Thaumastocheles, Wood-Mason, 1874

Tshudy, Dale M., Hyžný, Matúš, Veselská, Martina Kočová & Jagt, John W. M., 2022, Taxonomic revision of the extinct clawed lobster genus Oncopareia Bosquet, 1854 (Decapoda, Astacidea, Nephropidae), Palaeontologia Electronica (a 20) 25 (2), pp. 1-31 : 4-6

FOSSIL THAUMASTOCHELES -LIKE LOBSTERS – A HISTORICAL OVERVIEW

Oncopareia was erected for a single late Maastrichtian species, O. bredai Bosquet, 1854 , from what is now the Kunrade Formation (https:// ncs.naturalsciences.be/cretaceous/kunrade-formation) in the Kunrade area of southern Limburg, the Netherlands. The taxonomic history of the genus is complex, beginning with a type species that is an accidental composite of two lobsters ( Figure 2A– 2D ) that differ at the genus level: Bosquet (1854) unknowingly established O. bredai on the basis of the cephalothorax of one species ( Figure 2A ) and the pleon ( Figure 2B ) and claws ( Figure 2C ) of another. One of the two lobsters comprising the unwitting composite type series of O. bredai (sensu Bosquet) is entirely Hoploparia -like. The other lobster has a very similar, Hoploparia -like cephalothorax but Thaumastocheles -like pleon and claws (as discussed further below in the systematic section). These cephalothoraxes belong with the Thaumastocheles -like pleons and chelipeds in the Bosquet Collection. Bosquet seems to have attributed the Thaumastocheles -like pleon forms to deformation (Bosquet, 1854, footnote on p. 129 [119]). Pelseneer (1886, p. 166), who examined the Bosquet and Ubaghs collections, was the first to recognize the Thaumastocheles -like pleon form as real (i.e., undeformed) and meaningful (he said it was Thalassina -like, noting especially the ridge separating the terga and pleura. He illustrated this pleon type in a line drawing ( Pelseneer, 1886, fig. 4; Figure 2E here) and referred to it as a new species, Homarus bosqueti .

Subsequent to Bosquet’s erection of a composite type species, the taxonomic confusion surrounding fossil Thaumastocheles -like lobsters became even more serious. Workers in the late 1800s erected new genera at a time when access to information and communication among taxonomists was not what it is today. This led to synonymous genera, even for specimens that were anatomically fairly complete. Other scholars in the late 1800s and early 1900s described isolated chelipeds with bulbous palms and slender fingers armed with acicular denticles; most of these were misidentified at the infraordinal level until recently ( Tshudy, 1993).

Schlüter (1862) was the first to describe extinct lobsters with a morphology similar to that of extant Thaumastocheles and erected (p. 728) the genus Nymphaeops . The type species, N. coesfeldiensis (considered herein to be a junior synonym of O. bredai ; see below), was based on specimens which, although lacking well-preserved claws, were otherwise essentially complete. Schlüter (1862) rightly considered his new species to be distinct from Hoploparia mainly because it had a different (i.e., Thaumastocheles -like) pleon, with wide, trapezoidal terga and short pleura but also, in his opinion, a different pattern of carapace grooves. In the same paper, he named another new species, Nymphaeops sendenhorstensis (considered herein as indeterminate at the generic level), based on a specimen with cephalothorax, partial pleon, and large, isochelous claws.

From the Bosquet Collection, a single claw with a bulbous palm and acicular dentition was referred by Pelseneer (1886, p. 162 [2], fig. 1) to a new genus and species, Ischnodactylus inaequidens . Why he described this particular single claw, but failed to mention other claws with acicular denticles, is uncertain. Ironically, the claw he described was one of probably only two specimens at his disposal, which is not an astacidean lobster at all, but an axiidean ghost shrimp referable to the genus Ctenocheles . In the same paper, Pelseneer (1886) moved Hoploparia macrodactyla Schlüter , in von der Marck and Schlüter, 1868, to Ischnodactylus , based on the similarity of its claws to that of the type species.

