The recently published article “Tyrant dinosaur evolution
tracks the rise and fall of Late Cretaceous oceans” by Loewen et al. (2013) is
an exciting report of a new, unquestionably valid derived tyrannosauroid from
the American West. The new taxon, Lythronax
argestes, is important given its middle Campanian geological age, which
predates the others from Laramidia. In the interest of full disclosure, I did
not receive the manuscript for review at any stage during its course toward
publication.
Had I been a reviewer, I would have caught a rather
important discrepancy. On page two of their article, Loewen et al. (2013) claim
that Lythronax shares with “Teratophoneus and Bistahieversor in the presence of 11 maxillary alveoli”, and
restate this on page six, where Teratophoneus
“differs from Alioramus and all other
tyrannosauroids except Bistahieversor
and Lythronax in [the] presence of 11
maxillary alveoli”. However, the only specimen of Bistahieversor
that has a complete maxilla is the holotype (NMMNH P-27469), which clearly has
13 alveoli.
In their specimen list (2013: SI, Phylogenetic Analysis Characters), for Bistahieversor they include the holotype, the referred juvenile
(NMMNH P-25049), and a premaxillary tooth (United State National Museum 8355;
Gilmore, 1916). The maxillary tooth count character is
important because it is optimized as a synapomorphy of the Teratophoneus + derived tyrannosaurine clade (Loewen et al., 2013: S4). Also, I want to draw attention to the fact that the correct tooth count can be seen in the published
literature, which is shown in the carbon dust plate (and journal cover) of the holotype in Carr et
Williamson (2010).
However, this discrepancy does not affect the phylogenetic
results of Loewen et al. (2013) because the maxillary tooth counts of “11 to 13”
alveoli are coded as a single character state, “2” (2013: S2, character 298). This approach to coding does not test the hypothesis of a primitively 11-toothed clade, a situation that can be easily remedied. Given the conflated coding and
the discrepancy between the reported and actual tooth count of Bistahieversor, I would be interested in
seeing a short revision from the authors, where the tooth counts of 11 and 13 are coded separately and that for Bistahieversor is corrected.
References cited
Carr, T. D. and T. E. Williamson. 2010. Bistahieversor sealeyi gen. et sp. nov., a new tyrannosauroid from
New Mexico and the origin of deep snouts in Tyrannosauroidea. Journal of
Vertebrate Paleontology 30:1-16.
Gilmore, C. W. 1916. Vertebrate faunas of the Ojo Alamo,
Kirtland, and Fruitland Formations. Shorter Contributions to General Geology
98:279-309.
Loewen, M. A., Irmis, R. B., Sertich, J. J. W., Currie, P.
J., and S. D. Sampson. 2013. Tyrant dinosaur evolution tracks the rise and fall
of Late Cretaceous oceans. PLoS ONE 8: 1-14.
I've re-analysed the data set with character 298 rescored as you suggested, and it produced the same strict consensus among derived tyrannosauroids. In the new analysis, the number of maxillary teeth does not result a synapomorphy of any node along Tyrannosaurinae.
ReplyDeleteI've also tested a modified version of the analysis with the characters relative to the numbers of maxillary and dentary teeth and the position of the posteriormost maxillary tooth (characters 297, 298, 300) all reset as ordered (instead of unordered as in the original data set): the same topology as the original analysis has resulted.
Thus, it seems to me that the result in Loewen et al (2013) is not biased by a priori assumptions on teeth number/position character states.
Hi Andrea,
ReplyDeleteThank you very much for the rapid reanalysis! I did not expect any difference in topology, but I did expect there to be a difference in character optimization.
Sincerely,
Thomas
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