Uteodon aphanoecetes Carpenter & Wilson, 2008

Mcdonald, Andrew T., 2011, The taxonomy of species assigned to Camptosaurus (Dinosauria: Ornithopoda), Zootaxa 2783, pp. 52-68 : 56-59

Uteodon aphanoecetes Carpenter & Wilson, 2008 , comb. nov.

2008 Camptosaurus aphanoecetes Carpenter & Wilson , p. 232.

Holotype. CM 11337, nearly complete postcranium.

Paratypes. CM 15780, 41689, 79050; DINO 556, 1030, 1032.

Referred material. Disarticulated elements held in CM and DINO collections ( Carpenter & Wilson 2008).

Generic etymology. Ute (pronounced “yewt”) is the name of a Native American people who inhabit northeastern Utah, in the vicinity of Dinosaur National Monument. Odon comes from the transliterated Greek meaning “tooth”, and is a common root in the generic names of basal iguanodonts. The gender of the generic name is masculine.

Locality and horizon. Carnegie Quarry at Dinosaur National Monument, Uintah County, Utah; Brushy Basin Member of the Morrison Formation, lower–middle Tithonian ( Kowallis et al. 1998).

Generic diagnosis. As for the species by monotypy.

Specific diagnosis. Basal styracosternan distinguished by a single autapomorphy: occipital condyle projects farther ventrally than the basal tubera ( Fig. 7 ). Also distinguished from all other iguanodontians except Cumnoria prestwichii by the following unique combination of characters: scapula with acromion process that is convex along its cranial margin ( Fig. 3 B), convex dorsal margin of scapula ( Fig. 3 C), convex dorsal margin of ilium, dorsal margin of ilium thickens mediolaterally towards M. iliocaudalis platform, postacetabular process of ilium tapers to a point with break in slope along dorsal margin ( Fig. 6 A), distal end of ischium forms cranially expanded boot.

Remarks. The holotype of Uteodon aphanoecetes , CM 11337, was originally referred to Camptosaurus “ medius ” (= C. dispar ) by Gilmore (1925). Carpenter & Wilson (2008) reassessed the specimen and found that it differed sufficiently from specimens of C. dispar to warrant the creation of the new species C. aphanoecetes . The new phylogenetic analysis supports the distinction of Uteodon aphanoecetes from C. dispar , but does not recover a monophyletic Camptosaurus as conceived by Carpenter & Wilson (2008). Instead, Uteodon aphanoecetes and Cumnoria prestwichii (see below) are more derived than C. dispar in the reduced consensus tree and are therefore the most basal members of Styracosterna, which is defined as those species more closely related to Parasaurolophus walkeri than to Camptosaurus dispar ( Sereno 2005) ( Fig. 1 ). Furthermore, Uteodon is also found to be more derived than C. dispar in the agreement subtree ( Fig. 2 ). For the analysis, Uteodon aphanoecetes was coded based upon the holotype, paratypes, and referred specimens designated by Carpenter & Wilson (2008). Only specimens in the CM collection could be examined firsthand.

Uteodon aphanoecetes and Cumnoria prestwichii are quite similar to each other and different from Camptosaurus dispar . The holotype skeletons of Uteodon and Cumnoria both exhibit scapulae with convex dorsal margins, whereas scapulae of Camptosaurus dispar are straight or somewhat concave along their dorsal margins (e.g., USNM 2210, 4282, 5473, 5954, 5955; YPM 8611) ( Fig. 3 ). Furthermore, as noted above, the ilia of Cumnoria and Uteodon exhibit convex dorsal margins ( Fig. 6 ), similar to some more derived iguanodonts such as Iguanodon bernissartensis (IRSNB 1534) and Equijubus normani ( You et al. 2003), but different from the straight dorsal margin of the ilium of Camptosaurus dispar ( Fig. 4 ). Furthermore, Uteodon possesses an autapomorphy in the partial braincase of paratype specimen CM 15780: the occipital condyle projects far ventrally relative to the basal tubera. This condition differs from the basioccipitals of Camptosaurus dispar (USNM 5473, 5996, 5997; YPM 1856A, 1880) and Cumnoria (OXFUM J.3303), in which the basal tubera protrude farther ventrally than the occipital condyle ( Fig. 7 ).

