Yesterday we opened up a cladogram
by Nesbitt et al. 2017, for examination and taxon addition.
The first driving issue here
is one we looked at earlier and even earlier: the origin of the Aetosauria. Nesbitt 2011 and Nesbitt et al. 2017 considered similarly armored Revueltosaurus the basalmost taxon in the aetosaur branch. Barely armored Ticinosuchus nests nearby, one node crown ward (Fig. 1) and 8 steps removed.
the large reptile tree (LRT, 1560 taxa) nests Ticinosuchus as the proximal outgroup taxon to the Aetosauria. Revueltosaurus nests with Fugusuchus and Tasmaniosaurus, together forming a previously overlooked sister clade to traditional erythrosuchids, like Erythrosuchus.
A second driving issue is the simple addition of taxa
to another, larger, character list created by someone else and published in an academic journal. This is an experiment in doing so.
A third driving issue is character scoring,
checking Nesbitt et al. 2017 for errors and omissions, and if repairable, do so.
The MorphoBank Nesbitt character list needs a proofreader.
Several characters are not labeled and neither are their states, other than “State 0″, State 1”, etc. Those were deleted from my review of their cladogram since they contained no useful data. Before publishing, it’s best to take one last look around to see if everything is neat and tidy.
I realize that no character list is perfect,
but some in Nesbitt’s work look like they should be divided in two because a pair of dichotomies are presented. For instance:
- Does not possess a posterolateral process that envelops part of the anterior rams of the lacrimal.
- Possess a posterolateral process that envelops part of the anterior ramis of the lacrimal.
- Does not form part of the dorsal border of the antorbital fossa.
- Forms part of the dorsal border of the antorbital fossa.
In this case
I pretended choices 3 and 4 did not exist. I may be wrong in doing so. You decide. IMHO this one needs to go back to the shop to be split in two even though the matrix, as a whole, is still good enough to run.
A minor point, but worth mentioning:
Verbose characters with many letters tend to run off the edges of the columns provided by MacClade, even when set quite wide. Characters do this too often in Nesbitt 2017 (example above). If I may offer a suggestion? In the above example, #2 could have been stated as is (or shortened by deleting the grammatical articles), while #1 could have been shortened to: “does not.” In the LRT characters are really pared down to make them easy to read in relatively narrower MacClade columns.
For the skull of Ticinosuchus
Nesbitt and Nesbitt et al. scored very few characters, perhaps because they did not understand the roadkill-crushed skull enough make a reconstruction. This is where DGS works wonders. The addition of Ticinosuchus skull traits brought this taxon within one step of the Aetosauria, compared to its original nesting. Corrections to the post-crania shifted Ticinosuchus to the base of the Aetosauria, as in the LRT, with 9 steps needed to move it back to its Nesbitt nesting.
With its emphasis on ankle traits
and hind limb long bone end shapes, the Nesbitt et al. cladogram has its roots in a traits-based era when archosauriforms were divided according to ankle traits. This era is when the traditionally beloved, but since invalidated clade ‘Pseudosuchia‘ originated. Since the concavity or flatness of certain ankle elements cannot be determined or confirmed from published data, I had to ignore all such traits and rely on others from the list of 400 or so. The remainder still left plenty to work with.
Several characters in Nesbitt et al. 2017
are related to braincase foramina, sutures and processes. These are not employed by the LRT because they, too, are not readily visible in published data. Palatal and occipital traits, whenever visible, are scored. Unfortunately palate and occipital reconstructions for Ticinosuchus have not been generated and those for Revueltosaurus have not been published. Bottom line: omitting all the tiny and hard-to-see traits lets all the large and easy-to-see traits determine relationships resulting in a cladogram in which sister taxa indeed do like each other.
The addition of Fugusuchus (still need to add Tasmaniosaurus) and the re-scoring of errors and omissions moved Revueltosaurus to the Fugusuchus – Erythrosuchus clade away from Aetosauria. Ticinosuchus moved to the base of the Aetosauria (Fig. 2). Both of these are echoed in the LRT. Most of the rest of the Nesbitt et al. tree remains unchanged despite its difference from the LRT. Note: Euparkeria has moved one node root-ward, as in the LRT. Further testing is planned for several other taxa.
The resulting .nex file is available now by request,
but I would postpone asking for it until more housecleaning has been done to it.
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.
Nesbitt S et al. 2017. The anatomy of Teleocrater Rhadinus, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic). Journal of Vertebrate Paleontology 142-177. https://doi.org/10.1080/02724634.2017.1396539