Dracopelta

''Dracopelta'' (meaning “dragon shield”) is a monospecific genus of ankylosaur dinosaur from Portugal that lived during the Late Jurassic (uppermost lower Tithonian-upper Tithonian, 152.1-145.0 Ma) in what is now the Lourinhã Formation. The type and only species is ''Dracopelta zbyszewskii'', which is represented by a partial skeleton including unpublished material.

Discovery and naming

In 1963 or, more likely, early 1964, a partial skeleton was discovered during road construction works between the village of Barril and Praia da Assenta. Leonel Trindade confirmed the presence of the fossil in the area and photographed the specimen ''in situ''. Georges Zbyszewski and Octávio da Veiga Ferreir organized the excavation and extraction of the specimen in December 1964. Parts of the specimen were unprepared and misplaced, mixed in with a specimen of ''Miragaia''. The holotype specimen, MG 3 (formerly IGM 5787 and IGM 3), consists of dorsal vertebrae, articulated proximal ribs, osteoderms, an incomplete autopodium and unpublished material including a tibia, femur, and an ossified tendon. Currently new material pertaining to the holotype specimen is being described. The generic name, ''Dracopelta'', is derived from the Latin word ''draco'' (dragon) and the Greek word πέλτη, pelte, (Latinised to pelta), "small shield". The specific name, ''zbyszewskii'', honours Georges Zbyszewski, after his research on fossil vertebrates from Portugal.

The holotype was originally, and incorrectly, identified to be from the Kimmeridgian stage of Ribamar. However, Antunes and Mateus (2003) noted that at a locality named Ribamar, there are outcrops of Lower Cretaceous that date to the Valanginian and Albian stages and deemed it as highly unlikely that the specimen was obtained from that locality. Pereda-Suberbiola et al. (2005) determined that the specimen was from a locality constrained to the uppermost lower Tithonian-upper Tithonian which shows characteristics consistent with what is recognized in the Assenta Member of the Lourinhã Formation, an observation agreed upon by Russo and Mateus (2021).

In 2019, a specimen of an ankylosaur consisting of a nearly complete skull, articulated dorsal vertebrae, proximal half of ribs, articulated anterior caudal vertebrae, mostly complete and articulated synsacrum, fragments of disarticulated and broken ribs, femora, partial with attached pelvic shield, humerus, partial scapulocoracoid, tendons mostly attached to vertebrae, and osteoderms from the Lourinhã Formation was reported. The specimen is currently being studied on to clarify if it represents an additional, more complete specimen, of ''Dracopelta'' or a new taxon.

Description

''Dracopelta'' has an estimated body length of 3 metres (9.9 feet) and a weight of 300 kilograms (600 lb).Paul, G.S., 2010, ''The Princeton Field Guide to Dinosaurs'', Princeton University Press p. 231 The holotype specimen represents an adult individual.

Galton (1980) originally diagnosed ''Dracopelta'' based on the small flat osteoderms, small medial paired circular plated with raised centre and rims, long anterolateral plates, narrow nonprojecting overlapping dorsolateral plates and overlapping laterally projecting lateral plates in the thoracic region. Suberbiola et al. (2005) later diagnosed ''Dracopelta'' based on the presence of proximal phalanges II and III as long as wide and distinctive osteoderm morphology. The dorsal ribs are gently curved which indicates that the back was broad, much like that of other ankylosaurs, ''Dryosaurus'' and ''Camptosaurus'', and the base is at about the same level as the postzygapophyses and prezygapophyses. The prezygapophyses are just above the dorsal margin of the neural canal and are about 80 mm above the ventral rim of the centrum. The ribs are correlated with the possession of transverse processes that are inclined slightly upwards, a feature that differentiates it from ''Dacentrurus'', a stegosaur also from the Lourinhã Formation. The holotype preserves ossified tendons which is a feature seen in ankylosaurs, ornithopods and possibly ''Scelidosaurus''.

Suberbiola et al. (2005) noted that the manus of ''Dracopelta'' may have retained a primitive phalangeal formula, as in the nodosaurid ''Sauropelta'' and basal thyreophoran ''Scutellosaurus'', while ankylosaurids and stegosaurs showed a reduced phalangeal formula. Suberbiola et al. suggested that derived ankylosaurids and stegosaurs convergently evolved a tridactyl pes, with the loss of digit I, while '' Liaoningosaurus'' pertained a tetradactyl manus and a tridactyl pes. The authors interpreted that ''Dracopelta'' may have had cursorial adaptations as the autopodial structure falls into the metapodial range of the basal thyreophorans ''Scutellosaurus'' and ''Scelidosaurus'', which were probably subcursorial. The small size of ''Dracopelta'' is also consistent with the interpretation.

Classification

Galton (1980) originally assigned ''Dracopelta'' to Nodosauridae, based on the morphology of the osteoderms. However, Vickaryous et al. (2004) interpreted ''Dracopelta'' as Ankylosauria ''incertae sedis'' while Carpenter (2001) considered it as a ''nomen dubium'' based on the lack off diagnostic characteristic of the holotype specimen and assigned it as Polacanthidae ''incertae sedis'' based on the similarities between ''Gargoyleosaurus'' and '' Gastonia'' in osteoderm morphology.Vickaryous, M. K., Maryanska, T., and Weishampel, D. B. (2004). Chapter Seventeen: Ankylosauria. in The Dinosauria (2nd edition), Weishampel, D. B., Dodson, P., and Osmólska, H., editors. University of California Press. Suberbiola et al. (2005) were unable to recognize any polacanthid or nodosaurid characteristics and considered ''Dracopelta'' as a valid taxon based on the presence of proximal phalanges II and III as long as wide and distinctive osteoderm morphology. Due to the close proximities between the fauna of the Morrison Formation and Lourinhã Formation, ''Dracopelta'' might share close affinities with ''Gargoyleosaurus'' or ''Mymoorapelta''.

Paleoenvironment

The holotype specimen of ''Dracopelta'' was obtained from a layer from the Assenta Member of the Lourinhã Formation, which dates to the uppermost lower and upper Tithonian stage of the Late Jurassic. The member represents a fluvial channel and preserves small coalified plant fragments. The member is characterised by a succession of fluvial sandstones insinuated by erosive surfaces showing fossilised roots and bioturbation, indicating periodic subaerial exposure. ''Dracopelta'' would have coexisted with the carcharodontosaurian ''Lusovenator'', indeterminate turiasaurian sauropods, indeterminate crocodylomorphs, and an indeterminate ankylosaur, which may represent a second and more complete specimen of ''Dracopelta''.

See also

* Timeline of ankylosaur research

References

{{Taxonbar, from=Q132761

Ankylosauria
Dinosaur genera
Kimmeridgian dinosaurs
Lourinhã Formation
Taxa named by Peter Galton
Fossil taxa described in 1980
Dinosaurs of Portugal