Polygnathus is a genus of conodonts known from the Early Devonian to Early Carboniferous, with an apparatus including a more or less distinctly curved platform element (Bardashev et al. 2002). The platform bears a median carina that tends to disappear or become obscure at the posterior end (Sweet 1988).
The type species Polygnathus dubius was one of the first conodont species to be named for an assemblage rather than individual elements, though it is now agreed that the forms included in the original description do not represent a single taxon (Sweet 1988).
Time for teeth
Published 26 October 2009
Conodonts are among the iconic fossils of the Palaeozoic. Minute (in the millimetre size range) but extremely abundant, conodont elements* are tooth-like in appearance. The earliest forms were simple and fang-like; later forms were often blade-like with a median row of teeth. Their abundance and variety mean that conodonts are widely used in biostratigraphy, but for many years the identity of the animal they came from was unknown – whatever it was, it appeared to possess no other hard parts that would normally be preserved. It wasn’t until the 1980s that the first unequivocal conodonts with preserved soft parts were discovered, revealing them to be stem- or basal vertebrates** (Sweet & Donoghue 2001). Each of the conodont animals had a number of conodont elements arranged around the mouth and pharynx. Slender-pointed elements towards the front of the mouth would have seized or filtered prey, while many conodonts also possessed more robust elements further back in the pharynx to grind up their food. The figure below from Dzik (1991) gives a good idea of how it would have all worked, even if the result does look a bit like a carnivorous sock puppet (Dzik’s arrangement of the elements has also since been superceeded—see Purnell & Donoghue, 1997, for details). Those full-body fossils of conodonts that have been identified to date are eel- or lamprey-like, but it is worth keeping in mind that only two species of this very speciose lineage are known from such remains and we may not be seeing a proper representation of conodont diversity.
*Before the nature of conodonts was understood, most authors restricted the name to the fossils themselves; the then-hypothetical animal that produced these structures was referred to as a “conodontophore”. Since the current identification of conodonts has been accepted, this distinction has been abandoned.
**Conodonts had been found in association with soft body parts before, but the animals concerned are now agreed to have been predators or scavengers of conodonts (with conodont elements in their gut as a result) rather than the conodont animals themselves.
Polygnathus has been recognised as one of the largest of conodont genera—some 545 Early Devonian to Early Carboniferous species and subspecies have been assigned to it over the years (Weddige 2005). Polygnathus belonged to the conodont order Ozarkodinida, and would have had an apparatus of toothed elements similar to that shown below (not Polygnathus but another ozarkodinidan genus). The lower saw-like S elements at the front of the mouth would have been the initial graspers; the act of opening the mouth would have rotated the curved upper M elements forward, and their rotating back as the mouth closed would have probably drawn the prey in; and the two pairs of large P elements in the back would have sliced and diced the prey.
The Early Devonian members of Polygnathus were recently revised by Bardashev et al. (2002) in what I can only describe as one of the most taxonomically incredible papers it has ever been my misfortune to read. In the early days of conodont taxonomy, working purely from dissociated elements, different elements were treated as taxonomically separate entities. As the recognition developed that a single individual conodont animal would have possessed a number of differently formed elements (something that happened even before the discovery of conodont soft-body fossils as researchers noted that certain element types were always found in association, while specimens were occasionally found in which normally separate elements had become fused together), the older independent element taxonomy was replaced by a multi-element taxonomy based on the apparatus as a whole*. Bardashev et al. (2002), however, base their classification solely on the Pa or P1 element, the large posteriormost element in the model above. All other elements, they seem to claim, are useless for distinguishing taxa (which could be a problem for dealing with basal conodonts that don’t have P elements).
*At least ideally. In practice, of course, there are still a large number of cases in which the correct element associations cannot yet be reliably identified.
On the basis of Pa morphology, Bardashev et al. divide species of Polygnathus between six genera in two families—and this is where things really start to go down the rabbit hole. Members of the family Polygnathidae are divided between the temporally successive families Eognathodidae, Eopolygnathidae and Polygnathidae. Eopolygnathidae are derived from Eognathodidae and Polygnathidae from Eopolygnathidae. Now, the use of paraphyletic taxa is nothing unusual in micropalaeontology. But explicitly polyphyletic taxa? In the phylogeny presented by Bardashev et al., Eognathodidae gave rise to Eopolygnathidae on two separate occasions, with Eoctenopolygnathus descended from a separate group of eognathodids from Eocostapolygnathus and Eolinguipolygnathus (note also that there is no genus ‘Eopolygnathus‘, so ‘Eopolygnathidae’ is an invalid name under the ICZN). After that, Polygnathidae derives from ‘Eopolygnathidae’ eleven times—two separate origins of Ctenopolygnathus within Eoctenopolygnathus, four origins of Costapolygnathus from Eocostapolygnathus, five of Linguipolygnathus from Eolinguipolygnathus (the authors refer to these multiple origins as representing common ‘trends’ between the lineages). Bardashev et al. also name the type species of the new genus Costapolygnathus as Polygnathus dubius, which happens to be the type species of Polygnathus (a point that Bardashev et al. had commented upon themselves earlier in the paper). There are also cases where the type specimens of ‘undiagnostic’ species are assigned to new species named by Bardashev et al.—surely, if you can identify them to a species, they can’t be undiagnostic?
