Enaliarctos
Encyclopedia
Enaliarctos is an extinct genus of pinniped
.
Prior to the discovery of Puijila
, the five species in the genus Enaliarctos represented the oldest known pinniped fossils, having been recovered from late Oligocene
and early Miocene
(ca. 24-22 million years ago) strata of California
and Oregon
.
It had a short tail
and developed limbs with webbed feet. Unlike modern sea lion
s, it had a set of slicing carnassials; the presence of slicing (rather than purely piercing teeth in modern fish-eating pinnipeds) suggests that Enaliarctos needed to return to shore with prey items in order to masticate and ingest them. Still, Enaliarctos had some sea lion-like characteristics such as large eyes, sensitive whiskers
, and a specialized inner ear
for hearing underwater.
Enaliarctos has been heralded as the ancestor of all known pinnipeds, including the families Otariidae (fur seals and sea lions), Desmatophocidae
(extinct seal convergent pinnipeds), Phocidae (true seals), and Odobenidae
(walruses). Investigations of the biomechanics of Enaliarctos indicate that it used both its forelimbs and hindlimbs during swimming. Modern fur seals and sea lions only use their forelimbs, while true seals primarily use their hindlimbs for aquatic propulsion; lastly, the extant walrus uses both fore- and hindlimbs for swimming. It has been postulated that the condition in Enaliarctos is ancestral for all pinnipeds, and that forelimb swimming was lost in true seals while hindlimb swimming was lost in fur seals and sea lions. This is significant because there has been considerable debate as to whether pinnipeds share common ancestry. Interpretation of Enaliarctos indicates that all pinnipeds share a common ancestor (which, if it was not Enaliarctos, must have been something very similar such as the more newly discovered Puijila darwini.)
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...
.
Prior to the discovery of Puijila
Puijila
Puijila darwini is an extinct species of pinniped which lived during the Miocene epoch about 21 to 24 million years ago. Approximately a metre in length, the animal possessed only minimal physical adaptations for swimming...
, the five species in the genus Enaliarctos represented the oldest known pinniped fossils, having been recovered from late Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
and early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
(ca. 24-22 million years ago) strata of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
.
It had a short tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
and developed limbs with webbed feet. Unlike modern sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...
s, it had a set of slicing carnassials; the presence of slicing (rather than purely piercing teeth in modern fish-eating pinnipeds) suggests that Enaliarctos needed to return to shore with prey items in order to masticate and ingest them. Still, Enaliarctos had some sea lion-like characteristics such as large eyes, sensitive whiskers
Vibrissae
Vibrissae , or whiskers, are specialized hairs usually employed for tactile sensation. The term may also refer to the thick hairs found inside human nostrils, but these have no sensorial function and only operate as an airborne particulate barrier...
, and a specialized inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
for hearing underwater.
Enaliarctos has been heralded as the ancestor of all known pinnipeds, including the families Otariidae (fur seals and sea lions), Desmatophocidae
Desmatophocidae
Desmatophocidae is an extinct family of Pinnipeds.- Taxonomy :* Desmatophoca* AllodesmusSome sources also list the following genera:* Atopotarus* Megagomphos* Brachyallodesmus...
(extinct seal convergent pinnipeds), Phocidae (true seals), and Odobenidae
Odobenidae
Odobenidae is a family of Pinnipeds. The only living species is walrus.In the past, however, the group was much more diverse, and includes more than ten fossil genera.- Taxonomy :All genera, except Odobenus, are extinct.*Prototaria...
(walruses). Investigations of the biomechanics of Enaliarctos indicate that it used both its forelimbs and hindlimbs during swimming. Modern fur seals and sea lions only use their forelimbs, while true seals primarily use their hindlimbs for aquatic propulsion; lastly, the extant walrus uses both fore- and hindlimbs for swimming. It has been postulated that the condition in Enaliarctos is ancestral for all pinnipeds, and that forelimb swimming was lost in true seals while hindlimb swimming was lost in fur seals and sea lions. This is significant because there has been considerable debate as to whether pinnipeds share common ancestry. Interpretation of Enaliarctos indicates that all pinnipeds share a common ancestor (which, if it was not Enaliarctos, must have been something very similar such as the more newly discovered Puijila darwini.)