The Phonodus-Bolosaurus-Bashkyroleter connection

This post might be boring.
These are the unpopular, rarely studied plain-looking reptiles that ultimately gave rise to many of the most interesting clades.

Bolosaurids
are rarely studied, rarely included in phylogenetic analyses and little has been published on them. Bolosaurus and Belebey are the classic specimens. Long-legged Eudibamus has been added to this clade by traditional workers (Berman et al. 2000), but the large reptile tree nests it instead with basal diapsids, like long-legged Petrolacosaurus.

The busiest and most difficult corner
of the large reptile tree always seemed to be between Milleretta and Macroleter (Fig. 1).This subset of the tree also includes many previous enigmas here resolved, including  turtles.

Figure 1. A subset of the large reptile tree focusing on the taxa between Milleretta and Lepidosauriformes, perhaps the most difficult corner of the large reptile tree.

Figure 1. A subset of the large reptile tree focusing on the taxa between Milleretta and Lepidosauriformes, perhaps the most difficult corner of the large reptile tree.

Phonodus was originally considered a procolophonid.
(Modesto et al. 2010). Here (Fig. 2) Phonodus nests close to procolophonids, but closer to bolosaurids. As an Early Triassic taxon, Phonodus represents a late surviving member of a Late Pennsylvanian/Earliest Permian radiation that produced Early Permian diadectids and others. Based on its unusual teeth, Phonodus was highly derived.

Figure 1. Phonodus tracing. This turns out to be a basal bolosaurid.

Figure 2. Phonodus tracing. This turns out to be a basal bolosaurid, close to procolophonids. Note the deeply excavated squamosal. The naris was originally overlooked. 

A related taxon
Bashkyroleter (Fig. 3) was originally considered a nyctoleterid parareptile (not a valid clade). Here (Fig. 1) Bashkyroleter is basal to the bolosaur/diadectid/procolophon clade and pareiasaur/turtle clade AND the remainder of the lepidosauromorpha, including the lanthanosuchids proximally. So, it is a key taxon, largely overlooked except for one paper (Müller and Tsuji 2007) on reptile auditory capabilities.

Yes,
this solidification of the large reptile tree involved some topology changes. Science is self correcting. New data brings new insights. One of these new insights involved Bashykyroleter and a previously overlooked connection of the lateral to the naris. (Fig. 2).

Figure 2. Bashkyroleter appears to have a small naris/lacrimal connection.

Figure 3. Bashkyroleter appears to have a small naris/lacrimal connection as shown above. If anyone has a dorsal, occipital  or palatal view of this taxon, please send it along. Another deeply embayed squamosal. 

References
Berman, DS, Reisz RR, Scott D, Henrici AC, Sumida SS and Martens T 2000. Early Permian bipedal reptile. Science 290: 969-972.
Modesto SP, Scott DM, Botha-Brink J and Reisz RR 2010. A new and unusual procolophonid parareptile from the Lower Triassic Katberg Formation of South Africa. Journal of Vertebrate Paleontology 30 (3): 715–723. doi:10.1080/02724631003758003.
Müller J and Tsuji LA 2007. Impedance-Matching Hearing in Paleozoic Reptiles: Evidence of Advanced Sensory Perception at an Early Stage of Amniote Evolution. PLoS ONE 2 (9): e889. doi:10.1371/journal.pone.0000889. PMC 1964539. PMID 17849018

SVP 1 – Quetzalcoatlus and Azhdarchids

This post begins a review of select SVP abstracts from the recent convention.

Andres and Langston (2015 abstract)
limit the number of taxa referred to azhdarchidae (Quetzalcoatlus + Azhdarcho) to Turonian (Early Late Cretaceous, 90 mya) taxa using phylogenetic analysis. By definition and age that includes Zhejiangopterus (81 mya) as earlier work by Andres and Myers (2013) did so as well. I’m glad someone is continuing the work started by Wann Langston (RIP). Although the Andres tree is ripe with problems, this node is not a problem.

