Animalia Sereno 1986

IGUANODONTIA Sereno, 1986

Phylogenetic definition. The most inclusive clade containing Parasaurolophus walkeri Parks, 1922 but not Hypsilophodon foxii Huxley, 1869, or Thescelosaurus neglectus Gilmore, 1913 (Sereno, 2005).

Unambiguous synapomorphies. In the parsimony analysis, Iguanodontia is characterized by a maxilla with a broad and triangular dorsal process of the maxilla (21.1), a quadrate extending ventrally such that the quadratojugal is well removed from the mandibular condyle (60.1), a single wear facet on each cheek tooth (131.1), opisthocoelus post-axial cervical vertebrae (157.1), a distinct indentation on the scapula superior to the glenoid, termed here the supraglenoid fossa (199.1), and a manual digit III with three or fewer phalanges (236.1).

Two other synapomorphies recovered for this clade are elongate prezygopophyses on the distal caudal vertebrae (185.1), and chevrons that are strongly and asymmetrically expanded distally (188.1). The former of these is found only in Gasparinisaura and Leaellynasaura, and the latter in these genera plus Parksosaurus and Macrogryphosaurus. While they are present at the base of the clade, these characters are not widespread, and therefore not useful in diagnosing the clade.

There is only one overlapping character here with the diagnosis of Sereno (1986); the reduction of phalanges in digit III. The presence of “leaf-shaped” or mamillated denticles is more restricted within Styracosterna, and while most iguanodontians lack premaxillary teeth, both Talenkauen and Tenontosaurus dossi have one premaxillary tooth. Iguanodontia is recovered with jackknife support of 19 and Bremer support of 4.

Within the Bayesian topology, Iguanodontia (PP=0.43) lacks the basal pectinate region found in the parsimony analysis and is instead composed of the sister groups of rhabdodontoids and Dryomorpha. Gasparinisaura, Leaellynasaura, and Macrogryphosaurus are excluded from Iguanodontia, and are recovered instead with the hypsilophodontids. This rearrangement of taxa leads to different synapomorphies for Iguanodontia between the parsimony and Bayesian analyses. Synapomorphies for the Bayesian topology include: premaxilla flaring laterally to form a floor of the narial fossa (3.1), small antorbital fenestra (31.1), predentary with denticulate oral margin (87.1), ventral process of predentary deeply bifurcated (89.1), cheek teeth with crowns tapering toward the root (127.1, 128.1), cheek teeth that are closely packed without spaces between roots (126.1), cheek teeth with one wear facet on each tooth (131.1), cheek teeth lacking a basal ridge (“cingulum”) (148.1), caudal vertebrae with distal facets for chevrons much larger than proximal facets (183.0), humerus with an elongate deltopectoral crest (>43% humeral length) (214.1), manual digit III with three or fewer phalanges (236.1), first phalanx of manual digits II-IV more than twice the length of the second phalanx (239.1), ischium with an untwisted shaft (283.1), ischium with an expanded distal end (288.1), femur with a cranial intercondylar sulcus (300.1), and a caudal intercondylar sulcus partially roofed by the medial condyle (302.1).

Topology. In the parsimony analysis (Figures 6, 7), the basally branching portion of Iguanodontia forms a pectinate topology outside of Dryomorpha, which includes Gasparinisaura, Leaellynasaura, Macrogryphosaurus, Talenkauen, Valdosaurus, Anabisetia, Trinisaura, and Kangnasaurus. It is supported by a jackknife value of 19 and a Bremmer support of 4.

In the Bayesian analysis (Figures 6, 8), Iguanodontia bifurcates into rhabdodontoids and dryomorphans. Iguanodontia is supported by a posterior probability of 0.43.