Mylohyus was a Pleistocene peccary of North America, recognised by its elongated facial region and relatively rounded cheek teeth. Fossils include a notable skeleton from Friesenhahn Cave in Texas, but much of the record consists of separate jaws, teeth and limb bones. The names M. fossilis and M. nasutus are both used, and their status as separate species is debated. Dental comparisons suggest that Mylohyus browsed more than the open-country peccary Platygonus, though the exact menu is not preserved. It appears in the ice-age animal catalogue as a North American mammal whose cave record needs careful interpretation.
Quick facts
| Scientific name | Mylohyus Cope, 1869 |
|---|---|
| Often discussed forms | M. fossilis and M. nasutus |
| Group | Tayassuidae, the New World peccaries |
| Age | Pliocene to Late Pleistocene |
| Range | North America |
| Characteristic anatomy | Long facial region and rounded cheek teeth |
| Food evidence | Dental form and woodland associations |
| Open question | How many Pleistocene species should be recognised |
What can the fossils tell us?
Skulls and jaws show a facial region extending well ahead of the orbits. The upper canines point down, unlike the upward-curving tusks of true pigs. These features distinguish a peccary and help separate Mylohyus from other North American tayassuids.
The cheek teeth are lower and have rounder cusps than those of Platygonus compressus. That contrast has been used to infer greater browsing on leaves and shrubs. Tooth shape is a dietary proxy, not a preserved list of plants or a guarantee that every individual ate the same foods.
A long-nosed peccary skeleton from Friesenhahn Cave in Texas is an important museum specimen. Other cave assemblages contain only a few Mylohyus remains among many flat-headed peccaries. Cave use, predator accumulation and long-term deposition can all shape the sample; a cave assemblage is not automatically a herd census.
M. fossilis and M. nasutus have both been used for Pleistocene long-nosed peccaries. Differences in teeth and geography have been treated as species-level variation by some authors and as one variable lineage by others. The disagreement should remain visible until a revision supports a firmer boundary.
A peccary, not a true pig
Mylohyus belongs to Tayassuidae, the peccary family native to the Americas. Peccaries are relatives of Old World pigs, but they have a separate evolutionary history. Their upper canines point downward, while those of true pigs tend to curve upward. They also have less complex cheek teeth and reduced outer toes. Those details are visible in skeletons and jaws and help identify isolated fossils.
Edward Drinker Cope established Mylohyus in 1869. Earlier material had been described under other names, and later authors placed several forms in the genus. The history is typical of a fossil mammal first known from fragments: additional skulls and skeletons allow old diagnoses to be tested against a wider range of anatomy.
The long face and feeding teeth
The muzzle is longer than in the flat-headed peccary Platygonus compressus, giving the genus its familiar common name. The cheek teeth have more rounded cusps and are less suited to grinding coarse, gritty grasses. This pattern fits a browser taking leaves and shoots from woodland plants. It does not rule out seasonal or incidental foods that leave no unique dental signature.
Comparisons between teeth can reconstruct a broad feeding niche more confidently than a precise diet. No stomach contents establish a list of shrubs. An image of the animal reaching into foliage is an ecological interpretation based on the teeth and associated environments, not a preserved action.
Size and movement
Late Pleistocene individuals stood roughly three quarters of a metre at the shoulder. Published mass estimates cluster around 50 kilograms, with some reaching about 68 kilograms depending on the specimen and scaling method. These estimates are not direct measurements and may combine different ages, sexes or named forms.
The limb bones are relatively long and slender for a peccary. They are consistent with a capable terrestrial animal moving through woodland and along its edges. They do not establish high speed, long-distance migration or a particular gait. Joint surfaces constrain possible movement; they do not record an animal’s daily routine.
What cave deposits tell us
Friesenhahn Cave in Texas yielded an important long-nosed peccary skeleton now displayed in a museum collection. At other sites, Mylohyus remains are sparse compared with the numerous flat-headed peccaries found in some caves. This contrast has encouraged the idea that the long-nosed form was solitary or less likely to use caves.
That conclusion remains indirect. Cave deposits can form through repeated visits, carnivore activity, water transport and long periods of accumulation. At Guy Wilson Cave in Tennessee, two individuals were identified from teeth in a deposit where predator activity also affected the assemblage. The bones provide evidence about the site’s formation as well as the animal, and those processes must be separated before behaviour is inferred.
One species or more?
M. fossilis and M. nasutus are the most familiar Pleistocene names. Authors have used dental differences and geographic patterns to distinguish them, while others consider the variation consistent with one widespread species. Some datasets include both forms in overlapping regions, complicating a simple east–west division.
Until the boundaries are resolved, a profile of the genus should not treat one name as unquestionably valid or assume that every fossil belongs to it. A taxonomic review needs measurements from comparable teeth and skull regions, plus attention to age and individual variation. New fossils can refine the conclusion without changing what the current specimens physically preserve.
Extinction and limits of the record
The genus disappeared near the end of the Pleistocene, alongside many other large North American mammals. Climate and vegetation changed, and people were present in parts of the continent. The available record does not isolate one cause of extinction for Mylohyus. Its patchy distribution also means absence from a site is not proof that the animal never lived in the region.
Skulls, teeth and limb bones establish the animal’s anatomy. Diet and locomotion are inferred from those structures and from associated sediments. Solitary behaviour, exact coat pattern and a fixed extinction cause are not directly preserved. The evidence is strongest when each claim stays attached to the kind of fossil record that supports it.
Evidence, inference and reconstruction
| Level | What belongs here |
|---|---|
| Direct evidence | Long-faced skulls, rounded teeth, limb bones and cave specimens |
| Strong inference | A terrestrial peccary that browsed more than Platygonus |
| Uncertain | Species limits and social behaviour |
| Reconstruction | Coat, colour and a specific browsing scene |
Frequently asked questions
Was Mylohyus a pig?
It was a peccary in the New World family Tayassuidae, related to but distinct from true pigs in Suidae.
What made Mylohyus long-nosed?
Its skull had an elongated facial region. The upper canines pointed downward, as in other peccaries.
Did Mylohyus live alone?
Sparse cave finds compared with Platygonus have led to a solitary-life hypothesis, but cave accumulation and preservation can bias the record.
Are Mylohyus fossilis and M. nasutus separate species?
Both names appear in the literature. Their differences may indicate separate species or variation within one lineage, and the boundary remains debated.