News at the base of the Amniota part 1: Introduction

Over the next six or seven posts a new hypothesis on the origin of the Amniota will be presented. Get ready for several days of heresy.

If the following sounds like an abstract, that’s because it was one.
A large-scale phylogenetic analysis of basal amniotes is long overdue. Smaller, more focused studies typically followed tradition in creating their inclusion sets because an overarching study was not available to draw from. Too often this led to the recovery of dissimilar sister taxa by default. It is axiomatic that additional taxa test prior results by providing more nesting opportunities, so 389 specimen- and genus-based taxa are employed here. Several taxa formerly considered anamniotes; Gephyrostegus, Bruktererpeton and Eldeceeon, now nest as basalmost amniotes arising from the Seymouriamorpha. They confirm an earlier prediction that the first amniotes would have a small adult body size and contradict current analyses that nest large diadectomorphs as proximal sister taxa to the Amniota. The first amniote clade dichotomy produced an expanded Archosauromorpha (taxa closer to archosaurs, including Synapsida and Enaliosauria) and an expanded Lepidosauromorpha (taxa closer to lepidosaurs, including Caseasauria and Diadectomorpha). The present study sheds new light on the genesis and radiation of the Amniota. Phylogenetic miniaturization is present at the base of several clades, including the Amniota. The ancestry of all included taxa can now be traced back to Devonian tetrapods and every lineage documents a gradual accumulation of derived traits.

Figure 1. Cladogram of basal amniotes, a subset of the large reptile tree. Dots represent phylogenetic size reductions. Bootstrap scores are shown. Archosauromorpha in gray. Lepidosauromorpha in black at the bottom.

So this is part of what has been keeping my busy this year…
I added several taxa (Fig. 1) to the large reptile tree (not updated yet) that nested at or near the base of the Amniota. Their inclusion shed new light on the basalmost amniotes and subtly changed the tree topology of the large reptile tree. Gephyrostegus bohemicus (Fig. 2) moved to the very base of the Amniota while lacking any traditional amniote traits.

Figure 1. A new reconstruction of Gephyrostegus bohemicus. This specimen lived in the Westphalian, some 30 million years after the origin of the Amniota in the Visean, 340 mya. Note the lack of posterior dorsal ribs and the presence of a deep pelvis. These traits shared by all basalmost amniotes, may provide additional space for larger eggs in gravid females, but is also shared with males, if there were males back then. Otherwise, this taxon has none of the traditional amniote traits found in current textbooks. Nevertheless, it nested as the last common ancestor of lepidosauromorphs and archosauromorphs, so by phylogenetic bracketing, it laid amniotic eggs.

Traditional amniote traits include:

1. loss/fusion of the intertemporal
2. absence of the otic notch
3. loss/reduction of palatal fangs
4. appearance/expansion of the transverse flange of the pterygoid
5. loss of labyrinthine infolding of the marginal teeth
6. reduction of the intercentra
7. addition of a second sacral vertebra
8. narrowing and elongation of the humeral shaft
9. appearance of the astragalus from fused tarsal elements.

Ironically, many of the above traits are also found in microsaurs and seymouriamorphs, but not in basalmost amniotes. So there is homoplasy at play here.

Only phylogenetic analysis reveals the origin of the Amniota.
The key trait defining the Amniota is the production of amniotic eggs, a trait shared with all archosauromorphs (all taxa closer to archosaurs, including synapsids and mammals) and lepidosauromorphs (all taxa closer to lepidosaurs). Even though no amniotic eggs were found with the fossil Gephyrostegus bohemicus, phylogenetic bracketing (Fig. 1) indicates that G. bohemicus laid amniotic eggs. It nested as the more recent common ancestor of all lepidosauromorphs and all archosauromorphs (all other amniotes).

Outgroup taxon
Note that Silvanerpeton (Clack 1994, Fig. 2, Viséan, 331 mya) is the proximal anamniote outgroup taxon to the Amniota and lived 30 million years earlier than G. bohemicus.

Figure 2. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota.

