The systematic position of the Late Jurassic alleged dinosaur Macelognathus (Crocodylomorpha: Sphenosuchia)
Macelognathus vagans was described by O.C. Marsh in 1884 on the basis of a mandibular symphysis from the Upper Jurassic Morrison Formation of Wyoming, USA.In the past, this taxon was often considered a dinosaur, but later was also tentatively referred to the Crocodylia. Its phylogenetic identity has until now been enigmatic and its determination was hampered by the fact that the taxon was represented only by a mandibular fragment.Recently, some partial disarticulated skeletons, also from the Upper Jurassic Morrison Formation, but from a different locality, namely the Fruita Palaeontological Area, Colorado, have been studied and identified as sphenosuchians—an extinct sister-taxon of the Crocodyliformes (Crocodylomorpha). Two mandibles of this new material are morphologically identical with the holotype of Macelognathus vagans. On the basis of this new sphenosuchian material from the Fruita Paleontological Area it is possible for the first time to identify the enigmatic taxon Macelognathus vagans as a sphenosuchian crocodylomorph.The new material of Macelognathus vagans augments our knowledge of the diversity of sphenosuchians and for the first time provides postcranial information of this taxon. In addition, the new material from the Upper Jurassic Morrison Formation of the Fruita Paleontological Area extends the known stratigraphic range of sphenosuchians and constitutes the youngest definitive occurrence of a sphenosuchian, previously known from the Late Triassic to the Middle or Late? Jurassic.