Caenagnathid taxonomy has been controversial for decades because most species from the Campanian-Maastrichtian are known from parts which don't overlap with others. Caenagnathus collinsi, C? sternbergi and Leptorhynchos are known from mandibles, Chirostenotes, Hagryphus and Elmisaurus rarus are known from hands, and Macrophalangia, Elmisaurus rarus and E? elegans are known from metatarsi. In addition, two partial skeletons have been described. RTMP 79.20.1 preserves a manus and pes but no mandible, and has been agreed by most to be Chirostenotes. ROM 43250 doesn't preserve mandibles, manus or pes, and has been called Epichirostenotes. I don't think it differs significantly from Chirostenotes (RTMP 79.20.1 shares the sacrum, ischium and distal tibia), but its later age means it probably was different. I've been hoping Anzu would be the Rosetta Stone for caenagnathids, since it preserves mandibles, manual material and pedal material, along with sacrum, ischium and tibia. Alas, at least with the info provided by Lamanna et al., it doesn't seem to help much.
My first inclination was to check the phylogenetic analysis. The authors did an excellent job sampling basically all oviraptorosaurs and adding characters from the various oviraptorosaur analyses that began back with Maryanska et al. (2002). Though I do wonder where Protarchaeopteryx is and why the complete Similicaudipteryx specimens weren't coded. Note the much younger Yulong was included, the poorly illustrated Jiangxisaurus, and the barely codable Ojoraptorsaurus, so none of those seem like reasonable excuses. It probably explains why Similicaudipteryx ends up in Caudipteridae, since the holotype doesn't preserve the skull or manus. Also note Lamanna et al. use the incorrect Caudipterygidae instead of Caudipteridae. In any case, Caenagnathidae is a big polytomy in Lamanna et al.'s strict consensus tree, which is unsurprising if for no other reason than they included Ojoraptorsaurus, a dubious taxon known from an incomplete pubis and only codable for three characters. The authors then include only caenagnathids known from dentary material and find the same topology as in the Leptorhynchos paper.
But surely Anzu could help us do more? What about including only caenagnathids known from manual material (Chirostenotes, Elmisaurus, Hagryphus, Anzu)? Only pelvic material (Chirostenotes, Epichirostenotes, Anzu)? Only pedal material (Chirostenotes, Macrophalangia, Elmisaurus)? The authors don't test these, so I did. And they're all polytomies. I even gave intertaxon overlap its best chance by combining probably synonymous taxa like Longrich et al. (2013), so that collinsi and Macrophalangia are one, Chirostenotes and sternbergi are one, and Elmisaurus/Leptorhynchus is one OTU. But still, no resolution*.
* The one exception is the pelvic test, where Epichirostenotes is closer to Anzu than Chirostenotes (RTMP 79.20.1). Alas, this is based on one character, the ventral flange on the pubic peduncle of the ischium, supposedly lacking in the latter. Going back to the original description of RTMP 79.20.1 by Currie and Russell (1988), they state "The proximal end of the ischium is crushed, so that the iliac and pubic sutures cannot be distinguished" and their figure shows that area with a different texture and irregular outline, suggesting the lack of a flange is taphonomic. Even if it wasn't, Tyrannosaurus, Microraptor and Archaeopteryx all vary in this character.
|Gigantoraptor on the left (after Xu et al., 2007), Anzu on the right (after Lamanna et al., 2014). Which one is the main postcranial figure from a Nature publication, and which is from a PLoS ONE publication?|
So it seems the matrix just doesn't have the characters to distinguish Campanian-Maastrichtian caenagnathids. But we can compare Anzu to the other taxa ourselves, right? Well, kinda. This is my biggest complaint about the paper, namely that illustration- and description-wise, it might as well be in Science or Nature. The illustrations are gorgeous, don't get me wrong, but there are so few of them. A total of 20 postcranial elements are illustrated (only 6 in more than one view), out of 31 preserved kinds of appendicular elements and 47 vertebral elements, plus ribs, chevrons and gastralia. Sure illustrations take time, but what about photographs? This is PLoS ONE- there's no limit to the number of figures that can be included. The description is similarly lacking. This is the first uncontroversial caenagnathid to preserve a scapula, radius, ulna or fibula, but each of these elements gets only one sentence of description and the fibula isn't even illustrated outside the line drawing skeletal reconstruction. The measurement tables are also only partially complete. We have the first complete presacral series for a caenagnathid and a tail three-fourths complete, but only three cervicals, two dorsals of unstated position and the three distalmost caudals are measured. Even the materials list is vague. The holotype includes "multiple cervical and caudal vertebrae", "several
manual phalanges including unguals" and "several pedal phalanges including unguals", while CMN 78001 includes "several caudal vertebrae" and "several pedal phalanges including unguals". Why not just be exact? You can get a bit of this information from the measurement table, but not all of it since only some bones are measured.
All of this combines to make it very difficult to improve caenagnathid taxonomy using Lamanna et al. (2014). Want to compare the manus to Chirostenotes, Hagryphus and Elmisaurus rarus? You get three sentences, a drawing of ungual I in one view and measurements of five bones. Want to compare the sacrum to Chirostenotes and Epichirostenotes? You get two sentences and three measurements. Compare the pes to Macrophalangia, Chirostenotes and Elmisaurus? One sentence, a drawing of an unidentified pedal ungual in one view, and the length of nine bones. There's just very little to work with, so that the status of Anzu has changed remarkably little with its official publication. It remains important in theory, but with too little information released to work with much in practice. Hopefully, this is only a preliminary description that will be supplemented by a monograph in the future.
References- Currie and Russell, 1988. Osteology and relationships of Chirostenotes pergracilis (Saurischia, Theropoda) from the Judith River (Oldman) Formation of Alberta, Canada. Canadian Journal of Earth Sciences. 25, 972-986.
Currie, Godfrey and Nessov, 1994. New caenagnathid (Dinosauria: Theropoda) specimens from the Upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences. 30(10), 2255-2272.
Maryanska, Osmolska and Wolsan, 2002. Avialan status for Oviraptorosauria. Acta Palaeontologica Polonica. 47 (1), 97-116.
Schachner, Lyson and Hanks, 2006. A preliminary report of a new specimen of Chirostenotes (Oviraptorosauria: Theropoda) from the Hell Creek Formation of North Dakota. Journal of Vertebrate Paleontology. 26, 120A.
Xu, Tan, Wang, Zhao and Tan, 2007. A gigantic bird-like dinosaur from the Late Cretaceous of China. Nature. 844-847.
Lamanna, Sues, Schachner and Lyson, 2014. A new large-bodied oviraptorosaurian theropod dinosaur from the Latest Cretaceous of Western North America. PLoS ONE. 9(3), e92022.