Tyreophoran tracks from the Jurassic-Cretaceous boundary of Tunasniyoj, Bolivia: More steps beyond the ocean

APESTEGUÍA, S. Y GALLINA, P

Bruselas, Bélgica

Simposio; “Tribute to Charles Darwin and Bernissart Iguanodons: New Perspectives on Vertebrate Evolution and Early Cretaceous Ecosystems”; 2009

Museo de Ciencias Naturales de Bruselas

Tyreophorans are a clade of armored herbivorous dinosaurs that inhabited most of the world from Early Jurassic to Late Cretaceous. Basal forms are known from China (Tatisaurus), North America (Scutellosaurus), England (Scellidosaurus) and Germany (Emausaurus) (Norman et al, 2004). Despite derived clades (i.e., ankylosaurs) also inhabited Gondwana (e.g., Minmi) and latest Cretaceous immigrants (e.g., Antarctopelta) (Salgado and Gasparini, 2006), entered South America, no information is available concerning their basal forms. Here we report a superbly preserved and profusely represented track assemblage in Jurassic-Cretaceous boundary sandstones near Sucre, Bolivia. The four trackmakers include: three quadrupedal tyreophorans and one large theropod. The quadrupedal A is represented by 2 adults and 3 juveniles. The pes is four digits, paraxonic, with syndactily (digits I-II) and a separated heel. Manus is short, broad, pentadactyl, located medially in negative rotation. It’s a narrow trackway (Inner width: 0-5 cm). The quadrupedal B has tetradactyl pes impressions superimposing manus prints. No heel is distinguished. Manus is pentadactyl, kidney-shaped. All digits but V have evident claws. The quadrupedal C is rare. Pes is asymmetric with 4 digits, with digit I and IV opposed and digit II and III directed forwards. Manus is short and pentadactyl, with very small digits. The shape, sizes and relative length of the torso allows us to compare the track A with stegosaurians, B with basal tyreophorans and C with ankylosaurians (following Thulborn, 1990). The Tunasniyoj assemblage is the oldest dinosaur tracksite for Bolivia, and includes the oldest evidence for ankylosaurians, and the only stegosaurian trackway for the Southern Hemisphere.