PIMUZ T 2477: not quite Macrocnemus, despite appearances

Updated August 12, 2020
with a new figure 3 which shows the new position of the quadratojugal repaired in figure 2. Apologies for the oversight.

In summary: Miedema et al. 2020 decided not to include
a phylogenetic analysis (e.g. Fig. 1) and so make several mistakes as they describe a µCT scanned specimen (Fig. 2, 3) that turned out to be not quite Macrocnemus (Fig. 1), even though it looks just like one.

Figure 1. Subset of the LRT with the addition of the PIMUZ 2477 specimen.

Figure 1. Subset of the LRT with the addition of the PIMUZ 2477 specimen.

Miedema et al. 2020
take a look at the PIMUZ T 2477 specimen they assigned to Macrocnemus bassani (Figs. 1-4). When added to the large reptile tree (LRT, 1712+ taxa; subset Fig. 1) the PIMUZ T 2477 specimen nested closer to Dinocephalosaurus, next to the clade of Macrocnemus specimens.

Worse yet,
Miedema et al. 2020 promoted a traditional myth, that tanystropheids, like Macrocnemus, were archosauromorphs without testing lepidosaurs. The LRT tests both clades and Macrocnemus nests with lepidosaurs like Huehuecuetzpalli (Fig. 3) despite sharing many convergent traits with the very similar (by convergence) archosauromorph, Prolacerta.

Figure 2. The PIMUZ T 2477 specimen wrongly traditionally assigned to Macrocnemus.

Figure 2. The PIMUZ T 2477 specimen wrongly traditionally assigned to Macrocnemus. Some corrections and repairs  noted. The left maxilla tracing does not match the left maxilla µCT scan.

The palate was restored differently here
than in Miedema et al. 2020 (Fig. 2). So was the prefrontal.

Figure 1. Several Macrocnemus specimens to scale alongside the ancestral taxon in the LRT, Huehuecuetzpalli, and descendant taxa in the LRT, including Cosesaurus and the fenestrasaurs Sharovipteryx, Longisquama and Bergamodactylus. The similarities in transitional taxa should be obvious.

Figure 3. Several Macrocnemus specimens to scale alongside the ancestral taxon in the LRT, Huehuecuetzpalli, and descendant taxa in the LRT, including Cosesaurus and the fenestrasaurs Sharovipteryx, Longisquama and Bergamodactylus. The similarities in transitional taxa should be obvious.

Epipterygoid
“An elongate rod-like element is present underneath the basioccipital and parabasisphenoid in PIMUZ T 2477 (confirming earlier findings here). In this constellation, the rod-like part of the element extends dorsally along the anterior part of the prootic as in all extant Squamata.”

We looked at epipterygoids found in tritosaurs earlier here.

Ontogenetic stage of PIMUZ T 2477
“The smallest specimen, and so far, the only specimen considered a juvenile, MSNM BES SC 111, is slightly smaller in cranial length than PIMUZ T 2477 (ca. 38 mm and ca. 42 mm respectively).”

Not true. Phylogenetic analysis indicates no juveniles are known, only small adults. The BES SC 111 specimen is close to even smaller langobardisaurs, cosesaurs and pterosaurs.

“Juvenile specimens have relatively larger orbits and relatively larger crania compared to adults.”

Not true. Several tritosaurs known from juveniles and adults demonstrate isometric growth.

It is so important to start your study
with a phylogenetic analysis. Lacking an analysis Miedema et al. had no idea that

  1. their specimen did not nest with Macrocnemus
  2. their specimen was closer to Dinocephalosaurus
  3. that all such taxa were lepidosaurs (Peters 2007) in a new clade, the Tritosauria
  4. that no tanystropheids were archosauromorphs
  5. that no known Macrocnemus specimens were juveniles

These are the traditional problems
that come from students following their traditional professors and traditional textbooks, rather than finding out for themselves using phylogenetic analysis. Testing all the specimens as individual taxa is so important as we learned earlier regarding Dorygnathus, Rhamphorhynchus, Pteranodon and many other pterosaurs.

Once again the curse of Chris Bennett
ripples out. Several years ago a rejected paper on the Tritosauria (online at Researchgate.net) could have been cited, but Chris Bennett once told me, “You will never be published, and if you are published, you will not be cited.”

Postscript: 
In March 2020 O’Connor et al. produced a specimen, Oculudentavis, they promoted as an archosauromorph that turned out to be a lepidosaur. This week, under great pressure, the authors retracted their paper. The Miedema authors published the EXACT SAME mistake. Will Miedema et al. have to retract their paper, too? I doubt it. This was not a cover story and there will not be the same sort of pressure on this taxon.


References
Li C, Rieppel O and LaBarbera MC 2004. A Triassic aquatic protorosaur with an extremely long neck. Science 305:1931.
Li Z, Wang W, Hu H, Wang M, Y H and Lu J 2020. Is Oculudentavis a bird or even archosaur? bioRxiv (preprint) doi: https://doi.org/10.1101/2020.03.16.993949
Miedema F, Spiekman1 SNF, Fernandez V, Reumer JWF AND Scheyer1 TM 2020. Cranial morphologyof the tanystropheid Macrocnemus bassanii unveiled using synchrotron microtomography. Nature.com/scientificreports (2020) 10:12412. https://doi.org/10.1038/s41598-020-68912-4
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen, XII. Macrocnemus bassanii Nopcsa. Abh. Der Schweizierischen Palaeontologischen Gesellschaft LIX (1937).
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.

https://www.researchgate.net/publication/328388754_A_new_lepidosaur_clade_the_Tritosauria

https://www.nature.com/articles/s41598-020-68912-4#article-comments

wiki/Oculudentavis
wiki/Dinocephalosaurus
wiki/Macrocnemus

Another lepidosaur with a big antorbital fenestra

Quick backstory and summary:
Pterosaurs and their Middle Triassic precursors with a big antorbital fenestra are lepidosaurs (LRT 2020, Peters 2007). Macrocnemus is one of those Middle Triassic precursors, but this one is the only one has a large antorbital fenestra…by convergence.

Skull details on this specimen have been overlooked since 2007.
Macrocnemus fuyuanensis (Li, Zhao and Wang 2007; < 1 m in length; GMPKU P3001, Fig. 1), was the first and only member of this genus not considered conspecific by its authors (actually, no two are alike, see Fig. 3). Earlier we looked at the GMPKU specimen. Today the GMPKU specimen enters the large reptile tree (LRT, 1694+ taxa) today nesting with the T2472 specimen from Europe (Fig. 2).

