Bone histology sheds light on the nature of the “dermal armor” of the enigmatic sauropod dinosaur Agustinia ligabuei Bonaparte, 1999

BELLARDINI, FLAVIO; CERDA, IGNACIO A.

NATURWISSENSCHAFTEN

SPRINGER

Año: 2016 vol. 104

0028-1042

Agustinia ligabuei is an Early Cretaceous sauropoddinosaur from the northwest of Patagonia that is currently thetopic of debate with respect to its phylogenetic position andatypical dermal armor. The presence of four morphotypes oflaminar and transversely elongated putative osteoderms wasused to consider Agustinia as an armored sauropod. Regardingthe different hypotheses about the identity of the bony structuresof Agustinia (e.g., osteoderms, cervical or dorsal ribs,hypertrophied elements), a comparative histological analysishas been carried out. Histological evidence is presented hereinand reveals that none of the morphotypes of Agustinia shows aprimary bone tissue formed by structural fiber bundles as inother sauropod dinosaur osteoderms. Furthermore, on the basisof their gross morphology and microstructure, the bonystructures originally classified as types 1 + 4 and 3 are morecomparable respectively with dorsal and cervical ribs than anyother kind of dermal or bony element. Due to poor preservation,the nature of the type 2 cannot be assessed but is heretentatively assigned to a pelvic girdle element. Although aphylogenetic reassessment of Agustinia is not the purpose ofthis paper, our paleohistological analyses have broader implications:by not supporting the dermal armor hypothesis forAgustinia, its inclusion in Lithostrotia is not justified in theabsence of other diagnostic features.