Crocodiles are so hard, they even eat fruit

This was originally posted at: http://blogs.egu.eu/palaeoblog/?p=856

Seed dispersal by animals is incredibly important for plants to help them occupy new areas of land and reproduce. Usually, this happens using bugs, birds, or intrepid kittens, but probably the last animal on this planet you’d expect to disperse seeds is crocodiles – you know, those big beasties that take down bison for a snack. Well, turns out, they do, and it’s a process known as saurochory.

Not only that, but these king archosaurs, the vintage cousins of dinosaurs, the ones who you never smile at, eat fruit to get at seeds. A new study reviewed the diets of modern crocodiles, and showed that 13 of 18 species ate fruit of some sort (frugivory), along with a wide variety of plants.

Using animals as a method of seed dispersal is actually a cool form of mutualism – the plants get to spread their genes, and animals get a healthy snack, that isn’t in the form of some naff cracker. In other reptiles, seed dispersal is a well-known activity, although not as well understood as for insects, mammals, and birds, even in snakes and turtles.

A recent review study shows that for crocs, almost a quarter of the fruits consumed were of the ‘fleshy’ kind (think James and the Giant Peach, but with reptiles). However, none of the recordings were of direct observations of fruit eating, so exactly how or why they did is still a bit of a mystery.

The question of how is mostly a case of speculation, as it’s rare to directly observe a croc consuming fruit. Generally, it might be that there is no common reason, and it’s a series of partial consumption hypotheses that all just depend on the scenario a hunting croc is involved in. Perhaps they’re really good at sneaking up on and gobbling animals preoccupied with nomming fruits, which just happen to get caught up in the act in an apple-goat smoothie of sorts. The yucky extension of this is that the fruit has already been eaten, and gets transferred during the gulping process.  Alternatively, it could be a case of mistaken identity, where a sleepy croc might mistake a floating fruit for some sort of tasty nosh. If you have any hypotheses about why crocs might ingest fruit and plants, I’d love to hear – pop a comment below!

Why they did it could be for a range of reasons. Perhaps it’s similar to why dinosaurs consumed stones (gastroliths), to help with grinding food in their stomachs, and get a tasty treat in the process. The energy values of fruits are pretty high, so consumption could be for a nutritional benefit, which is cool as it shows that crocodiles have evolved beyond the need for nutritionists.

Perhaps this odd phenomenon might help in part to explain why crocodiles are such successful animals. If food of the meaty sort was ever in short supply, they had the capacity to diversify and track down other food sources, from vegetation and grasses, to getting their 5-a-day. Some ancient crocs called notosuchians, the cousins of the croc lineage leading to modern crocodylians, were fully land-dwelling (terrestrial), armoured, or herbivorous – they were seriously way more diverse in form than the remnants we see today. Imaginably, modern crocs are getting nostalgic, and trying to reclaim some of this former glory..

This review article actually reveals something interesting about the way scientists sometimes might operate. Crocs are obligate carnivores – their primary diet is meat – and as such, fruits are often classed as anomalous food items when found in their stomach contents or poop, and not considered in a physiological context. So, perhaps, it is that the mainstream view was crocs are carnivores, anything else is unimportant when it comes to diet, so ignored rather than feeding into evaluations of their diet and energy balances. That the review study picked up so many independently, but ignored, instances of crocs feeding on fruit and having ingested seeds is pretty solid evidence for this. Just shows that sometimes, stepping back and taking a broad look at evidence can reveal some pretty cool things!

P.S. Someone on DeviantArt needs to get on this and draw a croc making a fruit cake or something.

Article by Brian Switek (dinosaur sexpert): http://phenomena.nationalgeographic.com/2013/07/26/the-puzzle-of-the-frugivorous-crocs/

Article by Darren Naish: http://scienceblogs.com/tetrapodzoology/2008/10/03/alligators-eat-fruit/

Original paywalled article: http://onlinelibrary.wiley.com/doi/10.1111/jzo.12052/abstract

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