With two extinct, Thaumastocheles -like genera now published (i.e., Nymphaeops and Ischnodactylus ), Fritsch and Kafka (1887) erected the third one, Stenocheles , on the basis of three specimens from three different localities. Fritsch and Kafka (1887) described two species, Stenocheles esocinus and S. parvulus , for this material. Although resembling in many aspects the concept of Ischnodactylus published a year before, they made no comparison with it indicating that they were unaware of the latter when they prepared their own manuscript. Later, Hyžný et al. (2014) revised the original material referred to Stenocheles by Fritsch and Kafka (1887) and considered all three specimens distinct enough to be attributed to three different species, and erected a new one, Ctenocheles fritschi Hyžný, Kočová Veselská, and Dvořák, 2014 , to accommodate one of the syntypes of S. parvulus . Fritsch and Kafka (1887) did not select a type species for Stenocheles ; this was done by Glaessner (1969), who designated Stenocheles esocinus as such. This species is based on a pleon and associated claw with long, slender fingers and acicular dentition.

Subsequent to Fritsch and Kafka’s (1887) work came the discovery of more claws with bulbous palms and long, slender fingers and acicular dentition. These claws were referred mostly to Ischnodactylus by various authors. Böhm (1891) erected I. pectiniformis for a single claw, while Lőrenthey and Beurlen (1929) introduced Hoploparia eocenica (listed as I. (?) eocaenicus by Mertin, 1941) for partly preserved internal molds of cephalothoraxes and separate claws. Rathbun (1935) referred four new species, I. cookei , I. cultellus , I. texanus , and I.? dentatus to this genus; all were based on claw fragments. Finally, Beurlen (1939) assigned claws from the Oligocene of Hungary to Thaumastocheles . Most of these chelipeds were misidentified, as will be discussed in detail below.

Mertin (1941, p. 178) expanded the genus Oncopareia from one species, i.e., the type, O. bredai , to several on the basis of his examination of new, anatomically fairly complete material from the Upper Cretaceous of Braunschweig, northwest Germany. That material revealed the association of fossil remains of Thaumastocheles -like claws and pleons for the first time. Much earlier, Pelseneer (1886) had noticed the thaumastocheliform pleons (i.e., with short quadrate pleura) in the Bosquet Collection but he had not recognized the association with any pectinate chelipeds. With that recognition, Mertin (1941) attempted to resolve a situation wherein extinct Thaumastocheles -like lobsters had been described under different names. He synonymized Stenocheles Fritsch , in Fritsch and Kafka, 1887, and Ischnodactylus Pelseneer, 1886 , with Nymphaeops Schlüter, 1862 , and these, in turn, with Oncopareia .

The similarity of a Braunschweig pleon with that of Stenocheles esocinus (both of the Thaumastocheles type), in addition to some similarities between the Thaumastocheles- type claws of the two genera, led Mertin (1941) to relegate Stenocheles into the synonymy of Ischnodactylus . The similarity of the cephalothorax and pleon of the Braunschweig lobster to that of the type species, Nymphaeops coesfeldiensis , led Mertin (1941) to declare Stenocheles (= Ischnodactylus ) a synonym of Nymphaeops .

Mertin’s (1941) action, however, was too extensive, because not all of the species synonymized possess the Thaumastocheles -like pleon and pectinate claw upon which the grouping was based. Far more perplexing, however, is that he synonymized the above forms with Oncopareia , a genus which, as described by Bosquet (1854), has neither the Thaumastocheles -like pleon, nor claw which unite the three other fossil genera. In fact, the entire anatomy of Oncopareia in the original description of Bosquet (1854; but not Oncopareia as redefined herein) is highly typical of Hoploparia . Mertin’s synonymization seems to have been based entirely on the shared possession of a spiny rostrum in his Braunschweig material and in Oncopareia (sensu Bosquet, 1854) .

