8 of the 32 achievements are these egg-collecting achievements. These are fairly simple, since eggs are shown on the map.

After moving on to the next zone, you can go back to the previous zones by pressing Tab with the map open and selecting the zone you want.

Another fairly easy one, since walnuts also appear on the map. Each zone has a secret subzone, which the last of a zone's walnuts may be in and can only be entered once all eggs in the zone are collected. Secret zones will be represented on the map by a question mark once unlocked.

There are four walnuts in Savanna that may not be immediately apparent; the first is shown on the map near the Den that you started by; you have to shoot the basketball hoop on the side of the Den to get it (while you're there, shoot it 9 more times for the Most Valuable Dino achievement).

The last three do not visually appear on the map, they are in the secret zone which is an underground subzone with five rooms. The first walnut is in the third room while the last two are in the fifth room. See the Savanna Secrets achievement for more detail.

One walnut in Lake is also ♥♥♥♥♥♥ by shooting a basketball hoop on the island, the Lake's secret zone.

Seed pots will be revealed on each individual map once Marsh, a green stegosaurus, is spoken to, though the seed pots can be found and planted beforehand. See Marsh's location in each zone circled in red in the images below. Once on the map, they are an easy task just like eggs and walnuts, and cost 200 seeds each to plant. Some seed pots may be in the secret zones unlocked once all eggs are collected.

Gigantopedia pages are not shown on the map, making collecting them without a guide quite tedious. All zones have five pages for a total of 30 pages. See their locations in each zone in the images below; the pages are numbered as they appear in the Collectables Gigantopedia tab in the main menu.

There are 30 collectible statues in-game; 18 are unlockable by spending seeds, and you need 8,400 seeds total to buy them all. There are at least 3,000 seeds in each zone, and are replenished each time you load a zone in case you need more. The remaining 12 statues and their unlocking criteria are listed below:

Rocky's Racer - Collect all 5 skulls in the Savanna to Jungle race
Bill's Bubble - Collect all 5 skulls in the Jungle to Desert race
Tiny's Truck - Collect all 5 skulls in the Desert to Lake race
Mazu's Mobile - Collect all 5 skulls in the Lake to Glacier race
HURRAY! - Collect all 5 skulls in the Glacier to Volcano race
Stone of Friendship - Complete the adventure
Rocky - Collect all walnuts in Savanna
Bill - Collect all walnuts in Jungle
Tiny - Collect all walnuts in Desert
Mazu - Collect all walnuts in Lake
Cror and Totor - Collect all walnuts in Glacier
Gigantosaurus - Collect all walnuts in Volcano

5 achievements (Flat Out, Leaves Them Behind, Speed of Sand, Current Champ, and Ice Cool) are dedicated to placing 1st in the races between the zones. If you are only playing against computer-controlled characters, beating them is fairly easy.

Top skull-scorer is dedicated to collecting all golden skulls in all of the races. Each race has 5 skulls, often placed in shortcuts on the racetrack, but some are on the main road as well. There's no need to win the race to keep the skulls, so take your time, reverse, or even turn around if you have to.

This achievement is obtainable right at the start of the game; there is a basketball hoop with a ball on the side of the Den that you start next to in Savanna. Shoot the hoop ten times for the achievement. There are other basketball hoops in other zones that also work.

There are five carnivorous plants in Savanna, circled on the map in the image below. Simply run up to each one and hit them once.

Savanna's secret zone is a hole that can be jumped down once all eggs are collected. There are five rooms with multiple tunnels; only one leads to the next room, while the others lead you back into the same room you were in. From left-to-right, choose:

the 3rd tunnel in the first room;
the 4th tunnel in the second room;
the 1st tunnel in the third room (one walnut is in this room);
and the 2nd tunnel in the fourth room.
The fifth room has two walnuts and the "They stole the egg!" Gigantopedia page. Use Rocky to bust the boulder on the right and leave the cave for the achievement.

The Jungle's secret zone is a cave, unlocked once all eggs in the zone are collected. Inside it is a structure with several slides; ride each one to get the achievement.

The "ROAAAAAR!" Gigantopedia page and a couple seed pots are in this cave.

Use all fun objects; unfortunately I don't remember how I got this achievement, but I acquired it on my first playthrough by the Desert zone, before I went out of my way to get any achievements. If I had to guess, it is awarded for using objects like basketball hoops, slides, and swings, but certainly not all of them, just one of each type. This achievement can probably be obtained just by playing normally by the end of the third zone; making a minor effort to interact with most objects you come across should guarantee it.

The "critters" referred to in this achievement are the scorpions encountered in the Desert; hit them ten times. You don't need to stun ten different scorpions, stunning the same one ten times over will work.

The oasis is the Desert's secret zone, unlocked once all eggs are collected. Enter it and walk up to Trey, a blue triceratops, and speak with him to get the achievement.

Sail 200 meters in one of the canoes in Lake. If you plan on completing Lake 100% you will probably get this achievement without trying, but if not, simply sail around for a minute or two and you'll get it.

The island is the Lake's secret zone, unlocked once Termie, the plesiosaur, is scared away by constructing the fake Giganto using five pieces of building material. Termie will spit out the fifth piece once all eggs are collected. Once on the island, pick up all of the various balls laying around and shoot the basketball hoop with every one to get the achievement.

A bit of a shame to wreck such adorable snow-dinos, but there are 5 snow-dinos in Glacier; see their locations in the image below.

For To the Rescue there are four rock cranes to activate in Volcano, shown on the map, and are required to complete the zone.

After stopping the lava, approaching Giganto will trigger the final "race" in which you control Giganto in a quick-time event using the WASD keys - which can catch you off-guard if you're not expecting it. Complete it to get The End.