Monday, November 18, 2013

Literature review 2: Loewen et al., 2013

Carbon dust plate of the skull of the holotype (NMMNH P-27469) of Bistahieversor sealeyi in left lateral view © Dino Pulerà. The maxilla is colorized and its 13 tooth positions are labeled. For explanation see text. Abbreviation: NMMNH, New Mexico Museum of Natural History and Science, Albuquerque, NM.


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.

4 comments:

  1. 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.
    I'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.

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  2. Hi Andrea,

    Thank 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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