Dinosaur track

The Dinosaur Track is a stand-alone fossil that can be donated to the museum in all games to date.

In Animal Crossing
"Hoo, I say! Woo hoo! A fossilized footprint. Looks like some paleontology is afoot! Hoo hoo hoo! But truly, this is quite an earth-shaking find! I've never seen a specimen that can match it in beauty. The distinct three-toed foot tells us that this is the print of a theropod from... perhaps the Jurassic period, eh wot? It's impossible to discern anything more specific, but speculation is free, and a vital part of paleontology. Imagine a terrible carnivore stalking its prey... Its great weight pressing down into the earth... and... voila! History! Hoo, aren't I the blatherer! I beg your pardon, please! I do hope I didn't put you into a comatose state!" —Blathers

In
"Hoo, I must applaud this find! The fossil's condition simply could not be better! Based on the shape, I can only suspect this is the footprint of the T-rex! Unlike with bones, we can see the foot's shape, size, texture, and more! Why, we can even deduce how fast it ran! Hardly just any old footprint, eh wot? Hoo! I'm frightfully sorry! The thought of such mighty feet agitates me to no end!" —Blathers

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

In
"Why, I'd say this was the footprint of the mighty T.Rex! But don't just scoff as if this is any old footprint! Morso than even bones, dinosaur tracks provide us with a plethora of interesting information. Hoo, Yes, for example, they tell about the creature's skin locomotion speed, wot! HOO! I...beg your pardon! I was so enthralled, I...I spouted hot air like a boiling teapot, eh wot?"

In
"Unlike other fossils, fossilized foot-prints give us a glimpse of how the creature in question actually lived. Thanks to modern science, we can determine quite a lot about the particular gaits of some creatures. This includes how they supported their weight, their posture when walking, and even walking speed."

In
"Dinosaur tracks are fossilized footprints left on the bottom of the sea or on soft earth. From these fossils, we can deduce the creature's territory range as well as its relationship with its herd... It has even become possible to work out the creature's size, distinctive gait, and, shockingly, walking speed! These trace fossils are like social-media feeds, enabling us to follow the daily lives of the dinosaurs!"

Further information
Using just the image of the track to try and match it with the dinosaur it belonged to is almost impossible. However, it appears to be something with webbed feet, such as a spinosaurus.