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| Ampelognathus coheni Tykoski, Contreras and Christopher & Noto, 2023 |
ABSTRACT
Sediments of the Woodbine Group exposed in northeastern Texas were deposited along the southwestern margin of Appalachia as a series of near-shore, shoreline, distal lowland swamp, lake, and fluvial deposits during a regression of the Western Interior Seaway in early and middle Cenomanian time. The Lewisville Formation (upper Woodbine Group) of north Texas preserves the most diverse terrestrial fossil assemblage known from Appalachia, but remains of small ornithischian dinosaurs have been conspicuously absent from it. An almost complete left dentary from the Lewisville Formation represents a new, small-bodied ornithopod taxon, Ampelognathus coheni gen. et sp. nov. The dentary is generally similar to those in non-iguanodontian ornithopods such as Hypsilophodon, Changchunsaurus, Haya, and Convolosaurus. Ampelognathus occupied an expected but previously missing component of the ‘mid’ Cretaceous terrestrial fauna of southwestern Appalachia. The growing diversity of fossil vertebrates and renewed paleobotanical study in the Lewisville Formation reinforces the importance of the unit’s fossil record for understanding eastern North American terrestrial ecosystems during an important transitional period in the earliest Late Cretaceous.
SYSTEMATIC PALEONTOLOGY
DINOSAURIA Owen, 1842
ORNITHISCHIA Seeley, 1887
CERAPODA Sereno, 1986
ORNITHOPODA Marsh, 1881
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| DMNH 2021-05-02, holotype left dentary of Ampelognathus coheni, photos and labeled outline drawings in A, lateral; B, medial; C, dorsal; D, ventral; E, anterior; and F, posterior views. Abbreviations: a#, alveolus and numerical position in tooth row; anf, angular facet; cof, coronoid facet; cop, coronoid process; d6, dentary tooth 6 base; ds, dentary symphysis; mc, Meckelian canal; mg, Meckelian groove; pdd, dorsal facet for predentary; pdv, ventral facet for predentary; saf, surangular facet. Gray fill indicates recessed surfaces. Stippling indicates visible sediment. Cross-hatching indicates broken bone surface. Scale bars equal 5 mm. |
AMPELOGNATHUS COHENI, gen. et sp. nov.
Diagnosis—Ampelognathus coheni is distinguished from other, closely related ornithopod dinosaurs by: an approximately 45° counter-clockwise ‘twist’ or torsion of the middle and posterior sections of the dentary relative to the anterior part of the dentary, resulting in dorsomedial orientation of the axes of the posterior (distal) alveoli relative to the anterior (mesial) alveoli (autapomorphy); no diastema between predentary contact and first dentary alveolus; coronoid process weak or low, so that dentary height at the process is less than 150 percent mandibular height under the mid-part of the tooth row.
Etymology—‘Ampelo-,’ from Greek for grapevines in reference to its discovery in the emergency spillway for Grapevine Lake; ‘gnathus’ from Greek for jaw; ‘coheni,’ in honor of Murray Cohen, the avocational fossil enthusiast who found the specimen.
CONCLUSIONS:
Ampelognathus coheni is a new, non-iguanodontian ornithopod dinosaur established on DMNH 2021-05-02, a mostly complete left dentary from the Lewisville Formation (Woodbine Group) of Tarrant County, Texas. The dentary of A. coheni generally resembles those in other non-iguanodontian ornithopods. It is distinguished from them and the much larger-bodied contemporaneous hadrosauroid Protohadros byrdi by axial torsion of the anterior end of the dentary that directs the anterior alveoli dorsolaterally instead of dorsally, little to no separation or diastema between the predentary facet and first dentary alveolus, a low coronoid process so overall dentary height is less than 150 percent mandible height at the mid-point of the dentary, and relatively high dentary tooth count for its size. A phylogenetic analysis based on the dataset of Dieudonné et al. (Citation2021) places A. coheni as the sister taxon to a clade comprised of Thescelosaurus and Iguanodontia, a relationship weakly supported by the shared presence of a downturned anterior end of the dentary tooth row.
Ampelognathus is the first small-bodied ornithischian taxon known from the Lewisville Formation, and the Woodbine Group as a whole. Its presence adds to the diversity of fossil organisms known from the lower middle Cenomanian deposits of southwestern Appalachia, a time and place with an otherwise poor record of terrestrial ecosystems. The increasing knowledge of paleo-diversity along the west coast of the Appalachian landmass shortly after the final separation of Laramidia and Appalachia by incursion of the WIS should facilitate more comparisons and contrasts with similar-aged paleo-ecosystems preserved in units such as the Cedar Mountain Formation and Naturita Formations of Laramidia. This should provide a better understanding of the pattern and timing of floral and faunal divergence, and the resulting tempo of evolution on both sides of the WIS through the remainder of the Late Cretaceous.
Ronald S. Tykoski, Dori L. Contreras and Christopher Noto. 2023. The First small-bodied Ornithopod Dinosaur from the Lewisville Formation (middle Cenomanian) of Texas. Journal of Vertebrate Paleontology. e2257238. DOI: 10.1080/02724634.2023.2257238
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