Euposaurus: basal squamate/basal iguanid

Among the many lizards found in Late Jurassic  (155 mya) European lithographic limestones that have no living counterparts, there is one, Euposaurus (Fig. 1) that is basal to all members of the clade Iguania, which includes Iguana, the iguana; Phyronsoma, the horned lizard; Trioceros, the chameleon; and Draco, the rib-gliding lizard.

Euposaurus cirrensis, a basal squamate and basal  member of the clade Iguania.

Figure 1. Euposaurus cirrensis, (not the generic holotype) a basal squamate and basal member of the clade Iguania. The large orbit and less than fused ankles are primitive, not juvenile, traits.

Euposaurus cirinensis ( Lortet 1892, MHNL 15681, Late Jurassic, Kimmeridgian, 155 mya, 3.5cm snout vent length) nests as the basalmost member of the Iguania (Cocude-Michel 1963) and is a basal squamate. Evans (1994) assigned it to Squamata incerta sedis. The large skull and large orbit might seem to be juvenile traits, but all sister taxa share these traits. Liushusaurus and Calanguban are sister taxa at the base of the Scleroglossa.

Figure 2. Euposaurus insitu.

Figure 2. Euposaurus insitu.

Evans 1994 reexamined the three specimens attributed to Euposaurus and reported they “belong to different genera. Euposaurus thiolleri, the type species, is a juvenile pleurodont lepidosaur which is probably, but not certainly, a lizard. It has no characters which suggest that it is an iguanian and is here designated Lepidosauria incertae sedis. The remaining two specimens have an acrodont dentition and are juvenile rhynchocephalians. One is referable to Homoeosaurus; the other appears to belong to the group currently represented by Sapheosaurus, Kallimodon, Piocormus (aka Sapheosaurus) and Leptosaurus although the latter two may not be valid genera.”

Figure 2. Basal squamates. Here Euposaurus is a basal Iguania. Liushusaurus and Calanguban are basal Scleroglossa. Scandensia is presently their last common ancestor.

Figure 3. Basal squamates. Here Euposaurus is a basal Iguania. Liushusaurus and Calanguban are basal Scleroglossa. Scandensia is presently their last common ancestor.

Derived from ScandensiaEuposaurus is larger overall and has a larger skull with a robust palate. The tail is longer and more robust. The limbs are more robust. Scandensia is much smaller than its predecessor, the mis-named “Langobardisaurus” rossii, so the origin of lepidosaurs is one more case of miniaturization, as in mammals, birds and reptiles.

Figure 4. Langobardisaurus? rossii compared to tiny Scandensia.

Figure 4. Langobardisaurus? rossii compared to tiny Scandensia.

References
Cocude-Michel M 1963. Les rhynchocephaJes et les sauriens de calcaires
lithographiques (Jurassique supérieur) d’Europe occidentale. Nouvelles Archives
du Muséum d’Histoire Naturelle de Lyon 7: 1-187.
Evans SE 1994. A re-evaluation of the Late Jurassic (Kimmeridgian) reptile Euposaurus (Reptilia: Lepidosauria) from Cerin, France. Geobios 27(5):621-631.
Lortet M 1892. Les reptiles fossiles du Bassin du Rhone. Archives du Musee de
Histoire Naturelle, Lyon 5: 1-139.

image from planet-terre

Euposaurus corninesss 

Musée des confluences, Lyon / Pierre Thomas 

http://planet-terre.ens-lyon.fr/planetterre/objets/Images/Img307/307-rhynchocephales-Cerin-06.jpg

Drepanosaur skull: Pritchard and Nesbitt 2014 JVP abstracts

Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

Figure 1. Megalancosaurus including the palate, the only palate ever figured for a drepanosaur. This is not the specimen described by Pritchard and Nesbitt 2014.

Pritchard and Nesbitt (2014) present new skull data based on a 3D drepanosaur skull (posterior elements only) from the Triassic of Arizona. Comments follow.

From the abstract:
“Drepanosaurs are an enigmatic clade of Late Triassic diapsids from Europe and North
America with superficially chameleon-like bauplans. The phylogenetic position of the
group among diapsids is contentious. (1) Most hypotheses suggest that drepanosaurs are
basal archosauromorphs closely related to ‘protorosaurs’ (e.g., Protorosaurus,
Tanystropheus). (2) Other phylogenies place drepanosaurs as non-saurian diapsids,
suggesting a substantially older origin for the lineage. Clarifying the phylogenetic
position of drepanosaurs is important to understanding the degree of taxonomic
diversification among diapsids prior to the Permo-Triassic Extinction (PTE).
The poor quality of the drepanosaur fossil record has hampered an understanding of
their position. (3) Nearly all drepanosaur skeletal material is badly distorted (4), and all
described skulls are crushed such that phylogenetically important characters are
obscured. (5) A new drepanosaur specimen from the Late Triassic Coelophysis Quarry of
New Mexico includes a partial, three-dimensionally preserved skull. The postorbital
region of the skull, atlas-axis complex, and anterior cervical vertebrae are preserved in
near-articulation. (6) 3D reconstruction of micro computed tomography (CT) data allows the first detailed description of most drepanosaur skull bones. Many are surprisingly
plesiomorphic (e.g., squamosal with massive descending process, quadrate lacking
posterior concavity, occipital condyle with notochordal pit), sharing more in common
with non-saurian diapsids than early archosauromorphs. (7).

A phylogenetic analysis of 300 characters and 40 early diapsids supports the
hypothesis that drepanosaurs fall outside of Sauria. (8). This suggests a very long ghost
lineage (~35 million years), extending well into the Late Permian. The results of this
phylogeny suggest that both drepanosaurs and a number of early saurian lineages must 
have originated by the Late Permian. Although the fossil record suggests an enormous
morphological diversification among saurians following the PTE, a great deal of
taxonomic diversification among diapsids must also have occurred prior to the extinction.”