Azhdarchids and Obama

Figure 1. Click to enlarge. Here’s the 6 foot 1 inch President of the USA alongside several azhdarchids and their predecessors. Most were knee high. The earliest examples were cuff high. The tallest was twice as tall as our President.

From the abstract
“Over the past 30 years, [the azhdarchidae] has had hundreds of fragmentary specimens referred to it, spanning over 85 million years from the Late Jurassic to the latest Cretaceous. Newly described material of Azhdarcho and Quetzalcoatlus combined with a phylogenetic analysis of referred azhdarchid specimens, allows better resolution of the evolutionary relationships and history of the azhdarchid pterosaurs.”

“The earliest reported occurrences of azhdarchids in the Late Jurassic and Early Cretaceous are of ctenochasmatoids. [not sure which taxa Andres and Langston refer to here]. Despite a tendency to refer most Late Cretaceous pterosaur material to the Azhdarchidae, the clade only dates back to the Turonian. A tapejarid, ornithocheiran, thalassodromine, and the pteranodontids also survive to the early Late Cretaceous. Most of the specimens previously referred to the Azhdarchidae, but now recovered outside of the group, are on the azhdarchid branch as non-azhdarchid neoazhdarchians {again, which taxa?]. These specimens range from the Aptian, when the lineage would have split from the chaoyangopterids at the latest, to the latest Cretaceous, and so comprise the last surviving pterosaurs along with the Azhdarchidae and one Nyctosaurus specimen. The giant and smaller morphs of Quetzalcoatlus are recovered as sister taxa and so are closely related as either a single species or sister species.”

In the large pterosaur tree, there is a continuous lineage in the ancestry of azhdarchid pterosaurs going back to a sister to Huehuecuetzpalli (a basal tritosaur) and Macrocnemus (Middle Triassic tritosaur). Quetzalcoatlus and the azhdarchids were derived from a sister to Zhejiangopterus, Chaoyangopterus, Microtuben, Jidapterus, Sos 2428 (the flightless pterosaur), tiny B St 1911 I 31, CM 11 426, Ardeadactylus (which gave rise to Huanhepterus), Beipiaopterus, tiny and short legged TM 10341 and the SMNS 50164 specimen attributed to Dorygnathus (Fig. 1, Middle Jurassic). Nowhere in this lineage are any ctenochasmatoids, although Huanhepterus has been mistakenly referred to that clade.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen. These specimens demonstrate isometric growth in pterosaurs – which is heretical as these specimens are conveniently overlooked by the data deniers among pterosaur workers. 

This clade of pre-azhdarchids is remarkable
for demonstrating isometry during ontogeny in Zhejiangopterus (Fig. 2) and isometry during phylogeny starting with long-legged and long-necked B St 1911 I 31 (Fig. 3).

Pterodactylus? elegans? BSPG 1911 I 31 (no. 42 in the Wellnhofer 1970 catalog)

Figure 3. Pterodactylus? elegans? BSPG 1911 I 31 (no. 42 in the Wellnhofer 1970 catalog). Note the scale bar and the azhdarchid-like proportions in this tiny Late Jurassic azhdarchid precursor.

Brian Andres is the third of three pterosaur workers to have their cladogram of pterosaur phylogeny published on Wikipedia. Although all three have a similar topology (they all retain “The Pterodactyloidea”) at certain nodes, none have a similar topology in the broad sense. None include fenestrasaurs as outgroup taxa. None include several species (distinct specimens) from single genera and and none include the tiny pterosaurs found in the large pterosaur tree. As we learned earlier, phylogenetic miniaturization marked the genesis of several pterosaur clades, so the tiny pterosaurs are key to understanding phylogenetic relationships. We looked at the tree of Andres and Myers (2013) earlier here.

References
Andres B and Langton W 2015. Morphology and phylogeny of Quetzalcoatlus (Pterosauria: Azhdarchidae) Journal of Vertebrate Paleontology Abstracts 2015. 

Sulcavis – an enantiornithes bird without a sternum

Figure 1. Pre-bird and bird sternae. Note the replacement of the sternum with gastralia in Sulcavis.

