Wednesday, December 31, 2014

Neotyping past a diagnostic syntype - Majungasaurus edition

One of my pet peeves is the recent trend to petition the ICZN to designate a more complete specimen the neotype of a taxon when the fragmentary holotype hasn't even been shown to be undiagnostic.  A recent example is Paul and Carpenter's (2010) Allosaurus petition when the holotype hasn't even been well described outside a thesis or ever compared to the other accepted allosaurid genus (Saurophaganax).  Generally thoughts about which specimens are diagnostic varies, so regardless of how much laziness is involved in these petitions, there's excusable subjectivity too.  But while researching Allosaurus' case for the big New Years Theropod Database update, I found a Majungasaurus petition I hadn't heard about, and it's a weird one.

The applicable ICZN Article is 75.5- "When an author considers that the taxonomic identity of a nominal species-group taxon cannot be determined from its existing name-bearing type (i.e. its name is a nomen dubium), and stability or universality are threatened thereby, the author may request the Commission to set aside under its plenary power [Art. 81] the existing name-bearing type and designate a neotype."

Most of the original syntypes of Megalosaurus crenatissimus- A. Fourth premaxillary tooth FSL 92.306b (left) and posterior dentary tooth FSL 92.306a (right) in lateral view. B. Pedal ungual FSL 92.290 in side view. C. Distal caudal vertebra FSL 92.289 in lateral view. D. sacral centrum FSL 92.343 in lateral view. Scale equals 10 mm for A, and 30 mm for B-D.  After Krause et al., 2007.
A brief history of Megalosaurus/Majungasaurus crenatissimus is as follows.  Deperet (1896) described crenatissimus based on five unassociated elements- two teeth, two partial vertebrae, and a partial pedal ungual.  Lavocat (1955) later described a dentary he referred to crenatissimus, based on dental similarity.  More complete skulls and skeletons were described in the 90s and 00s.  Krause et al. (2007) tried to make the dentary the type specimen, but this can't be done without an ICZN petition, as I said at the time.  So they did the right thing in a way, and petitioned the ICZN (Carrano et al., 2009).

Neotype of Majungasaurus crenatissimus, dentary MNHN.MAJ 1 in A. lateral, B. dorsal, and C. medial views.  Scale equals 30 mm. After Krause et al., 2007.
The problem here is that for Article 75.5 to work, the type must be a nomen dubium.  Carrano et al. state "As several authors have confirmed (Sampson et al., 1996, 1998; Krause et al., 2007), the original Depret type specimens are indeed indeterminate as to genus and species, although they can be identified as belonging to the family ABELISAURIDAE. Thus the taxonomic identity of the species Megalosaurus crenatissimus as a nominal species-group taxon cannot be determined from the existing name-bearing type materials."  Sampson et al. (1996) never says this, and indeed refers a premaxilla to crenatissimus based on similarity to Deperet's syntype teeth.  Sampson et al. (1998) did support this position (merely via the statement "none of the specimens appear to be diagnostic to the generic level" that was not supported by any data), which is why they called the new more complete specimens Majungatholus atopus, a name based on a skull roof described in the 70s.

Most importantly though, Krause et al. (2007) say the opposite of what Carrano et al. claim they did.  Krause et al. state "Furthermore, detailed examination of the teeth preserved in MNHN.MAJ 1 [the dentary] by Smith (this volume) reveals that they fall within the same size and shape parameters as the two isolated teeth (FSL 92.306a-b) described by Depéret (1896a, b), those preserved in the gnathic elements of adult individuals described by Sampson and Witmer (this volume; e.g., FMNH PR 2008, 2100; UA 8709, 8716, and 8717), and the thousands of isolated teeth recovered from the Maevarano Formation by Mahajanga Basin Project personnel and others. The teeth of the Malagasy abelisaurid most closely resemble those of AMNH 1753, 1955, and 1960 from the Late Cretaceous of India (referred to Indosuchus raptorius by Chatterjee, 1978) but, importantly, the Malagasy taxon possesses weakly developed interdenticular sulci whereas the Indian specimens lack them (Smith, this volume)."

If we go to Smith's paper in Sampson and Krause's edited volume, we read- "The morphology of FSL 92.306a is basically as Depéret (1896) described it (Krause et al., this volume:fig. 4A), except that the distal curvature profile is less strongly curved. Overall, the crown is very similar in morphology to the distal dentary teeth of Majungasaurus discovered subsequently (Fig. 21). The DFA classified FSL 92.306a as Majungasaurus (26.74 D2, p .001; Table 2), supporting the hypothesis that the tooth is morphologically congruent with dental material of this animal. I am thus confident in referring this crown to Majungasaurus."