(1) not at all contentious. Drepanosaurs are derived from Jesairosaurus in the Tritosauria. This has been known for several years.

(2) Protorosaurus and Tanystropheus are not related to one another. This has been known for many years.

(3) Repeating a false allegation.

(4) crushed flat, but not otherwise distorted (see Fig. 2).

(5) Not so, IMHO.  Use DGS to retrieve data. Works every time.

(6) good news, but the key traits are found in the preorbital region. The big question is: did they have an antorbital fenestra? I see one on several specimens.

(7) These traits were first identified in Megalancosaurus. The occiput data is news. Non-saurian diapsids could include sauropterygians, ichthyosaurians, rib gliders and basal younginiforms according to traditional trees, which are outdated at best. Saurians include lepidosaurs and archosaurs. In this regard, drepanosaurs are saurians, tritosaur lepidosaurs.

(8) 40 is way too few taxa if you don’t know where drepanosaurs nest, especially if Jesairosaurus and Huehuecuetzpalli are excluded (I haven’t seen the inclusion set). Using 420 taxa drepanosaurs firmly nest within the Tritosauria and Lepidosauria, thus within the traditional definition of Sauria, which is a junior synonym of Amniota/Reptilia. Actually there is no long ghost lineage. Drepanosaurs originated in the Triassic following Jesairosaurus in the Early to Middle Triassic.

This is my take (Figs. 1, 2) on the skull of the drepanosaur Megalancosaurus. Note the occiput is not exposed in this 2D crushed specimen. It’s a fragile construction with a large naris, an antorbital fenestra, large orbit, diapsid temporal architecture (like that of a pterosaur) and a Y-shaped hyoid.

Interpretation of figure 6, the skull of Megalancosaurus.

Figure 7. Interpretation of figure 6, the skull of Megalancosaurus. Struts of bone surround antorbital fenestra here.

References
Pritchard A and Nesbiitt S 2014. The cranial morphology of drepanosaurs and the PermoTriassic diversification of diapsid reptiles. JVP abstracts 2014.

Squamate tree of life: Gearty and Gauthier 2014 JVP abstracts

Updated July 7, 2020
the LRT moves Meyasaurus, Indrasaurus and Hoyalacerta to the base of the Yabeinosaurus + Sakurasaurus clade within the Scleroglossa and Squamata.

Resolving the relationships of the Squamate tree of life.
An assessment of new approaches and problems.

In their JVP 2014 abstract Gearty and Gauthier (2014) mix morphological and molecule data on Squamates and this becomes ‘detrimental’ (their words, not mine) to results. So actually they do not resolve relationships. It’s just a topic header. And there’s no mention of the third squamate clade, the Tritosauria, which probably messes up their results, as earlier reported by Conrad (2008, see below) .

From the abstract:
“Since the division of The Deep Scaly Project into separate morphological and molecular teams, a truly integrated project of wide scope has not been attempted. Much more can be done to understand how the members of Squamata are related to one another through an approach that combines the importance of both morphological and molecular evolution. Here we have developed a novel three-step methodological approach to squamate phylogenetics that incorporates the newest phylogeny-creating techniques and data from previous morphological and genetic analyses. First, we analyze a large squamate morphological dataset using Lewis’s Mkv model under both a Bayesian and maximum likelihood framework. Second, we incorporate a previously constructed squamate DNA dataset and analyze the combined data within a ‘total evidence’ framework. Finally, we adopt a methodology that treats genes, rather than nucleotides, as the character of interest. We find that the separate analyses of the morphological and molecular datasets, even under Bayesian and maximum likelihood frameworks, still result in drastically different relationships between higher-order clades within Squamata.

Additionally, we find that the combination of these two datasets results in a phylogeny with limited support for either topology, although it definitively leans in the direction of the molecular results.

Finally, by reducing the molecular dataset to gene characters, we find significantly lower support for the higher-order relationships that are strongly supported in previous analyses. By combining these data with our morphological dataset, we discover that we have inversed the effect of the power in numbers problem.

We conclude that combining datasets, although possibly detrimental to results, should be treated as a source of understanding how the datasets may differ and how they may reflect different evolutionary histories.”

So, ladies and gentlemen… 
Take a lesson from Gearty and Gauthier and don’t mix genetics with morphology. I would trust genetics to find my long lost brother, or a criminal, but not to find any long lost clades. As we learned earlier here, not only can genes be homoplastic, but wrong interpretations can skew results.

From Conrad 2008
Most known squamates fit within one of the seven major radiations (Iguania, Gekkota, Lacertoidea, Scincoidea, Anguimorpha, Amphisbaenia, and Serpentes), but some fossil taxa defy placement within any of these groups. Recent descriptive and phylogenetic work suggests that some fossil taxa fall outside of the crown-group represented by this framework. Among these are Huehuecuetzpalli mixtecus (Reynoso, 1998), Hoyalacerta sanzi (Evans and Barbadillo, 1999; Evans et al., 2004), Scandensia ciervensis, ‘bavarisaurids’, and ‘ardeosaurids‘.

All of the misfits listed above, but the ardeosaurids, are tritosaurs. The ardeosaurids are proto-snakes. So this clade has been long recognized, just not identified in the literature. Yet.

Recent work
I’ve done some recent work with basal squamates from the Early Cretaceaous lithographic limestones and I’ll present a few of them here soon. For now, the tree topology here remains pretty darn close (but new taxa are being added, now up to 425).

References
Gearty W and Gauthier J 2014. Resolving the relationships of the squamate tree of life. An assessment of new approaches and problems. JVP abstracts 2014.

