An analysis of the embryos suggests they were born walking on four legs with short tails, long forelimbs and big heads. To morph into their adult shape -- walking on two legs with long tails, short forelimbs and small heads -- their various features must have grown at different rates.
"The proportions are just ridiculous," Reisz said.
Anyone seen a human baby recently? Ridiculousness is in the eye of the beholder.
In addition the dino babies lacked teeth, suggesting they needed lots of parental care. The remains furhtermore suggest that the four-legged gait of the later sauropod giants could have emerged directly by retaining the youthful form, rather than requiring a two-legged to four-legged lifestyle adaptation. But-- someone correct me-- aren't Diplodocus et al thought to have reared up on two legs on occasion?