Figure 1. Macrocnemus fuyuanensis (GMPKU-P-3001) in situ and as traced by the original authors, (middle) flipped with colors applied to bones, and (above) bone colors moved about to form a reconstruction. Darker yellow and darker green are medial views of premaxilla and maxilla. Note the long ascending process of the premaxilla and the palatal elements seen through the various openings all overlooked by those with firsthand access to the fossil. Epipterygoids are lepidosaur synapomorphies not present in protorosaurs.

Figure 1. Macrocnemus fuyuanensis (GMPKU-P-3001) in situ and as traced by the original authors, (middle) flipped with colors applied to bones, and (above) bone colors moved about to form a reconstruction. Darker yellow and darker green are medial views of premaxilla and maxilla. Note the long ascending process of the premaxilla and the palatal elements seen through the various openings all overlooked by those with firsthand access to the fossil. Epipterygoids are lepidosaur synapomorphies not present in protorosaurs.

This referred GMPKU specimen was brought to mind
when Scheyer et al. 2020 discussed in detail the larger holotype M. fuyuarnensis with the skull preserved in ventral view (IVPP V15001, Fig. 4). Scheyer et al. 2020 mistakenly considered it an archosauromorph due to taxon exclusion. Jiang et al. mistakenly considered it a protorosaurian due to taxon exclusion.

All prior workers also overlooked the twin epipterygoids
in the referred specimen (Fig. 1). This is a trait not found outside the Lepidosauria and is lost in several subclades of the Lepidosauria (e.g. Fenestrasauria).

All prior workers overlooked the tiny supratemporals,
which are easy to overlook unless you are looking for them based on phylogenetic bracketing. Taxon exclusion is, once again, the chief problem here. A poor tracing (e.g. Li et al. 2007; Jiang et al. 2011) is the secondary problem.

Figure 2. M. fuyuanensis GMPKU-P-3001 overall. This specimen nests with T2472 in figure 3.

Figure 2. M. fuyuanensis GMPKU-P-3001 overall. This specimen nests with T2472 in figure 3.

The antorbital fenestra
was previously (Li et al. 2007; Jiang et al. 2011) and recently (Scheyer et al. 2020) overlooked because earlier workers considered palatal bones to be rostral bones. That is repaired here (Fig. 1) using DGS methods.

Figure 1. Several Macrocnemus specimens to scale alongside the ancestral taxon in the LRT, Huehuecuetzpalli, and descendant taxa in the LRT, including Cosesaurus and the fenestrasaurs Sharovipteryx, Longisquama and Bergamodactylus. The similarities in transitional taxa should be obvious.

Figure 3. Several Macrocnemus specimens to scale alongside the ancestral taxon in the LRT, Huehuecuetzpalli, and descendant taxa in the LRT, including Cosesaurus and the fenestrasaurs Sharovipteryx, Longisquama and Bergamodactylus. The similarities in transitional taxa should be obvious.

The larger holotype IVPP V15001 specimen
(Fig. 4) preserves the skull upside down (mandible in ventral view). Other elements clearly show the pectoral girdle, pelvic girdle, manus and pes and other elements, more or less in articulation. These are typically scattered in European fossils of Macrocnemus.

Figure 7. The IVPP V15001 specimen of Macrocnemus fuyuanensis in situ. Colors and reconstructions added. Some disagreement here with the pectoral elements.

Figure 4. The IVPP V15001 specimen of Macrocnemus fuyuanensis in situ. Colors and reconstructions added. Some disagreement here with the pectoral elements. Note how the coracoids slide along the interclavicle bound by the sternum reidentified here from the original coracoid. The skull and mandibles are in the center in ventral view.

For those who forget how important the pectoral girdle is
in Macrocnemus and its descendants, others of you might remember the migration of the sternum to the interclavicle, the erosion if the anterior coracoid rim, the elongation of the scapula, the wrapping of the clavicles and the development of the anterior process of the interclavicle that gradually evolves to become the sternal complex in pterosaurs and their flapping precursors, the fenestrasaurs (Fig. 5). This is why it is vitally important to include more taxa in your analyses in order to keep the specimen you are describing in a proper phylogenetic context. All prior workers who studied Macrocnemus lack this context.

Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

Figure  5. Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

The Tritosauria (“third lizards”)
is a new squamate clade, now all extinct. The Tritosauria flourished in the Triassic, was reduced to only the Pterosauria during the Jurassic and Cretaceous, and became extinct thereafter. Several members have an antorbital fenestra, most in the lineage of pterosaurs. The GMPKU specimen has an antorbital fenestra convergent with those taxa.

In 2020 pterosaur experts
still have not presented a better hypothesis for the origin of pterosaurs, but prefer to follow their professors who taught them pterosaurs belong with dinosaurs (e.g. Avemetatarsalia, Ornithodira). When will the first one of them break away from promoting this myth?


References
Jiang D-Y, Rieppel O, Fraser NC, Motani R, Hao W-C, Tintori A, Sun Y-L and Sun Z-Y 2011. New information on the protorosaurian reptile Macrocnemus fuyuanensis Li et al., 2007, from the Middle/Upper Triassic of Yunnan, China. Journal of Vertebrate Paleontology 31: 2011-1237, DOI:10.1080/02724634.2011.610853
Li C, Zhao L and Wang L 2007.
A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Sci China Ser D: Earth Sci, 50(11): 1601–1605.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Scheyer TM, Wang W, Li C, Miedema F and Spiekman SNF 2020. Osteological re-description of Macrocnemus fuyuanensis (Archosauromorpha, Tanystropheidae) from the Middle Triassic of China. Vertebrata PalAsiatica. DOI: 10.19615/j.cnki.1000-3118.200525

wiki/Macrocnemus

A pre-Cosesaurus: the BES SC111 specimen

Earlier
here and here we looked at the pterosaur traits found in the lepidosaur tritosaur fenestrasaur, Cosesauru aviceps (Fig. 1).

Today
let’s look at Cosesaurus traits found in the more primitive BES SC 111 specimen (Fig. 1) traditionally assigned to the larger set of specimens traditionally attributed to Macrocnemus (Fig. 2).

Traditional paleontologists
consider the BES SC111 specimen a juvenile based on its size and short rostrum relative to other Macrocnemus specimens. The large reptile tree (LRT, 1412 taxa) nests the BES SC111 specimen apart from Macrocnemus, basal to Langobardisaurus + Fenestrasauria. Since tritosaurs mature isometrically, juvenile Macrocnemus specimens should have adult proportions, but none are known at present.

Phylogenetic miniaturization
produce smaller tritosaur specimens with a shorter rostrum via neotony. Rather than juvenile traits, late stage embryo (= pre-hatchling) traits are retained into adulthood. Phylogenetic bracketing indicates the BES SC111 specimen was close to adult size.

