This April first, have you considered sending  your loved ones a piece of old poop in the mail?

Sure, most people wouldn’t be too  thrilled to receive a gift like that. But if you happen to know any paleontologists,   then a petrified poop could be one  of the best gifts you could give.

Because while traditional fossils  - shells, bones, teeth - can tell   us what ancient animals were like when they  died, their poop can tell us how they lived. [♪ INTRO] I should make it clear right from  the beginning that I am in no way   advocating the giving of fresh poop to anyone. I’m talking about coprolites, which is  the technical term for a fossilized poop. Of course, lots of rocks can look like poop.

Brown, smooth and rounded, kinda grainy,   maybe even with the occasional chunk  of something unidentifiable in them… These can all be features of  a common beach pebble, too. But that doesn’t mean that every  pebble on the beach is a poop. You’re far more likely to pick up a fresh  specimen than a fossilized one on your vacation.

So instead, scientists look for a bunch  of other things to confirm their treasure. Some coprolite hallmarks are the same sort  of thing you’d expect to see in fresher poop. An outer patterning of contraction  marks and gas bubbles, and an internal   structure with pieces of undigested  debris can be the telltale signs.

But one big distinguishing feature is the  presence of calcium phosphate inside the rock,   which can come from the digestion  of bones and animal proteins. While lab analysis can confirm this,  palaeontologists have even been known to   identify coprolites in the  field by using the ‘lick test’. Yes, I said, “lick test.” Apparently, if you press your tongue against a  rock and it sticks a little as you pull it away,   then chances are you’ve just licked  a fossil bone or a fossil poop.

Lovely! It might sound gross, but  coprolites are really more   rock than poop by the time they reach your tongue. In order for them to be preserved, fossilization  needs to start pretty quickly after being   … deposited … so that they’re not recycled  by hungry bacteria and other decomposers.

Under the right conditions, the  soft, squishy stuff of poop becomes   completely replaced by hard, durable  minerals like that calcium phosphate. Carnivores eat all parts of their prey, and make  poop that is already full of bone debris, making   them more likely to be replaced and preserved,  compared to the poop of their herbivorous cousins. But calcium phosphate can come from other sources,   and poops from many different creatures  have been found in the fossil record.

The challenge then, is to figure out  exactly who pooped your fossil poop,   which is not always an easy task. Occasionally, chemical analysis  can find traces of DNA or other   biological molecules that can pin down the source,   but since everything is typically replaced with  new minerals, this kind of certainty is rare. Instead, scientists look at a whole bunch  of things to pin down the pooper - like   the age of the surrounding rocks and  the presence of other animal fossils.

Then, the coprolite’s size and  shape can be compared with modern   examples and the relevant anatomy of the culprit. In this way, paleontologists have identified  coprolites from trilobites, sharks,   crocodiles, dinosaurs, hyenas, and many more. So once you’ve confirmed your poop-shaped rock  really is poop, and you have a decent idea of who   it belonged to, then you can get to the good  stuff: figuring out how your creature lived.

The first insight is the most obvious one. Coprolites can tell you what an animal ate. Back in 1998, researchers looked in  detail at a Cretaceous coprolite so   large that it could only have been produced  by a huge animal, like Tyrannosaurus rex.

Inside the fossil, which is about as long  as a forearm and nearly twice as thick,   the researchers found bone fragments. And not just a few - up to half  of the entire coprolite was made   up of pieces of bone that had been  fractured before being swallowed. This study, when it came out, turned what we  thought we knew about T rex’s feeding on its head.

Based on how modern predatory reptiles feed,  scientists thought that these carnivorous   giants would have focused mainly  on tearing flesh off their victims. But the coprolite showed that they were  capable of making bigger chomps, ripping   flesh and crushing the bone of, for example, a  triceratops frill, in one devastating movement. This revelation helped to change our view of  T rex’s behaviour and its physical strength.

Previously, researchers had doubted that  the dino’s teeth were up to the task,   but this king-sized poop showed  definitively that they were. Not every dinosaur coprolite tells of  devastating predatory strength, though. Another study of Cretaceous coprolites, this time  thought to be produced by herbivorous Titanosaurs,   surprised scientists with the  range of plants they contained.

These fossil poops had fragments of cycads,   related to the modern sago palm, as well  as conifers and grasses inside them. That last one was a real shocker   The problem seems to be that grass,  without any woody structure to preserve,   doesn’t leave much of a  trace in the fossil record. But finding it in these gentle giants’  poops shows that they were not only there,   but they were already being used as a food source  for millions of years before the dino’s demise.

Coprolites are very good at giving us  a glimpse – albeit a mashed, crushed,   and half-digested glimpse - of what  passed through an extinct animal’s gut. But they are also surprisingly good at showing   us what was still in there  when the poop was produced. If an animal has internal parasites, like  worms or single-celled amoebas, then these   parasites typically reproduce by releasing eggs  and protective cysts out with the animal’s poop.

And when that poop becomes fossilized,  the parasite eggs can be too. Coprolites provide evidence for some of the oldest  parasites found so far in the animal kingdom. Clusters of tiny tapeworm eggs, each around a  tenth of a millimeter in diameter, have been   identified in 270-million-year-old  shark poop from the Permian period.

