Hadrosauromorpha

Hadrosauromorpha was first used in literature by David B. Norman in 2014 in a discussion of phylogenetics of Hypselospinus. In his 2014 paper Norman references another of his publications as the authority for Hadrosauromorpha, a chapter in the book Hadrosaurs.[1] However, the book was in fact published later, in 2015.[4] Following Article 19.4 of the PhyloCode, the authorship of the clade is thus Norman (2015), while the authorship of the definition is Norman (2014).[5]

Phylogeny

Many different versions of phylogenies have been conducted on the group of hadrosauromorphs.[2] Norman (2014) created his own analysis, which includes 105 different morphological characters and 27 select ornithopod taxa. His phylogeny is shown below, using his specific clade definitions:[1]

Hadrosauriformes (Altirhinus + Edmontosaurus)	Altirhinus       Eolambia       Equijubus       Probactrosaurus   Hadrosauromorpha   Tethyshadros       Levnesovia       Bactrosaurus       Gilmoreosaurus       Telmatosaurus     Euhadrosauria

Norman's definitions have been heavily criticized by Mickey Mortimer as being unnecessary changes which cause more confusion to classification.[6] Other phylogenetic analyses, like that of Xing et al. shown below, use traditional clade definitions (Hadrosauromorpha has been added as defined[1]) and have recovered different results.[2] Huehuecanauhtlus has also been found as one of the most derived hadrosauromorphans, between Gilmoreosaurus and Hadrosauridae.[3]

Skull and restoration of Eolambia, possibly one of the most basal hadrosauromorphans

Hadrosauroidea	Equijubus       Xuwulong       Probactrosaurus   Hadrosauromorpha   Jintasaurus       Eolambia     Protohadros         Levnesovia       Tanius       Bactrosaurus       Gilmoreosaurus       Shuangmiaosaurus       Nanningosaurus         Telmatosaurus     Tethyshadros         Claosaurus       Zhanghenglong       Nanyangosaurus     Hadrosauridae

Skeleton of Probactrosaurus, the taxon just outside Hadrosauromorpha

Probactrosaurus was selected as the outgroup to Hadrosauromorpha because of numerous differences that Norman (2014) thought to be significant. The tooth crowns in the dentary are asymmetrical and have multiple vertical ridges; there is a foramen in the surangular; and the quadrate bone has a more prominent depression for the articulation of the jugal. None of these features are found in the skulls of the more derived hadrosauromorphans. The premaxilla contacts the prefrontal, and the jugal contact with the ectopterygoid bone of the palate is reduced.[1]

In the appendicular regions, hadrosauromorphans the scapulae are not J shaped, instead having an overhanging projection. The lower forelimb bones are more slender in both hadrosauromorphans and Probactosaurus, unlike their more robust ancestors. Probactosaurus, however, possesses the basal condition of having a small, conical pollex, like in earlier ornithopods such as Iguanodon or Hypselospinus. This absence of a pollex is also linked to a reduction of the carpal bones, and a less mobile manus. The ilium bones of Probactrosaurus are more angular than in hadrosauromorphs, which lack a brevis shelf. It was also identified that the femoral shaft is straight in hadrosauromorphans and the pedal bones are truncated[1]