Saturday, January 23, 2016

Dracoraptor thoughts

So the Welsh coelophysoid has been published, with the dudebro name of Dracoraptor.  There seems to have been a lack of rigorous editing, as exemplified by "Podekosaurus", Eshanosaurus being a therizinosaurid (as opposed to -oid or -ian), BMNH and NHMUK being used in the same sentence for specimens, and that's just the first two pages.  I also think the kind of title this paper has is silly ("The oldest Jurassic dinosaur") since it just specifies position within a known range.  It's like having "The smallest dinosaur under two meters long" or "the westernmost dinosaur found in China." Pluses are it's in open access and the photos are color with great resolution.

As for the actual description, there's a discrepancy in the elements that are shown in the skeletal reconstruction (fig. 5), listed under the holotype, listed at the beginning of each anatomical area, and actually described.  For instance, figure 5 shows a squamosal, angular and articular as preserved (and not just as molds or tentatively identified), which are listed under holotype.  Yet only "more caudal elements of the lower jaws" are listed under the cranial elements heading, and none of these elements are described.  But a ?nasal is described and figured, but not in figure 5 or noted in the cranial intro.  In total it seems more written by committee than cohesive.

Color figures- holotype of Dracoraptor hanigani (NMW 2015.5G.3) with: A- supposed manual ungual III, B- supposed manual ungual II, C- supposed manual ungual I, D- supposed furcula (after Martill et al., 2016).  Black and white figures from left to right- pedal unguals I and II of Coelophysis bauri NMMNH P-42200 (after Rinehart et al., 2009); pedal ungual II in dorsal view of Liliensternus liliensterni syntype MB.R.2175 (after Huene, 1934); metacarpal II of Coelophysis? rhodesiensis holotype QG 1 (after Galton, 1971); furcula of kayentakatae holotype MNA V2623 in dorsal and anterior views (after Tykoski et al., 2002); ninth dorsal rib of Allosaurus fragilis USNM 8367 (after Gilmore, 1920). Red lines indicate element identifications I propose for Dracoraptor.
Note the maxillae are in medial view, as the figure caption states, but contra the text.  Contra the text and reconstruction, only the small anteriormost jugal groove probably articulated with the maxilla.  The longer ridge and groove on the main body is common in early dinosaurs (e.g. Herrerasaurus) and non-articulating.  The supraoccipital is in anterior (internal) view, not ventral view as stated by the text.  Note the large posttemporal fenestrae as in Silesaurus but unlike dinosaurs. 

The cervical is not opisthocoelous, contra the text, as the anterior central surface is slightly concave.  The supposed first caudal is near certainly a ?last sacral based on the broad transverse processes originating on the centrum (compare to e.g. Staurikosaurus).  The authors do call it "a partially sacralised element", but any ambiguity seems unnecessary.  The next element could easily be a sacral too, though its more fragmented condition makes this more uncertain.  I'm doubtful the supposed furcula is correctly identified.  One side is much narrower than the other, and each is curved in a different direction (thin side concave toward the outside of the angle).  Furcular arms are subequal in width, and those of coelophysoids (e.g. kayentakatae) are basically circular in section, so that twisting in Dracoraptor is not an excuse.  It's more probably a posterior dorsal rib, which are also similar in having a ridge along the outside corner. The tuberculum may be covered in matrix. 

Amusingly, Martill et al. state that on the humerus "a suture between the articulatory epiphyseal surfaces is well defined."  And for the ulna, "the proximal condyle surface is smooth and well defined, marked from the diaphysis by a prominent suture."  Dinosaurs aren't mammals, people.  They don't have separately ossifying epiphyses.  For the femur, "the femoral head (greater trochanter) is "hooked'."  Er, those are very different structures, not synonyms.  The authors say "A calcaneum is not present. Two distal tarsals (dt III & dt IV) and part of a putative third are present in a row."  I'm pretty sure no archosauriforms actually have three distal tarsals per pes (certainly no theropods do), so that 'putative third' is more likely the supposedly missing calcaneum, especially as it's placed right next to distal tarsal IV (confusingly labeled 'Ldtii'). 

