Basic Problems with “Life History of Rhamphorhynchus Inferred from Bone Histology…”

Today’s paper on Rhamphorhynchus bone histology (Prondvai et al. 2012) reported, “Whereas morphological studies suggested a slow crocodile-like growth strategy and superprecocial volant hatchlings, the only histological study hitherto conducted on Rhamphorhynchus concluded a relatively high growth rate for the genus. These controversial conclusions can be tested by a bone histological survey of an ontogenetic series of Rhamphorhynchus.”

The family tree of the Rhamphorhynchus.

Figure 1. Click to enlarge. The family tree of Rhamphorhynchus in phylogenetic order. Note only the very largest specimen was large enough to produce a hatchling the size of the smallest specimen based on an 8:1 ratio of adult to hatchling as in Pterodaustro and based on egg size/pelvic opening. If so, that means ALL the other Rhamphorhynchus specimens were juveniles despite their many morphological differences. No, this was a clade with a variety of morphologies and sizes, a fact overlooked by the Prondvai et al. (2012) study.

Rhamphorhynchus presents a wide variety of adult sizes with the largest specimens 8x as tall as the smallest (Fig. 1). Unfortunately, the authors gave no indication that the five specimens in their study were from the same single species (of several) within the genus which would have presented an ontogenetic series. This can be determined only by a cladistic analysis of several dozen Rhamphorhynchus specimens, including their five study specimens, but that first step was not done.  Figure 1 demonstrates a phylogenetic series (as determined by cladistic analysis) of the genus Rhamporhynchus. The morphological differences are easy to see. Even the pedal phalanges differ among species (Peters 2009), as noted earlier.

A selection of Rhamphorhynchus feet

Figure 2. A selection of Rhamphorhynchus feet compared to the new one associated with a large fish. Note the morphological differences exhibited by the new specimen, WDC CSG 255 (far right).

 

Furthermore
Substantial morphological change during growth does NOT occur in pterosaurs, as already demonstrated by embryos (especially Pterodaustro). What we’re looking for are tiny versions of the adults already known in the fossil record, and to my knowledge, no juveniles have yet been found that morphologically match 2x to 8x larger adults (the latter being the standard difference between hatchlings and adults as determined by hypothetical egg sizes matched to pelvic openings and the example of Pterodaustro). Ptweety is the only juvenile pterosaur I know of and it also has the proportions of an adult.

What Happens During a Phylogenetic Size Squeeze in Pterosaurs?
“Teens” start having babies. Sexual maturity comes sooner and sooner. Longevity decreases. Adult size decreases. Chinsamy et al. (2008) reported that sexual maturity in Pterodaustro occurred at half the largest size attained. Smaller hips produce smaller eggs. The bone histology of a small specimen with a shorter lifespan mimics the expected histology of a juvenile. Scapulocoracoid fusion likewise disappears during serial phylogenetic size reductions.

Superprecocial Flight
The limiting factor in superprecocial flight still appears to be dermal evaporation and desiccation due to a large surface of volume ratio in tiny pterosaurs. Only those pterosaurs hatching from eggs the size of the three published embryos appear to create a threshold size for flight shortly after hatching. Smaller hatchlings than this had to be terrestrial, hiding in damp leaf litter, rather than taking to the skies, so the lack of flying in hatchling pterosaurs reported by Prondvai et al. (2012) is likely correct, though not for the same reason.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Prondvai E, Stein K, Ősi A. and Sander MP (2012)
 Life History of Rhamphorhynchus Inferred from Bone Histology and the Diversity of Pterosaurian Growth Strategies.
PLoS ONE 7(2): e31392. doi:10.1371/journal.pone.0031392
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0031392

More Than Just a Pretty Propatagium

The CAGS specimen CAGS IG 02-81 originally attributed to Dendrorhynchoides (Lü et al. 2006, 18 steps different) and then to Jeholopterus (4 steps different) is neither genus, but has a suite of traits that distinguish it from both. But that’s not the point of today’s blog. We’re looking today at what appears to be an extraordinary propatagium unlike any other (Figure 1).

The CAGS specimen

Figure 1. The CAGS specimen attributed to Dendrorhynchoides and then to Jeholopterus, but is distinct from both. Note the dark triangle that appears to be a fibered propatagium (between the wrist and shoulder) more distinct than the remnants of the brachiopatagium.

A Propatagium with Aktinofibrils?
The apparent propatagium of the CAGS specimen appears to preserve all the traits of a brahiopatagium, which is unlike that of any other pterosaur. For instance, it has aktinofibrils! Elgin, Hone and Frey (2010) considered this an example of dermal shrinkage in the wing membrane. Actually the membranes are torn and folded without shrinkage. So, this is yet another one of Nature’s tricky illusions (like Sordes) deserving of a more vigorous examination.