And a sample of Triassic poop, which  researchers think was produced by   something like a crocodile, contains at  least five different types of parasite. The researchers think this unfortunate  animal probably got its parasites from   feeding on a range of other animals, like fish  and amphibians which had the parasites themselves. Findings like this not only give a complete  picture of an animal’s physiology, but they   can also help give information about  their population density and behaviour.

For example, scientists have studied the  numbers and types of eggs and cysts found   in ancient human poop, and in places they  routinely left their poop, like latrines. These show that among ancient  humans, the amount of parasitic   infections increased when they shifted  from nomadic to agricultural societies,   presumably as a result of more people  living together and sharing the same space. Not only that, but finding particular types   of parasites can give a clue  to how ancient humans lived.

For example, human coprolites from Peru and Chile,  dating to around 5,000 years ago, contain evidence   of tapeworms and flukes, which today are known to  be transmitted by eating raw or undercooked fish. Modern inhabitants of these countries can  still be infected with these parasites   from eating the traditional  Pacific coastal dish ceviche. The fossil parasites are seen by  researchers as evidence of this   traditional dish’s roots extending  far back into American prehistory.

So, coprolites can tell us  what an ancient animal ate,   but they can also give us a clue to  how efficiently their bodies worked. For instance, in the early 19th century,   spiral-shaped rock specimens were  thought to be the fossils of fir cones. But experimental work with modern fish  revealed that these snazzy spiral rocks   are actually produced inside the  intestines of fish like sharks,   making them a kind of internal coprolite:  a poop preserved before being pooped.

And in addition to being cool-looking, these  spiral intestine stones tell an important story. Because this kind of gut,  known as a ‘spiral valve’,   has evolved to have extra surface area  over which nutrients can be absorbed. They’re more efficient than  the traditional tubular style,   and a sign of a body and metabolism  suited to getting more out of every meal.

And remarkably, fossils of this kind  have been found in rocks dating all   the way back to the Ordovician,  around 450 million years ago. In contrast, dinosaur coprolites show that  these animals did things very differently. In Alberta, Canada, scientists picked  apart a perfectly preserved poop that   probably belonged to a carnivorous  tyrannosaurid from the late Cretaceous.

The internal texture was so finely  fossilized that the researchers   were able to find bundles of undigested  muscle fibers from the animal’s last meal. Not only that, but a Triassic coprolite  from Poland, thought to belong to a   reptilian dinosaur relative, was scanned  with X-rays to reveal whole beetles,   some of them with their legs  and antennae still intact. The specimen was so perfect that  researchers were able to show   that the undigested beetles were a new  species, previously unknown to science.

Not only are these impressive  feats of preservation,   but they also say a lot about the  gut transit time for these animals. For structures as fine as beetle antennae to  survive through a dinosaur’s body in one piece,   then that journey must have  been really really quick. That suggests that these dinosaurs had fast  digestion and high energy requirements,   favoring quantity over quality  when it came to their meals.

Unlike modern crocodiles, for example,  which can sit and digest for days. So we’ve seen that coprolites can tell us about an  animal’s diet, its parasites, and its digestion. But there’s one more insight we  can get from these fossil poops,   and that’s the creature’s  role in the wider ecology.

For example, researchers studied  35 coprolites discovered in a cave   in New Zealand, dating between  6,400 and about 700 years ago. Using DNA analysis, they showed  that these coprolites belonged to   the now-extinct moa - a large flightless  bird that was endemic to New Zealand. In the fossil poops, they found evidence  of 67 separate species of plant,   including a number of intact, undigested seeds.

This not only suggests that these birds  played an important role in helping to   disperse plant seeds for reproduction, but  it also reveals the extent of that dispersal. The variety of plant species in their  poops suggested that they browsed widely   between surrounding forests and grasslands,   and may have roamed more than 600  meters just to reach certain plants. In this way, the cave coprolites are helping  to paint a picture of the moa as it lived in   its environment: it was a generalist herbivore  with a wide-ranging impact on the local ecology.

So whether you want to learn about an  animal’s diet, the shape of its intestine,   or how far it walked for food,  coprolites have you covered. And we have you covered if you're  a SciShow Rocks Box subscriber. This month, we’re sending everyone a coprolite  from the late Cretaceous of Madagascar.

If you’re interested in getting authentic  fossils and minerals like that in the mail,   visit Complexly.store/rocks to find out more. And do feel free to take my word for it,  rather than licking it to test for yourself. If you’re a SciShow Rocks Box subscriber,  you’re going to love the latest Crash Course.

It’s finally time for Crash Course Geology! The Earth we know is very different than  it was two billion years ago… and yet,   geologic rules and processes remain the same. By uncovering these constants,  we can reveal our planet’s past,   learn how to thrive in the present,  and prepare for the future.

In this 25 episode series, you’ll  learn the basic principles of geology   as they guide you on a tour of the  Earth’s past, present, and future. And you can watch it right now on  the Crash Course YouTube channel! [♪ OUTRO]