Figure 1. The BES SC111 specimen attributed to Macrocnemus compared to Cosesaurus, the taxon transitional to pterosaurs. See text for detais.

Figure 1. The BES SC111 specimen attributed to Macrocnemus compared to Cosesaurus, the taxon transitional to pterosaurs. See text for detais.

Traits shared in the BES SC111 specimen and Cosesaurus:

  1. The skulls are virtually identical, including orbit size, antorbital fenestra, tooth size
  2. Torsos quite similar, both with many more gastralia than in ancestors
  3. Tail attenuated
  4. Interclavicle cruciform
  5. Sternum present
  6. Clavicles short, relatively straight and robust
  7. Scapula with longer posterior process (even longer in Cosesaurus)
  8. Metacarpal 4 is the longest, so is manual digit 4
  9. Ilium anterior process present (longer in Cosesaurus)
  10. Prepubis present (larger in Cosesaurus)
  11. Metatarsal 4 is the longest, so is pedal digit 4
  12. Metatarsal 5 is short
  13. Pedal 1.1 is elongate (longer in Cosesaurus)

Derived traits in Cosesaurus relative to BES SC111

  1. Overall smaller in Cosesaurus (neotony)
  2. Epipterygoid absent in Cosesaurus (neotony)
  3. Shorter neck in Cosesaurus (neotony)
  4. 5 sacrals in Cosesaurus (3 in BES SC111)
  5. Sternal complex in Cosesaurus with shifted elements
  6. Coracoid reduced to a curved stem in Cosesaurus (neotony, less ossification)
  7. Hand much larger in Cosesaurus (slightly longer than antebrachium)
  8. Centrale bones migrate to become preaxial carpal and pteroid in Cosesaurus
  9. Thyroid fenestra absent in Cosesaurus
  10. Pedal unguals rounded in BES SC111 
Tanystropheus and kin going back to Huehuecuetzpalli.

Figure 2. Tanystropheus and kin going back to Huehuecuetzpalli. Cosesaurus is not shown here (see figure 1).

Due to convergence,
adding taxa is, perhaps, the only way to split protorosaurs (= prolacertiformes) from tritiosaurs. Make sure you add Huehuecuetzpalli (Fig. 2) to any such analysis.

Figure 3. BES SC111 pectoral region. Colors correspond to figure 1.

Figure 3. BES SC111 pectoral region. Colors correspond to figure 1. The left scapula(?) is incomplete. The interclavicle and sternum are largely hidden beneath the vertebrae. Not sure what that elliptical bone is at upper left and blue. It may be two.

The shifting of pectoral elements
from Huehuecuetzpalli to pterosaurs was detailed earlier here and here.

Figure 4. BES SC111 pelvic region. Colors correspond to those in figure 1. Note the tiny blue prepubes.

Figure 4. BES SC111 pelvic region. Colors correspond to those in figure 1. Note the tiny blue prepubes.

Several indicators of bipedal ability
are present in the BES SC111 specimen, as in the extant Chlamydosaurus kingii.

  1. Elongate ilium anterior process
  2. More than two sacral vertebrae
  3. Prepubes + stiff belly (more gastralia)
  4. Attenuated tail
  5. Elongate cervicals
Figure 6. Green iguana demonstrating the curling of pedal digit 5 in tendril-toed arboreal lepidosaurs, as hypothesized in the BES SC111 specimen and pterosaurs.

Figure 5. Green iguana demonstrating the curling of pedal digit 5 in tendril-toed arboreal lepidosaurs, as hypothesized in the BES SC111 specimen and pterosaurs.

Cosesaurus and Rotodactylus, a perfect match.

Figure 5. Cosesaurus and Rotodactylus, a perfect match. Elevate the proximal phalanges along with the metatarsus, bend back digit 5 and Cosesaurus (left) fits perfectly into Rotodactylus (right).

The curling of pedal digit 5
in the Rotodactylus trackmakers (Fig. 6) is a lepidosaur trait (Fig. 5) carried to extremes in basal pterosaurs, like ‘Sauria aberrante’ and Dimorphodon.


References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier 12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. 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.
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Sanz JL and López-Martinez N 1984. The prolacertid lepidosaurian Cosesaurus aviceps Ellenberger & Villalta, a claimed ‘protoavian’ from the Middle Triassic of Spain. Géobios 17: 747-753. 

wiki/Cosesaurus
wiki/Macrocnemus

Cosesaurus vs. Saller 2016

Nobody wants Cosesaurus aviceps to be a pterosaur ancestor.
Everyone in paleo prefers pterosaurs to be closely related to dinosaurs and their last common ancestor, which is, according to Nesbitt 2011, a phytosaur. This is continually ‘proved’ in pterosaur studies by excluding Cosesaurus (e.g. Hone and Benton 2007, 2009; Benton 1999; Nesbitt 2011) and in Cosesaurus studies by omitting pterosaurs (e.g Saller dissertation 2016). Saller 2016 claims to not see pterosaur traits in Cosesaurus (Fig. x). That is because Saller did not include pterosaurs in his analysis.

Whoever is writing the Wikipedia page on Cosesaurus accepts Saller’s freehand interpretation (Fig. 1) and prefers Saller’s refusal to add pterosaurs to his cladogram. We talked about putting metaphorical ‘blinders’ on earlier.

Figure 1. Cosesaurus insitu. No bones are present. This is a natural mold that includes an amorphous blob, a jellyfish, that trapped one foot of this unique specimen.

Figure x. Cosesaurus insitu. No bones are present. This is a natural mold that includes an amorphous blob, a jellyfish, that trapped one foot of this unique specimen. This is about natural size.

Today we’ll take another look
at the tiny mold fossil that is Cosesaurus. It preserves a nearly completely articulated tiny lepidosaur tritosaur tanystropheid fenestrasaur (according to the large reptile tree, LRT, 1401 taxa) so sensitively preserved that it shares the matrix with an amorphous medusa (jellyfish) clearly presented.

Saller (p.148) wrote (Google translated from the original Italian):
“At the base of the orbit there is a depression that has been interpreted as a window  antorbital from Ellenberger (1977) and from Peters, which even distinguishes three antidotal windows (Peters, 2000). While the presence of a depression is certain, the conditions of conservation and the difficulty in identifying the sutures among the various elements makes it difficult to propose one of his own reliable interpretation. If it were really an antorbital window, this circumstance, together with the poor development of the subnarial process of the premaxillary, they would be elements a support of the hypothesis of an affinity with the pterosaurs.” 

Is an antorbital fenestra present in Cosesaurus?
Saller said he saw only a depression. You decide by examining these several pictures of the skull of Cosesaurus in various lighting angles (Fig. 1).