So the authors of the petition claim their own work supports Deperet's syntypes as undiagnostic, but their own cited work actually says the reverse- that one of Deperet's teeth is identical to those in more complete specimens AND that these Malagasy teeth can be distinguished from the most similar taxon.  Now we can argue about whether the tooth actually is diagnostic, but I think the more important issue here is that Carrano et al. seem to have misrepresented the conclusions of their own work as evidence in their petition.  Even if they changed their minds between 2007 and 2009, it would still be wrong to cite their older work for supporting a position it didn't.  So of course given the lack of Comments, the Commission would assume Carrano et al. are citing their own work correctly and pass the motion, as they think the work has verified Deperet's syntypes are undiagnostic, thus fulfilling Article 75.5.  And that's what they did, declaring the dentary to be the neotype in 2011.  But if they knew the cited work actually argued a syntype tooth was diagnostic, they might not have.  Though I can't recall a petition being rejected, so who knows.

It's history now, and the dentary will be the neotype unless another is petitioned into existence in the future, but what should have happened is for Krause et al. to make FSL 92.306a the lectotype of crenatissimus without the need of the ICZN, then if later studies found another taxon with identical teeth, the ICZN could be petitioned for a neotype.  Ah well, dentary it is.

References- Deperet, 1896. Note on the sauropod and theropod dinosaurs from the Upper Cretaceous of Madagascar. Bulletin de la Societe Geologique de France, 3rd series. 24, 176.

Lavocat, 1955. Sur une portion de mandibule de Théropode provenant du Crétacé supérieur de Madagascar. Bulletin du Muséum National d’Histoire Naturelle à Paris. 27, 256-259.

Sampson, Krause, Dodson and Forster, 1996. The premaxilla of Majungasaurus (Dinosauria: Theropoda) with implications for Gondwanan Paleobiography. Journal of Vertebrate Paleontology. 16(4), 601-605.

Sampson, Witmer, Forster, Krause, O'Connor, Dodson and Ravoavy, 1998. Predatory dinosaur remains from Madagascar: Implications for the Cretaceous biogeography of Gondwana. Science, 280, 1048-1051.

Krause, Sampson, Carrano and O'Connor, 2007. Overview of the history of discovery, taxonomy, phylogeny, and biogeography of Majungasaurus crenatissumus (Theropoda: Abelisauridae) form the Late Cretaceous of Madagascar. In Sampson and Krause (eds.). Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. SVP Memoir 8, 1-20.

Smith, 2007. Dental morphology and variation in Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. In Sampson and Krause (eds.). Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. SVP Memoir 8, 103-126.

Carrano, Krause, O'Connor and Sampson, 2009. Case 3487 Megalosaurus crenatissimus Depéret, 1896 (currently Majungasaurus crenatissimus; Dinosauria, Theropoda): Proposed replacement of the holotype by a neotype. Bulletin of Zoological Nomenclature. 66(3), 261-264.

Paul and Carpenter, 2010. Allosaurus Marsh, 1877 (Dinosauria, Theropoda): Proposed conservation of usage by designation of a neotype for its type species Allosaurus fragilis Marsh, 1877. Bulletin of Zoological Nomenclature. 67(1), 53-56.

ICZN, 2011. Opinion 2269 (Case 3487) Megalosaurus crenatissimus Depéret, 1896 (currently Majungasaurus crenatissimus; Dinosauria, Theropoda): Designation of a neotype. Bulletin of Zoological Nomenclature. 68(1), 89-90.

Monday, December 15, 2014

Gansus zheni is Iteravis

So two Jehol ornithuromorphs were just named- Iteravis huchzermeyeri and Gansus zheni.  While writing up their Database entries, I noticed Iteravis is from the new Sihedang locality, where "most of the new ornithuromorphs appear to represent a single new taxon, which we describe here."  zheni is also from Sihedang.  Hmm...

How are the papers?

First a brief comment on the papers' quality.  Both taxa are named by different groups of researchers- Iteravis by Zhou, O'Connor and M. Wang, and zheni by Liu, Chiappe, Zhang, Bell, Meng, Ji and X. Wang.  Zhou et al.'s description of Iteravis is much longer and more detailed than Liu et al.'s on zheni, though Liu et al. provide more closeups of the specimens.  One irritating thing about Liu et al.'s measurement table is that it excludes manual elements except for the carpometacarpus.  But it does waste space with previously published measurements of Gansus yumenensis.  And I just noticed now that Gansus' name is put above the wrong column, the one for the right side of zheni specimen BMNHC-Ph 1342.  Good thing we pay journals to typeset for us!  Also annoying is both papers mention specimens that are undescribed.  Zhou et al. mention "approximately 20 ornithuromorphs" from Sihedang, of which most are Iteravis, but which don't even get specimen numbers.  Liu et al. list BMNHC-Ph 1394 as a paratype of zheni, but its not illustrated, measured or described.  While there are a few things I think Zhou et al. got wrong, Liu et al. make more mistakes in both anatomy and grammar.  The main skeletal figures in Liu et al. (figures 1 and 2) have the specimen numbers switched, so figure 1 says its of BMNHC-Ph 1342 but is actually of BMNHC-Ph 1318, and the reverse is true of figure 2.  On the other hand, Zhou et al. claim they used the data matrix of O'Connor et al.'s (2011) redescription of Rapaxavis, but that paper has no phylogenetic analysis.  As far as I can tell, they actually used the matrix of O'Connor and Zelenkov's (2013) redescription of Ambiortus, which isn't even in their References list.  Both of these are pretty big blunders you would hope peer reviewers would catch.  In the analysis itself, Zhou et al. initially found one most parsimonious tree in TNT, then ran it a second time (with that first tree as the seed?) and found a whopping 9760 trees that were one step shorter.  They show both that first 847 step tree and the strict consensus of the 846 step trees, but why bother showing the less parsimonious tree that's misleadingly resolved?  And if you have a huge polytomy involving Iteravis and eight other taxa in your strict consensus, why not make any attempt to resolve it?!  It's VERY easy in TNT to remove any combination of taxa from your consensus tree and thus see which ones cause the polytomy.  My guess this time is that the fragmentary Limenavis is messing things up.  I'd check, but the authors didn't include their codings for Iteravis in the paper and there's no supplementary information.  Guess I'll be emailing Jingmai...