Traits that appear in the basal amniote, G. bohemicus, 
not present in Silvanerpeton:

1. prefrontal separate from postfrontal
2. premaxilla not transverse
3. major axis of naris less than 30º above jawline
4. naris lateral
5. nasals and frontals subequal
6. maxilla ventrally straight
7. longest metatarsal is number four

Nothing very ‘sexy’ about this list. Traditional amniote traits appear later. Like Gephyrostegus bohemicus, Silvanerpeton also lacks posterior dorsal ribs and has a deep pelvis. These traits may indicate that it was the most primitive known taxon to lay large amniotic eggs (in the Viséan), but Silvanerpeton doesn’t quite have the phylogenetic bracketing status that G. bohemicus enjoys. Even so, we’ll soon meet more Viséan taxa that were definite amniotic egg layers. yet were either not considered amniotes or paleontologists wondered about them without adequately testing them in phylogenetic analysis.

Traditional and conventional studies
indicate that diadectomorphs (Fig. 3) are the proximal outgroup taxa for the Amniota, despite the readily apparent differences. In the large reptile tree diadectomorphs nest deep within the Amniota, derived from millerettids.

Figure 3. Click to enlarge. Traditional phylogenies nest large diadectomorphs as amniote outgroup taxa. Here, however, small gephyrostegids share more traits with basal amniotes and are more similar in size. A. Diadectes. B. Orobates. C. Tseajaia. D. Limnoscelis. In the box, basal amniotes: E. Gephyrostegus bohemicus. F. Thuringothyris. G. Westlothiana. H. Hylonomus.

Recent phylogenetic analyses
(Gauthier et al., 1988; Laurin and Reisz, 1995, 1997, 1999; Lee and Spencer, 1997; Ruta, Coates and Quicke, 2003; Ruta, Jefferey and Coates, 2003; Laurin, 2004; Klembara et al., 2014) recovered large, lumbering Limnoscelis and Diadectes (Fig. 3) as proximal amniote outgroup taxa. However, Ruta, Coates and Quicke (2003:292) reported, “The morphological gap between diadectomorphs and primitive crown-amniotes is puzzling”. I think everyone can agree on that one. This puzzle was resolved when Ruta, Jefferey and Coates (2003) nested diadectomorphs and Solenodonsaurus within the Amniota with the addition of the synapsid, Ophiacodon, nesting as a basal taxon. Unfortunately, later workers, like the recent Gephyrostegus paper by Klembara et al. (2014) also nest diadectomorphs outside the Amniota. Taxon exclusion was the problem, like it always is.

More tomorrow…

References
Clack JA 1994. Silvanerpeton miripedes, a new anthracosauroid from the Visean of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84:369–76.
Gauthier, J A, G Kluge and T Rowe 1988. The early evolution of the Amniota; pp. 103–155 in M. J. Benton (ed.), The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds: Oxford: Clarendon Press.
Klembara J, J Clack, AR Milner and M Ruta 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:774–792.
Laurin M 2004. The evolution of body size, Cope’s rule and the origin of amniotes. Systematic Biologiy 53:594–622.
Laurin M and R R Reisz 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society 113:165–223.
Laurin M and R R Reisz 1997. A new perspective on tetrapod phylogeny; pp. 9–59 in S. S. Sumida and K. L. M. Martin (eds.), Amniote Origins: Completing the Transition to Land, Elsevier.
Lee MSY and PS Spencer 1997. Crown-clades, key characters and taxonomic stability: When is an amniote not an amniote?; pp. 6–84 in S. S. Sumida and K. L. M. Martin (eds.), Amniote Origins: Completing the Transition to Land, Elsevier.
Ruta M, MI Coates and DLJ Quicke 2003. Early tetrapod relationships revisited. Biological Reviews 78:251–345.
Ruta M, JE Jefferey and MI Coates 2003. A supertree of early tetrapods. Proceedings of the Royal Society, London B 270:2507–2516.

The LH 20523 specimen of Scandensia is really Tijubina

Two lizards were described in 2011.
Bolet and Evans (2011) described what they thought was ‘new material’ of Scandensia (LH 20523), but it had a very long stiff tail and tiny rib osteoderms. This specimen is only known from the posterior half (Fig. 1). Simões (2011) redescribed the complete Tijubina, which also had a very long stiff tail and tiny rib osteoderms. Both are from the Early Cretaceous, the former from Spain, the latter from Brazil.

