Acherontemys

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Acherontemys
Temporal range: Lutetian
~47–45  Ma
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Acherontemys heckmani holotype USNM V4213 img3.jpg
Holotype carapace
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Superfamily: Testudinoidea
Genus: Acherontemys
Hay, 1899
Species:
A. heckmani
Binomial name
Acherontemys heckmani
Hay, 1899

Acherontemys is an extinct genus of turtle from Eocene sediments in northwestern North America and comprising a single species Acherontemys heckmani. Acherontemys has been placed within the pond turtle superfamily Testudinoidea as part of the clade Pan-Emydidae.

Contents

Distribution

Original 1899 illustration Acherontemys heckmani Hay Fig6 USNM V4213 img1.jpg
Original 1899 illustration

The only known specimen of Acherontemys heckmani was recovered from strata of the Roslyn Formation in Kittitas County, Washington. At the time of description Oliver Perry Hay listed the "Roslyn sandstone" as being of Miocene in age. [1] The formation has subsequently been redated to be of Middle Eocene, Lutetian age, with date constraints between 47.58  ± 0.028 million years ago to 45.91  ± 0.021 million years ago. [2]

History and classification

The turtle was collected from rocks exposed along a coal seam in the Northern Pacific Railroads Northwestern Improvement Company No. 4 Mine. [1] The mine utilized a vertical shaft with hoist to access coal seams being mined, and had a pump system to prevent water influx filling the workings. [3] The fossil was spotted and recovered by P.Y. Heckman who then passed it on to the Smithsonian for study using paleobotanist Frank Hall Knowlton as an intermediary. Due to the nature of the matrix encasing the fossil, which was described by Oliver Perry Hay as "refractory", only the upper surface of the carapace was excavated, leaving the plastron encased at time of description. Hay's original descriptions of the genus and species were published in an 1899 Proceedings of the United States National Museum paper along with the species description of Hadrianus schucherti , now placed as Cymatholcus schucherti . While no information was given on the derivation of the species name, Hay chose to coin the genus name Acherontemys as a reference to the Acheron river, a "river of the fabled lower world", in combination with the turtle genus Emys . [1]

Hay expressed wishes that additional specimens might be recovered from the mine to give more understanding of the species. [1] However the mine suffered a catastrophic explosion and fire a decade later at 12:45 p.m on October 3, 1909, killing 10 workers and burning down all the mine building except the brick powerhouse. The mine was never reopened. [3]

Acherontemys was originally assigned to the paraphyletic Chelydridae by Hay, a placement maintained by Robert L. Carroll (1988). [4] J. Howard Hutchison (1992), however, classified it within Emydidae, [5] and this placement was maintained by Evangelos Vlachos (2016), who placed it in the Testudinoidea clade Pan-Emydidae. [6] Vlachos notes the extra-wide vertebral scutes as distinguishing A. heckmani from any other testudinoid taxa of North America, though the size is seen in some European geoemydids. [6]

Description

The broad shell of 181 mm (7.1 in) long by 118 mm (4.6 in) wide with a low depressed dome and smooth posterior margin with no serrations. [7] Along the central keel are a series of low bosses. The upper surface is smooth and the sutures are distinct while some areas of the costal shield surfaces are wrinkled. The scutes on the shell were comprised of five notedly large vertebrals, surrounding narrowed costals, and 23 total marginal scutes. Sixteen square marginals are placed, in pairs, at the ends of the four costal scutes, with the remaining marginals along the margins of vertebral scutes I and IV. The costal scutes are narrower than in other genera as a result of the enlarged vertebrals. The vertebrals are extra wide, with Hay (1908) listing vertebral I at 75 mm (3.0 in), vertebral II at 90 mm (3.5 in), vertebral III at 85 mm (3.3 in), vertebral IV at 75 mm (3.0 in) and vertebral V at 65 mm (2.6 in). Vetrabrals II and III are also longer then the other three, which are narrowed to compensate, so much so that the sulcus between III and IV is located over the sixth neural bone rather than the fifth. [7]

Hay interpreted the underlying bones of the shell as having eight neural bones and a single extra large suprapygal. [1] [7] This was later challenged, with Vlachos (2018), after reexamination of the holotype, finding seven pairs of neural bones combined with two suprapygals. He interpreted Hays neural 8 as "suprapygal I" placed directly anterior to "suprapygal II", Hays "pygal" bone, with a narrow front margin, elongated sides, and a rounded rear margin giving a pentagonal outline. [6] Both authors note the distinctly wide nature of superpygal II, which is rectangular in general outline and spans the width of the 3 rear peripheral bones. [7] [6] Along the front margin, damage to the edge of the specimen is noted, with the nuchal bone missing its front edge. [7]

Paleoenvironment

Deposition in the Roslyn Formation paleoenvironment featured westerly flowing rivers and streams [2] and the flora is noted to be lacking in palm trees, which are found in older lowland formations of the area. [8]

Related Research Articles

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The Acheron is a river in the Epirus region of northwest Greece. It is 52 km (32 mi) long, and its drainage area is 705 km2 (272 sq mi). Its source is near the village Zotiko, in the southwestern part of the Ioannina regional unit. The Acheron flows into the Ionian Sea in Ammoudia, near Parga.

