POHLSEPIA MAZONENSIS, AN EARLY `' FROM THE OF ILLINOIS, USA

by JOANNE KLUESSENDORF and PETER DOYLE

ABSTRACT. Pohlsepia mazonensis gen. et sp. nov. from the Mazon Creek Konservat LagerstaÈtte (Carboniferous) of Illinois is an exceptionally preserved soft-bodied fossil coleoid, with well-de®ned body and arms. Lacking an internal shell and possessing eight subequal and two modi®ed arms, Pohlsepia can be compared with both the living cirrate octopods and the decabrachian sepiardarids, both of which lack a well-developed internal skeleton. Given its sac-like body, lack of a well-de®ned head and presence of ®ns, Pohlsepia can be safely compared with modern cirrate octopods. It is the oldest known completely soft-bodied coleoid and as such has great signi®cance with respect to the phylogeny of the group, given that both the octobrachian and decabrachian clades have previously been thought to have evolved in the .

KEY WORDS: , Octobrachia, Konservat LagerstaÈtte, Mazon Creek, Carboniferous.

T HE preservation of with the soft parts intact is relatively uncommon in the fossil record, and is common only within the Coleoidea, a group which includes belemnoids and the familiar living , cuttle®sh and octopods. The majority of known records are of Mesozoic coleoids, and these have effectively been derived mostly from the Jurassic and Konservat LagerstaÈtten of Europe and the Middle East. A notable exception to this is the Upper Carboniferous Mazon Creek fauna of Illinois, USA, which famously preserves the soft parts of a wide range of phyla within sideritic concretions. Although many cephalopods have been recovered from the Mazon Creek fauna, soft parts are rare even here, and this deposit has yielded specimens of some of the oldest coleoids with soft-part preservation, including the ten-armed Jeletzkya douglassae (Johnson and Richardson 1968; Saunders and Richardson 1979), the origins of which have been much debated, and at least one other possible teuthid form (Allison 1987). The specimen described herein is one of the best preserved cephalopods recovered from the Mazon Creek fauna, and is preserved with arms, indistinct head, and body intact. It is unlike Jeletzkya douglassae, which has been interpreted as a belemnoid, although this is still in debate (D. T. Donovan, pers. comm. 1999), and although it has some morphological similarity to the specimen described by Allison (1987), the excellence of its preservation, and the absence of any shelly material, either externally or internally, provides an important record of great phylogenetic signi®cance. The aim of this paper is, therefore, to describe in detail the specimen, to compare it with known taxa, and to discuss its wider phylogenetic signi®cance.

STRATIGRAPHY AND DEPOSITIONAL SETTING The Mazon Creek LagerstaÈtte occurs within the Upper Carboniferous (Westphalian D: Pennsylvanian in North America) Francis Creek Shale Member of the Carbondale Formation in north-eastern Illinois. The Francis Creek Shale was deposited in a deltaic setting where high sedimentation rates effected rapid burial that resulted in the extraordinary fossil preservation within early diagenetic siderite concretions. Two biotic associations occur in this LagerstaÈtte: the Braidwood biota contains terrestrial plants and a variety of freshwater terrestrial organisms; and the Essex biota, which is dominated by a planktonic and nektonic taxa representation of nearshore marine to brackish water conditions (Richardson and Johnson 1971). The distribution patterns of these biotas delineate the limit of marine conditions and the transition to a swamp environment (Richardson and Johnson 1971). The type area for the Essex biota is the former Pit Eleven strip mine of the Peabody Coal Company in Will and Kankakee counties, Illinios (Johnson and Richardson

[Palaeontology, Vol. 43, Part 5, 2000, pp. 919±926] q The Palaeontological Association 920 PALAEONTOLOGY, VOLUME 43 1966; Richardson and Johnson 1971). Most Mazon Creek cephalopods, including the specimen described herein, were collected from the Essex biota at Pit Eleven (see Saunders and Richardson 1979).

