Primitivus: a new marine pre-snake, dolichosaur

There are those
who practice taxon exclusion in their search for taxon ancestors. Now, Paparella et al. 2018 can be counted among them as they bring us a wonderful new find, Primitivus manduriensis from the Late Cretaceous of Italy. They correctly nest it as a pre-snake and a dolichosaur (Fig. 1). Primitivus also preserves snake-like scales.

Figure 1. Like the LRT, Paparella et al. 2018 nest Primitivus with Pontosaurus, but this cladogram is missing several taxa that attract snakes away from mosasaurs.

Figure 1. Like the LRT, Paparella et al. 2018 nest Primitivus with Pontosaurus, but this cladogram is missing several taxa that attract snakes away from mosasaurs.

Unfortunately, due to taxon exclusion
the Paparella team nest Primitivus with the invalid clade ‘Pythonomorpha‘ (mosasaurs  + snakes) rather than the more broadly tested pre-dolichosaurs (= ardeosaurs): Ardeosaurus, Eichstättisaurus and tiny Jucaraseps, none of which are mentioned in the text. These taxa are ancestral to the dolichosaurs leading to snakes in the large reptile tree (LRT, 1236 taxa, Fig. 2). The LRT tests all these candidates and finds mosasaurs and varanids nest elsewhere, apart from snakes, dolichosaurs, ardeosaurs and geckos. Deletion of the ardeosaurs makes no change in the LRT tree topology. This is a strong nesting.

The Paparella team also nest tiny Tetrapodophis
at the stem of Mosasauroidea + Dolichosauridae and apart from snakes (Fig. 1), rather than basal to snakes, as in the LRT (Fig. 2).

Figure 2. Subset of the large reptile tree focusing on lepidosaurs and snakes are among the squamates.

Figure 2. Subset of the large reptile tree focusing on lepidosaurs and snakes are among the squamates. Primitivus nests with Pontosaurus here, but is not shown here. See it in the LRT.

Sadly,
an otherwise excellent paper has this fatal flaw due to taxon exclusion. Sometimes I wonder why workers don’t test taxa that years ago were found relevant in the LRT. That’s why the LRT is online, available 24/7 worldwide.

Figure 3. Primitivus skull in visible and UV light from Paparella et al. They did not identify bones, so DGS colors were added here.

Figure 3. Primitivus skull in visible and UV light from Paparella et al. They did not identify bones, so DGS colors were added here.

As we learned earlier,
phylogenetic miniaturization gave us both aquatic dolichosaurs (via tiny Jucaraseps) and later, terrestrial snakes (via tiny Tetrapodophis).

Figure 4. Primitivus in situ from Paparella et al. 2018 in visible light. UV images is distorted to match.

Figure 4. Primitivus in situ from Paparella et al. 2018 in visible light. UV images is distorted to match.

There is very little difference, apart from size,
between the larger Pontosaurus and the smaller Primitivus. Not sure why the Paparella team did not present skull identification in their primary publication.

Figure 3. Primitivus hand and foot from Paparella et al. 2018, DGS colors added here.

Figure 3. Primitivus hand and foot from Paparella et al. 2018, DGS colors added here.

References
Paparella I, Palci A, Nicosia U and Caldwell MW 2018. A new fossil marine lizard with soft tissues from the Late Cretaceous of southern Italy. Royal Society Open Science 5: 172411. http://dx.doi.org/10.1098/rsos.172411

Publicity including in vivo restorations:
https://www.cbc.ca/news/canada/edmonton/pretty-amazing-alberta-researchers-spot-new-fossil-species-and-its-lunch-1.4715056

https://phys.org/news/2018-06-scientists-species-ancient-marine-lizard.html

8 thoughts on “Primitivus: a new marine pre-snake, dolichosaur

  1. Here’s the thing – you seem to think the differences between most analyses and yours boil down to taxon sampling. But you haven’t actually tested this assertion – you add new taxa to your matrix, but all that tells us is that your matrix comes up with a different answer. It doesn’t tell us whether the cause is taxon sampling, character sampling, different morphological interpretations, or something else.

    So here’s what you should do: instead of adding a new taxon to your matrix, try adding additional taxa to theirs. That’s the only way to know whether the different results reflect different taxon sampling strategies.

    Have you done this? If not, why not?

    • Yes, I’ve done just what you suggest to Nesbitt 2011. In 2000 I did that with three or four prior analyses (adding fenestrasaurs) in Rivista Italiana. I must report that the last several .nex files I got did not have characters listed on the matrix. So adding them involves cross referencing long lists of data with the potential for confusion. So much easier to just look at a trait in the LRT .nex file and see where one changes to another and another. Not sure why they set it up that way, but I suspect in many cases these were borrowed matrices… accepted as is from prior authors, with just the new taxon added.

      So, it’s common practice to just add taxa to existing matrices. I do it weekly.

      Chris, I also tend to alert readers to mismatches in competing tree topologies (e.g. gliders nested with swimmers, flamingos nesting with grebes). These, to any logical thinker, should raise red flags of caution, but they don’t. In the LRT niches, morphologies, sizes are all pretty much gradual in appearance. Let me know if you see any ‘bogeys’.

      • Have you done it with this analysis? Because if not, you really shouldn’t claim the differences reflect taxon sampling. You’ve not demonstrated it.

      • Like I reported, in the Primitivus analysis, the authors did not include taxa that would attract snakes from mosasaurs, which is demonstrating it. Any set of characters should provide similar results, as demonstrated by skull only, post-crania only and full body taxa.

  2. BTW – if you want a “bogey,” your recent suggestion that sandgrouse are related to screamers is a flat-out howler.

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