Llanocetus

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Llanocetus
Temporal range: Priabonian[1]
↓
Skull of Llanocetus denticrenatus at the
Smithsonian Museum of Natural History
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Parvorder: Mysticeti
Family: †Llanocetidae
Genus: †Llanocetus
Mitchell, 1989[1]
Type species
†Llanocetus denticrenatus
Mitchell, 1989[1]

Llanocetus ( "Llano's whale" ) is a

suction feeder like the modern beaked and pygmy right
whales.

History

Llanocetus was described in 1989 by

epiphyses—which are the surfaces that the vertebra connects to the other vertebrae to—on the single preserved neck vertebra.[3]

Dating to the

Phylogenetic analysis grouped Llanocetus into the Eocene family Llanocetidae along with Mystacodon and an as yet undescribed specimen OU GS10897 from New Zealand.[3]

The

species name derives from Latin denti, teeth, and crena, notch, in reference to the tooth shape which is similar to the crabeater seal.[1]

Description

Llanocetus had several ancient characteristics reminiscent of archaeocetes. The

basilosaurid archaeocetes. However, the broad snout is unlike archaeocetes. Wearing patterns on the cheek teeth, the molars and premolars, indicate they sheared passed each other while biting, which would have given Llanocetus the ability to slice through flesh, and serration wearing indicates a gripping function. It had wide gaps (diastema) between the teeth.[3] Its teeth had one of the thickest enamel layers of any known baleen whale, 830–890 μm at the top and 350–380 μm at the base, which is also consistent with a shearing action.[6] It had a crest on the mandible which may have supported proper musculature to pucker its lips.[3]

All baleen whales have in their mouth palatal

tooth sockets, which has generally thought to be indicative of baleen. However, in Llanocetus, these sulci are present within the tooth sockets, meaning sulci are not always indicative of baleen, and the whale probably did not have baleen. Palatal sulci are generally associated with large gums, and this enhanced blood supply in these early whales may have eventually led to the secondary evolution of baleen in later whales.[3]

The estimated minimum length for this juvenile specimen is 8 m (26 ft), comparable to a modern-day adult minke whale, and exceeding the size of most whales until the Late Miocene. For most of the Oligocene and Miocene, whales generally stayed well below 6 m (20 ft) in length. Large size in baleen whales was thought to be linked to the evolution of baleen and bulk feeding behavior; however, Llanocetus is evidence that gigantism evolved multiple times in baleen whales. The size of Llanocetus is probably due to its polar environment or potential long-distance traveling.[3]

Paleobiology

Llanocetus, when it was first described, was thought to have been a filter feeder with a similar mechanism to the modern crabeater seal, based on the notched teeth which Mitchell thought fit together to strain food out of the water.[1] However, it is now thought to have been a suction feeder, and similar facial structures are seen in the modern-day suction-feeding beaked whales and the pygmy right whale.[3] It may have used a combination of suction feeding and raptorial behavior—whereby it used its teeth to hunt prey.[6]

Paleoecology

The La Meseta Formation represents the

giant penguins.[7]

References

  1. ^
    S2CID 84711164
    .
  2. S2CID 135434058
    .
  3. ^
    S2CID 21680283
    .
  4. ^ Lewis, John (7 December 2022). "Fossilised whale off to Smithsonian". Otago Daily Times Online News. Retrieved 7 December 2022.
  5. S2CID 131787838
    .
  6. ^
    S2CID 254693347
    .
  7. ^ a b Reguero, Marcelo A.; Marenssi, Sergio A.; Santillana, Sergio N. (2012). "Weddellian marine/coastal vertebrates diversity from a basal horizon (Ypresian, Eocene) of the Cucullaea I Allomember, La Meseta formation, Seymour (Marambio) Island, Antarctica" (PDF). Peruvian Journal of Biology. 19 (3): 275–284.
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