Humans aren’t the only creatures who share communal toilets — many mammals do this. In
fact, new research shows this behavior was an ancient evolutionary development.
Scientists have discovered a large, rhino-like reptile defecated in
“communal latrines” some 240 million years ago.
Image above: Artistic recreation of the ancient reptiles, dicynodonts, using their communal latrine. Courtesy of Emilio López Rolandi.
Communal
latrines, or defecation spots, are exactly what they sound like: Relatively
small areas where multiple individuals relieve themselves, sometimes at the
same time. Humans and housecats obviously defecate in communal latrines, but
studies show that a number of other mammals do, too, including meerkats,
lemurs,
spider
monkeys, and tiger
quolls (a kind of marsupial). The behavior is particularly common among
large herbivores, such as elephants,
horses
and rhinoceros.
Without
this behavior, people would likely have a major sanitation issue, especially
considering that there are now 7
billion of us on this planet. But why would animals bother to confine their
excrements to a small area?
https://gizmodo.com/what-does-a-world-of-7-billion-people-look-like-5855058
Turns
out, communal latrines have important biological functions. “In some
cases, the communal latrines define an area or territory,” says Martın
Hechenleitner, a paleontologist with CRILAR-CONICET
in Anillaco, Argentina. “In other cases, they prevent the re-infestation
of parasites.”
Despite
their usefulness, communal latrines have always appeared to be a mammalian
phenomenon. What’s more, these defecation spots are quite rare in the fossil
record. “It’s not easy to find these kinds of fossils,” Hechenleitner
tells io9. But recently, while studying the fossils in the outcrops of the
Chañares Formation in the La Rioja Province in northwestern Argentina, that’s
exactly what Hechenleitner and his colleagues found.
Uncovering the Toilets of the Ancients
The
eight communal latrines the researchers discovered were each 400 to 900 square
meters and 1.5 kilometers apart (they expect to find more latrines in the
future, as they’ve only surveyed 20 percent of the Triassic Chañares Formation
outcrops). These fields were loaded with fossilized
poo called coprolites — within the latrines, there were, on average,
67 coprolites per square meter, but in some areas the poo density reached 94 coprolites
per square meter. Given the amount of coprolites and their size variation, the
researchers believe the latrines were really communal, and used by many animals
of different ages.
https://gizmodo.com/tiny-remnants-of-fossilized-poop-tell-us-where-ancient-5963796
For
the most part, coprolites are easy to pick apart from other fossils. “They
have a particular structure and are really round, and usually have some cracks on
the surface,” Hechenleitner said. The coprolites the team found were
mostly ovoid or spheroidal in shape, but some were shaped like segmented
sausages and others looked like sausage coils. The researchers cut open some of
their samples to examine them under microscopes. “In the sections we found
many tiny fragments of vegetation,” Hechenleitner said, adding that this
further proved they were dealing with coprolites.
Within
the coprolites, the team found woody fragments, leaf fragments, fossil mosses
and fern-like spores. Importantly, CT scans of the fossils showed no evidence
of bone fragments, suggesting that the animals the poo belonged to were not
carnivores. But the Chañares Formation, which dates back to the Middle to Late
Triassic, holds a wealth of fossils of various ancient reptilian species, so the
researchers set out to determine who really used the communal latrines.
Some
of the coprolites were extremely large — up to 35 centimeters in diameter
— suggesting that they belonged to big herbivores. Using this information, the
team was able to rule out a number of different animals, such as Massetognathus, whose maximum skull
length is only 20.4 cm. Additionally, the high density of the coprolites and
the size of the communal latrines suggest that the coprolite producers were
very abundant.
With
these lines of evidence, the team figured that the latrines belonged to a
species of dicynodont, which is a group of four-legged, large-bodied,
mammal-like reptiles. Though they’re not sure yet, the researchers believe that Dinodontosaurus — the most
abundant dicynodont in their study area in the Chañares Formation — are
responsible for these fields of poo. These animals were among the largest
herbivores of the Triassic and could weigh up to 3,000 kg.
Though
dicynodonts have specialized mouths that would appear to allow for specific
movements necessary to chew vegetation, some researchers have previously
suggested that the animals may have been omnivores or even carnivores. But if dicynodonts
really did produce the coprolites in the latrines, it would mean that dicynodonts
were herbivores after all.
The
new discovery also indicates that the seemingly mammal-only behavior of
defecating in communal latrines developed before mammals first evolved. This
new find actually predates the previous fossil record of communal latrines by
220 million years. We may owe our sanitary practices to our reptile ancestors.
The
researchers now plan to study the fossils further and potentially discover why
the dicynodonts had communal latrines. “It’s a behavior tied to a particular
function, and we need to now explain what that function is,” Hechenleitner
said. By analyzing the contents of the coprolites, they also hope to learn more
about the animal’s environment. “These feces are very important to
understanding which plants covered the area 240 million years ago.”
Check out the study in Scientific Reports.
Inset image via Lucas E. Fiorelli/CRILAR – CONICET.
