Protostega

The first known Protostega specimen (YPM 1408) was collected on July 4 by the 1871 Yale College Scientific Expedition, close to Fort Wallace and about 5 months before Cope arrived in Kansas. However, the fossil that they found was never described or named. It was not named until 1872, when E. D. Cope found and collected the first identified specimen of Protostega gigas in the Kansas chalk in 1871. A variety of bones were found in yellow Cretaceous chalk from a bluff near Butte Creek.{{Cite journal|last=Cope|first=Edward|date=1871|title=A Description of the Genus Protostega, a Form of Extinct Testudinata|url=https://duwamish.lib.washington.edu/uwnetid/illiad.dll?Action=10&Form=75&Value=1861494|journal=Proceedings of the American Philosophical Society|volume=12|issue=86|pages=422–433}}{{Cite journal|last=Wiffen|first=J.|date=1981-03-01|title=The first Late Cretaceous turtles from New Zealand|journal=New Zealand Journal of Geology and Geophysics|volume=24|issue=2|pages=293–299|doi=10.1080/00288306.1981.10422718|bibcode=1981NZJGG..24..293W |issn=0028-8306}}

The Late Cretaceous was marked by high temperatures, with large epicontinental seaways.{{Cite journal|last1=Dennis|first1=K. J.|last2=Cochran|first2=J. K.|last3=Landman|first3=N. H.|last4=Schrag|first4=D. P.|date=2013-01-15|title=The climate of the Late Cretaceous: New insights from the application of the carbonate clumped isotope thermometer to Western Interior Seaway macrofossil|journal=Earth and Planetary Science Letters|language=en|volume=362|pages=51–65|doi=10.1016/j.epsl.2012.11.036|bibcode=2013E&PSL.362...51D|issn=0012-821X}} During the Mid-to-Late Cretaceous period the Western Interior Seaway covered the majority of North America and would connect to the Boreal and Tethyan oceans at times.{{Cite journal|last1=Schröder-Adams|first1=Claudia J.|last2=Cumbaa|first2=Stephen L.|last3=Bloch|first3=John|last4=Leckie|first4=Dale A.|last5=Craig|first5=Jim|last6=Seif El-Dein|first6=Safaa A.|last7=Simons|first7=Dirk-Jan H. A. E.|last8=Kenig|first8=Fabien|date=2001-06-15|title=Late Cretaceous (Cenomanian to Campanian) paleoenvironmental history of the Eastern Canadian margin of the Western Interior Seaway: bonebeds and anoxic events|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=170|issue=3|pages=261–289|doi=10.1016/S0031-0182(01)00259-0|bibcode=2001PPP...170..261S|issn=0031-0182}}{{Cite journal|last1=Petersen|first1=Sierra V.|last2=Tabor|first2=Clay R.|last3=Lohmann|first3=Kyger C.|last4=Poulsen|first4=Christopher J.|last5=Meyer|first5=Kyle W.|last6=Carpenter|first6=Scott J.|last7=Erickson|first7=J. Mark|last8=Matsunaga|first8=Kelly K. S.|last9=Smith|first9=Selena Y.|last10=Sheldon|first10=Nathan D.|date=2016-11-01|title=Temperature and salinity of the Late Cretaceous Western Interior Seaway|journal=Geology|language=en|volume=44|issue=11|pages=903–906|doi=10.1130/G38311.1|bibcode=2016Geo....44..903P|issn=0091-7613}} Within these regions are where the fossil of Protostega gigas have been found.{{Citation|title=Mooreville Chalk|date=2019-12-16|url=https://en.wikipedia.org/w/index.php?title=Mooreville_Chalk&oldid=931029488|work=Wikipedia|language=en|access-date=2020-03-04}}{{cite book| last1 =Lutz| first1 =Peter L. | author-link =Peter Lutz |first2=John A. |last2=Musick | title =The Biology of Sea Turtles | publisher =CRC Press | year =1996 | url =https://books.google.com/books?id=fhm2yGTBiN8C&q=Protostega&pg=PA10 | isbn =978-0-8493-8422-6| page =10}}

File:Protostega gigas.jpg]]

Protostega is known to have reached up to {{cvt|3|-|3.9|m|ft}} in length.{{cite web|author=Mike Everhart|url=http://oceansofkansas.com/turtles.html|title=Marine turtles from the Western Interior Sea|website=OceansOfKansas.com|archive-url=https://web.archive.org/web/20220407005422/http://oceansofkansas.com/turtles.html|archive-date=7 April 2022|url-status=live}} A specimen from the upper Taylor Marl is even larger, at {{cvt|2|m|ft}} in carapace length and {{cvt|4.2|m|ft}} in total length. Despite lacking its head and three limbs, it is well-preserved.{{cite journal|author=Derstler, K.; Leitch, A. D.; Larson, P. L.; Finsley, C.; Hill, L.|date=1993|url=https://www.academia.edu/2394297|title=The World's Largest Turtles - The Vienna Archelon (4.6 m) and the Dallas Protostega (4.2 m), Upper Cretaceous of South Dakota and Texas|journal=Journal of Vertebrate Paleontology|volume=13 (suppl. to no. 3)|issue=33A}} Cope's Protostega gigas discovery revealed that their shell had a reduction of ossification that helped these huge animals with streamlining in the water and weight reduction.{{Cite web|url=http://trieboldpaleontology.com/protostega.html|title=Protostega gigas by Triebold Paleontology, Inc.|website=trieboldpaleontology.com|access-date=2020-03-03}} The carapace was greatly reduced and the disk only extending less than halfway towards the distal ends of the ribs. Cope described other greatly modified bones in his specimen including an extremely long coracoid process that reached all the way to the pelvis and a humerus that resembled a Dermochelys,{{Cite book|last=Carnegie Institution of Washington|url=https://archive.org/details/carnegieinstitut75carn|title=Carnegie Institution of Washington publication|date=1908|publisher=Washington, Carnegie Institution of Washington|others=MBLWHOI Library}} creating better movement of their limbs.