SYSTEMATIC PALAEONTOLOGY

Class Cephalopoda Cuvier, 1797 Subclass Coleoidea Bather, 1888 Order ?Cirroctopoda Young, 1989

Genus Pohlsepia gen. nov.

Derivation of name. The genus is named in honour of James Pohl of Minnesota, formerly of Belgium, Wisconsin, who collected and donated the specimen to the Field Museum of Natural History. Jim regularly accompanied his father Joe Pohl, noted fossil collector, dairy farmer, and adventurer, on collecting trips to the strip mines of Illinois. Both Jim and Joe have collected many new taxa from the Mazon Creek LagerstaÈtte, which they have shared with the scienti®c community and generously donated to museums.

Type species. Pohlsepia mazonensis sp. nov.

Diagnosis. Shell absent; subcircular in outline and sac-like; dorsal mantle fused to indistinct head; ten circumoral appendages comprise eight equal arms and two arms modi®ed as tentacles; lobate ®ns longer than wide and free.

Pohlsepia mazonensis gen. et sp. nov. Text-®gure 1

Derivation of name. The new species is named for the well known Mazon Creek LagerstaÈtte where the holotype was found.

Diagnosis. As for genus.

Type specimen. PE51727, Field Museum of Natural History, Chicago, Illinois, USA.

Description of holotype. The specimen (Text-®g. 1) is exceptionally well preserved, providing a ventral view of its low relief, and is represented as a slight colour difference within the dark greyish brown siderite concretion, which is 80 mm long and 50 mm wide. Light coloured features in the concretion to the left posterior (and possibly to the right anterior) of the specimen probably represent ¯uids expressed from the after burial. Distinct body, head and arms can be distinguished, as well as a number of internal and delicate external features. The body of the coleoid, which has been compressed dorsoventrally, is subcircular and 35 mm wide at its broadest point, with two distinct and symmetrical ®ns at its anterior. These ®ns are narrow and con®ned to the posterior margin of the coleoid. The mantle appears to have crumpled slightly, causing the posterior ®ns to tilt slightly to the anterior. An internal feature to the posterior of the coleoid may be interpreted as either an or a gut trace; ink sacs are common in Mesozoic coleoids, and the ¯ask-like form of the trace is reminiscent of these. However, it is unusual for

TEXT-FIG. 1. A, Pohlsepia mazonensis, gen. et sp. nov., holotype, in siderite concretion, Upper Carboniferous (Westphalian D), Francis Creek Shale Member, Carbondale Formation, near Braidwood, Will County, Illinois; ´ 1´9. B, drawing of Pohlsepia mazonensis gen. et sp. nov.; ´ 1´9. Abbreviations: e, eye; ef, expressed ¯uid; f, ®n; fu, funnel; is?, ink sac (or gut trace); m, mandibles; ma, modi®ed arm (tentacle); r, . KLUESSENDORF AND DOYLE: CARBONIFEROUS `OCTOPUS' 921 922 PALAEONTOLOGY, VOLUME 43 the ink not to be preserved, as the melanin of coleoid ink is stable. A similar feature was also described from Allison's specimen of an unknown coleoid (Allison 1987). The specimen shows no sign of any internal shell or . The head is identi®able but indistinct from the body, and possesses mandibular architecture, eyes, a funnel and arms. Mandibles and radula are preserved in the head region as strong impressions. The mandibles are articulated, although crushed and dif®cult to identify, and the radula is preserved in situ between them. Radula are commonly preserved in many of the Mazon Creek cephalopods. However, unlike these, the present specimen has its radula obscured by matrix and is otherwise unidenti®able. A short funnel may be visible at the anterior centre of the head, indicating the ventral aspect of the view, and is distinct and broadly central although no cartilagenous locking apparatus is present. The eyes are preserved as small patches of dark pigment which are spaced on either side of the well-de®ned head, and the dark pigmentation is a typical feature of eyes in Mazon Creek vertebrates. The arm crown is indistinct, although its component arms are clearly circumoral, and both short arms and longer modi®ed arms (tentacles) may be distinguished. Only the right appendages are well preserved (left as seen in the ventral view), and comprise what appears to be four short arms (only three are de®nitely visible) and one longer tentacle. No hooks are present and suckers are not visible.

