Oganesyan, Cruz1, Prothero, Donald Ross2r>
(1) Geological Sciences, Cal Poly Pomona, Pomona, California, USA, (2) Department of Geological Sciences, California State Polytechnic University Pomona, Pomona, California, USA; Department of Vertebrate Paleontology, Natural History Museum of Los Angeles County, Los Angeles, CA, USA,
Abstract:
As an animal grows larger and subsequently heavier, it must also have limbs suitable enough to support their prodigious bodies. If they increased isometrically or otherwise gracile, they would be too flimsy and weak. The size of their limb bones must increase allometrically to achieve the needed strength. The same remains true for family Camelidae of the Ungulates. The evolution of Miocene to Pliocene North American camels from ancestral Procamelus occidentalis to descendant Gigantocamelus spatulus, Megatylopus gigas, and Megacamelus merriami saw them grow from approximately 1.2 meter at the shoulder to over 3.6 meters, and from an estimated 55 kg to over 4000 kg in the latter. In order to support this increased mass, the limbs grew faster in circumference than length. To test our hypothesis, we collected measurements from the long limb bones: humerus, radius, femur, tibia, and respective metapodials of 4 different continuous species of ancient dromedary camels for comparison. The results from the data we collected were negatively allometric and supported our hypothesis that the limbs became more stalky and less gracile as they evolved.