The supposed "?Metaacarpal of digit I" [sic] is a metacarpal II, very similar to rhodesiensis, more elongate than metacarpal I and more robust than metacarpal III.  Even Peters got this right in his reinterpretation, which is especially sad for Martill et al..  While I haven't identified all of the phalanges in this block, it's clear Martill et al.'s statement "they are assumed to be from the left manus as they are associated with the left radius and ulna" is in error.  For instance, the phalanx underlying the proximal radius is too large to belong to any manual digit and is probably pedal phalanx III-1, while supposed manual unguals I and III lack flexor tubercles ("I" shows an obvious depression in that area) and at least "III" is virtually straight.  These unguals more nearly match pedal unguals of e.g. Coelophysis and Liliensternus, while supposed ungual II is manual due to its curvature and large flexor tubercle.  Among other phalanges, that at the distal end of metacarpal II matches a manual phalanx II-1, that on the proximal end of metacarpal II belongs to manual digit III, that between unguals "I" and "II" looks like its from pedal digit II, and the small one by the anterior end of the dorsal centrum would be manual IV-1.  The latter suggests a less reduced digit IV than coelophysids or Herrerasaurus.  Thus the manual reconstruction with its short penultimate phalanges and metacarpal ratios should not be trusted.

The phylogenetic analysis is  based on Nesbitt et al.'s Tawa matrix.  One good thing is that Martill et al. split Nesbitt's composite characters, which had the effect of Nesbitt assuming non-homology for e.g. subnarial foramina in different positions, jugal ridges of varying sharpness, etc..  A negative point is that Martill et al. do not order any characters "because it assumes a complete fossil record and a direction to evolution."  But ordering does not assume these, it merely observes that some states are more similar to others.  So e.g. if a taxon has 5 premaxillary teeth, it's more similar to a taxon with 6 teeth than to one with 3 teeth.  Ironically, some of Martill et al.'s states imply ordering, such as their "6+ premaxillary teeth" state, which only makes sense if taxa with 6 teeth are more similar to taxa with 7, 8, etc. teeth than to those with less than six teeth.  They recover Dracoraptor as the basalmost coelophysoid, sister to Coelophysidae. I like how they note "an unnamed clade containing Velociraptor, Allosaurus and Piatnitzkysaurus."  Ah, you mean that obscure group called Tetanurae. ;)

Luckily for me, I have a version of Nesbitt et al.'s matrix on hand with characters properly ordered, and basically every basal dinosauriform added (as used in my Chilesaurus post).  I've also made a ton of corrections, though have by no means gone through the whole thing yet.  I did go through Martill et al.'s Dracoraptor codings though, and 15% are miscoded.  These range from consequences of my reidentifications above, to general errors (e.g. while coded as lacking a promaxillary fenestra, you can't tell that as the maxillae are in medial view), to times where I don't think the authors understood the character (e.g. it's coded as having an anterior hollow on the astragalus, but as used by Nesbitt this is a feature that has been lost in all avemetatarsalians).  After correcting Dracoraptor's codings, it emerges as sister to Neotheropoda (Ceratosauria+Tetanurae; Averostra of some authors).  But Neotheropoda has an odd topology where Chilesaurus is sister to Velociraptor, then Ceratosaurus, Piatnitzkysaurus and Allosaurus form a clade.  Because this makes the basal condition of Neotheropoda very different than the consensus, I deleted the highly modified Velociraptor.  Recall from the Chilesaurus post that Velociraptor only clades with Piatnitzkysaurus and Allosaurus in Nesbitt's uncorrected trees because it's miscoded for 24% of the characters that make it seem more like a "normal" theropod.  After Velociraptor's deletion Neotheropoda has the standard topology, and Dracoraptor is sister to a Daemonosaurus+Chilesaurus clade, which is itself sister to Avepoda (Neotheropoda of some authors).  This is rather like Cau's result, where Dracoraptor grouped with Daemonosaurus and Tawa.  In my trees, Tawa is the next taxon stemward.  Because Chilesaurus' basal theropod status is my pet theory and the taxon is also highly modified, I tried deleting it as well.  The result then is that Dracoraptor forms a polytomy with Tawa, Daemonosaurus, Coelophysidae and more derived theropods.

