Proganochelys

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Proganochelys
Temporal range: Late Triassic, 210  Ma
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Proganochelys AMNH.jpg
Skeleton of Proganochelys quenstedti, American Museum of Natural History
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Pantestudines
Clade: Testudinata
Genus:† Proganochelys
Baur, 1887
Species:
†P. quenstedti
Binomial name
†Proganochelys quenstedti
Baur, 1887
Synonyms
  • PsammochelysQuenstedt, 1889
  • StegochelysJaekel, 1914 non Lydekker, 1889
  • TriassochelysJaekel, 1918

Proganochelys is a genus of extinct, primitive stem-turtle. Proganochelys was named by Georg Baur in 1887 as the oldest turtle in existence at the time. The name Proganochelys comes from the Greek word ganos meaning 'brightness', combined with prefix pro, 'before', and Greek base chelys meaning 'turtle'. Proganochelys is believed to have been around 1 meter in size and herbivorous in nature. Proganochelys had been known as the most primitive stem-turtle for over a century, until the novel discovery of Odontochelys in 2008. [1] Odontochelys and Proganochelys share unique primitive features that are not found in Casichelydia, such as teeth on the pterygoid and vomer and a plate-like coracoid. [1]

Contents

Proganochelys is the oldest stem-turtle species with a complete shell discovered to date, known from fossils found in Germany, Switzerland, Greenland, and Thailand in strata from the late Triassic, dating to approximately 210 million years ago. [2] The location of these fossils suggest that Proganochelys was active throughout the continent of Laurasia. There are only two known species of Proganchelys, with little information as a result of a small fossil record. All Proganochelys quentesti fossils were discovered in Germany, while Proganochelys ruchae fossils were found in Thailand.

Psammochelys, Stegochelys, and Triassochelys are junior synonyms of Proganochelys. Chelytherium von Meyer, 1863 has been considered a synonym of Proganochelys by some authors, but Joyce (2017) considers it a nomen dubium given the fragmentary nature of the syntype material. Joyce (2017) also considered North American genus Chinlechelys to be a junior synonym of Proganochelys, though the author maintains the type species of the former genus, C. tenertesta, as a distinct species within the genus Proganochelys. [3]

Description and paleobiology

Restoration Proganochelys quenstedtii.jpg
Restoration
Type specimen Proganochelys holotype.JPG
Type specimen

Proganochelys was once considered to be the oldest known stem-turtle until the description of Odontochelys and Eorhynchochelys , a slightly earlier genera that lived in the Carnian stage of the Triassic. In had a fully developed shell 60–70 cm (2.0–2.3 ft) long. [4] A total length of Proganochelys was about 91 cm (3 ft). Its overall appearance resembled modern turtles in many respects: it lacked teeth on the upper and lower jaw, likely had a beak and had the characteristic heavily armored shell formed from bony plates and ribs which fused together into a solid cage around the internal organs. Proganochelys had a semi-beak like structure along with teeth fused to its vomer. The plates comprising the carapace and plastron were already in the modern form, although there were additional plates along the margins of the shell that would have served to protect the legs. Also unlike any modern species of turtle, its long tail had spikes and terminated in a club, its head could not be retracted under the shell and its neck may have been protected by small spines. While it had no teeth in its jaws, it did have small denticles on the palate. [5] The beak like structure suggests that the Triassic stem-turtles evolved from carnivorous stem-turtles to herbivorous as the loss of teeth and gain of the beak would benefit the crushing of plants in these stem-turtles.

