Spiekman and Scheyer 2019 discuss variation in Tanystropheus

In 2014 we looked at
the same subject, variation in Tanystropheus, from a graphic reconstruction framework (Figs. 1–3) tucked within a phylogenetic analysis.

Spiekman and Scheyer 2019 used a statistical and descriptive approach
to variation in Tanystropheus that, due to the limited nature of statistics, misses important aspects. Imagine all the work they put into their first hand observations and computations of every European specimen, but then somehow missing the big picture by not creating a single reconstruction from a crushed skull (as shown in figure 1).

And they completely missed out
on the fact  that Tanystropheus is a tritosaur lepidosaur, not an archosauromorph. That’s what the large reptile tree (LRT, 1622+ taxa)  is here for. Let others focus on the micro-details. Let the LRT handles the broader scope interrelationships, some of which have direct bearing on conclusions offered by Spiekman and Scheyer.

Figure 2. Tanystropheus with skull reconstructions based on two specimens, exemplar i and exemplar m.

Figure 2. Tanystropheus with skull reconstructions based on two specimens, exemplar i and exemplar m.

The authors introduce their paper:
“Tanystropheus represents one of the most enigmatic tetrapod taxa of the Triassic due to its unique morphology and palaeobiology. Its most striking aspect is its extremely long neck, which consists of a relatively small number (13, see Rieppel et al., 2010) of bizarrely elongated cervical vertebrae with reduced neural spines. This type of cervical vertebrae is unique among tetrapods and easily recognizable.”

No. Tanystropheus is not enigmatic. It is instead very well known and understood in a phylogenetic context. The morphology is not unique. Rather it has several similar sisters and even a long list of convergent taxa with similar long cervicals.

Figure 1. Click to enlarge. Four large Tanystropheus specimens in situ and reconstructed. The man silhouette is 6 feet (1.8m) tall.

Figure 2. Click to enlarge. Four large Tanystropheus specimens in situ and reconstructed. The man silhouette is 6 feet (1.8m) tall. Note the larger head on the largest specimen.

The authors state,
“Although it is unclear whether the two represent different species or distinct ontogenetic stages of the same species, a synonymy list and specimen list is provided for both morphotypes.” If only Spiekman and Schuyer had referenced the LRT or created their own wide gamut phylogenetic analysis, that lack of clarity would have been clarified. A cladogram is a powerful tool. Don’t write a paper without one.

Tanystropheus and kin going back to Huehuecuetzpalli.

Figure 3. Tanystropheus and kin going back to Huehuecuetzpalli. None of these taxa change during ontogeny. Rather they all develop isometrically.

More to the point,
all tested tritosaurs known from juveniles and adults, from Huehuecuetzpalli (Fig. 3) to Zhejiangopterus, display isometric growth during ontogeny. That means any minor or major differences can be attributed to phylogeny, not ontogeny, in the Tanystropheus clade. The answer is that simple. No need for statistical analyses. A wide gamut phylogenetic analysis, like the LRT, solves so many problems decisively and with clarity.


References
Spiekman SNF and Scheyer TM 2019. A taxonomic revision of the genus Tanystropheus (Archosauromorpha, Tanystropheidae). Palaentologia Electronica 22.3.80 PDF

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