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Allopleuron hofmanni (Gray, 1831)[1]

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{{Taxobox | name = Allopleuron hofmanni | fossil_range = late Maastrichtian | image = Allopleuron hofmanni NHMM 0001 1.jpg | extinct = 66.5 Myr ago | domain = Eukaryota | regnum = Animalia | phylum = Chordata | classis = Reptilia | ordo = Testudines | subordo = Cryptodira | superfamilia = Chelonioidea | genus = Allopleuron Baur 1888 | synonyms = "Chelonia faujasii" Authority1
Chelonia cretacea " Authority2 | synonyms_ref = [2]). Allopleuron hofmanni is known by many specimens including nearly complete skeletons (Winkler 1869[3]; Felder 1980[4][5][6], Mulder 2003[7]), one of the most complete specimens was previously designated under the name "Tortue de l'Athenée de Maastricht[3] is now housed in exhibits of Maastricht Museum of Natural History (NHMM). This fossil sea turtle displays clear adaptations to the marine realm including rigid flippers, low ossified shell as well as a reduction of temporal and cheek emarginations indicating the loss of neck retraction (Ubaghs XXXX, Mulder 2003[7], Hermanson 2022[8]). These combination of characters and the large size reached by Allopleuron hofmanni is indicative for a pelagic ecology.

The anatomy of Allopleuron hofmanni includes a mozaic of stem-chelonioid, cheloniid and dermochelyid characters making its attribution to a higher rank taxa uncertain despite he displays clearly chelonioid affinities[7] (see section phylogeny below).

History of the specimens

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Type Material Controversy

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It is noteworthy than the type material of Chelonia (Allopleuron) hofmanni as designated by Gray (1831)[1] consist in a chimeric assemblage including diverse species of fossil and sea turtles[7]. This is likely the result of a misunderstanding of the work of Cuvier (1824) in which the latter have described the sea turtles of Maastricht in the paragraph "Chelonées des environs de Maastricht" and have listed a long list of figures that illustrates the "Chelonée de Maastricht" but also some comparative material. In the work of Gray (1831) all these illustrations, as well as more figures from Faujas de Saint Fond (1799) are listed as type series of Allopleuron hofmanni, with some errors in the citations[7]. Fortunately, all subsequent authors agreed on the identity of Allopleuron hofmanni, despite the fact that no lectotype was designated.

In is work on fossil vertebrates of Belgium, Dollo (1909), indicated that the type specimen of Allopleuron hofmanni is a shell housed in the Teylers Museum (Haarlem, The Netherlands), but this affirmation was debunked[7].

Taxonomic history

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In its original publication (Gray 1831), Allopleuron hofmanni was published under the genus Chelonia [1]as many fossil sea turtle at this epoch. Later, Baur (1888)[9] created the new genus and combination Allopleuron hofmanni for this species because he figured the numerous differences with the current sea turtles including the unusual low ossified costal (= pleural) plates. Indeed, Allopleuron means anormal pleurals[9]. Subsequently, numerous spelling errors of Allopleuron hofmanni were reported from the literature [10].

Excavations

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Anatomical features

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The most recent summary about the anatomy of Allopleuron hofmanni was published by Mulder (2003).

Cranium and mandible

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Several fairly preserved crania and mandibles (including complete specimens) are known for Allopleuron hofmanni (Winkler, Ubaghs, Felder, Mulder), allowing the paleontologist to fully reconstruct the cranial anatomy of this species. However, for now no cranial CT-scan published data is available.

Allopleuron hofmanni displays a very unusual combination of skull traits. Indeed it displays multiple similarities with Cheloniidae (hard shelled sea turtles) such as an extensive secondary palate[7], but also features typical from Dermochelyidae (leatherback group) such as a jugual-squamosal contact[7],[11] or a low ossified braincase [7](absence of a parabasisphenoidal rostrum) as well as unusually primitive traits such as the presence of a splenial bone in the mandible[7] (absent in all current sea turtle but present in protostegidae and basal representatives)[12][13]. Despite the presence of a splenial bones, Allopleuron hofmanni displays many derived traits such as a reduction of temporal and cheek emarginations or a well developped secondary palate that are absents in early representatives of the stem-chelonioid group that bears a splenial such as Toxochelys latiremis[14], Nichollsemys baieiri[13] or Porthochelys laticeps[15].

Allopleuron hofmanni shares many anatomical similarities

Shell

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The shell of Allopleuron hofmanni presents several traits that traduce the low degree of ossification of its shell as extensive carapace and plastral fontanelles[7]. A notable feature of Allopleuron hofmanni is its massive nuchal bone that displays a deep anterior emargination[7] but also its even keel that runs on the midline of the shell (neural keel) and the presence of moderate serrations on its peripheral plates, characters also presents in other cretaceous basal chelonioids (stem-chelonioids) such as Asmodochelys parhami (Ctenochelyidae) [16] although Allopleuron hofmanni lacks the epineural bones present in this group[7].

Limbs and Girdles

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Confusions

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Skeleton of Erquelinnesia gosseleti (IRSNB R 0007) mistakenly labelled as Allopleuron hofmanni in the IRSNB exhibit


Taphonomic studies

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Paleobiogeography and paleoecology

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Phylogenetic placement

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Allopleuron hofmanni suffers from an instable position in phylogenetic trees, probably due to its mosaic of anatomical characters. Indeed, some studies retrieved this species as belonging to the stem group of chelonioids, others included it in the chelonidae (crown-cheloniid), whereas a recent work have placed it within the dermochelyid group[13] .