Zhou et al. think Sihedang is in the Yixian Formation and Liu et al. think it's in the Jiufotang Formation, and the latter seem correct as the pterosaur Ikrandraco is known from Sihedang and another Jiufotang locality.  The birds are near identical in size (femora 35 vs. 34.5-36.4 mm) and have similar morphology.  Let's compare diagnoses-

Iteravis' diagnosis

Iteravis is diagnosed by (after Zhou et al., 2014)-
A1. premaxillary corpus elongate and toothless. The premaxillary body is the same length in zheni, and lacks teeth there as well (fig. 3A, contra Liu et al. stating it is unclear whether teeth were present; see red line in my cranial figure).  Toothlessness in the premaxilla is actually a synapomorphy of birds closer to Aves than songlingornithids. 
A2. maxilla with numerous teeth.  Again stated to be uncertain in zheni by Liu et al., but five alveoli are visible in their figure 3A (see red angle in my cranial figure).  As for the tooth number, Zhou et al. merely report "several" in Iteravis, and only a couple are visible in their figure, so this matches as well.  Ornithuromorphs plesiomorphically have at least several maxillary teeth.
A3. rostrum 50% of skull length. This is also true in zheni, and in many other basal ornithuromorphs too- Archaeorhynchus, Hongshanornis, Jianchangornis, Schizooura, Longicrusavis, Yixianornis, etc..
A4. ethmoid bone lining rostral half of the orbit. Though unidentified in zheni, this is visible in figure 3B and even has the same posterodorsally angled ridge with expanded central portion (yellow lines in cranial figure).  Of course, this mesethmoid is widespread in maniraptoriforms, though rarely preserved.
A5. tubercle on caudal margin of minor digit phalanx. This is visible in zheni too (green line in my postcranial figure), though also in Yumenornis, Gansus (Li et al., 2011 fig. 2A) and Ichthyornis.  Clarke (2004) states this flexor process is also present in tinamous "and an array of other avian taxa", and as phalanx III-1 isn't preserved in other non-avian birds more derived than songlingornithids, it may be a character of this clade.
A6. pubes with dorsally expanded distal boot. The pubic boots are almost identical in Iteravis and zheni.  Boots that are dorsally/posteriorly expanded are plesiomorphic for theropods, and are found in other ornithuromorphs that retain boots such as Hongshanornis, Yanornis and Schizooura.
A7. narrow ischium with concave ventral margin and weak dorsal process at midpoint.  zheni has the same kind of ischium.  A number of ornithuromorphs have ventrally concave ischia (e.g. Chaoyangia, Schizooura, Changmaornis, Yixianornis, hesperornithines), and of these, Gansus, Piscivoravis and Yanornis have a weak mid dorsal process as well.

Skulls of Iteravis zheni. Top inset- Gansus zheni holotype BMNHC-Ph 1342. Top- Gansus zheni paratype BMNHC-Ph 1318. Bottom- Iteravis huchzermeyeri holotype IVPPV18958. Red line points to toothless premaxillary edge, supposedly uncertain in Gansus zheni.  Red angle shows possible maxillary alveoli.  Yellow line points to mesethmoid ridge similar in both specimens.  Blue line points to predentary, supposedly unpreserved in Gansus zheni. Modified after Liu et al. (2014) and Zhou et al. (2014).

