Hadrosauromorpha
Clade of derived hadrosauroid ornithopods lacking a pollex.
Hadrosauromorpha is a group of iguanodontian ornithopods. David B. Norman established it in 2014 to separate basal hadrosauroids—those with compressed hand bones and a thumb spike—from more advanced forms that lost these features. Under the PhyloCode, the clade is officially defined as the largest group that includes *Hadrosaurus foulkii* but excludes *Probactrosaurus gobiensis*. Which taxa fall inside the clade depends on the specific analysis used.
Norman first used the term in a 2014 paper on the phylogeny of *Hypselospinus*. In that paper, he credited another of his publications as the authority for the name—a chapter in the book *Hadrosaurs*. That book came out later, in 2015. According to Article 19.4 of the PhyloCode, Norman (2015) is the author of the clade name, while Norman (2014) is the author of its definition.
The original phylogenetic definition, given by Norman in both 2014 and 2015, was: all hadrosauroids closer to *Edmontosaurus regalis* than to *Probactrosaurus gobiensis*. Mickey Mortimer objected, arguing that the PhyloCode requires the type genus *Hadrosaurus* to appear in the definition. Using that corrected definition, Norman (2015) included Hadrosauridae, *Tethyshadros*, and *Bactrosaurus* within Hadrosauromorpha. In 2014, Norman had also included *Levnesovia*, *Gilmoreosaurus*, and *Telmatosaurus*—the last of which he later placed inside Hadrosauridae. A 2014 analysis by Xing et al. found that *Eolambia* and *Protohadros*, which Norman had placed outside the clade, actually fell within his definition, along with many other taxa.
Several phylogenetic analyses have been done on hadrosauromorphs. Norman (2014) produced his own tree using 105 morphological traits and 27 ornithopod taxa. Mortimer heavily criticized Norman’s definitions as unnecessary changes that only added confusion. In 2020, Madzia et al. recovered Hadrosauromorpha as part of a long grade of stem-hadrosaurs, with no major subgroups except for a cluster of Eurasian taxa.
Norman chose *Probactrosaurus* as the outgroup because of several key differences. In *Probactrosaurus*, the tooth crowns on the dentary are asymmetrical with multiple vertical ridges, there is a foramen in the surangular, and the quadrate has a pronounced depression for the jugal articulation. These features are absent in more derived hadrosauromorphs.
Quick Facts
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- Hadrosauromorpha
Facts from the source article.
Lore & Background
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. However, the book was published later, in 2015. 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).
The clade was first given a phylogenetic definition by Norman (2014 and 2015) as hadrosauroid taxa closer to Edmontosaurus regalis than Probactrosaurus gobiensis. This definition was contested by Mickey Mortimer, who stated that to follow the PhyloCode the taxon Hadrosaurus must be included in the definition, as it is the type genus of Hadrosauromorpha. By this definition, Norman (2015) considered Hadrosauromorpha to include Hadrosauridae, as well as the taxa Tethyshadros and Bactrosaurus. Norman in 2014 had included more taxa, such as Levnesovia, Gilmoreosaurus and Telmatosaurus, the last of which was considered inside Hadrosauridae by Norman in 2015.
Another phylogenetic analysis by Xing et al. in 2014 found that Eolambia and Protohadros, both found outside Hadrosauromorpha by Norman, fell within his definition, as well as a large number of other taxa. Norman's definitions have been heavily criticized by Mickey Mortimer as being unnecessary changes which cause more confusion to classification.
Reader's Guide
Hadrosauromorpha represents a significant clade within hadrosauroid ornithopods, defined by the loss of the pollex and associated manual modifications. Its formal definition under the PhyloCode—as the largest clade containing Hadrosaurus foulkii but not Probactrosaurus gobiensis—has led to varying taxonomic compositions across different phylogenetic analyses. Norman's original 2014 definition using Edmontosaurus regalis was contested by Mortimer, who insisted on including the type genus Hadrosaurus, resulting in a revised definition that nonetheless still yields different inclusions depending on the analysis. For instance, Norman (2015) included Hadrosauridae, Tethyshadros, and Bactrosaurus, while his 2014 analysis also included Levnesovia, Gilmoreosaurus, and Telmatosaurus. Xing et al. (2014) found even broader inclusion, placing Eolambia and Protohadros within the clade. The phylogenetic position of Hadrosauromorpha remains debated; Madzia et al. (2020) placed it in the middle of a long grade of stem-hadrosaurs, without large groups apart from a Eurasian cluster. Anatomically, hadrosauromorphs are distinguished from Probactrosaurus by asymmetrical tooth crowns with multiple ridges, a foramen in the surangular, a quadrate depression for the jugal, a non-J-shaped scapula with an overhanging projection, slender lower forelimb bones, absence of a pollex, reduced carpal bones, a less mobile manus, angular ilia lacking a brevis shelf, a straight femoral shaft, and truncated pedal bones. These features highlight the clade's evolutionary transition toward more derived hadrosaurids.
Did You Know?
- Hadrosauromorpha was first used in literature by David B. Norman in 2014, but its authorship is Norman (2015) per PhyloCode Article 19.4.
- The clade's definition was contested by Mickey Mortimer, who argued that Hadrosaurus must be included as the type genus.
- Norman (2014) included Levnesovia, Gilmoreosaurus, and Telmatosaurus in Hadrosauromorpha, but Norman (2015) placed Telmatosaurus inside Hadrosauridae.
- Xing et al. (2014) found that Eolambia and Protohadros fell within Norman's definition of Hadrosauromorpha, contrary to Norman's own results.
Frequently Asked Questions
What is Hadrosauromorpha?
It is a clade of derived hadrosauroid ornithopods, essentially the 'advanced' duck-billed dinosaurs that shed their thumb spike and simplified their hand structure. It sits within the broader iguanodontian family tree.
Who coined the name Hadrosauromorpha and when?
David B. Norman introduced the term in his 2014 paper examining the phylogenetic position of Hypselospinus. Under PhyloCode rules, the formal authorship is dated to 2015.
How is Hadrosauromorpha formally defined?
The PhyloCode node-based definition anchors it as the largest clade containing Hadrosaurus foulkii while explicitly excluding Probactrosaurus gobiensis. Exactly which species land inside the boundary shifts depending on which phylogenetic analysis you run.
What anatomy sets Hadrosauromorpha apart from basal hadrosauroids?
Members lost the pollex, show reduced and less mobile carpal bones, and possess a straighter femoral shaft along with truncated pedal elements. These hand and limb changes distinguish them from earlier forms that still retained compressed hand bones and a functional thumb spike.
Why did Norman create Hadrosauromorpha as a separate group?
He needed a name for the derived hadrosauroids that had already simplified their manus, separating them from basal forms that still carried compressed carpal bones and a thumb spike. It gives paleontists a clean label for that transitional morphological shift.
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