Interpretation of bony and soft tissue elements in the CAGS specimen.

Figure 2. Interpretation of bony and soft tissue elements in the CAGS specimen. Click to see rollover image. The actual propatagia are in blue. Torn and displaced brachiopatagial elements mask both propatagia. The parts marked "distal wing elements" are below the more superficial skeletal elements. As in other anurognathids, the distal wing elements were folded over the back, so here in ventral exposure, they are preserved deeper than the rest of the skeleton after dislocation. Can you find the sternal complex? I probably underestimated the preservation of wing membrane here, much of which is beneath the body. The pteroids are relaxed here.

Layered Membranes
As you might have guessed from the title of this blog, there’s more to it than meets the eye. DGS (digital graphic segregation) enabled the separation of this odd bit of anatomy into two separate overprinting layers. One is indeed the propatagium, essentially devoid of internal details as in other pterosaurs (perhaps because it is the extensor digitorum longus as blogged earlier). The other is  a torn section of the brachiopatagium, the part of the wing with all the aktinofibrils. The apparent lack of distal wing phalanges indicates parts of the wing were torn off their phalangeal moorings. Using DGS clarifies the mystery. Critical analysis has to be done, rather than accepting face value.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
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
Lü J-C, Ji S, Yuan C-X and Ji Q 2006. Pterosaurs from China. Geological Publishing House, Beijing, 147 pp.

A New Skull for Silvanerpeton

Silvanerpeton is not a Reptile
But it is a sister to Gephyrostegus, the proximal outgroup to the Reptilia. So it has a bearing on the base of the Reptilia.

A new skull for Silvanerpeton

Figure 1. A new skull for Silvanerpeton (in yellow) is somewhat different from the original reconstruction provided by Ruta and Clack (2006). This is based on tracing a photo of the specimen provided in Ruta and Clack (2006).

A New Skull Based on Tracings
Silvanerpeton miripedes (Clack 1994) Visean, Early Carboniferous ~335 mya, ~40 cm in length was originally illustrated with the skull shown in figure 1 (in white) and on this data Silvanerpeton was entered into the large reptile family tree. The addition of a contemporary, Eldeceeon (Smithson 1994) introduced certain problems (autapomorphies) into the dataset. Those problems sparked a review of the specimen that included tracing the skull from photographs provided in Ruta and Clack (2006). A new reconstruction based on specimen NMS G.1998.51.2 (in yellow, Fig. 1) had distinctly different traits. There are several specimens known. Perhaps the original was based largely on another specimen.

A new skull for specimen 1 attributed to Gephyrostegus.

Figure 1. A new skull for specimen 1 attributed to Gephyrostegus. Click to enlarge.

A New Reconstrucion of Gephyrostegus (specimen 1)
As part of the process of weeding out invalid autapomorphies, I also retraced and reconstructed a sister of Silvanerpeton, specimen 1 of Gephyrostegus (Brough and Brough 1967) (CGH IIIB 21 c. 587) and counterpart (MP451) to produce a revised skull for that specimen (Fig. 2). Note the virtual loss of the otic notch, the development of the transverse pterygoid flange and those long reptilian toes, more robust than in the larger Silvanerpeton.

A New Nesting
Taxa shifted slightly from the prior tree due to the addition of Eldeceeon and the reinterpretation of traced traits. Both Silvanerpeton and specimen 1 moved away from Utegenia and toward Gephyrostegus. This clarifies the lineage of pre-reptiles. Needless to say at this point, diadectids and limnoscelids do not nest as pre-reptiles, but well within the new Lepidosauromorpha.

A Serial Size Reduction
Silvanerpeton was a 40 cm tetrapod. Specimen 1 of Gephyrostegus and G. watsoni were a quarter of its size. Silvanerpeton appeared just 25 million years after Ichthyostega, and the first amniotes may have been contemporaries, just getting started. These data fall in line with Carroll’s (1970) hypothesis on tiny tetrapods without a tadpole stage were the first to lay tiny amniotic eggs, as blogged just a few days ago.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf.
Carroll RL 1991. The Origin of Reptiles in Origins of the Higher Groups of Tetrapods: Controversy and Consensus.  Schultze H-P and Trueb L (eds). Cornell University Press.
Carroll RL 2008. 
Problems of the Origin of Reptiles. Biological Reviews 44(3):393-431.
Carroll RL 2009. 
The Rise of the Amphibians 365 Million Years of Evolution. The Johns Hopkins University Press. 360 pp.
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.
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.
Smithson TR 1994. Eldeceeon rolfei, a new reptiliomorph from the Viséan of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (3-4): 377–382.

wiki/Silvanerpeton
wiki/Eldeceeon

How Can Two Trees Look So Different?