zheni's diagnosis

zheni is diagnosed by Liu et al. purely by characters that supposedly distinguish it from Gansus yumenensis-
B1. broader U-shaped furcula with an interclavicular angle of approximately 60 degrees (as opposed to ~40 degrees for Gansus yumenensis).  This is untrue, as interclavicular angles in zheni are ~45 and ~53 degrees.  Iteravis' is 54 degrees and Gansus' is ~42 (listed as ~38 by You et al., 2006).  The numbers for zheni and Gansus should be taken with caution though, as their furculae are distorted.  Similar angles to Iteravis and zheni are found in Archaeorhynchus, Jianchangornis, Parahongshanornis, Hongshanornis, Schizooura, Songlingornis and Yixianornis.  Almost all basal ornithuromorphs have U-shaped furculae.
B2. cnemial crests of tibiotarsus extending distally less than in Gansus yumenensis.  This is untrue, as Gansus has a very short cnemial crest extending 4% of tibiotarsal length (excluding the apomorphic proximal extension of the crest), while zheni's cnemial crest is 15% of tibiotarsal length (not 25% as the authors state).  Iteravis' is 8% (comparable to the authors' estimate of 10%).
B3. manual digit II (major digit) proportionally shorter than in Gansus yumenensis.  Phalanges II-1+2 are 86-96% of metacarpal II in zheni compared to 102% in Iteravis.  This is compared to 81-83% in Gansus, so the character is incorrect.  Similar values to Iteravis are found in Tianyuornis (85%), Yumenornis (87%), Piscivoravis (88%), Schizooura (93%), Archaeorhynchus (91-96%) and Yanornis martini (95-107%).
B4. pedal digit IV slightly longer than digit III (pedal digit IV is markedly longer than digit III in Gansus yumenensis). The ratio (ignoring unguals) in zheni is 99-106% compared to 110% in Iteravis.  The ratio in Gansus is 110-122%, so is usually larger, but not always distinct.  Schizooura is the only other basal ornithuromorph which overlaps Iteravis/zheni, with a ratio of 100%.
B5. ratio of pedal digit III/tarsometatarsus about 1.1 (it is approximately 1.0 in Gansus yumenensis). Ignoring unguals (which are rarely measured), the ratio is 89-97% in Iteravis and 97% in zheniGansus actually overlaps this with ratios of 74-101%.  Several other basal ornithuromorphs also overlap Iteravis, such as Jianchangornis (97%), Piscivoravis (94%), Yanornis martini (94-96%) and Y? guozghangi (97%). 
B6. claws of pedal digits III and IV lacking a prominent pendant flexor tubercle (present in Gansus yumenensis).  This is also true in Iteravis and all other basal ornithuromorphs, as the flexor tubercle morphology of Gansus is an autapomorphy.

Skeletons of Iteravis zheni. Left- Gansus zheni paratype BMNHC-Ph 1318. Center- Gansus zheni holotype BMNHC-Ph 1342. Right- Iteravis huchzermeyeri holotype IVPP V18958. Yellow line points to supposed median ventral synsacral groove which is more likely taphonomic.  Green line points to flexor process on manual phalanx III-1. Purple line points to omal process on lateral coracoid, supposedly absent in Iteravis (note the impression in the matrix).  Modified after Liu et al. (2014) and Zhou et al. (2014).
Other supposed differences

You can see that given their diagnoses, Iteravis and zheni only differ in slightly different ratios that are usually closer to each other than between the two measured zheni specimens.  There are also several characters which differ in their descriptions.   

zheni is said to have a "small, rostrally tapered, and tear-shaped" external naris (mistakenly cited as the internal naris), but given the odd premaxillary shape in BMNHC-Ph 1318, the premaxilla and maxilla are probably crushed in largely ventral view (note several possible alveoli in the maxilla and the deep bone under them which would be the palatal shelf; see red angle in my cranial figure), artificially shortening and tapering the anterior narial edge.  Liu et al. state zheni's naris posteriorly overlaps the antorbital fenestra, which would barely be true in their interpretation, while the labeled nasal fragment in Iteravis suggests this isn't so in that taxon.  However, the antorbital fenestral area in both specimens is a jumble of bone fragments and multicolored sediment reflecting the fragile nature of that region in birds and the separation of slabs which exposed it.  Thus any edge of the fenestra is impossible to identify exactly.  Liu et al. claim "Unlike other Jehol ornithuromorphs [including Iteravis] ... no pre-mandibular ossification is visible in any of the two studied specimens."  This would be easily explainable by taphonomy as both skulls are rather poorly preserved and the element is small and loosely connected to the dentaries.  Regardless, there are possible predentaries in each specimen- contacting the premaxillae just in front of the dentary in BMNHC-Ph 1342 and attached to the left dentary tip projecting dorsally in BMNHC-Ph 1318 (blue lines in my cranial figure).

