Murrhardtia staeschei, Szczygielski & Sulej, 2016, Szczygielski & Sulej, 2016

Szczygielski, Tomasz & Sulej, Tomasz, 2016, Revision of the Triassic European turtles Proterochersis and Murrhardtia (Reptilia, Testudinata, Proterochersidae), with the description of new taxa from Poland and Germany, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 177 (2), pp. 395-427 : 406-407

MURRHARDTIA STAESCHEI

Murrhardtia staeschei , described in 2000 by Karl & Tichy, is another ambiguous taxon. Karl & Tichy (2000: 66) summarized all of the similarities and differences between the seven Triassic and Jurassic turtle taxa (including Proterochersis and Murhardtia) by listing 17 statements (characters) in a table. Eight of the nine characters proposed by the authors as diagnosing Murrhardtia staeschei from Proterochersis robusta are actually absent in the type Proterochersis robusta (and Proterochersis intermedia , herein treated as synonymous) material ( Fig. 1 ), so the comparison is not meaningful. As correctly noted by Gaffney et al. (2006), most of these characters seem to be taken from the illustration created by Fraas (1913). In that drawing Fraas (purely hypothetically) reconstructed the parts that were absent in the fossil material available to him (i.e. the anterior lobe of the plastron and the carapacial rim) as a generalized turtle, and did not indicate which areas of his reconstruction are actually based on fossils. Even though in the text it was clearly stated which fragments were missing, and the holotypes of both Proterochersis robusta and Proterochersis intermedia are in the SMNS collection, which was studied by Karl & Tichy, the autors appear to have treated Fraas’ reconstruction as the only base for comparisons. The characters used by Karl & Tichy (2000: 66) are listed as follows.

A pair of mesoplastra present (character 3)

In the third column of their table, Karl & Tichy (2000) stated that Murrhardtia is diagnosed by a pair of mesoplastra (unlike Proterochersis ), but in the eighth column (‘two pairs of mesoplastra present’) both Proterochersis and Murrhardtia are listed as having two pairs of mesoplastra. In fact, it is impossible to infer the number of the mesoplastra in any of the three specimens referred to in that paper, and although Karl & Tichy indicate that they analysed more material from SMNS, they fail to refer to it using catalogue numbers.

Complete separation of epiplastra by entoplastron (character 4)

Karl and Tichy stated that epiplastra in Murrhardtia are completely separated by entoplastron, and that in Proterochersis they are not separated. Fraas illustrated the epiplastra of Proterochersis contacting each other in front of the entoplastron (a common condition in modern turtles), but this part is missing from the original fossil material.

Distinct caudal notch present (character 5)

A distinct caudal notch was reported to be present in Murrhardtia and absent in Proterochersis by Karl and Tichy. That part is missing in the original material for Proterochersis .

Inframarginals present (character 9)

Karl and Tichy stated that inframarginals are present in Murrhardtia and absent in Proterochersis . It is the only character that can actually be compared in Proterochersis and Murrhardtia material. Unfortunately, it is wrongly interpreted – in the holotype of Proterochersis robusta the outline of the last inframarginal is visible, albeit with surface damage ( Fig. 10G, J ).

Infraplastrals present (character 10)

Karl and Tichy stated that infraplastrals are present in Murrhardtia but absent in Proterochersis . In fact they refer to abdominals, as they incorrectly interpret the gulars (not present in the original material; note that Karl & Tichy does not follow the scute terminology proposed by Hutchison & Bramble, 1981; so their intergulars and gulars are gulars and extragulars of Hutchison & Bramble, 1981; respectively) portrayed by Fraas (1913) as humerals. Nonetheless, type specimens of Proterochersis robusta and Proterochersis intermedia have abdominals as discussed for Murrhardtia material.

Gulars separated by two intergulars (character 11) Karl and Tichy state that gulars (extragulars sensu Hutchison & Bramble, 1981) of Murrhardtia are separated by paired intergulars (gulars sensu Hutchison & Bramble, 1981), and that this is not the case in Proterochersis . Once again this character is not applicable to Proterochersis because of the absence of that part in the fossil material, and is only based on the hypothetical reconstruction by Fraas.

Nuchalzack may be formed (character 12)

The nuchalzack is stated as present in Murrhardtia and absent in Proterochersis . An enigmatic character, not appropriately explained in the text. Illustrated as a triangular process on the cervical scute, it is actually absent in any of the shells. A similar structure is visible in the CSMM specimen of Murrhardtia , but the anterior margin of its cervical scute is clearly broken off, so the protruding prickle is just a rough edge of the break (but this specimen is rather unique in having its cervical scute bowed dorsally). Karl & Tichy pinpoint SMNS 16442 as having the strongest ‘nuchalzack’, but its cervical scute is virtually the same as that of SMNS 17561, which is supposed to be weakly expressed. Nonetheless, this character is not applicable to Proterochersis .

Only one unpaired gular present (character 14)

Karl and Tichy state that only one unpaired gular is present in Proterochersis , whereas two are present in Murrhardtia . As already mentioned, characters concerning that part are not applicable to Proterochersis .

Nuchal bone no wider than peripherals (character 15)

Nuchal bone being no wider than peripherals was stated as present in Proterochersis , and a wider nuchal was suggested for Murrhardtia . There is no trace of nuchal or peripheral sutures on the Proterochersis robusta or the Proterochersis intermedia holotypes, and therefore this character is not applicable. Unlike the other characters this was not taken from the illustration made by Fraas, and no source is given.

In sum, none of the characters used by Karl and Tichy to discriminate between Proterochersis and Murrhardtia is valid, and therefore we agree with the conclusion of Gaffney et al. (2006) that Murrhardtia staeschei should be considered a younger synonym of Proterochersis robusta .

Figures

Figure 1. Proterochersis robusta, SMNS 17561: A, C, shell in dorsal view; B, D, shell in ventral view. C, D, approximate extent of preserved bone in holotypes of Proterochersis robusta (hatched right upwards) and Proterochersis intermedia (hatched right downwards, shaded areas show approximate extent of plaster covering the dorsal surface of the specimen), and the characters noted by Karl & Tichy (2000) as diagnostic to Murrhardtia (light grey), are shown. Dark grey is matrix. Scale bar: 30 cm.

Figure 10. A–F, caudal notch of Proterochersis robusta in posterior view, SMNS 17561 (A and D), unnumbered CSMM (B and E), and SMNS 16603 (C and F, note that despite the lack of the central part of the last vertebral, the outline of the caudal notch is visible thanks to coarser, differently coloured sediment); G, J, posterior part of the right bridge of the holotype of Proterochersis robusta (SMNS 12777) in ventral view, revealing an outline of the damaged last inframarginal; H, K, anterior part of the holotype of Proterochersis robusta (SMNS 12777) in dorsal view, with an empty cavity left by the last cervical vertebra (note that it was not displaced, and nor can any discontinuities with the thoracic vertebral column be seen, indicating fusion as described in Proterochersis porebensis sp. nov.); I, L, anterior part of carapace and vertebral column of the holotype of Keuperotesta limendorsa gen. et sp. nov. (SMNS 17757) in ventral view, with the two last cervical vertebra free and relocated; M, the holotype of Keuperotesta limendorsa gen. et sp. nov. (SMNS 17757) in lateral left view (note the distinct broadened posterior parts of vertebrals II–IV and nearly straight profile of the first vertebral); N, Proterochersis robusta (SMNS 17561) in lateral left view (note the rounded profile and smooth changes of the vertebral elevation). Dark grey is matrix; hatched is damaged or broken bone. Not drawn to scale.