The large reptile tree nested the LH 20523 specimen with Tijubina, in the middle of the Tritosauria, several nodes away from Scandensia. The holotype of Scandensia nests between basal rhynchocelphalians and basal squamates + tritosaurs. It doesn’t have a long stiff tail or dorsal osteoderms. Distinct from the LH 20523 specimen, Scandensia has a lumbar region of very short ribs.

Figure 1. Tijubina and Scandensia holotypes. Scandensia is a much larger genus. The tail is not well preserved and could be longer in Scandensia. Note the lumbar area in Scandensia not present in Tijubina. Also note the great size of metatarsal 4 in Tijubina, not present in Scandensia.

The LH 20523 specimen has a regenerated tail with cartilaginous growth. The authors estimate the tail was 3x the the snout vent length, which they note contrasts with the holotype of Scandensia, which has subequal tail and snout-vent lengths. This is the first clue that these two are not the same taxon. But then, they reasoned, the Scandensia tail may have been incompletely preserved or regenerating.

Figure 2 The LH 25023 specimen that Bolet and Evans (2011) referred to Scandensia, but nests here with Tijubina.

Bolet and Evans (2011) were surprised to see osteoderms around the rib cage because the holotype of Scandensia does not have these. This is the second clue.

The very robust fourth metatarsal is a trait shared with Tijubina, not with Scandensia, a third clue.

Figure 3. Ankles of the LH 20523 specimen. Here Bolet and Evans see a single astragalocalcaneum (in yellow on the drawing, and present in all squamates) but the photo does not support a single proximal ankle bone. Rather a split appears between the astragalus and calcaneum, as in all tritosaurs.

Bolet and Evans report a single astragalocalcaneum, as in Scandensia, but the photo of the LH 20523 specimen shows a split between the proximal ankle bones and the shape is different than shown. Was this wishful thinking? or more precise observation. No tritiosaurs have a fused proximal tarsus, so this would be an autapomorphy if true.

Were Bolet and Evans aware of Tijubina?
I don’t think so. It is not mentioned in their paper. A query to both authors goes unanswered at present.

References
Bolet A and Evans SE 2011. New material on the enigmatic Scandensia, an Early Cretaceous lizard from the Iberian Peninsula. Special Papers in Palaeontology 86:99-108.
Bonfim Júnior DC and Marques RB 1997. Um novo lagarto do Cretáceo do Brazil (Lepidosauria, Squamata, Lacertilia – Formação Santana, Aptiano da Bacia do Araripe. Anuário do Instituto do Geociencias 20:233-240
Bonfim-Júnior F de C and Rocha-Barbosa O 2006. A Paleoautoecologia de Tijubina pontei Bonfim-Júnior & Marques, 1997 (Lepidosauria, Squamata Basal da Formação Santana, Aptiano da Bacia do Araripe, Cretáceo Inferior do Nordeste do Brasil). Anuário do Instituto de Geociências – UFRJ ISSN 0101-9759 Vol. 29 – 2 / 2006 p. 54-65.
Evans SE and Barbadillo LJ 1998. An unusual lizard (Reptilia: Squamata) from the Early Cretaceous of Las Hoyas, Spain. Zoological Journal of the Linnean Society 124:235-265.
Simões TR 2012. Redescription of Tijubina pontei, an early cretaceous lizard (Reptilia; Squamata) from the crato formation of Brazil. An Acad Bras Cienc. Feb 2, 2012. pii: S0001-37652012005000001. [Epub ahead of print].

 

Skull-less Majiashanosaurus could represent the post-crania of the skull-only Palatodonta at the base of the Placodontia

The Early Triassic skull-less Majiashanosaurus discocoracoidis (Jiang et al. 2014) was originally nested with Dianopachysaurus and Keichousaurus within the eosauropterygia. Not sure why yet, but in the large reptile tree (not yet updated) it nests at the base of the Placodontia along with the skull only Palatodonta, which we tried to guess the post-crania of earlier here.

From the abstract:
“The transverse processes of the dorsal vertebrae are not distinctively elongated. The dorsal ribs are single-headed, and the clavicles articulate on the anteromedial aspect of the scapula. The humerus is curved. These features allow assignment to a new sauropterygian taxon. The interclavicle has no posterior process, and the scapula is of typical eosauropterygian shape, with a broad and ventrally expanded glenoidal portion that is separated from a narrow posterodorsal blade by a distinct constriction. The coracoid is round and plate-like without a waist. This feature is different from that of all other known eosauropterygians, but resembles that of placodonts.”