Turtles: still not related to Eunotosaurus, a turtle-mimic

Bever et al. (2014) report that Eunotosaurus (Fig. 1) is a turtle ancestor. This has been falsified in phylogenetic analysis (and see below). We learned earlier that Eunotosaurus is a turtle-mimic that actually nests with Acleisotorhinus, leaving no known descendants. Phylogenetic turtle ancestors include Stephanospondylus (Fig. 2), which does not have temporal fenestration. However, bolosaurids (Bolosaurus and Belebey), taxa known only from skulls, are also close to the base of this lineage and do have lateral temporal fenestra.

Eunotosaurus and its sister taxa, Acleistorhinus and Milleretta RC14.

Figure 1. Eunotosaurus and its sister taxa, Acleistorhinus and Milleretta RC14.

From the Bever et al. abstract: “The reptile skull is an increasingly utilized model for understanding the evolution and development of vertebrate adaptation. Turtles are an important yet enigmatic piece of this puzzle. The earliest uncontroversial stem turtles exhibit a fully anapsid skull with an adductor chamber concealed by bone. If this lack of fenestration reflects conservation of the ancestral condition, then turtles are an extant remnant of an early reptile radiation that excludes the other living forms. If turtles are nested within crown Diapsida, then their anapsid skull is a secondary configuration built on a diapsid structural plan. No direct paleontological evidence yet exists for this reversal, a situation that epitomizes a general lack of consilience between the fossil record and the molecular signature of living taxa and one that obfuscates attempts to synthesize broad evolutionary patterns across Reptilia.

“Eunotosaurus africanus is a 260 Ma fossil reptile whose status as an early stem turtle continues to be strengthened by new cranial and postcranial synapomorphies. Here we use computed tomography (CT) to study the temporal region of Eunotosaurus and to formulate a model for the origin of the anapsid and diapsid skulls of modern amniotes. Expression of a lower temporal fenestra (LTF) supports the hypothesis that the closed cheek of modern turtles is secondary (1). The ventrally unbounded nature of the LTF places Eunotosaurus at odds with parareptiles (2), but also with pandiapsids where an unbounded LTF is known only in conjunction with the more conservative upper temporal fenestra (UTF) (3). The region housing the diapsid UTF is overlain by an elongate supratemporal in Eunotosaurus. In contrast to the plesiomorphic condition, digitally removing the supratemporal reveals a moderate-sized opening circumscribed by the same elements that define the UTF (4). Additional evidence that this covering is secondary is drawn from the observation that in Eunotosaurus the supratemporal overlaps the postorbital, whereas plesiomorphically these two elements are abutting or the postorbital overlaps the supratemporal. We propose (5) Eunotosaurus captures an early step in the evolution of the anapsid turtle skull in which the UTF was secondarily covered by the supratemporal before being obliterated through expansion of neighboring dermal elements (6). The recognition of such a critical transitional form facilitates the articulation of meaningful transformational and functional models that can be tested with future paleontological discoveries and rapidly emerging developmental data.”

1). Pure speculation when done without phylogenetic analysis.

2). The post-crania of Eunotosaurus is clearly derived, so the skull is also, reduced from the ‘synapsid’ grade skull found in the following (non-synapsid) millerettids: Acleistorhinus, Feeserpeton, Australothyris, Oedaleops, Eothyris, Ennatosaurus, Casea and Cotylorhynchus, taxa closer to Eunotosaurus than Eunotosaurus is to turtles.

3). Like Owenetta and basal lepidosauriforms like Paliguana, Gephyrostegus and the rib-gliders, like Icarosaurus, all clearly distinct from turtles.

4). The same could be said of any of the taxa in (2).

5). “Propose” is another word for “speculate without evidence.” For this idea to have weight, they should “show” or “demonstrate,” but they cannot do this phylogenetically if they include bolosaurids and Stephanospondylus.

6). Except in basal turtles the supratemporal is a long bone rimming the posterior cranium, as in related pareiasaurs, bolosaurids and Stephanospondylus.

Figure 8. Click to enlarge. Stephanospondylus based on parts found in Stappenbeck 1905. Figure 8. Click to enlarge. Stephanospondylus based on parts found in Stappenbeck 1905. Several elements are re-identified here. Note the large costal plates on the ribs, as in Odontochelys. The pubis apparently connected to a ventral plastron, not preserved. The interclavicle was likely incorporated into the plastron.

Figure 2. Click to enlarge. Stephanospondylus based on parts found in Stappenbeck 1905. Several elements are re-identified here. Note the large costal plates on the ribs, as in Odontochelys. The pubis apparently connected to a ventral plastron, not preserved. The interclavicle was likely incorporated into the plastron.

Turtles are so firmly nested in their present tree topology that you can remove (as I did) Stephanospondylus, all four pareiasaurs, and both bolosaurids and the tree topology does not change. I even deleted the Macroleter clade. Turtles still don’t nest with Eunotosaurus. This has been known online for the last three years.

References
Bever GS, Lyson T and Bhullar B-A 2014. Fossil evidence for a diapsid origin of the anapsid turtle skull. SVP 2014 Abstracts pg. 91

New smallest Pteranodon: Bennett 2014 JVP abstract

Figure 1. Pteranodon ingens. Full size and little Ptweety the baby Pteranodon, not curated.

Figure 1. Pteranodon ingens. Full size and little Ptweety the baby Pteranodon, not curated. Alongside in black is a hypothetical hatchling half the size of Ptweety. With a 1.5m wingspan, Ptweety is still the smallest, compared to Bennett’s 1.76 m wingspan. The Bennett Pteranodon is not shown.

I was hoping a curated specimen would follow Ptweety, the baby Pteranodon (Fig. 1). It was just a matter of time. Here it is in the 2014 JVP abstracts.