Bardashev et al.‘s (2002) reclassification was criticised and rejected by Mawson & Talent (2003), who maintained that because it only covered Early Devonian taxa, it created a strong disconnect in apparent diversity between Early and Late Devonian. This criticism, I must say, is unfair—all revisions have to start somewhere, and to demand an ‘all or nothing at all’ approach in such cases would be to effectively prevent much possibility of large taxonomic groups being revised at all. Potentially more problematic (but unfortunately not supported with specific examples) is Mawson & Talent’s implication that some of the new ‘species’ recognised by Bardashev et al. are in fact variants of other species and not phylogenetically distinct entities.
Bardashev & Weddige (2003) published a brief note in which they corrected the objective synonymy of Polygnathus and Costapolygnathus by publishing a new genus Eucostapolygnathus that they said “includes the same species as Costapolygnathus – except the species dubius“. In a reply to Mawson & Talent’s comments, Weddige (2005) defended Bardashev et al.‘s (2002) use of a high number of taxa on the basis that the latter had been a ‘pure form-taxonomic study’. Or, more extensively:
The genus subdivision proposed by BARDASHEV, WEDDIGE & ZIEGLER (2002) might be regarded as a subgeneric subdivision. In form-taxonomy, however, and the paper represents a pure form-taxonomic study, subgenera are not in usage. Because of the pure form-taxonomy, moreover, resp. because of a more or less subgeneric level of the proposed subdivision, a multielement reference, e. g. by suspect statistics, is not needed, for the first. Thus, a distinctive serious discussion has to focus on (form-) taxonomic characters, i. e. the valuation and order of the diagnostic characters as they are used for the generic subdivision by BARDASHEV et al. Admittedly, a broadly splitted form spectrum, often including revolutionary ideas, is a hard diet. On the other hand, a well known unchanged form spectrum is a usual and therefore easy diet that, moreover, becomes much easier to digest when the spectrum, or parts of it, is furthermore lumped. The differentiation in “splitters” and “lumpers” is an inadequate simplification—since the study by BARDASHEV et al. is not only a splitting because of different new taxa, it has rather more the character of a synthesis because of its search for phylogenetic lines by which single species were “lumped”). Thus, the study is a lumping on a quality level, higher than a taxonomic lumping that resigns to differentiate and searches for a conservative comfortable easy diet. Conservatives bloc progress, that is their job—and it would be a total misunderstanding that a SDS commission or a Working Party is entitled to condemn per joint decision (that could not be the target of a discussion!).
So in reply to accusation of being splitters, Weddige replies that no, they were lumpers, but his definition of ‘lumping’ can only be described as an Inigo Montoya moment. There is also the problem that Bardashev et al. was self-evidently not a purely form-taxonomy study. Form taxa are those based on morphological distinctions only that cannot be confirmed as phylogenetically distinct units—but Bardashev et al. (2002) presented their readers with no less than nine representations of preferred phylogenetic hypotheses, as well as specifically commenting on the descent of every one of the taxa they described. If these were only ‘form taxa’, then those ‘lineages’ are completely meaningless, and you, my friend, have just been treated to seventy-seven pages of intellectual masturbation.
Systematics of Polygnathus
Characters (from Bardashev et al. 2002, for Eocostapolygnathus + Costapolygnathus): Platform more or less distinctly curved, margins of platform reaching posterior end, ornamented by nodes or transverse ridges; carina reaching posterior end, with or without adcarinal grooves; basal cavity varying in size, symmetric- to asymmetric-flanged.
