Saturday, January 24, 2015

BANDit cladogram evaluated - James and Pourtless 2009

Besides Hou et al. (1996), the only BANDit (Birds Are Not Dinosaurs) cladistic analysis has been that of James and Pourtless (2009).  Little has been said about this paper, with most of the commentary noting the backwards philosophy the authors had in coding characters with supposedly controversial homology as unknown instead of letting phylogenetic analysis establish homology.  Well I finally looked at it in a little detail, and found a far larger issue.

First, let's go over the basic tests and conclusions of James and Pourtless' study.  After making the almost correct observation that no published cladistic analysis has tested whether birds are dinosaurs (Senter 2004 did, but while the authors cite it they don't comment on it in that regard), James and Pourtless aim to correct this by constructing their own dataset with alternative proposed bird ancestors included.  With basal archosauriforms as the outgroup, the authors also include crocodylomorphs,  Longisquama, a few other pseudosuchians and numerous theropods.  Running their dataset of 242 characters and 79 taxa, they recover a large number of MPTs.  These are only ever illustrated as majority rule bootstrap trees after a posteriori pruning of taxa, and each alternative tree is basically a well supported Archosauria with a massive polytomy between crocodylomorphs, numerous theropod lineages and birds.  Longisquama weakly (55% bootstrap) groups with birds if 21 "controversially homologous" characters (which are only coded for non-dinosaurs) are excluded and non-bird maniraptorans are pruned away.  Statistical tests were done, seemingly showing the 'basal archosaur' (= Longisquama), crocodylomorph and dinosaur hypotheses of bird origins aren't any worse than each other.

Figure 12 of James and Pourtless (2009), showing majority rule bootstrap tree with numerous taxa including all maniraptorans pruned away a posteriori.  *Gasp* It looks like birds are closer to non-dinosaur Longisquama and that even crocs could be as close to birds as dinosaurs.  Were BANDits right all along? (Spoiler- NO)
How to explain this?  First, I should note that when you run their data, the resulting MPTs are pretty standard.  As shown in my typed cladogram below, while there are plenty of weird details going on in Theropoda, the basic structure of birds within Pennaraptora within Maniraptora within Coelurosauria within Theropoda within Saurischia within Archosauria is present.  The only odd relevant aspects are Effigia is an ornithomimosaur and Longisquama is deeply embedded in Pennaraptora.  Note there's no way of knowing Effigia groups with ornithomimosaurs by reading the paper, as its exact results aren't mentioned and it's always pruned out of the figured trees.  I find this suspicious.  In any case, Longisquama being sister to ornithines is discussed since this is the current favored alternative of BANDits.  Besides the paltry literature, the authors depended on photos at the KU for their coding of the genus, and present a cranial reconstruction.  This reconstruction looks as if it was done assuming a theropodan morphology for the taxon.  For example, there's a T-shaped structure at the anterodorsal corner of the orbit, interpreted as a lacrimal by the authors.  But it would also compare well to a prefrontal in a basal diapsid like Coelurosauravus, where the lacrimal is reduced.  Similarly, the strip under the supposed supraorbital ridge (yellow) would match the posterodorsal strip of the lacrimal/prefrontal in Coelurosauavus.  Or the wedge just behind this, while unidentified by the authors, would match the postfrontal of Coelurosauravus.  The supposed antorbital fossa (red) matches the external naris of Coelurosauravus well, and even the big posterodorsal hole ("?" in their figure) would match Coelurosauravus' if it's a supratemporal fenestra as identified by most previous authors.  This isn't to say that Longisquama is a close relative of Coelurosauravus (as Senter 2004 recovered), merely that the lens you view a fossil like Longisquama through based on photos can affect your identifications.  The controversial aspects of Longisquama's anatomy are similarly all coded as theropod-like- thecodont teeth, antorbital fenestra with maxillary fenestra, furcula, etc..

