View Full Version : Making prehistoric animals

2013-11-07, 03:44 AM
Previously: http://www.giantitp.com/forums/showthread.php?t=276822

Please don't post in that thread.

Most significant bits from the old thread:

Weight:Height:HD relationship

Weight = (height ^ 3) / 1.024
or inversely:
Height = (weight x 1.024) ^ (1/3)

Typical HD = height (length for quadrupeds) in feet / 4; where numbers are available, use the estimated weight to calculated a "spherical cow height" and base HD off that.

Double the above number for carnivores.

Don't count tail when determining HD unless the creature is essentially limbless (fish, snakes) or the tail is functional (has a thagomiser, or acts as a counter-balance)

Typical Environments

Note: Some terrain types may not exist because the appropriate plant life has not yet evolved (no forests in the Cambrian). Some terrain types might involve strange plant life, but still be essentially the same (Carboniferous forests are essentially giant ferns). However, if a given terrain type exists at all, it is in game rule terms no different from what it was in modern times.

{table=head]Period | Dominant Life | MYA | O2 | CO2 | Temperature C | Special Air Rules
Ediacaran| (no macroscopic life) | 635-541 | 40% | 1600% | unknown | Very Low Oxygen
Cambrian | Invertebrates | 541-485 | 63% | 1600% | 21 C | Low Oxygen
Ordovician | Invertebrates | 485-443 | 68% | 1500% | 16C | Low Oxygen
Silurian | Fish | 443-419 | 70% | 1600% | 17 C | Low Oxygen
Devonian | Fish, Amphibians | 419-359 | 75% | 800% | 20 C | Low Oxygen
Carboniferous | Amphibians, Insects | 359-299 | 163% | 300% | 14 C | Oxygen-Enriched
Permian | Therapsids | 299-252 | 115% | 300% | 16 C |
Triassic | Dinosaurs | 252-201 | 80% | 600% | 17 C | Low Oxygen
Jurassic | Dinosaurs | 201-145 | 130% | 700% | 16.5 C |
Cretaceous | Dinosaurs | 145-66 | 150% | 600% | 18 C | Oxygen-Enriched
Paleogene | Mammals | 66-23 | 130% | 200% | 18 C |
Neogene | Mammals | 23-2 | 108% | 100% | 14 C |
Quaternary | Mammals | 2-0 | 104% | 100% | 14 C |

MYA indicates millions of years ago.

Atmospheric O2 and CO2 levels are relative to present day. Early Earth atmospheres had incredibly high CO2 levels (although still not high enough to significantly affect modern human visitors in a time travel scenario). These were gradually locked away into fossils (and eventually, coal and other fossil fuels).

The Carboniferous period had an unusually O2-rich atmosphere, which allowed for insects to reach the largest sizes they ever did historically.

Plant life first colonised land during the Silurian period. Prior, and during most of that, land terrain will generally be bare rock punctuated by desert and mud. "Soil" would not yet have formed, without meaningful quantities of dead plant matter to compost and lock the debris in place.

The Cambrian period was dominated by trilobites, the largest of which (Isotelus) reached 28 inches in length, and 3 inches in height. Nothing living in this period poses a meaningful threat to humans, although the atmospheric composition might be a danger.

Oxygen Levels

Reading around the high-O2 atmosphere issue, I'd suggest the following rule:

High Oxygen Atmosphere: Characters in high-O2 air gain a +2 bonus on checks made to sustain forced marches, long-distance swimming, running, and similar acts of exertion requiring stamina. Such atmospheres do not grant any special bonus in drowning/suffocation or high altitude situations.

In addition, fires burn more fiercely. All non-magical fire damage is increased by 50%, as if under the effect of the Empower Spell feat (except obviously, it's not magical). This does not affect damage from scalding water or radiated heat - only actual fire.

Magical fire that lasts for extended periods (such as wall of fire) is also affected as if by the Empower Spell feat, but magical fire that is instantaneous in duration (such as fireball) is not affected.

In the Early Earth, this applies to the Carboniferous and Cretaceous periods.

Low Oxygen: In some periods of Earth's history, the oxygen content was quite low, such that the oxygen content was equivalent to that on a mountain in present-day Earth.

In a low-oxygen environment, characters must succeed on a Fortitude save each hour (DC 15 +1 per previous check) or become fatigued. This fatigue lasts until the character enters an environment with a normal oxygen level. In a modern environment, this is achieved by descending to low altitude. In Early Earth environments, this will typically require magic.

Any character who spends one month in such an environment becomes acclimatised, and no longer suffers this fatigue penalty or needs to make these Fortitude saves. A character who spends two months away from such an environment is no longer acclimatised. Creatures native to the environment (historical time period) are automatically considered to be acclimatised.

In the Early Earth settings, this applies to the Cambrian, Ordovician, Silurian, Devonian, and Triassic periods.

