Dacentrurine stegosaurs (Dinosauria): A new specimen of Miragaia longicollum from the Late Jurassic of Portugal resolves taxonomical validity and shows the occurrence of the clade in North America

Abstract

The stegosaur species Miragaia longicollum was erected based on a partial anterior skeleton from the Upper Jurassic of Portugal. Until then, almost all stegosaur specimens in Portugal and Spain had been identified as Dacentrurus armatus, the sister taxon of M. longicollum and only other member of the clade Dacentrurinae. The holotypes of the two species have little overlap, since the holotype of D. armatus is mostly a posterior skeleton, so the classification of other specimens to either species is unclear and the validity of M. longicollum has been questioned and debated. Here we describe a largely complete specimen of M. longicollum discovered in 1959 in Atouguia da Baleia, Peniche, Portugal, consisting of both anterior and posterior portions of the skeleton. Comparisons to the holotypes of dacentrurines and other stegosaurs shed light on the convoluted relationships of this group. We conclude that M. longicollum is valid and rather different from D. armatus, and provide a revised diagnosis of M. longicollum, as well as revised diagnoses for D. armatus, Dacentrurinae, and the first diagnosis of the genus Miragaia, granting stability to these taxa and allowing new considerations to be given on the classification of other Iberian stegosaurs. This new specimen is, to date, the most complete dinosaur described from Portugal and the most complete stegosaur described from Europe. Miragaia shared anatomical features that show a close affinity to Alcovasaurus longispinus, confirming this to be the first known dacentrurine stegosaur in America, coherent with the hypothesis of an ephemeral land bridge between North America and Iberia that allowed faunal exchange.

The complexity of tracking stegosaurs and their gregarious behavior

“…In addition, considering the similarities in the metatarsals of several stegosaur species 5 , 27 , 38 and the fact that two main clades of stegosaurs inhabited the Iberian Peninsula during the Late Jurassic 5 , 25 – 28 , it is not possible to infer that some of the differences in the samples could also be a consequence of footprints produced by trackmakers of different species. Another possible biological explanation could even be sexual dimorphism, as suggested by some osteological features in different stegosaur species (see 5 , 44 and references therein).…”

Stegosaur tracks from the Upper Jurassic of Portugal: new occurrences and perspectives

“…Fossilized skeletal remains of three stegosaur species have been found in Portugal, all from Upper Jurassic deposits of the Lusitanian Basin: possible Dacentrurus (=Omosaurus) armatus (Lapparent & Zbyszewski, 1957;Galton, 1991;Escaso et al, 2007b), Stegosaurus cf. ungulatus (Escaso et al, 2007a) and Miragaia longicollum (Mateus et al, 2009;Costa & Mateus, 2019).…”

“…10) reflects the stratigraphic distribution of Stegosaurus (Milàn & Chiappe, 2009;Pascual-Arribas & Hernández-Medrano, 2016;Lockley et al, 2017), but Stegopodus seems to be much more common than Deltapodus. Abundant skeletal remains of stegosaurines are known from the Morri- son Formation (Stegosaurus and Hesperosaurus; Lockley et al, 2017), but dacentrurines are also known from this formation, as Alcovasaurus longispinus Galton & Carpenter, 2016 was recently reinterpreted as the first confirmed dacentrurine in North America, congeneric with Miragaia longicollum (Costa & Mateus, 2019).…”

New dinosaur, crocodylomorph and swim tracks from the Late Jurassic of the Lusitanian Basin: implications for ichnodiversity

“…The dinosaur osteological record reported in the Lusitanian Basin is markedly high compared with the footprint record. Dinosaurs from different groups have been identified throughout the basin, including theropods (Malafaia et al 2017a), ornithopods (Rotatori et al 2020), sauropods (Mocho et al 2017) and thyreophorans (Costa and Mateus 2019). The crocodylomorph record has recently been shown to be remarkably rich, with at least six taxa reported (Guillaume et al 2020).…”