From the Bennett abstract:
“An earlier study of all available specimens of the pterosaur Pteranodon from the
Smoky Hill Chalk Member of the Niobrara Formation found a bimodal size distribution. The small size class with estimated wingspans in life of ~3.1-4.8 m was twice as abundant as the large, with wingspans of ~4.8-6.7 m, and immature specimens formed ~15% of each class suggesting that they cannot be age classes. The bimodal distribution was interpreted as evidence of sexual dimorphism and the absence of specimens smaller than ~3 m wingspan was interpreted as evidence of bird-like parental care during rapid growth to adult size before flying and feeding independently. A new immature specimen of Pteranodon with an estimated wingspan of only 1.76 m demonstrates that juveniles were capable of flying and feeding independently, contradicting the interpretation of parental care during rapid growth. Instead Pteranodon apparently was precocial, flying and feeding independently during several years of growth to adult size as previously observed in Rhamphorhynchus, Pterodactylus, and Pterodaustro. Therefore, the absence of Pteranodon juveniles and a similar absence of Nyctosaurus juveniles from the Smoky Hill Chalk indicates those taxa had multi-niche ontogenies, occupying distinct niches in different locations and environments at different stages of their life history. Thus, the Smoky Hill Chalk represents a pelagic feeding environment of Pteranodon and Nyctosaurus adults whereas hatchlings and juveniles presumably fed on smaller prey in lacustrine, riverine, estuarine, or coastal environments. The pterosaur records of most other Lagerstätten are consistent with multi-niche ontogeny being the norm in pterosaurs. For example, the record of Azhdarcho in the Bissekty Formation consists of hatchlings and adults and represents a breeding ground, that of the Solnhofen Limestone consists primarily of hatchlings and juveniles and represents a nursery environment of juveniles in sheltered lagoons near breeding grounds whereas those of the Romualdo and Cambridge Greensand Formations consist of adults and represent coastal feeding environments of adults. One exception seems to be the record of Pterodaustro in the Lagarcito Formation, which consists of eggs, hatchlings, juveniles, and adults in a single location and environment; however, that may reflect a special environment required to effectively utilize the filter-feeding specializations of the taxon.”

Bennett has been the target of many Pterosaur Heresies blogposts.
And for good reason: (no gender classes, this represent several species evolving from small, small-crest forms to several clades of large, large-crest forms, etc. etc. etc.).

Here Bennett is right on the money
when he agrees to different niches for juvenile and adult pterosaurs, which we discussed earlier here, due to the rarity of juvenile pterosaurs in the fossil record, a topic in which Bennett takes the opposite stance.

Not mentioned in the Bennett abstract
is the fusion of the extensor tendon process to manual 4.1, which occurs in all Pteranodon specimens (even Ptweety) and no Nyctosaurus specimens except the crested ones. The same goes for scapula and coracoid fusion (fused in Pteranodon, not in Nyctosaurus). I wonder what the data is on his new juvenile Pteranodon?

Figure 2. Ptweety the juvenile Pteranodon. Note the presence of a fused extensor tendon process, a long rostrum and small orbit in this isometrically identical juvenile pterosaur.

Figure 2. Ptweety the juvenile Pteranodon. Note the presence of a fused extensor tendon process, a long rostrum and small orbit in this isometrically identical juvenile pterosaur.

The presence of hatchling Azhdarcho specimens in a breeding ground comes as something of a surprise. Good news! The literature (Averianov 2010) only refers to a juvenile/immature specimen represented by a notarium (4cm long, compared to a 6.5 notarium for an unrelated adult mid-size Pteranodon adult.)

Bennett does not mention the growth series in Tapejara and Zhejiangopterus. The abstract was probably written before the Caiuajara nesting site. Pterodaustro embryos and hatchlings are well known (Chiappe et al. 2004, Chinsamy et al. 2008, Codorniú and Chiappe 2004). The various growth series described by Bennett (1995, 1996) actually represent individual species if not genera. This he would discover by phylogenetic analysis.

Ptweety will never be published because it was extracted and prepared without documentation and the last I heard it was a standing mount at an online retail store. Good to hear that another juvie Pteranodon is out there and hopefully will soon be published.

On a side note: 
The blog post on the evolution of frogs is getting an unusually large number of hits. Not sure why. Let me know if there is anything else you want to learn more about.

References
Averianov AO 2010. The osteology of Azhdarcho lancicollis Nessov 1984 (Pterosauria, Azhdarchidae) from the Late Cretaceous of Uzbekistan. Proceedings of the Zoological Institute RAS. 314(3):264–317.
Averianov AO 2013. 
Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae). Paleontological Journal 47 (2): 203-209. DOI: 10.1134/S0031030113020020
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen limestone of Germany: year classes of a single large species. Journal of Paleontology 69, 569–580.
Bennett SC 1996. Year-classes of pterosaurs from the Solnhofen limestones of Germany: taxonomic and systematic implications. Journal of Vertebrate Paleontology 16:432–444.
Bennett, SC 2014. New smallest specimen of the pterosaur Pteranodon and multi-niche ontogeny in pterosaurs. Journal of Vertebrate Paleontology abstracts, Berlin Conference 2014.
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Chiappe LM, Codorniú L, Grellet-Tinner G and Rivarola D. 2004. Argentinian unhatched pterosaur fossil. Nature, 432: 571.
Codorniú L and Chiappe LM 2004. Early juvenile pterosaurs (Pterodactyloidea: Pterodaustro guinazui) from the Lower Cretaceous of central Argentina. Canadian Journal of Earth Science 41, 9–18. (doi:10.1139/e03-080)

How the pterosaur got its wings, according to Tokita 2014

When a paper with the title, “how the pterosaur got its wings”
(Tokita 2014, Harvard U.) shows up, you know I’ll be interested. This one reviews the literature on morphology and heads straight into the world of molecules, a first for a fossil taxon last seen 65 mya. I’ve been chided for speculation, but here Tokita has a golden ticket.