Thus it seems Cau's and my matrices agree in placing Dracoraptor by Daemonosaurus.  Note both share three premaxillary teeth (also in Chilesaurus and Tawa), short snouts with few maxillary teeth (also in Chilesaurus, not in Tawa), a lacrimal flange that does not overlap the antorbital fenestra (not in Tawa; unknown in Chilesaurus), and elongate cervicals with single pleurocoels (also in Tawa; elongate centra but double pleurocoels in Chilesaurus). 

References- Gilmore, 1920. Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. Bulletin of the United States National Museum. 110, 1-154.

Huene, 1934. Ein neuer Coelurosaurier in der thüringischen Trias [A new coelurosaur in the Thuringian Trias]. Paläontologische Zeitschrift. 16(3/4), 145-170.

Galton, 1971. Manus movements of the coelurosaurian dinosaur Syntarsus and opposability of the theropod hallux. Arnoldia. 5(15), 1-8.

Tykoski, Forster, Rowe, Sampson and Munyikwa, 2002. A furcula in the coelophysid theropod Syntarsus. Journal of Vertebrate Paleontology. 22(3), 728-733.

Rinehart, Lucas, Heckert, Spielmann and Celeskey, 2009. The Paleobiology of Coelophysis bauri (Cope) from the Upper Triassic (Apachean) Whitaker quarry, New Mexico, with detailed analysis of a single quarry block. New Mexico Museum of Natural History and Science Bulletin. 45, 260 pp.

Martill, Vidovic, Howells and Nudds, 2016. The oldest Jurassic dinosaur: A basal neotheropod from the Hettangian of Great Britain. PLoS ONE. 11(1), e0145713.

Friday, January 15, 2016

Nanotyrannus was a groovy baby

The title works best when read in Austin Powers' voice.

So a new paper's out, and let's just say it's not very good.  Schmerge and Rothschild's (2016) premise is that Nanotyrannus has a lateral dentary groove, so based on this and adding it to Brusatte et al.'s (2010) tyrannosauroid matrix, it's an albertosaurine instead of a tyrannosaurine, let alone a juvenile Tyrannosaurus.

The first problem is that the lateral dentary groove has never been a great character, since its depth varies so much between taxa that numerous genera have been coded both ways in different TWG analyses.  I would say for instance that the slight longitudinal depression in Dryptosaurus (Brusatte et al., 2011; fig. 3A) doesn't qualify, contra the authors.  Indeed, Carr (online) list additional tyrannosauroids he interprets as having the groove, which were not coded that way by Brusatte et al..  Of these, I'd agree with Raptorex, and the juvenile Bistahieversor and Tarbosaurus, but view e.g. the Bistahieversor type and Alioramus (altai's type) to be more like Dryptosaurus.  Thus I agree with Headden (DML, 2016) that the character shows ontogenetic variation.  But my main point is that it's so subjective that authors can't agree on which morphologies count, and that any attempt to quantify depth and continuity (many individuals have grooves that vary in depth along the dentary, most obviously visible in the CT scan of Tarbosaurus juvenile IGM 107/7) won't be easy.

Dentaries of tyrannosauroid taxa (some flipped) showing degree of lateral groove.  Left (top to bottom)- Bistahieversor juvenile paratype NMMNH P-25049 (after Carr and Williamson, 2010); Tarbosaurus juvenile IGM 107/7 (after Tsuihiji et al., 2011); Nanotyrannus BMRP 2002.4.1 'Jane' (after Schmerge and Rothschild, 2016); Raptorex juvenile holotype LH PV18 (after Sereno et al., 2009). Right (top to bottom)- Dryptosaurus holotype ANSP 9995 (after Brusatte et al., 2011); Bistahieversor holotype NMMNH P-27469 (after Carr and Williamson, 2010); Alioramus IGM 100/1844 (after Brusatte et al., 2012); Tyrannosaurus FMNH PR2081 (after Brochu, 2003).  I'd say those on the left have a strong groove while those on the right lack one, and the least Dryptosaurus has less of a groove than e.g. Bistahieversor or Tyrannosaurus, contra Schmerge and Rothschild's recoding of it.  Also note deeper grooves are common in juvenile tyrannosaurids.

