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Keasius

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Keasius
Temporal range: 41.2–11.63  Ma Middle Eocene–Middle Miocene
Austromola angerhoferi.jpg
Restoration, with Austromola
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Division: Selachii
Order: Lamniformes
Family: Cetorhinidae
Genus:† Keasius
Welton, 2013 [1]
Type species
†Keasius taylori
Welton, 2013
Other species
  • †Keasius parvus
    (Leriche, 1908) [2]
  • †Keasius septemtrionalis
    Reinecke, von der Hocht, & Dufraing, 2015 [3]
  • †Keasius rhenanus
    Reinecke, von der Hocht, & Dufraing, 2015
Synonyms
Genus synonymy
Species synonymy
  • K. parvus
      • Cetorhinus parvus
        Leriche, 1908

Keasius is an extinct genus of basking sharks that lived during the Cenozoic. It contains four valid species, which have been found in North America, Europe, and Antarctica. [1] [3]

Contents

Description

In terms of size, Keasius individuals were considerably smaller than extant basking sharks, with estimated total lengths around 4.5–6.8 metres (15–22 ft) m based on gill raker-body proportions, versus the up to 11 metres (36 ft) maximum for basking shark(C. maximus). [5] [1] These morphological differences highlight Keasius as a basal form within the Cetorhinidae family, likely occupying a transitional role in the evolution of planktivorous lamniform sharks during the Eocene to Miocene. Fossil evidence places Keasius as a close relative or potential direct ancestor to Cetorhinus, with transitional forms appearing in the Oligocene-Miocenee that bridge archaic and derived traits, such as intermediate gill raker morphology observed in Sakhalin Island deposits. [6]

Paleobiology

Keasius species were specialized planktivores that employed a filter-feeding mechanism analogous to that of the modern basking shark Cetorhinus maximus. Fossilized gill rakers, teeth, and vertebral centra reveal a passive filtration system, where individuals swam with their mouths agape to draw in water via ram ventilation, straining zooplankton and small nektonic organisms from the water column. The close spacing and reduced size of teeth in preserved dentition further supported retention of minute prey particles while expelling excess water through the gills, as evidenced by specimens from Oligocene deposits in Germany. [7]

References

  1. 1 2 3 Welton, B.J. (2013). "A new archaic basking shark (Lamniformes: Cetorhinidae) from the late Eocene of western Oregon, U.S.A., and description of the dentition, gill rakers and vertebrae of the recent basking shark Cetorhinus maximus (Gunnerus)". New Mexico Museum of Natural History and Science Bulletin. 58: 1–48.
  2. ↑ Leriche, M. (1908). "Sur un appareil fanonculaire de Cetorhinus trouvé à l'état fossile dans le Pliocène d'Anvers". Comptes rendus hebdomadaires des séances de l'Académie des sciences. 146 (16): 875–878.
  3. 1 2 Reinecke, T.; von der Hocht, F.; Dufraing, L. (2015). "Fossil basking shark of the genus Keasius (Lamniforme, Cetorhinidae) from the boreal North Sea Basin and Upper Rhine Graben: evolution of dental characteristics from the Oligocene to late Middle Miocene and description of two new species". Palaeontos. 28: 39–98.
  4. ↑ von der Hocht, F. (1978). "Bestandsaufnahme der Chondrichthyes-Fauna des unteren Meeressandes (Oligozän, Rupelium) in Mainzer Becken". Mededelingen van de Werkgroep voor Tertiaire en Kwartaire Geologie. 15 (3): 77–83.
  5. ↑ Pacific Shark Biology, Research and Conservation Part A
  6. ↑ Four - The biology and ecology of the basking shark: A review
  7. ↑ Review of the Paleobiology of Some Neogene Sharks and the Fossil Records of Extant Shark Species


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