<==Polygnathus Hinde 1879BWZ02 (see below for synonymy) |--+--P. sokolovi Yolkin, Weddige et al. 1994 [=Eocostapolygnathus sokolovi]BWZ02 | `--+--P. hindei Mahkova & Apekina 1980 [=Eocostapolygnathus hindei]BWZ02 | `--P. tamara Apekina 1989 [=Eocostapolygnathus tamara]BWZ02 |--+--LinguipolygnathusBWZ02 | `--‘Eocostapolygnathus’ yolkini Bardashev, Weddige & Ziegler 2002BWZ02 | |--E. y. yolkiniBWZ02 | `--E. y. erinae Bardashev, Weddige & Ziegler 2002BWZ02 `--+--P. kitabicus Yolkin, Weddige et al. 1994 [=*Eocostapolygnathus kitabicus]BWZ02 |--+--‘Eocostapolygnathus’ pierrei Bardashev, Weddige & Ziegler 2002BWZ02 | `--+--P. juferevi Aksenova 1987 [=Eocostapolygnathus juferevi]BWZ02 | `--+--‘Costapolygnathus’ mariannae Bardashev, Weddige & Ziegler 2002BWZ02 | `--‘Costapolygnathus’ telfordi Bardashev, Weddige & Ziegler 2002BWZ02 `--+--P. excavatus Carls & Gandl 1969 (see below for synonymy)BWZ02 |--+--‘Eocostapolygnathus’ polinae Bardashev, Weddige & Ziegler 2002BWZ02 | `--+--P. inversus Klapper & Johnson 1975 [=Costapolygnathus inversus]BWZ02 | `--+--P. quadratus Klapper, Ziegler & Mashkova 1978 [=Costapolygnathus quadratus]BWZ02 | `--‘Costapolygnathus’ snigirevae Bardashev, Weddige & Ziegler 2002BWZ02 `--+--+--P. gronbergi Klapper & Johnson 1975 [=Eocostapolygnathus gronbergi]BWZ02 | `--+--‘Costapolygnathus’ jacksoni Bardashev, Weddige & Ziegler 2002BWZ02 | `--‘Costapolygnathus’ schenkae Bardashev, Weddige & Ziegler 2002BWZ02 `--+--‘Eocostapolygnathus’ philipi Bardashev, Weddige & Ziegler 2002BWZ02 `--+--P. laticostatus Klapper & Johnson 1975 [=Costapolygnathus laticostatus]BWZ02 `--+--P. gilklapperi Mawson & Talent 1994 [=Costapolygnathus gilklapperi]BWZ02 `--+--P. benderiBWZ02 |--P. costatusBWZ02 | |--P. c. costatusBWZ02 | |--P. c. karapetoviBWZ02 | |--P. c. oblongusBWZ02 | |--P. c. partitusBWZ02 | `--P. c. sogdianensisBWZ02 |--P. parawebbi Chatterton 1974BWZ02, KU04 |--P. patulus Klapper 1971 [=Costapolygnathus patulus, P. costatus patulus]BWZ02 |--P. pseudofoliatus Wittekindt 1966BWZ02, D02 |--+--P. eifliusBWZ02 | `--P. ovatinodosusBWZ02 `--+--P. kennettensisBWZ02 `--+--P. ensensis [=P. xylus ensensis]BWZ02 |--P. varcusBWZ02 |--P. xylusBWZ02 `--+--P. ansatus Ziegler & Klapper 1976BWZ02, D02 [incl. P. hemiansatus Bultynck 1987D02] `--P. timorensis Klapper, Philip & Jackson 1970D02 Polygnathus incertae sedis: *P. dubius Hinde 1879 [=Costapolygnathus dubius]BWZ02 P. aequalis Klapper & Lane 1985D02 P. bartensis (Druce 1969)WM03 P. beckmanniN79 P. bicavatusS88 P. biconstrictusS88 P. bischoffi Rhodes, Austin & Druce 1969WM03 P. brevis Miller & Youngquist 1947KU04 P. communis (Branson & Mehl 1934)WM03 |--P. c. communisZP86 `--P. c. carinusZP86 P. corrugatusS88 P. dengleri Bischoff & Ziegler 1957KU04 P. distortusS88 P. diversus Helms 1959KU04 P. elongonodosusS88 P. evidens Klapper & Lane 1985KU04 P. experplexusS88 P. flabellusS88 P. flaccidusS88 P. giganteusS88 P. glaberS88 |--P. g. glaberS88 `--P. g. bilobatusS88 P. homoirregularisS88 P. inflexusS88 P. inornatusS88 P. kockelianusN79 P. latifossatus Wirth 1967D01, AS93 P. lodinensis Pölsler 1969KU04 P. longiposticusS88 P. mehliS88 P. mungeonsisM62 P. nodocostatus Branson & Mehl 1934D02 P. nodosusS88 P. obliquicostatusS88 P. obtectusS88 P. ordinataH62 P. pacificus Savage & Funai 1980D02 P. pennatuloideusS88 P. pennatus Hinde 1879KU04 P. rugosusN79 P. semicostatus Branson & Mehl 1934D02 P. spicatusS88 P. styriacusS88 P. subirregularisS88 P. subnormalis Vorontsova & Kuz’min 1984KU04 P. unicornis Müller & Müller 1957KU04 P. vexatusS88 P. webbi Stauffer 1938 [incl. P. normalis Miller & Youngquist 1947]D02
Polygnathus Hinde 1879BWZ02 [=Costapolygnathus Bardashev, Weddige & Ziegler 2002BWZ02; incl. Eocostapolygnathus Bardashev, Weddige & Ziegler 2002BWZ02, Macropolygnathus Cooper 1939H62]
Polygnathus excavatus Carls & Gandl 1969 [=Polygnathus webbi excavata, Eocostapolygnathus excavatus, P. dehiscens excavatus]BWZ02
*Type species of generic name indicated
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