As usual the author starts off with analogous birds descending from theropods and bats descending from unknown ‘small arboreal mammals.’ See the real story here.

When the Tokita gets down to pterosaurs, he reports the following, “Although the phylogenetic position of pterosaurs within reptiles still remains controversial (Unwin, 2006), a close relationship with a lineage of Archosauria such as the Late Triassic Scleromochlus, a member of the clade that includes birds and dinosaurs (Ornithodira), has been  suggested (Hone & Benton, 2007; Witton, 2013).” As you’ll recall, these references are among the worst sources out there for pterosaur ancestry. No references were made to the one and only validated ancestry of pterosaurs among the tritosaur –  fenestrasaurs, the one that keeps getting ignored.

See, folks, publication is not all its cracked up to be.

Tokita repeats the traditional propaganda, “However, as for bats, transitional fossils with intermediate anatomical features linking pterosaurs with ancestral reptiles remain to be found. The scenario that pterosaurs evolved from an arboreal tetrapod with gliding (parachuting) ability was inferred from data on limb functional morphology and has been widely accepted (Bennett, 1997, 2008; Unwin, 2006; Witton, 2013).”

As occasional readers will realize, nothing could be further from the truth.

Tokita wishes to “speculate about the potential developmental basis of pterosaur wing evolution given recent advances in the developmental biology of other flying vertebrates as well as of non-volant vertebrates” or “infer potential cellular and molecular mechanisms underlying phenotypic evolution in extinct vertebrates.”

Repeating the sins of Bennett (2003, 2008) without a critical eye
Tokita (2014, figs. 2, 3) colorizes the oddly reconstructed forelimb of Anhanguera from Bennett (2003, 2008) in which Bennett runs the tendons of extension and flexion across the anterior and posterior wrist when in every other tetrapod these cross the dorsal and palmar sides while rotating the free fingers palmar side anteriorly, which is not found in any pterosaur fossil. Bennett also removes the pteroid from the deltopectoral tendon when it is ideally placed to receive it. And totally out of his imagination, Bennett switches flexors with extensors to fold the wing finger. This is the topsy-turvy world we live in guyz! I’d cry if I was five years old again. The side-by-side illustrations of bats and birds that Tokita includes are very instructive in this matter, but the question of the many dissimilarities with pterosaurs (as Bennett reconstructs them) was never raised.

Compare all five fingers, not just the three easy ones.
Tokita compares the first three fingers to putative ancestors among the Archosauriformes. Euparkeria, Scleromochlus and Lagosuchus, completely oblivious to the fact that in these three taxa finger four is a vestige if present at all.

Tokita mistakenly refers to the pteroid bone
as unique to pterosaurs, ignoring the literature (Peters 2002, 2009) that reports it in Cosesaurus and for that matter all basal lepidosaurs as the pteroid and preaxial carpal are simply migrated centralia (Peters 2002, 2009).

Tokita repeats the propaganda
without evidence that the brachiopatagium stretched to the anterior surface of the ankle. Of course this ignores Zittel (1882) as Elgin, Hone and Frey (2011) did earlier.

Tokita reports, “The first finger of bats is inconspicuous, like the anterior three fingers of pterosaurs.” Few scientists think so. The thumb is not a vestige, it’s just not gigantic. Maybe the term, ‘inconspicuous,’ is just a poor choice of words.

Molecules arise
Then Tokita finishes that chapter with a report on bat and bird wing muscles and the elongation of digit 4. At this point, Tokita gets into the cellular and molecular mechanisms underlying digit identify and I’m lost. But so is Tokita. His figure 4 orients the first three digits of a hypothetical early stage pterosaur embryo anteriorly, rather than parallel to the rest. This busts both the Peters and Bennett pterosaur finger orientation hypotheses and goes off in a different direction.

Then he moves to the pectoral girdle.
Tokia reports, that pterosaurs retained the architectural pattern found in non-avian tetrapods, including lizard, crocodiles and mammals. Actually pterosaurs converge a great deal with avians. So again, very topsy-turvy here. Not sure he ever put two 3d skeletons side by side, because birds and pterosaur pectoral girdles are extremely similar. Rather he states “in pterosaurs…architectural pattern was similar to those in primitive tetrapods rather than those in birds.” 

Hmmm. So all the textbooks on convergence in vertebrate flight are wrong?

I don’t think Tokita understands
that the clavicles wrapped posteriorly around the sternum, unlike any other reptiles other than fenestrasaurs. The terms “clavicle” or “sternal complex” do no show up with regard to pterosaurs in his paper. He also doesn’t understand the the pterosaur coracoids were ventrally locked in place, like bird coracoids, unlike basal amniote coracoids, that ride their medial slot. And he didn’t not that the scapulae in pterosaurs were strap-like, as in birds, not as in basal amniotes.

Another bungle:
Tokita reports, “At the later origin of the Pterodactyloidea, a drastic change occurred in the metacarpals, which changed from being the shortest and least variable in length of the major wing elements in non-pterodactyloids to being the longest and most variable in length (Witton, 2013; Andres et al., 2014).” Actually this is never true. Manual 4.1 is always as long or longer than metacarpal 4. Tokita has no clue that the origin of longer metacarpals occurred in the hatchlings of the smallest of the pterodactyloids at the base of each of the four pterodactyloid-grade clades.

Let us also remember that at least two referees and a few editors approved this.

References
Bennett SC 2003. Morphological evolution of the pectoral girdle of pterosaurs: myology and function. In Evolution and Palaeobiology of Pterosaurs, Geological Society Special Publications 217 (eds E. Buffetaut and J.-M. Mazin), pp. 191–215. Geological Society of London, London.
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
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Unwin DM 2005. The Pterosaurs: From Deep Time. Pi Press, New York.
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Zittel KA 1882. Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Palaeontographica 29: 7-80.