Longisquama skull (counterslab of PIN 2584/4) and interpretation of James and Pourtless (2009) on top.  Coelurosauravus skull reconstruction at bottom after Evans and Haubold (1987), modified so that the entire spiked temporal element is the squamosal after Schaumberg et al. (2007).  I see the supposed antorbital fossa (afo in red), but don't think its obviously a fossa, as opposed to a fenestra (e.g. the naris) or bone process itself.  Similarly, the entire ventral edge of the supposed antorbital fenestra (aof) looks like a crack to me, including the supposed dorsal process of the maxilla (dpm), supposedly there to support an interfenestral bar.  I don't see any posterior edge of the antorbital fenestra either, so that that whole area could be a solid maxilla.  The ventral process (vp) is apparent, but if anything seems separated from the nasal by a suture (shown by the green space).
As for the matrix, there are of course lots of miscodings (e.g. character 5 is for dermal armor, which is coded unknown for almost all theropods and Effigia, plus coded absent in Ceratosaurus, the one theropod that actually has it).  Some of the characters are formed terribly while others are partitioned in a way that weights them (e.g. each dentigerous element has its own character for tooth serrations, each a three state ordered character of the form '0- all serrated; 1- some serrated; 2- none serrated'; thus any taxon leading from serrated to unserrated teeth needs six steps to do so).  The 21 "controversially homologous" characters include every manual character due to the I-II-III vs. II-III-IV issue, though oddly these aren't even coded for dinosaurs with five digits like Herrerasaurus.  There's also a huge imbalance of taxa, with a whopping 45 non-avian theropods plus 16 birds, only 9 pseudosuchians, 3 non-archosaurs, Eoraptor, Marasuchus and Scleromochlus.  These are all issues, but not the most important one.

|--Proterosuchus
`--+--Euparkeria
...`--+--Erythrosuchus
......`--+--Pseudosuchia(Ornithosuchus,Postosuchus,Crocodylotarsi)
.........|--Scleromochlus
.........|--Marasuchus
.........`--+--Eoraptor
............`--+--Herrerasaurus
...............|--Carnosauria("Syntarsus",Dilopho,Cerato,Sinraptor,Allo,Tyranno)
...............`--+--Juravenator
..................|--Sinosauropteryx
..................|--Compsognathus+Huaxiagnathus
..................|--Guanlong+Dilong
..................|--Effigia+Ornithomimosauria
..................|--Microvenator
..................`--+--Coelurus
.....................|--Ornitholestes
.....................|--Falcarius
.....................`--+--Therizinosauroidea
........................`--+--Oviraptorosauria+Dromaeosauridae
...........................`--+--Troodontidae
..............................`--+--Pelecanimimus+Avimimus+Parvicursorinae
.................................`--+--Caudipteryx
....................................`--+--Longisquama
.......................................`--Ornithes


Actual strict consensus of James and Pourtless' data, simplified so that genera which form monophyletic clades are represented by their clade names.  Note no dinosaurs were coded for manual characters, Effigia is an ornithomimosaur, and Longisquama is deeply nested in Theropoda.

No, the biggest problem with James and Pourtless' analysis is that its matrix consists mostly of characters designed to diagnose coelurosaur clades (e.g. 96 from Clark et al.'s 2002 TWG analysis; 26 from Chiappe's 2002 bird analysis) plus those suggested by BANDits to group Longisquama and crocs with birds.  So what happens when you analyze Longisquama in a coelurosaur/bird matrix after reconstructing its skull with theropod presumptions and pretending no dinosaur preserves hands?  Given it doesn't preserve sacrum, pelvis, hindlimbs or tail, and that the vertebrae are basically uncodable, it emerges as a coelurosaur.  When chatting with Nick Gardner about this I joked "I bet if you coded e.g. Coelurosauravus' front half into the matrix, it would be coelurosaurian too."  So I coded Coelurosauravus' front half, the same parts preserved for Longisquama, and lo...

|--Proterosuchus
`--+--Euparkeria
...`--+--Erythrosuchus
......`--+--Pseudosuchia(Sclero,Ornithosu,Posto,Crocodylo)
.........`--+--Marasuchus
............`--+--Eoraptor
...............`--+--Herrerasaurus
..................`--+--Carnosauria("Syntarsus",Dilopho,Cerato,Sin,Allo,Tyranno)
.....................`--+--Compsognathidae
........................`--+--Guanlong+Dilong
...........................`--+--Microvenator
..............................`--+--Ornitholestes
.................................`--+--+--Coelurosauravus
....................................|..`--+--Effigia
....................................|.....`--Ornithomimo (inc. Pele,Longisquama)
....................................`--+--Coelurus
.......................................`--+--Falcarius
..........................................`--+--Therizinosauroidea
.............................................`--+--Ovirapt(inc.Caudi)+Dromaeo
................................................`--+--+--Troodontidae
...................................................|..`--Avimimus+Parvicursorinae
...................................................`--+--Sinovenator
......................................................`--Ornithes