A recent paper by Tsuji, Müller and Reisz (2012) reexamined the nycteroleterid, Emeroleter, a long-legged sister to Nyctiphruretus and Macroleter. Their traditional tree (Figure 1) nested Diadectidae and Limnoscelidae outside the Amniota, among many other odd nestings that, unfortunately, recover “sisters” that too often don’t resemble one another. Such odd nestings may be due to misinterpretations, to too many missing taxa between the oddballs or to too few characters employed (136 vs. 228). A contributing factor has to be the lack of an understanding of the diphyletic nature of the complete reptile family tree. The lack of strong support between the clades in the Tsuji, Müller and Reisz tree(Fig. 1) is telling. There are far too few taxa here for the gamut of included taxa.

Sister Problems
In the Tsuji, Müller and Reisz (2012) tree Diadectes nests in its traditional position, outside the Amniota, a whopping 16 nodes away from its sister Procolophon in the large tree. In the Tsuji, Müller and Reisz (2012) tree mesosaurids nest as sisters to Captorhinidae and Millerettidae + Eunotosaurus, none of which resemble mesosaurids.

I’d like to see the Tsuji, Müller and Reisz reconstruction of the the Eudibamus skull, which nests in their tree as a sister to Belebey (known only from a skull). No skull reconstruction or closeup of Eudibamus has ever been published other than here. The slender and long-toed post-crania of Eudibamus is much closer to that of other basal diapsids, like Petrolacosaurus, rather than to short-toed and thick-ribbed millerettids and Eunotosaurus, the only sisters of Belebey with known post-crania.

Lanthanosuchus should have nested with Macroleter. To their credit, Diadectes is indeed a “close enough”sister to Limnoscelis. Younginiformes are indeed sisters to Araeoscelida. Millerettidae are indeed sisters to Eunotosaurus. The pareiasaurs are related to one another as are the nycteroleterids.

Tsuji, Muller and Reisz (2012) tree of basal reptiles.

Figure 1. Tsuji, Muller and Reisz (2012) tree of basal reptiles. Only those branches with support over 66 are highlighted with yellow circles. Note how few branches are highlighted.

Results of the Large Heretical Tree, Pruned to Match
By greatly expanding the taxon list more confidence can be placed in the nesting of individual taxa because there are so many more opportunities available for them to nest. Figure 2 presents a greatly reduced version of the large tree, pruned to more closely match the taxon list of Tsuji, Müller and Reisz (2012). I would have thought the two trees would be closer to each other in topology, but they are not. I’m not surprised by the lack of resolution here (Fig. 2) at the bases of the three recovered main clades (in color). There are many other taxa excluded between the clades, as recovered in the large tree. This is what happens to small studies with too large a gamut and too few taxa.

The large tree pruned to match the taxon list of Tsuji, Muller and Reisz (2012).

Figure 2. The large tree pruned to match the taxon list of Tsuji, Muller and Reisz (2012). While the pruned tree reflects the results recovered from the large tree, it does not match the Tsuji, Muller and Reisz tree. One must be very wrong. Here it matters little how much support is present to support the branches because so many taxa have been excluded here from the large tree with complete resolution.

How Do Scientists Test One Tree Against Another?
How can one judge the validity of one tree versus another? The Tsuji, Müller and Reisz (2012) tree was created by professional paleontologists. These PhDs had direct access to the specimens. I did not have any of these advantages. However…

In counterpoint, everyone knows that adding taxa and character traits to a cladistic analysis is like adding greater diameter to a telescope lens or mirror. More taxa and characters = greater resolution. The large study is a magnitude larger than the Tsuji, Müller and Reisz (2012) tree. Larger size provides greater confidence in tree topology because more possibilities are covered rather than excluded.

As blogged several times earlier, sister taxa should look like one another. Take mesosaurs. Sister taxa should have long jaws, a retracted naris, an elongated torso and tail, short paddle-like limbs and a long pedal digit 5. We find such traits in Wumengosaurus, Askeptosaurus, Utatsusaurus and other enaliosaurs. We don’t find those traits in sisters recovered by Tsuji, Müller and Reisz (2012), captorhinids and millerettids.

I’m stymied to see so many tree topology differences in the two similar taxon list trees. I wish the character list of Tsuji, Müller and Reisz (2012) followed the traditional order of: skull, mandible, axial and appendicular characters, but they are all mixed up. Given this disorganization, it will be difficult to wade through the data point by point. When I have more to say on this, I will do so.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Tsuji, Müller and Reisz 2012. Anatomy of Emeroleter levis and the Phylogeny of the Nycteroleter Parareptiles. Journal of Vertebrate Paleontology 32 (1): 45-67. doi:10.1080/02724634.2012.626004.