Liu et al. state zheni has "a broad ventral groove running along the entire exposed surface" of the synsacrum, while Zhou et al. state Iteravis has "a flat ventral surface".  The latter seems true, but the 'groove' in zheni seems to be the taphonomic collapse of the hollow interior as seen in its tibiotarsi, humeri and ulnae (yellow line in my postcranial figure).  Zhou et al. states Iteravis lacks "the cranial hook present in Gansus", while it is clearly present in zheni's coracoids.  Yet both coracoids are broken in this area in Iteravis, and the left shows a depression in the matrix which seems to indicate the hook's original presence (purple line in my postcranial figure).  Liu et al. state zheni has a "prominent and triangular-shaped laterocranial process", which is absent in Iteravis.  Yet this process is also absent in the illustrated zheni specimens BMNHC-Ph 1318 and 1342.  Liu et al. cites BMNHC-Ph 1394 as having the process, but until this specimen is illustrated, it can be considered polymorphic at best to misinterpreted at worst.  zheni is said to lack ossified uncinate processes, whereas Iteravis is reported to preserve "one probable uncinate process".  All three specimens have ribcages which are only partly articulated and exposed though, so its easily possible uncinate processes are hidden if present in zheni, or that the one was misidentified in Iteravis.  Liu et al. state zheni has a deltopectoral crest on the humerus "which extends more than one-third the total length of the bone", while Iteravis' is described as extending "the proximal one-third of the humerus", but the crest in the latter is almost entirely covered by other elements so cannot be measured.  Iteravis' carpometacarpus is described as incompletely fused versus completely fused in zheni, but the specimen is slightly smaller than zheni specimens (humeri 97% of BMNHC-Ph1318, 95-97% of BMNHC-Ph1342) so could be expected to have less fusion.  Liu et al. say zheni lacks an extensor process on metacarpal I, while Iteravis is said to have a small extensor process.  Both taxa have the same morphology though, which is comparable to the extensor flange of basal paravians and not the extensor process of some ornithuromorphs.

As noted above, the authors give very different lengths for Iteravis' and zheni's cnemial crests (10 vs. 25% of tibiotarsal length), though the real apparent values are 8% vs. 15%.  The discrepancy largely seems due to zheni's tibiotarsi being preserved in anterior view, where the collapse of the element causes a median groove that exaggerates structures on either side such as the laterally placed cnemial crest.  Iteravis' right tibiotarsus is in medial view, but the left element is partially covered by the sternum and has a taphonomic concavity that extends the apparent length of the cnemial crest.  Iteravis' fibula is described as "just over half the length of the tibiotarsus", while zheni's is said to only extend "to nearly the midshaft of the tibia."  In reality, all specimens have distal ends hidden by the tibiotarsus so cannot be exactly measured.  Liu et al. state "the proximal phalanges of all pedal digits are longer than any of their respective distal phalanges" in zheni, while Zhou et al. say Iteravis has a slightly longer II-2 than II-1.  Their own measurement table shows zheni is polymorphic for this though.  Iteravis is reported to have a pedal digit IV shorter than III in contrast to zheni, but as noted above, the ratio excluding unguals is 110% in Iteravis vs. 99-106% in zheni.  So Iteravis actually has the longer digit IV, but there's more variation in zheni than difference between it and Iteravis.

Given the lack of difference between Iteravis and zheni, they are near certainly synonyms.  Iteravis was published online October 29th vs. zheni on November 14th.  We might think huchzermeyeri wins over zheni by 16 days, except for the fact Zhou et al. didn't include a ZooBank registration.  So the physical publication time is what counts, which is December 1. Thus zheni wins by 30 days.  A good example of why people need to register their names. Still we have the question...

Is this Gansus?

Liu et al. diagnosed Gansus by-
C1. hooked omal projection of the sternolateral process of the coracoid. This is actually polymorphic in Gansus (absent in CAGS-IG-04-CM-012; O'Connor and Zelenkov, 2013), and also present in Ichthyornis.  Both are miscoded in the matrix.
C2. sternum with a caudomedially curved outermost (lateral) trabecula. This is more accurately understood as having a distal expansion of the posterolateral process that is expanded medially but not much laterally, which makes the end seem to curve medially.  It is also present in Jiuquanornis, Hongshanornis, Jianchangornis, Yumenornis and Ambiortus. Notably, this isn't actually the character coded for in the analysis, which is the angle the process projects at.
C3. intermembral index (length of humerus + ulna)/(length of femur + tibiotarsus) between 0.9 and 1.1. zheni actually falls outside of this range sometimes, with a ratio of 1.06-1.12.  Parahongshanornis (.9) and Yixianornis (1.07) also fall within this ratio.
C4. intermetacarpal space terminating distal to the distal end of metacarpal I.  This is unreliable, as it varies with metacarpal I length as well as how the laminar metacarpal III is crushed in relation to metacarpal II.  
C5. metatarsal II shorter than metatarsal IV (metatarsal II extends distally only as far as the base of the trochlea of metatarsal IV). Metatarsal II is near universally shorter than IV in basal ornithuromorphs, with their exact trochlear relation difficult to judge in specimens preserved with tarsometatarsi in dorsal view. However, metatarsal II is as short compared to IV as in Gansus or moreso in Ichthyornis and hesperornithines at least.  This is coded as such in the matrix, but the basal hesperornithines Enaliornis and Baptornis are miscoded as having longer mtIIs, as is Vegavis.  With these corrected, all included birds more derived than songlingornithids have the state, except Apsaravis and Gallus.
C6. proximal pedal phalanges longer than distal pedal phalanges. This is true in almost every basal ornithuromorph, with zheni and Gansus ironically being the only taxa with some discordant specimens (both in digit II).  Note while this is a character in the analysis, it is properly coded as present in all ornithuromorphs in the matrix so does not resolve as a Gansus character.  Why it was then included in their emended diagnosis for the genus, I have no idea.
C7. pedal digit IV longer than digit III. zheni is polymorphic for this, as noted above.  Hesperornithoids also exhibit the state, more developed than zheni or Gansus.  The character was not included in their analysis.
They also listed one other character which united zheni and Gansus in their analysis-
C8. supracoracoidal nerve foramen of coracoid displaced so that it[s] nerve no longer passes through the coracoid. Zhou et al. state this is untrue in Iteravis. The foramen is difficult to see in specimens crushed in two dimensions, so it is very possible Liu et al. miscoded zheni.  Or it may be polymorphic.  Archaeorhynchus, Jianchangornis, Patagopteryx, Hongshanornis and Longicrusavis also lack this foramen, but only the former two are coded as such in the matrix.

