Steal an Egg Prehistoric zone: all eight dinosaur eggs, the Bronto, and how rare each one is

Each Prehistoric pet has its own infobox on the wiki, and all eight agree with the wiki's Pets and Eggs table on rarity and income, so the Steal an Egg Prehistoric zone has no income conflict to report. The Prehistoric zone page (rev 1764, last edited 20 September 2026) shows the same eight cards with the same values under the heading "All Prehistoric Pets" and a chip reading "8 Pets".

The rarity ladder is uneven. There is no Common or Epic pet here: the zone starts at Rare with the Dodo, then Legendary (Pterodactyl) and Mythic (Ankylosaurus). Two pets share the Cosmic tier, Triceratops and Bronto, and two share the Secret tier, T-Rex and Tralaledon. Mosasaurus is the only Eternal, and there is no Divine. The nearest Divine in zone order is Cosmic's Unicorn, which the Pets and Eggs table lists one zone higher.

The reward column follows a clean pattern. Every one of the eight infoboxes lists a cash reward exactly 100 times the pet's per-second income: $280/s with $28k, $22K/s with $2.2m, $1.5M/s with $150m, all the way to $180M/s with $18b. The Speed part of the reward climbs less neatly. Bronto's +300k is lower than Triceratops' +360k even though Bronto earns more per second. Hatching one of each pet would add 3,000k Speed in rewards on our arithmetic (240k + 270k + 330k + 360k + 300k + 420k + 480k + 600k).

Grow times split the zone in two. The five lower pets finish between 1m 30s and 11m, the same order of time as the 5-minute egg reset that the wiki's Eggs page describes. The three top pets need 2h 30m (T-Rex), 3h (Tralaledon) and 6h (Mosasaurus), so an egg from the top of the table sits in a pen for hours before it pays.

The wiki's Drop Rates page says its numbers were found in the game files at ReplicatedStorage/Data/Areas. For Prehistoric it lists Dodo 39.066058, Pterodactyl 26.044039, Ankylosaurus 20.835231, Triceratops 4.929402, Bronto 6.995959, TRex 0.991743 (internally named Tyrannosaurus Rex), Tralaledon 0.826453 and Mosasaurus 0.311113. The eight values add up to 99.999998 on our arithmetic, so in this zone each one reads almost exactly as a share out of 100. This site still divides every value by its zone's listed total, as it does for zones whose values do not sum so neatly.

The list is not sorted by rarity. Triceratops sits above Bronto, yet Bronto's value is the larger of the two, and both are Cosmic. On the Drop Rates figures the Bronto is about 1.4 times as common as the Triceratops (6.995959 ÷ 4.929402), and its infobox also lists the higher income, $1.5M/s against $1.2M/s. The wiki gives no reason for the order; it simply lists the values. For anyone hunting the brontosaurus egg specifically, that is the useful part: of the two Cosmic dinosaurs, it is both the more common and the better earner.

To turn a value into something practical, treat it as the chance that one Prehistoric egg spawn is that pet. The chance of seeing at least one in N spawns is then 1 − (1 − p)^N. On the Drop Rates figures, a Bronto has an even chance of turning up within 10 spawns and a nine-in-ten chance within 32. The T-Rex needs 70 spawns for an even chance and 232 for nine in ten. Tralaledon needs 84 and 278. Mosasaurus needs 223 and 739. Counting T-Rex, Tralaledon and Mosasaurus together (2.129309 of the zone total), one of the three has an even chance within 33 spawns and a nine-in-ten chance within 107, or about one top-three egg per 47 spawns on average.

Weighting each pet's listed income by its share gives an average of about $1.27M/s for a random Prehistoric egg at normal size with no mutation (our arithmetic: the sum of share × income across all eight). Almost $560K/s of that average comes from the Mosasaurus alone, and the top three together supply about $1.07M/s of it. The Dodo, the most common egg in the zone, contributes about $109/s.

