Monster Monday: Anomalocaris, Top Predator of the Cambrian Seas

Today's Monster Monday is anomalocaris, an odd-looking predator that moved through prehistoric waters with a row of oar-like fins, grasping prey in its barbed claws and drawing it in toward its circular mouth of serrated plates.  You can think of it as a 'dire shrimp'.

via Wikimedia

Life-restoration of anomalocaris

Anomalocaris is the world's first apex predator, dwarfing most other creatures of the Cambrian seas (541–485.4 million years ago).  Of course, it didn't take much to be the biggest back then - anomalocaris was about a meter long - so I've also included a giant anomalocaris the size of a rowboat that should prove to be more of a challenge for low-level adventurers.

It is certain that anomalocaris fed on soft-bodied animals like worms and pikaia (a free-swimming creature thought to be the ancestor of all vertebrates), but there is some debate as to whether it also ate hard-shelled creatures like trilobites.  Giant fossilized turds containing broken bits of trilobite exoskeleton seem to indicate that anomalocaris (or some predator almost as large) was eating trilobites, but some paleontologists have questioned whether anomalocaris' mouth parts were strong enough to crush such shells.  It may have subsisted on worms that it sucked out of the sea floor.  In any case, the anomalocarises statted up below are assumed to have strong mouth parts capable of gnawing on stalwart adventurers.

anomalocaris painting by Ratianidze, via Wikimedia

Anomalocaris, looking decidedly Lovecraftian

The following text in gold is available as Open Game Content under the OGL. Open Game Content is ©2016 Jonah Bomgaars.

This three-foot creature glides forward on rippling oar-like lobes, spiked appendages waving menacingly from either side of its round mouth

Anomalocaris         CR 1

XP 400

N Small vermin (aquatic)

Init +1; Senses darkvision 60 ft.; Perception +1

DEFENSE

AC 13, touch 12, flat-footed 12 (+1 Dex, +1 size, +1 natural)

hp 13 (2d8+4)

Fort +5, Ref +1, Will +1

Immune mind affecting effects

OFFENSE

Speed 5 ft., Swim 30 ft.

Melee bite +2 (1d6 plus grab)

Special Attacks gnaw (1d6)

STATISTICS

Str 11, Dex 12, Con 14, Int --, Wis 13, Cha 2

Base Atk +1; CMB +1 (+3 grapple); CMD 12

SPECIAL ABILITIES

Gnaw (Ex)

An anomalocaris gnaws at its prey, dealing bite damage, when it makes a successful grapple check (including the one made as part of a grab with its bite attack). 

ECOLOGY

Environment any oceans

Organization solitary

Treasure none

Anomalocaris, Giant      CR 3

XP 800

N Large vermin (aquatic)

Init +1; Senses darkvision 60 ft.; Perception +1

DEFENSE

AC 16, touch 10, flat-footed 15 (+1 Dex, -1 size, +6 natural)

hp 30 (4d8+12)

Fort +7, Ref +2, Will +2

Immune mind affecting effects

OFFENSE

Speed 5 ft., Swim 40 ft.

Melee bite +6 (2d6+6 plus grab)

Special Attacks gnaw (2d6+6)

STATISTICS

Str 19, Dex 12, Con 17, Int --, Wis 13, Cha 2

Base Atk +3; CMB +8 (+10 grapple); CMD 21

SPECIAL ABILITIES

Gnaw (Ex)

An anomalocaris gnaws at its prey, dealing bite damage, when it makes a successful grapple check (including the one made as part of a grab with its bite attack). 

ECOLOGY

Environment any oceans

Organization solitary

Treasure none

Anomalocaris is a predator of primeval seas.  Its three-foot-long, segmented body is broadened by a lateral array of a dozen paddle-like lobes; these grow longer toward the creature’s midsection, giving it an oval or diamond-shaped outline.  These lobes, along with a tail resembling that of a shrimp, propel it through the water with an undulating motion.  Its rounded head is topped with two large compound eyes on short stalks.  A circular mouth of overlapping, serrated plates occupies the underside of the head.  The anomalocaris has two six-inch-long barbed claw-like appendages that it uses to graps prey and pull it towards its grinding mouth. 

   Occasionally, much larger anomalocarids are seen rising up from the black depths of the sea.  These beasts can reach the size of a small boat, and they gorge themselves on the plentiful prey to be found in the surface waters before retreating back to their cold and briny domains.  

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-your anomalous d20 despot