Figure 1. Click to enlarge. Pre-bird and bird sternae. Note the replacement of the sternum with gastralia in Sulcavis.

Ever since the advent
of the dual sternae in Velociraptor and kin, and of the single sternum in Archaeopteryx (Fig. 1), most birds had/have an ossified sternum. One exception is the enantiornithine bird, Sulcavis (Fig. 1-4).

Sulcavis geeorum (O’Connor et al. 2013, Early CretaceousBMNH Ph-000805) is a robin-sized enantiornithes with a relatively small skull and, remarkably, no sternum. Teeth with grooved enamel radiating from the tips gave it its name (sulcus = groove). That was seen as the most distinctive feature. A sternum replaced by gastralia was not considered an issue (see below).

Soft tissue
Although the specimen includes some soft tissue, O’Connor et al. report one pubis missing and another present only proximally. The ischium was reported missing. My examination identifies areas were both pubes (green) and ischia (magenta) used to be (Fig. 2).

Figure 1. Sulcavis in situ with GIF animation original tracing from O'Connor et al. in black and white. Colors identify elements originally reported as missing. Pubis (green), ischium (magenta), ilium (cyan).

Figure 2. Sulcavis in situ with GIF animation original tracing from O’Connor et al. in black and white. Colors identify elements originally reported as missing. Pubis (green), ischium (magenta), ilium (cyan). Reconstruction in figure 2. A proximal ischium was mislabeled a sacral rib.

Enantiornithes are like basal birds
except for the following traditional traits listed by O’Connor et al. 2013 :

  1. Pygostyle proximally forked and distally constructed with ventrolateral processes
  2. Furcula Y-shaped and dorsolaterally excavated
  3. Coracoid with convex lateral margin
  4. Proximal humerus rises dorsally and ventrally to centrally on the concave head
  5. Metacarpal 3 longer than mc2
  6. Distal tarsals fused to metatarsals, but metatarsals unfused distally
Figure 2. Sulcavis reconstruction. PILs on foot. Note the lack of a sternum.

Figure 3. Sulcavis reconstruction. PILs on foot. Note the lack of a sternum. The pedal ungual length and curvature indicate an arboreal lifestyle.

Unfortunately, none of theses traits are listed as characters in the large reptile tree, yet Sulcavis nests with Cathayornis sharing the following traits distinct from other birds:

  1. Skull not shorter than cervicals
  2. Posterior quadrate straight
  3. More than 4 premaxillary teeth
  4. Posterior mandible deeper anteriorly
  5. Retroarticular descends
  6. Metatarsals 2-3 aligned with 1
  7. Pedal 2.2 > p2.1

More pertinent taxa would reduce this list.

Figure 3. Sulcavis skull as originally interpreted (above) and traced using the DGS method (middle) to create a reconstruction (below).

Figure 4. Sulcavis skull as originally interpreted (above) and traced using the DGS method (middle) to create a reconstruction (below). Note, several bones here were not originally identified. It looks possible that a substantial mandibular fenestra might have been present.

Due to the contrived problem
of digit identification in birds and bird-like theropods described and falsified here, O’Connor et al. describe the three manual digits as the

  1. alular digit
  2. major digit
  3. minor digit

Such renaming of digits 1-3 is totally unnecessary.

Re: The sternum
O’Connor et al. report, “No direct information regarding the morphology of the sternum is preserved.” That’s because there is no sternum in this taxon (Figs, 1, 2). The gastralia run right up to the coracoids. So, does this taxon appear to demonstrate how the sternum in enatiornithine birds is formed? Yes, by enlarging and fusing the gastralia, not as a new single, complete bone.

Sternae also appear in dromaeosaurs and oviraptors by convergence. Twin sternae in these taxa do not appear to be homologous with the single sternum of birds. A single sternum originates as a small bone, wider than long followed by a long set of gastralia extending to the pubis, distinct from large twin sternae.

References
O’Connor JK, Zhang Y, Chiappe LM, Meng Q, Quanguo L, Di L 2013. A new enantiornithine from the Yixian Formation with the first recognized avian enamel specialization. Journal of Vertebrate Paleontology 33(1):1-12.