Figure 1. The skull of Cosesaurus traced using DGS methods and lit at various angles. Some of these are negatives of a negative mold, giving a positive view. Saller was not sure about the antorbital fenestra, probably because it is represented by an elevated portion in the mold.

Figure 1. The skull of Cosesaurus traced using DGS methods and lit at various angles. Some of these are negatives of a negative mold, giving a positive view.  See how they change, revealing new details? Black dot is a fossil air bubble. Judge for yourself whether or not you see an antorbital fenestra here. Compare this skull with Bergamodactylus, the basalmost Triassic pterosaur.

We must let Saller 2016 finish his thought (from above):
The analysis of the postcranial skeleton [of Cosesaurus] offers however, very little space for this interpretation.” So, Saller denies or discounts what he sees on the rostrum, because he does not see pterosaur traits in the post-crania. [ Hello, Larry Martin! ] Even so, by not including any pterosaurs in his cladogram, Saller fails to test the possibility that just an antorbital fenestra is enough to make Cosesaurus a transitional taxon basal to pterosaurs.

Don’t drop the ball when you’re just about to make a touchdown.
Was PhD candidate Saller advised to not test pterosaurs in his cladogram? I’d like to find out. 

If the post-crania is Saller’s only anti-pterosaur issue, 
let’s take another look at the various post-cranial pterosaur traits found in
Cosesaurus that Saller did and didnot see. It will help to segregate them using DGS methodology.

Figure 2. Cosesaurus torso and forelimbs. The hot pink stem-like coracoids are found in pterosaurs. So are the strap-like scapula, distinct from the discs found in Macrocnemus. There is a close association of the clavicles, interclavicle and sternum. In pterosaurs this is known as a sternal complex.

Figure 2. Cosesaurus torso and forelimbs. The hot pink stem-like coracoids are found in pterosaurs. So are the strap-like scapula, distinct from the discs found in Macrocnemus. There is a close association of the clavicles, interclavicle and sternum. In pterosaurs this is known as a sternal complex. Note how the humerus disappears when the lighting angle changes. That little sphere is a fossilized air bubble. Yellow frills are feathery, pro-aktintofibrils. 

Some data are hard to ‘see’ even under a microscope.
Some data need to be visually segregated in order to see what is really going on in a fossil. Saller gives no indication that he traced any portion of Cosesaurus for his dissertation. Nor did he create a negative of the negative mold. I can tell you from leaning over a microscope looking at Cosesaurus in Barcelona, it is impossible to comprehend this specimen without creating a positive and using tracings to help simplify and segregate elements on a computer monitor. Saller did not use all the tools at his disposal. Neither did I while writing Peters 2000. Now I know better.

Here (Fig. 2) DGS methods segregate the pectoral elements from the ribs and gastralia. The coracoids have a curved stem, as in the Triassic pterosaur, Bergamodactylus— distinct from the discs in more basal tritosaurs/tanystropheids. The sternum, interclavicle and clavicles are coincident and just about to fuse in Cosesaurus, creating a sternal complex, as in pterosaurs—distinct from more basal tritosaurs/tanystropheids. Saller 2016 did not see this.

Saller reports he did see the strap-like scapulae, distinct from the discs found in Macrocnemus… and even though the pterosaur traits keep adding up by Saller’s own admission, still that was not enough to add pterosaurs to his cladogram. Is this an example of peer-group pressure?

Why does the humerus disappear
when the lighting angle is moved (Fig. 2)? Because it is crushed upon the dorsal vertebrae. Only certain lighting angles reveal the right humerus. Why does it crush so completely? Because it is hollow. Can you name another small Triassic reptile with extremely hollow arm bones?

Figure 3. The pelvis of Cosesaurus with prepubis in green and 5 sacrals, not 2 as Saller interprets the fossil.

Figure 3. The pelvis of Cosesaurus with prepubis in green and 5 sacrals, not 2 as Saller interprets the fossil.

Saller 2016 looked at the pelvis
and reported only two sacrals present, despite the long ilium he noted. There are five sacrals in Cosesaurus. Sacral are added in response to a bipedal stance — needed whenever flapping its arms (remember the stem-like coracoid is the clue to this behavior).

Saller failed to see the prepubes. One is pretty obvious here (Fig. 3 in green), but I missed it, too prior to writing Peters 2000.  Prepubes add anchors for femoral adduction, which happens when the knees are brought closer to the midline, typically for bipedal locomotion.

More pterosaur traits tomorrow. 


Just in time—a pertinent quote from Dr. John Ostrom,
“With the announcement of the first dinosaurs with feathers from China, Ostrom (then age 73) was in no mood to celebrate. He is quoted as saying‘I’ve been saying the same damn thing since 1973, `I said, `Look at Archaeopteryx!’” 


References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier 12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Kellner AWA 2015. Comments on Triassic pterosaurs with discussion about ontogeny and description of new taxa. Anais da Academia Brasileira de Ciências (2015) 87(2): (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690.
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.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. 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
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Saller F 2016. Anatomia, paleobiologia e filogenesi di Macrocnemus bassanii Nopcsa 1930 (Reptilia, Protorosauria). Alma Mater Studiorum – Università di Bologna Dottorato di Ricerca in Scienze della Terra Ciclo XXVII 206pp.
Sanz JL and López-Martinez N 1984. The prolacertid lepidosaurian Cosesaurus aviceps Ellenberger & Villalta, a claimed ‘protoavian’ from the Middle Triassic of Spain. Géobios 17: 747-753.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

wiki/Bergamodactylus
wiki/Cosesaurus

A small, bipedal Macrocnemus: PIMUZ T4823

It’s a bipedal, but folded specimen
with a skull and neck resting against its own spine (like Langobardisaurus).

The PMUZ T4823 specimen
of Macrocnemus (Peyer 1937; Figs. 1, 2) had such short forelimbs that it foreshadowed one of its more famous fully bipedal relatives, Sharovipteryx (Fig. 3). I even wondered if they were somehow sisters, but the LRT said, ‘no’, they were only convergent.

Figure 1. 'Macrocnemus' specimen PIMUZ T4832 in situ. Having the skull and neck bent back against the spine makes this a good problem for DGS to attempt.

Figure 1. ‘Macrocnemus’ specimen PIMUZ T4832 in situ. Having the skull and neck bent back against the spine makes this a good problem for DGS to attempt. Even colorized, this specimen still needs to be unfolded to make proper sense of its morphology and proportions. Photo from Saller 2016.

This specimen is hard to figure out
without unfolding that long neck (Fig. 2). When that happens, using DGS methods, the T4823 specimen starts to make sense. If you’re like me, sometimes the brain just needs to see things in vivo, not as if it was tucked into an eggshell.