The second problem is that even if Schmerge and Rothschild had an unassailable, quantifiable character difference between Nanotyrannus and Tyrannosaurus that was not known to be ontogenetically variable, it's STILL just one character.  They're being BANDit-esque in assuming one character can override the totality of character evidence.  Sure they go on to list five other characters supposedly shared between Nanotyrannus and albertosaurines, but not only are some obviously plesiomorphies  (maxillary fenestra placed posteriorly; rounder orbit; greater dentary tooth count), the authors actually got the maxillary fenestra character backwards (they claim "contact of the maxillary fenestra with the rostral margin of the antorbital fossa" unites Nanotyrannus and albertosaurines).  The juvenile Tarbosaurus and Maleevosaurus' type are sufficient to show it's expected in juvenile Tyrannosaurus anyway.  What about the cladistic analysis, you ask?  While I haven't seen the matrix yet*, I'm betting the authors coded Nanotyrannus as if it was an adult.  And we already know juvenile tyrannosaurines emerge more basally when coded as adults.  Carr (2005) found Nanotyrannus' holotype to be sister to Daspletosaurus+Tarbosaurus+Tyrannosaurus, and the Stygivenator holotype to be "in a polytomy consisting of Teratophoneus and all non-tyrannosaurine tyrannosauroids."  Tsuihiji et al. (2011) found their Tarbosaurus juvenile to emerge sister to albertosaurines+tyrannosaurines.  So this is an unsurprising result even assuming Schmerge and Rothschild's coding was competent.

Edit- the matrix is terribly undercoded.   Only one character of 27 coded for the nasal and lacrimal, the squamosal and quadratojugal are completely uncoded, the entire skull roof, palate and braincase uncoded, postdentary mandibular bones uncoded, only one postcranial character coded.  Did nobody check the matrix and notice the huge swath of question  marks?!  Seriously, Cretaceous Research, this is just sad.

Finally, the authors don't understand how to compute character changes, when they compare the steps necessary to move Nanotyrannus to Tyrannosaurus' sister OTU.  Note we're never presented with the actual number of steps such a move adds to the analysis, let alone told if that number is statistically significant.  Instead, Schmerge and Rothschild just show the distribution of their dentary groove character if the move is made.  Even accepting their coding is correct, the correct answer is that moving Nanotyrannus to Tyrannosaurus would add a single step, namely Nanotyrannus evolving that character in convergence with albertosaurines.  But the authors claim "this tree requires 5 more independent losses of the dentary groove than the tree proposed in this study."  Wha?!  How do they justify this?  Because for some never explained reason, the authors assume the groove is present along the entire 'backbone' of the cladogram, so that every tyrannosauroid that lacks the groove independently loses it.  How terribly unparsimonious!  This takes 11 steps in their tree 3B, whereas the most parsimonious phylogenetic reconstruction would take only four steps assuming the groove is present in the outgroup as the authors believe.  All that's necessary is the loss of the groove for taxa more derived than proceratosaurids, then independent development in Dryptosaurus, albertosaurines and Nanotyrannus.  I can only suppose the authors view the groove as being incapable of parallel development.  It's just formed by a branch of the (?)trigeminal nerve being more depressed into the dentary's lateral surface, hardly the "dramatic change (e.g., metamorphosis) [that] would need to be invoked to explain the loss of this feature through maturation" that Schmerge and Rothschild claim.

Cladogram of tyrannosauroids with deep lateral dentary grooves indicated with bold lines.  Middle- figure 3B from Schmerge and Rothschild (2016) showing their proposed evolution of dentary grooves.  Top- number of steps assumed by Schmerge and Rothschild, with steps indicated by circles.  Bottom- most parsimonious distribution of steps given an outgroup with dentary grooves.

In conclusion, I don't see how this paper made it to publication.  The anatomical structure in question has a controversial distribution, Tsuihiji et al. (2011) destroys the entire premise but is never addressed or referenced, the authors never even consider that coding Nanotyrannus as an adult is problematic (Carr 1999 showed that the holotype has immature bone grain, so even if it's an albertosaurine, it's a juvenile), and they don't understand how character state reconstruction works.  Using 'key characters', presumptions about reversability, an ignorance of the recent literature, misunderstanding cladistics... did Schmerge inherit BANDit-style biases working at the University of Kansas?

References- Carr, 1999. Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Theropoda). Journal of Vertebrate Paleontology. 19(3), 497-520.

Brochu, 2003. Osteology of Tyrannosaurus rex: Insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. Society of Vertebrate Paleontology Memior. 7, 138 pp.