Trees of Life: Birds and Pterosaurs

Yale’s Richard Prum recently announced that the Tree of Life of Birds is almost complete. A genomic analysis of 198 species of birds was published in the Oct. 7 edition of the journal Nature. Prum reported, ““In the next five or 10 years, we will have finished the tree of life for birds.” I presume that means fossil taxa will also be included and scored by morphological traits because genes (genomic traits) are not available.

It is not the first time…
Trees of Life for Birds were announced earlier here, here, here and here.

Having been through a similar study, I support all such efforts. AND I will never attempt to add any but a few sample birds to the large reptile tree. Others have better access to specimens and they have a big head start on the process.

Unfortunately,
some workers have ignored the pterosaur tree of life. Recently Mark Witton ignored isometric growth patterns in pterosaurs to agree with Bennett (2013) that the genus Pterodactylus includes tiny short-snouted forms, mid-sized long-snouted forms (including the holotype, of course) and large small-heron-like forms. Witton reports, “Speaking of adulthood, it was also only recently that we’ve obtained a true sense of how large Pterodactylus may have grown. We typically imagine this animal as small bodied – maybe with a 50 cm wingspan – but a newly described skull and lower jaw makes the first unambiguous case for Pterodactylus reaching at least 1 m across the wings (Bennett 2013).”

We looked at Bennett’s paper earlier in a three part series that ended here. The taxon Witton refers to is actually just a wee bit larger than the holotype and is known from a skull, so wingspread can only be guessed. The tiny short-snouted forms are actually derived from the short-snouted scaphognathids as shown here.

The Pterodactylus lineage and mislabeled specimens formerly attributed to this "wastebasket" genus

Figure 1. Click to enlarge. The Pterodactylus lineage and mislabeled specimens formerly attributed to this “wastebasket” genus. Others have split the largest specimens of Pterodactylus from the others without employing a phylogenetic analysis.

You might recall
that one of the largest complete Pterodactylus specimens (Fig. 1) recovered by the large pterosaur tree was mistakenly removed from this genus and lumped with Ardeadactylus, a basal pre-azhdarchid, all without phylogenetic analysis.

Agreeing with Bennett,
Witton deletes some taxa that actually belong to this genus, while accepting others that do not belong, all based on eyeballing specimens without a phylogenetic analysis that includes a large gamut of specimens (that does not delete the tiny forms). Eyeballing taxa is not the way to handle lumping and splitting. Phylogenetic analysis is. We looked at the Pterodactylus wastebasket problem here.

References
Bennett  SC 2012 [2013]. New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift (advance online publication) doi: 10.1007/s12542-012-0159-8
http://link.springer.com/article/10.1007/s12542-012-0159-8

Will the real Minmi please stand up?

Updated July 11, 2021
after hearing about Leahy et al. 2015, who renamed the skull of Minmi, ‘Kunbarrasaurus‘ and provided high resolution data provided below.

Earlier the ankylosaurs, represented by Minmi, (Figs 1, 2) were phylogenetically and heretically separated from their putative Thyreophoran sisters, like Stegosaurus. A phylogenetic analysis nested the former with the basal orinithischian, Scelidosaurus, while nesting the latter with the more derived and much smaller ornithischian, Scutellosaurus. All prior studies presumed Scelidosaurus and Scutellosaurus were sisters in armor. In the large reptile tree the two armored clades of ornithischians developed their defenses by convergence.

Minmi paravertebrai (min-my, Molnar 1960, early Cretaceous, 3m, Fig. 2) ) is one of the most popular dinosaurs and very likely THE most popular ankylosaur. It’s small and Australian. It’s been an illustration, a sculpture, a toy, and a stamp––all in addition to its original role as a fossil (Fig. 1).

When I went searching for Minmi data
I found little consistency in Minmi reconstructions (Fig. 1). Many seem to be based on something other than the original fossil (Fig. 2). Some have a nodosaur-like skull. Some have legs that are too long. Others make up their own armor.

