Читать книгу Hadrosaurs - David A. Eberth - Страница 55

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 the systematic review above that the anatomies of the contemporary taxa Bolong and Jinzhousaurus are very similar. A range (plexus, as in Figure 2.24) of neoiguanodontian taxa forms a cluster between Hypselospinus and Hadrosauromorpha. These taxa have proved difficult to arrange consistently in any published phylogeny, and this may well reflect anatomical incompleteness and/or a phase of comparatively rapid evolution (and possibly disparate character acquisition) among and between ornithopods during the early Late Cretaceous.