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View Full Version : Ornithology in Lesser Gravity - Teratorns, Rocs, and Size Limits



Lythande
11-25-2014, 04:05 AM
I have idly decided I want rocs in my fantasy world (mostly because I'm fascinated by megafauna, my favorite of which is argentavis). For that matter I want wyverns too, but I think that presents even more problems, so I'll start with rocs.

I want them to be relatively plausible, so mostly I'm wondering if there's any particular reason a bird couldn't get to the size of the giraffe-huge pterosaurs. Of course, those pterosaurs are built nothing like the birds of prey or at least scavengers I'm interested in, but my mountains are pretty near the ocean so I could go with seabirds if that's my only good option for enormous birds. And they do live in mountains, so they don't really need to worry about a running or flapping start.

My world has .8g, which I assume means they can get bigger. Let us say for the sake of argument they don't also get weaker in the lower gravity, because they were originally genetically engineered.

"Magic" in this world is caused by very responsive nanites, so enhanced strength and durability or even small antigravity fields are possible, but they would become correspondingly heavier, so it seems like a bad route to go down.

King Neptune
11-25-2014, 04:35 AM
Go for it! What would the gravity be on this planet? I think there's a bird with a wing spread of 20 feet, even in these degenerate times. Cut the gravity in half, and you might have one with a panther sized body and forty or fifty foot wingspread, but you don't want the wings all that big, because they would be cumbersome; they'd get in the way, and it would be difficult to take off.

Drachen Jager
11-25-2014, 04:39 AM
The larger the flyer the more efficient, so you don't need a lower gravity to have big flyers.

The main thing big flyers need, is what any megafauna needs, a food source. Make it a lush 'paradise' loaded with nutrient-rich plant life and I'd have no problem believing in the megafauna.

Lythande
11-25-2014, 04:52 AM
The larger the flyer the more efficient, so you don't need a lower gravity to have big flyers.

The main thing big flyers need, is what any megafauna needs, a food source. Make it a lush 'paradise' loaded with nutrient-rich plant life and I'd have no problem believing in the megafauna.

Man, that just gave me the image of the rocs preying on my little 4-foot jungle elves that live in my rainforest canopy... I'm pretty sure that's awesome.

blacbird
11-25-2014, 10:25 AM
First, there are flying bird fossils known on Earth which are twice the size of any modern flying bird, so some did begin to approach the size of pretty big pterosaurs.

Second, and perhaps more important to your premise, is that a lesser gravitational force will also mean a thinner atmosphere (google Mars), thereby rendering flight more difficult, not easier.

caw

Lythande
11-25-2014, 10:40 AM
I thought Mars's lack of atmosphere was less due to its gravity and more down to the fact that it doesn't have an appreciable magnetic field, so the atmosphere was stripped away by solar radiation.

Although I'm sure you have a point, which makes me unhappy. Poo. :(

I suppose I could counter the gravity by altering the atmosphere and climate, since nothing happens in the cold parts of my world at the moment anyway... I seem to recall the giant dragonflies were possible because of a thicker atmosphere many millions of years ago... *wanders off on a musing tangent*

(I am familiar with ancient giants birds though; the Argentavis Magnificens mentioned in my OP was a probably-scavenger with a wingspan of some 7-8 meters, which makes me positively agog. The biggest pterosaurs were even bigger though - the largest was like a giraffe with a giant head and wingflaps, and a wingspan like a Cesna. I want that sort of magnificence :D )

Drachen Jager
11-25-2014, 11:10 AM
Then just do it.

It's called fiction.

blacbird
11-25-2014, 11:10 AM
II seem to recall the giant dragonflies were possible because of a thicker atmosphere many millions of years ago.

Not an inappropriate observation, but not really correct, either. The giant insects of the Carboniferous, well known through fossil remains, could grow so large not because of the atmosphere being thicker, but because of it containing 50% more oxygen than today. There were also gigantic spiders and centipedes back then, which didn't fly. Terrestrial arthropods have a rather inefficient biological method of absorbing oxygen, and that tends to restrict how large they can get. With the 32% oxygen content of the Carboniferous atmosphere, and the lack of competition from other terrestrial animals (no reptiles, mammals or birds), they got a lot bigger than they do today with about 21% atmospheric oxygen.

caw

Lythande
11-25-2014, 12:15 PM
Aha, you're right. For some reason I was thinking it had gone the other way, with higher carbon dioxide.

Wikipedia has introduced me to Arthropleura (http://en.wikipedia.org/wiki/Arthropleura), the centipedes of which you speak. *shudder* I think I found some monsters for my world...

TheNighSwan
11-25-2014, 03:58 PM
I've read one of the reasons large pterosaurs went extinct is that their style of flying required relatively calm winds, which were the prevalent climate in their time, but changed after the Cretaceous, rendering them maladaptive and allowing more efficient flyers like birds to outcompete them (although it should be noted that birds and pterosaurs co-existed for more than 80 million years before pterosaurs went extinct).

Albedo
11-25-2014, 05:39 PM
Poor pterosaurs ultimately just got unlucky in the K-Pg unpleasantness, I think. All too big and specialised to survive a Cormac McCarthy's The Road-style hellscape on an all-cockroach diet for the next few hundred millennia, unlike some mammals, avian dinos and assorted lizardy things.

I have a Quetzalcoatlus in my current WIP. One faction uses it as kind of kamikaze biological V1. Cos the only thing better than pterosaurs is exploding pterosaurs.

But exploding Haast eagles could work too.