The relatively large heads and eyes and rounded snouts of infant animals evoke a sympathy-nurturing response in humans and perhaps other animals as well. Certainly the potential for stimulating this response was evident in the Age of Dinosaurs, whose fossilized juveniles often show these big-headed, wide-eyed characteristics. These traits are exemplified in the juvenile remains of Mussaurus patagonicus, whose features are so highly infantile it is possible they represent unhatched embryos. (Mussaurus is pictured here as a recent hatchling, with a hypothetical egg "tooth" on the tip of its nose and a coat of feathers for thermoregulating its small body.)

When describing M.patagonicus, Bonaparte and Vince noted similarities between the rounded skull of Mussaurus juveniles and the rounded skulls of sauropods like Camarasaurus and Cetiosaurus. Adult Mussaurus, like other prosauropods, had long, low skulls. Bonaparte and Vince suggested that the evolution from prosauropods to sauropods involved the retention of a juvenile-type skull throughout their entire lives. This retention of juvenile characteristics is called neoteny ("holding youth") and is a fairly common evolutionary occurence. Our own species, for example, retains a large, bulbous skull and underdeveloped snout compared to our primate ancestors. The suggestion of neotenous sauropods has not yet been subjected to rigorous analysis, but it is entertaining to think that the face of Earth's largest animals can be traced back to a tiny Mussaurus skull less than 5 centimeters long.