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Re: [dinosaur] Apatoraptor, new caenagnathid oviraptorosaur from Late Cretaceous of Alberta, Canada



So, some brief observations. Some comments may be had in the future by Mickey, but these are my own.

Excellent use of CT to derive hidden information from a mostly unprepared block. While much of the specimen is exposed, some remains hidden. Reconstruction of the mandible is based on incomplete information; from the visible right to the hidden left mandibular rami. However, the symphyseal portion of the Lowe jaw is shattered and scattered, which the reconstruction takes some liberties correcting. Despite this, some of the matrix coding is derived from this reconstruction, where the features are ambiguous.

Funston and Currie go to some lengths - understandably so - to distinguish their taxon from Epichirostenotes curriei (ROM 43250). The overlapping material between the two specimens is scarce, limited to vertebrae, and of these dorsal vertebrae in the new specimen (TMP 93.51.1) little is available due to encrusting matrix. So we are left with descriptions of cervical vertebrae, most of which were likewise hidden and unrefined in their analysis. The new specimen description describes principally the ventral and lateral surfaces of the preserved cercivodorsal series, including so-called cervicodorsals. The authors assume all vertebrae of the cervical series are present (I assume due to their apparent proximity to the mandible, as they otherwise do not say). A trapezoidal bone is present of the skull, which is presumed to be the palatine, and resembles what has been described of ROM 43250. Funston and Currie distinguish Epichirostenotes curriei from their new taxon on two sets of criteria, the first being morphological and the other ontogenetic. First, they provide for "winglike" transverse processes of the cervical vertebrae in Epichirostenotes, which is what is deemed a transverse process fused to its rib, and the absence of this in their new taxon; and of the presence in Epichirostenotes but the absence in the new taxon of a postzygapophyseal lamina, or the lack in Epichirostenotes of an infradiapophyseal fossa. While calling into question themselves about placement of these vertebrae, to better facilitate comparison, the authors at once also note the similar levels of fusion of the neurocentral joints in exposed vertebrae. Rib comparisons suggest that Epichirostenotes material doesn't contain a rib with a proximal pneumatic foramen and a lamina connecting the capitulum and tuberculin; but even the authors note this differentiation is ambiguous due to absent material in ROM 43250. Size in ROM 43250 compared to TMP 93.51.1 suggest the former is 52% larger than the latter, or that that is the ratio of their cervical vertebrae.

So my first concern is that the issue of ontogeny is at once dismissed by the similar fusion of neurocentral joints, and that that is that. Ontogeny, as we've been discovering through investigations into ceratopsians, tyrannosaurids, birds, crocs, and even sauropods, isn't so clean. And in the absence of relatively complete material clearly referrals to whatever ROM 43250 is, it seems obvious to me that whatever TMP 93.51.1 is, that animal may likely be a younger, but still somatically mature version of the previously named taxon. But similarly, I have to question naming of Epichirostenotes, then of Apatoraptor following it, because of this concern. Epichirostenotes, if TMP 93.51.1 could be referrable to it on geographic, stratigraphic, morphologic, and even the question of differences on ontogenetic grounds, would be valid; but as long as the type is diagnostic, the value of the better specimen merely elucidates, but does not supplant. That there is limited evidence that the two specimens are so distinct from one another they deserve distinct taxonomic nomenclature.

The phylogenetic analysis is itself somewhat problematic, but not for reasons stated above. Aside from the removal of state ordering, the authors also excluded from one branch of the analysis Leptorhynchos gaddisi, a type species, on the grounds of its mandible-ness (it's inclusion causing a polytomy) a priori to the analysis run, rather than pruning it after the fact. They also a priori exclude Ojoraptorsaurus boerei a priori altogether, due to completeness, but this is irrelevant, and harmful: as it bears a unique suite of character states, it may still serve interesting information overall. The authors also add Protarchaeopteryx robusta, but as I am reminded by Mickey Mortimer, failed to include characters that connect it to Incisivosaurus gauthieri, by Senter et al 2004 who argued for the latter species' referral to Protarchaeopteryx.

Support recently for referral of non-overlapping remains to taxa named from cranial bits or partial hands and feet by authors (Sues, Averianov, others, for Caenagnathasia, in which fused mandibles differing largely in size are assumed to be congruent, but wisely rendered as Caenagnathasia sp.; Funston and Currie for Elmisaurus rarus, without similar concerns to referral) stems from the need to place new specimens in context, but this seems to have been the opposite approach. There is no doubt TMP 93.51.1 is important, elucidating, valuable. But problematic to its description is the creation of a unique binomen without concern for the issues that it brings.

On Apr 12, 2016 9:15 PM, "Ben Creisler" <bcreisler@gmail.com> wrote:

Ben Creisler
bcreisler@gmail.com

A new paper:

Gregory F. Funston & Philip J. Currie (2016)
A new caenagnathid (Dinosauria: Oviraptorosauria) from the Horseshoe Canyon Formation of Alberta, Canada, and a reevaluation of the relationships of Caenagnathidae.
Journal of Vertebrate Paleontology (advance online publication)
DOI:10.1080/02724634.2016.1160910
http: // www.tandfonline.com/doi/full/10.1080/02724634.2016.1160910

Our understanding of caenagnathids has benefited from recent discoveries, including nearly complete skeletons from the Hell Creek Formation of Montana. However, their phylogenetic relationships remain unclear. A new specimen from the Horseshoe Canyon Formation of Alberta has implications for the phylogeny and paleobiology of these creatures. The partial skeleton is articulated and includes a mandible, a full cervical and dorsal series of vertebrae, a right pectoral girdle and arm, a sternum, gastralia, a partial ilium, and a partial hind limb. The mandible is edentulous and the articular ridge is intermediate in form between Caenagnathus collinsi and Chirostenotes pergracilis. The neck is long and composed of at least 11 well-pneumatized cervical vertebrae with fused cervical ribs. The dorsal ribs have finger-like uncinate processes dissimilar in shape to those of other oviraptorosaurs. The pectoral girdle is large and typically maniraptoran, except that the glenoid of the scapulocoracoid faces laterally instead of posteroventrally. The arm is well muscled and can be interpreted to have been a pennibrachium, as indicated by ulnar papillae on the ulna. The manus is characterized by a short first metacarpal but an elongate phalanx I-1 and oviraptorid-like phalangeal proportions in the second digit. These and other features indicate that the specimen represents a new taxon, Apatoraptor pennatus, gen. et sp. nov. Phylogenetic analysis resolves the complicated relationships of Caenagnathidae and allows the evolution of display features to be traced throughout Oviraptorosauria.


http: // zoobank.org/urn:lsid:zoobank.org:pub:122957D7-F65F-4A2C-86AF-386AE8AAF2C4