So, is it Leptosaurus? Kallimodon? Or neither?

Rauhut and Lopez-Arbarello (2016)
compare several complete specimens of Late Jurassic rhynchocephalians from Germany (Fig. 1) with a newer specimen from Schamhaupten, JME-Scha 100 (lower left of Fig. 1).  that was earlier described by Renesto and Viohl 1997 as Leptosaurus pulchellus, JME-Scha 40. (Why the number change?) The holotype, Leptosaurus neptunium (Fig. 1b, was described earlier by Fitzinger 1837, but referred to Kallimodon by Cocude-Michel 1963. So that sets the stage for the study.

We looked at this taxon earlier here when Renesto and Viohl published on it.

Figure 1. Taxa considered by Rauhut and López-Arbarello include Homoeosaurus, Leptosaurus, Kallimodon and rhynchocephaian specimen from Schamhaupten, JME-Scha 100.

Figure 1. Taxa considered by Rauhut and López-Arbarello include Homoeosaurus, Leptosaurus, Kallimodon and rhynchocephaian specimen from Schamhaupten, JME-Scha 100.

From the Rauhut and Lopez-Arbarello abstract:
“Unfortunately, the taxonomy of the rhynchocephalians from these units has not been satisfactorily established so far, which hampers studies of their evolutionary importance.” 

Actually
the large reptile tree (LRT) has taken the first steps toward that goal (Fig. 2). Though not aware of the Leptosaurus holotype, I used instead the JME-Scha specimen in its place based on the work and nomenclature of Renesto and Viohl 1997. Not sure, but the holotype of Leptosaurus looks quite a bit like the Homoeosaurus specimens I used for data. 

Figure 2. Subset of the large reptile tree, the Rhynchocephalia. This clade also includes Rhynchosauria, Azendohsaurus and Trilophosaurus.

Figure 2. Subset of the large reptile tree, the Rhynchocephalia. This clade also includes Rhynchosauria, Azendohsaurus and Trilophosaurus.

From the Rauhut and Lopez-Arbarello abstract:
“Differences to the type of Kallimodon pulchellus include the morphology of the maxillary teeth, the phalangeal formula of the manus, and the shape of the posterior process of the second sacral rib. An important difference with the type of Leptosaurus neptunius is the higher number of premaxillary teeth in the specimen from Schamhaupten (four versus two), despite a significantly larger body size, whereas there is rather a tendency to reduce the number of premaxillary teeth through fusion during ontogeny in rhynchocephalians.” 

Rauhut and Lopez-Arbarello conclude
that the JME Scha specimen cannot be referred to either Kallimodon or Leptosaurus, but they do not rename the JME Scha specimen.

Unfortunately
the authors do not realize that the tiny JME Scha specimen is the branching off point in the LRT for the toothed rhynchocephalian, Azendohsaurus and its sister Trilophosaurus, which has no premaxillary teeth because these taxa are not included on the Rauhut and Lopez-Arbarello family tree (Fig. 3). They also did not realize that Priosphenodon is the branching off point for the origin of rhynchosaurs.

Figure 3. Rhynchocephalian cladogram from Rauhut and López-Arbarello lacks many pertinent taxa and includes one, Homoeosaurus, that belongs elsewhere.

Figure 3. Rhynchocephalian cladogram from Rauhut and López-Arbarello lacks many pertinent taxa and includes one, Homoeosaurus, that belongs elsewhere. The LRT nests Kallimodon with Sphenodon and Saphenosaurus with Noteosuchus.

Other problems with the Rauhut and Lopez-Arbarello family tree
include the unwarranted inclusion of Homoeosaurus. In the LRT Homoeosaurus nests within the protosquamates the only matrix to test it on a large gamut of taxa. The authors also include several taxa that were not included in the LRT, like Eilenodon, represented only by a posterior jaw fragment. On the other hand, missing taxa from the Rauhut and Lopez-Arbarello rhynchocephalian tree (Fig 3) include:

  1. Megachirella
  2. Marmoretta
  3. Ankylosphenodon
  4. Heleosuchus
  5. Sphenotitan
  6. Noteosuchus
  7. Trilophosaurus
  8. Azendohsaurus
  9. Eohyosaurus
  10. Mesosuchus
  11. Rhynchosaurus
  12. Bentonyx
  13. Hyperodapedon

You might not like this, if you like traditional studies
but these taxa all nest within the clade Rhynchocephalia in the LRT. And Gephyrosaurus is no longer the most primitive of the lot.

Perhaps 
Rauhut and Lopez-Arbarello will someday expand their taxon list. That’s why the LRT is here… to make taxon selection simple, complete and verifiable, not just traditional. The hard work has already been done for you. All you have to do is focus on your clade of interest!

References
Cocude-Michel M 1963. Les Rhynchocéphales et les Sauriens des Calcaires lithographiques (Jurassique supérieur) d’Europe occidentale.– Nouvelles Archives du Muséum d’Histoire Naturelle de Lyon 7: 1–187.
Fitzinger LJF 1837. Vorläufiger Bericht über eine höchst interessante Entdeckung -Dr. Natterers in Brasil. Oken’s Isis.
von Meyer H 1850. Mittheilungen an Professor Bronn gerichtet: Neües Jahrbuch fur Mineralogie, Geologie und Palaontologie, Bd 18, p. 195-204.
Rauhut OWM and Lopez-Arbarello A 2016. Zur Taxonomie der Brückenechse aus dem oberen Jura von Schamhaupten (On the taxonomy of the rhynchocephalian from the Late Jurassic of Schamhaupten). Archaeopteryx 33: 1-11; Eichstätt 2016.
Renesto S and Viohl G 1997. A sphenodontid (Reptilia, Diapsida) from the late Kimmeridgian of Schamhaupten (Southern Franconian Alb, Bavaria, Germany). Archaeopteryx 15:27-46

 

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