Читать книгу Hadrosaurs - David A. Eberth - Страница 60

1. Loss of all but the primary ridge on dentary and maxillary tooth crowns.

2. Ilium with its posterodorsal margin everted and ventrally deflected forming a pendule positioned dorsal to the posteroventral margin of the lateral expansion of the ischiadic peduncle.

3. Pendule on the ilium anteroposteriorly shorter than deep.

4. No lateral expansion of the ischiadic peduncle, so that this area is flush with the lateral wall of the ilium.

5. See Prieto-Márquez (2010:457–461) for an extended consideration of the character states that may be used to diagnose Hadrosauridae (= Euhadrosauria, this account).

Comments Prieto-Márquez (2010:456) argued that the clade Euhadrosauria was not “defined” (the implication being that it lacked a phylogenetic definition, although it should be recognized that such definitions did not come into practice until later than 1993) and he thus considered it to be ambiguous; he also objected to its usage because he claimed that it violated recommendations in the ICZN (1999) concerning the naming of “family group” taxa by not having as its root the name of a nominal taxon. Invoking the ICZN “family group” concept to derived iguanodontians implies a degree of stability of taxon relationships that is not consistent with the type of accumulative science practiced by paleontologists. The recent history of systematic evaluations of hadrosaurians and their near relatives typifies this problem. Consistency is not the general rule, even though it is an obvious aspiration (cf., Horner, 1985, 1990, 1992; Sereno, 1986, 1998; Weishampel and Horner, 1990; Weishampel et al., 1993; Head, 1998; Norman, 2002, 2004; Horner et al., 2004; Prieto-Márquez, Weishampel, and Horner, 2006; Gates and Sampson, 2007; Evans and Reisz, 2007; Godefroit et al., 2008; Dalla Vecchia, 2009; Evans, 2010; Prieto-Márquez, 2010, 2011; Wang et al., 2010; McDonald, 2012b; Wu and Godefroit, 2012).

Prieto-Márquez’s suggestion that the stem of the family group name (Euhadrosauria) does not derive from the nominal taxon name Hadrosaurus, is at best specious: the origin of the name is self-evident and the use of the prefix serves a specific role by polarizing the nomenclature in order to reflect one aspect of tree topology. It can also be observed that a logical extension of Prieto-Márquez’s concerns about the validity of the family group name Hadrosauridae is that the nominal taxon Hadrosauridae is based upon a taxon that has in the past been considered a nomen dubium (Prieto-Márquez, Weishampel, and Horner, 2006), whose position within any topology is probabilistic (Prieto-Márquez, 2010), and could be considered sedis mutabilis – especially considering the fragmentary and incomplete nature of its remains.

More recently Prieto-Márquez (2011) has contradicted previous work by proposing that Hadrosaurus foulkii is indeed a valid taxon, which he assigns (on its own) to the subfamily Hadrosaurinae (as in Prieto-Márquez, 2010). In addition he now defines the node-based clade Hadrosauridae as “the clade stemming from the the most recent common ancestor of Hadrosaurus foulkii and Parasaurolophus walkeri” (Prieto-Márquez, 2011:67). His clade Saurolophidae (= Euhadrosauria in this account) is given a node-based definition: “the last common ancestor of Saurolophus osborni, Lamebosaurus lambei, and all its descendants” (Prieto-Márquez, 2011:67; it is not made explicit why he has abandoned the use of Parasaurolophus in favour of Lambeosaurus as one specifier in this instance) and he concludes with the proposition that this latter clade (Saurolophidae = Euhadrosauria in this account) includes “the two major hadrosaurid clades: Saurolophinae and Lambeosaurinae” (Prieto-Márquez, 2011:67). Phylogenetic definition of the taxonomic scheme proposed by Weishampel et al. (1993) with respect to Hadrosauridae (the least inclusive, node-based clade containing Telmatosaurus transsylvanicus and Parasaurolophus walkeri) and Euhadrosauria (see above) solves a number of problems put forward by Prieto-Márquez (2011), and necessitates only adopting Saurolophinae for the clade traditionally recognized as Hadrosaurinae. However, if future phylogenetic analyses recover Hadrosaurus foulkii as a member of this clade, Hadrosaurinae would have precedence.