Megalodontidae

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Megalodontidae
Megalodon from the Triassic, exhibited in the Munich Museum Mensch und Natur

Megalodon from the Triassic , exhibited in the Munich Museum Mensch und Natur

Temporal occurrence
Ordovician to Middle Jurassic
zapprox. 471 to 161 million years
Locations
  • Worldwide
Systematics
Autolamellibranchiata
Heteroconchia
Heterodonta
Rudists (Hippuritoida)
Megalodonts (Megalodontoidea)
Megalodontidae
Scientific name
Megalodontidae
Morris & Lycett , 1853

The Megalodontidae are an extinct family of bivalves (Bivalvia) in the order of the Rudists . The oldest representatives appeared in the Ordovician and the youngest representatives died out in the Jura .

features

The shells of the Megalodontidae are medium to large in size and have almost the same flaps (with very few exceptions). In outline, the housings are roughly triangular to oval. They have vertebrae curled forward and have relatively thick shells. The lock plate is solid with one or more teeth on each flap. In some genera there are also lateral teeth. The ligament is external, the pallial line is entire. The anterior sphincter is relatively far dorsal and on the anterior edge of the lock plate. The surface of the housing is usually smooth and has fine growth streaks. In some shapes, the growth strips can also be made stronger. Weak radial ribs are only found in a few forms.

Occurrence

The Megalodontidae occurred worldwide. They mostly lived in shallow seas behind or close to reefs or half buried in soft bottoms. The first species of this group appear for the first time in the Ordovician , and the last species die out in the Upper Jurassic. However, the systematic affiliation of the so far oldest genus to the Megalodontidae has not yet been confirmed by other researchers. The occurrence in the Silurian is considered certain .

Systematics

“Cow step clams” in the Dachstein limestone below the Great Gosau Glacier in the Austrian Eastern Alps

The family currently contains just over 20 genera:

  • Conchodon Stoppani, 1865
  • Cumularia Spriestersbach, 1919
  • Durga Boehm, 1894
  • Eomegalodus Spriestersbach, 1915
  • Ferrazia Reed, 1932
  • Juramegalodus Sirna, 1974
  • Krumbeckia servant, 1915
  • Megalodon J. de Carle Sowerby, 1827
  • Megalomoidea Cox, 1964
  • Neomegalodon Guembel, 1864
  • Pachymegalodon Guembel, 1864
  • Pachyrisma Morris & Lycett, 1850
  • Paramegalodus Cox, 1969
  • Parvimegalodon Karczewski, 1992
  • Pinzonella Reed, 1932
  • Prosocoelus Keferstein, 1857
  • Protodiceras Boehm, 1891
  • Protomegalodon Vostova, 1971
  • Quemocnomegalodon Yao, Se & Zhang, 2003
  • Rhaetomegalodon Vegh-Neubrandt, 1969
  • Rossiodus Allasinaz, 1965
  • Schismadon Cook, 1995
  • Triadomegalodon Vegh-Neubrandt, 1974

However, some genera are so poorly described that their family affiliation is very uncertain. The independence of some genres is also contested; some authors only treat them as sub-genres or as more recent synonyms. The compilation was based on the Treatise on Invertebrate Paleontology and the Zoological Record .

literature

  • LR Cox et al .: Treatise on Invertebrate Paleontology Part N Mollusca 6 Bivalvia (vol. 2 of 3). N491-N951, The University of Kansas & Geological Society of America, Boulder, Colorado, 1969.
  • Michael Amler, Rudolf Fischer & Nicole Rogalla: Mussels . Haeckel library, Volume 5. Enke Verlag, Stuttgart 2000, ISBN 3-13-118391-8 .