What's in some poop from 6 million years ago?

In 2018, several piles of poop fossils were discovered in California, USA. They are from the late Miocene epoch, 6.4 to 5.3 million years ago, and the owner is an extinct canid. Although the name is not very pleasant, coprolite can provide a lot of information about ancient animals. For example, this pile of dog poop from millions of years ago allows us to discover the unusual eating habits of these canids.

This extinct canid, scientifically known as Borophagus parvus, belongs to the subfamily Caninae. Based on tooth fossils, they weighed about 24 kilograms, between the size of today's wolves and jackals. Unlike today's dogs, the Caninae subfamily loved to eat bones - but they didn't seem to be very good at eating bones .

Through a few pieces of feces, scientists speculated on the life scenes of Borophagus parvus in the past: they could gnaw bones and may have lived in groups｜Mauricio Antón

Dogs that are good at eating bones are not common

The coprolites found in California contain 14 dung balls in total. Scientists have performed CT scans on them to examine the broken bones - most of them are broken and difficult to identify; the largest of them is a rib fragment more than 3 cm long , which may come from an animal as large as a black-tailed deer (which can weigh more than 100 kg).

A coprolite and its bone fragments (indicated by different colors in D, and one of the bone fragments is magnified in E) | Reference [1]

This diet is quite different from that of modern canids. Generally speaking, modern canids are not adapted to eating bones . They will gnaw the meat on the bones, or chew smaller bones and swallow them; but they are not adapted to eating large bones, and the sharp bone fragments that are not chewed may pierce the stomach (so it is very dangerous to feed dogs with whole chicken bones).

There are only three species of hyenas among the living carnivores that have evolved to eat bones. Mr. Lu Xun gave an accurate description of the hyena's diet in "Diary of a Madman":

...There is a creature called "Hai Yina" (the transliteration of the English word hyena), which has very ugly eyes and appearance; it often eats dead meat, and even very large bones, which it chews into pieces and swallows down its stomach. It's scary to think about it.

Spotted hyena (Crocuta crocuta), the most bone-eating animal in the world｜sharpphotography.co.uk

Solid bones contain about 30% organic matter (mainly collagen), and the hollow part contains nutritious bone marrow - of course, both of which are not easy to eat. Hyenas, who are good at eating bones, have developed many abilities to adapt to this in the history of evolution : they have extremely strong molars and premolars, and the enamel crystals on the surface of the teeth are arranged in a zigzag shape, making them stronger; hyenas have wide cheekbones, and a bone bulge on the skull can attach huge bite muscles. The mouth is shorter than that of a wolf, which is more labor-saving from the principle of leverage; the cavity in the middle of the hyena's skull is large, which can disperse the pressure of biting, which also makes its forehead look like an "adze head".

In addition, because hyenas chew bones every day, the tips of their molars are severely worn, which is also evidence for us to judge that animals eat bones.

The extinct family of canids also had many adaptations for eating bones : strong teeth, zigzag tooth enamel structure, large skull muscle attachment area, short and thick mouth, and forehead ridge to disperse the pressure of biting. The wear of its molar tips is also obvious.

Skull of a canine (B. secundus) | References [1]

Not a professional bone eater?

Although the skull of the Destroyer Canis lupus shows that it was adapted to eating bones, its feces provide evidence from the other side - the Destroyer Canis lupus does not seem to be as professional as hyenas in eating bones.

The most bone-eating hyena is the spotted hyena, whose feces contain a lot of white powder, which is calcium salts produced by bone digestion. However, the feces of the hyena are full of bone fragments, which is more like the spotted hyena's two relatives, the brown hyena and the striped hyena. They do not digest bones as thoroughly , and although their feces are also white, they are not as white as the spotted hyena, which looks like a pile of golf balls.

Spotted hyena feces, white as golf balls | Danielle Free

As for why the Demoiselles are not as professional as the spotted hyenas in eating bones, we don't have an answer yet.

Canids evolved earlier than hyenas to adapt to eating bones (although none of them survive to this day), but they have never reached the level of hyenas in terms of bone eating specialization . Now, the grinding ability of hyena teeth has been highly degraded, and the premolars have been enlarged and specialized into special tools for biting bones.

Predator or scavenger?

Another interesting piece of information comes from the shape of the fecal ball . The feces are certainly not in the shape of ice cream like in "Arale", but a series of particles - pointed at both ends and close to beads in the middle.

At this time, paleontologists used their strange detective skills: they found that among these 14 dung balls, 5 were probably the first ones to come out , because their shapes were all big at one end and small at the other; another one was pointed at the end, and the order of the others was unknown.

That is to say, these 14 dung balls are not from the same pile of feces, but from at least five piles . This may be the "toilet" of social animals, where everyone defecates together and uses the smell to establish a border line - wolves and hyenas still do this today. This also indirectly shows that this extinct dog should have lived in a group .

These 14 coprolites did not come from the same poop | Natural History Museum of Los Angeles County

Another question is: Is this dog a scavenger or a predator? As the only three animals in existence that specialize in eating bones, brown hyenas and striped hyenas basically eat dead bodies, while spotted hyenas hunt 80% of their food.

Previous studies have speculated that some species of the subfamily of the dreaded dog may be hunters. They lack the sharp claws of cats, so they may rely on teamwork to take down large prey - which also happens to be consistent with the large rib fragments in the dreaded dog feces (of course, it cannot be ruled out that they just picked up the carcass of a large animal). Another indirect evidence is that the fossils of Borophagus parvus are quite numerous and widely distributed in North America. As a predator, the spotted hyena is also numerous and widely distributed, far more than its scavenging relatives - the habit of predation has helped its family prosper, and perhaps also helped the dreaded dog to reproduce and grow .

A 1902 depiction of a terrifying dog | Charles R. Knight

The last members of the subfamily of Chasmaporthetes died out 2 million years ago, and since then a small number of Chasmaporthetes (an extinct hyena) have appeared in North America, but the number of fossils is very small. After the disappearance of Chasmaporthetes, this ecological niche of eating bones has basically been vacant.

No matter how much you may have looked down on the "sea urchins", large animals that chew large bones play an important role in the ecological environment . They bypass small scavengers and microorganisms and accelerate the cycle of animal carcasses into nature. Now that there are no canines, we still have a limited understanding of what changes have taken place in North America.

References

[1] Xiaoming Wang, Stuart C White, Mairin Balisi, Jacob Biewer, Julia Sankey, Dennis Garber, Z Jack Tseng, (2018). First bone-cracking dog coprolites provide new insight into bone consumption in Borophagus and their unique ecological niche. eLife7:e34773. https://doi.org/10.7554/eLife.34773

Author: Red Queen

Editor: Mai Mai

Image credit: Danielle Free

This article comes from GuokrNature (ID: GuokrNature)

If you need to reprint, please contact sns@guokr.com

Welcome to forward to your circle of friends