Compiled by Adam Pritchard and Matt Borths of the Past Time podcast
This week we have discussed the legs, feeding apparatus and likely diet, and general familial history of Gastornis. One of the only other anatomical features we have not discussed in detail are the wings of this animal I noted before that the wings appear to be more developed than those of the true terror birds. This lends itself to a more well developed keeled sternum that is often associated with flight muscles. These muscles appear to be weakly developed in Gastornis; however, their existence and the development of the keeled sternum, regardless of how slight that keeling is, allow some insight into the evolutionary position of Gastornis in Anseriformes in relation to the capability of flight within the family. There is a reason that ducks and geese are high fat, heavily muscled birds; that in turn has led to their inclusion in our diet. Ducks and geese have low aspect wing ratios and less than desirable aerodynamically shaped bodies. They tend to be a little rotund, but most herbivorous animals are as they require more gut to process vegetation. Gastornis was also probably a fairly rotund bird as it would have also required significantly more digestive tract than the carnivorous contemporary birds around them. Gastornis was not flying though, so the fact that its family tree members have a lot of muscle to power themselves through the air definitely influenced its keeled sternum and possibly causing Gastornis to also have enormous muscles in the chest. One conclusion we can draw from this is that Anseriformes were flying both before and after the terrestrially confined Gastornis was running around the forests of the northern hemisphere.