Prehistoric Dinosaur Mimics

Mimicry is one of the most well-recognized forms of defense in the animal kingdom.  For those who need a refresher, mimicry is defined in biology as the very close resemblance of one organism, or part of an organism, to a different species of organism.  This is usually meant to trick would-be predators.  Common examples are caterpillars with patterns to look like large snakes, or butterflies with spots on their wings that make them look like owls.

A snake!  Actually it's just an upside-down caterpillar.  But frogs, lizards, and songbirds, frequent predators of caterpillars and prey to snakes, might hesitate when attacking this it. Photo: Andreas Kay

How likely do you think mimicry in prehistoric animals was?  Given how vast biodiversity is, I have no doubt that some sort of mimicry took place millions of years ago, but to what extent? And in which species?  Did large non-avian dinosaurs mimic?

Recently on social media I have noticed a slight trend in artists posting images of ceratopsians and hadrosaurs with coloration on their frills and crests meant to mimic the faces of tyrannosaurs.  At first, this might seem like a plausible defense strategy.  Tyrannosaurs, from what we know, were usually the top predators in any community they inhabited during the late Cretaceous.  In fact, it is often said that the only animal that a tyrannosaur would ever need to fear was a larger tyrannosaur!

An adult Lambeosaurus already doesn't have much to fear from any of the other creatures that would be scared off by a tyrannosaur anyway.

But that phrase is exactly why I am highly skeptical of this being a likely mimic strategy.  The sight of a tyrannosaur would no doubt send every other animal in the area running...except for possibly another tyrannosaur.  The problem with this on a ceratopsian or a hadrosaur is the fact that we know tyrannosaurs were the main predators of both of these kinds of dinosaurs.  An adult Chasmosaurus or Lambeosaurus already doesn't have much to fear from any of the other creatures that would be scared off by a tyrannosaur anyway.  Ironically, their only real predator is the only one that wouldn't be scared by it.  In some cases they may even attract the very predator they would hope to repel!

There's two reasons why a tyrannosaur might be outright drawn into the image of its own species.  The first is like many vertebrates, tyrannosaurs needed to find a mate in order to reproduce.  So it is likely that at least during certain parts of the year, a tyrannosaur would mistake a mimicking Lambeosaurus as a potential partner only to discover that it's a meal upon closer inspection.

It is likely that at least during certain parts of the year, a tyrannosaur would mistake a mimicking Lambeosaurus as a potential partner only to discover that it's a meal upon closer inspection.

The second reason is that we have substantial fossil evidence that at least some tyrannosaurs engaged in intraspecies combat, specifically in the form of biting each other on the face, thanks to healed teeth marks in some skulls.  Plus, territorialism is very common across many kinds of large meat-eaters in general so this makes sense.  So a tyrannosaur might see a ceratopsian with its likeness on its frill, mistake it for a rival, and charge in for a challenge only to discover that it is once again a meal upon closer inspection.

A tyrannosaur might see a ceratopsian with its likeness on its frill, mistake it for a rival, and charge in for a challenge only to discover that it is once again a meal upon closer inspection.

Lastly, and perhaps this is best reason why visual mimicry wouldn't work for repelling tyrannosaurs, is the fact that we have very strong evidence that tyrannosaurs had excellent senses of smell.  So even though these plant-eating dinosaurs would look like a fearsome predator, a tyrannosaur would be able to identify them as what they truly were before they even saw them assuming the wind was blowing in the right direction.

That being said, I highly doubt mimicry in large plant-eating dinosaurs of large meat-eating dinosaurs (their direct predators) was very likely in real life.  And to be fair, most of the artists I witnessed producing these pieces admit that it was just for fun, which is fine.  However, it still got me thinking a lot about mimicry in general and I decided it was an interesting enough subject to cover for this post.