Figure 2. 'Macrocnemus' specimen PIMUZ T4832 lifted from the in situ figure 1 at right, and unfolded at left. Not everything is guaranteed correct here, but it's pretty close. At 72 dpi screen resolution, this image is full scale.

Figure 2. ‘Macrocnemus’ specimen PIMUZ T4832 lifted from the in situ figure 1 at right, and unfolded at left. The skull is shown in situ and reconstructed. Not everything is guaranteed correct here,  The lower pelvis is a big guess because the elements may be tucked under the sacrum. At 72 dpi screen resolution, this image is full scale.

The anterior dorsal ribs of the T4832 specimen were also extra long,
perhaps creating a wide, aerodynamic, pancake-like torso, again, as in Sharovipteryx (Fig. 3) or Draco.

Note the five sacrals that helped support this sprawling lepidosaur (according to the LRT) while bipedal.

The pectoral girdle is tiny with small, disc-like coracoids. Thus, the T4832 specimen was not flapping, like Sharovipteryx (Fig. 3).

There was a soft tissue rostral crest. Soft tissue is impressed everywhere else, too.

Like Sharovipteryx, a pair of large hyoids extend neck skin, creating an aerodynamic strake or throat sac.

That is a very slender set of cervicals for such a large skull. Perhaps most of the bone was preserved below the surface. Remember, this is a cast of the destroyed original. In any case, this was a gracile specimen. If like all other Macrocnemus specimens, it had hollow bones, too.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Figure 3. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

This is not the first time
someone has suggested that Macrocnemus was facultatively bipedal. Nopcsa 1931 and Rieppel 1989 thought so, too.

This is not the first time
that a member of the Macrocnemus family became bipedal (Fig. 3). Actually most of the descendants of Macrocnemus were bipedal, whether on land or in the water.

Figure 5. Subset of the LRT focusing on the Tritosauria. Note the separation of one specimen attributed to Macrocnemus.

Figure 5. Subset of the LRT focusing on the Tritosauria. Note the separation of one specimen attributed to Macrocnemus.

Saller writes (translated by Google form Italian):
PIMUZ T4823: cast of the holotype, originally kept at the Civic Museum of Natural History of Milan (Museum Civico de Storia Naturale in Milano) was destroyed during the Second World War. Exemplary in a bad state of  conservation, described by Peyer (Peyer, 1937). Includes skull, neck, trunk, parts of the limbs and the front portion of the tail.”

Rieppel (1989) writes: 
T2473: Specimen “Besano III” (Peyer, 1937). The specimen was collected in the “Sciti bituminous” of Besano and turned over to the Museum Civico de Storia Naturale in Milano after its description by Peyer (1937),, where it was destroyed during World War II. A cast of the specimen is preserved in Zurich. The specimen is fragmentary, but includes a well-preserved hind limb.”

A renumbered specimen?
Rieppel (1989) makes no mention of PIMUZ T 4822, T4823, T4833 or T4834, but his description of the well-known specimen, A III/208. is listed first and matches this description, so it is likely renumbered in Saller 2016,

References
Li C, Zhao L-J and Wang L-T 2007A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Science in China D, Earth Sciences 50(11)1601-1605.
Nopcsa F 1931. Macrocnemus nicht Macrochemus. Centralblatt fur Mineralogie. Geologic und Palaeontologie; Stuttgart. 1931 Abt B 655–656.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen XII. Macrocnemus bassanii Nopcsa. Abhandlung der Schweizerische Palaontologische Geologischen Gesellschaft pp. 1-140.
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Rieppel, O 1989. The Hind Limb of Macrocnemus bassanii (Nopcsa) (Reptilia, Diapsida): Deverlopment and Functional Anatomy. Journal of Vertebrate Paleontology. 9 (4): 373–387.
Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.
Saller F 2016. Anatomia, paleobiologia e filogenesi di Macrocnemus bassanii Nopcsa 1930 (Reptilia, Protorosauria). Alma Mater Studiorum – Università di Bologna Dottorato di Ricerca in Scienze della Terra Ciclo XXVII 206pp.

PIMUZ – Palaeontologisches Institut und Museum, University of Zuerich, Zurigo, Switzerland.

Macrocnemus skull in DGS

This started with
a fuzzy photo of a  complete fossil Macrocnemus specimen, PMR T2472 (Fig 1).

Figure 7. Skull of the T2472 specimen attributed to Macrocnemus. Epipterygoids are displaced to the orbit and anterior orbit region.

Figure 1. Skull of the T2472 specimen attributed to Macrocnemus with higher resolution. Earlier mistakes (below) are corrected here.  Epipterygoids are displaced to the orbit and anterior orbit region.

Figure 1. GIF animation of PMR T2472, a large Macrocnemus in situ and reconstructed from a fuzzy photo.

Figure 1. GIF animation of PMR T2472, a large Macrocnemus in situ and reconstructed from a fuzzy photo.

Many specimens attributed to Macrocnemus
are known, each one a little different phylogenetically. Reports of a ‘juvenile’ Macrocnemus refer to the phylogenetically basalmost and smallest of the known specimens, the one closest to its outgroup taxon, the tritosaur lepidosaur, Huehuecuetzpalli.

It’s good to remind yourself
before reading the reference titles, that Macrocnemus and kin are not protorosaurs (= prolacertiforms), nor are they archosauriforms. Even I made the same mistake (Peters 2000b) in my more naive days before the LRT recovered Macrocnemus and kin as tritosaur lepidosaurs in Peters 2007.

From this rather ordinary taxon arises 
such diverse and exotic taxa as Dinocephalosaurus, Sharovipteryx, a variety of Tanystropheus, several Langobardisaurus, Longisquama and pterosaurs. Peters 2007 reported, “The basal lizard, Huehuecuetzpalli is the most primitive taxon in this newly revealed third squamate clade between Iguania and Scleroglossa. Two branches arise from it. Jesairosaurus is basal to the Drepanosauridae. Three distinct specimens of Macrocnemus give rise to the Tanystropheidae,the Langobardisaurinae and to the Fenestrasauria respectively.” Jesairosaurus and Drepanosauridae are now basal lepidosauriformes.

References
Li C, Zhao L-J and Wang L-T 2007A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Science in China D, Earth Sciences 50(11)1601-1605.
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Nopcsa F 1931. Macrocnemus nicht Macrochemus. Centralblatt fur Mineralogie. Geologic und Palaeontologie; Stuttgart. 1931 Abt B 655–656.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen XII. Macrocnemus bassanii Nopcsa. Abhandlung der Schweizerische Palaontologische Geologischen Gesellschaft pp. 1-140.
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.

wiki/Macrocnemus

 

Another long-necked embryo tritosaur: Li et al. in press

This appears to be
yet another Tanystropheus-like and Dinocephalosaurus-like taxon, yet not closely related to either. Earlier we looked at another similar embryo, still within its mother.

