Stupendemys
Stupendemys | |
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A young adult Stupendemys specimen | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Order: | Testudines |
Suborder: | Pleurodira |
Family: | Podocnemididae |
Genus: | †Stupendemys Wood, 1976 |
Species | |
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Synonyms | |
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Stupendemys is an
History and naming
Stupendemys was first named in 1976 by Roger C. Wood based on specimen
In February 2020, Cadena and colleagues published a paper describing material discovered during the routine excavations in theThe name Stupendemys is a combination of "stupendous", meaning extremely impressive, and the Latin word "emys" for freshwater turtle.[2] The species name meanwhile honors the National Geographic Society. However, the name Stupendemys geographicus, as coined by Wood, is grammatically incorrect, as Stupendemys constitutes a feminine generic name. The name was eventually corrected to Stupendemys geographica in 2021 in accordance with the International Code of Zoological Nomenclature (ICZN).[2][5]
Description
The skull of Stupendemys is roughly triangular in top view and the edges of the jaws converge at the front of the snout in a straight edge. The skull is dorsally extremely inflated by the
The
Size
Stupendemys is the largest known species of freshwater turtle currently known to science, with several specimens reaching a carapace length exceeding 2 meters. The largest specimen of Stupendemys is CIAAP-2002-01, an almost complete carapace with a parasagittal length of 2.86 meters. This exceeds the size of the Vienna-specimen of the Cretaceous sea turtle Archelon, the largest known turtle, (carapace length 2.20 meters).[4]
The weight of Stupendemys was estimated based on the straight carapace length, with calculations indicating a weight of 871 kg for CIAAP-2002-01 and 744 kg for MCZ(P)-4376, the former largest known specimen of Stupendemys. However, these estimates do not compensate for the large embayment present at the front of the shell. A more precise body mass estimate might be achieved by calculating the average between the results of weight estimates based on midline length and parasagittal length. Applying this method yields a weight of 1,145 kg for the largest Stupendemys specimen.[4]
The evolution of such an enormous size may have been multi-facetted and caused by a combination of factors including pressure from predators, habitat size and favorable climatic conditions, although Stupendemys temporal range indicates that it managed to survive through times of global cooling following the middle Miocene climatic transition (MMCT). Lastly, the giant size could have a phylogenetic link and be ancestral to Stupendemys, with several other related forms being known to have possessed gigantic proportions.[4]
Phylogeny
Although initially believed to be a
Podocnemidoidae |
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Paleobiology
Paleoecology
Following the 2021 research of Cadena and colleagues, the Pebas Mega-Wetlands housed at least two species of giant side-necked turtles: Stupendemys and Caninemys. Despite their similar size (both sporting a carapace length greater than 2 meters), they vary greatly in skull morphology, with Caninemys proposed to have been deploying a vacuum feeding strategy combined with a strong bite supported by tooth-like structures of the maxilla, while a more durophagous-omnivorous diet has been suggested for Stupendemys. This difference in diet and feeding strategy would be in accordance with Gause's Law, by which two species competing for the same ecological niche cannot coexist with one another for a long period of time without either differentiating or one dominating over the other in the long run. In addition to the different skull morphology, the two taxa may have also been able to coexist due to the sheer size of the Pebas Mega-Wetlands they inhabited, as this ecosystem stretched over most of northern South America during the Middle Miocene. This reason may also prevent the two taxa from being in direct competition over nesting grounds and basking spaces.[5]
The diet of Stupendemys may have been very diverse and broad, possibly including molluscs and other hard shelled prey as well as vertebrate prey as suggested by Meylan and colleagues for Caninemys. At its size it would have been easily capable of consuming various fish, snakes and small crocodilians. A broad dietary width would have helped Stupendemys in maintaining its large body size. Furthermore, Cadena and colleagues also highlight the role of turtles as seed-dispersers in modern-day Amazonia, consuming fruit of palms for example (Arecaceae), seasonally sometimes in great quantities, even if they are not typically part of their standard diet. With its wide gape, Stupendemys would qualify as a megafaunal frugivore and seed disperser.[4]
Sexual dimorphism
The absence of horns on most Stupendemys specimens indicates that they were not used as a defense mechanism. However, their forward-facing position on the carapace may indicate that they were used in intraspecific combat. Cadena and colleagues hypothesize that the horns may have been a sexually dimorphic trait exclusively found in males, suggesting them to have been used similar to the horns and antlers found in artiodactyls. Among extant turtles similar behavior can be found in snapping turtles, some of the largest freshwater turtles alive, which are known to fight for dominance in overlapping territories. This hypothesis is supported by the presence of a deep, elongated scar along the left horn of CIAAP-2002-01, which could have been left by the horn of a rival male that engaged it in combat. The authors further suggest that in Stupendemys the males may have been the larger sex, similar to the condition seen in the modern podocnemids. However other traditionally sexually dimorphic traits of the turtle shell, such as a deeper anal notch or a xiphiplastral concavity, have not yet been observed in Stupendemys fossils.[4]
Ontogeny
Prior to the 2021 study of Cadena and colleagues, only adult specimens of Stupendemys had been described. The discovery of a specimen with a carapace length smaller than 1 meter gives an insight into the changes the animal undergoes while reaching maturity. In addition to its small size, the animal is identified as a juvenile to young adult based on the absence of large horns and shallow anal notch. The inner nuchal notch, anterior expansion of the peripherals 1 and 2, irregular nodular contours, inner contact between the 7th and 8th costals and the relative size of the plastral lobes and their arrangement (except for the pectorals) remains relatively consistent with size.[5]
One of the most significant changes of the carapace of Stupendemys is its height. With age the shell of the turtle grows significantly flatter, while the nuchal region develops a pronounced upturn of its anterior margin and peripheral 1, creating a wide and deep anteromedial embayment of the carapace. The 2nd and 3rd
Paleoenvironment
During the Middle Miocene, the area inhabited by Stupendemys was part of an interconnected series of lakes, rivers, swamps and marshes that drained into the Caribbean known as the Pebas Mega-Wetlands, which included the Colombian
As the Pebas System began to disappear with the onset of the transcontinental Amazon Drainage, Stupendemys persisted in the wetlands of the northern
See also
- softshell turtle
- Archelon, a giant sea turtle of the Cretaceous
- Largest prehistoric animals
References
- ^ "†Stupendemys Wood 1976 (sideneck turtle)". Fossilworks.
- ^ a b c d Wood, R. C. (1976). "Stupendemys geographicus, the world's largest turtle". Breviora. 436: 1–31.
- ^ .
- ^ PMID 32095528.
- ^ PMID 35005268.
- PMID 38471564.
- S2CID 206528591.
- ^ "Giant fossil matamata turtles (matamatas part V)". Archived from the original on 2011-10-11. Retrieved 2011-10-11.