Dinosaur egg

The Dinosaur Egg is a stand-alone fossil that can be donated to the museum in all Animal Crossing games prior, where it is absent.

In Animal Crossing
"Hoo, I say! Hoo upon hoo! A fossilized egg! Excellent! I must apologize for that atrocious pun. So sorry. I just got carried away in my eggcitement, eh wot? Because this is a grade-A specimen. Hoo hoo hoo! Now, I hate to admit this, but I cannot identify the species of dinosaur that produced this particular egg. I can envision its hatching, though, and from the shards, a new life slowly emerging, a miracle of flesh and bone! Hoo, the wonder of it all! The drama. The spectacle! The ebb and flow! The grass and grit! Life, I say! Life! Hoo, mercy! Hoo my, indeed! I must apologize profusely. I...I was lost in the moment. My beak flaps on its own!"

In
"Utterly amazing, this is! What a perfect specimen! Figuring out what kind of egg this is might seem easy, but it's actually not. In fact, I must admit that I have no idea how to go about it, eh wot? Still, that very mystery is what's so fascinating about a dinosaur egg! Ah! Hoo. I'm awfully sorry. Inexplicable mysteries tend to set my beak blabbing." —Blathers

The dinosaur track is displayed on the right side of the second fossil room, on the top left pedestal.

In City Folk
"Hoo, I say! Hoo upon hoo! A fossilized egg! Eggcellent! I must apologize for that atrocious pun. So sorry. I just got carried away in my eggcitement, eh wot? Because this is a grade-A specimen. Hoo hoo hoo! Now, I hate to admit this, but I cannot identify the species of dinosaur that produced this particular egg. I can envision its hatching, though, and from the shards, a new life slowly emerging, a miracle of flesh and bone! Hoo, the wonder of it all! The drama. The spectacle! The ebb and flow! The grass and grit! Life, I say! Life! Hoo, mercy! Hoomy, indeed! I must apologize profusely. I...I was lost in the moment. My beak flaps on its own!" —Blathers

In New Leaf
"Dinosaur eggs vary in size depending on the species, but larger ones can reach about a foot in length. If the egg was fossilized when it was just about to hatch, sometimes intact bones can be found inside. However, it is generally rather difficult to determine the exact species a fossilized egg belongs to."