  1. 1 2 3 Gray, John Edward (1831). Synopsis reptillium; or, Short descriptions of the species of reptiles. London: Treuttel, Wurtz, and Co.
  2. ↑ Giebel, 1847<ref> <ref>Keferstein, 1834<ref> }} Allopleuron hofmanni is a fossil sea turtle from the late Maastrichtian (Late Cretaceous) of Belgium and the Netherlands, it originates from the Maastricht Formation (occurs in Meerssen and Nekum Members<ref>E., Mulder; J., Jagt; E., Kuypers; M. H., Peeters; P., Rompen (1998). "Stratigraphic distribution of Late Cretaceous marine and terrestrial reptiles from the Maastrichtian type area" (PDF). Oryctos. 1: 55–64.
  3. 1 2 T. C., Winkler (1869). Des tortues fossiles conservées dans le Musée Teyler et dans quelques autres Musées (Archives Museum Teyler ed.). Haarlem: Héritiers Loosjes. {{cite book}}: |archive-url= requires |archive-date= (help)CS1 maint: date and year (link)
  4. ↑ P.J., Felder (1980). "Resten van fossiele Zeeschildpadden gevonden in het Krijt van Limburg" (PDF). Natuurhistorisch Maandblad. 69 (Deel1): 78–85.
  5. ↑ P.J., Felder (1980). "Resten van fossiele Zeeschildpadden gevonden in het Krijt van Limburg" (PDF). Natuurhistorisch Maandblad. 69 (Deel II): 100–104.
  6. ↑ P.J., Felder (1980). "Resten van fossiele Zeeschildpadden gevonden in het Krijt van Limburg" (PDF). Natuurhistorisch Maandblad. 69 (Deel III): 117–124.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 E.W.A., Mulder (2003). Comparative osteology, palaeoecology and systematics of the Late Cretaceous turtle Allopleuron hofmanni (Gray 1831) from the Maastrichtian type area In (On the latest Cretaceous tetrapods from the Maastrichtian type area). Publicaties van het Natuurhistorisch Genootschap in Limburg. pp. 23–92.{{cite book}}: CS1 maint: date and year (link)
  8. ↑ Hermanson, Guilherme; Benson, Roger B. J.; Farina, Bruna M.; Ferreira, Gabriel S.; Langer, Max C.; Evers, Serjoscha W. (2022-10-11). "Cranial ecomorphology of turtles and neck retraction as a possible trigger of ecological diversification". Evolution. 76 (11): 2566–2586. doi:10.1111/evo.14629. ISSN 0014-3820.
  9. 1 2 G., Baur (1888). [10.1126/science.ns-11.268.144-a "Unusual dermal ossifications"]. Science. 268: 144–144. {{cite journal}}: Check |url= value (help)
  10. ↑ O, Kuhn (1964). Fossilium Catalogus, Volume I: Animalia, Part107, Testudines. The Hague, The Neatherlands: Junk. pp. 299 pp.{{cite book}}: CS1 maint: date and year (link)
  11. ↑ Evers, Serjoscha W.; Benson, Roger B. J. (2018-07-18). "A new phylogenetic hypothesis of turtles with implications for the timing and number of evolutionary transitions to marine lifestyles in the group". Palaeontology. 62 (1): 93–134. doi:10.1111/pala.12384. ISSN 0031-0239.
  12. ↑ Evers, Serjoscha W.; Barrett, Paul M.; Benson, Roger B. J. (2019-05-01). "Anatomy ofRhinochelys pulchriceps(Protostegidae) and marine adaptation during the early evolution of chelonioids". PeerJ. 7: e6811. doi:10.7717/peerj.6811. ISSN 2167-8359.{{cite journal}}: CS1 maint: article number as page number (link) CS1 maint: unflagged free DOI (link)
  13. 1 2 3 Menon, Juliette C. L.; Brinkman, Donald B.; Hermanson, Guilherme; Joyce, Walter G.; Evers, Serjoscha W. (2024-07-12). "New insights into the early morphological evolution of sea turtles by re-investigation of Nichollsemys baieri, a three-dimensionally preserved fossil stem chelonioid from the Campanian of Alberta, Canada". Swiss Journal of Palaeontology. 143 (1). doi:10.1186/s13358-024-00323-8. ISSN 1664-2376.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  14. ↑ Matzke, Andreas T. (2009-07-06). "Osteology of the skull of Toxochelys (Testudines, Chelonioidea)". Palaeontographica Abteilung A. 288 (4–6): 93–150. doi:10.1127/pala/288/2009/93. ISSN 0375-0442.
  15. ↑ Williston, S. W. (1899). "A New Turtle from the Kansas Cretaceous". Transactions of the Annual Meetings of the Kansas Academy of Science. 17: 195. doi:10.2307/3623891. ISSN 1933-0545.
  16. ↑ Gentry, Andrew D.; Ebersole, Jun A.; Kiernan, Caitlin R. (2019-12). "Asmodochelys parhami, a new fossil marine turtle from the Campanian Demopolis Chalk and the stratigraphic congruence of competing marine turtle phylogenies". Royal Society Open Science. 6 (12): 191950. doi:10.1098/rsos.191950. ISSN 2054-5703. {{cite journal}}: Check date values in: |date= (help)CS1 maint: article number as page number (link)
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