Figure 1. The many ways the Australian ankylosaur, Minmi, has been portrayed. Each one is different.
Figure 1. The many ways the Australian ankylosaur, Minmi, has been portrayed. Each one is different. The illustration in the lower right hand corner appears to most closely resemble the original fossil material.

That’s why
Minmi is shown here (Fig. 2) as a reconstruction, along with its original fossil and tracings. There should be a one-to-one correspondence of elements here. At least that was the intention. The distal tail is unknown and restored here.

Figbure 2. Minmi paravertebra as found, tracings in both dorsal and ventral aspect and reconstruction based on the tracings. The skull is not heavily armored, so provides skull sutures, colorized here from hints provided by Molnar. 

Minmi paravertebra was recovered as the most basal anklylosaur by Thompson et al. 2011. Overall smaller than most ankylosaurs, the skull was larger, the torso shorter and the legs relatively longer than larger, later forms like Ankylosaurus and Euoplocephalus.

Updtated Kunbarrasaurus (formerly Minmi) from Leahy et al. 2015. Colors added here.
Figure data of Kunbarrasaurus (formerly Mnimi) from Leahy et al. 2015, colors added here.

Distinct from the more basal Scelidosaurusthe torso of Minmi was wider than tall. The pubis was a vestige. The limbs were all subequal in length. The ilia rotated laterally so their medial surfaces became dorsal, acting like armor plates. Individual osteoderms were larger. No temporal fenestra appear on the skull as bone infilled all those cavities.

Interesting gut contents
consist of fragments of fibrous or vascular plant tissue, fruiting bodies, spherical seeds, and vesicular tissue (possibly from fern sporangia). The fragments are uniform in size and cut cleanly, indicating oral processing supported by inset teeth probably within cheeks.

References
Haubold H 1990. Ein neuer Dinosaurier (Ornithischia, Thyreophora) aus dem Unteren Jura des nördlichen Mitteleuropa. Revue de Paleobiologie 9(1):149-177. [In German]
Leahey et al. 2015. Cranial osteology of the ankylosaurian dinosaur formerly known as Minmi sp. (Ornithischia: Thyreophora) from the Lower Cretaceous Allaru Mudstone of Richmond, Queensland, Australia. PeerJ 3:e1475; DOI 10.7717/peerj.1475
Molnar RE 1980. An ankylosaur (Ornithischia: Reptilia) from the Lower Cretaceous of southern Queensland. Memoirs of the Queensland Museum 20:65-75
Thompson RS, Parish JC, Maidment SCR and Barret PM 2011. Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora). Journal of Systematic Palaeontology 301-312.

Minmi YouTube video here.

wiki/Minmi

DGS applied to Batrachognathus (anurognathid pterosaur)

Batrachognathus volans (Figs. 1, 2) is a derived anurognathid pterosaur with large binocular eyes and a very short metacarpus. Many of the bones are preserved as bones. Others are preserved as ephemeral impressions. This roadkill fossil (Fig. 2) can be interpreted with clarity using DGS (digital graphic segregation), a falsely maligned method of tracing crushed in situ fossils from photographs in use by many paleontologists.

Figure 3. Batrachognathus volans recontructed. Note the tail is not half again as long as the humerus and not provided with stiffening spines, casting doubt on the identification of the Costa specimen.

Figure 3. Batrachognathus volans recontructed. Note the tail is not half again as long as the humerus and not provided with stiffening spines, casting doubt on the identification of the Costa specimen.

Below
is the in situ specimen, PIN 13, of Batrachognathus. Every five seconds a tracing overlaps the original image. Each color represents a different bone and these colors were transferred to the reconstruction (Fig. 1), assuring accuracy. All the parts fit like parts in a model airplane. All the parts match sister taxa. When left and right parts are present, they match.

Fig 2. GIF animation of Batrachognathus with tracings of bones over the bones and their impressions.

Fig 2. GIF animation of Batrachognathus with tracings of bones over the bones and their impressions. While some bones are easy to discern, others are not and the chaos of this specimen needs segregation and simplification to understand it. In a reconstruction all the parts fit and match left to right.