Ornithischia: Which One Was Most Basal?

Updated April 22, 2014 as poposaurs now nest as basal archosaurs. 

Which dinosaur represents the most basal ornithischian?
As others before him, Marc Spencer (2007) recovered Pisanosaurus as the most basal ornithischian in his online Masters thesis. A monophyletic Genasauria was recovered with two major clades: Eocursor+ Cerapoda and Fabrosauridae + Thyreophora. Lesothosaurus was recovered within the Fabrosauridae, along with a clade consisting of StormbergiaAgilisaurus. The Heterodontosauridae was recovered as the basalmost taxon of the Cerapoda.

Nesbitt (2011) remarked, “Pisanosaurus is almost always found as the basalmost member of Ornithischia (Langer and Benton, 2006; Butleret al., 2007, 2008b; Irmis et al., 2007a) because of the combination of ornithischian synapomorphies and archosaur plesiomorphies, such as the anteroventrally directed pubis…Most recently, Heterodontosaurus was found as a basal ornithischian near Pisanosaurus (Butler et al., 2008b). This position better reflects the fossil record of Ornithischia and suggests that some of the ‘‘odd’’ features (e.g., the hand) of Heterodontosaurus present in non-ornithischian dinosaurs (e.g., Herrerasaurus) may represent plesiomorphies of Dinosauria rather than autapomorphies of Heterodontosaurus.”

Nesbitt’s (2011) tree was not able to resolve basal Ornithischia. Saturnalia, Lewisuchus and Marasuchus nested as outgroup sisters. ScelidosaurusDaemonosaurus and Massospondylus kaalae were not included.

Figure 1. Daemonosaurus and kin. Derived from a sister to the basal theropod, Herrerasaurus, Daemonosaurus, Pisanosaurus and Massospondylus are close sister taxa (within 1 step of each other). Daemonosaurus now nests at the base of the Ornithischia. Scelidosaurus and Heterodontosaurus are its closest sisters within that clade. BTW, I'm curious about Scelidosaurus. A tracing of a photograph produced a mandible with a convex ventral margin of the mandible, but old drawings do not. Which is valid?

Figure 1. Daemonosaurus and kin. Derived from a sister to the basal theropod, Herrerasaurus, Daemonosaurus, Pisanosaurus and Massospondylus are close sister taxa (within 1 step of each other). Daemonosaurus now nests at the base of the Ornithischia. Scelidosaurus and Heterodontosaurus are its closest sisters within that clade. BTW, I’m curious about Scelidosaurus. A tracing of a photograph produced a mandible with a convex ventral margin of the mandible, but old drawings do not. Which is valid?

More Taxa = Greater Resolution
Here, in the large reptile study, Daemonosaurus and Pisanosaurus nest at the base of the Ornithischia. Earlier the tree nested poposaurs with phytodinosaurs, but as of April 22, 2014, poposaurs nest as basal archosaurs.

 Scutellosaurus

Figure 2. Scutellosaurus. Perhaps not in the process of adding armor, but losing it.

What About Scutellosaurus?
According to the large tree the smaller and more lightly armored Scuttelosaurus (Colbert 1981) and unarmored Lesothosaurus nest higher in the ornithischian clade. So a serial and phylogenetic size reduction seems to have occurred in this clade. Eocursor and Lesothosaurus were similar to one another and lacked armor.

 

Figure 3. Yinlong overall. This basal ceratopsian had a larger skull, shorter neck and shorter tail than Hexinlusaurus, its phylogenetic predecessor.

Figure 3. Yinlong overall. This basal ceratopsian had a larger skull, shorter neck and shorter tail than Hexinlusaurus, its phylogenetic predecessor.

And Yinlong?
Among the basal ceratopids is Yinlong (Xu et al. 2006, Fig. 3), a Late Jurassic survivor of an earlier radiation. It retained premaxillary fangs and was primarily bipedal.

Other Saber-Toothed Ornithischians
I refer the reader to this website by Jaime Headden for more saber (or sabre)-toothed basal ornithischians. There were several that I’d like to learn more about.

The Antiquity of Scelidosaurus
Scelidosaurus lived during the Late Sinemurian, within 5 million years of the Latest Triassic. The much smaller Scuttelosaurus (Fig. 2) was a contemporary. Thulborn (1977) classified Scelidosaurus within the Ornithopoda, but recent workers ally Scelidosaurus with ankylosaurs and stegosaurs. Scelidosaurus retained elongated maxilla teeth, a vestigial pedal digit 5, lacked much of a prepubic process on the pubis and had a relatively small postnarial process of the premaxilla, all traits shared with more primitive taxa.

