Celebrating 300 Taxa in the Large Reptile Tree

Science is all about constants.  
The evolution of reptiles has been set in stone (literally). What we’re looking for now is a constant model that reconstructs that family tree with clues provided by the fossils we know …and how well we know them. We want to remove all the former mystery from this pursuit. After all, it is 2012. Everything else has been figured out by now…why not the reptile?

So when the taxon list in the large reptile tree rises to 300, as it just did, its worth a look to see what changes have occurred. (It’s a milestone, after all).

First of all, nothing earth-shattering.
In fact, none of the new taxa have changed the tree topology (= original order (going back several tree generations)). This tree continues to grow in good health, becoming fuller as more leaves and nodes are added. All sisters continue to look alike, which is the key after all. That’s how evolution works. Descendants look like ancestors. Sisters look like sisters. In the large reptile tree former enigmas have been nested. Mistaken nestings created by smaller earlier and concurrent studies have been rectified. Additional taxa have been added without changing the tree topology. No other study on reptile relations can claim the same certainty and consistency.

I believe we have a very good tree here.
And I’m looking forward to the next milestones at 350 and 400 taxa (so far not counting the pterosaurs nor the therapsids). The present tree provides several tests of relationships, of bone identities and of sutures vs. cracks. Errors have been acknowledged and repaired. Oversights have been reexamined. Hopefully we all will never rest on our laurels, traditions or paradigms. I look forward to making changes, but only if it gets us closer to modeling more accurately the actual reptile family tree.

Keep those discoveries coming! 
And as I mentioned earlier, if ANYONE finds two taxa in the large reptile tree that should not be sisters, please bring these to my attention. So far no one has despite some earlier comments. If there are any mismatches, please let me know.

We’ll talk about it.

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Tapejara (Pterosaur) Growth Pattern

The traditional paradigm is that pterosaurs experienced allometric growth, like mammals, birds and crocodilians. If so the rostrum should be shorter and the eye sockets (orbits) should be proportionally larger.

The heretical view holds that pterosaurs experienced isometric growth with little proportional differences in embryos, juveniles and adults. Currently this is supported by the evidence of embryos and the few juveniles known, including Ptweety, the Pteranodon Tupuxuara.

Now we have another juvenile, a Tapejara. Here (Fig. 1) the published tracings of the juvenile Tapejara have been enlarged to best fit the adult Tapejara. Here the proportions are virtually identical, with no rostral shortening or orbit enlargement. The main difference is the depth of the nasal and the angle of the jaw.

Tapejara (Pterosaur) growth patterns

Figure 1. Tapejara (Pterosaur) growth patterns demonstrating, once again, isometric growth in which virtually no proportional differences distinguish juveniles from adults. In grey, the juvenile to scale with an adult. Overlay, the juvenile enlarged to the size of the adult. The depth of the nasal, over the orbit, appears to be the biggest difference here, but then again we’re dealing with drawings here. Could that nasal be rotated slightly?

Go with the evidence. Don’t follow traditions and paradigms.

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
Eck K, Elgin RA and Frey E 2011.
 On the osteology of Tapejara wellnhoferi KELLNER 1989 and the first occurrence of a multiple specimen assemblage from the Santana Formation, Araripe Basin, NE-Brazil. Swiss Journal of Palaeontology, doi:10.1007/s13358-011-0024-5.
Kellner AWA 1989. A new edentate pterosaur of the Lower Cretaceous from the Araripe Basin, northeast Brazil. Anais da Academia Brasileira de Ciências 61, 439-446.

wiki/Tapejara
wiki/Tupandactylus

A [Formerly] Unknown Tapejarid

The website Pterosaur.net published an image of an “unknown tapejarid” (aka the Rio tapejarid, Fig. 1), which is a largely articulated torso missing most of its ribs and gastralia. Here we’ll try to figure out what sort of tapejarid this torso is.

[Added a day late, I found the paper Sayão and Kellner (2006) that describes this specimen, MN 6588-V. Apologies. Still the authors were not able to identify it. ]

In situ tracing of the unknown "Rio" tapejarid from Pterosaur.net

Figure 1. In situ tracing of the unknown “Rio” tapejarid MN 6588-V from Pterosaur.net

I was surprised to see this image published as “unknown.” Here we’ll try to lend a hand in identifying this headless specimen.