I won my own bet.  Interestingly, this tree also has a lot more resolution and details which agree with the consensus (e.g. Pelecanimimus in Ornithomimosauria, Caudipteryx in Oviraptorosauria), and Longisquama is moved from Avialae to Ornithomimosauria.  Note Coelurosauravus is not thought by anyone to have anything to do with dinosaurs or birds, but still ends up as a maniraptoriform in James and Pourtless' matrix.  This fairly neatly proves my idea that Longisquama could be a far more basal diapsid and still emerge as a coelurosaur.  Note too that Longisquama is also an ornithomimosaur once the front half of Coelurosauravus is included, perhaps suggesting more signal between them than between Longisquama and birds.

So my conclusion is that very few characters were included that would support e.g. Tetanurae, Avepoda, Theropoda, Saurischia, Dinosauromorpha.  Just enough are included to get a basically consensus phylogeny even without manual characters, though not enough to properly place Effigia or the front half of Coelurosauravus.  The latter plus the theropodan assumptions in Longisquama's anatomy makes placement of thus genus particularly untrustworthy.  Certainly, not enough characters were included to survive bootstrap analysis, where random characters are deleted or repeated and the analysis is rerun.  It doesn't mean that "both the "early-archosaur" and "crocodylomorph" hypotheses are at least as well supported as the BMT [BAD] hypothesis", it means that James and Pourtless made a crappy analysis.

References-  Evans and Haubold, 1987. A review of the Upper Permian genera Coelurosauravus, Weigeltisaurus and Gracilisaurus (Reptilia: Diapsida). Zoological Journal of the Linnean Society. 90(3), 275-303.

Hou, Martin, Zhou and Feduccia, 1996. Early adaptive radiation of birds: Evidence from fossils from Northeastern China. Science. 274, 1164-1167.

Senter, 2004. Phylogeny of the Drepanosauridae (Reptilia: Diapsida). Journal of Systematic Palaeontology. 2, 257-268.

Schaumberg, Unwin and Brandt, 2007. New information on the anatomy of the Late Permian gliding reptile Coelurosauravus. Palaontologische Zeitschrift. 81(2), 160-173.

James and Pourtless, 2009. Cladistics and the origin of birds: A review and two new analyses. Ornithological Monographs. 66, 78 pp.

Thursday, January 15, 2015

Is Linheraptor a synonym of Tsaagan?

One of the first theropod papers of 2015 is Xu et al.'s defending Linheraptor as being distinct from Tsaagan, after they were synonymized by Senter (2011) and Turner et al. (2012).  I provisionally synonymized them on the Database because Turner's arguments seemed sound, though I haven't actually studied the problem myself.  One interesting aspect here is that this paper is basically a criticism of the details and methods of Turner et al., which was basically a published version of part of Turner's (2008) thesis.  Yet Norell is a coauthor, who was not only a coauthor of Turner et al., but also Turner's advisor for his thesis. 

Unfortunately, after reading Xu et al.'s arguments, my conclusion is that a LOT of work went into arguing a point no one disputes- the holotypes are not identical.  The authors make a huge point of the number of characters they found which differ between the holotypes- sixty-one.  Also that many of these are found in some dromaeosaurids, but not others.

Xu et al. correctly state "Proposals of synonymy are usually based on a judgment that putative diagnostic differences between the taxa in question are individual, ontogenetic, or sexually dimorphic variations rather than taxonomic ones, making one of the new taxa invalid. Taxonomically informative variations can sometimes be distinguished from intraspecific ones if a sample large enough to provide a basis for rigorous investigation of patterns of variation is available."  They then say "In the present case, Evans et al. (2013), Senter et al. (2012) and Turner et al. (2012) attributed the proposed diagnostic features distinguishing L. exquisitus from T. mangas to individual intraspecific variation, but avenues for testing this hypothesis are limited because each species is currently represented only by a single individual."

Well, no.  You don't need the exact species under consideration to study the extent of individual variation, you can use relatives.  Turner himself had the right idea to use the multiple known skulls of the closely related Velociraptor mongoliensis as the basis for judging differences between Tsaagan and Linheraptor.  Xu et al.'s response to this is rather comical- "a comprehensive taxonomic review [of Velociraptor] has yet to be published to determine how observed morphological variations relate to inter- or possibly intraspecific factors. This can be addressed by including all Velociraptor specimens in a specimen-level phylogenetic analysis, by using morphometric methods to quantify the variation present and by deepening our understanding of the biological significance of the variations observed. Until this work has been completed it is in our view that noticeable variations between L. exquisitus and T. mangas are grounds for taxonomic separation."

