Creative creatures

As SF writers, we may think we have a complete free hand to create new creatures, but it isn't so.  The laws of physics will work the same elsewhere in the universe, and they give us the framework for, and provide the restrictions on, what we can create.

Our imagined life forms are constrained by the type of planet they live on.  What is its atmosphere like, what is the gravity there?  If the planet is smaller than Earth it will have lighter gravity and the creatures there may be able to run and leap much further than on Earth.  But the atmosphere might be thinner than a human is used to, and might cause us some problems.

Or perhaps your aliens don't live on or in a planet, but in the midst of the as-yet undiscovered dark matter that we think makes up ninety per cent off the universe.  They would be radically different creatures than planet-dwellers.  Would they eat dark matter for energy? And how would they reproduce?  Would they be swarms of microscopic beings with a group-mind?

If we're planet-bound, we have to consider the effects of evolution by natural selection on our creatures, and the principles of convergent evolution.  And when we stick to those rules it's difficult to come up with a unique creature that doesn't exist in some form on Earth, or in its waters.

Bioluminescence, parthenogenesis, electrical sensing of the environment, echolocation with natural sonar, navigation with natural magnetic compasses, thermal imaging, the use of the skeleton.  All these features are utilised by creatures on our own planet.  Raiding them, we can create unique new combinations.

Avatar's Na'vi are recognizeably humanoid, but they're ten feet tall and breathe an atmosphere slightly different from Earth's.  Anne McCaffrey's Hrrubans from the Doona books are walking big cats with language and high tech.  They characterise rank as being a "broad stripe", encompassing the wisdom of age.  The reference is to the broad stripe of contrasting colour running down the back of their fur.

In my Panthera books I've invented jagotheras, kingcats, and goldcats.  They're intended to be future versions of jaguars, cheetahs, and lions, but each has their own recogniseable habitat and markings that are based on what exists on Earth today.

It's easy for us to create exotic creatures, the skill lies in imagining the food webs, biospheres, and physical quirks of their homes that make them believable but different.