A recent paper by Kevin Padian (2013) promoted two ideas: “I suggest two changes in thinking about the beginning of the ‘‘Age of Dinosaurs’’: first, the event that we call the (phylogenetic) origin of dinosaurs was trivial compared to the origin of Ornithodira; and second, the ‘‘Age of Dinosaurs’’ proper did not begin until the Jurassic.”
Yes, this is a ‘think piece’,
and it’s a great summary of dinosaur thinking throughout the last 200 years, but it doesn’t represent current thinking. Padian is still trotting out old paradigms parked within this “history of paleontology” article. A couple of problems here:
First, there is no such clade as the Ornithodira.
Because it contains both dinosaurs and pterosaurs, each of which occupy positions on opposite branches in the large reptile tree, the “Ornithodira” includes the same taxa as the Reptilia (= Amniota). Padian still clings to the unsupportable and falsified hypothesis that pterosaurs are sisters to dinosaurs and also keeps the blinders on with regards to the Fenestrasauria.
Second, Padian’s 3 Reasons for a Jurassic Age of Dinosaurs are not news.
1. Ornithischians do not appear until the Jurassic
Granted, but their poposaur dinosaur sisters are known throughout the Triassic (Lotosaurus = Early Triassic). Padian does not realize that poposaurs were dinosaurs. Neither does Padian recognize that Daemonosaurus nests as a basal ornithischian from the Triassic.
2. Saurischian dinosaurs were larger in the Early Jurassic.
Granted, but this is old news. And they don’t get really big until the Late Jurassic, tens of millions of years later. Even so, factor 3 comes into play…
3. All non-crocodylomorphs “pseudosuchians”(= rauisuchians, phytosaurs, aetosaurs) become extinct prior to the Jurassic.
Granted, but this is old news. Their extinction does indeed clear the slate for the radiation of dinosaurs and, lest we forget… crocs, which invaded marine environs.
Padian reports, “This review began by parsing the question of the origin of dinosaurs into three kinds of problems: dinosaur monophyly and relationships; dinosaurian functional-ecological advances; and the timing and pacing of dinosaur origins and diversification.”
Unfortunately Padian shows up with bad data as he reports, “It was not only dinosaurs but also their closest relatives –lagosuchids, lagerpetids, silesaurids and pterosaurs – that shared a suite of structural, functional and metabolic features that differentiated them considerably from other reptiles before the Late Triassic onwards.”
According to the large reptile tree, lagerpetids and pterosaurs were not related to dinosaurs. So those metabolic features did not differentiate ‘ornithodires’ from other reptiles. Rather, these three disparate clades attained similar abilities and morphologies by convergence. Lagerpetids and their chanaresuchid sisters did not survive into the Jurassic. Neither did the nonvolant relatives of pterosaurs.
To his discredit
Padian ignores prior literature (Peters 2000, 2011) that matched Rotodactylus ichnites to basal fenestrasaurs like Cosesaurus. He kept his blinders on.
Brusatte SL Niedźwiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem-lineage deep into Early Triassic. Proceedings of the Royal Society of London, Series B, 278, 1107-1113.
Padian K 2013. The problem of dinosaur origins: integrating three approaches to the rise of Dinosauria. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, Available on CJO 2013 doi:10.1017/S1755691013000431
Peabody FE 1948. Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah. University of California Publications, Bulletin of the Department of Geological Sciences 27: 295-468.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605