97 - Are Mammalian Wormian Bones (intrasutural) Correlated to Phylogeny or Ecology?

Poster Board Number: 97
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Abstract Body : Wormian bones, also known as intrasutural bones, are an anatomical variation in which an extra ossification center develops within the sutures and fontanelles of the skull. Previous literature surveys found that Wormian bones are found broadly throughout Mammalia. Previous researchers have also suggested that Wormian bone occurrences are related to function, developing in response to mechanical stress. However, little is known about their occurrence rates and variation in suture location. Here, we aim to sample mammal groups to gain more detailed insight into the frequency of occurrence of Wormian bones within specific groups and in which sutures they are predominantly found. We hypothesize that the locations of Wormian bones within individual mammal skulls will be correlated with the phylogenetic relationships and/or ecological roles of the studied mammal species, in contrast to a null hypothesis of a random distribution of Wormian bone occurrences.
We systematically sampled 789 mammal skulls from the Sam Noble Museum (Norman, Oklahoma) to explore rates of occurrence in each group and recorded their anatomical location. We looked at 10 different species total.
From our survey, we found that in the carnivoran taxa sampled (Ursus americanus, Lontra canadensis, and Mephitis mephitis), there were higher rates of Wormian bones in the rostrum sutures, which we defined as the sutures between the nasals, premaxillae, and maxillae. Odocileus virginianus and Sylvilagus floridanus had the highest rates of Wormian bone occurrences and the majority of them were interparietals. Interestingly, these two groups had very low occurrences of Wormian bones in the anterior sutures and none were found in the rostrum, contrasting with the carnivoran specimens.
The contrasts in anatomical locations between the carnivores and herbivores may indicate that the differences result from differing mechanical stresses imposed by differing dietary demands. However, this begs the question of whether the similarities between the carnivoran taxa are due to similarities in diet or phylogeny. Because the results for the more distantly related deer and rabbit groups are similar, this may point to the Wormian bones being more correlated with their similar diets rather than phylogeny. More sampling of different clades and application of quantitative phylogenetic comparative methods are needed in order to further parse out the primary factors influencing Wormian bone location.
This work adds more data to the little that is known about Wormian bones in non-human mammals. The findings here may support a correlation between Wormian bone location and ecology. Future work will include more sampling of clades of varying ecologies.