Very Low Oxygen Environment: This environment is hostile to normal animal (including "vermin") life. Every six hours, a character that needs oxygen must pass a Fortitude save (DC 15 +1 per previous check) or take one point of ability damage to all six ability scores. It is not possible to become acclimatised to a very low oxygen environment.

In the Early Earth settings, this applies to the Ediacaran (and earlier?) periods.

What's New?

So I want to come back to this project. The idea is to make complete monster write-ups for prehistoric beasts based on what is actually known about them.

The most fundamental known stat is their physical size, from which HD are derived.

Movement: Travel modes can be determined from their body form, and combined with their size class gives a typical speed for the creature. We can supose that hunter/carnivores will be at the faster end of the range, and exceptionally short-limbed creatures at the slower end of the range.

Natural Armour: Size class gives typical natural armour values, but the truth is we don't actually have much reliable information. Do we?

Special Senses: Scent is fairly standard on mammals and reptiles. Given that it is not standard on birds, it could be entertaining to exclude it from dinosaurs.

Darkvision (heatvision) is common in snakes. Has it evolved independently elsewhere?

Low-light vision is primarily found in animals that operate around dawn and dusk. Given that eyes may not have had time to evolve to such complex levels, it is entirely possible that this feature (and darkvision) were absent in the early Earth.

Marine mammalian predators should have the aquatic equivalent to scent.

Apparently, reptiles and dinosaurs have rather poor hearing (cite (http://science.nationalgeographic.co.uk/science/prehistoric-world/rise-mammals/#page=3)). Their Listen checks should probably not get many ranks spent on them.

Bats have "sonar" senses (squeaks plus 3d echolocation), and cetaceans have an aquatic equivalent. This is essentially D&D blindsense or blindsight.

Any flying creature should have notable bonuses to vision-based Perception.

Some of the earliest creatures might not have sight as we know it (eg. motion only, heat only, intense light sense, etc). Special rules for this may need to be written up.

Swallow Whole: This is fairly cinematic. Nonetheless, let's give it to any creature with sufficiently large mouths and size class.

Rage: As seen in D&D badgers and wolverines. Any general rules on what creatures should have this?

Improved Grab: This is only for creatures with two claw attacks and a shape that allows it to rear up. That probably restricts it to some mammals only, possibly a very small number of dinosaurs. However, some creature do an improved grab that depends on bite attacks. There is no standardised rule for this ability in 3.5e.

Trip: Some D&D animals have this. I never quite understood why.

Hold Breath: Some land animals can do this (eg. D&D crocodiles). Presumably, some early land exploring animals did the inverse of this.

Ability Scores: Hard to determine directly. They are pretty much all animals or vermin in game terms though. Typical modifiers:

Strength: Size, bonus for hunter/carnivore, penalty for particularly delicate limbs, penalty for flying creatures (due to light bone structure)

Constitution: Size, duration that species survived, bonus for multiple environments

Dexterity: Size, bonus for manipulative limbs, long limbs, or tail (if tail is weaponised, prehensile, or counterbalancing); penalty for subdermal armour

Intelligence: Bonus for complex diet (ie. omnivore), bonus for multiple habitats (still probably not going to rise above 3 though)

Wisdom: Bonus for multiple senses, penalty for an exceptionally short time on planet Earth.

Charisma: I have no idea.

Suggestions on what else could affect these are greatly appreciated.

2013-11-07, 06:51 AM
Oxygen Levels


Low Oxygen: In some periods of Earth's history, the oxygen content was quite low, such that the oxygen content was equivalent to that on a mountain in present-day Earth.

Very Low Oxygen Environment: ...

In the Early Earth settings, this applies to the Ediacaran (and earlier?) periods.Actually, there have been a number of recent studies which show incredibly strong evidence that this was simply not the case. One study (an article about it can be found here (http://www.astrobio.net/pressrelease/4373/earths-early-atmosphere)) indicates "that the atmosphere of Earth just 500 million years after its creation was not a methane-filled wasteland as previously proposed, but instead was much closer to the conditions of our current atmosphere." Just something to consider...

2013-11-07, 07:17 AM
500 million years after Earth (the period that article is writing about) was created is quite a long distance in time away from the Ediacaran period. Wikipedia claimed the Ediacaran period atmosphere was low-oxygen, to the tune of around 40% of modern levels. That's quite a lot, but still not enough to maintain consciousness and a clear head over an extended period. I have no direct information on oxygen levels in earlier periods, and as there was no macroscopic life before that point, I consider it irrelevant to this project.

Of course, if you want to play with normal oxygen levels in the Ediacaran, be my guest.The point being that the rise in oxygen levels is attributed to bacteria activity producing free oxygen, beginning around 2.8 Ga. If there's already a higher starting point for oxygen, this increase would make the low oxygen issues less noticeable.

I'm not trying to derail your idea with this. I just think that if you're going to do a "campaign setting" based on early earth that you should use the latest theories and evidence. Personally, I think this is a great idea and can't wait to see the final results.