Carr, 2005. Phylogeny of Tyrannosauroidea (Dinosauria: Coelurosauria) with special reference to North American forms. PhD thesis. University of Toronto. 1170 pp.

Sereno, Tan, Brusatte, Kriegstein, Zhao and Cloward, 2009. Tyrannosaurid skeletal design first evolved at small body size. Science. 326(5951), 418-422.

Carr and Williamson, 2010. Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea. Journal of Vertebrate Paleontology. 30(1), 1-16. 

Brusatte, Norell, Carr, Erickson, Hutchinson, Balanoff, Bever, Choiniere, Makovicky and Xu, 2010. Tyrannosaur paleobiology: New research on ancient exemplar organisms. Science. 329, 1481-1485.

Brusatte, Benson and Norell, 2011. The anatomy of Dryptosaurus aquilunguis (Dinosauria: Theropoda) and a review of its tyrannosauroid affinities. American Museum Novitates. 3717, 53 pp.

Tsuihiji, Watabe, Tsogtbaatar, Tsubamoto, Barsbold, Suzuki, Lee, Ridgely, Kawahara and Witmer, 2011. Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia. Journal of Vertebrate Paleontology. 31(3), 497-517.

Brusatte, Carr and Norell, 2012. The osteology of Alioramus, a gracile and long-snouted tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia. Bulletin of the American Museum of Natural History. 366, 197 pp.

Carr, online 2016.

Headden, DML 2016.

Schmerge and Rothschild, 2016. Distribution of the dentary groove of theropod dinosaurs: Implications for theropod phylogeny and the validity of the genus Nanotyrannus Bakker et al., 1988. Cretaceous Research. 61, 26-33.

Tuesday, January 12, 2016

How not to redefine Ornithuromorpha

The answer is "any possible way."  As in, DON'T redefine Ornithuromorpha Chiappe et al. 1999, which has until now only been given two definitions, both node-based.  There's Chiappe's (2001) original "Patagopteryx + Vorona + Ornithurae" and his later (2002) more refined "Patagopteryx + Ornithurae", both based on the same topology, with a trichotomy between Patagopteryx, Vorona and Ornithurae.  Ornithurae in this case is Chiappe's version which was Hesperornis plus modern birds.

Yet in the description of their new bird Dingornis [edit] Dingavis longimaxilla (first mentioned in Wang et al., 2015), O'Connor et al. (2016) redefine Ornithuromorpha to be stem-based.  Their Ornithuromorpha is "The first ancestor of Neornithes that is not also an ancestor of the Enantiornithes, and all of its descendants."

Holotype of Dingavis longimaxilla IVPP V20284 (scale = 20 mm; after O'Connor et al., 2016).

First of all, will everyone PLEASE start paying attention to Phylocode Article 11.1- "All specifiers used in node-based and branch-based definitions of clade names, and one of the specifiers used in apomorphy-based definitions of clade names, are species or specimens."  Chiappe had the excuse that he was working over a decade ago.  But in 2016 that doesn't cut it.  And it's SO easy!  Just say "Passer domesticus < - Enantiornis leali".  Done!

Second, O'Connor et al.'s excuse is that "Although the proposed definition does not strictly equate with the published node-based definition, it does provide a formal definition for the current widespread usage of this term in most recent literature (Bell et al. 2010; O’Connor et al. 2010; S. Zhou et al. 2013a; M. Wang et al. 2015)."  Let's review those...
- Bell et al. (2010) in their description of Hollanda have Patagopteryx as the most basal taxon closer to modern birds than enantiornithines, so have no need for a different definition than Chiappe's and don't explicitly use one either.
- O'Connor et al. (2010) in their description of Longicrusavis have the same situation.
- Zhou et al. (2013) in their description of new Archaeorhynchus specimens don't even show a topology or mention Patagopteryx.  Notably, Zhou and Zhang (2006) in the original description of Archaeorhynchus just deleted Patagopteryx from the matrix they used without justification.  Why do you hate Patagopteryx so much, Zhou?
- Wang et al. (2015) in their description of new Gansus material do indeed place Ornithuromorpha in the wrong position, as they have Archaeorhynchus and Jianchangornis further from modern birds than Patagopteryx or Vorona, yet include them among Ornithuromorpha.  Note O'Connor was second author here.
So only one paper listed actually uses Ornithuromorpha as if it were a stem, and that shared a coauthor.  Hardly a convincing case that the usage is "widespread."  Sure there are other papers that use it this way, but almost all have O'Connor as a coauthor.  You don't get to use a name incorrectly tens of times and then say "looks like all the papers are using it this way, we better change it."