Li, Rieppel and Fraser in press (2017)
bring us a new curled up (as if in an egg, but without a shell) embryo from the Guanling Formation (Anisian), Yunnan province, China (Figs. 1, 2). The specimen is unnamed and not numbered. It appears to combine the large head and eyes of langobardisaurs with the short limbs and many cervical vertebrae of Dinocephalosaurus. Please remember, in this clade, juveniles do not have a short rostrum and large eyes unless their parents also had these traits.

Figure 1. The unnamed and not numbered Triassic embryo Li et al. assign to a new species close to Dinocephalosaurus.

Figure 1. The unnamed and not numbered Triassic embryo Li et al. assign to a new species close to Dinocephalosaurus. At 72 dpi monitor resolution, this image is 2.5x life size. Here bones are colorized, something Li et al. could have done, but avoided. I’m happy to report that the line drawing was traced by Li et al. on their own photo. The two are a perfect match.

Unfortunately
Li et al. have no idea what they’re dealing with phylogenetically. They relied on old invalidated hypotheses of relationships. They report the specimen:

  1.  is a marine protorosaur and an archosauromorph – actually it is a marine tritosaur lepidosaur. Taxon exclusion and traditional bias hampered the opinion of Li et al. They did not perform a phylogenetic analysis.
  2. is closely related to Dinocephalosaurus – actually it is more closely related to the much smaller, but longer-legged Pectodens (Figs. 4, 5). In the large reptile tree (LRT, 1036 taxa) 8 steps are added when the embryo is force-nested with Dinocephalosaurus. The embryo is distinct enough that the new specimen deserves a new genus.
  3. confirms viviparity – probably not (but see below). The specimen is confined within an elliptical shape (Fig. 1), as if bound by an eggshell or membrane, which was not preserved. Perhaps, as in pterosaurs and many other lepidosaurs, the embryo was held within the mother’s body until just before hatching, within the thinnest of egg shells and/or membranes.
  4. is too immature to describe it as a new taxon – not so. Tritosaur lepidosaurs (from Huehuecuetzpalli to Pterodaustro) develop isometrically. Thus, full-term embryos and hatchlings have adult proportions.
Figure 2. The specimen from figure 1 unrolled for clarity. This specimen most closely resembles the basal langobardisaur, Pectodens, not Dinocephalosaurus. Remember, tritosaurs develop isometrically. Embryos closely resemble adults. That's why three scale bars are included.

Figure 2. The specimen from figure 1 unrolled for clarity. This specimen most closely resembles the basal langobardisaur, Pectodens, not Dinocephalosaurus. Remember, tritosaurs develop isometrically. Embryos closely resemble adults. That’s why three scale bars are included. This specimen has feeble limbs but a strong swimming tail, distinct from that of Dinocephalosaurus.

Li et al. report
“In the fossil record only oviparity and viviparity can be distinguished, Ovoviviparity of different intermediate stages, which is often observed in modern squamates would then be referred to the category of viviparity, whatever the stages of maturity and nutritional patterns are.” Yes, they correctly report ovoviviparity in squamates, which are the closet living relatives of tritosaur lepidosaurs. That’s exactly what we have here.

Figure 1. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4.

Figure 3. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4.

Li et al. report,
“[The] skeleton is preserved tightly curled so as to produce an almost perfect circular outline, which is strongly indicative of an embryonic position constrained by an uncalcified egg membrane.”

Figure 2. Pectodens skull traced using DGS techniques and reassembled below.

Figure 4. Pectodens skull traced using DGS techniques and reassembled below. No sclerotic ring here. 

Distinct from Pectodens the new genus embryo has:

  1. 24 cervicals
  2. 29 dorsals
  3. 2 sacrals
  4. and about 64 caudals
Figure 1. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017.

Figure 5. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017. The skull shown here is the original reconstruction. Compare it to figure 4.

Li et al overlooked:

  1. strap-like coracoids, strip-like clavicle and T-shaped interclavicle
  2. scattered manual elements
  3. pelvic girdle
  4. ectopterygoid, jugal, articular, angular, surangular

Li et al. report:
“The fewer cervical vertebrae (24 as opposed to 33 (based on an undescribed specimen kept in the IVPP)), and the presence of sclerotic plates are features inconsistent with Dinocephalosaurus.This embryo therefore documents the presence of at least one additional dinocephalosaur-like species swimming in the Middle Triassic of the Eastern Tethys Sea.

“Scleral ossicles have previously not been described in any protorosaur.”
– but they are common in tritosaur lepidosaurs, like pterosaurs.

Figure 6. Pectodens adult compared to today's embryo and its 8x larger adult counterpart after isometric scaling.

Figure 6. Pectodens adult compared to today’s embryo and its 8x larger adult counterpart after isometric scaling. Looks more like Pectodens than Dinocephalosaurus, doesn’t it? See taxon inclusion WORKS! Sclerotic rings were omitted here to show skull bones. The ring would have had a smaller diameter if if were surrounding a sphere, rather than crushed flat. 

A word to traditional paleontologists:
Don’t keep digging yourself deeper into invalidated hypotheses and paradigms. Use the LRT, at least for options.

Don’t give up on naming embryos
and adding them to phylogenetic analysis, especially if they are tritosaur lepidosaurs. Hatchlings nest with adults so you can used hatchlings in analysis.

Don’t avoid creating reconstructions.
That’s a great way to discover little splinters of bone, like clavicles and coracoids, that would have been otherwise overlooked.

The LRT is here for you.
BETTER to check this catalog prior to submission rather than have your work criticized for being unaware of the latest discoveries or overlooking pertinent taxa AFTER publication.

References
Li C, Rieppel O, Fraser N C, in press. Viviparity in a Triassic marine archosauromorph reptile. Vertebrata PalAsiatica, online here.

Pectodens: basal to tanystropheids and pterosaurs

It’s always good
to see another tritosaur. That’s the lineage that gave rise to a menagerie of taxa, including pterosaurs. That’s a heretical hypothesis of relationships recovered by the large reptile tree (LRT, 997 taxa).

Figure 1. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017.

Figure 1. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017.

Li et al. 2017 conclude:
“A new, small terrestrial tetrapod is described from the Middle Triassic of Yunnan, China. Pectodens zhenyuensis n. gen. n. sp. bears very characteristic elongate teeth forming a comb-like marginal dentition. The elongate cervicals of Pectodens zhenyuensis n. gen. n. sp. with low neural spines together with the morphology of the cervical ribs are features consistent with protorosaurs, such as Macrocnemus. However, the imperforate puboischiadic plate, simple rounded proximal tarsals, and a straight 5th metatarsal are primitive characteristics. Unlike tanystropheids, but in common with Protorosaurus (personal observation, N.C. Fraser, 2013), both lack a thyroid fenestra in the pelvis.”