If DGS can be successfully used here
(Fig. 2) it can be used on other specimens as well. There is no need to avoid this technique if you want to understand a fossil more fully. Yes, you should listen to the worries and fears of the data deniers, then decide for yourself after trying the DGS technique yourself.

References
Bakhurina NN 1988. [On the first rhamphorhynchoid from Asia: Batrachognathus volansRiabinin 1948, from Tatal, western Mongolia]. Abstract of paper in Bulletin of the Moscow Society for the Study of Natural History, Geological Section 59(3): 130 [In Russian].
Rjabinin AN 1948. Remarks on a Flying Reptile from the Jurassic of Kara-Tau. Akademia Nauk, Paleontological Institute, Trudy 15(1): 86-93.

wiki/Batrachognathus

Coelurosauravus wingless predecessor: Palaegama

Coelurosauravus (Fig. 1, Piveteau 1926, Late Permian ~250 mya, ~40 cm in length) was an arboreal lepidosauriform with an odd collection of dermal rods that opened laterally to produce ‘wings’ suitable for display or perhaps gliding. No one previously has produced an ancestor taxon.

Related taxa,
including Mechistotrachelos, Icarosaurus, Kuehneosaurus and Xianglong, produced variations on the Coelurosauravus design, all convergent with the living rib-glider, Draco, an iguanid not related to any of the above taxa.

Coelurosauravus also has wide, temporal crests shared only with Mecistotrachelos. Earlier we discussed the homology of the dermal rods (not ribs) of kuehneosaurs with those of Coelurosauravus.

Figure 1. Palaegama and Coelurosauravus to scale. The latter has dermal rods that frame gliding/display membranes.

Figure 1. Palaegama and Coelurosauravus to scale. The latter has dermal rods that frame gliding/display membranes. No other taxon nests closer to the base of the gliding clade.

The outgroup taxon
in the large reptile tree for these odd arborealists is Palaegama (Fig. 1, Carroll 1975). It preserves no hint of lateral dermal rods and has no temporal crest. It is such an unpopular taxon that it has not yet earned a Wikipedia entry. Among 588 taxa in the large reptile tree, no other is closer to Coelurosauravus and the kuehneosaurs.

As a basal lepidosauriform, 
Palaegama (Late Permian) also nests with the basalmost lepidosaurs, including the basalmost sphenodontid, Megachirella, the basalmost tritosaur Tijubina (Early Cretaceous) and the basalmost pre-squamate, Lacertulus (Late Permian), all ‘lizardy’ taxa of similar morphology.

So
Palaegama is really an important taxon nesting near the bases of several clades. It deserves more press, scrutiny and credit.

Distinct from predecessor taxa,
Palaegama has long strong limbs and long digits, like those of its headless sister, Saurosternon. The Palaegama skull is wide and flattened. Due to these traits it is possible that Palaegama leaped from tree to tree prior to the addition of lateral membranes stiffened with fibers.

Carroll (1975, 1977)
understood that Palaegama might have had a role in the origin of lizards, but those publications preceded computer-assisted phylogenetic analysis and Carroll was not aware of the pre-squamate and tritosaur clades, nor did he make the connection to Coelurosauravus.

A large gamut cladogram is ideal for solving many such problems.

References
Carroll RL 1975. Permo-Triassic ‘ lizards ’ from the Karroo. Palaeontologia africana 18, 71–87.
Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359 -396.

On becoming a reptile: a new list of traits

With the nesting
of Gephyrostegus bohemicus as the last common ancestor to all other reptiles in the large reptile tree, it is worthwhile to list the traits that developed at this node versus the outgroup taxon, Silvanerpeton (Fig. 1). This new list becomes important because Gephyrostegus has no traditional amniote traits.

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 an odd sort of homoplasy at play here.

