Protostegidae

Taxobox
name = Protostegidae
fossil_range = Cretaceous

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image_width =200px
image_caption ="Archelon", the largest member of the family.
regnum = Animalia
phylum = Chordata
classis = Sauropsida
ordo = Testudines
subordo = Cryptodira
familia = †Protostegidae
familia_authority = Cope, 1872
subdivision_ranks = Genera
subdivision =†"Archelon" †"Chelosphargis" †"Desmatochelys" †"Notochelone" †"Protostega" †"Rhinochelys" †"Santanachelys" †"Terlinguachelys"

Protostegidae is a family of extinct marine turtles that lived during the Mesozoic Era. The family includes some of the largest sea turtles that ever existed. The largest, "Archelon", had a head a meter long. While like most sea turtles, they had flattened bodies and had flippers for front appendages, protostegids had minimal shells like leatherback turtles of modern times.

Anatomy

As some of the first marine turtles, the protostegids set the general body plan for future species of sea turtles. Protostegids have a generally depressed turtle body plan, complete with four limbs, a short tail and a large head at the end of a relatively short neck. Like other sea turtles, they possess oar-like front appendages specially-evolved for swimming in the open ocean. Similar to the closely-related and still-extant Dermochelyidae, protostegids possess extremely reduced carapaces. Some specimens have skeletal protrusions from their ribs almost wrapping around the turtles' 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 are their almost-disproportionately large heads. Specifically, some specimens of "Archelon" have been found with heads that were a meter long. In addition, the members of the family had somewhat reduced plastrons as well.cite book | last =Lutz | first =Peter L. | authorlink =Peter Lutz | coauthors =John A. Musick | title =The Biology of Sea Turtles | publisher =CRC PRess | date =1996 | location = | pages =432pp. | url =http://books.google.com/books?id=fhm2yGTBiN8C&dq=protostegidae | doi = | id = | isbn =0849384222]

Ecology

Trophic ecology

While all members of the family are extinct, palaeoecological studies on the members of the family has provided some insight into the ecological roles of the "Protostegidae". Analysis of fossil organs of some protostegids has revealed entire stomachs containing fossilized shellfish. The turtles themselves are postulated to have been preyed upon by the major predators of the time. Fossil protostegids have been found with tooth impressions from the large lamnid sharks of the time.cite journal | last =Shimada| first =Kenshu| authorlink =Kenshu Shimada|coauthors=M.J. Everhart, G. E. Hooks III| title =Ichthyodectid fish and protostegid turtle bitten by the Late Cretaceous lamniform shark, "Cretoxyrhina mantelli"| journal =Journal of Vertebrate Paleontology| volume =22| issue =3| pages = 106| date =2002| url = | doi = | id = | accessdate = ] Two specimens of "Protostega gigas" have been discovered to have tooth marks from large sharks. In addition, teeth of the extinct shark "Cretoxyrhina mantelli" have been found embedded in at least one "Protostega" skeleton.cite journal | last =Shimada| first =Kenshu| authorlink =Kenshu Shimada|coauthors=G. E. Hooks III| title =Shark-bitten protostegid turtles from the upper Cretaceous Mooreville chalk, Alabama| journal =Journal of Paleontology| volume =78| issue =1| pages =205–210| date =January 2004| url =http://jpaleontol.geoscienceworld.org/cgi/content/extract/78/1/205 | doi=10.1666/0022-3360(2004)078| accessdate = ]

Evolutionary history

The family's oldest member is "Santanachelys gaffneyi", known from a specimen excavated from Brazil in 1998. The species first appeared during the Early Cretaceous. As an early sea turtle, "Santanachelys" had several unspecialized characteristics such as distinguishable digits in its flipper-like arms. Later relatives' flippers were completely fused together for more efficient swimming.cite journal | last =Hirayama| first =Ren| authorlink =Ren Hirayama | title =Oldest known sea turtle| journal =Nature| volume =392 | issue = 6677| pages = 705–708| date =1998-04-16| url =http://www.nature.com/nature/journal/v392/n6677/full/392705a0.html | doi =10.1038/33669| accessdate =2007-09-04] As with most large fauna of the era, the "Protostegidae" died out during the events of the Cretaceous–Tertiary extinction event that led to the extinction of the dinosaurs.cite journal | last =Zangerl | first =Rainer | authorlink =Rainer Zangerl | title =The vertebrate fauna of the Selma Formation of Alabama, Part III. The turtles of the Family Protostegidae | journal =Chicago Field Museum Mem. | volume =3 | issue =3 | pages = | date =May 1953 | url = | doi = | id = | accessdate = ] Through phylogenetic analysis, it has been determined that the closest living relatives of this particular family are the leatherback turtles in the family "Dermochelyidae", both of which are monophyletic.cite journal | last =Meylan| first =Peter A.| authorlink =Peter Meylan| coauthors=Ren Hirayama|title =The Paleontology and Phylogenetics of "Sea Turtles"| journal =Proceedings of the 19th Annual Symposium on Sea Turtle Conservation and Biology | volume =19 | issue = | pages = 104| date =September 2000 | url = | doi = | id =NOAA Technical Memorandum NMFS-SEFSC-443 | accessdate = ]

