New material of the choristodere Lazarussuchus – Matsumoto et al. 2013

What a wonderful new fossil!
A complete and articulated Lazarussuchus (Hecht 1992) has just been described by Matsumoto, et al. (2013). The new specimen (Fig. 1, below) comes from the Paleocene of France.

Figure 1. Lazarussuchus, the old specimen (above) and the new specimen (below) from Matsumoto et al. 2013.

Figure 1. Click to enlarge. Lazarussuchus, the older Hecht 1992 specimen (above) and the newer specimen (below) from Matsumoto et al. 2013, to the same scale. The differences are subtle, including a longer neck and more robust limbs. These two were definitely congeneric but not conspecific.

Distinct from an earlier specimen
the new specimen has a taller skull, a distinct pelvis and more robust limbs. At the same scale the skulls were nearly identical in length, but in the new specimen the neck was more robust and nearly twice as long.

Unfortunately, by way of taxon exclusion,
the writers (Matsumoto, et al. 2013) got their phylogeny backwards. They reported, “Despite its age, most phylogenetic analyses place Lazarussuchus at or close to the base of the choristoderan tree, implying a very long unrecorded history.”  In contrast, the large reptile tree (also see fig. 2) nested Lazarussuchus as a derived choristodere. After all it had lost its lateral temporal fenestra, a primitive trait present in other choristoderes. Moreover, the Matsumoto (2013) tree nested choristoderes with sauropterygians and their tree improperly rooted with  Youngina.

One problem:
Matsumoto et al. included two basal sauropterygians and two lepidosaurs in their tree. These are not closely related to choristoderes in the large reptile tree. So, sadly, this group of scientists had no scientific basis or guidance for choosing their inclusion set as a subset from a much larger tested set. Instead they chose what they felt like choosing.

Another problem:
Matsumoto et al. did not include the real closest known taxa to choristoderes.

Figure 2. Matsumoto et al. (2013, left) with the addition of Ichthyostega and Cephalerpeton for rooting. Same tree with added taxa separates the sauropterygians from the choristoderes.

Figure 2. Matsumoto et al. (2013, left) nested sauropterygians with choristoderes. Here with the addition of Ichthyostega and Cephalerpeton for rooting, much the same tree topology is present. Same tree with added taxa from the large reptile tree properly separates the sauropterygians from the choristoderes.

Testing Matsumoto (2013) with the Large Reptile Tree
Starting with the 235+ taxa in the large reptile tree and deleting all but those taxa used by Matusmoto et al. (2013) and, like them, setting Youngina as the outgroup, I recovered much the same tree, except Gephyrosaurus nested at the base of Petrolacosaurus + Araeoscelis and Prolacerta nested closer to the Choristodera. Within the Choristodera Champsosaurus nested as a basal taxon.

Non-controversial outgroup taxa
Instead of guessing which taxon should be the outgroup, why not go all out?  Ichthyostega, a basal tetrapod, and Cephalerpeton, a basal reptile serve as non-controversial outgroups for all reptiles. Adding them to the matrix (Fig. 2, left) moves Youngina closer to Prolacerta and little else.

Adding several more pertinent taxa
Let’s add more taxa from and based on the large reptile tree (Fig. 2, right) as another test. That recovers a tree topology much more like the large reptile tree in which a longer list of various younginoids, Doswellia and Diandongosuchus nest close to the Choristodera. The sauropterygians now correctly nest further away with other Enaliosauria. The new Lepidosauromorpha, including Mesosuchus, nest together (in blue) and so do the new Archosauromorpha (in yellow), but they did not split from each other following Cephalerpeton, as in the large reptile tree. The reason: Too few pertinent taxa at the critical point were missing to make that division appear where it should.

The Nasal Question
Conventional thinking and Matsumoto et al. (2013) identify the two medial bones anterior to the frontals as prefrontals (Fig. 3, lavender). This is a common and traditional mistake when dealing with choristoderes. Following this pattern Matsumoto et al. identify the nasals (pink) as those tiny supranarial bones. This is false paradigm that probably goes back to Champsosaurus, in which the premaxilla is literally split into two separate bones, the ascending process and the tooth-bearing portion, due to the migration of the once dorsal nares back to the tip of the snout from its plesiomorphic position on top of the snout. All choristodere workers have since assumed the ascending process was the nasal since the real nasal and prefrontals are fused in Champsosaurus. So, given the examples of the closest known taxa (Figs. 3,4), in Matsumoto et al. (2013) the ascending process of the premaxilla was falsely labeled a nasal and the nasals were falsely labeled prefrontals.

 

Figure 3. The misidentification of the rostral bones in Lazarussuchus according to Matsumoto (2013, above) and relabeled below. Sister taxa demonstrate the continuing presence of large nasals that meet medially and the extent of the premaxilla ascending process. This false paradigm has to stop. Also see figure 4 for Youngina BPI 2871, which has a longer snout.

Figure 3. The misidentification of the rostral bones in Lazarussuchus according to Matsumoto (2013, above) and relabeled below. Sister taxa demonstrate the continuing presence of large nasals that meet medially and the extent of the premaxilla ascending process. This false paradigm has to stop. Also see figure 4 for Youngina BPI 2871, which has a longer snout.

Saved by the sister taxa
Related taxa (Figs. 3, 4), like Younginia, Younoides, Cteniogenys and Diandongosuchus demonstrate the conservative arrangement of the rostral bones. The prefrontals of Lazarussuchus did not meet medially, but were located at their conventional places, separated by large nasals. Not sure why (other than the Champsosaurus issue mentioned above) experts are missing this. Lack of more parsimonious related taxa indicated Matsumoto et al. (2013) have no idea where choristoderes nest in the reptile family tree. Here, when given 235+ other opportunities, choristoderes nest with younginiforms and within the pararchosauriforms: Doswellia, parasuchia and proterochampsia in the large reptile tree.

Fenestrae Coming and Going
Lazarussuchus is a diapsid lacking the lateral temporal fenestra present in sister taxa like Diandongosuchus and Younginoides (Fig. 3) and another choristodere, Cteniogenys (Fig. 4). Diandongosuchus is among the first taxa in its lineage to develop an antorbital fenestra, convergent with several other taxa with antorbital fenestra.

Youngina BPI 2871 and its descendants, according to the large reptile tree, the choristodere Cteniogenys and the chanaresuchid, Gualosuchus.

Figure 4. Youngina BPI 2871 and its descendants, according to the large reptile tree, the choristodere Cteniogenys and the chanaresuchid, Gualosuchus.

It’s discouraging when paleontologists do no apply due diligence to their work and leave it to  amateurs to correct their mistakes. Such mistakes can be eliminated and tested with widespread use of the large reptile tree, which has been available world wide for nearly two years now.

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.

Reference
Evans SE and Hecht MK 1993. A history of an extinct reptilian clade, the Choristodera: longevity, Lazarus-Taxa, and the fossil record. Evolutionary Biology 27:323–338.
Hecht MK 1992. A new choristodere (Reptilia, Diapsida) from the Oligocene of France: an example of the Lazarus effect. Geobios 25:115–131. doi:10.1016/S0016-6995(09)90041-9.
Matsumoto R, Buffetaut E, Escuillie F, Hervet S and Evans S 2013. New material of the choristodere Lazarussuchus (Diapsida, Choristodera) from the Paleocene of France.

wiki/Lazarussuchus

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