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Unenlagiid Affinities for Imperobator antarcticus (Paraves: Theropoda): Paleobiogeographical Implications
Article
Date:
2025Publishing House and Editing Place:
ASOCIACION PALEONTOLOGICA ARGENTINAMagazine:
AMEGHINIANA, vol. 62 ASOCIACION PALEONTOLOGICA ARGENTINASummary *
Abstract. Imperobator antarcticus is a paravian dinosaur based on fossil remains of the left and right hind limbs from the Cape Lamb Member(lower Maastrichtian) of the Snow Hill Island Formation, Antarctica. The only known specimen includes the tibia, astragalus, ca lcaneum,fragments of metatarsals, and non-ungual and ungual phalanges. It was originally described as a paravian with uncertain affinities, as it exhibitsa mosaic of characters, such as the fusion of the calcaneum and fibula, a non-ginglymoid metatarsal II, and the absence of hyper-specializationof pedal digit II, forming the raptorial digit typical of deinonychosaurian dinosaurs. Previous authors indicate that it may be related todromaeosaurids and unenlagiids. Imperobator was included in the TWiG data matrix to recognize its phylogenetic affinities. This comprehensivedataset was further improved by re-scoring and reanalysis of most unenlagiids. Additionally, 11 new taxa (including Imperobator and SouthAmerican paravians like Pamparaptor and Overoraptor) were added, resulting in a data matrix of 175 taxa and 850 characters. The STAR 1methodology proposed by previous authors was followed to construct phylogenetic trees. As a result,Imperobator antarcticus is nested withinthe Unenlagiidae clade. Despite its incomplete nature,Imperobator exhibits a subarctometatarsalian pes, a condition regarded as a Unenlagiidaesynapomorphy by the present analysis. In dromaeosaurids, such as eudromaeosaurians and halszkaraptorines, metatarsal III is notlateromedially compressed, shows subparallel medial and lateral margins, and is not constricted between metatarsals II and IV. Imperobatorantarcticus constitutes an important addition to the list of Late Cretaceous dinosaurs shared by South America and Antarctica. Information provided by the agent in SIGEVAKey Words
CretaceousAntarcticaParavesImperobator antarcticus