[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
In all the excitement, I'm not sure the actual paper on the new
dinosauromorph (_Dromomeron romeri_) was actually mentioned here. Here's
Randall B. Irmis, Sterling J. Nesbitt, Kevin Padian, Nathan D. Smith, Alan
H. Turner, Daniel Woody, and Alex Downs (2007). A Late Triassic
dinosauromorph assemblage from New Mexico and the rise of dinosaurs.
Science 317: 358-361.
Abstract: "It has generally been thought that the first dinosaurs quickly
replaced more archaic Late Triassic faunas, either by outcompeting them or
when the more archaic faunas suddenly became extinct. Fossils from the
Hayden Quarry, in the Upper Triassic Chinle Formation of New Mexico, and an
analysis of other regional Upper Triassic assemblages instead imply that the
transition was gradual. Some dinosaur relatives preserved in this Chinle
assemblage belong to groups previously known only from the Middle and
lowermost Upper Triassic outside North America. Thus, the transition may
have extended for 15 to 20 million years and was probably diachronous at
So far, only hindlimb elements have been assigned to _Dromomeron_, and these
closely resemble those of _Lagerpeton_. In addition to _Dromemeron_, the
Hayden Quarry also yielded a "_Silesaurus_-like dinosauriform" that may be
the same as _Eucoelophysis_ (but so far there's no overlapping diagnostic
material, which is required to establish that they are the same); a
coelophysoid; _Chindesaurus bryansmalli_ (basal saurischian); and a host of
The accompanying phylogeny shows a clade comprising _Lagerpeton_ and
_Dromomeron_ as the most basal dinosauromorph clade. Irmis &c do not
mention the name Lagerpetonidae, which is available for this new clade
(Arcucci, 1986). Higher up (as sister taxon to Dinosauria) is a clade
comprising _Silesaurus_, _Eucoelophysis_ and the new Hayden Quarry
"silesaur" (if not the same as _Eucoelophysis_). Elsewhere, Nesbitt et al.
(2007) suggested that _Pseudolagoschus_ (=?_Lewisuchus_) may belong to this
"silesaur" clade. Pterosaurs (represented by _Eudimorphodon_ and
_Dimorphodon_) are recovered by Irmis &c as the sister taxon to
The tree in Fig. 3 includes a long ghost lineage for the
Dinosauria+"silesaur" line after it diverged from basal dinosauriform line
(_Marasuchus_). I did wonder if certain poorly known ornithodirans may
belong on this dinosaur line, such as _Avipes_ or _Saltopus_, but they may
be too fragmentary or poorly preserved to be sure.
The only quibble I have with the _Dromomeron_ paper is that they call the
crocodilian stem group "Pseudosuchia". I much prefer Crocodylotarsi or
Crurotarsi, rather than having a clade called "Pseudosuchia" that includes
both Suchia and Crocodilia!
Nesbitt, S.J., Irmis, R.B., and Parker, W.G. (2007). A critical
re-evaluation of the Late Triassic dinosaur taxa of North America. Journal
of Systematic Palaeontology 5 (2): 209?243.
Arcucci, A. (1986). Nuevos materiales y reinterpretacibn de _Lagerpeton
chanarensis_ Romer (Thecodontia, Lagerpetonidae nov.) del Triasico medio de
La Rioja, Argentina. Ameghiniana 23: 223-242.
Don't get caught with egg on your face. Play Chicktionary!