Helohyidae were a group of
artiodactyl
The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poste ...
mammals.
They were most prominent in the mid-to-upper
Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
(~50 to 39 million years ago).
Description
Helohyidae share vague similarities to present-day
pigs, though were slimmer in build. They possessed prominent
canine
Canine may refer to:
Zoology and anatomy
* a dog-like Canid animal in the subfamily Caninae
** '' Canis'', a genus including dogs, wolves, coyotes, and jackals
** Dog, the domestic dog
* Canine tooth, in mammalian oral anatomy
People with the ...
s and
molars with
bunodont cusps, bulging dental wreaths, and wrinkled enamel. Their upper molars were usually squared, due to the enlargement and displacement of the
metaconule, but there was also a small
hypocone and
hypoconule. The
paraconule was reduced and there was no
mesostyle. Their lower molars increased in size as they proceeded to the bottom of the jaw, and the
paraconid was small or absent. Some forms (e.g. ''Gobiohyus'') possessed small
diastemas that separated the premolars from each other. The snout was usually elongated (e.g. in ''Helohyus''), but in some forms ascribed to this family (''
Achaenodon''), it was very short. Compared to other primitive artiodactyls such as
dichobunids, they possessed higher sagittal ridges; the genus ''Achaenodon'', in particular, possessed a large sagittal crest and its size was much larger than those of other helohyids.
Classification
The family Helohyidae was established by Marshall in 1877 to accommodate some forms of early artiodactyl mammals of the American Eocene. In addition to the genus ''Helohyus'', the North American ''Parahyus'' and ''Achaenodon'' were later ascribed to this family. Other forms come from the Upper-Middle-East Eocene of Asia (''Gobiohyus'' of Inner Mongolia, ''Pakkokuhyus'' of Burma and ''Progenitohyus'' of Thailand. The latter form may be close to the origin of the family of hippo-like anthracotheres. The artiodactyl ''Simojovelhyus'' was once thought to be an unusually late-surviving genus of helohyid from the Upper Oligocene (extending the families temporal range by around 10 million years), however recent studies consider it a
peccary
A peccary (also javelina or skunk pig) is a medium-sized, pig-like hoofed mammal of the family Tayassuidae (New World pigs). They are found throughout Central and South America, Trinidad in the Caribbean, and in the southwestern area of No ...
.
Helohyids have been variously classified as relatives of archaic dichobunids or as close to the origin of
anthracotheres. The current opinion is to classify them as relatives of the dichobunids.
[McKenna and Bell, 1997; Stucky, 1998; Rose, 2006]
References
{{Taxonbar, from=Q10294574
Prehistoric mammal families