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<span class="mw-page-title-main">Cryptodira</span> Suborder of reptiles

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The Cochin forest cane turtle, also known as Kavalai forest turtle, forest cane turtle or simply cane turtle, is a rare turtle from the Western Ghats of India. Described in 1912, its type locality is given as "Near Kavalai in the Cochin State Forests, inhabiting dense forest, at an elevation of about 1500 feet above sea level". Only two specimens were found at that time, and no scientist saw this turtle for the next 70 years. It was rediscovered in 1982, and since then a number of specimens have been found and some studies have been conducted about its phylogeny and ecology.

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Stupendemys is an extinct genus of freshwater side-necked turtle, belonging to the family Podocnemididae. It is the largest freshwater turtle known to have existed, with a carapace over 2 meters long. Its fossils have been found in northern South America, in rocks dating from the Middle Miocene to the very start of the Pliocene, about 13 to 5 million years ago. Male specimens are known to have possessed bony horns growing from the front edges of the shell and the discovery of the fossil of a young adult shows that the carapace of these turtles flattens with age. A fossil skull described in 2021 indicates that Stupendemys was a generalist feeder.

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<i>Phosphatodraco</i> Late Cretaceous genus of pterosaur

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<i>Hesperotestudo</i> Genus of turtle

Hesperotestudo is an extinct genus of tortoise native to North and Central America from the Early Miocene to the Late Pleistocene. Species of Hesperotestudo varied widely in size, with a large undescribed specimen from the Late Pleistocene of El Salvador reaching 150 cm (4.9 ft) in carapace length, larger than that of extant giant tortoises. Historically considered a subgenus of Geochelone, it is now considered to be distantly related to that genus. Its relationships with other tortoises are uncertain. The exposed areas of the bodies of Hesperotestudo species were extensively covered with large dermal ossicles, which in life were covered in keratin. It has been suggested that species of Hesperotestudo were relatively tolerant of cold weather. Hesperotestudo became extinct at the end of the Pleistocene roughly co-incident with the arrival of the first humans in North America. There is apparently a site in Florida where one individual may have been killed that some suggested were evidence of butchering, although others suggested that the turtle was neither cooked nor does a ledge that was found near it date at the same time as it.

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References

  1. 1 2 3 4 5 Hay, O.P. (1899). "Descriptions of two new species of tortoises from the Tertiary of the United States". Proceedings of the United States National Museum. 22 (1181): 21–24. doi:10.5479/si.00963801.22-1181.21.
  2. 1 2 Eddy, M. P.; Umhoefer, P. J.; Miller, R. B.; Donaghy, E. E.; Gundersen, M.; Senes, F. I. (2017). "Sedimentary, volcanic, and structural processes during triple-junction migration: Insights from the Paleogene record in central Washington". From the Puget Lowland to East of the Cascade Range: Geologic Excursions in the Pacific Northwest. pp. 156–157. doi:10.1130/2017.0049(07). ISBN   978-0-8137-0049-6.
  3. 1 2 Swift, Mary (2009-10-30). "Today marks centennial of 1909 Roslyn mine disaster". Ellensburg Daily Record. Ellensburg, Washington. Retrieved 2023-12-11.
  4. Carroll, R. L. (1988). Vertebrate Paleontology and Evolution. W. H Freeman Company.
  5. Hutchison, J. H. (1992). "Western North American reptile and amphibian record across the Eocene/Oligocene boundary and its climatic implications". In Prothero, D.R.; Berggren, W.A. (eds.). Eocene-Oligocene Climatic and Biotic Evolution. Princeton University Press. pp. 451–463. doi:10.1515/9781400862924.451. ISBN   978-1-4008-6292-4.
  6. 1 2 3 4 Vlachos, E (2018). "A Review of the Fossil Record of North American Turtles of the Clade Pan-Testudinoidea". Bulletin of the Peabody Museum of Natural History. 59 (1): 3. doi:10.3374/014.059.0101. hdl: 11336/117896 . ISSN   0079-032X. S2CID   214641639.
  7. 1 2 3 4 5 Hay, O.P. (1908). "The fossil turtles of North America". Carnegie Institution of Washington Publication. 75. U.S. Government Printing Office: 221–222.
  8. Mustoe, G.E. (2001). "Washington's fossil forests". Washington Geology (29): 10–20.