In the previous post we introduced the aetosaurs, a strange and fascinating group of armour-plated quadrupedal Triassic crurotarsans. Equipped with stout limbs, a strange upturned snout and (usually) toothless jaw tips, aetosaurs have been interpreted as omnivores, herbivores, and even as armadillo-like generalists. But it’s not just their lifestyles that have been the subject of controversy. By following the publication dates of various recent technical papers on these animals, it seems that some aetosaur workers themselves have been acting in a controversial manner…
Aetosaur fossils were first documented by Louis Agassiz (1807-1873) in 1844, although the Stagonolepis specimen that he described was misinterpreted by him as an armoured fish. While aetosaur research has a long and noble history, study of the group has undergone something of a renaissance in recent years, as is the case with so many groups of Mesozoic reptile. Accordingly, a large number of new aetosaur genera have been named since the 1980s, including Paratypothorax Long & Ballew, 1985, Longosuchus Hunt & Lucas, 1990, Redondasuchus Hunt & Lucas, 1991, Lucasuchus Long & Murry, 1995, Acaenasuchus Long & Murry, 1995, Coahomasuchus Heckert & Lucas, 1999 and Tecovasuchus Martz & Small, 2006, though not all of these taxa are accepted by all aetosaur workers. Several additional taxa await naming and description [the scene at the top, depicting a sunny day in the Late Triassic, shows an aetosaur, some dicynodonts and a basal dinosaur. I don't know who the artist was (thought it might be Peter Snowball, but it ain't), image from here].
New species have also been named within long-recognised genera. 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 recognised species was D. haplocerus, famous for the large recurved spikes that grow off its cervical osteoderms [shown in adjacent image, borrowed from here], 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 has caused all the problems…
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 Zeigler et al.’s usage) of the Snyder Quarry at Rio Arriba County, New Mexico (as explained by Parker (2007), Zeigler et al.’s paper is dated 2002 but was not published until Spring 2003). 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) (Zeigler et al. 2003). We know 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’ (Parker & Irmis 2005). This perspective was first published in an abstract (Parker 2003) and the same view was later alluded to in a paper on the vertebrate fauna of Petrified Forest National Park (Parker & Irmis 2005), and in other papers [adjacent image shows paramedian osteoderms of Aetosaurus].
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 (Lucas et al. 2006). In other words, we now have two new generic names published for the same taxon: Heliocanthus and Rioarribasuchus. I don’t want to seem accusatory, but Lucas et al.’s naming of Rioarribasuchus has the general feeling of a claim-jump about it: it’s almost as if Lucas et al. knew that Parker was going to publish a new name for the Snyder Quarry aetosaur, and therefore quickly rushed out their own new generic name in order to beat him to it. Is this really what happened? It certainly looks like it.
What makes this situation all the more suspicious is that a similar thing has happened elsewhere in the aetosaur literature. In 1991, 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 (Hunt & Lucas 1991). 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 [adjacent pic is yet another life restoration of D. haplocerus, and not a particularly good one I'm sorry to say].
This is where this story takes an odd turn. 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).
So there you have it. Ha – and you thought dinosaurs were controversial! And I haven’t even mentioned the long series of exchanges that occurred between members of the NMMNH team and Simon Harris, David Gower and Mark Wilkinson. Another time, maybe.
PS – while searching for images that could accompany this article I found BUGGER ALL in the way of good pieces of art. A plea: artists, please stop drawing bloody theropods and do some nice crurotarsan pictures!
Refs – –
Harris, J. D. 2004. ‘Published works’ in the electronic age: recommended amendments to Articles 8 and 9 of the Code. Bulletin of Zoological Nomenclature 61, 138-148.
Heckert, A. B., Lucas, S. G. Sullivan, R. M., Hunt, A. P. & Spielmann, J. A. 2005. The vertebrate fauna of the Upper Triassic (Revueltian: early-mid Norian) Painted Desert Member (Petrified Forest Formation: Chinle Group) in the Chama Basin, northern New Mexico. New Mexico Geological Society Guidebook 56, 302-318.
– ., Zeigler, K. E. & Lucas, S. G. 2003. Aetosaurs (Archosauria: Stagonolepididae) from the Upper Triassic (Revueltian) Snyder Quarry, New Mexico. New Mexico Museum of Natural History and Science, Bulletin 24, 115-126.
Hunt, A. P. & Lucas, S. G. 1991. A new aetosaur from the Redonda Formation (Late Triassic: Middle Norian of east-central New Mexico, USA). Neues Jahrbuch fur Geologie und Palaontologie, Monatshefte 1991, 728-736.
Long, R. A. & Murry, P. A. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science, Bulletin 4, 1-254.
Lucas, S. G., Hunt, A. P. & Spielmann, J. A. 2006. Rioarribasuchus, a new name for an aetosaur from the Upper Triassic of north-central New Mexico. New Mexico Museum of Natural History and Science, Bulletin 37, 581-582.
– ., Zeigler, K. E., Heckert, A. B. & Hunt, A. P. 2005. Review of Upper Triassic stratigraphy and biostratigraphy in the Chama Basin, northern New Mexico. New Mexico Geological Society Guidebook 56, 170-181.
Martz, J. W. 2002. The morphology and ontogeny of Typothorax coccinarum (Archosauria Stagonolepididae) from the Upper Triassic of the American Southwest. Unpublished M.S. thesis, Texas Tech University (Lubbock, TX).
Parker, W. 2003. Revised taxonomy of the Late Triassic aetosaur Desmatosuchus (Archosauria: Crurotarsi) from the southwestern United States. Journal of Vertebrate Paleontology 23 (3 Suppl.), 85A.
– . 2007. Reassessment of the aetosaur ‘Desmatosuchus‘ chamaensis with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia). Journal of Systematic Palaeontology 5, 41-68.
– . & Irmis, R. B. 2005. Advances in Late Triassic vertebrate paleontology based on new material from Petrified Forest National Park, Arizona. New Mexico Museum of Natural History and Science, Bulletin 29, 45-58.
Spielmann, J. A., Hunt, A. P., Lucas, S. G. & Heckert, A. B. 2006. Revision of Redondasuchus (Archosauria: Aetosauria) from the Upper Triassic Redonda Formation, New Mexico, with description of a new species. New Mexico Museum of Natural History and Science, Bulletin 37, 583-587.
Zeigler, K. E., Heckert, A. B. & Lucas, S. G. 2002. A new species of Desmatosuchus (Archosauria: Aetosauria) from the Upper Triassic of the Chama Basin, north-central New Mexico. New Mexico Museum of Natural History and Science, Bulletin 21, 215-219.