Comparison with Jeletzkya douglassae. Jeletzkya douglassae is a well-known coleoid from the Mazon Creek fauna (Johnson and Richardson 1968; Saunders and Richardson 1979) but may be distinguished from the current specimen on the following characteristics: an arm crown comprising ten subequal arms; distinct arm-hooks; a torpedo-like body shape; and an indistinct shell. These features have led to a general acceptance that this taxon represents the soft-body parts of a belemnoid, although whether a true belemnite or an aulacocerid is still under debate (Doyle et al. 1994; Pignatti and Mariotti 1995; D. T. Donovan, pers. comm. 1999). Pohlsepia mazonensis is distinct from this taxon in the presence of a differentiated arm crown, the absence of hooks and an internal shell, and in the subcircular body shape.

Comparison with Allison's specimen. Allison (1987) has described a ten-armed coleoid from the Mazon Creek fauna which he did not name. The specimen is poorly preserved and is elongate, with the head and arms extended. The body is globular and preserves posterior lateral ®ns which are similar in morphology to that of the specimen currently under investigation. No mandibles or radula are preserved or described, but identi®able eyes and possible ink sac or internal gut trace are amongst the features discussed. The ten arms are elongate and lacking their anterior tips. However, it is possible that they are differentiated and in this way are similar to the specimen currently under discussion. In general terms, Allison's specimen may be safely compared with the current one and is in all probability representative of Pohlsepia. Allison's specimen has suffered some form of post-mortem contortion, with the head back and has been compressed dorsolaterally. This explains some of the basic structural differences, but it is otherwise similar to Pohlsepia in the form of its globose body, in the presence of posterior ®ns, and in the absence of any internal shell residue.

SYSTEMATIC POSITION OF POHLSEPIA General comments A recent classi®cation of the Coleoidea has argued for division into three major groups: the Hyatt, 1884, the Decabrachia Boettger, 1952 and the Octobrachia Fioroni, 1981 (Doyle et al. 1994; an alternative is presented in T. Engeser' s web site, the Fossil Coleoidea Page, http://userpage.fu-berlin.de/ ,palaeont/fossilcoleoidea/welcome.html). These divisions are made on the basis of the shell and importantly, of the arm crown. Belemnoids have ten equal arms, usually with hooks; octobrachids have ten arms in which the second pair is modi®ed or lost, while the decabrachids have ten arms in which the fourth pair have been modi®ed into tentacles. All three have some form of shell, although this may be modi®ed, particularly with regard to the phragmocone. Typically, the belemnoids have an entire phragmocone with a counterbalancing rostrum, the decabrachids have a modi®ed phragmocone, usually ventrally open or absent, while the octobrachids typically have no phragmocone and just a dorsal vestige of the shell. Current authorites record the earliest undoubted coleoids (the belemnoids) as early , with both the octobrachids and decabrachids appearing in the Jurassic (Doyle 1993; Doyle et al. 1994). These ®nds KLUESSENDORF AND DOYLE: CARBONIFEROUS `OCTOPUS' 923 are based mostly upon shell material, although some notable arm crown material, particularly that of Jeletzkya, has con®rmed the presence of coleoids with ten subequal arms in the Carboniferous. The absence of an identi®able shell in Pohlsepia is therefore signi®cant and demonstrative of a much earlier origin for the Decabrachia/Octobrachia than has previously been envisaged. The following discussion attempts to examine the position of Pohlsepia in relation to the two main groups with shell modi®cation.

