Vertebrates, Invertebrates and Plants

Again, Hone and Benton (2005) added additional ideas to the paper by Kingsolver and Pfennig (2004). They suggest three other possible “caps” on the evolution on large size. First of all, they suggested that there could be morphological constraints on the organisms (Hone and Benton, 2005). Their main example of this is the giraffe. If its neck were to get much longer, it would require, in turn, a more powerful heart in order to pump the necessary blood to the head (Hone and Benton, 2005).

Secondly they suggest possible niche overlap and a resultant increase in competition to prevent too large an increase in size. Also, like Hallam (1975) they bring up the point that in times of mass extinction, smaller organisms with shorter generation times would be more able to adapt to harsh conditions (Hone and Benton, 2005). Finally, Hone and Benton (2005) also suggest that organisms which evolve to be much larger may eventually speciate. This would likely only have an effect on the results if the taxa were being examined at the species level as opposed to the level of genera.