Possible reasons for tree topology differences

1. The large reptile tree does not include Dianopachysaurus and Keichosaurus. The former has the proportions and size of a juvenile (on a Google search). I’ll have to take a first look at the latter.
2. The Jiang et al. tree excluded many enaliosaur taxa which would have attracted several of the included pachypleurosaurs (eosauropterygians) away from that clade.

In the large reptile tree shifting Majiashanosaurus to Paraplacodus adds only two steps. And these taxa are all sisters to basal eosauropterygians like Pachypleurosaurus). Since the number of cervicals is unknown, the number of pre sacrals is also unknown, but with only 19 dorsals and the present nesting, the number of cervicals is likely less than that of Pachypleurosaurus. This is one of the most basal taxa in which the clavicles are dorsal to the interclavicle, which has no medial posterior process.

References
Da-Yong Jiang, et al. 2014. The Early Triassic eosauropterygian Majiashanosaurus discocoracoidis, gen. et sp. nov. (Reptilia, Sauropterygia), from Chaohu, Anhui Province, People’s Republic of China, Journal of Vertebrate Paleontology, 34:5,1044-1052, DOI: 10.1080/02724634.2014.846264

The BES SC 111 specimen of Macrocnemus – DGS helps reconstruct it

Previously considered (Renesto S and Avanzini M 2002) a juvenile due to its size, the BES SC 111 specimen of Macrocnemus (Fig. 1) sheds light on the origin of such diverse lineages as the Tanystropheidae (Langobardisaurus, Fig. 2) and the Fenestrasauria (Cosesaurus through the Pterosauria, Fig. 2). It also nests at the base of other Macrocnemus specimens including the oddly bizarre, Dinocephalosaurus (Fig. 3).

Figure 1. Click to enlarge. Stages in the DGS tracing and reconstruction of the the Macrocnemus BES SC 111 skull. I did not realize the the palatal bones were so visible. There’s a palatine and ectopterygoid over the nasal and frontal, for instance. So earlier mistakes were made that are corrected here. The right mandible is traced here only along its ventral rim.

Derived from
an early Triassic sister to Huehuecuetzpalli and/or Jesairosaurus, the BES SC 111 specimen seems to have at least a depression in the dorsal maxilla that will ultimately become an antorbital fenestra in the Fenestrasauria. Note the resemblance of this skull to that of Cosesaurus and Langobardisaurus (Fig. 2). They all share a retracted naris, large orbit, bent quadrate, short postorbital region and relatively short teeth.

The reduction of pedal digit 5 in all known Macrocnemus specimens demonstrates the BES SC 111 nests at the base of the Macrocnemus lineage. An unknown sister without this reduction would be basal to Langobardisaurus and the Fenestrasauria.

Figure 2. Macrocnemus BES SC 111 compared to sister taxa, Langobardisaurus, Cosesaurus and the basal pterosaur, MPUM 6009. 

Figure 3. Dinocephalosaurus to scale with a large Macrocnemus specimen, T4822, and the smaller ones from figure 2.

The take-away from this is: large odd reptiles sometimes have their origin in not-so-large, not-so-odd reptiles like the BES SC 111 specimen. At the same time, small odd reptiles may have the same origin. Make sure you add the plain, old reptiles to your cladograms. That’s where the spectacular taxa have their origin.

References
Li C, Zhao L-J and Wang L-T 2007. A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Science in China D, Earth Sciences 50(11)1601-1605.
Nopcsa F 1931. Macrocnemus nicht Macrochemus. Centralblatt fur Mineralogie. Geologic und Palaeontologie; Stuttgart. 1931 Abt B 655–656.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen XII. Macrocnemus bassanii Nopcsa. Abhandlung der Schweizerische Palaontologische Geologischen Gesellschaft pp. 1-140.
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.

wiki/Macrocnemus

‘Aerodactylus’ nests with Pterodactylus antiquus. It’s not a new genus.

