Wednesday, June 27, 2012

A. sediba ate like a giraffe

Amanda Henry and colleageus report in Nature on the diet of Australopithecus sediba.  The results are somewhat surprising, with carbon isotope values indicating an almost exclusively C3 diet (trees, leaves,  fruit, bark etc), even thought A. sediba lived in an environment with plentiful C4 resources (grasses and sedges).  Dental microwear complexity analyses indicate some hard object feeding, consistent with that seen in P. robustus. Finally, taxonomic identification of the plant phytoliths preserved in the dental calculus of one of the specimens supports a diet including fruit and bark.  

These results are somewhat surprising given that most other early hominins had a diet with considerably more C4 resources.  A. sediba continues to be weird and interesting, and adds new evidence that early hominin diets were more diverse than we have previously acknowledged

Full Citation:
Henry, AG et al. (2012). The diet of Australopithecus sediba Nature DOI: 10.1038/nature11185

Monday, June 25, 2012

Fossil ears and ancient primate locomotion

Ryan and colleages report in the Preceedings of the Royal Society B on a large study of fossilized inner ears of primates. In particular this study examined the size of the semicircular canals, part of the vestibular apparatus. This portion of the inner ear consists of three fluid filled tubes that are oriented at right angles to one another.  The brain detects the movement of fluid through these canals, and this is a crucial part of how critters (ourselves included) detect angular rotation and maintain balance during locomotion.  

The relative size of these canals is related to locomotor agility. Fast moving, agile critters tend to have larger semicircular canals. These bony tubes often get preserved as fossils, and with the help of CT scanning technology, they can be imaged and measured. This data helps illuminate the locomotor style of extinct primates, even those with no post-cranial fossils preserved. Ryan and colleagues offer locomotor agility reconstructions for 17 fossil anthropoids (the group that includes monkeys and apes - including humans humans). This study reveals three major aspects of primate locomotor agility.  First, that the earliest anthropoids were slow and not very agile. Second, that New World monkeys from the Miocene are notable for being much more agile than earlier anthropoids.  Finally, this study suggests that the earliest Old World monkeys were relatively agile, even though later Miocene descendants were relatively slow. 

Cast of semicircular canal of Aegypopithecus zeuxis. Ryan et al. ,2012  Figure 1.

Full Citation:
Ryan et al. (2012). Evolution of locomotion in Anthropoidea: the semicircular canal evidence Proceedings of the Royal Society B DOI: 10.1098/rspb.2012.0939