Unenlagiidae is the name commonly used to envelop a small cadre of southern, Gondwana-only theropods. Recently, some papers have been published that cast new perspectives on these taxa, including a review of the group. Some forthcoming papers even concern the purpose of this blog, but I will not go into them until they are published.
The term Unenlagiidae was coined by José Bonaparte for a group containing then very-similar Unenlagia and Rahonavis (Bonaparte, 1999; he used the name to include the Australian “bird-like” theropod Timimus hermanni [Rich et al., 1993]). While used by other systematists, the name was changed to Unenlagiinae due to a convolution of the ICZN, which mandates that -idae endings are used for the “family” rank, and -inae is used for the “subfamily” rank; the ICZN argues that when an author names a taxon any any rank within the “family” level, he or she names all of them simultaneously, thus allowing Bonaparte the authorship of two names, even when he only intended the first. Nonetheless, the common term for this group is now Unelagiinae, a practice that I think should fall out of favor, as supporting this convention supports the use of rank-based nomenclature on top of it, and abandoning rank-based nomenclature allows freedom (and correct authorship of taxonomic acts) to coin taxa where useful, and at no other time. But I digress.
The first of two works are a review of the Unenlagiidae, as a subgroup of Dromaeosauridae (Gianechini & Apesteguia, 2011) while the other concerns itself with the placement of this group among theropods (Agnolin & Novas, 2011). The first deals with the identity of all the various taxa that have been assumed to be a member of this group, while the second tests this by placing them into phylogenetic analyses. First, here are the taxa used by virtually all authors in order of naming:
Unenlagia comahuensis Novas & Puerta, 1997
Rahonavis ostromi Forster, Sampson, Chiappe & Krause, 1998
Unenlagia paynemili Calvo, Porfiri & Kellner, 2004
Neuquenraptor argentinus Novas & Pol, 2005
Buitreraptor gonzalezorum Makovicky, Apesteguía & Agnolín, 2005
Austroraptor cabazai Novas, Pol, Canale, Porfiri & Calvo, 2009
Not included in the above illustration are several unenlagiids, Neuquenraptor argentinus and Unenlagia paynemili. Of course, this was at the time intentional: Neuquenraptor has not been fully illustrated, and this I was reluctant producing a skeletal from such limited information, as well as the lack of measurments of the key features; the same is also true of Unenlagia paynemili which was, as of Buitreraptor gonzalenzorum, potentially a synonym of each other (Makovicky et al., 2005). This is a little tricky: If Neuquenraptor argentinus is a junior synonym of Unenlagia paynemili, then the older species name takes priority, but a measure of taste suggests that Neuquenraptor is still a useful name for the species it contained, even if this name is a synonym of other species, allowing the combination Neuquenraptor paynemili. This doesn’t seem to be a potential issue as of yet: Gianechini & Apesteguía (2011) argue that paynemili and argentinus may not synonyms, as they differ in a few key regions (including a relatively longer pdII-1), but since this comparison is not present between the holotypes but only due to referred specimens, synonymy is not testable — the taxa are best kept separate for now.
Gianechini & Apesteguía (2011) provide their own skeletals for the two omitted taxa:
Note that the Buitreraptor gonzalezorum skeletal in both diagrams above is actually the same: Gianechini & Apesteguía (2011) modified my skeletal (with attribution, so I am happy — if I recall, Sebastián Apesteguía asked me for permission, not that I am troubled if he hadn’t) “fluffed” the outline with feathers, and dropped the arms, then slightly reposed the right leg and jaw. Nonetheless, a bigger view of the skeletal. The authors are focusing on South American Unenlagiidae, so Rahonavis ostromi (Forster et al., 1998) is omitted, as it derives from the Maastrichtian of the Maeverano Formation of Madagascar (so while it is the smallest unenlagiid, it is also the youngest).
Note then that Unenlagiidae trends in scale: the youngest South American taxon, Austroraptor cabazai, is the largest, while the smallest is also the oldest, Buitreraptor gonzalezorum. Agnolín & Novas (2011) found that Rahonavis ostromi is the most basal member of the group, splitting off from the taxa, in a modification of the Theropod Working Group (TWG; Agnolín & Novas use “TWiG,” forming a pronouncable acronym) matrix found in Hu et al. (2009), and thus supportive of a potentially long ghost lineage leading from the tiny origins of the group towards increasingly “giant” size in Unenlagia and Austroraptor. Agnolín & Novas (2011) also support placement of the Unenlagiidae in a clade called Avialae, which is comprised of all taxa closer to birds than to dromaeosaurids (I will not go into the technical definition here, it’s far longer and there’s much more to it than that, and it may change depending on who you listen to: see here), along with Alvarezsauridae (another taxon recently gaining in members).