File:Fossil sea turtle.jpg

Edward Cope described Protostega gigas as having a large jugal that reached to the quadrate along with a thickened pterygoid that reached to the mandibular articulating surface of the quadrate.{{Cite journal|last=Hirayama|first=Ren|date=1994|title=Phylogenetic systematics of chelonioid sea turtles|journal=Island Arc|language=en|volume=3|issue=4|pages=270–284|doi=10.1111/j.1440-1738.1994.tb00116.x|bibcode=1994IsArc...3..270H |issn=1440-1738}} The fossil featured a reduction in the posterior portion of the vomer where the palatines meet medially. Another fossilized specimen showed that a bony extension, that would have been viewed as a beak, was lacking in the Protostega genus.{{Cite web|url=http://oceansofkansas.com/ProtostegaDig.html|title=Protostega_dig-2011|website=oceansofkansas.com|access-date=2020-03-03}} The premaxillary beak was much shorter than that of Archelon. In front of the orbital region the skull was elongated with a broadly-roofed temporal region. The jaws of the fossil showed a large crushing surface. The quadrato-jugal was triangular with a posterior edge that was concave, with the entire bone being convex from distal view. The squamosal appeared to have a concave formation on the surface at the upper end of the quadrate. In Cope's fossil the mandible was preserved almost perfectly and from this he recorded that the jaw was very similar to the Cheloniidae and the dentary had a broad for above downward with a concave surface, marked by deep pits in the dentary.

Cope concluded that these animals were most likely omnivores and consumed a diet of hard shelled crustacean creatures, due to the long symphysis of its lower jaw. Protostega also likely fed on seaweed and jellyfish or scavenged on floating carcasses as well, like modern turtles.

The classification of Protostega was complicated at best. The specimen that Cope discovered in Kansas was hard to evaluate with the preservation condition. The fossil shared many characteristics with the genus Dermochelys and the family Cheloniidae. Cope wrote about the characteristics that distinctly separated this particular species from the two controversial groups. The differences he described were that the fossil had a reduced or lacking amount of dermal ossification on the back, the articulation of the pterygoid and quadrates, the presence of a presplenial bone in the jaw, a lack of an articular process on the back side of the nuchal, simple formation of the radial process on the humerus, and a peculiar bent formation of the xiphiplastra. He concluded that Protostega gigas was an intermediate form between Dermochelys and Cheloniidae.{{Cite book|last=Case|first=Ermine Cowles|url=https://books.google.com/books?id=icrRAAAAMAAJ&q=protostega+classification&pg=PA21|title=On the Osteology and Relationships of Protostega|date=1897|publisher=Ginn|language=en}}

Examining the bone tissue microstructure (osteohistology) of Protostega revealed growth patterns similar to modern leatherback sea turtles with rapid growth to large body size. Leatherbacks lack a typical reptile metabolism, instead having high resting metabolic rates and the ability to hold a body temperature higher than their surroundings. If Protostega had similar bone growth patterns to leatherbacks, it is hypothesized that they both had a similar metabolism. This rapid growth to adult body size in sea turtles would also indicate rapid growth to reproductive maturity, which would have been a great advantage in their survival. However, comparing Protostega to its more basal relative Desmatochelys shows that not all protostegids had the same growth patterns. This indicates that rapid growth to large size evolved late within the lineage, perhaps in response to the evolution of large mosasaurs like Tylosaurus. Given uncertainties in the phylogenetic placement of protostegids relative to living sea turtles, it is unclear if the evolution of rapid growth rates and possible elevated metabolism were convergent with modern leatherbacks or if the two were more closely related.{{cite journal|last=Wilson|first=Laura E.|year=2023|title=Rapid growth in Late Cretaceous sea turtles reveals life history strategies similar to extant leatherbacks|journal=PeerJ|volume=11|at=e14864|doi=10.7717/peerj.14864|pmid=36793890 |pmc=9924133 |doi-access=free }}

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Category:Protostegidae

Category:Late Cretaceous turtles of North America

Category:Prehistoric turtle genera

Category:Taxa named by Edward Drinker Cope

Category:Mooreville Chalk

Category:Extinct turtles

Category:Fossil taxa described in 1872