So until we perform these studies which have been published so far for zero (specimen-level phylogenetic analysis), ?five (using morphometric methods to quantify the variation present) and ?zero (deepening our understanding of the biological significance of the variations observed) Mesozoic theropods on Velociraptor, we can't treat multiple specimens of it as one taxon?  That's a bit of a far goalpost, don't you think?  The morphometric studies done on other theropods haven't even resolved their taxonomy (e.g. Allosaurus, Archaeopteryx), so I'm skeptical a similar study on Velociraptor would yield useful results either.  If we were to extend Xu et al.'s demands to other taxa, we'd basically have to say we know nothing yet of intraspecific variation in Mesozoic theropods.

Differences between the Tsaagan (first and third rows) and Linheraptor (second and fourth rows) holotypes. After Xu et al. (2015).
Xu et al. include extensive comparisons to other dromaeosaurid taxa for each difference noted.  They say "Taken together, the distributions of these features among dromaeosaurids not only demonstrate that L. exquisitus is a valid taxon distinct from T. mangas but also provide important information on dromaeosaurid interrelationships."  Yet in almost every case, there's only one skull known for each other taxon as well.  Thus if e.g. Tsaagan shares a character with the Dromaeosaurus holotype not found in Linheraptor, yes it could mean that's a phylogenetically useful character uniting the first two genera, but it could also mean it's an individually variable character that the one preserved specimen of Dromaeosaurus happens to share with the only specimen of Tsaagan and not the only specimen of Linheraptor.

You'd have to see how the character distribution worked out in total, as if e.g. Tsaagan and Dromaeosaurus shared a lot of derived characters not found in Linheraptor, that would be increasingly good evidence for a phylogenetic signal (or sexual dimorphism or ontogenetic change, I suppose) instead of coincidence.  Needless to say, Xu et al. do not do this and indeed find even more characters shared between Tsaagan and Linheraptor.

My basic response to Xu et al. is "Could I find 61 comparable differences between two skulls and necks of specimens near universally agreed to be Tyrannosaurus rex? Yes I could."  Indeed, in every example I've looked into, from Allosaurus to Microraptor to Archaeopteryx, every specimen differs in numerous other ways from every other.  Importantly, the differences never sort themselves into mutually exclusive pools, so that instead of Morph A having traits ABCD and Morph B having traits 1234, we instead get a specimen with 1B34, one with 123D, one with A2C4, one with 12C4, etc..  So either every known relatively complete and described Mesozoic theropod individual is its own species, or Mesozoic theropods had significant individual variation, just like living organisms.  I know which option I choose.

Variation in three Velociraptor mongoliensis skulls. Top- holotype AMNH 6515, middle IGM 100/25 (fighting specimen), bottom IGM 100/982.  Note the numerous differences (anterior premaxillary angle in holotype, maxillary fenestra shape in top two, anterior antorbital fenestra shape, ventral lacrimal process angle in 982, posterior jugal outline in holotype, etc.).  After Norell et al. (2006).


To finish up the criticisms, I find Xu et al.'s statement that "In some taxonomic studies, some taxonomic indicators have been based on superficial rather than detailed morphological comparisons" to be based on problematic examples.  They say "Saurornitholestes and Deinonychus have been regarded as junior synonyms of Velociraptor based on overall similarities (Paul, 1988), although both are now widely accepted as valid taxa (e.g., Turner et al., 2012)."  But Paul never advocated those as being the same species, merely different species in one genus.  That's a completely different issue, since genera are (more) subjective and Turner's analysis even finds these to be monophyletic to the exclusion of Dromaeosaurus, the only other decently described dromaeosaurid Paul knew of (Paul questioningly includes Adasaurus as a dromaeosaurine but notes "not enough has been published for us to be certain of anything").  If the authors wanted an example of bad Paul synonymization, they had the easy target of his 2010 synonymization of Tsaagan with Velociraptor, but not Deinonychus or Saurornitholestes.

"Similarly, the basal tyrannosauroid Guanlong has been suggested to be a sub-adult individual of the basal tetanuran Monolophosaurus based on the fact that the two taxa are both characterized by a cranial crest and several other superficially similar features (Carr, 2006), though this proposal has received little acceptance (Brusatte et al., 2010, 2012)."  Well, Carr's argument was only an SVP abstract, so it hasn't had a chance to be detailed yet.  Seems like a low blow.