Third, by redefining names you're countering the entire point of phylogenetic nomenclature.  The beauty of the system is that regardless of your topology, you can apply clade names because their definitions stay constant.  Just find Passer and Ornithomimus in your tree and you'll always know where Maniraptora goes.  But if you pull a Sereno and declare Maniraptora to be "Oviraptor + Passer" instead, then your concept is no longer the same.  Ditto for Ornithuromorpha.

"Passer domesticus < - Enantiornis leali" is certainly a clade that deserves a name, but it's not the more exclusive Ornithuromorpha.  We didn't call the clade Ornithurae just because the BANDits got it wrong so often in the 90s, and we should aim to be better this time as well.

As an aside,  O'Connor et al. state "Although we do not consider [Gansus zheni] to be referable to Gansus, previously only known from the Xiagou Formation (You et al. 2006), we also recognize minor differences that suggest they are not referable to Iteravis huchzermeyeri."  After my in depth study, I'm skeptical.  Notably, O'Connor et al. did not add zheni to their matrix, although Iteravis emerged in a polytomy with Gansus
Is Dingavis from the same locality another synonym of Iteravis?  While it does seem to share the ventrally concave ischium with small mid dorsal process (also in Piscivoravis, Yanornis and Gansus), pedal digit IV is shorter (89% of III excluding unguals; compared to 99-110% in Iteravis), the ectethmoid (lacrimal of O'Connor et al.) is more acute, the carpometacarpus more elongated, and phalanx III-1 lacks the lateral process.  So offhand, I'd agree they're distinct.

References- Chiappe, 2001. Phylogenetic relationships among basal birds. In Gauthier and Gall (eds). New perspectives on the origin and early evolution of birds: Proceedings of the international symposium in honor of John H. Ostrom. Peabody Museum of Natural History. 125-139.

Chiappe, 2002. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. University of California Press. 448-472.

Zhou and Zhang, 2006. A beaked basal ornithurine bird (Aves, Ornithurae) from the Lower Cretaceous of China. Zoologica Scripta. 35, 363-373.

Bell, Chiappe, Erickson, Suzuki, Watabe, Barsbold and Tsogtbaatar, 2010. Description and ecologic analysis of Hollanda luceria, a Late Cretaceous bird from the Gobi Desert (Mongolia). Cretaceous Research. 31(1), 16-26.

O’Connor, Gao and Chiappe, 2010. A new ornithuromorph (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity. Journal of Vertebrate Paleontology. 30(2), 311-321.

Zhou, Zhou and O'Connor, 2013. Anatomy of the basal ornithuromorph bird Archaeorhynchus spathula from the Early Cretaceous of Liaoning, China. Journal of Vertebrate Paleontology. 33(1), 141-152.

Wang, Clarke and Huang, 2015. Ornithurine bird from the Early Cretaceous of China provide new evidence for the timing and pattern of the evolution of avian skull. Journal of Vertebrate Paleontology. Program and Abstracts 2015, 233.

Wang, O'Connor, Li and You, 2015. New information on postcranial skeleton of the Early Cretaceous Gansus yumenensis (Aves: Ornithuromorpha), Historical Biology. DOI: 10.1080/08912963.2015.1006217

O'Connor, Wang and Hu, 2016. A new ornithuromorph (Aves) with an elongate rostrum from the Jehol Biota, and the early evolution of rostralization in birds. Journal of Systematic Palaeontology. DOI: 10.1080/14772019.2015.1129518

Wednesday, January 6, 2016

Chiappeavis is just another Pengornis

The last Mesozoic dinosaur named in 2015 is Chiappeavis magnapremaxillo (O'Connor et al., 2015b), electronically published on December 31st.  First of all, what a stupid species name.  Second, examination of the supposed diagnostic characters shows that like Parapengornis and IVPP V18632, it's just another example of Pengornis houi.  Which is a shame because Luis Chiappe really deserves a bird named after him.  So before anyone names a 'Chiappeornis', let's make sure it's a really distinctive specimen, okay?  It's also disappointing because O'Connor has an entire section of her thesis lamenting the fact so many enantiornithines are named without adequate diagnoses.  But here she's doing that herself (and yes, the contributions credit her with writing the manuscript).  I'll also note the paper lacks a measurement table and that Pengornithidae can be paraphyletic in their analysis depending on their assumptions (fig. S1E).  Anyway, let's look at the evidence...

