Wednesday, July 13, 2016

Is Gualicho Aoniraptor?

A very cool theropod was published today- Gualicho shinyae (Apesteguia et al., 2016).  It's a large taxon from the Huincul Formation of Argentina, notable for having tiny, didactyl arms and generally resembling Deltadromeus.  The authors propose both are related to megaraptorans instead of ceratosaurs... and wait, didn't we just have this situation (Motta et al., 2016)?  I might as well be the first person* to propose this seemingly obvious synonymy- Gualicho is the same taxon as the recently named Aoniraptor.  Both are from the same formation, of similar size (mid caudals ~87 vs. 83 mm), and Gualicho has two diagnostic characters noted for Aoniraptor- "anterior mid-caudal vertebrae with fan-shaped prezygapophyses lacking a discernible articular surface for contacting the postzygapophyses; presence of a blunt and thick process on the lateral surface of the prezygapophyses of anterior midcaudal vertebrae", and might have the third- "mid-posterior caudals with a pair of nonarticular flat surfaces located on the posterodorsal corner of the centrum."  As Aoniraptor was named first (June 16th vs. July 13th), it has precedent over Gualicho.  Edit #2: As Brad McFeeters notes in a comment below, the volume Aoniraptor was named in has yet to be physically published and does not contain a ZooBank registration, thus Gualicho has precedent.

*Edit: After posting this, I learned both Andrea Cau (here) and Brad McFeeters (on Facebook) independently came to the same conclusion.  Guess it really was an obvious synonymy. ;)

I'm skeptical that these and Deltadromeus belong in Tetanurae, as it only takes 4 steps to move them to Ceratosauria in Apesteguia et al.'s version of Carrano's tetanurine analysis, and Deltadromeus wasn't added to their version of Novas' tetanurine analysis which also lacks any ceratosaurs except the outgroup Ceratosaurus.  They note "Gualicho does exhibit some apparent ceratosaurian synapomorphies, most notably a robust MT III with posteriorly expanded proximal articulation and a flange-like m. iliofibularis tubercle."  It would have been interesting to run them in a ceratosaur analysis.

Holotypes of Gualicho shinyae (MPCN PV 0001; top) and Aoniraptor libertatum (MPCA-Pv 804; bottom) in posterior (E), anterior (F), left lateral (G) and dorsal (H) views.  Modified from Apesteguia et al. (2016) and Motta et al. (2016).

 Wonder where they go in the Lori analysis....

References- Apesteguía, Smith, Juárez Valieri and Makovicky, 2016. An unusual new theropod with a didactyl manus from the Upper Cretaceous of Patagonia, Argentina. PLoS ONE. 11(7), e0157793.

Motta, Aranciaga Rolando, Rozadilla, Agnolin, Chimento, Brisson Egli and Novas, 2016. New theropod fauna from the Upper Cretaceous (Huincul Formtation) of northwestern Patagonia, Argentina. In Khosla and Lucas (eds.). Cretaceous period: Biotic diversity and biogeography. New Mexico Museum of Natural History and Science Bulletin. 71, 231-253.

Wednesday, July 6, 2016

Is Lagerpeton a proterochampsian? The Dromomeron angle

Sorry for the lack of posts (or Database updates) lately, as I've been working with Scott Hartman to add Lori to the coelurosaur matrix and finalizing that study.  But I started writing this as a DML reply and figured why not make it a post instead...

Novas and Agnolin (2015) have an abstract on Lagerpeton that proposes it is actually a proterochampsian sister to Tropidosuchus.  If true, this would be a rare time David Peters got something right, as he had this idea back in 2011- .  I hope Novas and Agnolin credit him if they write a paper on this.

