INVESTIGADORES
OTERO Alejandro
congresos y reuniones científicas
Título:
LOCOMOTORY SHIFTS IN DINOSAURS DURING ONTOGENY
Autor/es:
CHAPELLE KIMBERLY; JONAH CHOINIERE; BENSON ROGER; ALEJANDRO OTERO
Lugar:
Albuquerque
Reunión:
Congreso; 78 Annual Meeting of the Society of Vertebrate Paleontology; 2018
Resumen:
Massospondylus carinatus is an iconic South African basal sauropodomorph dinosaurknown from an array of well-preserved specimens representing a nearly completeontogenetic series from embryos to adults. It has previously been hypothesized that M.carinatus experienced a change in gait during ontogeny: hatchlings were obligatequadrupeds, whereas adults were facultative bipeds. This hypothesis is surprising?withinDinosauria there are several instances of lineages evolving quadrupedality from bipedality,but no counter examples. The ontogenetic postural shift from quadrupedality to bipedalityhas been found in several other dinosaur taxa, and has even been suggested to represent theancestral condition for the entire group. However both non-destructive and quantitativemethods for testing this have been lacking. Our research group recently described areliable, quantitative method for determining tetrapod posture based on the relativerobustness of the forelimb compared to the hindlimb. Here, we modify this method for useon ontogenetic datasets, including both growth series and histological data, and apply it toa wide range of tetrapods, including mammals, crocodylomorphs, and dinosaurs. We findthat the method provides an excellent proxy for postural changes during development. Thegrowth trajectories of animals that are obligate quadrupeds from birth (such as bovids) canreadily be discerned from those that are obligate bipeds since birth and from animals thatchange posture during ontogeny (such as humans). Our results clearly show that M.carinatus was a biped from hatching, and possessed bipedal skeletal proportions even inovo. Other dinosaurs, like Mussaurus, have limb proportions consistent with a shift inposture from quadrupedal to bipedal during their developmental sequence. Phylogenetichypotheses imply different interpretations of this finding because Mussaurus may representeither (1) a recent evolutionary origin of bipedalism from quadrupedal sauropodiformancestors, or (2) a close bipedal relative to the ancestor of quadrupedal sauropodiforms. Ifthe latter is found to be correct, then our data suggest that bipedal to quadrupedal posturalshifts in dinosaurs may have been presaged by adoption of novel stances at earlierontogenetic stages.