Synapomorphies and autapomorphies

Proganochelys possess a few chelonian synapomorphies including: a bony shell containing fused ribs, neural bones with fused thoracic segments, and a carapace and plastron that enclose the pelvic and shoulder girdle. [6] Proganochelys was also known for its autapomorphy features which included a tail club and a tubercle on the basioccipital. [6] The tail of Proganochelys was noticeably long and is hypothesized to have been used as a club for protection against predators. Although evolution of the shell has been clearly defined, the mechanisms behind the movement of the neck has been a subject of debate for Proganochelys. It has been hypothesized that Proganochelys were able to retract their necks by tucking in their skull under the front of their shell when needed. [7]

Shell

Life restoration of Proganochelys Proganochelys model.jpg
Life restoration of Proganochelys

The broadened ribs on Proganochelys show "metaplastic ossification of the dermis". [8] The enlarged ribs suggest that the endochondral rib ossifications were joined by a second ossification instead of having expanded ribs. [8] The 220-million-year-old stem-turtle Odontochelys only has a partially formed shell. [9] Odontochelys is believed to only possess the underside element of a shell known as a plastron. The 5-million-year difference that distinguish Odontochelys from Proganochelys tell us that the evolution of the shell occurred relatively quickly in time. [8] Proganochelys possess both a carapace, the upper formation of the shell, and the plastron, the lower. The shell is believed to be used for protection an enhanced feature for survival. Proganochelys fits well into the order as a turtle, as the shell of Proganochelys is in agreement with the evolution of other stem-turtles. [6]

Skull

The dermal roofing elements of Proganochelys include a large nasal, a fully roofed skull, a flat squamosal, and an absent pineal foramen. [6] Palatal characteristics include paired vomers, and a dorsal process containing premaxilla. [6] An open interpterygoid vacuity along with a prominent elongated quadrate are notable basicranial elements. [6] Overall, Pragonchelys is characterized by having few chelonian features and having a relatively generalized amniote skull. [6] The skull of Proganochelys quenstedti from Trossingen, West Germany, retains a number of well-known amniote features not found in any other turtle. For instance, the lacrimal bone, supratemporal bone, and lacrimal duct are notable structures that are kept. [6] Furthermore, some traits that are present in modern turtles are not present in Proganochelys and therefore must have come after the evolution of the shell. For instance, jaw differentiation, the fusion of the vomer, and the loss of the lacrimal are clear examples of traits that evolved after the evolution of the shell in Proganochelys. [10]

Proganochelys hard skeleton Proganochelys quenstedti 1.JPG
Proganochelys hard skeleton

Discovery

The earliest fossils of Proganochelys were discovered in Germany in the rural towns of Halberstadt, Tübingen, and Trossingen. [11] The fossils were found in an elaborate formation of shales, sandstones, and some limestone piles, with the formation believed to be between 220 and 205 million years old. [11] Consensus among Geologists placed the fossils in the middle of the Norian, around 210 million years ago, although this is largely an estimate. [11] In addition to Proganochelys, the rock formations in Germany have also given fossils for the stem-turtle Proterochersis . [6] Fossils have also been found the Klettgau Formation of Switzerland. [12]

Paleoecology

The specific ecology of the Late Triassic stem-turtles has been disputed and a major point of disagreement for many years among scientists. [13] Triassic stem-turtles, including Proganochelys, appear to have been both aquatic and terrestrial. [13] Shell proportions are believed to be correlated to the environment in which a turtle lives in, seen in modern turtles today. Using this concept, scientists were able to infer on the habitat in which Proganochelys may have lived in. A comparison between modern turtles and Proganochelys found that it was not likely that stem-turtles had differentiated into specialized ecologies such as open water swimmers or solely terrestrial turtles in the Late Triassic period. [13] If this is the case, a freshwater habitat would be the most likely environment for Proganochelys to have lived in. On the other hand, it is noted that some believe Proganochelys were solely terrestrial. Shell bone histology of extant turtles revealed congruence with terrestrial turtles for the earliest basal turtles, including Proganochelys, taxa in one study. [14] The common ancestry of all living turtles is believed to be aquatic, while the earliest turtles are believed to have lived in a terrestrial environment. [15]

Environment and forelimbs

Forelimbs are believed to be a physical feature that reflects the preferences and adaptations to a specific environment, indicating the environment a turtle would be most likely to reside in. Based on morphological data, Proganochelys is believed to have lived in a semi-aquatic environment, [15] though a 2021 study groups it with tortoises and other terrestrial taxa. [16] Turtles possessing short hands are believed to be most likely terrestrial, while turtles with long limbs are more likely to be aquatic. [15] The majority of all testudines are short-handed and terrestrial, while all cheloniods are long-handed and aquatic. [15] A study on its shell anatomy further conforms to a semi-aquatic mode of life. [17]

Classification

Proganochelys belongs to the group of tetrapods with a shell known as Testudinata and is the oldest primitive stem turtle. The group does not include Odontochelys.