Of course,
the chief and key trait of amniotes (= reptiles) is the development of the amniotic membrane,surrounding the embryo. The amnion is only the first of several membranes (later including the egg shell) that reduce egg fluid desiccation. This fragile layer of protection permits eggs to be laid on land, but at first only in moist environments.   Klembara et al. (2014) did not recognize Gephyrostegus as a basal amniote because they employed too few amniotes in their matrix. This was probably due to a mindset biased toward thinking about Gephyrostegus as a pre-amniote, in line with all other traditional paleontologists.

A new list of amniote/reptile traits
(Fig. 1) sets Gephyrostegus apart from its more primitive sister, Silvanerpeton. Yes, this is heretical thinking, but results from letting the matrix scores determine all taxon nestings.

Figure 1. Silvanerpeton and Gephyrostegus to the same scale. Each of the two frames takes five seconds. Novel traits are listed. This transition occurred in the early Viséan, over 340 mya. Gephyrostgeus is more robust and athletic with a larger capacity to carry and lay eggs.

Figure 1. Silvanerpeton and Gephyrostegus to the same scale. Each of the two frames takes five seconds. Novel traits are listed. This transition occurred in the early Viséan, over 340 mya. Gephyrostgeus is more robust and athletic with a larger capacity to carry and lay eggs.

Overall
Gephyrostegus bohemicus was more robust and athletic when compared to its phylogenetic predecessor, Silvanerpetion miripedes (Fig. 1). In G. bohemicus the skull, girdles and limbs were all larger relative to the torso. The carpus and tarsus were ossified. The ribs were longer, but fewer in number with a larger lumbar area. Thus the torso was capable of carrying more eggs more rapidly over terrestrial obstacles. The deeper pelvis could expel larger eggs. In summary, the evidence shows that basal reptiles were more fecund and agile than pre-reptiles and those traits were the keys to our success at that node. You can see a video highlighting the origin of humans, including the amniote transition, here.

Large reptile tree traits that appear in the basal amniote, G. bohemicus, 
not present in Silvanerpeton: 

  1. prefrontal (barely) 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

Phylogenetic miniaturization
often occurs at the base of novel tetrapod clades. As a pattern, size reduction continued with the advent of amniotic eggs in reptiles, as we learned earlier here, despite the slightly larger size of Gephyrostegus, which may have been substantially larger than its thirty million years older Viséan sister. Certainly tiny reptiles were present in the Viséan in the form of Westlothiana and Casineri on the archosauromorph branch and later with Thuringothryis and Cephalerpeton on the lepidosauromorph branch. Phylogenetic miniaturization has also been overlooked by the latest studies, which generally disregard ‘size’ as a character trait.

Those who had access to the fossils themselves
(Klembara et al. 2014) were not able to make these conclusions because they did not have, nor did they choose to access online, a large gamut cladogram of amniotes. In this case, and many others, the large reptile tree proves again to solve problems despite lacking firsthand access to pertinent fossils. This is heresy, contra to traditional thinking.

On a side note, 
PterosaurHeresies wishes all those vertebrate paleontologists attending in Dallas, Texas, a grand convention filled with good cheer and camaraderie. Wish I could be there with y’all. We’ll review about two dozen published abstracts following the closing ceremonies.

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 (for 1993), 369–76.
Jaeckel O 1902. Über Gephyrostegus bohemicus n.g. n.sp. Zeitschrift der Deutschen Geologischen Gesellschaft 54:127–132.
Klembara J, Clack J, Milner AR and Ruta M 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:774–792.
Ruta M and Clack, JA 2006 A review of Silvanerpeton miripedes, a stem amniote from the Lower Carboniferous of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences, 97, 31-63.

Gilmoreteius (=Macrocephalosaurus) revisions

Figure 1. Macrocephalosaurus (=Gilmoreteis) in several views. Data from Sulimski 1975.

Figure 1. Macrocephalosaurus (= Gilmoreteis, ZPAL MgR-I jI4) in several views. Data from Sulimski 1975. Note the subtle and not so subtle differences between the detailed tracing and the simplified drawing.

