A Late Cretaceous nodosaurid ankylosaur (Dinosauria: Ornithischia) from marine sediments of coastal California

Abstract

A partial nodosaurid ankylosaur skeleton, consisting primarily of the ilia, hindlimbs, posterior dorsal armor, plus partial forelimb elements and additional armor, was recovered from the marine Point Loma Formation, late Campanian age, north of San Diego, California. The specimen is similar to contemporaneous species of Panoplosaurus and Edmontonia from terrestrial sediments of the western interior, but there are also similarities to the armor of Stegopelta landerensis from marine sediments of earliest Cenomanian age from Wyoming. Skeletal elements critical for generic determination are not preserved, and the specimen is identified as Nodosauridae, incertae sedis. An associated marine invertebrate fauna and nannoplankton flora have revealed some discrepencies in the correlation systems used for Upper Cretaceous marine rocks of coastal California. Hollow limb bones of the specimen are interpreted as a preservational artifact. Nodosaurids had broad ecological tolerances, and visited riparian and coastal environments more frequently than other dinosaurs. However, a review of morphologic and distributional evidence fails to support a theory of amphibious or aquatic habits for nodosaurids.

A new ankylosaurid from the late Cretaceous Two Medicine Formation of Montana, USA

“…Ford and Kirkland (2001) erected Aletopelta coombsi based on SDNHM 33909, a specimen from the broadly contemporaneous Point Loma Formation of coastal California. The specimen was originally described by Coombs and Demere (1996) as Nodosauridae indet. Referral of Aletopelta to the Ankylosauridae is debatable as some of the characters used to identify it as ankylosaurid are unconvincing, e.g., limb and armour morphologies.…”

“…Gilmore (1930) referred the specimen to Dyoplosaurus acutosquameus based primarily on tooth morphology. Although dentition may not be taxonomically useful for ankylosaurs below the familial level (Coombs and Demere 1996; personal observations), the teeth of USNM 11892 do represent a morphological extreme among teeth of late Campanian ankylosaurid specimens from Montana and Alberta. The teeth have a shelf-like labial cingulum and a unique Z-shape to the carina in occlusal view.…”

Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs

“…Discussion. SDNHM 33909 was originally described as an indeterminate nodosaurid that shared some similarities to Edmontonia, Panoplosaurus and Stegopelta (Coombs & Dem er e 1996). Ford & Kirkland (2001) reassessed the specimen as an ankylosaurid ankylosaur, and, considering it taxonomically distinctive, named it Aletopelta coombsi.…”

“…Although the specimen includes elements from many regions of the body, assessing the taxonomic affinities of SDNHM 33909 is hampered by the taphonomic condition of most of the bones. The specimen was preserved in marine sediments, where the skeleton was scavenged by invertebrates and sharks, and acted as the substrate for encrusting pelecypods (Coombs & Dem er e 1996). The articular ends are missing from all of the limb elements, making comparisons with other species difficult.…”

External and internal structure of ankylosaur (Dinosauria, Ornithischia) osteoderms and their systematic relevance

“…The North American taxa, Edmontonia longiceps Sternberg, 1928, Edmontonia rugosidens (Gilmore, 1930), and Panoplosaurus mirus Lambe, 1919, are in large part differentiated on the basis of osteoderm morphology and textures (Carpenter, 1990). Osteoderms contributed the primary characters in the diagnosis of Aletopelta Ford and Kirkland, 2001, and to the clarification of the familial assignment of the genus (Coombs and Demere, 1996;Ford and Kirkland, 2001). In a redescription of Ankylosaurus magniventris Brown, 1908, Carpenter (2004 partially rediagnosed the genus using characters of the cervical half rings, osteoderm surface texture, and osteoderm keel placement.…”