A recent online paper in PLOS by Vidovic and Martill (2014) proposed that the BSP AS V 29a/b specimen (n15 in the Wellnhofer 1970 catalog, Figs. 1-5) formerly attributed to Pterodactylus scolopaciceps (Meyer 1860) was actually more closely related to Cycnorhamphus. They gave it a new name, “Aerodactylus.”

I know this sounds technical. I’ll make it simple with pictures and links.

From their abstract:
A cladistic analysis demonstrates that Aerodactylus is distinct from Pterodactylus, but close to Cycnorhamphus Seeley, 1870, Ardeadactylus Bennett, 2013a and Aurorazhdarcho Frey, Meyer and Tischlinger, 2011, consequently we erect the inclusive taxon Aurorazhdarchidae for their reception.

Figure 1. BSP AV S 29a/b, formerly attributed to Pterodactylus, Vidovic and Martill rename Aerodactylus. Scale bar = 2cm. Upper image distorted to match lower image. Looks like it is swimming or walking.

The BSP specimen is gorgeous and complete.
It looks like quadrupedal in situ (Fig. 1). I’m happy to take this opportunity to finally create a reconstruction (Fig. 5) and add it to the large pterosaur tree (not updated yet), especially considering the current drama brought on by this change of genus.

Unfortunately,
my results do not support the Vidovic and Martill (2014) results. In the large pterosaur tree BSP AS V 29a/b is recovered as a sister to the original pterosaur, the first one ever described, Pterodactylus antiquus (Figs. 3, 4).

The authors also have the traditional mindset, falsified several times recently.
From their abstract:
“The majority of pterosaur species from the Solnhofen Limestone, including P. scolopaciceps are represented by juveniles. Consequently, specimens can appear remarkably similar due to juvenile characteristics detracting from taxonomic differences that are exaggerated in later ontogeny.”

The authors fail to recognize the several juveniles that are not morphologically different than adults here, here, here and here, along with the three embryos that are not different from adults here, here and here.

Okay, so let’s take a look at the contenders.
Vidovic and Martill (2014) nested BSP AS V 29 a/b with the their purported cycnorhampid Gladocephaloideus (Fig. 2, and why was it not mentioned in the abstract?)

Figure 2. Click to enlarge. Here three pterosaurs considered sisters by Vidovic and Martill 2014 are shown to scale. In the large pterosaur tree, these taxa do NOT nest together. It is clear to see they are not closely related. These specimens show variety, not similarity.

In Evolution
there is supposed to be a gradual change from one taxon to another. Sister taxa should share a long list of traits. Here (Fig. 2) they don’t.

Here are the competing contenders
It turns out that this Pterodactylus, BSP AS V 29a/b, really IS a Pterodactylus. It shares many more traits with its sisters (Fig. 3).

Figure 3. Click to enlarge. The large pterosaur tree nests these three taxa together. So this Pterodactylus really is a Pterodactylus, just a distinct species. These specimens show similarity, with a little variety.

What a mess!
And why? What was it about this very run-of-the-mill pterosaur made anyone think it was anything but what it is, a Pterodactylus.

Figure 4. Subset of the large pterosaur tree, with the BSP AS V 29a/b specimen added.

Re: Gladocephaloideus, Ardeadactylus and Aurorazhdarcho…
In the large pterosaur tree, Gladocephaloideus nests with Gegepterus within the Ctenochasmatoidea.

Ardeadactylus nests with Huanhepterus and other proto-azhdarchids. Pterodactylus longicollum is not related, but nests on the other side of the Pterodactylus antiquus holotype (Fig. 4). Yes, this genus generally gets bigger as members become more derived.

Aurorazhdarcho nests with Eoazhdarcho and Eopteranodon at the base of Nyctosaurus + Pteranodon.

So none of these taxa are really related to one another.

Getting back to the juvenile problem
Vidovic and Martill (2014) considered the SMF R 4072 specimen to be a juvenile Pterodactylus. However in phylogenetic analysis, it nests at the base of Germanodactylus. The fear of adding tiny Solnhofen specimens to phylogenetic analysis is unwarranted. A tree that includes them has been on the web for three years. And juvenile pterosaurs identical to parents are well known, but ignored.

The authors had direct access to the specimens and I did not. 
I hope you see that direct access to the specimens is no guarantee of validity. Conversely, lack of direct access to the specimens is no hinderance to critical observation.