However, something not addressed by Novas and Agnolin is how Dromomeron relates.  According to Nesbitt (2011), Tropidosuchus lacks all lagerpetonid characters shared by Lagerpeton and Dromomeron- Anterolateral tuber of the proximal portion of the femur absent, the anterolateral face is flat (302-1), Femoral head hook shaped in medial and lateral views (306-1), Ventral emargination present on anterolateral side of the femoral head (310-1), Crista tibiofibularis larger than the medial condyle (326-1), Dorsally expanded process on the posterolateral portion of the tibial facet of the astragalus expanded into a distinct, raised process (5 posterior ascending process of Sereno and Arcucci, 1994a) (355-1), Concave articular surface for the fibula on the calcaneum (378-2).  Of the proterochampsian characters noted by Novas and Agnolin as present in Lagerpeton, Dromomeron lacks two- femoral 4th trochanter proximodistally expanded; caudal surface of distal tibia with a middle tubercle surrounded by two shallow concavities; but has one- astragalus with anteromedial corner acute.  Others are unknown since Dromomeron is so fragmentary, but at least "elongate and compact metatarsus with metatarsal V reduced and devoid of phalanges" would be expected in a taxon close to Marasuchus (which has the conditions), so that works for either placement of Lagerpeton.  Then there are the dinosauriform-like characters of Lagerpeton scored by Nesbitt as absent in Tropidosuchus- Straight cnemial crest (328-1); Longest metatarsal longer than 50% of tibial length (383-1); Metatarsal V "hooked" proximal end absent, and articular face for distal tarsal 4 subparallel to shaft axis (398- 1).  And the archosaurian characters of Lagerpeton scored as absent in Tropidosuchus- Articular surfaces for fibula and distal tarsal IV on the calcaneum continuous (380-1), Anteromedial tuber of the proximal portion of the femur present (300-1), Tibial facet of the astragalus divided into posteromedial and anterolateral basins (366-1).

Phylogeny of eucrocopodans recovered by Ezcurra (2016), with Novas and Agnolin's (2015) proposed reidentification of Lagerpeton indicated in red (modified from Ezcurra, 2016).

Taking all of this into account (with the caveats that I haven't checked the accuracy of any characters except the proterochampsian states of Dromomeron, and that this only uses unambiguous characters listed by Nesbitt), Novas and Agnolin have ten characters that might need to converge if Lagerpeton is a dinosauriform relative, but there are nine characters that might need to converge if Lagerpeton is a proterochampsian (the seven from Nesbitt listed here plus two listed by Novas and Agnolin).  So that's one step in favor of a proterochampsian identity.  But if Dromomeron is a proterochampsian too, that adds three more steps (the two listed above plus dinosauromorph character 313 of Nesbitt that is present in Dromomeron but unknown in Lagerpeton).  Thus dinosauriform-relative Lagerpeton is two steps shorter.  And if Dromomeron is a dinosauriform relative but Lagerpeton is not, that adds five steps (the six lagerpetonid characters that would need to be convergent minus the proterochampsian-like acute astragalar corner).

So basically, ignoring Dromomeron might make proterochampsian Lagerpeton a slightly better option but a proterochampsian Dromomeron turns those odds around, and a proterochampsian Lagerpeton but a dinosauriform-relative Dromomeron is even worse.  So pending further analysis, I favor the traditional view (note Ezcurra's huge 2016 archosauromorph analysis which sampled proterochampsian diversity also recovered this topology).  If Lagerpeton is a proterochampsian, then Lagerpetonidae is a junior synonym of Proterochampsia definition-wise (and Proterochampsidae ICZN-wise).  However, Novas and Agnolin are wrong in claiming "The exclusion of Lagerpeton from the dinosaur lineage results in the removal of the clade Dinosauromorpha, which was originally conceived to encompass Lagerpeton plus Dinosauriformes."  The only proposed definition of Dinosauromorpha that mentions Lagerpeton is one of Sereno's (1991) which is "Lagerpeton chanarensis, Lagosuchus talampayensis, Pseudolagosuchus major, Dinosauria (inc. Aves), and all descendants of their common ancestor."  Following this definition, Dinosauromorpha merely moves stem-ward to be the Proterochampsia+Archosauria clade which is AFAIK otherwise unnamed.  The other proposed definitions are all basically "taxa closer to dinosaurs than pterosaurs", so Dinosauromorpha would stay where it is even if Lagerpeton isn't a member.

References- Sereno, 1991. Basal archosaurs: Phylogenetic relationships and functional implications. Society of Vertebrate Paleontology Memoir. 2, 1 53 pp

Nesbitt, 2011. The early evolution of archosaurs: Relationships and the origin of major clades. Bulletin of the American Museum of Natural History. 352, 292 pp.

Novas and Agnolin, 2015. Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the Middle Triassic of NW Argentina. Libro de resúmenes del V Congreso Latinoamericano de Paleontología de Vertebrados. 48.

Ezcurra, 2016. The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ. 4:e1778.