**Spoiler Ahead**

Here's an idea that would actually excuse the ridiculously fast growth rate.

When we see the scene where David bombs the "engineers", we see what appear to be full grown creatures bursting out of these humanoids almost within seconds.

I have been wondering for some time if this is indicative that when the intended dose of black goo is delivered to the host, it is meant to birth a full grown creature instantly and that accelerated growth rate also means a much shorter lifespan.

It is possible that the variations we are familiar with which takes hours or perhaps a day to gestate, are an incomplete form due to a smaller dosage of the black goo. So they rely more on the host DNA than the black goo and take on more of the host traits such as longer gestation and longer lifespan.

The creatures from the bombing may have died only a few days/weeks after the event. This has got me thinking now that the gestation/growth rate topic deserves it's own thread.

Yes - I also think that the dose makes a significant difference.
In Prometheus, Holloway drank only one drop, as opposed to the engineer at the beginning of the movie, who drank a full glass, and his body fell apart almost immediately. But I'm not sure about the effect on the lifespan...

Maybe they all died of starvation, after killing all the animals on the planet?...

Thank you :)

Also, I think the black goo that was dropped is not entirely predictable based on what we know.  It may have just disintegrated the engineers, similar to what transpired in Prometheus.  

I said it before the movie came out and say it again after I saw it, there is too far a split in the Alien community between the people who loved Prometheus (myself included) and the people who wanted more alien.  IMO Covenant suffered as a result of the latter.  

Ridley is right.  The Alien is cooked.  Give us the mythos regarding the Engineers and the back story to the original Xenomorph's depicted on the temple mural in Prometheus and well be happy. 

WilliamPotter

"Also, I think the black goo that was dropped is not entirely predictable based on what we know.  It may have just disintegrated the engineers, similar to what transpired in Prometheus."

I've only watched AC once, but as far as I could see, there were full sized black creatures jumping out of most the engineers shown in the bombardment scene. It wasn't always easy to make them out, but as far as I could see, there were bodies coming out of bodies.

Yes - they were bodies coming out of some of them. Some just fell apart, but some got aliens out of them... 

We really know quite little about that planet, and it might well have no significantly evolved animal or avian life.

Alternatively, the animal life might just have gotten the hell out of dodge when the Black Goo was deployed, to animal instincts, that's seem like a forest fire or such massive cataclysm I suspect.

There also might well have been animal life in the area that's just quiet, Field mice, Lynx and many others don't make a lot of noise.

As I understand it, It looks like all the animals were killed by aliens after the goo attack. And so - what has happened to all the aliens after that?...

Its a large planet they could have left the area in search of more life to consume it has been ten years and they have a whole planet to explore. 

Assuming whatever came out of the engineers was a carnivore, then they probably died off, it's been 10 years since the bombing.

I agree that the most likey explanation is time and/or that a lot of the fauna - David clearly remarks that the pathogen only effects the "meat" - was simply broken down to very simple, celluar lifeforms.

We also know that the pathogen seems unpredictable to say the least.  Either way, time seems the be the answer.  I doubt whatever survived would be able to reproduce anyway, and the things that did survive we know are made hyper-aggressive by the pathogen, so they probably fairly quickly destroyed each other.

Yes. It makes sense that time, hunger or self-annihilation are a probable answers.  But that means that the new deadly creation is not as "Perfect Organism" as David stated.

This leads to another question -

In "Aliens" - they were alive, after killing all the "meat". They were alive and waiting. Does anyone remember for how long did they wait till the expedition team with Ripley arrived?