The cladogram below follows an analysis by Jérémy Anquetin (2012). [18]

Habitat

Proganochelys is considered to have lived in the giant continent Laurasia during the Triassic period. The fossil records show that Proganochelys might have lived anywhere in between Thailand and Germany. During the Triassic period, Laurasia was primarily dry and warm, especially in arid areas. Proganochelys shared their environment with a variety of dinosaurs. Proganochelys lived in small water bodies such as ponds, but it was mainly earthbound.

Related Research Articles

<span class="mw-page-title-main">Turtle</span> Order of reptiles characterized by a shell

Turtles are reptiles of the order Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira and Cryptodira, which differ in the way the head retracts. There are 360 living and recently extinct species of turtles, including land-dwelling tortoises and freshwater terrapins. They are found on most continents, some islands and, in the case of sea turtles, much of the ocean. Like other amniotes they breathe air and do not lay eggs underwater, although many species live in or around water.

<span class="mw-page-title-main">Paracryptodira</span> Extinct clade of turtles

Paracryptodira is an extinct group of reptiles in the clade Testudinata, known from the Jurassic to Paleogene of North America and Europe. Initially treated as a suborder sister to Cryptodira, they were then thought to be a very primitive lineage inside the Cryptodira according to the most common use of the latter taxon. They are now often regarded as late-diverging stem-turtles, lying outside the clade formed by Cryptodira and Pleurodira. Paracryptodires are divided into three main groups, Compsemydidae, known from the Late Jurassic to Paleocene of North America and Europe, Pleurosternidae, known from the Late Jurassic to Early Cretaceous of North America and Europe, and Baenidae, known from the Early Cretaceous to Eocene of North America. The latter two groups are more closely related to each other than to Compsemys, forming the clade Baenoidea.

<i>Thalattosaurus</i> Extinct genus of reptiles

Thalattosaurus meaning "sea lizard," from the Attic Greek thalatta (θάλαττα), "sea," and sauros (σαῦρος), "lizard," is an extinct genus of marine reptile in the family Thalattosauroidea. They were aquatic diapsids that are known exclusively from the Triassic period. It was a 2–3 metres (6.6–9.8 ft) long shellfish-eating reptile with paddle-like limbs and a down-turned rostrum occurring in the Lower and Middle Triassic Sulphur Mountain Formation of British Columbia as well as the Upper Triassic Hosselkus Limestone of California. It has gained notoriety as a result of studies on general diapsid phylogeny.

<span class="mw-page-title-main">Turtle shell</span> Shield for the ventral and dorsal parts of turtles

The turtle shell is a shield for the ventral and dorsal parts of turtles, completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements such as the ribs, parts of the pelvis and other bones found in most reptiles. The bone of the shell consists of both skeletal and dermal bone, showing that the complete enclosure of the shell likely evolved by including dermal armor into the rib cage.

<i>Acerosodontosaurus</i> Extinct genus of reptiles

Acerosodontosaurus is an extinct genus of neodiapsid reptiles that lived during the Late Permian of Madagascar. The only species of Acerosodontosaurus, A. piveteaui, is known from a natural mold of a single partial skeleton including a crushed skull and part of the body and limbs. The fossil was discovered in deposits of the Lower Sakamena Formation. Based on skeletal characteristics, it has been suggested that Acerosodontosaurus individuals were at least partially aquatic.

<i>Laidleria</i> Extinct genus of amphibians

Laidleria is an extinct genus of temnospondyl that likely lived between the Early to Middle Triassic, though its exact stratigraphic range is less certain. Laidleria has been found in the Karoo Basin in South Africa, in Cynognathus Zone A or B. The genus is represented by only one species, L. gracilis, though the family Laidleriidae does include other genera, such as Uruyiella, sister taxon to Laidleria, which was discovered and classified in 2007. 

