapid evolutionary rates in early dinosaur evolution, beginning more than 200 million years ago, as dinosaur body sizes diversified rapidly to fill new ecological niches, including herbivory. High rates were maintained only on the evolutionary line leading to birds, which continued to produce new ecological diversity not seen in other dinosaurs. Small body size might have been key to maintaining evolutionary potential (evolvability) in birds, which broke the lower body size limit of about 1 kg seen in other dinosaurs. Our results suggest that the maintenance of evolvability in only some lineages explains the unbalanced distribution of morphological and ecological diversity seen among groups of animals, both extinct and extant. Important living groups such as birds might therefore result from sustained, rapid evolutionary rates over timescales of hundreds of millions of years.

As this paper is predicated on nifty statistical analysis one has to be careful at taking the results at face value. Subsequent reanalysis might yield a different conclusion. But it is certainly an intriguing possibility that clade-level selection of some sort might be operating. I’m still very skeptical of what to even think about this, or how to conceptualize the dynamic. But that’s often a good thing.

 
• Category: Science • Tags: Dinosaurs, Evolution, Macroevolution 
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Classic 1897 painting of Diplodocus


Contemporary depiction of Diplodocus
Credit: Nobu Tamura

A few weeks ago I happened to listen to a fascinating interview on NPR with Brian Switek, the blogger behind Laelaps, and author of Written in Stone: Evolution, the Fossil Record, and Our Place in Nature. Switek was discussing his newest book, My Beloved Brontosaurus: On the Road with Old Bones, New Science, and Our Favorite Dinosaurs. To be frank I was captivated by the discussion, and immediately purchased a copy of the book. The reason is simple: despite our current divergent interests Brian Switek began at the same place I did, with dinosaurs. Though after reading My Beloved Brontosaurus I can’t assert that my dinomania matched Switek’s, it was of the same quality. The difference is that while Switek remained true to dinosaurs, my own interests wandered into other domains. Today I am focused more upon evolutionary forces operating on the scale of thousands of years within a species, rather than geological scale transmogrifications. But every now and then I wonder about dinosaurs, and whatever happened to them over the past 20 years after my “dinosaurs years” faded into the distance.

And that exactly where Switek takes me with My Beloved Brontosaurus. I read The Dinosaur Heresies in the early 1990s, but that book is now 25 years old. Yes, like everyone else I’ve seen glimmers of the controversies of the debates about dinosaur metabolism and plumage over the years, but to truly get to the guts of the matter of what people think one needs to comprehend the scientific literature, not just watch NOVA specials. And that is what Switek does, as he tours us through abstruse and esoteric journals in paleobiology to get the heart of the matter in terms of what scientists believe and know. For me the narrative was especially fascinating because I am approximately the same age as the author, and experienced many of the same cultural changes in our perceptions of dinosaurs. From lethargic large lizards to bright feathered monstrosities.

There are three primary threads in My Beloved Brontosaurus. First, a cultural history of our society’s perception of what dinosaurs looked like, how they lived, what they were in some fundamental fashion. Second, there is the cutting edge science as to what we now know of dinosaur anatomy, behavior, and systematics. Third, there is Switek’s personal biography as it relates to dinosaurs, and his reminiscences of the experience of being at various field sites.

Credit: LadyOfHats

Our perception of dinosaurs and what we know about them today in a scientific manner are obviously related. Switek’s distillation of the latest peer reviewed literature would make far less sense if we didn’t have an understanding from where we came in terms of our perceptions and preconceptions. In the late 19th and early 20th centuries dinosaurs were “terrible lizards” literally in their depction. They were green or gray sprawling reptiles, torpid and cold-blood creatures which were destined for the dust-bin of history (ergo, “he is such a dinosaur!”). Today the view is totally different. Dinosaurs are not extinct, because birds seem to be a derived lineage of theropod dinosaurs (and the extinction of the non-avian lineage is but for the grace of meteor!). It is now the majority view that many, if not most, dinosaurs were both warm blooded, and, had feathers. Not only did they have feathers, but paleontologists have been able to reconstruct the pigmentation of some dinosaurs. Would you believe they had the plumage of magpies!

If you want to know if dinosaurs were social, what they sounded like, and why they may have risen to prominence in the late Triassic, My Beloved Brontosaurus has you covered. Switek’s scope of knowledge is awesome. In Jerry Coyne’s Why Evolution is True he is referred to as a graduate student in paleontology at Rutgers. The reality is that when those words were written Switek was an undergraduate. But it’s easy to see how one could just assume he had to be a graduate student. His peregrinations across the country in search of museums and dig sites reflects a personality which one ideally would find in a graduate student, but alas far too often one does not.

One point in this book that I do want to explore is the controversy over the extinction of the dinosaurs. The public perception is that the K-T boundary exists because of a massive meteor impact. But a few years ago I saw an interview with the paleontologist Peter Ward where he denied that this was established and accepted science, which took me aback. I was interested to see that in Switek’s telling this seems a minority position, and that most scholars still accept the K-T event’s paramount importance. This is reassuring, because too often historical scientists fixate on uniformitarianism to an almost irrational extent. The wiping away of massively charismatic genera after genera all across the world over the space of a < 1 million years suggests something genuinely catastrophic. Denying the likelihood of a major exogenous shock, as opposed to a more prosaic confluence of events, bespeak a paradigmatic narrowness. If there is anything My Beloved Brontosaurus did it was to prevent me from wasting my time reading the literature in this area.

I’m hoping Switek keeps following up with these sorts of books. This is in the classic “news you can use” for nerds genre.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Dinosaurs, Evolution, Paleontology 
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There’s a very long review out which presents a theory for how sauropod dinosaurs could scale up to such enormous sizes, Biology of the sauropod dinosaurs: the evolution of gigantism. ScienceDaily is promoting the likelihood that sauropods did not chew, and so could make do with very small heads which could be supported by long necks, as the big factor. But this is a model with many moving parts. Here’s the verbal list from the conclusion:

(1) Sauropod dinosaurs as the largest terrestrial animals ever represent a challenge to evolutionary biologists trying to understand body size evolution.

(2) The study of the upper limit of body size must address extrinsic as well as intrinsic factors, and it must be determined whether this limit is set by the bauplan of the organisms or by physical and ecological constraints imposed by the environment. Among several possible approaches, we chose the resource perspective because it has been shown that resource availability and maximal body size correlate closely (Burness et al., 2001).

(3) In the interplay of the biology of sauropod dinosaurs with their environment, a unique combination of plesiomorphic features (i.e., inherited from their ancestors) and evolutionary novelties emerge as the key for a more efficient use of resources by sauropods than by other terrestrial herbivore lineages. Plesiomorphic features of sauropods were many small offspring, the lack of mastication and the lack of a gastric mill. The evolutionary innovations were an avian-style respiratory system and a high basal metabolic rate.

(4) We posit that the long neck of sauropods was central to the energy-efficient food uptake of sauropods because it permitted food uptake over a large volume with a stationary body.

(5) In the Late Triassic and Early Jurassic (210–175 million years ago), the combination of biological properties listed above led to an evolutionary cascade in the sauropodomorph lineage characterized by selection for ever larger body size, mainly driven by predation pressure from theropod dinosaurs.

(6)From the Middle Jurassic onward, sauropod dinosaurs dominated global terrestrial ecosystems only to succumb to the catastrophic environmental change at the end of the Cretaceous 65 million years ago.

And here’s a schematic illustrating the interplay of evolutionary forces & constraints:

nf9

The paper is open access, so you should read it yourself if you’re interested.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Biology, Dinosaurs, Evolution 
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Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at http://www.razib.com"