The authors thanked, Chris Bennett (Fort Hayes), David Hone (London), and Dino Frey (Karlsruhe) ‘for the useful comments made during the project.’ And this is why I have trouble getting pterosaur papers published.

I hope now you can appreciate when I say the world of pterosaur study is like a funhouse mirror where everything is distorted and, in this case at worst, makes no sense, yet is supported by professional workers.

And let’s leave on a good note

Figure 5. Pterodactylus specimen BSP AS V 29a/b reconstructed. Soft tissue shows where the naris opens. Presumeably the small hole at the front of the antorbital fenestra. But there is a larger hole further back! This specimen has the usual wingtip claw, fifth toe claw and fifth manual digit. It may also have a few more ribs than usual, which might go along with the smaller pelvis.

BSP AS V 29 a/b is a premiere specimen.
It looked so much like other Pterodactylus ()Fig. 3) that I ignored it until now. A bit of soft tissue fills most of the antorbital fenestra leaving a small hole up front (the naris?) and a larger hole further back. The sternum is smaller relative to the humerus than in other Pterodactylus specimens. The twin teeth at the mandible tips are easy to see. These fuse to become one sharp tooth in germanodactylids and their descendants. There is nothing about this specimen that says it is anything but a Pterodactylus.

After this paper, Hermann von Meyer must be rolling over in his grave.

References
Vidovic SU and Martill DM 2014. Pterodactylus scolopaciceps Meyer, 1860 (Pterosauria, Pterodactyloidea) from the Upper Jurassic of Bavaria, Germany: The Problem of Cryptic Pterosaur Taxa in Early Ontogeny. PLoS ONE 9(10): e110646. doi:10.1371/journal.pone.0110646

 

New clade of enigmatic early archosaurs? No.

Updated one day after publication. The taxa come from the Supp. Data, most not shown in the greatly simplified chronological cladogram.

Recently, Butler et al. (2014)
recovered a “new clade of enigmatic early archosaurs” comprised of Yonghesuchus, Gracilisuchus and Turfanosuchus.

Figure 1. Do these taxa nest in a single clade? No. Turfanosuchus, Gracilisuchus and Yonghesuchus. Each nests more closely with other taxa. Yonghesuchus nests with the crocodylomorph Dromicosuchus. Gracilisuchus nests with Saltopus as a much more basal crocodylomorph. Turfanosuchus nests at the base of the Poposauridae.

Unfortunately they added the unrelated Mesosuchus (lepidosaur), Vancleavea (thalattosaur) and two pterosaurs (lepidosaurs).

And they did not add the true sisters of Gracilisuchus (Pseudhesperosuchus, Decuriasuchus, Lewisuchus, Saltopus, the SMNS 12591 specimen and Scleromochlus).

Red Flags
In the Butler et al. (2014) tree the following purported sister taxa are all “odd bedfellows” that do not look like one another.

1. Prolacerta is derived from Mesosuchus (and presumably the rhynchosaurs)
2. Euparkeria is derived from Tropidosuchus and Chanaresuchus.
3. Tropidosuchus and Chanaresuchus are derived from Vancleavea.
4. Vancleavea is derived from Erythrosuchus.
5. Pterosaurs are derived from parasuchians!!!!!!
6. Lagerpeton is derived from pterosaurs.
7. Ornithosuchia is derived from Lewisuchus.
8. Theropoda is derived from Ornithischia.
9. Ornithosuchia is a sister to Pterosauria, also derived from Parasuchia.
10. Revueltosaurus is a sister to the Aetosauria and derived from Ornithosuchia
11. The new Gracilisuchus clade is derived from Revueltosaurus.
12. Poposaurus and the poposaurs are derived from Qianosuchus, Xilosuchus and Arizonasaurus
13. Prestosuchus and the Rauisuchidae is derived from Ticinosuchus.
14. Hesperosuchus and the Crocodylomorpha are derived from Rauisuchidae.

Say it ain’t so!
As you can see, many of these relationships don’t make sense. Sister taxa share very few traits with one another (pterosauria and parasuchia, is the worst such example). Many relationships are upside down with basal taxa, like theropods, derived from derived taxa, like ornithischia. (M. Mortimer also had this problem a few years ago).

