Product Code Database
Entelodontidae is an Extinction family of pig-like artiodactyls (even-toed Ungulate) which inhabited the Northern Hemisphere (Asia, Europe, and North America) from the late Eocene to the early Miocene Epoch, about 38-19 million years ago. Their large heads, low snouts, narrow gait, and proposed Omnivore diet inspires comparisons to Suidae (true pigs) and Tayassuid (peccaries), and historically they have been considered closely related to these families purely on a morphological basis. However, studies which combine morphological and molecular (genetic) data on artiodactyls instead suggest that entelodonts are cetancodontamorphs, more closely related to Hippopotamus and Cetacea through their resemblance to Pakicetus, than to hyotheriinae like Kubanochoerus and other ungulates.
The snout was narrow and elongated, especially in later species. The cranium was robust, with strong zygomatic and Postorbital bar arches forming the rim of voluminous Temporal fossa, separated by a sharp sagittal crest. However, the rear of the skull was also much shorter than the snout, and the braincase was relatively small. Most of the braincase contributed to large paranasal sinuses and Olfactory bulb at the front, while the cerebrum was underdeveloped. Large olfactory bulbs are likely indicative of a good sense of smell. Moreover, the orbits (eye sockets) are oriented further forwards than in most artiodactyls, suggesting that entelodonts had binocular vision. Compared to other artiodactyls, the jaw was slender at the rear, with a short, triangular coronoid process which is shifted forwards. The mandibular condyle (jaw joint) is set back and below the level of the tooth row. The mandibular symphysis (chin) was fused, and the Pterygoid bone along the middle of the roof of the mouth were connected by a strong Synarthrosis.
The incisors are closely packed but do not develop a distinct straight chopping surface. They range from chisel-shaped in some entelodonts ( Archaeotherium) to massive and rounded in others ( Daeodon). The canines have thick Tooth enamel and are circular in cross section, unlike most artiodactyls. In older individuals, the tip of the upper canine often heavily worn or even chipped off. Premolars are triangular when seen from the side, with a large and conical main cusp. They are elongated from front-to-back and widely-spaced, taking up a large portion of the tooth row. The molar teeth are bunodont, with very low and rounded cusps rather than shearing surfaces. Bunodont teeth are common in other omnivorous mammals, including pigs, bears, and humans. The upper molars have up to six cusps and a low crest (a precingulum) on the front edge of the crown. In all but the earliest entelodonts, the lower molars have only four main cusps. The front two cusps (the metaconid and protoconid) may be connected by a horizontal crest and are slightly larger than the rear two cusps.
Though the low jaw joint provided more room for the temporalis muscle, it also posed a problem for the Masseter muscle muscle. The masseter, which extends from the zygomatic arch to the lower rear corner of the mandible, is a major component of the chewing apparatus in herbivorous artiodactyls. While other artiodactyls added torque to the muscle by raising the jaw joint, entelodonts instead expanded the rear of the jaw downwards, as a deep, curved flange. Moreover, the characteristic jugal flanges of entelodonts were covered with muscle scars on the inside, likely attachment points to strengthen the masseter. Only a few modern mammals have overdeveloped projections on the zygomatic arch, including Xenarthra, Kangaroo, and certain Rodent. Like entelodonts, these mammals use their equivalent projections as a means of providing extra space for the attachment of the masseter muscle, and develop robust cranial bars to resist the resulting forces on the skull. The pterygoideus muscle, which follows a similar path and function to the masseter, also benefited from the deep flange at the back of the jaw.
The function of the mandibular tubercles is not certain, but they may also be related to jaw musculature. They are only clearly correlated with the size of the individual, though a few taxa ( Brachyhyops and Cypretherium) can be diagnosed by the absence of a specific pair of mandibular tubercles. Generally, the posterior (rear) mandibular tubercles develop later in life than the anterior (front) pair, and none of the tubercles stop growing as the animal develops. The use of the anterior tubercles is unclear; one speculative idea suggests that they served as an attachment point for strong lip muscles in particularly herbivorous entelodonts. The posterior tubercles may provide a link to the Digastric muscle muscle which helps to open the jaws. Hippos, which have a particularly complex and well-developed digastricus, occasionally develop a tubercle to support the digastricus in an equivalent area on the jaw.
The jaw joint of entelodonts was likely more strongly connected than the loose jaws of most other artiodactyls. The mandibular condyle was convex and inserted into a strongly concave facet (Mandibular fossa) on the zygomatic arch, which would have restricted front-to-back (propalinal) jaw movement. Nevertheless, the structure of the mandibular condyle itself allowed for a wide range of movement, and the laterally bowed zygomatic arch provided some room for side-to-side (transverse) movement driven by the masseter and pterygoideus. The low, unconstrained jaw joint and short coronoid process may correspond to long muscle fibers. This points to a hinge-like jaw suspension with a very wide gape, similar to some modern carnivorans such as Felidae (cats). Based on the shape of the mandibular condyle, the maximum gape possible based on the underlying bones (though not necessarily the widest gape possible in life) was about 109 degrees in Archaeotherium.