The total evidence here suggests C4 is invalid, C1, C3, C6, C7 and ?C8 are polymorphic in at least one those species, C5 is symplesiomorphic, and C2 is true in several other taxa.  Changing the ten miscodings noted above (with zheni conservatively coded as polymorphic for the coracoid foramen), zheni ends up basal to Gansus and birds closer to the crown.  Checking which characters supported this, I found most were based on miscodings as well*.  Correcting these left zheni basal to Gansus, supported only by its gastralia.  Yet Gansus specimens may have taphonomically lost their gastralia (e.g. no crania are connected to any), so this isn't the greatest evidence.  Enforcing zheni to be Gansus results in trees one step longer, so is basically as parsimonious.  Thus neither position is well supported, and the new combination Iteravis zheni is used until good evidence for referring it to Gansus is presented.

* Ichthyornis and Apsaravis miscoded as having fused dentaries; Gansus miscoded as having an extensor process on metacarpal I; Gansus miscoded as having a first manual digit shorter than 50% of metacarpal II length; Gansus miscoded as having a manual ungual II subequal to or longer than I; Schizooura, Gansus, Ichthyornis, Anas and Gallus miscoded as having proximodorsal ischial processes, when they have mid-dorsal processes like other ornithuromorphs (except Patagopteryx which has both and was miscoded as lacking the proximodorsal one); zheni miscoded as having 8 and/or 10 sacrals instead of ~8-10.

Finally, the 22 miscodings noted above change the ornithuromorph part of the tree.
Liu et al. had- (Arc(Pat(Vor(Schiz((Hong,Long)(Jian((Song(Yan,Yix))(Gans(Hesp(Ich(Veg,Aves)))))))))))
... with Apsaravis either just more derived than Gansus or sister to Vegavis+Aves.
The new tree is- ((Vor,Pat)(Schiz(Arc,Jian,Song,Yan,Yix(Long,Hong)(Gans(Ich(Aps(Hesp(Veg,Aves))))))))
Not that I trust the latter tree either, as 22 corrected states centered around one node changed that much, further corrections will probably have greater effects.

References- Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.

You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.

Li, Zhang, Zhou, Li, Liu and Wang, 2011. New material of Gansus and a discussion on its habit. Vertebrata PalAsiatica. 49(4), 435-445.

O'Connor, Chiappe, Gao and Zhao, 2011. Anatomy of the Early Cretaceous enantiornithine bird Rapaxavis pani. Acta Palaeontologica Polonica. 56(3), 463-475.

O'Connor and Zelenkov, 2013. The phylogenetic position of Ambiortus: Comparison with other Mesozoic birds from Asia. Paleontological Journal. 47(11), 1270-1281.

Liu, Chiappe, Zhang, Bell, Meng, Ji and Wang, 2014. An advanced, new long-legged bird from the Early Cretaceous of the Jehol Group (northeastern China): Insights into the temporal divergence of modern birds. Zootaxa. 3884(3), 253-266.

Zhou, O'Connor and Wang, 2014. A new species from an ornithuromorph (Aves: Ornithothoraces) dominated locality of the Jehol Biota. Chinese Science Bulletin. 59(36), 5366-5378.

Wednesday, December 3, 2014

Norman's nomenclature's notoriously negative

Norman (2014) just published a revision of the iguanodont Hypselospinus, and while I have no opinion on the issues of synonymization, his treatment of nomenclature is deeply flawed.

