Revisions to Claudiosaurus and Atopodentatus

Housekeeping in the LRT,
plus a dash of DGS (Figs. 1, 2), shed new light on the skulls of two aquatic younginiforms, Claudiosaurus (Fig 1), and Atopodentatus (Fig. 2). These two now nest a little more closely to one another.

Figure 1. Claudiosaurus skeleton based on changes in January 2022. Click to enlarge. The nasals are narrow and parallel. The maxilla is much deeper. The quadratojugal is absent.
Figure 2. Atopodentatus skull in situ. Colors added here. The nasals are narrow and parallel. The maxilla is much deeper. The quadratojugal is absent.

While reviewing scores
in the large reptile tree (LRT, 2049 taxa) apomorphies in the MacClade files have brought attention to hundreds of errors and just as many true apomorphies.

Claudiosaurus was added to the LRT more than ten years ago
and several years before colors were applied to bones.

Atopodentatus was added more recently,
before DGS colors became standardized. Several errors were noticed today as this taxon was compared to Claudiosaurus. This is only one example of hundreds reviewed recently.

Turns out in both taxa
the nasals are narrow and parallel. The maxilla is much deeper. The quadratojugal is absent.

Every low-resolution node in the LRT had been under review
over the past ten days or so. Corrections are a continuing process. This has been very rewarding with minor discoveries popping up several times a day.

As a result,
the fish subset of the LRT is now fully resolved. So is the theropod-bird subset. The much larger mid-subset of the LRT has about 1300 taxa. Corrections have brought the number of most parsimonious trees down to 50 or so. That means only three or four small clades remain that lack full resolution. The most recent changes to the topology of the LRT involve only slight shifts to closely related taxa. No big shifts.

To obtain that goal,
a few far-from-complete taxa have been removed and set aside as ‘red taxa’ in the LRT, in addition to the hundreds of corrections described above.

Thank you for your patience and readership.
I learn as I go. There is no time crunch. This is not an expensive endeavor, but it is time-intensive. This online experiment has been ongoing for more than a decade. Lessons from more recent taxa have helped to shed light on earlier errors — once I reexamine them. Housekeeping provides that opportunity.

Thankfully this online experiment was never committed to print.
Changes are inevitable. A great number have already been reported, each one with a time stamp. This could not have been done without a few centuries of workers finding and describing taxa. IMHO this experiment could not have been done earlier without today’s computer software, PDFs and lots of time without other responsibilities.


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