About

Choosing a random animal from Earth's estimated 8.7 million species is not a trivial sampling problem. Naive implementations using Math.random suffer from modulo bias when mapping a continuous [0,1) float to a discrete index i ∈ {0, 1, …, n−1}. This generator uses crypto.getRandomValues for uniform distribution across the animal pool. The dataset covers 150 species spanning 6 taxonomic classes: Mammalia, Aves, Reptilia, Amphibia, Actinopterygii, and Invertebrata. Each entry includes IUCN Red List conservation status, habitat classification, dietary category, and verified biometric ranges. Filters operate via set intersection, reducing the candidate pool P before sampling.

Note: lifespan and weight figures represent population averages from field studies. Captive specimens often exceed these ranges. The "Least Concern" status does not imply abundance in all regions. This tool approximates biodiversity sampling assuming equal weighting across included species. Regional biodiversity indices like Simpson's D or Shannon's H′ require population density data not modeled here.

Formulas

The generator selects an animal from a filtered candidate pool using cryptographic randomness. Given a full dataset D of n animals and a set of active filters F, the candidate pool is computed as:

P = { a ∈ D | a satisfies ∀ f ∈ F }

The random index i is generated using rejection sampling on a 32-bit unsigned integer from crypto.getRandomValues to eliminate modulo bias:

i = r mod |P| , where r < ⌊ 2³²|P| ⌋ ⋅ |P|

The probability of selecting any single animal a from the filtered pool is uniformly:

P(a) = 1|P|

Where D = full animal dataset, F = set of active filter predicates (class, habitat, diet, conservation status), P = filtered candidate pool, r = cryptographically random 32-bit unsigned integer, i = selected index into P.

Reference Data

Animal	Class	Habitat	Diet	Conservation	Avg. Lifespan	Weight Range
African Elephant	Mammalia	Savanna	Herbivore	Vulnerable	60 - 70 yr	4,000 - 6,000 kg
Snow Leopard	Mammalia	Mountain	Carnivore	Vulnerable	15 - 18 yr	22 - 55 kg
Blue Whale	Mammalia	Ocean	Carnivore	Endangered	80 - 90 yr	100,000 - 150,000 kg
Bald Eagle	Aves	Forest	Carnivore	Least Concern	20 - 30 yr	3 - 6.3 kg
Emperor Penguin	Aves	Antarctic	Carnivore	Near Threatened	15 - 20 yr	22 - 45 kg
Komodo Dragon	Reptilia	Tropical	Carnivore	Endangered	25 - 30 yr	70 - 90 kg
Green Sea Turtle	Reptilia	Ocean	Herbivore	Endangered	60 - 80 yr	65 - 130 kg
Poison Dart Frog	Amphibia	Tropical	Carnivore	Least Concern	3 - 15 yr	1 - 7 g
Axolotl	Amphibia	Freshwater	Carnivore	Critically Endangered	10 - 15 yr	60 - 225 g
Clownfish	Actinopterygii	Ocean	Omnivore	Least Concern	6 - 10 yr	10 - 30 g
Giant Pacific Octopus	Invertebrata	Ocean	Carnivore	Least Concern	3 - 5 yr	10 - 50 kg
Monarch Butterfly	Invertebrata	Grassland	Herbivore	Endangered	0.5 - 0.75 yr	0.3 - 0.5 g
Red Panda	Mammalia	Forest	Herbivore	Endangered	8 - 14 yr	3 - 6.2 kg
Narwhal	Mammalia	Arctic	Carnivore	Least Concern	40 - 50 yr	800 - 1,600 kg
Scarlet Macaw	Aves	Tropical	Omnivore	Least Concern	40 - 50 yr	0.9 - 1.5 kg
Galápagos Tortoise	Reptilia	Tropical	Herbivore	Vulnerable	100 - 175 yr	150 - 250 kg
Pangolin	Mammalia	Tropical	Carnivore	Critically Endangered	10 - 20 yr	1.6 - 33 kg
Seahorse	Actinopterygii	Ocean	Carnivore	Vulnerable	1 - 5 yr	0.5 - 10 g
Mantis Shrimp	Invertebrata	Ocean	Carnivore	Least Concern	3 - 6 yr	10 - 200 g
Arctic Fox	Mammalia	Arctic	Omnivore	Least Concern	3 - 6 yr	1.5 - 9 kg
Japanese Spider Crab	Invertebrata	Ocean	Omnivore	Least Concern	50 - 100 yr	16 - 20 kg

Frequently Asked Questions

The generator maintains a history buffer of the last 50 selections. When generating, it attempts to pick from the candidate pool excluding recently shown animals. If the filtered pool is smaller than the history buffer, the history is partially cleared to ensure results remain available. This mimics sampling without replacement until the pool exhausts.

Filters operate via set intersection. If you select Class = Amphibia, Habitat = Arctic, and Diet = Herbivore simultaneously, the intersection may be empty because no amphibians in the dataset inhabit arctic regions as herbivores. The tool displays a notification and suggests relaxing one or more filters. This is a correct mathematical result, not a bug.

The statuses reflect the IUCN Red List assessments as of 2024. Conservation statuses are periodically reassessed - for example, the Giant Panda was downlisted from Endangered to Vulnerable in 2016. The tool's dataset is a snapshot and does not auto-update. Always cross-reference iucnredlist.org for current assessments on specific species.

It uses crypto.getRandomValues(), which draws from the operating system's cryptographic random number generator (CSPRNG). This provides entropy from hardware sources (thermal noise, interrupt timing) and is not deterministic like Math.random()'s PRNG. The practical difference for animal selection is negligible, but it guarantees uniform distribution without modulo bias through rejection sampling.

Yes. The print stylesheet formats the current animal card as an A4-compatible reference sheet with all taxonomic details, habitat, diet, conservation status, and the fun fact. Teachers can generate and print cards for biology lessons, taxonomy exercises, or conservation awareness projects. The reference table also prints as a standalone species cheat sheet.

Weight ranges represent wild adult specimens under typical conditions. Captive animals frequently exceed the upper bound due to controlled diets and reduced energy expenditure. For example, captive African Elephants can exceed 7,000 kg versus the listed wild range of 4,000-6,000 kg. Juvenile and seasonal weight variation is not captured in these ranges.