Holotype of Chiappeavis magnapremaxillo STM 29-11 (after O'Connor et al., 2015).

Several characters were listed as supposedly diagnostic. The premaxilla was said to have a larger body and convex ventral margin, but the convex element has far too long of a ventral margin to be a premaxilla, so is more likely an incomplete maxilla with the base of the ascending process. The actual right premaxilla is then just the small anterodorsal portion right below the partially preserved left premaxilla, and has no visible ventral margin.

Left (top to bottom)- skull of Chiappeavis magnapremaxillo as seemingly interpreted by O'Connor et al. (2015b) (top), without interpretation (middle), and as interpreted by me (bottom) (after O'Connor et al., 2015b).  Right (top to bottom)- skulls of Parapengornis eurycaudatus holotype IVPP V18687 (top; after Hu et al., 2015), IVPP V18632 (middle; after Hu et al., 2014), and Pengornis houi holotype IVPP V15336 (after O'Connor and Chiappe, 2011).  Premaxilla colored red, maxilla colored blue, and nasal colored green.

The posterodorsal premaxillary process was claimed to be longer than other pengornithids, almost reaching the frontals. Yet this bone is highly abraded just posterior to figure 2A's 'l pm' label, so that this posterior portion could easily belong to the right nasal instead. This is bolstered by the fact it's the same width as the left nasal and that the right nasal is otherwise missing. These cranial reinterpretations also make far more sense as they match the morphology and preservation of other pengornithids, which would be expected as the postcrania are nearly identical.

The synsacrum has eight vertebrae (as in IVPP V18632; Parapengornis' is only partly preserved), while the authors claim Pengornis' holotype has seven. Yet the description of the latter says only that seven are visible, but that the anterior end is covered, and indeed there could easily be another one beneath the ilium. STM 29-15 (a Jiufotang pengornithid briefly described by O'Connor et al., 2015a) only has seven but is obviously younger based on its unfused sterna.

The "median trabeculae" of Chiappeavis are said to have concave lateral margins, but no such structure exists, so the authors clearly meant the posterolateral processes. Their slight lateral concavity is also seen in Parapengornis' holotype though not in STM 29-15 and perhaps IVPP V18632 (difficult to determine from the low resolution figure of the latter), while Pengornis' holotype doesn't preserve the sternum. [Edit] O'Connor cordially informed me she meant the posteromedian process, so incorrectly pluralized the term instead of my assumption that she used the wrong positional adjective ("median trabeculae is totally a valid term MORON - they fuse into xiphial region. check Baumel bitch" as per O'Connor pers. comm., 1-16-2016).  However, concave lateral edges on the posteromedian process are also present in IVPP V18632, absent in STM 29-15, and unknown in both Pengornis and Parapengornis. So this doesn't support Chiappeavis' validity either.

Sternum of Parapengornis eurycaudatus holotype IVPP V18687 showing concave lateral edge of posterolateral process (right edge of teal line) and [see discussion above] low posteromedian angle (purple lines) (after Hu et al., 2015).

The posteromedian angle of the sternum is said to be narrow, but while its 53 degree angle is a bit less than IVPP V18632's (at 68) or STM 29-15's (at 66), Parapengornis' holotype could have an identical angle if complete, and again Pengornis' holotype doesn't preserve the element.

Finally, the authors claim the proximal articular surface of the tibia is laterodistally inclined, but this is only true of the left tibia, with the right tibia having a right angle between the surface and the long axis of the bone. Furthermore, Pengornis' holotype and IVPP V18632 both have inclined surfaces, though Parapengornis' holotype lacks them. Given the variation in Chiappeavis' holotype, the variation is likely due to perspective or taphonomy.