"In addition to considering L. exquisitus to be a synonym of T. mangas, Turner et al. (2012) scored some character states for [Sinornithosaurus] millenii based on IVPP V 169041). However, V 16904 is not referable to S. millenii for two key reasons. First, V 16904 is inferred to be more ontogenetically advanced than the holotype specimen of S. millenii (V 12811) based on fusion features (the neurocentral sutures are fully closed in the preserved vertebrae of V 16904 but are evident in at least some vertebrae of V 12811, the proximal tarsals are fused to the tibia in V 16904 but remain separate in V 12811), but is significantly smaller than the latter specimen; and second, V 16904 differs from the holotype of S. millenii in some important morphological features, such as the fact that all of the teeth lack denticles in the former specimen but have denticles in the latter."  Here we have a brief example of the splitter mindset- differences equal taxonomic separation.  For just a few counter-examples- the Mei referred specimen has a tibiotarsus and fused presacral neurocentral sutures but is 80% the size of the holotype that doesn't; the Sinovenator paratype has a tibiotarsus but is 89% the size of the holotype that doesn't; Microraptor specimens can have serrations on both carinae (NGMC 00-12-A), only distal serrations (holotype) or no serrations (IVPP V13320).  Again, either we have a ton of unrecognized coexisting species, or species exhibit variation.

As far as good points go, besides more details and gorgeous photos of the amazingly complete Linheraptor skull (e.g. both scleral rings are articulated and in place), Xu et al. are right to criticize some sloppiness in Turner's work.  But they missed out on the least justified problem Turner had regarding Linheraptor- if he viewed it as synonymous with Tsaagan, WHY didn't he code the basically complete Linheraptor specimen for Tsaagan's OTU?!

In conclusion, Xu et al. state "... the contrast between our own perception of L. exquisitus as a valid taxon with many distinguishing features and the view that L. exquisitus is a junior synonym of T. mangas (Evans et al., 2013; Senter et al., 2012; Turner et al., 2012) presents an example of the principle that “similarity lies in the eyes of the beholder” (Clark, 1992)."  As seven of the eight authors of this paper were authors of the Linheraptor description, I might be forgiven for wondering if "similarity lies in the eyes of the namer" has some relevance as well. :)

References- Norell, Clark, Turner, Makovicky, Barsbold and Rowe, 2006. A new dromaeosaurid theropod from Ukhaa Tolgod (Omnogov, Mongolia). American Museum Novitates. 3545, 51 pp.

Turner, 2008. Phylogenetic relationships of paravian Theropods. PhD Thesis. Columbia University. 666 pp.

Senter, 2011. Using creation science to demonstrate evolution 2: Morphological continuity within Dinosauria. Journal of Evolutionary Biology. 24, 2197-2216.

Turner, Makovicky and Norell, 2012. A review of dromaeosaurid systematics and paravian phylogeny. Bulletin of the American Museum of Natural History. 371, 1-206. 

Xu, Pittman, Sullivan, Choiniere, Tan, Clark, Norell and Wang, 2015. The taxonomic status of the Late Cretaceous dromaeosaurid Linheraptor exquisitus and its implications for dromaeosaurid systematics. Vertebrata PalAsiatica. 53(1), 29-62.

Saturday, January 10, 2015

Big "New Years" Theropod Database update

Happy only over a week from New Years everyone!  Time for a Theropod Database update.  Besides all of the new taxa, there's a huge revising of Morrison allosaurids and Baharija taxa (check out the tetanurine Bahariasaurus).  Enjoy all of the updates.

Thursday, January 8, 2015

"Madsenius" and "Wyomingraptor"

As part of the huge Allosaurus rehaul coming in my annual "New Years" (*cough* it's already January 8th *cough*) Database update, I looked over all proposed Morrison allosaurs.  Two of the most mysterious are the nomina nuda "Madsenius" and "Wyomingraptor", but I think I have them figured out.  Enjoy.