Mertin (1941) transferred to Oncopareia all three fossil genera, Nymphaeops , Ischnodactylus , and Stenocheles , as well as the fossil species Hoploparia macrodactylus and Enoploclytia paucispina Schlüter , in von der Marck and Schlüter, 1868. Into the same group, he tentatively moved Stenocheles parvulus , Hoploparia biserialis , Homarus muncki Pelseneer, 1885 , and, with some reservation, the extant genus Thaumastocheles . He excluded O. heterodon Bosquet, 1854 , and mentioned that Nymphaeops belgicus Forir, 1887 , and Ischnodactylus pectiniformis were based on material that was insufficient to permit comparison.

Mertin (1941, p. 178) redefined Oncopareia to include Thaumastocheles -like characteristics; most notably, the pleon and claw with acicular dentition. He did this not because the type species, O. bredai , had these features, but because some different, Thaumastocheles -like species possessed them, and some of these, in turn, had a spiny rostrum generic character for Oncopareia Bosquet, 1854 . Thus, on the basis of the shared possession of a spiny rostrum, the Thaumastocheles -like extinct species were allied with O. bredai , and the latter – being first-named – became the type species. Apparently, Mertin (1941) disregarded the Hoploparia / Homarus -like pleon and the absence of Thaumastocheles -like claws in Bosquet’s original publication. Nonetheless, he did establish Oncopareia as an extinct ancestor of Thaumastocheles – a concept that gained traction in the literature.

Mertin (1941, p. 180) noted the strong similarity of Oncopareia to the extant Thaumastocheles (i.e., carapace groove pattern, a very spiny rostrum, a smooth carapace, a lateral ridge on the pleon, pleonal pleura, etc.). He opined ( Mertin, 1941, pp. 178, 180) that it was doubtful that the fossil and extant forms could be separated on the genus level.

Oncopareia was treated in detail by Tshudy (1993), who examined the type material of Oncopareia bredai . Although never published, results of his research found their way into several works dealing with thaumastocheliform lobsters ( Tshudy and Sorhannus, 2000a, 2000b; Tshudy and Saward, 2012; Chang et al., 2017). Differences in the cephalothorax groove pattern in Oncopareia bredai and Hoploparia beyrichi were graphically presented by Tshudy and Sorhannus (2000b, fig. 2) and are redrawn here in Figure 1D–1E . The present contribution, finally, aims to resolve the taxonomic status of Oncopareia bredai as the type species of the genus Oncopareia and discusses all taxa treated as Oncopareia at any time in the light of the present revision.

Figures

FIGURE 1. Morphology of cephalothorax and a general habitus of studied taxa. A, Cephalothorax of nephropid lobsters with selected morphological characters (modified from Tshudy and Sorhannus, 2003). B, Habitus of thaumastocheliform lobsters, exemplified by Thaumastocheles zaleucus (from Calman, 1911). C, Habitus of ctenochelid ghost shrimps, exemplified by Ctenocheles balssi (from Kishinouye, 1926). D, Groove pattern of Oncopareia bredai Bosquet, 1854 (redrawn from Tshudy and Sorhannus, 2000b, fig. 2.2). E, Groove pattern of Hoploparia beyrichi Schlüter, 1862 (redrawn from Tshudy and Sorhannus, 2000b, fig. 2.3).

FIGURE 2. Oncopareia bredai (sensu Bosquet, 1854), as a composite species. A, Cephalothorax of O. bredai (from Bosquet, 1854, pl. 10, fig. 5). B, Pleon of Hoploparia beyrichi Schlüter, 1862 (from Bosquet, 1854, pl. 10, fig. 6). C, Claw of H. beyrichi (from Bosquet, 1854, pl. 10, fig. 71b). D, Composite drawing from Mertin (1941, text-fig. 9e). E, Pleonal segments 1 and 2 of O. bredai (as Homarus bosqueti Pelseneer, 1886; from Pelseneer, 1886, fig. 4).