Two values repeat elsewhere on the Drop Rates page. Tralaledon's 0.826453 is identical to Kraken's in Abyss Ocean, and Mosasaurus's 0.311113 differs from Cosmic's Eternal Lunar Dragon (0.311104) only in the sixth decimal place.

What the page does not say matters as much. It does not give the number of eggs a nest spawns at each 5-minute reset, or whether every nest rolls from the same list, so these spawn counts cannot be turned into minutes of play. It also says nothing about egg size or colour mutations, which the Mutations page describes as separate rolls. The full method, with every zone, is on /steal-an-egg-drop-rates.

The Biomes page (rev 1823, edited 20 September 2026) puts the Prehistoric requirement at 18M. The Prehistoric zone page, edited the same day, shows a chip reading "17,000,000 – 18,000,000 Speed Required". The older Zones page (rev 585) gives "~17,000,000–18,000,000" and adds that sources disagree "particularly for Jungle and Prehistoric". This page uses 18M, the higher figure, because Biomes also warns that bigger eggs slow you down and need more than the listed speed, and that having enough Speed to enter a biome "does not necessarily mean you have enough Speed to safely return with a large Egg".

Getting in is a big step. The gate is 7.2 times Abyss Ocean's 2.5M. Getting out is far bigger: Cosmic's 700M is about 39 times Prehistoric's 18M, the steepest ratio between neighbouring zones on the Biomes table (our arithmetic). A player who reaches Prehistoric therefore faces the longest climb on the table before the next zone opens. How the wiki says Speed is trained is covered on /steal-an-egg-speed.

Against the zone before it, Prehistoric's top egg is both better paid and more common. Abyss Ocean's Eternal, El Maja, is listed at $130M/s with a Drop Rates value of 0.08889 and a grow time of 5h 30m. Mosasaurus is listed at $180M/s with 0.311113, about 3.5 times El Maja's value, and grows in 6h. Abyss Ocean's two Cosmics, Whale Shark at $700K/s and Beluga Whale at $850K/s, both earn less than Triceratops and Bronto.

Against the zone after it, the picture shifts. Cosmic's Eternal Lunar Dragon is listed at $250M/s with a 7h grow time and a value of 0.311104. At almost the same spawn value it pays about 1.39 times as much as Mosasaurus ($250M ÷ $180M), but it sits behind a gate roughly 39 times higher.

The guardian the Biomes page names is the T-Rex, and a T-Rex egg is also the zone's lower Secret. The wiki lists the guardian by name and the pet by infobox; it does not say whether the two are the same model in the game. The Dr. Scramble Event page uses the guardian as a landmark: Lost Part #2 of the Stolen Experiment Vault quest "is located behind the bush in Prehistoric, near the T-Rex". The quest itself is covered on /steal-an-egg-dr-scramble.

On freshness: the Prehistoric zone page was last edited on 20 September 2026, the newest edit among its eight pet infoboxes is Dodo's on 16 October 2026, and the Roblox Games API shows the game itself last updated on 21 October 2026 at 16:46 UTC. Neither source says whether that update changed anything in Prehistoric.

The Rift Event page (rev 1703, last edited 19 September 2026) describes a permanent Rift banner that rotates through three egg pools roughly every 3 hours. Two of them draw on Prehistoric. Riftbeasts takes Volcano, Abyss Ocean, Prehistoric and Cosmic eggs; Shattered Rift takes Prehistoric, Cosmic, Cherry Blossom and Titan Temple eggs. Both pools put this zone's pets in the same difficulty tiers: Dodo and Pterodactyl are Easy, Ankylosaurus is Medium, and Triceratops and Bronto are Hard. The page says the Rift Sacrifice asks for 3 random pets and grants 1 exclusive Rift Egg. Its FAQ adds that pity "carries over regardless of leaving the game or the banner changing"; the Boss Mastery side of the Rift is covered on /steal-an-egg-boss-mastery and the banners on /steal-an-egg-rift-event.

