CREATURE_BODY_PLAN_TAXONOMY.md

creatures/CREATURE_BODY_PLAN_TAXONOMY.md

The creature body-plan taxonomy — how many skeletons exist

Proposal tier. Authored 2026-08-13. Named for Josh's veto per the standing rule that

beyond-floor additions are declared rather than slipped in.

Why this is the first thing, not the forty-second

T0_Creature_Roster classifies creatures biologically: 82 rows say mammal. A bat, a whale, an

elephant and a rat are all mammals and share no rig, no skeleton, no animation, and no scale. 47

rows say folklore, which describes provenance and not a body at all. There is no body-plan column

on the registry, and height_m is populated on 7 of 187 rows.

So the roster today cannot drive a rig or a scale. That is the actual blocker under the creature

lane, and it gets worse with volume: the canon requirement is roughly 2,000 species

(docs/ASSET_BUILD_LIST.md). Assign body plans well and that is ~30 skeletons with ~2,000 meshes

hung off them. Assign them badly, or not at all, and it is 2,000 rigging problems.

A body plan is not biology. It is limb topology plus spine articulation plus ground contact —

the three things a skeleton encodes. Two animals in different orders share a plan when they share

those; two animals in the same order do not when they don't.

The taxonomy — 30 plans

Terrestrial vertebrate

• quadruped_digitigrade — walks on toes, flexible spine, retractable or fixed claws. Tiger,

leopard, clouded leopard, sun-bear-adjacent felids and canids.

• quadruped_unguligrade — hoofed, stiff spine, long distal limb. Deer, sambar, buffalo, boar,

pig, rhinoceros.

• quadruped_plantigrade — full-foot contact, heavy forelimb, rearing-capable. Bears.
• quadruped_graviportal — column limbs, no gallop, mass-dominated gait. Elephant. Separate from

plantigrade because the gait solver and foot IK differ fundamentally.

• quadruped_small — short spine, scurrying gait, high step frequency. Rats, small rodents,

small mustelids.

• primate_arboreal — tail, grasping hands and feet, brachiation-capable shoulder. Macaques,

langurs.

• primate_great_ape — no tail, arm-dominant locomotion, knuckle or fist contact. Orangutan.
• hominin_biped — shares the human skeleton. Ebu Gogo, Orang Pendek, Nittaewo, Bigfoot.

This is the highest-leverage row in the table: a hominin cryptid rides the same rig as a

character, so the entire human animation library and the MetaHuman retarget path reach it for

free. Scale differs; topology does not.

Flying

• avian_perching — passerine proportions, short wing, perching foot. Sparrow, raven, parrot.
• avian_raptor — long wing, talon foot, hooked bill, soaring pose set. Eagle, falcon, vulture.
• avian_wading — long neck and legs, folded-neck flight. Ibis, stork, crane, pelican.
• avian_terrestrial_raptor — raptor head on wading legs, strikes with the foot. Secretary bird.

Its own plan because neither parent plan animates it.

• avian_ratite — flightless, vestigial wing, running biped. Ostrich.
• chiropteran — membrane wing carried on elongated digits, inverted roost. Bats, flying foxes.

Nothing in the feathered plans transfers.

Reptile

• varanid — sprawling quadruped, lateral undulation, heavy tail. Komodo dragon, monitors.
• crocodilian — sprawling with a high-walk mode, armoured dorsal, tail-driven swim.
• serpentine — spine only, no limbs. Pythons, cobras.
• chelonian — shell constrains spine and limb arc absolutely.

Aquatic

• fusiform_fish — standard fin set, lateral undulation. Reef cohorts, carp, catfish, barb.
• elasmobranch — shark fin set and heterocercal tail. Whale shark.
• cetacean — horizontal fluke, mammalian ribcage, blowhole. Dolphins.
• sarcopterygian — lobe-finned, limb-like fin bases. Coelacanth. One row today, but it is a

living fossil whose whole point is that its fins are almost limbs, and the standard fish rig

destroys exactly that.

Invertebrate

• arachnid — eight legs, cephalothorax.
• insect_hexapod — six legs, three body segments.
• mollusc_soft — no skeleton; simulated or blend-shape driven.

Folklore composites that need their own rig

These are not a "folklore" bucket. Each earns a plan because its silhouette cannot be animated by

any plan above.

• winged_humanoid — human topology with a wing pair added at the scapula. Mothman.
• serpentine_multiheaded — a branching spine, which no single-chain serpentine rig solves. Naga,

the seven-headed balustrade water-lord.

• long_neck_aquatic — long neck, barrel body, paddle limbs. Mokele-mbembe, Nguma-monene, the

Loch Ness form, Bunyip's aquatic read.

• giant_avian — raptor topology at a scale where wing membrane sag, feather cards and flight

cadence all change. Thunderbird, Ropen.

• pinniped_amphibious — flipper forelimb, terrestrial hauling gait.
• detached_visceral — a head and trailing viscera with no body, flight by drift. Krasue / Ap.

Genuinely unlike anything else in the table and it needs a bespoke simulated chain.

• composite_guardian — statue-derived guardian forms: Singa, Mahakala, the gate naga. Often

static or semi-static, animating from a stone rest pose rather than a creature gait.

What this buys

The two rules that keep it honest

1. A plan is claimed by topology, never by culture or provenance. "Folklore" is not a body

plan. A folklore being gets the plan its described body actually has, and if it has none, it

earns a new plan and the new plan is named here.

2. A row with no cited description does not get a guessed plan. It goes to UNASSIGNED with

the missing canon named. A wrong plan is more expensive than an empty one, because a wrong plan

is discovered after the rig is built.

Care note

Assigning hominin_biped to Ebu Gogo, Orang Pendek and Nittaewo is a statement about **skeleton

topology for rigging purposes only**. These are beings in living oral traditions and, in the Ebu

Gogo case, adjacent to a real palaeoanthropological record on Flores. The plan column says how the

mesh articulates. It says nothing about what they are, and it never routes their depiction — that

stays with the region page, the design sheet and the care tier.

Generated by harness/site/structure_site.py — the URL path is the repo path. review root