Dryomorpha
Phylogenetic Definition This node-based clade is defined as Parasaurolophus walkeri, Dryosaurus altus, their common ancestor, and all of its descendants.
Character Acquisition at This Node
ACCTRAN: 4, 20, 53, 54, 58, 59, 61, 65, 68, 81, 85, 89, 91.
DELTRAN: 12, 20 33, 53, 54, 58, 59, 82, 83, 85.
Condensed Diagnosis
1. Maxillary tooth crowns are apicobasally elongate and characterized by the possession of a narrow, elevated primary ridge on the labial surface of the crown that is positioned slightly distal to the midline.
2. Dentary tooth crowns exhibit a clearly defined, but low, primary ridge that is offset distally to the midline.
3. In lingual view a shoulder-like edge is formed between the denticle that marks the tip of the primary ridge and the point of inflection that marks the start of the subvertical mesial margin of the crown.
4. The quadrate bears a well-defined semicircular notch on the central portion of the anterior margin of the jugal wing that is spanned anteriorly by the quadratojugal. With the quadratojugal in articulation a fully enclosed quadrate (paraquadratic) foramen is formed.
5. Predentary with divergent, ventrolateral processes.
6. The obturator process of the ischium is positioned proximally (separated by an embayment from the pubic peduncle of the ischium) on the anteromedial edge of the shaft of the ischium.
7. The ischial shaft has a subcircular cross section along almost its entire length and there is a small anterior expansion of the distal tip of the ischial shaft that forms a “boot.”
8. The femoral shaft displays an anterior intercondylar groove that is defined by a pair of ridges that form on the adjacent edges of the dorsal part of the distal articular condyles.
Comments There is a marked contrast between the style of morphological differentiation of the dentition in basal clypeodontans and that in dryomorphans, which suggests that a new morpho-functional trajectory (probably linked to oral food processing) had emerged. Additional characters, such as the development of a bilobate posteroventral processes on the predentary, probably served to reinforce a structurally weak dentary symphysis and may reflect alterations to jaw function. A ventrally bilobate predentary also appears sporadically in basal clypeodonts (rhabdodontids), but this is interpreted as an example of convergence (homoplasy) in the larger-bodied tenontosaurs and the very late appearing (Maastrichtian) rhabdodontids. The ischial characters (such as the positioning of the obturator process and curvature of the ischial shaft) also appear sporadically and probably convergently in Maastrichtian rhabdodontids.
Ankylopollexia
Phylogenetic Definition This node-based clade (Fig. 2.26) can be defined as Parasaurolophus walkeri, Camptosaurus dispar, their common ancestor, and all of its descendants.
Character Acquisition at This Node
ACCTRAN: 2, 15, 46, 51, 57, 69, 72.
DELTRAN: 2, 4, 15, 30, 45, 51, 57, 64, 68, 69, 72.
Condensed Diagnosis
1. Conical pollex ungual.
2. Short, block-shaped metacarpal I is sutured at an oblique angle against the radiale and carpal 2.
3. Carpo-metacarpal block formed by suturing of the individual elements.
4. Manus digit IV bears an ungual phalanx that is small and shows no obvious grooves for attachment and growth of a claw or hoof.
5. Occlusal plane of the premaxilla and predentary deflected ventrally.
6. Ventral margin of the jugal is arched and forms a prominently angled projection posteriorly.
7. Acromion process of the scapula curved anteriorly at its proximal end.
Comment It is unfortunate that the structure of the carpus and manus is presently unknown among dryosaurs, since this might have a significant bearing on the status of the ankylopollexian clade.
Neoiguanodontia (“New Iguanodonts”)
Phylogenetic Definition The node-based clade can be defined as Parasaurolophus walkeri, Hypselospinus fittoni, their common ancestor, and all of its descendants.
Character Acquisition at This Node
ACCTRAN: 9, 13, 27, 34, 40, 48, 61, 62, 66, 67, 70, 73, 80, 81, 87, 88, 89, 90, 92.
DELTRAN: 40, 48, 62, 66, 67, 70, 73, 80, 81, 87, 88, 89, 90, 92.
Condensed Diagnosis
1. The marginal denticles on the mesial and distal margins of maxillary and dentary tooth crowns form curved ledges that are ornamented with mammillae/papillae.
2. The posterodistal corner of dentary crowns, when viewed lingually, exhibit inrolling of the marginal denticulate edge to form an oblique ledge-like structure (sometimes referred to as a cingulum).
3. Posterior dentary dentition extends medial to the coronoid process, and from which the dentition is separated by a narrow, horizontal ledge that represents a posterior extension of the lateral cheek recess.
4. Coronoid process elevated and its axis lies perpendicular to the long axis of the dentary ramus.
5. Antorbital fenestra (and fossa) reduced in size and forms an oblique channel between the maxilla and lacrimal.
6. The articulation between the jugal and maxilla comprises an oblique, finger-like posterolateral projection from the maxilla that fits into a complementary elongate slot on the anteroventral surface of the jugal.
7. The supraoccipital is excluded from the posterodorsal margin of the foramen magnum by a shelf-like structure formed by dorsomedial processes of the exoccipitals that meet in the midline.
8. Sternal bones develop an oblique, posterolateral, rod-like extension that ends in an articular boss.
9. Metacarpals II–IV of the manus are elongate, bundled together and held in place by development of collateral ligaments that are sometimes ossified.
10. Manus unguals II and III are dorsoventrally flattened, asymmetrical and generally hoof-like.
11. Posterior pubic ramus is slender and significantly shorter than the shaft of the ischium (this character is homoplastic in rhabdodontids and tenontosaurids).
12. Pedal ungual phalanges are dorsoventrally flattened and bluntly truncated distally, but retain well-developed claw grooves bilaterally.
Comments The position of Hypselospinus with respect to the sister clade comprising Bolong, Jinzhousaurus, Barilium, Iguanodon, and Mantellisaurus (= Iguanodontidae) and Hadrosauriodea needs to be more accurately determined (Norman, in press). It is also clear, following