The wiki contradicts itself here. The Update 6 notes on the Updates page say "The Rift Trade-In Machine has been replaced by Dr. Scramble's Laboratory", while the Rift Event page still describes Rift Sacrifices. Both statements are reported here because the wiki has not reconciled them.

Dr. Scramble's Laboratory (rev 2268) calls its banner permanent and rotates three pools. Only one uses Prehistoric: Biohazard, which draws from Prehistoric, Cosmic and Cherry Blossom eggs. Its Prehistoric list reads Rare: Dodo · Legendary: Pterodactyl · Mythic: Ankylosaurus · Cosmic: Triceratops, Bronto. Prehistoric is also the one zone that Biohazard uses and the Experimental and Unstable DNA banners do not. Update 6 says eggs can now be handed in directly instead of being hatched first. The Biohazard Egg infoboxes list Nuceodile (Secret, $5B/s on its infobox, while the wiki's Module:Pets/Data lists $500M/s), Nuclear Mantis (Eternal, $1.5B/s), Toucax (Cosmic, $30M/s), Radcoon (Cosmic, $2.2M/s) and Toxic Rat (Mythic, $180K/s).

One pattern runs through both banner systems in Steal an Egg: Prehistoric eggs are wanted only from the bottom of the table. No Rift or Laboratory list asks for the T-Rex, Tralaledon or Mosasaurus. The lists stop at the Cosmic tier for this zone, so the five lower pets have a second use while the Secrets and the Eternal do not.

Colour mutations change the arithmetic for the eggs you keep. The Mutations page (rev 1822) gives Golden ×2.5 with a roll weight of 4 out of 100, Rainbow ×3.5 with 1 out of 100 and Silver ×1.2 with 6 out of 100, and states that final income is base × mutation multiplier × size multiplier. On our arithmetic at normal size:

Prehistoric is not the game's only home for extinct animals: the Extinction Egg holds more, and it belongs to a different system. The Update 6 notes on the Updates page announce it under the heading "New Paid Egg — Extinction Egg": it "contains 6 new extinct animals", has a "Small chance to REROLL your hatch", and "Rerolls give you a rare SKELETAL VERSION of that animal". None of its pets lists Prehistoric as a biome, and the wiki does not say the egg appears in Prehistoric nests.

The wiki's infoboxes fill in part of the list. Two pets name the Extinction Egg as their egg: Glyptodon (Legendary, $22.5K/s, reward $2.2m) and Sabertooth (Divine, $5B/s). The Skeletal Egg infoboxes name six animals, matching the "6" in the update notes: Skeletal Glyptodon (Secret, $550M/s), Skeletal Terrorbird (Secret, $750M/s), Skeletal Giant Sloth (Secret, $900M/s), Skeletal Dunkleosteus (Eternal, $2.5B/s), Skeletal Gigantus (Eternal, $4B/s) and Skeletal Sabertooth (Divine, $9B/s). The plain Dunkleosteus, Giant Sloth, Gigantus and Terrorbird pages exist with empty infoboxes. The wiki's Module:Pets/Data (rev 2020) does list them: Terrorbird (Mythic, $110K/s), Giant Sloth (Cosmic, $4M/s), Dunkleosteus (Secret, $300M/s) and Gigantus (Eternal, $1B/s), though it files all four under the Skeletal Egg rather than the Extinction Egg, so their egg is not settled on the wiki.

Three gaps are worth stating plainly. The wiki gives no Robux price for the Extinction Egg on these pages, no reroll chance for the Skeletal versions, and no Extinction Egg section on the Drop Rates page. The Extinction Egg's Sabertooth is also a different pet from Snow's Sabertooth Tiger, a Mythic listed at $35K/s.

The comparison with the zone is still useful. The lowest Skeletal pet, Skeletal Glyptodon at $550M/s, already earns about three times the Mosasaurus' $180M/s, and the Divine Sabertooth's $5B/s is nearly 28 times it (our arithmetic). Those figures come from a paid egg, though, while everything in the table above comes from nests that anyone with 18M Speed can raid.