Pterosaur tails tell tales… Unwin et al. 2014 JVP abstract

Unwin et al. (2014)
describe an increasing number of tail vertebrae in a purported ontogenetic series (hatchling to juvenile to adult in a series of purported Darwinopterus specimens.) Although this is unheard of elsewhere among vertebrates, Unwin et al. link this trait to the origin of pterodactyloid-grade pterosaurs. And it should be mentioned that Unwin et al. are the only workers who nest darwinopterids basal to pterodactyloids. Andres nests anurognathids there. Kellner nests Rhamphorhynchus there. I nest tiny dorygnathids and scaphognathids there by convergence (e.g. Fig. 1) four times.

From the Unwin et al. 2104 abstract:
“The evolution of pterodactyloids from basal pterosaurs in the Early-Middle Jurassic involved a complex series of anatomical transformations that affected the entire skeleton. Until recently, almost nothing was known of this major evolutionary transition that culminated in the Pterodactyloidea, a morphologically diverse and ecologically important clade that dominated the aerial environment throughout the mid-late Mesozoic. The discovery of Darwinopterus, a transitional form from the early Late Jurassic of China, provided the first insights into the sequence of events that gave rise to the pterodactyloid bauplan and hinted at an important role for modularity, but was largely silent regarding the anatomical transformations themselves, or the evolutionary mechanism(s) that underlay them. A series of recent finds allowed us to construct a complete postnatal growth sequence for Darwinopterus. By comparing this sequence with those for Rhamphorhynchus and Pterodactylus, pterosaurs that phylogenetically bracket Darwinopterus, it is possible to map key anatomical transformations such as the evolution of the elongate, complex tail of basal pterosaurs into the short, simple tail of pterodactyloids. In Darwinopterus hatchlings the tail is shorter than the dorsal-sacral series (DSV) and consists of around 18 simple vertebral ossifications. The tail is longer (1-2 x DSV) in juveniles and has a normal complement of about 30 caudals, but only reaches its full length (2-3 x DSV) and complexity in adults. Basal pterosaurs largely conform to this pattern, although some species, including Rhamphorhynchus, have longer tails with up to 40 caudals. Generally, the tail of adult pterodactyloids, including Pterodactylus, resembles that of Darwinopterus hatchlings (≤18 ossified vertebrae; tail ≤0.7 x DSV; vertebrae simple, blocky), but occasionally develops a little further (e.g. in Pterodaustro) corresponding to the condition seen in early juveniles of Darwinopterus and paralleling the developmental pattern observed in long-tailed pterosaurs. The short tail of adult pterodactyloids, and anurognathids, basal pterosaurs that also have relatively short tails, appears to be neotenic, resulting from a sharp decrease in growth rate compared to the rest of the skeleton. This mechanism, heterochrony acting upon a distinct anatomical module to effect a large-scale morphological transformation, can be applied to other modules to generate the derived features (e.g. elongate neck and metacarpus, reduced fifth toe) that typify the pterodactyloid bauplan.”

Problem #1
Among professional pterosaur workers, only Unwin et al. nest Darwinopterus as the stem pterodactyloid. No one else does. Andres nests anurognathids with pterodactyloids. Kellner nests Rhamphorhynchus with pterodactyloids. Readers of this blog and reptile evolution.com know that when you add the sparrow- to hummingbird-sized Solnhofen pterosaurs, you get four clades of pterodactyloid-grade pterosaurs.

Figure 1. Scaphognathians to scale. Click to enlarge.

Figure 1. Scaphognathians to scale. Click to enlarge.

Problem #2
Are the specimens truly juvenile Darwinopterus? Or do they represent smaller genera or species, perhaps closely related, or not? Currently no two Darwinopterus specimens are conspecific. No two are identical. See them here. By comparing purported Rhamphorhynchus and Pterodactylus juveniles to putative adults I’m afraid Unwin et al. are playing with a pack of Jokers. Those smaller specimens are distinct species and genera, as recovered in the large pterosaur tree. Everyone should know by now that pterosaur juvenile pterosaurs are isometric matches to their adult counterparts, from several well-known examples. Any differences in Darwinopterus likewise mark phylogenetic, not ontogenetic differences.

Problem #3
Rhamphorhynchus and Pterodactylus only phylogenetically bracket Darwinopterus if the inclusion set is reduced to these three taxa. Otherwise they nest several nodes away from each other with lots of intermediate taxa as you can see here.

Problem #4
Unwin et al. claim the caudal count increases with maturity in Darwinopterus (18 in hatchlings, 30 in juveniles and adults). Put these into a cladogram and they probably become disparate taxa. Where else does the vertebral count nearly double during ontogeny? Nowhere. Those caudal counts for the larger specimens have to be estimates. Not every tail is complete. It appears as if the caudal count could vary among the larger specimens as well.

Problem #5
I see no mention of a phylogenetic analysis with regard to the various Darwinopterus specimens. This is a problem as Unwin et al. do not want to test their observations with the only method known to lump and split taxa. In the large pterosaur tree IVPP V 16049 nests with YH2000. 41H111-0309A nests with ZMNH M 8782. All four Darwinopterus taxa nest as a sister clade to Kunpengopterus + Archaeoistiodatylus and this combined clade is a sister to Wukongopterus, then the PMOL specimen of Changchengopterus, then Pterorhynchus. This major clade nests between Dorygnathus and Scaphognathus, both of which ultimately give rise to the two pairs of basalmost pterodactyloids.