The results of the phylogenetic analysis and the morphological differences explicated above strongly suggest that Uteodon aphanoecetes and Cumnoria prestwichii should not be considered congeneric with Camptosaurus dispar ; Uteodon and Cumnoria are recovered as basal styracosternans more derived than Camptosaurus dispar . It is thus a straightforward matter to reinstate the existing genus Cumnoria ( Seeley 1888) for “ Camptosaurus ” prestwichii (see below). However, a more difficult dilemma is the status of “ Camptosaurus ” aphanoecetes , which does not have a pre-existing genus into which it can be conveniently placed. As described above, this species is very similar to Cumnoria prestwichii , distinguished only by a single autapomorphy of the braincase. Thus, the possible taxonomic revision that immediately arises is to create the new combination Cumnoria aphanoecetes . However, such a move presupposes that future phylogenetic analyses and discoveries will find a sister-taxa relationship of Cumnoria prestwichii and “ Camptosaurus ” aphanoecetes . The topologies presented herein could change with additional new taxa and new material, most especially additional cranial elements of “ Camptosaurus ” aphanoecetes (in addition to the known right dentary DINO 556 and partial braincase of CM 15780). It is this labile nature of the phylogeny that prompts the creation of the new genus and combination Uteodon aphanoecetes . This species can thus occupy any position relative to Cumnoria prestwichii and Camptosaurus dispar in future analyses without necessitating still another taxonomic reassignment. From the standpoint of taxonomic stability, giving Uteodon aphanoecetes its own new genus is preferable to committing it to the genus Cumnoria.

Figures

FIGURE 1. Reduced consensus tree of 11,850 MPTs of 358 steps each, following ordering of 22 multistate characters and safe taxonomic reduction. Camptosaurus dispar is highlighted in yellow and Uteodon aphanoecetes and Cumnoria prestwichii in blue. Numbers below and to the left of some nodes correspond to the following clade names: 1, Ornithopoda; 2, Iguanodontia; 3, Rhabdodontidae; 4, Dryomorpha; 5, Dryosauridae; 6, Ankylopollexia; 7, Styracosterna; 8, Hadrosauriformes; 9, Hadrosauroidea.

FIGURE 2. Agreement subtree of 11,850 MPTs of 358 steps each, following ordering of 22 multistate characters and safe taxonomic reduction. Camptosaurus dispar is highlighted in yellow and Uteodon aphanoecetes in blue. Numbers below and to the left of some nodes correspond to the following clade names: 1, Iguanodontia; 2, Rhabdodontidae; 3, Dryomorpha; 4, Dryosauridae; 5, Ankylopollexia; 6, Styracosterna; 7, Hadrosauriformes; 8, Hadrosauroidea; 9, Hadrosauridae.

FIGURE 3. (A) USNM 4282, left scapula of Camptosaurus dispar in lateral view; (B) CM 11337, cranial end of the right scapula of Uteodon aphanoecetes in lateral view; (C) CM 11337, left scapula of Uteodon aphanoecetes in lateral view; (D) OXFUM J. 3303, right scapula of Cumnoria prestwichii in lateral view. Abbreviations: cap, convex cranial margin of the acromion process; tap, triangular acromion process. Scale bar in A equals 10 cm; scale bar in B equals 5 cm.

FIGURE 4. Ilia of Camptosaurus dispar in lateral view. (A) right ilium of YPM 1877 (holotype) from Quarry 13; (B) right ilium of YPM 8622 from Quarry 13; (C) left ilium of USNM 5473 from Quarry 13; (D) left ilium of YPM PU 14553 from Cleveland-Lloyd Dinosaur Quarry. Abbreviations: mlt, mediolateral thickening; pas, break in slope along dorsal margin of postacetabular process. Images in A, B, and D are copyright YPM. Scale bar equals 10 cm.

FIGURE 6. Left ilium of CM 11337 (holotype of Uteodon aphanoecetes) in (A) ventrolateral view showing the convex dorsal margin, (B) lateral view, (C), caudal view. Sacrum and ilia of CM 11337 in (D) dorsal view. Right ilium of CM 11337 in (E) lateral view. Right ilium of OXFUM J. 3303 (holotype of Cumnoria prestwichii) in (F) lateral view. Abbreviations: dmi, dorsal margin of ilium; mlt, mediolateral thickening; pas, break in slope along dorsal margin of postacetabular process.

FIGURE 7. Partial braincases of Camptosaurus dispar, Uteodon aphanoecetes, and Cumnoria prestwichii. (A) YPM 1880 in left lateral view (image copyright YPM); (B) CM 15780 in right lateral view (image courtesy of M. Lamanna); (C) OXFUM J. 3303 in right lateral view. Abbreviations: bt, basal tubera; oc, occipital condyle. Scale bar equals 5 cm.