The 'Rio' tapejarid reconstructed.

Figure 2. The ‘Rio’ tapejarid reconstructed. The overall size, the length of the torso and the distinctly narrow neck on the postacetabular process of the ilium all indicate affinity with Tapejara. Prepubes are rare in this clade, so good to see them here, with a shape distinct from cousin Huaxiapterus.

A Probable Tapejara
The elongated torso, the shape of the posterior ilium and the overall size indicate a close affinity with Tapejara in lieu of a phylogenetic analysis. As in other tapejarids, the relatively short coracoids produce a “bottom decker” wing attachment to the torso in which the wing attached relatively lower on the torso. The prepubes were robust with a relatively short stem and tiny perforation. The anterior ilium was quite gracile.

The Tapejaridae

Figure 1. Click to enlarge and see the unknown tapejarid (Not shown here) to scale with the others. This is the Tapejaridae, including Sinopterus, Huaxiapterus, Tapejara, Tupandactylus, Tupuxuara and Thalassodromeus

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
Eck K, Elgin RA and Frey E 2011. On the osteology of Tapejara wellnhoferi KELLNER 1989 and the first occurrence of a multiple specimen assemblage from the Santana Formation, Araripe Basin, NE-Brazil. Swiss Journal of Palaeontology, doi:10.1007/s13358-011-0024-5.
Kellner AWA 1989. A new edentate pterosaur of the Lower Cretaceous from the Araripe Basin, northeast Brazil. Anais da Academia Brasileira de Ciências 61, 439-446.
Sayão JM and Kellner AWA 2006. Novo esquelito parcial de pterossauro (Pterodactyloidea, Tapejaridae) do membro Crato (Aptiano), Formação Santana, Bacia do Araripe, Nordeste do Brasil. Estudos Geológicos 16(2):16-40.

wiki/Tapejara

Doin’ the “Pterosaur Walk”

A man acting like a pterosaur on the beach

Figure 1. Man acting like a pterosaur on the beach with ski poles (click for blogspot). Note the vertical backbone and ski poles contributing to stability, not thrust. His mate (or daughter) is walking bipedally.

Footprints from around the world tell us that pterosaurs of all sizes walked on prehistoric beaches. Today we have two competing configurations hypothesizing how pterosaurs did this. I like the configuration demonstrated above (Fig. 1) and it is supported by matching tracks to trackmakers, following the thrust vectors and considering methods by which pterosaurs might launch themselves into the air.

The traditional and majority view (Bennett 1997, Fig. 2) posits that the backbone was nearly horizontal and the fingers impressed the sediment far ahead of the shoulders (Fig. 1). This has been criticized here and here on several grounds.

Walking pterosaur according to Bennett

Figure 1. Click to animate. Walking pterosaur according to Bennett 1997. Note the forelimbs provide no forward thrust, but merely act as props.

The heretical minority opinion posits that the backbone was held much more vertically (diagonally) such that the toes impressed beneath the center of balance while standing, slightly behind while walking (as in humans, Fig. 2) and that the fingers impressed much closer to the center of balance – when they could (in Pteranodon, for instance, they could not).

Pterodactylus walk matched to tracks according to Peters

Figure 2. Click to animate. Plantigrade and quadrupedal Pterodactylus walk matched to tracks. Note the more vertical backbone and the forelimbs not contributing thrust to locomotion, only stability.

Otherwise the fingers did NOT contribute thrust to forward progression while walking. In this pose pterosaurs could merely lift their ski-pole like arms to launch themselves bipedally. Such a pose also follows from bipedal ancestry and a secondary acquisition of a quadrupedal pose as demonstrated, among other traits, by a backward-pointing finger #3.

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
Bennett SC1997. Terrestrial locomotion of pterosaurs: a reconstruction based on Pteraichnus trackways. Journal of Vertebrate Paleontology, 17: 104–113.

Mesosaurus Mistake?

The recent interpretation of a lateral temporal fenestra in Mesosaurus (Piñeiro et al. 2012, Fig. 1) was accompanied by a new interpretation of the premaxilla/maxilla suture. Added to this problem, the published restorations of the Mesosaurus skull in lateral and dorsal views don’t match (Fig. 1). Note the shifting of the fenestrae among other sutural changes.  Unfortunately, no sister taxa have the premaxilla/nasal configuration that Piñeiro et al. (2012) propose.

