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By DataBase Center for Life Science (DBCLS) -, CC BY 4.0,, Diplocaulus
By DataBase Center for Life Science (DBCLS)
CC BY 4.0, https://commons.wikimedia.

Originally Posted by Shade of the En World forums. 

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This three-foot-long amphibian has a pancack-shaped body and a large, boomerang-shaped head. Its legs are short, and its tail is long and flat. A diplocaulus is a prehistoric amphibian with an odd-shaped head. This oversized head makes it difficult to swallow by the many larger predators in its environment. A diplocaulus spends most of its time on the bottom of rivers and streams, waiting for small fish and insects on which to prey. A diplocaulus is about 3 feet long.

Diplocaulus is known for the long protrusions on the sides of its skull, which cause the skull to be shaped similar to a boomerang. Judging from its weak limbs and relatively short tail, it is presumed to have swum with an up-and-down movement of its body, not unlike cetaceans today. The wide head could have helped the creature glide through the water. Also, it is thought to have had defensive purposes as any predator (even the large-headed Eryops) would have a hard time trying to swallow a creature with such a wide head.

Small animal (Aquatic)
Hit Dice1d8+1 (5 hp)
Speed5 ft. (1 square), Swim 40 ft.
Armor Class14 (+2 size, +2 Dexterity), touch 14, flat-footed 12
Base Attack/Grapple+0/-9
AttackBite +4 melee (1d4-1)
Full AttackBite +4 melee (1d4-1)
Space/Reach2-1/2 ft./0 ft.
Special Attacks
Special QualitiesAmphibious, hard to swallow, hydrofoil, Low-Light Vision
SavesFort +3, Ref +2, Will +0
AbilitiesStrength 9, Dexterity 14, Constitution 13, Intelligence 1, Wisdom 11, Charisma 5
SkillsHide +12, Listen +3, Move Silently +7, Spot +3, Swim +8
FeatsAlertnessWeapon Finesse (B)
EnvironmentWarm aquatic
Challenge Rating1/2
AlignmentAlways neutral
Advancement2 HD (Tiny), 3-4 HD (Small)
Level Adjustment


A diplocaulus generally attempts to escape if threatened by a larger creature.

Hard to Swallow (Ex): A diplocaulus counts as one size category larger for the purposes of being swallowed whole.

Hydrofoil (Ex): A diplocaulus gains a +4 bonus on any Swim check made to Swim against a current.

Skills: A diplocaulus has a +4 racial bonus on all Hide and Move Silently checks. A diplocaulus has a +8 racial bonus on any Swim checks to perform some special action or avoid a hazard. It can always take 10 on Swim checks even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.

Originally appeared in Dragon Magazine #112 (1986) as “Labrynthodont”.

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