First, Norman uses the term "nomen dubium in two different ways.  The correct way is illustrated by his discussion of Delapparentia, where he declares it a nomen dubium because it can't be distinguished from other iguanodonts.  This is also how he uses it for Siamodon and Penelopognathus.  However, he uses it incorrectly when he claims junior synonyms are nomina dubia.  A nomen dubium cannot be distinguished from two or more taxa, so that we can't know what it was.  But if you can't distinguish it from only one other taxon, then we know what it was and it's a junior synonym instead.  So contra Norman, he views Huxleysaurus, Darwinosaurus, Dollodon, Proplanicoxa, Sellacoxa, Mantellodon, Vectisaurus, Sphenospondylus and Kukufeldia as junior synonyms, NOT nomina dubia.  It's particularly difficult to figure out what Norman's concept of 'nomen dubium' is since there are cases where the same species is given different status depending on which genus it's paired with.  Iguanodon seeleyi and Wadhurstia fittoni are listed only as synonyms, yet Dollodon seeleyi and Huxleysaurus fittoni are listed as synonyms AND nomina dubia?!  What?  That makes no sense.

Secondly, Norman doesn't seem to 'get' phylogenetic nomenclature.  He brings up numerous ornithopod examples of how "topological change can occur in trees resulting from different systematic analyses", which is true.  He finds Tenontosaurus closer to Hypsilophodon than to Iguanodon, whereas most other modern analyses find the opposite, etc..  But then he says "Topological change will generate nomenclatural inconsistency that compromises the technique of clade anchoring. Consistency (a universal aspiration amongst taxonomists) underpins the advocacy of phylogenetic definitions but can only be assured if (and when) phylogenetic trees maintain consistent relational topologies."  This doesn't compromise the technique, it's the point of the technique!  If we all have a concept of Iguanodontia as (Iguanodon < Hypsilophodon) and Hypsilophodontidae as (Hypsilophodon < Iguanodon)*, then we can just say Norman recovered Tenontosaurus as a hypsilophodontid while Butler found it in Iguanodontia and know what that means.  The clades aren't supposed to have stable membership, they're supposed to have stable positional relationships to certain taxa.  So when Norman states Iguanodontia as defined above "is misleading in the sense that it clusters OTUs as anatomically dissimilar (dentally, cranially, and postcranially) as Tenontosaurus (and other hypsilophodontians, in the usage employed here - Figs 50, 52) with Dryosaurus and Camptosaurus that have definitively Iguanodon-like teeth", he's missing the point.  It doesn't matter how dissimilar the taxa in a clade are, the fact they form that clade with Iguanodon as opposed to Hypsilophodon is all that matters.

* All definitions I use here are simplified in not listing the type species for each genus for clarity's sake.

Norman's (2014) nomenclature on left vs. traditional/suggested nomenclature on right.  Modified after Norman (2014).

Finally we have Norman's taxa and definitions themselves.

Clypeodonta is defined as "Hypsilophodon foxii, Edmontosaurus regalis, their most recent common ancestor, and all of its descendants."  So the only non-clypeodont ornithopods are orodromines, Asian thescelosaurines and sometimes American thescelosaurines (in Boyd-based and Scheetz-based analyses but not Butler-based ones).

Norman defines Hypsilophodontia as "Hypsilophodon foxii, Tenontosaurus tilletti, their most recent common ancestor, and all of its descendants", but this is a senior synonym of Clypeodonta in most topologies since Tenontosaurus is an iguanodont in them.  It's also problematic because Hypsilophodontidae is already defined as (Hypsilophodon < Parasaurolophus) thanks to Sereno (1998).  Hypsilophodontidae thus covers the same taxa as Hypsilophodontia in Norman's cladogram, and in the absence of any proposed non-hypsilophodontian hypsilophodontids it seems unnecessary.  Note also that this puts an -ia clade inside of an -idae clade, which is unintuitive thanks to our Linnaean training.  Ironically, Cooper (1985) first proposed Hypsilophodontia as a clade equivalent to Clypeodonta.

Iguanodontia is defined as "Edmontosaurus regalis and all taxa more closely related to E. regalis than to the taxa subtended to the clade (Hypsilophodontia) that includes Hypsilophodon foxii and T. tilletti."  This is a horrible definition.  An obvious issue is that Edmontosaurus is used instead of Iguanodon, which violates Article 11.7 of the Phylocode.  The more pressing issue is that the definition is self-destructive if the consensus is correct in placing Tenontosaurus closer to Edmontosaurus than to Hypsilophodon.  If that consensus is correct, Edmontosaurus is itself subtended by the clade that includes Hypsilophodon and Tenontosaurus, so it refers to impossible taxa that are more closely related to themselves than to themselves.  Funny that after railing against definitions that only work in certain phylogenies, Norman creates a definition for a commonly used name that only works in his own heterodox phylogeny.

Ankylopollexia is redefined as "Edmontosaurus regalis and all taxa more closely related to E. regalis than to Dryosaurus altus" instead of the original (Camptosaurus + Parasaurolophus).  Why bother to redefine this when both definitions cover the same known taxa?  Also how about using a taxon with a actual pollex in the definition?  It's as if someone used Harpymimus as the internal specifier for Arctometatarsalia.