Wear facets on entelodont teeth support three-part food processing. First, the incisors and canines bite in a strong orthal motion, grabbing and puncturing food. Then, the food is transferred back to the premolars, which breaks apart tough parts of the food with similar movements. Finally, the food is crushed and ground up by the molars, using a combination of orthal and transverse grinding. This same basic process is seen in modern pigs and peccaries, which have similar dentition. Individuals may have preferred one side of the jaw for chewing, as premolars and molars often show an asymmetrical distribution of wear between the left and right sides of the mouth.
The same adaptations useful for processing tough plant material would be equally useful for carrion and bones, which could have been major components of the diet for some entelodonts. Unlike pigs, the youngest juvenile entelodonts had a full set of 32 deciduous teeth. The teeth were sharp, slender, and semi-serrated, less suitable for crushing tough food compared to adult entelodonts.
In many entelodonts, the canine teeth acquire rounded wear surfaces at their tips, indicating regular use on hard material such as bones. Similar patterns of canine wear are observed in modern cats, which rely on strong bites administered through their canine teeth when killing prey. In some species the bases of the canines are scoured by smooth grooves, a trait consistent with abrasions from sediment-covered plant material such as roots. These grooves instead could have been produced by stripping long, fibrous vegetation, such as water-rich grape vines. Daeodon is known to have had a distinctive type of "piecrust" tooth wear at the tips of the premolars, with a flat Dentin surface surrounded by chipped Tooth enamel. This has also been observed in living Hyena. Few contemporary mammals approached entelodonts in the extent of adaptations consistent with scavenging. Fossils with large scrapes and puncture marks are found throughout entelodont-bearing sites in the American Great Plains, including a skull of Merycoidodon with an embedded incisor of the entelodont Archaeotherium.
Entelodonts may have engaged in active predation, though the extent of this behavior is debated. Several species of modern pigs occasionally engage in predation, and even traditional herbivores like camels show dental wear consistent with scavenging. If they did engage in predation, entelodonts would not have been alone: many other contemporary mammals filled apex predator niches, including cat-like saber-toothed nimravidae, amphicyonidae ("bear-dogs"), and Hyaenodontidae creodonta. One of the most apparent examples of circumstantial evidence for predation is a fossil found in the White River Formation of Wyoming, representing a cache of partial skeletons and other remains of the early camelid Poebrotherium. The carcasses were covered with large punctures on the skull, neck, and the transition from the thoracic to Lumbar vertebrae Vertebra, which have been attributed to predation and scavenging by Archaeotherium. Entelodon
Following the confusion between Entelodon and Elotherium, entelodont fossils continued to be discovered in Europe. Large entelodonts were also described from North America starting in 1850, though most new genera were eventually lumped into Archaeotherium and Daeodon. By the beginning of the 20th century, entelodont skeletal anatomy was well-understood from the quantity of fossils discovered by that point. In 1909, a massive complete skeleton of "Dinohyus" hollandi (= Daeodon), CM 1594, was described and put on display at the Carnegie Museum of Natural History. As the 20th century continued, Asian entelodonts were discovered ( Eoentelodon, Paraentelodon), as well as some of the earliest known members of the family ( Eoentelodon, Brachyhyops).
Some authors considered entelodonts to be too "primitive" for comparison to modern bunodont artiodactyls. In these studies, entelodonts were placed in "Palaeodonta", a group shared with various other extinct families. Choeropotamidae, Cebochoeridae, and Helohyidae were frequently associated with entelodonts, sometimes even as potential ancestors. Later, the superfamily Entelodontoidea was named to encompass Entelodontidae and their supposed closest extinct relatives. In modern studies, Entelodontidae is generally considered the only family within Entelodontoidea.
Many studies argued that entelodonts had close relations to living pigs, peccaries, and hippos. Various groups have been developed and named in reference to a pig-like anatomy, with names such as Suina (Gray, 1868) and Suiformes (Jaeckel, 1911) being emplaced in varying contexts. A restricted definition of Suina is still in use, as a major artiodactyl suborder encompassing Tayassuidae (peccaries) and Suidae (pigs). Early Cladistics Phylogenetics of artiodactyls placed Entelodontidae as the sister taxon to a Tayassuidae + Suidae clade. This seemed to justify the frequent morphological comparisons between entelodonts and pigs.
Many former genera of entelodonts have been synonymized. For example, some authors have synonymized Dinohyus with Daeodon shoshonensis, a species described from fragmentary material by Cope.
Entelodonts appear in the third episode of the popular BBC documentary Walking with Beasts, where, in the program, the narrator always refers to the creatures as "entelodonts" rather than a more specific genus, such as Entelodon. The same creatures appear in another BBC production, the 2001 remake of The Lost World.
Entelodonts were also the main focus of episode 4 of National Geographic Channel's show Prehistoric Predators in an episode titled "Killer Pig". The episode featured a number of claims unproven or disproven by science, such as Archaeotherium (identified as "entelodont") being the top predator of the American Badlands, and evolving directly into the even larger Daeodon (called "Dinohyus" in the episode).
|
|