Possible Solution 
I noted earlier that the Darwinopterus clade left no descendants. They also did not produce any small taxa like Dorygnathus and Scaphognathus did. Other workers thought the smaller Scaphognathus specimens were juveniles, despite the morphological differences. I can only wonder if the same situation is happening in the Darwinopterus clade? Perhaps what the Unwin team found are the smaller specimens previously missing from their clade branch. Even so, and sadly, this clade was not able to survive into the Cretaceous, small or not, because no known Cretaceous pterosaurs share darwinopterid traits. They are all accounted for with presently known tiny ancestors.

References
Unwin D, Lü J-C, Pu H-Y, Jim X-S  2014. Pterosaur tails tell tails of modularity and heterochrony in the evolution of the pterodactyloid bauplan. JVP 2014 abstracts

Things I didn’t know about phylogenetic analyses based on DNA molecules.

In my never ending quest to understand reptile phylogeny
I was fortunate to read Scotland et al. (2003) and Jenner (2004). Thankfully the latter rebutted the former. Scotland et al. are all plant scientists, so bear in mind, they deal with far fewer ‘moving parts’ in the taxa they study.

Scott et al. (2004) wrote: “We present the view that rigorous and critical anatomical studies of fewer morphological characters, in the context of molecular phylogenies, is a more fruitful approach to integrating the strengths of morphological data with those of sequence data. This approach is preferable to compiling larger data matrices of increasingly ambiguous and problematic morphological characters.

“In conclusion, problems surrounding character coding of morphological data reduce the number of unambiguous morphological characters for analysis. The crucial issue for morphology is that the already small number of morphological characters is further compromised by ambiguous homology assessment.

“DNA is much simpler. There is no ambiguity that the unit of comparison is the nucleotide and that adenine, guanine, cytosine, and thymine represent different versions of the same entity.
 
“Hillis and Wiens (2000) stated that dense taxon sampling is the greatest advantage of morphological data, citing recent simulation studies demonstrating the importance of taxon sampling for accurate phylogeny estimates (Hillis, 1996, 1998; Graybeal, 1998). For example, in one simulation study, Graybeal (1998) demonstrated that under some conditions phylogenetic accuracy was improved as the number of taxa increased, but not when more characters were added.”
There it is!. That’s what I’ve been saying!
Here’s the main problem with too few characters
according to Scotland et al. 2003):

“Another important issue relative to increased taxon sampling, in the context of morphological data, relates to the potential decreased number of unambiguous charactersas more taxa are added to a study. Characters that were discrete [in smaller studies] are no longer discrete when additional taxa were added.”
What the large reptile tree tells us:
Discrete characters are fine (they were Larry Martin’s favorite subject). But they’re not important in the scheme of things. What is important, as we’ve always heard, is the suite of characters present in each taxon. Let’s face it, sister taxa share all the characters that lump them together, except for the few that split them apart. And that happens again and again at every one of the 415 nodes in the large reptile tree.

A raft of clarity from Jenner 2004.
Jenner argued against Scotland et al. (2003) like this: “Scotland et al. (2003) evaluated the role of morphology in phylogeny reconstruction, and concluded that morphological evidence offers no hope to resolve phylogeny at any taxonomic level. Consequently, they advocated a very restricted role for morphology in phylogenetics, mainly by mapping selected morphological characters onto molecular phylogenies. I critically examined the scientific basis for the arguments of Scotland et al. (2003), and found them to be unconvincing.”

This is most enlightening from Jenner 2004:
“Nucleotides are characters of relatively low complexity, and the character state space for nucleotides is much more restricted than for morphology. In certain circumstances this creates a considerable danger that the same nucleotide has evolved independently in the same position, and this realization has been an incentive to develop models of evolution that estimate the probability that the same nucleotides at a site are historically identical, and to explore the value of more complex molecular characters. In contrast, morphology generally presents a richer space of more complex characters, which allows a more fine-grained comparison of potential homology, and this may help explain why in certain cases morphology may be qualitatively superior to molecules when considered per character.

“Scotland et al. (2014, 541) claim that these problems of “subjectivity and interpretation” are absent from molecular data, because “areas of ambiguity [in sequence alignment] can be excluded.” As recent research shows, to choose this way of least resistance may be thoroughly misleading, and this short statement seriously underplays the degree of subjectivity and interpretation asocial ted with molecular phylogenetics.”

Jenner then discussed more than a decade of 18S rDNA studies that suggested bird/mammal affinities, which, of course, was in conflict with morphological studies and other molecular data. Jenner continued:

“After the 18S data was analysed in various different ways by different workers, they concluded that this was an example of different molecules giving significantly different estimates of phylogeny. However, a recent study by Xia et al. (2003) convincingly showed that the conflict between 18S data and the traditional and other molecular data was an artifact attributable to two main factors: misalignment of sequences, and inappropriate estimation of base frequency parameters.

“Crucial to the resolution of this paradox was the incorporation in the molecular data set of those regions of the 18S molecule that were most variable, and most difficult to align unambiguously. This study clearly showed that restricting the data set to only the least unambiguous sites might produce a thoroughly misleading phylogeny. The problem that ‘different workers will perceive and define characters in different ways’ is therefore certainly not limited to morphological data.”

Ater reading Jenner (2004), you won’t wonder about DNA studies anymore. They’re not perfect and may never be. They don’t work for fossil taxa (you knew that already) and they often come up with bizarre results.

References
Graybeal A 1998. Is it better to add taxa or characters to a difficult phylogenetic problem? Systematic Biology 48:9-17.
Hillis DM 1996. Inferring complex phylogenies. Nature 383:140- 141.
Hillis DM 1998. Taxonomic sampling, phylogenetic accuracy, and investigator bias. Syst. Biol. 47:3-8.
Hillis DM and Wiens JJ 2000. Molecules versus morphology in systematics. Pp 1-19 in Phylogenetic analysis of morphological data (J. J. Wiens, ed.). Smithsonian Institution Press, Washington, D.C.
Jenner RA 2004. Value of morphological phylogenetics. Accepting Partnership by Submission? Morphological Phylogenetics in a Molecular Millennium. Systematic Biology 53333-359.
Scotland RW, Olmstead RG and  Bennett JR 2003. Phylogeny Reconstruction: The Role of Morphology. Systematic Biology 52:539-548.
Xia X, Xie Z and Kjer KM 2003. 18S ribosomal RNA and tetrapod phylogeny. Systematic Biology 52:283-295.

