the same would hold true for sauropods barring any unknown, unique characteristics that set the soft tissue anatomy of their necks apart from that of other animals. Apatosaurus, like Diplodocus, would have held its neck angled upward with the head pointing downward in a resting posture. Kent Stevens and Michael Parrish (1999 and 2005) state Apatosaurus had a great feeding range; its neck could bend into a U-shape laterally. The neck's range of movement would have also allowed the head to feed at the level of the feet. Matthew Cobley et al. (2013) dispute this, finding that large muscles and cartilage would have limited movement of the neck. They state the feeding ranges for sauropods like Diplodocus were smaller than previously believed, and the animals may have had to move their whole bodies around to better access areas where they could browse vegetation. As such, they might have spent more time foraging to meet their minimum energy needs. The conclusions of Cobley etal. are disputed by Taylor, who analyzed the amount and positioning of intervertebral cartilage to determine the flexibility of the neck of Apatosaurus and Diplodocus. He found that the neck of Apatosaurus was very flexible. Physiology Given the large body mass and long neck of sauropods like Apatosaurus, physiologists have encountered problems determining how these animals breathed. Beginning with the assumption that, like crocodilians, Apatosaurus did not have a diaphragm, the dead-space volume (the amount of unused air remaining in the mouth, trachea, and air tubes after each breath) has been estimated at about for a specimen. Paladino calculates its tidal volume (the amount of air moved in or out during a single breath) at with an avian respiratory system, if mammalian, and if reptilian. On this basis, its respiratory system would likely have been parabronchi, with multiple pulmonary air sacs as in avian lungs, and a flow-through lung. An avian respiratory system would need a lung volume of about compared with a mammalian requirement of , which would exceed the space available. The overall thoracic volume of Apatosaurus has been estimated at , allowing for a , four-chambered heart and a lung capacity. That would allow about for the necessary tissue. Evidence for the avian system in Apatosaurus and other sauropods is also present in the pneumaticity of the vertebrae. Though this plays a role in reducing the weight of the animal, Wedel (2003) states they are