"Wyomingraptor"

Tithonian, Late Jurassic
Brushy Basin Member of the Morrison Formation, Wyoming, US
(Nail Quarry)
(TATE 542) (adult) tooth (36 mm) (Bakker, 1997)
(TATE 543) (adult) tooth (20 mm) (Bakker, 1997)
(TATE 544) (adult) tooth (9.9 mm) (Bakker, 1997)
(TATE 550) (juvenile) tooth (6.6 mm) (Bakker, 1997)
(TATE coll.; material of "Wyomingraptor") 138 juvenile to adult teeth, three adult individuals including distal caudal vertebrae, forelimb, pubes and ischia (Bakker, 1997)

Cast of "Wyomingraptor" forelimb (TATE coll.) (originally hosted on Tate Geological Museum website).
This name was published in the column 'Dr. Bob's Dinofacts' in response to a question from a reader (Anonymous, 1997). The author (possibly Bakker himself) suggested it for a Tate Geological Museum specimen currently labeled Allosaurus. From 1997 until 2006, the Tate Museum included a "Wyomingraptor" section in its exhibits page, stating Bakker has proposed that name for a new genus of allosaur found at Como Bluff including a photographed forelimb. In the PaleoWorld episode "Killer Raptors" (episode 7 of season 4) aired in 1997, Bakker claims the only theropod preserved in Nail Quarry is "Wyomingraptor" (though note this is untrue, as the "Brontoraptor" material was also found there). The material (three adults and numerous juvenile to adult teeth) was detailed in Bakker (1997) where he simply calls them Allosaurus. Hartman (DML, 2000) wrote that Bakker has been "attempting to erect a new genus of allosaur, which he dubs "Wyomingraptor." He has been using this name for some time, but recently has found a specimen he thinks is different enough from the type(s) to warrant generic distinction." Given Bakker's notoriety as a splitter, the Nail specimens are likely to just be Allosaurus fragilis in any case. The photographed forelimb is similar to A. fragilis USNM 4734 except for being more robust, at least in metacarpal I, phalanx II-1 and II-2. Indeed, the robust first metacarpal is similar Torvosaurus, though the elongate phalanx I-1, radius and ulna are not. The forelimb is stated to be a cast, so it's not certain how much is based on real Nail fossils. It's possible some elements were scaled incorrectly from other specimens or are complete fabrications. It's also possible some material such as metacarpal I actually comes from the "Brontoraptor" individuals and that the forelimb is a chimaera. Further evaluation awaits description of the Nail material, which has yet to be distinguished from Saurophaganax either.

"Madsenius"

Tithonian, Late Jurassic
Brushy Basin Member of the Morrison Formation, Utah, US
(Cleveland-Lloyd quarry)
(DINO 2560, = UUVP 6000; probable intended holotype of "Madsenius trux") (7.9 m, 1.32 tons) complete skull (845 mm), nearly complete skeleton (lacking first caudal vertebra, chevrons, forearms, several pedal phalanges) including femora (880, 850 mm), tibiae (730, 745 mm), astragalus and metatarsals III (375, 372 mm) (Madsen, 1976)

Figure from Bakker (2000), which I think demonstrates his concept of "Madsenius trux", represented by the lower 'creosaur' skull of DINO 2560 (= UUVP 6000).
This name was orginally reported in a children's book (Lambert, 1990) as "a proposed new allosaurid theropod to be formally named and described." Olshevsky (1991) listed it under Allosauridae as a taxon "to be described from the Morrison Formation by R. T. Bakker; based on distinctive skull material and other remains previously referred to Allosaurus and Creosaurus." Williams (online, 2004) mentioned the combination "Madsenius trux", leading Olshevsky (online, 2004) to say "trux" "was to have been Bakker's original type species epithet for the as-yet-unpublished genus Madsenius. According to him, it fits Madsen as appropriately as it fits Madsenius" [etymology- Latin trux means "fierce, rough, savage, wild"].

While nothing else unique has been written regarding "Madsenius", I believe clues in the literature point to its probable identity. Since at least 1988, Bakker has proposed two kinds of Morrison allosaur, the classic short-snouted fragilis vs. long-snouted 'atrox' dichotomy. Bakker (2000) cited the latter species as "The creosaur-type allosaurid (unfortunately, the type of Creosaurus MARSH is, by itself, indeterminate): Dinosaur National Monument skeleton University of Utah UUVP 6000 ..." as opposed to "True Allosaurus MARSH: specimens from the type locality of Allosaurus fragilis MARSH - the skeleton United States National Museum USNM 4734 ..." In that paper, he stated "These two types of skulls are easy to tell apart from the quadrate, lower temporal fenestra, and depth of the mandible; however, I find it impossible to separate the two taxa from isolated snout bones or post-crania." This matches the "distinctive skull material" noted by Olshevsky, and the 'long-snouted' skulls have been referred to both Allosaurus and Creosaurus by different workers, also matching Olshevsky's comment. Furthermore, UUVP 6000 (later recatalogued as DINO 2560) was the basis of Madsen's (1976) classic Allosaurus monograph and "Madsenius" clearly refers to Madsen. Putting everything together, I think it's apparent "Madsenius" was to be Bakker's name for creosaur-type allosaurs when he realized the Creosaurus holotype couldn't be assigned to either variety. UUVP 6000 was probably supposed to be the holotype.

