Alocodon

''Alocodon'' is a genus of ornithischian dinosaur known from multiple teeth from the Middle or Late Jurassic. The taxon was first described in 1973 by Richard A. Thulborn for an assemblage of teeth from the Pedrógão locality of Portugal, distinguished by an enlarged central denticle on the teeth, with the name taken from the Greek ''alox'' and ''odon'' meaning 'furrow tooth'. The type specimen, a single tooth, is stored in the Museu Geológico do Instituto Geológico e Mineiro in Lisbon, Portugal, formerly having been kept in the collections of the Free University of Berlin as IPFUB P X 1, and comes from an individual under in length. Though it was originally described as having been found in an unnamed deposit in the Portuguese Leiria District of upper Callovian age, it was identified as having come from the lower Oxfordian Cabaços Formation. Alongside the 158 isolated teeth from Portugal assigned to ''Alocodon'', some isolated teeth from the Bathonian Forest Marble and Chipping Norton Formations of England have been assigned to as cf. ''Alocodon sp.'' based on similarity.

''Alocodon'' was originally referred to as a member of the ornithopod family Fabrosauridae by Thulborn in 1973, closest to ''Fabrosaurus'' but also related to ''Echinodon'' and '' Trimucrodon''. Peter M. Galton retained it in the family in 1978, though he noted that there were significant differences between ''Alocodon'' and ''Fabrosaurus'', and the Middle to Late Jurassic fabrosaurids ''Alocodon'', ''Trimucrodon'' and ''Echinodon'' were representative of three independent branches of the family, with ''Nanosaurus'' not preserving enough material to determine its relationships. Galton then suggested in 1983 that ''Alocodon'' was related to ''Othnielia'', based on similarities of the teeth, placed within the ornithopod family Hypsilophodontidae. Given that the species was only represented by teeth, ''Alocodon'' was designated as a ''nomen dubium'' in 1990 by David B. Weishampel and Lawrence M. Witmer, as an indeterminate member of Ornithischia outside Ornithopoda. While a basal ornithischian position outside Ornithopoda was retained by Paul Sereno in 1991, it was considered a possibly valid taxon based on its broad central denticle.

José Ruiz-Omeñaca reclassified ''Alocodon'' in 1999, based on a reconsideration of features and classifications specified previously. Though it had similarities to ornithopod, Ruiz-Omeñaca instead placed it within Thyreophora as an intermediate taxon, as the tooth crown was asymmetrical, with the cingulum on one side higher than the other, and no ridges present on the crown. Weishampel, Witmer and colleague David B. Norman followed their 1990 opinion on ''Alocodon'' in 2004, though they noted that further study could potentially support the validity of the taxon. Features of the teeth identified by José I. Canudo and colleagues in 2004 instead supported a more specific position for ''Alocodon'', as a member of Ankylosauria. Canudo ''et al.'' based this assignment on the anatomy of the denticles and cingulum of the crown. A denticulate cingulum present in ''Alocodon'' was also identified as an ankylosaur feature, by Paul M. Barrett and colleagues in 2010, though more material was considered necessary to verify the importance of the feature. ''Alocodon'' was considered an ornithopod by Filippo M. Rotatori and colleagues in 2020. Because of its incomplete nature, ''Alocodon'' has been excluded from phylogenetic analyses.

A diversity of fauna is known from the Praia de Pedrógão locality alongside ''Alocodon'', including the pterosaur ''Rhamphorhynchus'', fragments of the shell of a turtle, remains of ''Goniopholis'' and another intermediate crocodilian, material from a kuehneosaurid and another unnamed lizard, an unnamed salamander, and teeth from the teleost fishes ''Caturus'', ''Lepidotes'' and '' Proscinetes'', and two hybodontid sharks: ''Asteracanthus'' and an unnamed small form. Footprints and teeth of a very large theropod also indicate their presence in the locality.

References

Ornithischian genera
Middle Jurassic dinosaurs of Europe
Jurassic Portugal
Fossils of Portugal
Lourinhã Formation
Fossil taxa described in 1975
Taxa named by Richard A. Thulborn
Nomina dubia

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