Taxonomic history

In 1888, the Belgian zoologist George Albert Boulenger published his classification of the Testudinata within the ninth edition of the Encyclopaedia Britannica. The genus "Protostega" was placed within the family "Sphargidae" under the suborder "Athecae". A year or so later, the entire suborder was downgraded by Karl Alfred von Zittel into a family within the "Cryptodira".cite journal | last =Baur| first =George| authorlink =George Baur| title =On the Classification of the Testudinata | journal =The American Naturalist | volume =24 | issue =282 | pages = 530–536| date =June 1890 | url = http://links.jstor.org/sici?sici=0003-0147(189006)24%3A282%3C530%3AOTCOTT%3E2.0.CO%3B2-T| doi = | id = | accessdate =| month =Jun| year =1890 ]

In 1994, Hirayama proposed a three-family subdivision of the sea turtle superfamily based on cladistic analysis; "Protostegidae" was given full, formal family status in the system, containing most of the extinct genera including "Archelon" and a previously undescribed protostegid.cite journal | last =Hirayama| first =Ren| authorlink =Ren Hirayama| title =Phylogenetic systematics of chelonioid sea turtles | journal =Island Arc| volume =3 | issue =4 | pages = 270–284| date =December 1994 | url = http://www.blackwell-synergy.com/doi/abs/10.1111/j.1440-1738.1994.tb00116.x?journalCode=iar| doi =10.1111/j.1440-1738.1994.tb00116.x | id = | accessdate =2007-09-04 ] The unidentified specimen was fully described in 1998, as the species "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.

References

Further reading

*cite book | last =Lutz | first =Peter L. | authorlink =Peter Lutz | coauthors =John A. Musick | title =The Biology of Sea Turtles | publisher =CRC PRess | date =1996 | location = | pages =432pp. | url =http://books.google.com/books?id=fhm2yGTBiN8C&dq=protostegidae | doi = | id = | isbn =0849384222

*cite web | last =Kazlev | first =M. Alan | authorlink =M. Alan Kazlev | title =Mesozoic Marine Reptiles | work =Palaeos Mesozoic | publisher =Palaeos | date =2003-09-15 | url =http://www.palaeos.com/Mesozoic/marine_reptiles.html | accessdate =2007-09-03

*cite journal | last =Case| first =E. C.| authorlink =George Baur| title =On the osteology and relationships of Protostega | journal =Journal of Morphology| volume =14| issue =| pages = 21–60| date =1897 | url = | doi = | id = | accessdate =

*cite journal | last =Cope| first =Edward Drinker| authorlink =Edward Drinker Cope| title =A description of the genus Protostega| journal =Proceedings of the Academy of Natural Sciences of Philadelphia| volume =| issue =| pages = 422–433| date =1872 | url = | doi = | id = | accessdate =

*cite journal | last =Cope| first =Edward Drinker| authorlink =Edward Drinker Cope| title =Note of fossils obtained by Mr. Russell S. Hill, including bones of "Protostega gigas"| journal =The American Naturalist| volume =12| issue =| pages = 137| date =1878 | url = | doi = | id = | accessdate =

*cite journal | last =Hay| first =O.P.| authorlink =| title =On certain portions of the skeleton of "Protostega gigas"| journal =Field Columbian Museum, Publications, Zoological Series| volume =1| issue =| pages = 57–62| date =1895 | url = | doi = | id = | accessdate =

*cite journal | last =Hay| first =O.P.| authorlink =| title =On "Protostega", the systematic position of "Dermochelys", and the morphogeny of the chelonian carapace and plastron| journal =The American Naturalist| volume =32| issue =| pages = 929–948| date =1898 | url = | doi = | id = | accessdate =

*cite journal | last =Sternberg| first =C.H.| authorlink =| title ="Protostega gigas" and other Cretaceous reptiles and fishes from the Kansas chalk| journal =Transactions of the Kansas Academy of Science| volume =19| issue =| pages = 123–128| date =1905| url = | doi = | id = | accessdate =

*cite journal | last =Wieland| first =G. R.| authorlink =| title =The protostegan plastron| journal =American Journal of Science| series=4|volume =5| issue =| pages = 15–20| date =1898| url = | doi = | id = | accessdate =

*cite journal | last =Wieland| first =G. R.| authorlink =| title =The osteology of "Protostega"| journal =Carnegie Museum, Memoirs| volume =2| pages = 279–298| date =1906| url = | doi = | id = | accessdate =

*cite journal | last =Wieland| first =G. R.| authorlink =| title =Plastron of the "Protosteginae"| journal =Carnegie Museum, Annals| volume =4| pages = 8–14| date =1906| url = | doi = | id = | accessdate =

*cite journal | last =Wieland| first =G. R.| authorlink =| title =Revision of the "Protostegidae"| journal =American Journal of Science| series=4|volume =27| issue =| pages = 101–130| date =1909| url = | doi = | id = | accessdate =

*cite journal | last =Williston| first =S. W.| authorlink =| title =On the hind limb of "Protostega"| journal =American Journal of Science| series=4|volume =13| issue =| pages = 276–278| date =1902| url = | doi = | id = | accessdate =