Styracosterna is redefined as "Batyrosaurus rozhdestvenskyi, E. regalis, their common ancestor, and all of its descendants" instead of the original (Parasaurolophus < Camptosaurus).  Again, both definitions cover the same taxa in Norman's cladogram, so there was no reason to make a new one.  Norman says application of the old definition "is compromised by
the increased complexity of camptosaur-grade (Camptosauridae sensu Sereno) iguanodont interrelationships (McDonald, 2011: fig. 1), as exemplified by the positions of Uteodon and Cumnoria."  But what's the problem if Uteodon and Cumnoria are styracosternans?  That's an interesting fact, and it's not like Sereno (1986) mentioned either genus when naming Styracosterna.  More importantly, why choose Batyrosaurus as your internal specifier?!  That was named 26 years after Styracosterna and found to be a hadrosauroid close to Probactrosaurus and Eolambia in its original description.  If that's right, Norman's Styracosterna would be a much less inclusive clade than historically recognized.  So again Norman creates a definition that only works in his heterodox phylogeny.  I don't know which topology is right, though Norman's does create a huge ghost lineage for the Santonian Batryosaurus if it's that basal.

Norman unofficially calls a clade of taxa 'iguanodontoids', but this clade already has a valid and defined name- Iguanodontidae.  The latter family was defined as (Iguanodon < Parasaurolophus) by Sereno (1998), so if Norman were effectively using the power of phylogenetic nomenclature, he could just say he found Proa, Jinzhousaurus, Bolong, Barilium and Mantellisaurus to be iguanodontids and we'd know what he means.

Hadrosauriformes is redefined as "Altirhinus kurzanovi, E. regalis, their common ancestor, and all of its descendants", instead of the original (Iguanodon + Parasaurolophus).   This changes the clade to be less inclusive for no reason, excluding iguanodontids.  Note both definitions violate Article 11.7, which requires Hadrosaurus to be used as an internal specifier.  Like the styracosternan situation, Norman's redefinition uses an internal specifier which was not even named when the clade was named (Altirhinus named in 1998 vs. Hadrosauriformes in 1997). 

Hadrosauromorpha is a new name for (Edmontosaurus < Probactrosaurus), which should again use Hadrosaurus as per Article 11.7.  Besides that, I think this taxon is a good one subsecting a long stem and using a classic genus.

Finally, Euhadrosauria is defined as "Parasaurolophus, Saurolophus, Edmontosaurus, their most common ancestor, and all of its descendants."  It hasn't been defined before to my (limited) knowledge, and this does correspond to the clade in Weishampel et al.'s (1993) phylogeny where they named it.  The problem is that in Prieto-Marquez-based phylogenies (which are 98% of all recent hadrosaur phylogenies), Hadrosaurus itself falls just outside this clade.  A Euhadrosauria excluding Hadrosaurus is counterintuitive to say the least.  Weishampel et al. created Euhadrosauria as "the traditional grouping of hadrosaurines and lambeosaurines", as opposed to the more basal Telmatosaurus.  Since Telmatosaurus is still considered more basal than Hadrosaurus, the phylogenetic definition (Hadrosaurus + Lambeosaurus) seems obvious.  This way it will always include the same taxa whether Hadrosaurus is in its traditional position by Kritosaurus or just basal to the main hadrosaur split.

It seems pretty obvious the ideal definitions using eponymous taxa and original concepts are-
Clypeodonta- (Hypsilophodon + Hadrosaurus)
Hypsilophodontidae- (Hypsilophodon < Hadrosaurus)
Iguanodontia- (Iguanodon < Hypsilophodon)
Dryomorpha- (Dryosaurus + Hadrosaurus)
Dryosauridae- (Dryosaurus < Hadrosaurus)
Ankylopollexia- (Camptosaurus + Hadrosaurus)
Camptosauridae- (Camptosaurus < Hadrosaurus)
Styracosterna- (Hadrosaurus < Camptosaurus)
Hadrosauriformes- (Iguanodon + Hadrosaurus)
Iguanodontidae- (Iguanodon < Hadrosaurus)
Hadrosauroidea- (Hadrosaurus < Iguanodon)
Hadrosauromorpha- (Hadrosaurus < Probactrosaurus)
Euhadrosauria- (Hadrosaurus + Lambeosaurus)

I don't know why no one's suggested those yet.  All eponymous, match original definitions except for replacing genera with standardized ones, plenty of node-stem triplets...  Phylogenetic nomenclature isn't rocket science.

Reference-  Norman, 2014. On the history, osteology, and systematic position of the Wealden (Hastings group) dinosaur Hypselospinus fittoni (Iguanodontia: Styracosterna). Zoological Journal of the Linnean Society. DOI: 10.1111/zoj.12193