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, 276 (1663), 1815-21

A New Long-Necked 'Sauropod-Mimic' Stegosaur and the Evolution of the Plated Dinosaurs

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A New Long-Necked 'Sauropod-Mimic' Stegosaur and the Evolution of the Plated Dinosaurs

Octávio Mateus et al. Proc Biol Sci.

Abstract

Stegosaurian dinosaurs have a quadrupedal stance, short forelimbs, short necks, and are generally considered to be low browsers. A new stegosaur, Miragaia longicollum gen. et sp. nov., from the Late Jurassic of Portugal, has a neck comprising at least 17 cervical vertebrae. This is eight additional cervical vertebrae when compared with the ancestral condition seen in basal ornithischians such as Scutellosaurus. Miragaia has a higher cervical count than most of the iconically long-necked sauropod dinosaurs. Long neck length has been achieved by 'cervicalization' of anterior dorsal vertebrae and probable lengthening of centra. All these anatomical features are evolutionarily convergent with those exhibited in the necks of sauropod dinosaurs. Miragaia longicollum is based upon a partial articulated skeleton, and includes the only known cranial remains from any European stegosaur. A well-resolved phylogeny supports a new clade that unites Miragaia and Dacentrurus as the sister group to Stegosaurus; this new topology challenges the common view of Dacentrurus as a basal stegosaur.

Figures

Figure 1
Figure 1
(a) Skeletal reconstruction of M. longicollum based on type specimen ML433, except the ilium and pubis (in grey), which are based upon the referred specimen (ML433-A), and have been scaled up. (b) Phylogeny and chronostratigraphy of Stegosauria. Strict consensus of five MPTs obtained from a branch-and-bound search (CI=0.617; RI=0.718; RC=0.458) Aal, Aalenian; Alb, Albian; Ans, Anisian; Apt, Aptian; Baj, Bajocian; Brm, Barremian; Bth, Bathonian; Ber, Berriasian; Clv, Callovian; Cmp, Campanian; Crn, Carnian; Cen, Cenomanian; Con, Coniacian; Hau, Hauterivian; Het, Hettangian; Kim, Kimmeridgian; Lad, Ladinian; Maa, Maastrichtian; Nor, Norian; Oxf, Oxfordian; Plb, Pliensbachian; Rht, Rhaetian; Sin, Sinemurian; Tth, Tithonian; Toa, Toarcian; Tur, Turanian; Vlg, Valanginian. E, Early; M, Middle; L, Late. Nodes: 1, Thyreophora; 2, Eurypoda; 3, Stegosauria; 4, Stegosauridae; 5, Dacentrurinae, n. clade; 6, Ankylosauria; the values in parenthesis show the number of cervical vertebrae; question marks represent insufficient stratigraphic resolution. (c) Skull in (i) dorsal and (ii) lateral views. (d) Sixteenth cervical vertebrae of M. longicollum ML433, in (i) right lateral and (ii) posterior views (for more details see the electronic supplementary material). an, angular; max, maxilla; na, nasal; pm, premaxilla; po, postorbital. Scale bar corresponds to 10 cm for the skull and vertebrae, and to 1 m for the skeletal reconstruction.

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