What is needed is a large reptile tree in which basal taxa are basal to derived taxa and all sisters look alike (share most traits). In the large reptile tree, sister taxa look quite a bit like one another. The authors should have cast a critical eye on these results, which are very similar to those of Nesbitt (2011), who also recovered many strange bedfellows.

If I had proposed that pterosaurs arose from parasuchians,
the ridicule would be endless and justified, as it is here. Taxon exclusion seems to be the culprit again, along with the tradition of using previously published matrices, even those riddled with Red Flags and strange bedfellows.

In the large reptile tree, Gracilisuchus nests with the SMNS 12591 specimen, Saltopus and Scleromochlus at the base of the Archosauria. Turfanosuchus nests at the base of the Poposauridae, between Decuriasuchus and the base of the Archosauria, not far from Gracilisuchus. Yonghesuchus, nests between Dromicosuchus and Protosuchus.

And, because this is Science, you can repeat these experiments to see for yourself which taxa share more traits — that make sense.

References
Butler et al. 2014. New clade of enigmatic early archosaurs yields insights into early  pseudosuchian phylogeny and the biogeography of the archosaur radiation. BMC Evolutionary Biology  14:128. doi:10.1186/1471-2148-14-128
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

The Proterosuchus holotype – restoration and imagination

Several skulls and skeletons have been attributed to Proterosuchus, the basalmost archosauriform. Unfortunately the holotype is the worst of the lot.

Figure 1. Top and bottom images of Proterosuchus holotype from Ezcurra and Butler 2014. Middle with missing pieces imagined and restored based on other specimens. As you can see, the bones and impressions of bones are very difficult to see. Colorizing the bones, as I do in DGS, is an amazing way to present what those two observed in the fossil.

A recent paper by Ezcurra and Butler 2014 explores the many skulls of Proterosuchus.

From the abstract
“Based upon a comprehensive re-examination of all known specimens, as well as examination of other proterosuchid taxa in collections worldwide, we conclude that the holotype of Proterosuchus fergusi (Fig. 1) is undiagnostic… As a result, we recognize a minimum of four archosauriform species following the Permo-Triassic mass extinction in South Africa. Our results suggest a greater species richness of earliest Triassic archosauriforms than previously appreciated, but that archosauriform morphological disparity remained low and did not expand until the late Early Triassic – early Mid-Triassic.”

This skull, IMHO, cannot be used in phylogenetic analysis, and it hasn’t been used in that way. However, add a few other taxa identified by museum numbers and you’re good to go.

References
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Ezcurra, MD and Butler RJ. 2014. Taxonomy of the proterosuchid archosauriforms (Diapsida: Archosauromorpha) from the earliest Triassic of South Africa, and implications for the early archosauriform radiation. Palaeontology. (advance online publication)
DOI: 10.1111/pala.12130 http://onlinelibrary.wiley.com/doi/10.1111/pala.12130/abstract
Ezcurra MD, Butler RJ and Gower D 2013. ‘Proterosuchia’: the orign and early history of Archosauriformes. Pp. 9–33 in S. J. Nesbitt, J. B. Desojo, R. B. Irmis (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and Their Kin. Geological Society, London, Special Publications 379.
Welman J 1998. The taxonomy of South African proterosuchids (Reptilia, Archosauromorpha). Journal of Vertebrate Paleontology 18:340–347.
Welman J and Flemming  AF 1993. Statistical analysis of the skulls of Triassic proterosuchids (Reptilia, Archosauromorpha) from South Africa. Palaeontologia africana 30:113–123.

wiki/Proterosuchus

 

A closer look at Sikannisuchus huskyi

Earlier we looked at the skull roof of Sikannisuchus. Unfortunately, I ignored those long mandible bits and pieces. These give us more clues to restore the missing parts in lateral view (Fig. 1).

Sikannisuhus huskyi restored on must a view bits and pieces. Nesting with Postosuchus provides clues to the shapes of the missing parts. That’s a nice long skull. Must have been a BIG reptile.

If I made any errors, or the clues point in another direction, let me know.

References
Nicholls EL, Brinkman DB and Wu K-C 1998. A new archosaur from the Upper Triassic
Pardonet Formation of British Columbia. Canadian Journal of Earth Science 35: 1134–1142.

A closer look at Jesairosaurus

Updated November 29, 2015 with a new reconstruction and nesting for Jesairosaurus.