Eileanchelys is an extinct genus of primitive turtle from the Middle Jurassic (Bathonian) period some 164 million years ago of Britain. Only one species is recorded, Eileanchelys waldmani. It is the best-represented turtle from the Middle Jurassic, because of the amount of specimens that can be assigned to it. The turtle is also one of the oldest turtles ever found to be aquatic, and might represent a milestone in turtle evolution.

<i>Odontochelys</i> Extinct genus of reptiles

Odontochelys semitestacea is a Late Triassic relative of turtles before Pappochelys was discovered and Eunotosaurus was redescribed, Odontochelys was considered the oldest undisputed member of Pantestudines. It is the only known species in the genus Odontochelys and the family Odontochelyidae.

<i>Eunotosaurus</i> Extinct genus of reptiles

Eunotosaurus is an extinct genus of amniote, possibly a close relative of turtles. Eunotosaurus lived in the late Middle Permian and fossils can be found in the Karoo Supergroup of South Africa and Malawi. Eunotosaurus resided in the swamps of what is now southern Africa. Its ribs were wide and flat, forming broad plates similar to a primitive turtle shell, and the vertebrae were nearly identical to those of some turtles. Accordingly, it is often considered as a possible transitional fossil between turtles and their prehistoric ancestors. However, it is possible that these turtle-like features evolved independently of the same features in turtles, since other anatomical studies and phylogenetic analyses suggest that Eunotosaurus may instead have been a parareptile, an early-diverging neodiapsid unrelated to turtles, or a synapsid.

Doleserpeton is an extinct, monospecific genus of dissorophoidean temnospondyl within the family Amphibamidae that lived during the Upper Permian, 285 million years ago. Doleserpeton is represented by a single species, Doleserpeton annectens, which was first described by John R. Bolt in 1969. Fossil evidence of Doleserpeton was recovered from the Dolese Brothers Limestone Quarry in Fort Sill, Oklahoma. The genus name Doleserpeton is derived from the initial discovery site in Dolese quarry of Oklahoma and the Greek root "herp-", meaning "low or close to the ground". This transitional fossil displays primitive traits of amphibians that allowed for successful adaptation from aquatic to terrestrial environments. In many phylogenies, lissamphibians appear as the sister group of Doleserpeton.

<span class="mw-page-title-main">Testudinata</span> Clade of reptiles

Testudinata is the group of all tetrapods with a true turtle shell. It includes both modern turtles (Testudines) and many of their extinct, shelled relatives (stem-turtles), though excluding Odontochelys and Eorhynchochelys, which are placed in the more inclusive Pantestudines.

Kayentachelys is an extinct genus of turtle known only from the "silty facies" of the Lower Jurassic Kayenta Formation in northeastern Arizona on the lands of the Navajo Nation.

<span class="mw-page-title-main">Evolution of reptiles</span> Origin and diversification of reptiles through geologic time

Reptiles arose about 320 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms. So defined, the group is paraphyletic, excluding endothermic animals like birds that are descended from early traditionally-defined reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their synapsid ancestors. So defined, Reptilia is identical to Sauropsida.

Chinlechelys is an extinct genus of stem-turtle belonging to Testudinata. It lived in the Norian age of the Late Triassic and is the oldest turtle known from North America. Among turtles it is unique, mostly because of its very thin shell. The type and only species, C. tenertesta, was named and described with the genus by Walter G. Joyce et al. in 2009. It was probably terrestrial, and was found by Joyce et al. to be closely related to Proganochelys, another terrestrial testudinatan.

<span class="mw-page-title-main">Pantestudines</span> Clade of reptiles

Pantestudines or Pan-Testudines is the proposed group of all reptiles more closely related to turtles than to any other living animal. It includes both modern turtles and all of their extinct relatives. Pantestudines with a complete shell are placed in the clade Testudinata.