So I wonder if there was a more likely form of mimicry in prehistoric dinosaurs.  To explore this further we need to look at mimicry today and how it works.  In general, if an animal exhibits mimicry to ward off predators, it will typically mimic the likeness of an animal at least two levels above them on the food chain.  This way, they are mimicking a predator that will almost definitely scare away their direct predators, but at the same time the higher predator they are mimicking usually won't view them as a regular food source, as well.

A butterfly mimicking an owl is specifically doing so to scare away smaller birds, which themselves are regularly preyed on by real owls.

For example, butterflies that mimic the face of an owl with yellow spots on their wings are specifically trying to scare away their main predator, smaller birds, which themselves are regularly preyed on by real owls.  At the same time, real owls very rarely, if ever, eat butterflies.  So the butterfly isn't really taking a risk looking like an owl.

In general, if an animal exhibits mimicry to ward off predators, it will typically mimic the likeness of an. animal at least two levels above them on the food chain.

So back to the idea of mimicking a tyrannosaur.  I came up with a fun little idea of a much smaller plant-eater that may not find itself in direct contact with tyrannosaurs as often due to it living in more dense underbrush, but does have to worry about being preyed on by smaller predators, like dromeosaurs. So what if they had some sort of mimicry of a large, toothy monster on their bodies?  I'm not saying it's a true hypotheses of mine, but it's less unlikely than the imagery on a larger plant-eater.

Smaller plant-eating dinosaurs may not have been regularly be preyed on by adult tyrannosaurs.  So looking like one may have helped it survive attacks by more direct predators, like dromeosaurs.  

Another form of less specific mimicry is coloration to form generalized eyespot patterns that don't particularly mimic any specific species.  This is actually already commonly depicted by paleoartists, especially when it comes to ceratopsian frills.  Bold, circular patterns to give the illusion of eyes is common in a lot of animals alive today.

Are these Butterfly fish looking at you?  Which end is the head and which is the tail? Photo credit: Chris Huss

The first way this can help an animal is to draw attention from the place where the real eyes are, the head.  This can throw a predator off when attacking, and might save the animal's life.  Being directly chomped on the head is usually a death sentence.  But being bitten elsewhere might be a better chance of survival.

The second way general eyespots can help an animal is to suggest to a predator that it is being watched when in fact, it very well may not be.  A ceratopsian with eyespots could be completely oblivious as it munches away on plants while a tyrannosaur is taking a few extra seconds deciding if it's even worth it to try and ambush.  In nature, a few seconds can be more than enough time for the prey animal to realize it is being stalked and give it a start in running away or defending itself.

A dinosaur sporting eyespots could be completely oblivious while a tyrannosaur is taking a few extra seconds deciding if it's even worth it to try and ambush.

Mimicry is a widely successful form of defense that can be observed across many kinds of organisms alive today.  It was very likely also utilized in prehistoric species, but to what extent and in which species is still mostly a mystery.  What do you think?  Do any other kinds of prehistoric animals seem likely candidates for mimicry?


References

Bona, Sebastiano De, et al. “Predator Mimicry, Not Conspicuousness, Explains the Efficacy of Butterfly Eyespots.” Proceedings of the Royal Society B: Biological Sciences, vol. 282, no. 1806, 2015, p. 20150202.

Peterson, J. E.; Henderson, M. D.; Sherer, R. P.; Vittore, C. P. (2009). "Face Biting On A Juvenile Tyrannosaurid And Behavioral Implications". PALAIOS. 24 (11): 780–784. Bibcode:2009Palai..24..780P. doi:10.2110/palo.2009.p09-056r. Archived from the original on August 11, 2013.

Tanke, Darren H.; Currie, Philip J. (1998). "Head-biting behavior in theropod dinosaurs: paleopathological evidence (PDF). Gaia. 15: 167–184. Archived from the original (PDF) on 2008-02-27. [not printed until 2000]

Witmer, L. M.; Ridgely, R. C. (2009). "New Insights Into the Brain, Braincase, and Ear Region of Tyrannosaurs (Dinosauria, Theropoda), with Implications for Sensory Organization and Behavior". The Anatomical Record. 292(9): 1266–1296.