Mesosaurus skull with lateral temporal fenestra.

Figure 1. Mesosaurus skull with lateral temporal fenestra. From Piñeiro et al. 2012. Note the many differences in bone shape not attributable to the two distinct views. More rigorous attention would have aligned the fenestra and sutures in both views of these apparently freehand sketches.

Mesosaurus skull reconstructed based on data from Modesto (2006).

Figure 2. Mesosaurus skull reconstructed based on data from Modesto (2006).

Modesto
had it right.

Modesto (2006) delineated and identified the premaxilla and nasal of Mesosaurus (Fig. 2) and these sutures also agree with those of sister taxa, as recovered by the large reptile tree. With or without the skull, mesosaurs don’t shift within the tree.

Rostrum of Mesosaurus (dorsal view).

Figure 3. New tracings of the Piñeiro et al. (2012) rostral skull of Mesosaurus. On the left the bones are colored in the new interpretation. At right blue indicates published interpretation of nasals, unlike those of any other sister.

The split or separation of the nasals seen in thalattosaurs and sauropterygians (by convergence) has its origin in mesosaurs. In these taxa the elongated premaxilla contacts (sometimes just barely) the frontals. In ichthyosaurs, like wumengosaurs and mesosaurs, the premaxilla does not contact the frontals. Even so, it does split the nasals at least anteriorly.
Don’t Forget the von Huene (1940) Interpretation.
von Huene (1940) spent a considerable amount of time examining several Mesosaurus specimens and he was the first to interpret a lateral temporal fenestra (Fig. 4). He also interpreted nasals extending anteriorly a short distance beyond the nares as in the Piñeiro (2012) interpretation.

Almost overlooked, von Huene’s interpretations of the rostrum are much narrower than those of Piñeiro et al. (2012) indicating some variation in the specimens they were looking at. Certainly these are distinct species. Perhaps distinct genera?

Mesosaurus according to von Huene 1940.

Figure 4. Mesosaurus according to von Huene 1940. Color added to nasals in blue and premaxilla in yellow. This interpretation of the premaxilla/nasal suture matches that of Piñeiro et al. (2012).

Which is Correct?
Neither Piñeiro et al. (2012) nor von Huene (1940) compared their specimens to sisters recovered by the large reptile tree in which the premaxilla bisects the nasals. The image below is recolorized from Piñeiro (2012) showing two interpretations: 1) a longer premaxilla and 2) a possible interdigitating nasal and premaxilla. Hard to say given the data (Fig. 2).

Two reinterpretations of the premaxilla/nasal suture in a recolorized restoration of Mesosaurus

Figure 5. Two reinterpretations of the premaxilla/nasal suture in a recolorized restoration of Mesosaurus by Piñeiro et al. (2012). See Fig. 1 for the original. Also more squamosal has been restored on one side. It is not only possible, but likely that there is variation in several aspects of Mesosaurus from quarry to quarry and from species to species.

What’s Interesting
Here you see variation in interpretation between three paleontologists (one being the Piñeiro team). Look around and you’ll see the maxilla extends beyond mid orbit in two interpretations, but not the Modesto (2004) one. The tooth count differs in all three. The rostral proportions differ. The lateral temporal fenestra differs. The premaxilla/nasal suture differs. The frontal/nasal suture differs. Granted, they are not all looking at the same specimens. And now you can see why it is so important in phylogenetic analysis to use specimens for taxa, even if incomplete.

The Good Thing Is…
Mesosaurus will never again be lumped with basal anapsids like pareiasaurs and captorhinids. Hopefully…

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
Gervais P 1865. Du Mesosaurus tenuidens, reptile fossile de l’Afrique australe. Comptes Rendus de l’Académie de Sciences 60:950–955.
Laurin M and Reisz RR 1995. 
A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society 113:165-223.
Modesto SP 1999. 
Observations on the structure of the Early Permian reptile Stereosternum tumidum Cope. Palaeontol. Afr. 35, 7–19.
Modesto SP 2006. The cranial skeleton of the Early Permian aquatic reptile Mesosaurus tenuidens: implications for relationships and palaeobiology. Zoological Journal of the Linnean Society 146 (3): 345–368. doi:10.1111/j.1096-3642.2006.00205.x.
Modesto SP 2010.The postcranial skeleton of the aquatic parareptile Mesosaurus tenuidensfrom the Gondwanan Permian. Journal of Vertebrate Paleontology 30 (5): 1378–1395. doi:10.1080/02724634.2010.501443.
Piñeiro G, Ferigolo J, Ramos A and Laurin M 2012.
 Cranial morphology
of the Early Permian mesosaurid *Mesosaurus tenuidens* and the evolution of
the lower temporal fenestration reassessed. Comptes Rendus Palevol.
von Huene F 1941. Osteologie und systematische Stellung von Mesosaurus. Palaeontogr. Abt. A. 92, 45–58.