Earlier we looked at Jesairosaurus (Jalil 1991) and the origin of the Drepanosauridae. Today we’ll take a closer look at Jesairosaurus.

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Jesairosaurus was originally considered a procolophonid, then a prolacertiform
Sure it has a long neck, but in phylogenetic analysis, it doesn’t nest with Prolacerta or Marlerisaurus, but after the basal lepidosauriform Palaegama and prior to drepanosaurs and kuehneosaurs. Note the dorsal nares and large orbit. There’s a very tall scapula here, a precursor to the tall stem in drepanosaurs.

Distinct from most lepidosauriforms,
Jesairosaurus has fairly large thecodont teeth. Gastralia appear here for the first and last time in this lineage. The ventral pelvis isn’t fused, but the thyroid fenestra is gone.

Like most lepidosauriforms,
the scapulocoracoid was not fenestrated. And there’s a nice ossified sternum there.

On a side note…
As you know, I’m always attempting to improve the data here. Several months ago I mentioned to a detractor that most prior workers reported  forelimbs present in Sharovipteryx. Only Unwin et al. (2000) thought they were buried in the matrix. My detractor claimed the opposite, that I was the only one to see forelimbs. No word yet on this issue. Still waiting.

Another detractor claimed I had seen soft tissue on a Bavarian museum fossil pterosaur. When I asked which specimen, he refused to provide the number.

In a third case I asked to see a closeup of a pterosaur mandible tip that had been published. I wondered if the sharp tip might be a tooth, as it is in other sharp mandible pterosaurs. The offer was refused with the phrase, “trust us, it’s not there.” I replied “trust” is antithetical to Science. No reply and no closeup yet.

So, is it so hard to provide a museum number? A closeup of a photograph? Or a reply to a note on forelimbs? Should we trust other scientists? Or should we test and confirm or refute? There may be cooperation among other paleontologists. Or maybe they’re all very protective of their data. Evidently I also have a very bad reputation, and that may be the reason for the lack of cooperation. These things happen when paradigms are broken.

References
Jalil N-E 1997. A new prolacertiform diapsid from the Triassic of North Africa and the interrelationships of the Prolacertiformes. Journal of Vertebrate Paleontology 17(3), 506-525.
Unwin DM, Alifanov VR and Benton MJ 2000. Enigmatic small reptiles from the Middle-Late Triassic of Kyrgyzstan. In: Benton M.J., Shishkin M.A. & Unwin D.M. (Eds) The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge U. Press: 177-186.

wiki/Prolacertiformes

 

 

When DNA analyses return untenable results

Sometimes DNA and RNA provide great insight into phylogenetic relationships.

Other times… not so much.

Ultimately molecule analyses have to be supported by morphological studies that enable us to see the gradual accumulation of traits in lineages. If we can’t see those gradual evolutionary changes, then we must assume there are agents in the DNA that are obfuscating relationships, rather than illuminating relationships.

Two cases in point:

Hedges & Poling (1999) argued that Sphenodon was more closely related to archosaurs than to squamates. This would require independent acquisition of a wide range of specialized features and takes no account of the fossil histories of the groups in question, according to Evans (2003).

Wiens et al., (2012) produced a molecule study of extant taxa that rearranged prior squamate trees, nesting Dibamus and gekkos at the base while nesting Anguimorpha and Iguania as derived sister clades. For those who don’t know Dibamus too well, it has no legs and a very odd skull morphology. In the large reptile tree it nests with other legless scincomorphs, with which it shares a long list of character traits.

Unfortunately these DNA studies, like ALL DNA studies, ignore fossil taxa.

But we need them.

On the other side of the coin recent work by Losos on extant anoles in the Carribbean seems to have turned up some interesting and viable results.

Not sure where to draw the line. Be careful out there.

References
Evans SE 2003. At the feet of the dinosaurs: the early history and radiation of lizards. Biological Reviews 78:513–551.
Hedges SB and Poling LL 1999. A molecular phylogeny of reptiles. Science 283, 998–1001.
Wiens JJ, et al. 2012. Resolving the phylogeny of lizards and snakes (Squamata) with extensive sampling of genes and species. Biology Letters. 2012 8, doi: 10.1098/rsbl.2012.0703.