References
Colbert EH 1981. A primitive ornithischian dinosaur from the Kayenta Formation of Arizona. Bulletin of the Museum of Northern Arizona 53:1-61.
Crompton AW and Charig AJ 1962. A new ornithischian from the Upper Triassic of South Africa. Nature 196:1074-1077
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.
Norman D 2001. Scelidosaurus, the earliest complete dinosaur in The Armored Dinosaurs, pp 3-24. Bloomington: Indiana University Press.
Spencer MR 2007. A Phylogenetic Analysis of the Basal Ornithischia (Reptilia, Dinosauria). Online Thesis.
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society Bpublished online 
Thulborn, RA 1977. Relationships of the lower Jurassic dinosaur Scelidosaurus harrisonii. Journal of Paleontology. 51: 725-739
Xu X, Forster CA, Clark J M and Mo J 2006. A basal ceratopsian with transitional features from the Late Jurassic of northwestern China. Proceedings of the Royal Society B: Biological Sciences. First Cite Early Online Publishing. online pdf
wiki/Daemonosaurus
wiki/Heterodontosaurus
wiki/Scelidosaurus
wiki/Scutellosaurus
wiki/Yinlong

The Tiny Gephyrostegus and The Tiny Origin of the Reptilia

This page is no longer valid. Please see the update at:
https://pterosaurheresies.wordpress.com/2014/11/02/news-at-the-base-of-the-amniota-part-3-the-amniotic-egg/

And at: www.reptileevolution.com/gephyrostegus_watsoni.htm

Gephyrostegus-size

Figure 1. Two species of Gephyrostegus, the closest outgroup taxon to the Reptilia, in size comparisons to Cephalerpeton, the most primitive reptile. As you can see, Gephyrostegus watsoni was smaller than both. Whether G. watsoni (Fig. 2) was a juvenile or not (it is not a tadpole but certain tiny bones remain unossified), the fact remains that the earliest of reptiles were all smaller than Gephyrostegus bohemicus and they stayed small for several succeeding phylogenetic nodes. 

Carroll’s Hypothesis
As blogged earlier, Dr. Robert L. Carroll (1970) figured out that the earliest of all reptiles, the ones that biologically invented the amniotic egg, would be small specimens similar to Gephyrostegus. Carroll (2008) wrote: “On the basis of the present fossil record, all adequately known Palaeozoic reptiles appear to have had a common ancestry among the predecessors of the known gephyrostegids.” Carroll (2008) considered the possibility of a long ghost-lineage for gephyrostegids, unfortunately he did not undertake a cladistic analysis like the one here. Later Carroll (2009) dismissed his earlier hypothesis because, […gephyrostegids] lack many definitive features [of reptiles] and the best-known genus only occurs long after the appearance of unquestioned amniotes.” 

Gephyrostegus watsoni

Figure 2. Gephyrostegus watsoni. This tiny specimen retained an intermedium in the skull roof, a hallmark of non-reptiles. Small manual phalanages were poorly ossified. The pelvis likely connected to only one sacral vertebra, another non-reptile hallmark.

The Importance of Small Body Size
Carroll (2008) wrote, “Study of the earliest known reptiles and their closest relatives among contemporary amphibians indicates that the initial adaptation leading to the emergence of the class was assumption of a terrestrial habit, with accompanying small body size. The small body size of the immediate ancestors of reptiles would have made it possible for them to produce sufficiently small eggs that they could develop in damp places on land without initially being supported and protected by extraembryonic membranes.”

Carroll (1991) presumed the hatchling of tiny early reptiles would have been very large relative to the adult, skipping the tadpole stage and adapting to life immediately as an adult. He noted living salamanders that lay eggs on land have the largest hatchling to adult ratio. Carroll (1991) estimated the size of such an egg at 1 cm with an adult of 10 cm in snout-vent length. Cephalerpeton was exactly that size. Gephyrostegus watsoni (Fig. 2) was less than half that size.

The Origin of the Reptilia
Here Gephyrostegus is the closest outgroup taxon to the Reptilia and Cephalerpeton is the most primitive reptile (despite being 30 million years younger than the oldest known fossil reptiles, Westlothiana and Casineria). Another species, Gephyrostegus watsoni, was smaller than both. Whether G. watsoni was a juvenile or not (it is not a tadpole but certain tiny bones remain unossified), the fact remains that the earliest of reptiles were all smaller than Gephyrostegus bohemicus and basal reptile stayed small for several succeeding phylogenetic nodes.