Oddest of these, of course, is Rahonavis ostromi.
While the smallest, it has the longest arms, as indicated by the extremely long radius and ulna. It has been implied to be a powered flier, due to the laterally-facing scapular glenoid (if the scapula is correctly oriented with the flat of the scapular blade laying horizontally flat) that would permit the humerus to elevate above the transverse plane when extended outward; this can be inferred without a humerus, but when using the humerus of other unenlagiids, especially that of Unenlagia comahuensis (even though it has a relatively short humerus, and this a relatively short arm), it can be speculated the the forelimb was longer than the entire presacral vertebral column and skull, or the leg, both features previously known only in Avialae of a form similar to Archaeopteryx lithographica or closer to modern birds than that.
Key to the Unelagiidae are several unique features, including a dorsally concave postacetabular ala (posterior lobe); a narrowed posteroventral heel to the pdII-2 phalanx, which is raised into “switchblade” form in unenlagiids, dromaeosaurids and troodontids (the analysis that finds this apomorphic of Unenlagiidae does so because it places them in a group which basally lacks this feature, including the Alvarezsauridae, while troodontids and microraptorian dromaeosaurids also possess the narrow heel); and longitudinal ridges or keels on the teeth (a feature which will be discussed in a bit, a paper is in press on this topic).
[Edit: I had mislabeled the phalanges as "md" and not "pd" (for "pedal digit" instead of "manual digit").]
Additionally, it should be noted that on my modification, I used the Unenlagia paynemili holotype number for both specimens: Calvo et al. (2004) do not mention finding pdII-1, and it is not listed in the hypodigm. The inference is made primarily due to the inclusion of both phalanges together in Porfiri et al. (2011), but also the presence of the this image (via Wikimedia Commons), which shows both phalanges together with other remains of the holotype of Unenlagia paynemili (listed as “Unenlagia sp.”. There some concerns here, whether the phalanx is correctly associated, as it bears the primary evidence that prevents synonymy between Unenlagia paynemili and Neuquenraptor argentinus. I should note though, that despite this, there are differences in the original phalanges, pdII-2:
Note the red line, as this denotes the lateral margin of the proximal articulation with pdII-1 (the bone remaining represents the intercotylar ridge of the proximal articulation). In MUCPv-349, this line is gradually curved, with a broad arc; in MCF PVPH 77, this line has an abrupt bend, and a narrow arc, with the arms leading off the arc being extremely shallow. This may mean nothing, save that more ossification of the proximal end of the phalanx occurs in MCF PVPH 77, but the material is shown at the same scale, as in the figure above, implying the two specimens are of the same size; thus, if any further ossification would occur in MUCPv-349, it would only get larger than MCF PVPH 77. The shapes of the posteroventral “heels” are also different, but at this point, I’d chalk this up to the same reason the articulation’s curve is different. Are they the same taxon? I am less certain of this than I might be, simply because the shared overlap in material does not show identical morphology, while arguing ontogeny is not a cause for the differences.
Also useful for identifying unenlagiids are the extremely short ischium, a shortened distal process (where the symphysis is formed), and a large proximodorsal process on the ischium, which nearly contacts the ilium and forms an acute angle with the distal process; middle dorsal vertebrae may not be pneumatically invaginated, a feature seen in some taxa, but not in others; a somewhat S-shaped pubis that is vertically arranged relative to the sacrum (it is perpendicular to the sacral long-axis); scapulae with their dorsal and ventral (medial and lateral with oriented sensu some authors) margins parallel rather than diverging or converging, and without a large distal expansion, but with only the very distal end converging together or tapering; and a large, triangular and acromion process parallel to the scapular long-axis. Only the first three are considered diagnostic of Unenlagiidae (including Rahonavis ostromi), as defined in Agnolín & Novas (2011).
In the same issue as the two papers mentioned before, Porfiri et al. (2011) name a new “deinonychosaur,” Pamparaptor micros. Represented by a partial pes (MUCPv-1163) originally referred to Neuquenraptor argentinus by Porfiri et al. during the 23rd JAVP (see Porfiri et al., 2007, as part of the proceedings of that meeting), it was reevaluated due to unique morphologies.