If we accept this explanation, Bakker's characters supporting "Madsenius" can be evaluated. Bakker states the ventral quadrate angles posteriorly in DINO 2560, forming a deeply concave posterior edge to the element unlike A. fragilis AMNH 600. The posterior angle formed by the dorsal and ventral quadrate edges is 24 degrees in AMNH 600 compared to 30 degrees in the UUVP coll. quadrate illustrated by Madsen and 27 degrees in his cranial reconstruction of DINO 2560. Bakker's DINO 2560 illustration shows an unprecedented angle of 52 degrees. Angles in other specimens are 18 (AMNH 30798), about 44 (BYU 571/8901), 30 (DINO 11541), 43 (MOR 693), 15 (SMA 005/02) and 34 degrees (USNM 4734). For the laterotemporal fenestra, Bakker states the restriction caused by the ventral squamosal process is greater in A. fragilis AMNH 600 (least anteroposterior length of fenestra 15% of dorsoventral height) than DINO 2560 (26% in Madsen's reconstruction, 28% in Bakker's). Measurements in other specimens are about 25% (AMNH 666), 31% (AMNH 30798), < 24% (BYU 571/8901), 38% (DINO 11541), 20% (ML 415), 40% (MOR 693), 38% (SMA 005/02) and 16% (USNM 4734). Mandibular depth is 19% of length in Bakker's DINO 2560 (similar to 19% in Madsen's reconstruction) and 24% in his A. fragilis illustration, though the latter is a composite between AMNH 666 (which has only a partial surangular) and 5753 (which does not include mandibular elements). So even this minor 5% difference cannot be determined. Values in other specimens are  about 19% (AMNH 30798), about 21% (BYU 571/8901), 17% (DINO 11541), 19% (MOR 693) and 20% (SMA 005/02). The above comparison suggests mandibular depth is fairly constant in known allosaurids, though quadrate angling and laterotemporal fenestra proportions vary widely. Yet importantly, the latter conditions both exhibit intermediates instead of two distinct clusters, and do not covary- AMNH 30798 and SMA 00/02 have low quadrate angles but wide laterotemporal fenestrae, while USNM 4734 has a high angle but restricted fenestra. Note neither of these conditions vary with stratigraphy either, and indeed the A. fragilis types and DINO 2560 are both from the Brushy Basin Member. Nor does it vary geographically, with Wyoming specimens encompassing almost the entirity of the variation. Based on this study then, "Madsenius" can be considered a synonym of Allosaurus fragilis and another example of Bakker's notorious splitting.

References-  Madsen, 1976. Allosaurus fragilis: A revised osteology. Utah Geological and Mineral Survey Bulletin. 109, 1-163.

Lambert, 1990. The Dinosaur Data Book. New York, Avon Books. 320 pp.

Olshevsky, 1991. A revision of the parainfraclass Archosauria Cope, 1869, excluding the advanced Crocodylia. Mesozoic Meanderings. 2, 196 pp.

Anonymous, 1997. Dr. Bob's dinofacts. Tate Geological Times. 5(2), 3.

Bakker, 1997. Raptor family values: Allosaur parents brought great carcasses into their lair to feed their young. In Wolberg, Sump and Rosenberg (eds). Dinofest International, Proceedings of a Symposium, Academy of Natural Sciences. 51-63.

Bakker, 2000. Brontosaur killers: Late Jurassic allosaurids as sabre-tooth cat analogues. Gaia. 15, 145-158.

Hartman, DML 2000. http://dml.cmnh.org/2000Oct/msg00066.html

Olshevsky, 2004 online. https://groups.yahoo.com/neo/groups/paleo_bio_dinosaur_ontology/conversations/messages/6655

Williams, 2004 online. https://groups.yahoo.com/neo/groups/paleo_bio_dinosaur_ontology/conversations/messages/6646

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