“Protopterosaurus” – still the official poster child for pterosaur ancestry

Wild 1984 had just finished describing the first Triassic pterosaurs when he proposed a hypothetical pterosaur ancestor (Fig. 1) that was re-illustrated by Wellnhofer (1991) in his famous pterosaur encyclopedia. Today, nearly 30 years later, most pterosaur experts are still crossing their fingers, hoping for just such a creature to appear in the fossil record, having dismissed and rejected (Hone and Benton 2007, 2008) several actual candidates proposed by Peters (2000), now some 12 years ago, and supported by a greatly expanded phylogenetic analysis here.

"Protopterosaurus" t

Figure 1. “Protopterosaurus” the hopeful hypothetical ancestor of pterosaurs created by Wild (1984) and supported by Wellnhofer (1991). Not sure why the tail was so thick and the hind limbs were so short. Cosesaurus demonstrates that the flying membrane aft of the forelimb originated distally, not medially, with a narrow-gauge occasionally bipedal trackway in which pedal digit 5 impressed far behind the other pedal digits, known as Rotodactylus. So, this should be a runner and flapper first, then a tree climber.

So the question is, how well does the hypothetical ancestor stack up against the real McCoys, as determined by phylogenetic analysis? [Think Cosesaurus.] 

And what  would “Protopterosaurus?” be? A lizard or an archosaur?

What is “Protopterosaurus”?
Wild (1984) and Wellnhofer (1991) both illustrated “Protopterosaurus” as an unarmored arboreal quadrupedal reptile with laterally extended limbs and digit 4 the longest on all four digits. Thus it can’t be an archosaur! Hmm. With that morphology it would have nested in the lizard or protorosaur clades with a strong lean toward the former. In several regards “Protopterosaurus” resembled something between Huehuecuetzpalli and Macrocnemus, (the latter Wild was quite familiar with), but with a much thicker tail.

Unfortunately we can’t peer beneath the skin here. “Protopterosaurus” was illustrated ‘in vivo.’

The Head
The naris was displaced from the tip of the snout in “Protopterosaurus” as in fenestrasaurs, not archosaurs. The naris preceded a depression, presumably an antorbital fenestra, as in Cosesaurus and archosaurs. The snout was pointed in both dorsal and lateral views (more like Cosesaurus). The eyes were raised above the midline of the back of the skull, probably due to a deep jugal. That’s not duplicated in any candidate, all of which had a larger orbit expanded nearly to the jawline, with a very shallow jugal.  The retroarticular process extended far behind the cranium, producing an anteriorly leaning quadrate. Likewise, that is not found in any candidate except, perhaps, Jesairosaurus.

The Neck, Torso and Tail
The cervical series in “Protopterosaurus” was as long as the skull and the neck was robust, as in most candidates. No S-curve was given to the dorsal series. No armor was present either. The caudals must have been provided with wide transverse processes and deep chevrons as the tail is illustrated to be thick and meaty, like that of most archosaurs and lizards — and unlike the tritosaurs and fenestrasaurs, including pterosaurs, all of which had a very thin bony tail.

The Appendices
The forelimbs of “Protopterosaurus” extended laterally with fingers of increasing length laterally, especially digit 4, which was as long as the humerus+ulna. Cosesaurus had fingers 3 and 4 virtually subequal when it developed a prepubis, pteroid, a locked down coracoid, sternal complex, membranes and an antorbital fenestra. So the flight digit came later, in Longisquama. Finger 5 was a vestige in “Protopterosaurus“. Finger 5 in reality was always short, but did not become a vestige until the pterosaur stage. The metacarpals of “Protopterosaurus” were illustrated longer medially than laterally, which is not duplicated in any candidate.