Figure 2. Pectodens skull traced using DGS techniques and reassembled below.

Figure 2. Pectodens skull traced using DGS techniques and reassembled below. Here a quadratojugal process of the jugal is identified and other parts are assembled with greater accuracy than a freehand sketch (Fig. 1).

Pectodens zhenyuensis (Li et al. 2017; IVPP V18578; Anisian, Middle Triassic; 38cm in length) was originally considered a diapsid and a possible protorosaur. Here Pectodens nests between Macrocnemus and Langobardisaurus (Fig. 3). Originally the interclavicle, sternum and quadratojugal were overlooked.

Note the large orbit, the long metarsal 5 and the perforated pubis. The elongate caudal transverse processes anchor powerful leg muscles.

Occasionally within the Tritosauria
metatarsal 5 is not short, but elongate. It is always axially twisted. The pubis and ischium typically angle away from one another, but sometimes produce a thyroid fenestra. Tritosaurs have a sternum, like many other lepidosaurs do. Protorosaurs do not have a sternum.

Li et al. did not attempt a phylogenetic analysis.
Instead they made educated guesses as to the affinities of Pectodens, overlooking the variation present in related taxa revealed in a cladogram. Pulling a Larry Martin (highlighting or letting yourself get confused by one or two traits) is never a good idea. Better to let hundreds of traits determine the exact nesting of a taxon without bias. Let the taxa nest themselves. Let the convergent traits simply be convergent traits.

Earlier we looked at the pectoral girdle and sternum of Langobardisaurus, Huehuecuetzpalli and other tritosaurs. Pectodens fits right in.

The posterior maxillary teeth in Pectodens
are wider at their base presaging the grinding teeth found in Cosesaurus, basal pterosaurs and Langobardisaurus.

Note the way the fingers and toes
bend anteriorly during use. That’s a lepidosaur trait. Pectodens would have had sprawingling hind limbs given its simple femoral head. Tracks matching such curved toes are known from the Middle Triassic.

Li et al. considered Pectodens to be the first terrestrial taxon
from the its locality. And that’s definitely a probability. However, given that Tanystropheus and others may have been underwater bipedal predators (squid parts were found in their torso), let’s leave open the possibility that Pectodens was maybe dipping its toe in the water.

Figure 1. Subset of the LRT focusing on Tritosauria. Pectodens nests here basal to the Characiopoda (Tanystropheids + Fenestrasauria including pterosaurs).

Figure 1. Subset of the LRT focusing on Tritosauria. Pectodens nests here basal to the Characiopoda (Tanystropheids + Fenestrasauria including pterosaurs).

Let’s not continue to nest tanystropheids
with protorosaurs. Sure they share several traits by convergence, but they are not related to one another as determined by a large gamut analysis, the LRT.

References
Li C, Fraser NC, Rieppel O, Zhao L-J and Wang L-T 2017. A new diapsid from the Middle Triassic of southern China. Journal of Paleontology.7 pp. doi: 10.1017/jpa.2017.12

 

The skull of Litorosuchus in detail

Revised November 17, 2018
with a new nesting for Litorosuchus next to the protorosaur, Jaxtasuchus.

Earlier we looked at Litorosuchus (Li et al. 2016; Figs. 1, 2), a new protorosaur with an antorbital fenestra that was originally considered to be an aquatic basal archosauriform, nesting with the thalattosaur, Vancleavea, which was also considered to be an aquatic basal archosauriform. Unfortunately, neither resembles each other and neither resembles any other archosauriform because they both nest elsewhere in the family tree of reptiles when given the opportunity. Both suffered from academic taxon exclusion.

Figure 1. Litorosuchus skull reconstructed from tracings in figure 2. That antorbital fenestra does not make it an archosaurifom. At least two other clades also produce an antorbital fenestra.

Figure 1. Litorosuchus skull reconstructed from tracings in figure 2. That antorbital fenestra does not make it an archosaurifom. At least two other clades also produce an antorbital fenestra. The gracile temporal bones are in contrast to the robust maxilla and long teeth.

Today,
thanks to M. Mortimer, I have the paper which includes closeups of the skull (Fig. 2). I’ll start off by saying I was able to add or change 36 scores for Litorosuchus with the new data. Many traits were added from the palate.

Litorosuchus nests
the armored aquatic protorosaur, Jaxtasuchus.

Figure 2. Litorosuchus in situ with a new tracing of the inverted and displaced posterior premaxilla with several teeth.

Figure 2. Litorosuchus in situ with a new tracing of the inverted and displaced posterior premaxilla with several teeth.

First of all,
this is an excellent specimen. And virtually all the bones are well exposed enabling the creation of an accurate reconstruction (Fig. 1). Unfortunately, when Li et al. saw an antorbital fenestra they assumed Litorosuchus was related to archosauriformes and so excluded unrelated taxa that also have an antorbital fenestra, like fenestrasaurs and derived protorosaurs. As a result, some bones not found in archosauriformes were ignored originally in Litorosuchus.

  1. The Li et al. lacrimal is actually the medial descending process of the nasal
  2. The Li et al. surangular is actually several posterior mandible bones, including the coronoid, surangular and articular.
  3. The actual lacrimal is a small bone displaced to the middle portion of the right nasal. It is small and somewhat tear-shaped, as in Macrocnemus.
  4. The Li et al. jugal is too deep because part of it includes a slender pterygoid.
  5. The small postfrontal, supratemporal and squamosal were not identified by Li et al. but are indeed present.
  6. A tiny pineal opening is present.
  7. The straight and robust quadratojugal is still firmly attached to the posterior jugal, doubling its length.

This turned out to be
an overlooked opportunity for the Li team, who, unfortunately, restricted their inclusion set to just archosauriforms and their outgroups (plus one by-default nested thalattosaur and two by-default nested pterosaurs).

References
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Nesbitt SJ 2011. The early evolution of archosaurians: relationships and the origin of major clades. Bull Amer Mus Nat Hist 352:1–292.
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.

 

Litorosuchus: an armored protorosaur, not an archosauriform

Revised November 17, 2018
with a new nesting of Litorosuchus with the aquatic, armored protorosaur, Jaxtasuchus.

Li et al. 2016 describe
a Middle Triassic (240mya) semi-aquatic reptile,  Litorosuchus somnii based on a complete and articulated skeleton (Fig. 1) together with hard and soft dermal tissue (see below). Note the antorbital fenestra without a fossa. That’s a key trait that led the Li team astray.

