Juvenile Mosasaurs

The other night it occurred to me that I had never seen a specimen identified as a juvenile mosasaur. That's because none exist (actually there's a jaw bone that was misidentified for a while, but that appears to be it). For something as relatively common as mosasaurs with as wide of a geologic range and diversity of species and genera, it seemed odd to me that none would be known. After all, even the elusive T. rex had subadult specimens known and even some that would really count as juveniles. I then though to myself that there would be several reasons for why this would happen. First of all, a smaller animals is less likely to preserve. However, smaller animals, with much more delicate bones than those of a mosasaur (eg fish and a few birds) have been readily preserved in the Niabrara, Kansas chalk. Perhaps there were just very few jouveniles swimming around in environments where they could be preserved. Interspecific cannibalism is certainly known for mosasaurs so it stands to reason that a little guy would just get eaten up such that the vast majority of the population is composed of animals much too large to be preyed upon. This sort of thing is seen in crododiles where juveniles are quite inconspicuous and the adults live for a very long time once too large to be eaten by most predators. The fear of being preyed upon also results in a behavioral reason for a lack of preservation. Were a young mosasaur to spend the majority of his young life in estuaries (an environment quite poor for preservation and seen much less commonly than deltas or open seas) and only venture into open water once too large to subsist on the small estuarine fauna, then that too would explain the lack of early ontonogenic stages. The last idea would be that these reptiles gave live birth as some variety of snake do as did ichthyosaurs ( I don't know about plesiosaurs). Snakes typically give birth to a large number of very small young, but ichthyosaurs and modern marine mammals only birth one comparatively large young at a time. It could be then that the young mosasaur reached adulthood rather quickly, decreasing the probability of leaving juvenile fossils. Of course the truth probably lies in a combination of several of these factors.