Reptiles
Distinguished from basal tetrapods, basal reptiles lose their palatal fangs, the intertemporal (a tiny skull roof bone) and the occipital notch at the back of the skull. The occiput includes a large supraoccipital bone linking the skull roof bones to the back of the braincase. The pterygoid developed a transverse flange. The intercentra were reduced to crescents. The proximal tarsals integrated to form an astragalus and calcaneum, which was present in Gephyrostegus and reversed in Weslothiana.

Rapid Size Increase?
Carroll (2008) wrote: The rapid increase in body size in all lineages of Pennsylvanian reptiles indicates the prior development of an amniotic egg.” Perhaps not with reptiles first appearing some 340 million years ago (e.g. Casineria to Hylonomus) and not getting much bigger for the next 40 million years (e. g. Cephalerpeton to Milleretta).

A chronology of the basal Reptilia.

Figure 3. Click to enlarge. A chronology of the basal Reptilia.

Diadectids
Carroll (2008) was not able to establish the specific relationships of the Diadectidae. Here that clade is buried deep within the new Lepidosauromorpha.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf.
Carroll RL 1991. The Origin of Reptiles in Origins of the Higher Groups of Tetrapods: Controversy and Consensus.  Schultze H-P and Trueb L (eds). Cornell University Press.
Carroll RL 2008. Problems of the Origin of Reptiles. Biological Reviews 44(3):393-431.
Carroll RL 2009. The Rise of the Amphibians 365 Million Years of Evolution. The Johns Hopkins University Press. 360 pp.

wiki/Gephyrostegus
wiki/Cephalerpeton

Flipping the Nasal on Tanystropheus

Dr. Stefania Nosotti (2007) published an excellent and well-illustrated report on several smaller Tanystropheus specimens. Unfortunately the skulls of the articulated specimens were preserved in ventrolateral view obscuring the dorsal view. Several other disarticulated specimens helped fill the gaps.

Tanystropheus exemplar a

Figure 1. Tanystropheus exemplar a skulls demonstrating different interpretations of the nasal bone. The original interpretation above. A revised interpretation below.

Original Reconstruction
Nosotti (2007, Fig. 1) reconstructed the nasals in Tanystropheus with a long common median border beginning at mid naris and expanding laterally beyond the naris. Unfortunately this configuration does not match that of sister taxa (most notably the large Tanystropheus) in which a long premaxilla ascending process separates the nares, extends far beyond them and the nasals laterally border the nares and decrease in width posteriorly. By merely flipping the nasal reconstructed by Nosotti (2007) and adding a slender ascending process  (a fragile bone prone to crushing and breakage) to the premaxilla, a match is made to sister taxa.

Tanystropheus exemplar a.

Figure 2. Tanystropheus exemplar "A" overall. Click for more info.

There’s also the Premaxilla
The premaxilla doesn’t rise along the lateral rim of the naris in sister taxa like exemplar “K” (fig. 3). The rising ascending process goes back to Huehuecuetzpalli.

These exercises demonstrate the need to compare specimens to sister taxa. If autapomorphies are found, then perhaps the autapomorphies need a second look, and perhaps a revised reconstruction more in line with sister taxa – if possible and valid.

Peters (2000) made similar mistakes in Cosesaurus in which I interpreted autapomorphic elements in the pectoral and pelvic girdles that had more synapomorphic distributions.

Figure 3. The skull of the large Tanystropheus, exemplar "K". Premaxilla and nasal highlighted.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Nosotti S 2007. Tanystropheus longobardicus (Reptilia, Protorosauria: Reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano, Vol. XXXV – Fascicolo III, pp. 1-88.

Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

Tijubina – A New Tritosaur Sister to Huehuecuetzpalli

Tijubina pontei (Bonfim and Marques 1997) was a tiny Early Cretaceous lizard from the Crato Formation (late Aptian) of northeast Brazil. In a recent redescription Simões (2012) reported Tijubina lacked the posteroventral and posterodorsal processes of the dentary and the tibial/fibular length equaled the femoral length. Its posterior dentary teeth were robust, cylindrically based, unsculptured and bore no cuspids. Simoes (2012) nested Tijubina in a basal position among the Squamata. Reynoso (1998) reported a similar nesting for Huehuecuetzpalli. Neither considered the possibility that both specimens nested in a third squamate clade, the Tritosauria, outside of the Iguania + Scleroglossa.

Figure 1. The skull of Tijubina reconstructed (left) and in situ dorsal view, skull roof missing (right). Click for more info. Some skull parts identified here are disputed by Simoes (pers comm).

Late Survivors
Both Huehuecuetzpalli and Tijubina were late survivors of a 130 million year earlier Late Permian radiation of lizards. Tijubina is distinguished by its teeth, which are larger posteriorly and shaped like cylinders instead of sharp points. Tijubina was about half the size of its Huehuecuetzpalli.

Tijubina in situ

Figure 2. Tijubina in situ, nearly full size on a 72dpi screen. Click to enlarge.