The femur was no longer than the humerus in “Protopterosaurus” and the tibia was no longer than the femur. These proportions are not found in present candidates, all of which had a longer hind limb than forelimb and relatively larger hind limbs compared to the torso. All candidates, from Scleromochlus to Cosesaurus, have been illustrated as bipeds and narrow-gauge tracks are known for a sister to Cosesaurus. Thus the lateral limbs and belly down configuration are not duplicated in any candidate. The foot in “Protopterosaurus” was about the length of the tibia, which is correct. Pedal digit 5 extended no further than p4.1 or p4.2, which is also correct with regard to Cosesaurus. Scleromochlus and its sisters had a vestige to no pedal digit 5, which essentially removes them from pterosaur sisterhood candidacy.

Soft Tissue
Flying squirrel-like membranes in “Protopterosaurus” extended from finger 4 to the knee, remaining shallow until reaching the elbow. Current evidence (Peters 2009) indicates that membranes developed distally first, just the opposite of the hypothetical traditional model. Current evidence indicates that flapping as a secondary sexual behavior also preceded gliding, so “Protopterosaurus” had it backwards. Minor membranes appear in “Protopterosaurus” behind the acetabulum and a propatagium (strangely without a pteroid and preaxial carpal) appeared in front of the forelimb. We know Cosesaurus had a pteroid and preaxial carpal (Peters 2009), but no propatagium is known in relation to it.

Wellnhofer (1991) considered the development of wing membranes as an aid in falling, parachuting and surviving, then in gliding to expand the range of escape and exploitation. Last to develop would be the enlarged sternum and pectoral girdle to add thrust to gliding. This is the opposite of what actually happened, as reported earlier and demonstrated in Cosesaurus, which used flapping as a secondary sexual behavior after becoming bipedal.

So, the imagined creature, “Protopterosaurus,” had many traits later found in the actual ancestors of pterosaurs, but missed several others. Not sure why current studies in pterosaur ancestry are not at least considering the possibility that fenestrasaurs and tritosaurs are good candidates for this honor. The first PhD to do so will be much less embarrassed by the last twelve years than the last PhD to do so will be.

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
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Wild R 1984.  
A new pterosaur (Reptilia, Pterosauria) from the Upper Triassic (Norian) of Friuli, Italy. Gortania Mus Friulano Stor Nat 5: 45-62.
Wellnhoffer P 1991.  The Illustrated Encyclopedia of Pterosaurs. London: Salamander. 192 pp.

Pterosaurs landing in trees – part 3 – Longisquama

Earlier we demonstrated pterosaurs grappling tree trunks and perching on tree branches. Today we’ll report on the origin of this behavior in Longisquama (Fig. 1).

Figure 1. Longisquama on a tree trunk.

Figure 1. Longisquama on a tree trunk.

My What Long Fingers You Have Grandma!
The origin of tree clinging likely occurred in sister to Longisquama, the current outgroup for the Pterosauria. The fingers of Longisquama were larger than those of any pterosaur. Fingers one through three and five became smaller as the wing finger, #4, became larger.

The PILs Have Something to Say
In Longisquama the PILs of manual digit 4 were not aligned with those in digits 1-3. This indicates they no longer worked as a set and that metacarpal 4 + digit 4 likely were rotated into the plane of the wing, as in pterosaurs. This means, like pterosaurs, Longisquama was able to flex (or hyperflex) digit 4 in the plane of the wing and while clinging to trees, the wing would have created yet one more display trait, opening and closing tangential to the diameter of the tree trunk. Pterosaurs emphasized the wings and de-emphasized the dorsal frill.

Short Arms
The relatively short arms of Longisquama meant that the long legs had to crouch more, which created a pre-loaded spring ready to release for the next leap/glide. The arms lengthened in pterosaurs.

Finger 4 – Not Quite Ready for Flight, but Great Looking!
Before finger 4 became large enough to support gliding and flapping flight it served as yet ANOTHER decoration on Longisquama, already at no shortage for display traits. As in pterosaurs, finger four was free to flex in the plane of the wing, on a tangent to the diameter of the tree (Peters 2002). I did not realize at the time of that publication how large the fingers of pterosaur predecessors, like Longisquama, had become.

New discoveries bring new insights.

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
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.