Tibiotarsi of (left to right; flipped if necessary so that lateral is to the left) both of Pengornis houi holotype IVPP V15336 (after Zhou et al., 2008), right of IVPP V18632 (after Hu et al., 2014; left is in medial view), both of Parapengornis eurycaudatus holotype IVPP V18687 (after Hu et al., 2015), left of STM 29-15 (after O'Connor et al., 2015a; right is fragmented); and Chiappeavis magnapremaxillo holotype STM 29-11 (aftter O'Connor et al., 2015b).  Angle of proximal edge indicated in green; note that Chiappeavis' angles differ and that Pengornis' are both ventrolaterally angled.

Besides the characters listed in the diagnosis, O'Connor et al. note the short anterior cervicals are like the Parapengornis holotype but unlike Pengornis' holotype. As the latter is larger than the others, this may support ontogenetic cervical elongation.

They also correctly note the long pygostyle is like Pengornis' holotype, but unlike IVPP V18632 or Parapengornis' holotype.

Finally, the short metatarsal I is said to be like Pengornis' holotype, and is additionally like IVPP V18632 but unlike Parapengornis' holotype or STM 29-15. 

Thus the only real difference from Pengornis' holotype is the shorter anterior cervicals, and while there are a few differences from other pengornithid specimens (laterally concave posterolateral posteromedian sternal processes unlike STM 29-15 and (?)IVPP V18632; narrower posterior sternal angle than STM 29-15 and IVPP V18632; long pygostyle unlike STM 29-15, IVPP V18632 and Parapengornis' type; short metatarsal I unlike STM 29-15 and Parapengornis' type), there's no pattern of character distribution that would suggest separate pengornithid species (e.g. Parapengornis shares the cervical length, posterolateral process concavity and probably sternal angle, while IVPP V18632 is different in cervical length but shares metatarsal I length).  This is illustrated in the following table, showing the distribution of all real differences proposed to diagnose Jiufotang pengornithid taxa (known in more than two specimens) that aren't obviously ontogenetic- 

B- femoral length (mm) to indicate possible age.
C- robust base of maxillary ascending process.
D- low interclavicular angle.
E- metatarsal I short.
F- long anterior cervical vertebrae.
G- long pygostyle.
H- long posterodorsal lacrimal process.
I- laterally concave posterolateral posteromedian sternal process.
J- narrow posteromedian sternal angle.

Note the lack of a pattern unrelated to size.  Indeed, all but E, F and I correlate with size, and two of those conflict with each the other.  It's true that size is not fully correlated with osteological development in this series (e.g. STM 29-15 has unfused sternals unlike the slightly smaller IVPP V18632), but that's true of other taxa as well (e.g. Anchiornis, Archaeopteryx, Shenzhouraptor, Sapeornis, Archaeorhynchus).  So it's just like with Archaeopteryx and Microraptor- all specimens show uncorrelated differences, thus either every specimen is its own species or as far as we can tell they're a single species that shows variation.  Based on this I conclude all Jiufotang pengornithids should still be still retained in Pengornis houi.

References-  Zhou, Clarke and Zhang, 2008. Insight into diversity, body size and morphological evolution from the largest Early Cretaceous enantiornithine bird. Journal of Anatomy. 212, 565-577.
O'Connor and Chiappe, 2011. A revision of enantiornithine (Aves: Ornithothoraces) skull morphology. Journal of Systematic Palaeontology. 9(1), 135-157.
Hu, Zhou and O'Connor, 2014. A subadult specimen of Pengornis and character evolution in Enantiornithes. Vertebrata PalAsiatica. 52(1), 77-97.
Hu, O'Connor and Zhou, 2015a. A new species of Pengornithidae (Aves: Enantiornithes) from the Lower Cretaceous of China suggests a specialized scansorial habitat previously unknown in early birds. PLoS ONE. 10(6), e0126791.
O'Connor, Wang, Zheng, Hu, Zhang and Zhou, 2015b. An enantiornithine with a fan-shaped tail, and the evolution of the rectricial complex in early birds. Current Biology.
O'Connor, Zheng, Sullivan, Chuong, Wang, Li, Wang, Zhang and Zhou, 2015a. Evolution and functional significance of derived sternal ossification patterns in ornithothoracine birds. Journal of Evolutionary Biology. 28(8), 1550-1567.