<span class="mw-page-title-main">Sichuanchelyidae</span> Extinct family of turtles

Sichuanchelyidae is a family of extinct turtles in the clade Testudinata. It includes all perichelydians that are more closely related to Sichuanchelys than Meiolania, Helochelydra, or any extant turtles.

<i>Pappochelys</i> Extinct genus of reptiles

Pappochelys is an extinct genus of diapsid reptile possibly related to turtles. The genus contains only one species, Pappochelys rosinae, from the Middle Triassic of Germany, which was named by paleontologists Rainer Schoch and Hans-Dieter Sues in 2015. The discovery of Pappochelys provides strong support for the placement of turtles within Diapsida, a hypothesis that has long been suggested by molecular data, but never previously by the fossil record. It is morphologically intermediate between the definite stem-turtle Odontochelys from the Late Triassic of China and Eunotosaurus, a reptile from the Middle Permian of South Africa.

Eorhynchochelys is an extinct genus of stem-turtle from the Late Triassic Xiaowa Formation of southwestern China.

<span class="mw-page-title-main">Mesochelydia</span> Clade of reptiles

Mesochelydia is a clade within Pantestudines, more inclusive than Perichelydia, but less than Testudinata. The clade is known from the Early Jurassic to the Present, and contains all Jurassic representatives of Testudinata aside from Australochelys. The ancestral condition for Mesochelydia is thought to be aquatic, as opposed to terrestrial for Testudinata. They are distinguished from more basal testudinatans by the presence of the following characters: strap like pectoral girdle, supramarginals absent, reduced posterior entoplastral process, eleven pairs of peripherals, elongate processus interfenestralis, paired basioccipital tubercles, fully formed cavum tympani and antrum postoticum, single vomer, confluent external nares, lacrimals and supratemporals absent.

<i>Proterochersis</i> Extinct genus of turtles

Proterochersis is an extinct genus of turtle from the Late Triassic period of Europe. It is known from a large number of fossils uncovered in Germany and Poland. The genus was named from fossil remains from Germany in 1913 by Fraas, who recognized two species: P. robusta and P. intermedia. Since then, Szczygielski and Sulej have found that the differences described by Fraas could be the result of intraspecific variation, meaning that P. intermedia are synonymous with P. robusta. They also decided to classify more recent fossil findings from Poland as two new species, P. limendorsa and P. porebensis. A study from 2021 concluded that fossil turtle remains described in 1865 as Chelytherium obscurum are probably synonymous with Proterochersis. Generally, the rules of nomenclature advocate that the oldest taxonomic name should replace more recent ones, but Szczygielski choose to keep the name Proterochersis.