Figure 1. Litorosuchus somnii was wrongly considered a sister to Vancleavea and wrongly considered an archosauriform. In the LRT it nests with Macrocnemus, a tritosaur lepidosaur that also has members with an antorbital fenestra. Click to see an enlarged rollover image.

Figure 1. Litorosuchus somnii was wrongly considered a sister to Vancleavea and wrongly considered an archosauriform. In the LRT it nests with Macrocnemus, a tritosaur lepidosaur that also has members with an antorbital fenestra. Click to see an enlarged rollover image.

Unfortunately 
Li et al. nested Litorosuchus with the armored and aquatic Vancleavea (Nesbitt et al 2009, Fig. 2), which they still insist is an aberrant stem archosaur (Nesbitt et al. 2009, Nesbitt 2011) despite lacking an upper temporal or antorbital fenestera, among a long list of other autapomorphies. Five years ago here Vancleavea was nested with Helveticosaurus in the Thalattosauria in the large reptile tree (LRT) where it remains today. Taxon exclusion burned the Nesbitt et al. 2009 study on Vancleavea and the Nesbitt 2011 study on archosaurs. Two of those team members (Nesbitt and Stocker) are also on the Li et al. 2016 team. Sadly, Li et al. 2016 got burned again for the same reason.

Vancleavea campi

Figure 2. Vancleavea skeleton, sans osteoderms.

Taxon exclusion
So certain that Litorosuchus was an archosauriform, Jaxtasuchus was not included in the Li et al. study matrix (based on Nesbitt et al. 2009 and additions thereafter) despite their overall resemblance to the new taxon. In the LRT Litorosuchus nests strongly within Jaxtasuchus, (Fig. 3) another clade that has members with an antorbital fenestra, a trait that appears at least 4 times within the Reptilia.

Figure 2. The armored aquatic protorosaur, Jaxtasuchus, is smaller and less complete than Litorosuchus.

Figure 3. The armored aquatic protorosaur, Jaxtasuchus, is smaller and less complete than Litorosuchus.

Let’s take a look at the Li et al. abstract,
then discuss the protorosaur affinities of the new taxon.

Figure 2. Litorosuchus in situ with a new tracing of the inverted and displaced posterior premaxilla with several teeth.

Figure 4. Litorosuchus in situ with a new tracing of the inverted and displaced posterior premaxilla with several teeth.

From the Li et al. abstract:
“Reptiles have a long history of transitioning from terrestrial to semi-aquatic or aquatic environments that stretches back at least 250 million years. Within Archosauria, both living crocodylians and birds have semi-aquatic members. Closer to the root of Archosauria and within the closest relatives of the clade, there is a growing body of evidence that early members of those clades had a semi-aquatic lifestyle [1]. However, the morphological adaptations to a semi-aquatic environment remain equivocal in most cases. Here, we introduce a new Middle Triassic (245–235 Ma) archosauriform, Litorosuchus somnii, gen. et sp. nov., based on a nearly complete skeleton from the Zhuganpo Member (Ladinian [241–235 Ma]) of the Falang Formation, Yunnan, China. Our phylogenetic analyses suggest [2] that Litorosuchus is a stem archosaur closely related to the aberrant Vancleavea just outside of Archosauria. The well-preserved skeleton of L. somnii bears a number of morphological characters consistent with other aquatic-adapted tetrapods including: a dorsally directed external naris, tall neural spines and elongate chevrons in an elongated tail, a short and broad scapula, webbed feet, long cervical vertebrae with long slender ribs, and an elongated rostrum with long and pointed teeth [3]. Together these features represent one of the best-supported cases of a semi-aquatic mode of life for a stem archosaur [4]. Together with Vancleavea campi, the discovery of L. somnii demonstrates a growing body of evidence that there was much more diversity in mode of life outside Archosauria. Furthermore, L. somnii helps interpret other possible character states consistent with a semi-aquatic mode of life for archosauriforms, including archosaurs.” [5]

Notes

  1. Why restrict the taxon search to the clade Archosauria (crocs + dinos) a priori when Litorosuchus looks nothing like any of them? Better to add the new taxon to a large gamut analysis and let the scores determine the clade nesting, especially knowing that an antorbital fenestra, if present, is convergent over several unrelated clades.
  2. The results only ‘suggest’ [we call this a weasel-word because you can weasel your way out of it] because Litorosuchus bears no resemblance to its ‘by default‘ sister taxa. In the LRT the nesting is sure and secure, supported by a long list of traits used as evidence and readily apparent just by looking (Fig. 3).
  3. These are the basic traits of Jaxtasuchus (Fig. 3). Someone evidently had their blinders on.
  4. Stem archosaurs (sensu LRT, crocs + dinos only) were bipedal and terrestrial.  Basal archosauriformes (sensu LRT, like Proterosuchus) were indeed semi-aquatic. Jaxtasuchus also had a semi-aquatic lifestyle. Perhaps they competed.
  5. Jimi Hendrix said it best, “Castles made of sand slip into the sea, eventually.” The only question is, how long with the Nesbitt, Stocker excluded taxon cladogram take to find more solid footing with a larger gamut matrix?

I only had to take a look at the foot of Litorosuchus
to know that the Li team had missed a golden opportunity to discuss protorosaur affinities. The long pointed skull with the long premaxillary ascending process together with the long neck and short limbs all link Litorosuchus to Jaxtasuchus, not Vancleavea. The length and depth of the tail occur within this clade, along with the presence of dermal  armor. The antorbital fenestra was present in Jaxtasuchus and Pamelaria.

Diandongosuchus nests as a basal phytosaur when choristoderes and basal younginoids are included, far from Qianosuchus, which also does not nest with poposaurs, which are all bipedal (or formerly bipedal) herbivores, a far cry from Diandongosuchus.

Figure 4. Diandongosuchus nests as a basal or stem phytosaur and was coeval with Litorosuchus.

Diandongosuchus is discussed within the Li et al. text
because it is semi-aquatic, coeval and an archosauriform. However it is unrelated to archosaurs except through Youngina UC1528 and basalmost Proterosuchus specimens. Diandongosuchus is therefore unrelated to Litorosuchus in the LRT except through archosauriform reptiles. And yes, Nesbitt and Stocker claimed credit for discovering that Diandongosuchus (Fig. 4) was a basal phytosaur when you heard that here first, four years ago. Either this is proof that they don’t Google or proof that they like to stick to outmoded paradigms while ignoring the greater evidence.

References
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Nesbitt SJ 2011. The early evolution of archosaurians: relationships and the origin of major clades. Bull Amer Mus Nat Hist 352:1–292.
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.