Not a Juvenile
Simoes (2012) described Tijubina as immature due to a imcompletely calcified joints, a wide open sternal fontanelle (hole), unfused pectoral and pelvic elements. Adult tritosaur lizard sisters are likewise incompletely calcified. Unlike Huehuecuetzpalli, and despite its smaller size, the carpal elements of Tijubina were well ossified. The lack of dorsal and ventral processes of the posterior dentary are traits shared with Huehuecuetzpalli.

Manus of Tijubina identifying carpal elements.

Figure 2. Manus of Tijubina identifying carpal elements. Metacarpal 4 is largely beneath mc5. Here the two centrale are ossified along with the other carpal elements and present. The carpus is unossified in adult Huehuecuetzpalli.

The carpus is not ossified in Huehuecuetzpalli, but it is well ossified in the much smaller Tijubina and both centrale are present. Earlier I wondered if the pteroid and preaxial carpal were migrating at the evolutionary stage represented by Huehuecuetzpalli because the carpus was poorly ossified. That would have been an ideal time to do it! Here Tijubina may have been a sister Huehuecuetzpalli, but the latter was closer to fenestrasaurs including pterosaurs.

 

Figure 3. The pelvis and possible prepubis and Tijubina. Is this the origin of the prepubis? Or just a splinter or two of bone in the position of the prepubis. I can't tell for sure. Phylogenetically Tijubina was scored without a prepubis and pteroid.

Figure 3. The pelvis and possible prepubis and Tijubina. Is this the origin of the prepubis? Or just a splinter or two of bone in the position of the prepubis. I can’t tell for sure. Phylogenetically Tijubina was scored without a prepubis and pteroid.

Cosesaurus through pterosaurs all have a prepubis, a new bone extending beyond the ventral margin of the pubis. So the prepubis appeared some time prior to Cosesaurus. It may or may not be present in Langobardisaurus. It is not present in Huehuecuetzpalli. A possible prepubis may be present in Tijubina (Fig. 3). On the other hand, that little fleck of bone(s) may just be a splinter from the damaged pubis. No problem either way.

A Long Tibia
Since the tibia was subequal to the femur, Tijubina was likely a sprinter and a possible occasional biped, like many living lizards with similar proportions. Such traits and behaviors likely led to the development of a prepubis in sister taxa.

Pes of Tijubina.

Figure 4. Pes of Tijubina. PILs added.

Pes
The pes of Tijubina had tendril-like toes, indicating an arboreal lifestyle. Like Huehuecuetzpalli and Cosesaurus the proximal phalanges of digit 5 were long. The tarsals were not coossified, a trait typical of many (but not all) tritosaurs. Fenestrasaurs (including pterosaurs) did not ossify two distal tarsals. Drepanosaurs and all living lizards co-ossified the proximal tarsals.

Summary
Tijubina was a late-surviving representative of the Tritosauria, a clade of lizards that ultimately gave rise to tanystropheids, drepanosaurs and pterosaurs. The cylindrical teeth were autapomorphies not found in other clade members. The tiny size and crushed nature of the specimen prevent confirmation of several possible fenestrasaur-like traits.

Huehuecuetzpalli, Tijubina, Cosesaurus and Macrocnemus are basal tritosaurs.

Huehuecuetzpalli, Tijubina, Cosesaurus and Macrocnemus are basal tritosaurs.

References
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.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
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].

Tanystropheus Feet: Keys to Speciation

The Traditional View
Wild (1978) established the concept that the small, multi-cusp toothed specimens attributed to Tanystropheus were juveniles of the larger forms without multi-cusped teeth. This would involve morphological changes during ontogenetic growth.

The question is, why wasn’t phylogenetic evolution (speciation) offered as an alternative?

The Heretical View
Earlier I blogged that the differences were too many to support an ontogenetic growth series between the smaller Tanystropheus specimens and the larger ones. Today we’ll look at the feet and you can decide whether or not such changes can be attributed to ontogeny or are better explained as a phylogenetic change attributed to evolution. Of course the split would have occurred earlier and the two species would have been adapted to distinct niches based on size and tooth morphology.

Tanystropheus feet with morphological changes noted.

Figure 1. Tanystropheus feet with morphological changes noted. Click for more info.

As in Pterosaurs
Peters (2011) was able to speciate various specimens attributed to Pterodactylus, Pteranodon, Rhamphorhynchus, Germanodactylus and other pterosaurs by looking only at  the variation in the foot morphologies. The same process is present here. If these two Tanystropheus pedes represent younger and older variations of the same species, why do the distinct changes that appear in the jaws (distinct teeth, for instance) extend to the feet?

