Penguins Against Trump

Hey, geologist here, otherwise known as pick boy! I assume you are referring to a non-fossilized Penguin, which is simply an alive or recently deceased Penguin that has not yet been lithified in a slow process where the molecules of its corpse, somehow arrested from the far more common pathways of rotting away, are slowly replaced by SiO2, silica dioxide, sand/quartz whatever you want to call it in a facsimile structure that records a process of a corpse being smushed and maybe cooked for a very long time.

Think about it, the way Geologists originally created a consistent conceptual framework they could identify sequences of different time periods, without the ability to do any fancy scientific dating with advanced instruments (late 1800s, early 1900s) was by noticing and paying attention to the corpses of animals that happened to fall into a pile of anoxic mud, and were buried and buried and buried and buried. If you look at enough dead stuff stuck in rock, you begin to see patterns and those patterns became the basis for the structuring of the Geologic Record that we now use today. Those clever assholes were able to do this long before we could quantitatively define how big these spans of time were or prove with some kind of measurement with a device that something was much older than something else that a weak little Physicist would be helpless without.

See.. the really fiddly problem about poking around looking at dead things that fell into muck is that at the same time in history the muck was different everywhere you went... right? Same as now, so then how do you group time periods together if there isn't necessarily consistent environments and thus maddeningly the smushed piles of dead creatures are going to be potentially different even if the smushed corpse piles are from THE SAME time in history?

The solution Geologists created was the concept of an Index Fossil, which is the extremely overconfident teenager of the evolutionary history world. Index Fossils are the fossilized remains of a species that did three things:

1. It had LOTSSSS of sex and was very successful at getting into everybody's business and causing a mess, this species spread all over the planet and into lots of different environments, it was the opposite of an old curmudgeonly grandpa who wanted to stick to their little routine and life.
2. Utterly committed to its "party hard" strategy of going all in, this species was initially very successful, procreated all over the world, and then crucially totally flamed out in a totally catastrophic fashion, thus appearing and disappearing abruptly in the Geologic Record. Before you ask, no Humans have not yet been updated to be considered Index Fossils in the Geologic Record but I suspect we will, we are superb Index Fossils for a future curious Alien Geologist to discover!
3. When this species died, it had to leave something cool behind, like a shell or talons or something extreme that people would later find. Maybe some cool teeth or preppy pink yacht club shorts.

Nature is Poetry, Geologists first got a handle on what, how much and how big when thinking about Earth's history from studying the teenage obnoxious rich kid Chads of evolution.

TL;DR A Penguin is a type of sedimentary rock that hasn't had its molecular structure replaced in the process of water forming the fossil replacement structure of chert yet. A "penguin rock" as we might refer to it is really more like a cucumber to a pickle, if a pickle is a rock.