References

  1. 1 2 Li, C.; Wu, X.-C.; Rieppel, O.; Wang, L.-T.; Zhao, L.-J. (2008). "An ancestral turtle from the Late Triassic of southwestern China" (PDF). Nature. 456 (7221): 497–501. Bibcode:2008Natur.456..497L. doi:10.1038/nature07533. PMID   19037315. S2CID   4405644.
  2. ↑ Prothero, D. R. (2015). The Story of Life in 25 Fossils: Tales of Intrepid Fossil Hunters and the Wonders of Evolution. New York, NY: Columbia University Press. ISBN   9780231539425.
  3. ↑ Joyce, W. G. (2017). "A Review of the Fossil Record of Basal Mesozoic Turtles" (PDF). Bulletin of the Peabody Museum of Natural History. 58 (1): 65–113. doi:10.3374/014.058.0105. S2CID   54982901.
  4. ↑ Hans-Dieter Sues (August 6, 2019). The Rise of Reptiles. 320 Million Years of Evolution. Johns Hopkins University Press. pp. 50–52. ISBN   9781421428680.
  5. ↑ Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 66–67. ISBN   978-1-84028-152-1.
  6. 1 2 3 4 5 6 7 8 9 Gaffney, E. S.; Meeker, L. J. (1983). "Skull morphology of the oldest turtles: a preliminary description of Proganochelys quenstedti". Journal of Vertebrate Paleontology. 3 (1): 25–28. doi:10.1080/02724634.1983.10011953.
  7. ↑ Werneburg, I. (2015). "Neck motion in turtles and its relation to the shape of the temporal skull region". Comptes Rendus Palevol. 14 (6–7): 527–548. doi: 10.1016/j.crpv.2015.01.007 .
  8. 1 2 3 Lyson, T. R.; Bever, G. S.; Bhullar, B.-A. S.; Joyce, W. G.; Gauthier, J. A. (2010). "Transitional fossils and the origin of turtles". Biology Letters. 6 (6): 830–833. doi: 10.1098/rsbl.2010.0371 . PMC   3001370 . PMID   20534602.
  9. ↑ Schoch, R. R.; Sues, H.-D. (2015). "A Middle Triassic stem-turtle and the evolution of the turtle body plan". Nature. 523 (7562): 584–587. Bibcode:2015Natur.523..584S. doi:10.1038/nature14472. PMID   26106865. S2CID   205243837.
  10. ↑ Lee, M. S. Y. (1993). "The Origin of the Turtle Body Plan: Bridging a Famous Morphological Gap". Science. 261 (5129): 1716–1720. Bibcode:1993Sci...261.1716L. doi:10.1126/science.261.5129.1716. PMID   17794877. S2CID   32907587.
  11. 1 2 3 Gaffney, E. (1990). The comparative osteology of the Triassic turtle Proganochelys. Bulletin of the American Museum of Natural History. Vol. 194. hdl:2246/884. ISSN   0003-0090.
  12. ↑ Scheyer, Torsten M.; Klein, Nicole; Evers, Serjoscha W.; Mautner, Anna-Katharina; Pabst, Ben (December 2022). "First evidence of Proganochelys quenstedtii (Testudinata) from the Plateosaurus bonebeds (Norian, Late Triassic) of Frick, Canton Aargau, Switzerland". Swiss Journal of Palaeontology . 141 (1): 17. doi: 10.1186/s13358-022-00260-4 . ISSN   1664-2376. PMC   9613585 . PMID   36317153.
  13. 1 2 3 Lichtig, A. J.; Lucas, S. G. (2017). "A simple method for inferring habitats of extinct turtles". Palaeoworld. 26 (3): 581–588. doi:10.1016/j.palwor.2017.02.001.
  14. ↑ Scheyer, T. M.; Sander, P. M. (2007). "Shell bone histology indicates terrestrial palaeoecology of basal turtles". Proceedings of the Royal Society B: Biological Sciences. 274 (1620): 1885–1893. doi:10.1098/rspb.2007.0499. PMC   2270937 . PMID   17519193.
  15. 1 2 3 4 Joyce, W. G.; Gauthier, J. A. (2004). "Palaeoecology of Triassic stem turtles sheds new light on turtle origins". Proceedings of the Royal Society of London. Series B: Biological Sciences. 271 (1534): 1–5. doi:10.1098/rspb.2003.2523. PMC   1691562 . PMID   15002764.
  16. ↑ Dudgeon, Thomas W.; Livius, Marissa C. H.; Alfonso, Noel; Tessier, Stéphanie; Mallon, Jordan C. (2021). "A new model of forelimb ecomorphology for predicting the ancient habitats of fossil turtles". Ecology and Evolution. 11 (23): 17071–17079. doi:10.1002/ece3.8345. PMC   8668755 . PMID   34938493. S2CID   244700219.
  17. ↑ Gabriel S. Ferreira, Guilherme Hermanson, Christina Kyriakouli, Dawid Dróżdż & Tomasz Szczygielski, Shell biomechanics suggests an aquatic palaeoecology at the dawn of turtle evolution, Article Open access Published: 18 September 2024
  18. ↑ Anquetin, J. (2012). "Reassessment of the phylogenetic interrelationships of basal turtles (Testudinata)". Journal of Systematic Palaeontology. 10 (1): 3–45. doi:10.1080/14772019.2011.558928. S2CID   85295987.
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