[Just a quick notice: This is based on my Unenlagia comahuensis skeleton, with a redrawing of some features (the pes, feathers) I had not included, and a reposing of others (jaw and manus, the latter rotated well below the wrist joint so that you can see the point where it originally was angled nearly vertically. I'm not annoyed by this, but the authors do not acknowledge me, and that's something I think should be avoided in the future.]
Pamparaptor micros is diagnosed by the peculair features of its metatarsus, including the incredible width of the second (MTII) relative to the others (in troodontids, for example, the fourth — MTIV — is the broadest, while in dromaeosaurids MTII and MTIV are close to the same width), and this width persists along the length of the metatarsus, whereas in other “deinonychosaurs” (Deinonychosauria is the name given to the clade containing Troodontidae and Dromaeosauridae, and generally includes Unenlagiidae in some analyses), the third (MTIII) is narrow proximally (becoming pinched by MTII and MTIV) and becomes broadest distally, where is supports the large third toe (md3). This foot is thus peculiar in also supporting a very robust, broad second toe (md2), and more gracile md3 and md4. MTIV is expanded into a broad blade along its flexor surface, a feature that is present in microraptorian dromaeosaurids, but not so much in other deinonychosaurs. This implies to the authors that their taxon is a deinonychosaur, but otherwise uncertain where else it may go.
So the first thing that pops up is whether this specimen represents an unenlagiid, given this post is kind of about them. That the pes was originally referred to Neuquenraptor argentinus is a minor quibble, as this tells us very little: Only the precise morphology of the material should be relevant. Taxa known with preserved pes include all previously referred taxa except Unenlagia comahuensis Novas & Pol (1997), although Porfiri et al. only compare it to Neuquenraptor argentinus. Problematically, few of these remains have been described in detail, obscuring their comparison by external observers (i.e., me). But few have the autapomorphic features of Pamparaptor micros, and the metatarsus at least of that taxon is fairly divergent (in the subequal length of MTIII and MTIV, which resembles troodontids [Porfiri et al., 2011]); the diagnostic nature of posteroventral “heel” of mdII-2 is not illustrated (see above).
It is not possible, in my view, to exclude Pamparaptor micros from Unenlagiidae, but as much as it is not possible to include it, and Porfiri et al. (2011) are essentially safe in their conservatism.
Agnolín, F. L. & Novas, F. E. 2011. Unenlagiid theropods: Are they members of the Dromaeosauridae (Theropoda, Maniraptora)? Anais da Academia Brasileira de Ciências 83(1):117-162.
Bonaparte, J. F. 1999. Tetrapod faunas from South America and India: A palaeobiogeographic interpretation. Proceedings of the Indian National Science Association 65A(3):427-437.
Calvo, J. O., Porfiri, J. D. & Kellner, A. W. A. 2004. On a new maniraptoran dinosaur (Theropoda) from the Upper Cretaceous of Neuquén, Patagonia, Argentina. Arquivos do Museo Nacional 62:549-566.
Forster, C. A., Sampson, S., Chiappe, L. M. & Krause, D. 1998. The theropod ancestry of birds: New evidence from the Late Cretaceous of Madagascar. Science 279:1915-1919.
Gianechini, F. A. & Apesteguía, S. 2011. Unenlagiinae revisted: Dromaeosaurid theropods from South America. Anais da Academia Brasileira de Ciências 83(1):163-195.
Makovicky, P. J., Apesteguía, S. & Agnolín, F. L. 2005. The earliest dromaeosaurid theropod from South America. Nature 437:1007-1011.
Novas, F. E. & Pol, D. 2005. New evidence on deinonychosaurian dinosaurs from the Late Cretaceous of Patagonia. Nature 433:858-861.
Novas, F. E., Pol, D., Canale, J. I., Porfiri, J. D. & Calvo, J. O. 2009. A bizarre Cretaceous theropod dinosaur from Patagonia and the evolution of Gondwanan dromaeosaurids. Proceedings of the Royal Society of London, Series B 126:1101-1107.
Novas, F. E. & Puerta, P. 1997. New evidence concerning avian origins from the Late Cretaceous of NW Patagonia. Nature 387:390-392.
Porfiri, J. D., Calvo, J. O. & dos Santos, D. 2011. A new small deinonychosaur (Dinosauria: Theropoda) from the Late Cretaceous of Patagonia, Argentina. Anais da Academia Brasileira de Ciências 83(1):109.116.
Rich, T. H. & Vickers-Rich, P. 1993. Neoceratopsians and ornithomimosaurs: Dinosaurs of Gondwana origin? National Geographic Research and Exploration 10:129-131.