User:Meghunter99/Aetosaur controvery

Desmatosuchus is a particularly large and robust aetosaur, first named by Ermine Cowles Case (1871-1953) in 1920, but originally described by E. D. Cope (1840-1897) in 1892 as Episcoposaurus. Until recently the only recognized species was D. haplocerus, famous for the large recurved spikes that grow off its cervical osteoderms, but a second species, D. chamaensis, was named in 2003 and a third, D. smalli, was named in 2005. It is that second species, D. chamaensis, that is under dispute.

In 2003, Kate Zeigler and colleagues from the New Mexico Museum of Natural History (NMMNH) named a new aetosaur species from the Chinle Formation (= Petrified Forest Formation) of the Snyder Quarry at Rio Arriba County, New Mexico. This material was not new, but in fact had been mentioned several times in the literature prior to 2003.

Identifying the osteoderms of the Snyder Quarry aetosaur as similar to those of Desmatosuchus haplocerus, the NMMNH team referred this species to that genus, naming it D. chamaensis. They differentiated it from D. haplocerus on the presence of a recurved spike on the paramedian osteoderm (in D. haplocerus no spike is present: instead there is a bump), on the gracile shape of the spikes on the lateral osteoderms (in D. haplocerus the same spikes are more robust), and on the gracile cervical osteoderms (in D. haplocerus the cervical osteoderms are, again, more robust). It is now known from other papers that the NMMNH team were still regarding the Snyder Quarry aetosaur as a species of Desmatosuchus as late as 2005. (Heckert et al. 2003, 2005, Lucas et al. 2005).

However, the Snyder Quarry aetosaur was also being studied by William G. Parker of Petrified Forest National Park. Rather than concluding that this species was a member of Desmatosuchus, Parker concluded in a 2003 masters thesis that the Snyder Quarry aetosaur 'shares almost no characters with Desmatosuchus, instead is more closely related to Paratypothorax, and represents a distinct genus'. This perspective was first published in an abstract and the same view was later alluded to in a paper on the vertebrate fauna of Petrified Forest National Park, and in other papers.

Finally, in the January 2007 issue of Journal of Systematic Palaeontology, Parker argued that D. chamaensis represented a new taxon which he named Heliocanthus. Unlike other aetosaurs, the paramedian osteoderms at the hip region and tail-base of this taxon possess a short, anteriorly directed spike. Many other features also differentiate the Snyder Quarry aetosaur from Desmatosuchus and all other aetosaurs. Parker (2007) showed that the osteoderms of the Snyder Quarry aetosaur were misinterpreted by the NMMNH team.

Given that, as mentioned above, the NMMNH team were still referring to this taxon as Desmatosuchus chamaensis as late as 2005, it seems somewhat odd that, two weeks prior to the appearance of Parker's Heliocanthus paper, Lucas et al. published a two-page paper in which they argued that the scute morphology of D. chamaensis was distinct enough from other aetosaur genera to warrant the naming of a new taxon, Rioarribasuchus. Now, there were two new generic names published for the same taxon: Heliocanthus and Rioarribasuchus.

A similar incident regarding aetosaurs also occurred in 1991, when Adrian Hunt and Spencer Lucas of the NMMNH named Redondasuchus reseri for isolated osteoderms from the Redonda Formation of New Mexico. They diagnosed this aetosaur on the basis of the shape and proportions of its osteoderms, and on the lack of raised bosses or of a radial pattern on the osteoderms. Long & Murry (1995) disagreed with the idea that such scutes were unique and diagnostic, and regarded Redondasuchus reseri as a synonym of the wide-bodied species Typothorax coccinarum.

In an unpublished thesis, Jeffrey Martz of Texas Tech University also re-evaluated Redondasuchus and concluded that the holotype osteoderms of this aetosaur were misinterpreted. In fact it seemed that Hunt & Lucas (1991) had interpreted some osteoderms both back-to-front, and as coming from the wrong side of the body. What they interpreted as a strange down-curve at the lateral edge of a left paramedian osteoderm was in fact a far less unusual change in angle near the medial edge of a right paramedian osteoderm. On the basis of this reinterpretation and other features, Martz (2002) concluded that Redondasuchus strongly resembled Typothorax, and most likely represented a small species of that taxon.

It wasn't Martz who put out a paper correcting this interpretation, citing his own thesis in the process.... but the NMMNH team. Spielmann et al. (2006) happily acknowledged Hunt & Lucas' prior misinterpretation of the Redonda Formation aetosaur osteoderms: however, they discussed the new interpretation as if it was a novel idea, even though they both cited Martz (2002), and produced figures that were uncannily similar to his. As with the apparent claim-jump regarding Parker's work on the Snyder Quarry aetosaur, one cannot help but get the impression that the NMMNH team knew of unpublished conclusions and produced a paper that pre-empted someone else's work.

I can't help but think that something odd has happened here, on two occasions. What does everyone else think about this? Furthermore, what can, and should, be done? One final thing. Apparently, the new name for the Snyder Quarry aetosaur, Rioarribasuchus, was published shortly before Parker's new name for the same taxon, Heliocanthus, as mentioned earlier. However, does this mean that the latter is destined for objective synonymy? Maybe not.

In a 2004 paper, Jerry Harris argued that DOI (Digital Object Identifier) codes can now be used to 'date' the digital publication of an article, and that controversies over the exact timing of a publication's appearance could be resolved by examining the DOI code (Harris 2004). Jerry used the small theropods Epidendrosaurus and Scansoriopteryx as examples, both of which are likely synonymous but were published within weeks of each other. A DOI for Parker's Heliocanthus paper is available on the webpage of the Journal of Systematic Palaeontology, but I haven't yet seen the DOI for the Rioarribasuchus paper. The idea of using DOIs to determine nomenclatural priority is, so far as I know, still under discussion and no rules have been formulated, but this might be worth thinking about. Having said all that, this discussion is probably moot given that I'm not aware of any indication that Parker's paper was published prior to the start of 2007 (whereas the Rioarribasuchus paper was published at the end of 2006).