Protostegidae

Source: Wikipedia, the free encyclopedia.

Protostegids
Temporal range: Cretaceous,[1][2] Valanginian–Maastrichtian
Life restoration of
Archelon ischyros
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Clade: Panchelonioidea (?)
Family: Protostegidae
Cope, 1873 [3]
Type species
Protostega gigas
Cope, 1872
Genera

Protostegidae is a family of

extinct marine turtles that lived during the Cretaceous period. The family includes some of the largest sea turtles that ever existed. The largest, Archelon, had a head one metre (39 in) long. Like most sea turtles, they had flattened bodies and flippers for front appendages; protostegids had minimal shells like leatherback turtles
of modern times.

Anatomy

Rhinochelys nammourensis
from Lebanon

As some of the first

extant, possibly closely related Dermochelyidae, protostegids possessed extremely reduced carapaces. Some specimens had skeletal protrusions from their ribs almost wrapping around their bodies in place of a complete shell. Like modern sea turtles, protostegids had sharp beaks. One of the defining characteristics of the members of the family was their almost-disproportionately large heads. Specifically, some specimens of Archelon have been found with heads one metre (39 in) long. In addition, the members of the family had somewhat reduced plastrons, as well.[5]

Ecology

Trophic ecology

While all members of the family are

Cretoxyrhina mantelli have been found embedded in at least one Protostega skeleton.[7]

Evolutionary history

Protostega gigas

The family's oldest members include an

era, the Protostegidae died out during the events of the Cretaceous–Paleogene extinction event that led to the extinction of the dinosaurs.[9]

The exact

eucryptodiran turtles lying outside the crown group of Cryptodira (the least inclusive clade containing all living cryptodirans) and closely related to Solnhofia parsonsi;[11] Santanachelys had a similar phylogenetic position in the analysis conducted by Anquetin (2012), who stressed that future studies should include more protostegids to confirm this phylogenetic placement.[12] If confirmed, these results would prove that protostegids weren't close relatives of leatherback turtles (or in fact any living cryptodirans), but instead "represent an independent lineage of marine turtles that originated in the Late Jurassic".[11] The analyses conducted by Sterli (2010) and Sterli & de la Fuente (2011) recovered Santanachelys (and, presumably, the entirety of Protostegidae) as even more distantly related to living cryptodirans; it was found to be basal turtle lying outside the crown group of turtles (the least inclusive clade containing cryptodirans and pleurodirans).[13][14]

A phylogenetic analysis conducted by Cadena and Parham (2015) recovered Protostegidae within the crown group of Cryptodira; specifically the family was recovered as belonging to Chelonioidea and more closely related to the leatherback sea turtle than cheloniids are.[8]

Taxonomic history

In 1888, the Belgian zoologist

Athecae, and the family Protostegidae was named by Edward Drinker Cope in 1873.[3] A year or so later, the entire suborder was downgraded by Karl Alfred von Zittel into a family within the Cryptodira.[15]

In 1994, Hirayama proposed a three-family subdivision of the

Santanachelys gaffneyi. The genus Santanachelys was appended to the family after the new species was described. This specimen was later to be analyzed to be the family's oldest member.[4]

References

  1. ^ "Protostegidae". The Paleobiology Database. Retrieved 27 July 2013.
  2. ^ .
  3. ^ .
  4. ^ .
  5. .
  6. ^ Shimada, Kenshu; M.J. Everhart; G. E. Hooks III (2002). "Ichthyodectid fish and protostegid turtle bitten by the Late Cretaceous lamniform shark, Cretoxyrhina mantelli". Journal of Vertebrate Paleontology. 22 (3): 106.
  7. S2CID 129391058
    .
  8. ^ a b Edwin A. Cadena and James F. Parham (2015). "Oldest known marine turtle? A new protostegid from the Lower Cretaceous of Colombia". PaleoBios. 32 (1): 1–42.
  9. ^ Zangerl, Rainer (May 1953). "The vertebrate fauna of the Selma Formation of Alabama, Part III. The turtles of the Family Protostegidae". Chicago Field Museum Mem. 3 (3).
  10. ^ Meylan, Peter A.; Ren Hirayama (September 2000). "The Paleontology and Phylogenetics of "Sea Turtles"". Proceedings of the 19th Annual Symposium on Sea Turtle Conservation and Biology. 19: 104. NOAA Technical Memorandum NMFS-SEFSC-443.
  11. ^
    S2CID 85998318. Archived from the original
    (PDF) on 6 June 2013.
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Further reading