Recent work
here and here on the scleroglossan squamate, Slavoia also introduced new data on its sister,  Macrocephalosaurus (recently renamed Gilmoreteius, Fig. 1, holotype: MCN 1867, referred specimen ZPAL MgR-I jI4, Sulminski 1975) and resulted in a slight revision of scoring on Macrocephalosaurus (Fig. 2).

Figure 2. Subset of the large reptile tree. Gillmoreteius nests within a clade of basal Scleroglossa within the Squamata and Lepidosauria. Two of the tested Slavoia specimens nest as sisters while a third (112) nests with pre-amphisbaenids.

Figure 2. Subset of the large reptile tree. Gillmoreteius nests within a clade of basal Scleroglossa within the Squamata and Lepidosauria. Two of the tested Slavoia specimens nest as sisters while a third (112) nests with pre-amphisbaenids.

According to Sulminski (1975)
‘Macrocephalosauridae differ from all known Sauria (lizards) in having a vorner/pterygoid contact. In many respects the Macrocephalosauridae show more resemblances to the Scincomorpha than to the Iguania, and are tentatively referred to the former. However, the morphology of the dentition and the manner of tooth replacement in the Macrocephalosauridae is of the iguanid type, whereas the heterodont dentition and elongate frontal proportions are scincomorph characters. The supratemporal is fused to the squamosal. The tail is relatively long, probably longer than the body.’

These earlier workers did not access the large reptile tree  (subset in Fig. 2). Sulminski did not note that among squamates, both Sineoamphisbaena and Amphisbaena also develop a vomer/pterygoid contact, but these contacts are not found in closely related sister taxa. Thus, all appear to be by convergence and are not that important. Other lepidosaurs, like SphenodonHomoeosaurus and Macrocnemus also have this contact by convergence.

As others have noted earlier,
Gilmoreteius was a likely plant-eater based on those multi-cusped tiny teeth and large torso.

Note:
In figure 1 all images are from the Sulminski (1975) paper. Sulminski illustrated the skull slightly different in each case, one detailed and one simplified. Of course, sometimes such changes affects scoring. In this case, not so much. Have not run into a paper showing two different illustrations of the same specimen. Which one should we gather data from? Probably the more detailed one in this case.

References
Gimore CW 1943. Fossil lizards of Mongolia. Bulletin of the American Museum of Natural History 81(4):361-384.
Langer MC 1998. Gilmoreteiidae new family and Gilmoreteius new genus (Squamata Scincomorpha): replacement names for Macrocephalosauridae Sulimski, 1975 and Macrocephalosaurus Gilmore, 1943. Comunicacoes do Museu de Ciencias e Tecnologia 11: 13-18.
Mo J-Y, Xu X and Evans SE 2009.
 The evolution of the lepidosaurian lower temporal bar: new perspectives from the Late Cretaceous of South China. Proceedings of the Royal Society doi: 10.1098/rspb.2009.0030 online paper
Sulimski A 1975. Macrocephalosauridae and Polyglyphanoodontidae (Sauria) from the Late Cretaceous of Mongolia. Palaeontolgia Polonica 33:25-102. online here.

Four years of Pterosaur Heresies

I overlooked the anniversary
On July 12, 2011 the Pterosaur Heresies was first published online to support the website ReptileEvolution.com with news and reviews. At that time the large reptile tree included 238 taxa. Four years and 1440 posts later that number has grown to 586 taxa with greater resolution between sisters due to their greater number and reduced distance.

The tree topology
from back then is largely the same now with a diphyletic Reptilia arising from gephyrostegids, but now Gephyrostegus bohemicus nests as the basalmost reptile, the one that laid the first amniotic eggs and the last common ancestor of all known reptiles. It has no traditional amniote skeletal traits.

There were several other accomplishments
along the way, most gained by having a large gamut cladogram of reptile interrelationships to check smaller, more focused, more traditional published reports. Several myths were busted (but most of those will never die among traditional paleontologists). Several enigmas were resolved. Several mistakes were corrected, both in here and out there.

Thank you for your interest in this site.
While most of the enigmas and mysteries have been verifiably resolved, there are always new ones that pop up occasionally.