The character/taxon ratio

The large reptile tree currently has 415+ taxa and it keeps on growing. It also has 228 characters, the same number as when the taxon list was barely over 100. Paleontologist like to see a 3:1 character:taxon ratio, which was the average according to Sanderson and Donoghue (back in 1989). Perhaps unfortunately, the large reptile tree has a character:taxon ratio of about 0.5:1 or about six times smaller than ‘the ideal’.

This brings to mind a famous phrase
‘In theory, theory and practice are the same. In practice, they rarely are.’

This 3:1 ratio is apparently important, because referees often bring it up. At the same time they discount the fact that the tree is fully resolved, which makes me wonder…

Scotland et al. (2003) wrote: “Although the number of characters needed for accurate phylogeny reconstruction is difficult to estimate, the number of characters needed in simulation studies to recover accurate trees is an order of magnitude greater than that available from morphology.” They also claim, “the low character/taxon ratio in many morphological studies itself precludes high support values.”

Of course, in practice (in the large reptile tree), this is proven false. There are high support values throughout (unless two taxa are very incomplete and nest as sisters). So the 3:1 character:taxon ratio has to go the way of the dodo. It’s useless. Based on an average reported back in 1989, it has since then earned some sort of mythical status.

And the same goes for the CI (Consistency Index). 
Paleontologists like to see a high CI. How high is high? Good question. In the large reptile tree it is higher in every subset of the tree (so there’s a clue). I was recently chided for having a very low CI of 0.094 in the large reptile tree (coupled with a completely resolved tree, which, if you think about it, is quite a feat). As you already know, the low CI of the 415 taxon study is due to its very large size and the fact, a well-recognized fact, that homoplasy is rampant within the Amniota with many clades sharing many traits by convergence. In counterpoint, the referee pointed to another large study (Conrad 2008) of squamates that he felt was pert-near ideal. Unfortunately the Conrad study also had a very low CI of 0.1499. That fact must have escaped under the radar.

Well… that’s what happens in large amniote analyses.
It can’t be a bad thing in one case, but acceptable in another.

References
Conrad JL 2008. Phylogeny and systematics of Squamata (Reptilia) based on morphology. Bulletin of the American Museum of Natural History 310:182 pp.
Jenner RA 2004. 
Value of morphological phylogenetics. Accepting Partnership by Submission? Morphological Phylogenetics in a Molecular Millennium. Systematic Biology 53333-359.
Sanderson MJ and Donoghue MJ 1989.
Patterns of variation and levels of homoplasy. Evolution 43:1781-1795.
Scotland RW, Olmstead RG and  Bennett JR 2003. Phylogeny Reconstruction: The Role of Morphology. Systematic Biology 52:539-548.

Giant Alaska pterosaur tracks indicate floating pterosaurs

Figure 1. Pterosaur tracks from Alaska. Note the lack of pedal tracks and the large size of the manus tracks.

Figure 1. Pterosaur tracks from Alaska. Note the lack of pedal tracks and the large size of the manus tracks.

Figure 2. Closeup of a giant pterosaur manus track. Digits identified.

Figure 2. Closeup of a giant pterosaur manus track. Digits identified.

A recent paper ( ) described giant Late Cretaceous pterosaur tracks from the far north in Alaska. These are likely made by large azhdarchids, like Quetzalcoatlus.

At 18 centimeters long by 6 centimeters wide, the bigger pterosaur tracks are “very large” compared to others that have been reported, Fiorillo’s team says.

The more diminutive set of prints, meanwhile, was only about one-fourth as large — about 6 centimeters by 4 centimeters.

Manus only tracks were likely produced by floating and poling pterosaurs as we talked about earlier with Tapejara. Here the size and proportions of the manus tracks, along with the location and time period all point toward giant azhdarchids.

Figure 1. The azhdarchid pterosaur Quetzalcoatlus floating and poling producing manus only tracks.

Figure 3. The azhdarchid pterosaur Quetzalcoatlus floating and poling producing manus only tracks.

It is important to appreciate the great size of the pterosaurs that made such large manus tracks, especially so since the fingers that made the impressions are among the smallest parts on the pterosaur itself.

Figure 1. Quetzalcoatlus specimens to scale.

Figure 4. Quetzalcoatlus specimens to scale. Here digit 3 is approximately 18 cm long, matching the size of the track. The manus of Quetzalcoatlus is poorly known. These are based on Zhejiangopterus and Azhdarcho. The second finger could have been shorter to match the tracks. The ability of digit 3 to rotate posteriorly harkens back to the lepidosaur ancestry of pterosaurs.

Manual 3.1 of Azhdarcho (Fig. 4) shows how that digit was able to bend posteriorly. Like most lizards, the fingers were rather free to rotate on bulbous articular surfaces.

Figure 2. Manual 3.1 for Azhdarcho. Note the bulbous proximal portion.

Figure 5. Manual 3.1 for Azhdarcho. Note the bulbous proximal portion enabling posterior bending.

 

References
Fiorillo AR et al. 2009. A pterosaur manus track from Denali National Park, Alasak range, Alaska, United States. Palaios 24: 466-472.

Fiorillo AR et al. 2014. Pterosaur tracks from the Lower Cantwell Formation (Campanian–Maastrichtian) of Denali National Park, Alaska, USA, with comments about landscape heterogeneity and habit preference. Historical Biology DOI:10.1080/08912963.2014.933213

Online report.