This is especially important in a clade that otherwise demonstrates isometric growth patterns. (They don’t change much as they mature, contra traditional studies.)

Perhaps a more parsimonious solution is to place the smaller specimen in the bushy lineage of the larger specimen. Different sizes = different diets = different teeth.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bassani F 1886. Sui Fossili e sull’ età degli schisti bituminosi triasici di Besano in Lombardia. Atti della Società Italiana di Scienze Naturali 19:15–72.
Li C 2007. A juvenile Tanystropheus sp.(Protoro sauria: Tanystropheidae) from the Middle Triassic of Guizhou, China. Vertebrata PalAsiatica 45(1): 37-42.
Meyer H von 1847–55. Die saurier des Muschelkalkes mit rücksicht auf die saurier aus Buntem Sanstein und Keuper; pp. 1-167 in Zur fauna der Vorwelt, zweite Abteilung. Frankfurt.
Nosotti S 2007. Tanystropheus longobardicus (Reptilia, Protorosauria: Reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano, Vol. XXXV – Fascicolo III, pp. 1-88
Peyer B 1931. Tanystropheus longobardicus Bass sp. Die Triasfauna der Tessiner Kalkalpen. Abhandlungen Schweizerische Paläontologie Gesellschaft 50:5-110.
Renesto S 2005. A new specimen of Tanystropheus (Reptilia Protorosauria) from the Middle Triassic of Switzerland and the ecology of the genus. Rivista Italiana di Paleontologia e Stratigrafia vol. 111, no. 3, 377–394. online pdf
Wild R 1973. Die Triasfauna der Tessiner Kalkalpen XXIII. Tanystropheus longobardicus (Bassani) (Neue Ergebnisse). – Schweizerische Paläontologische Abhandlungen 95: 1-16.

wiki/Tanystropheus

A New Nose for Herrerasaurus

A new nose for Herrerasaurus

Figure 1. A new nose for Herrerasaurus, courtesy of DGS (digital graphic segregation, see below) and Digimorph. The original restoration of the premaxilla (lower right) represents a crack in the maxilla. Click for more info on Herrerasaurus.

The original reconstruction of the Herrerasaurus (Reig 1963) rostrum (Fig. 1)  included a very large post-narial process of the premaxilla, which wasn’t there. That “suture” was a crack in the maxilla.

The skull of Herrerasaurus

Figure 1. The skull of Herrerasaurus with color overlays delineating select bones. Note the post-narial expansion of the nasal and the reduced post-narial process of the premaxilla. An enlarged post-narial premaxilla does not appear until Daemonosaurus at the base of the Phytodinosauria.

What Drew My Attention
No dinosaur sister taxa had such a large post-narial process of the premaxilla. Not until Daemonosaurus, at the base of the Phytodinosauria, does the post-narial process of the premaxilla expand in dinosaurs and then not so much. Moreover, there’s no overlapping of the premaxilla by the nasal in dinos. These two bones meet each other evenly. Also the maxilla commonly overlaps the premaxilla in dinosaurs and this was not reproduced in the original reconstruction.

DGS and Digimorph
To determine the actual sutures, Digital Graphic Segregation turned out to be useful. Digimorph also features Herrerasaurus and it’s worth a look in various views (yaw works nicely), including comparing the left and right sides for confirmation.

Cladistic Analysis
I would not have focused on the nasal if it wasn’t so different from that of other dinosaurs and so similar to the outgroup taxon, a non-dinosaur and a fellow basal archosaur, Gracilisuchus (Romer 1972, Fig. 2.) Trialestes (Reig 1963) nests between these two, but the nasal area in question is missing in the one and only specimen. Note the many shared traits of Gracilisuchus and Herrerasaurus.

Gracilisuchus nose

Figure 2. Gracilisuchus, a basal archosaur with a very similar nasal bone - and overall a good match overlooked by all prior workers as a sister taxon to Herrerasaurus. Even here the premaxilla does not underlap the nasal. Click for more data.

No Substitute for First-Hand Examination?
This plesiomorphic nose detail on Herrerasaurus had been overlooked by all prior workers who published on this specimen. They’ve held the specimen in their hand. Having never seen the fossil except in photos, here’s my contribution.

It’s been said time and again “there’s no substitute for first-hand observation,” but here’s the exception, joining a long list of others (Vancleaveapterosaur wing shapes, etc.) frequently blogged here at PterosaurHeresies.com.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Novas FE 1994. New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto.
Reig OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Sereno PC and Novas FE 1993. The skull and neck of the basal theropod Herrerasaurusischigualastensis. Journal of Vertebrate Paleontology 13: 451-476. doi:10.1080/02724634.1994.10011525.

wiki/Herrerasaurus
wiki/Sanjuansaurus