Pohlsepia as a decabrachid The Decabrachia Haeckel, 1866 comprises coleoids which commonly have a reduced internal shell and which have synapomorphy in the modi®cation of the fourth pair of arms in the arm crown (Engeser 1990; Doyle et al. 1994; and T. Engeser's web site, the Fossil Coleoidea Page, see above for address). The group includes several coleoids in which the shell is mostly plesiomorphic, notably the which has a multilayered conotheca with aragonitic rostrum, but it also includes the Teuthida (Doyle et al. 1994). The presence of ten arms, absence of hooks, the free posterior lobate ®ns, and the fusion of head and funnel to the mantle observed in the current specimen are consistent with decabrachian af®nities for this specimen. The body shape and lack of clearly de®ned head rule it out as a potential oegopsid ancestor, while the absence of shell places it apart from the otherwise plesiomorphic condition of many decabrachians. However, owing to the excellence of the preservation of this specimen, direct comparison may be made to modern sepiadariids, a family of sepiids (or sepiolids; D. T. Donovan, pers. comm. 1999) with no known fossil record. The general characterisics of Pohlsepia, in particular the absence of an internal shell and the small size of the specimen described (mantle length of 2´5 cm), correlates well with that observed in the sepiadariids, which have mantle lengths ranging from 2±4 cm (Lu et al. 1992). It seems unlikely, however, that Pohlsepia can be assigned to this group because of the absence of a shell, which is an apomorphy for only select groups of the decabrachia. This suggests divergence at a much earlier stage in the Palaeozoic than has previously been suggested (Text-®g. 2). Although one could postulate that the absence of a shell would militate against preservation of potential sepiardariid ancestors, it is less easy to explain why a shelled ancestor for the Decabrachia, representative of the plesiomorphic condition, would not have been discovered in rocks of pre-Mazon Creek age (Text-®g. 2).

Pohlsepia as an octobrachid The Octobrachia Haeckel, 1866 includes coleoids which commonly have a reduced or absent internal shell and which have synapomorphy in the modi®cation or loss of the second pair of arms in the arm crown (Engeser 1990; Doyle et al. 1994; and T. Engeser's web site, the Fossil Coleoidea Page). The group includes the fossil Teudopsidae and Trachyteuthididae (which have strong vampyromorph af®nities), the Vampyromorpha, the cirrate and incirrate octopods, and the fossil Loligosepiina (Doyle et al. 1994). Of these, only the octopods lack any form of shell, and Pohlsepia may be directly compared with the octopods and particularly their fossil representatives. Pohlsepia may be considered as an octopod on the basis that: (1) it does not possess a well-de®ned head; (2) it has a sac-like body; and (3) the ®ns resemble those of cirrate octopods. Engeser (1988) has reviewed the known fossil soft-bodied representatives of the octopods, namely the genus Woodward, 1896 and mid Jurassic genus Proteroctopus Fischer and Riou, 1982. Palaeoctopus is identi®ed as an undoubted octopus and has much in common with Pohlsepia. Palaeoctopus has no identi®able shell, eight subequal arms (with suckers), a sac-like body, a poorly de®ned head, and free posterior ®ns (Woodward 1896; Robson, 1930). According to Engeser (1988), Proteroctopus is less convincing because, although it too has no shell and eight arms, it has a clearly de®ned head. It also has clearly de®ned ®ns. Engeser (1988) has postulated that this genus may be either a `teuthid' or a stem-group octopod. The octobrachian af®nities of Allison's (1987) Mazon Creek , here reassigned to Pohlsepia mazonensis, have been recently discussed by Engeser (1990). Importantly, the af®nity of this specimen seemed to Engeser to hinge on the nature of the sac-like body, as this feature is an autapomorphy of the Octopoda (Berthold and Engeser 1987; Engeser 1990). Engeser (1990) considered that the specimen could 924 PALAEONTOLOGY, VOLUME 43

TEXT-FIG. 2. Revised phylogenetic tree for the Coleoidea in the light of the discovery of Pohlsepia mazonensis. Two alternatives are presented based on the opposing trees of Engeser (unpublished but available on Engeser's web site, the Fossil Coleoidea Page) in the upper ®gure and Doyle et al. (1994) in the lower one. In both, Pohlsepia is presented as a stem octobrachian, rather than a decabrachian, as this avoids the need for more than one shell reduction in the decabrachians. represent a stem lineage of the octopods, before differentiation of the second arm pair. The discovery of an additional, better preserved specimen with a de®nite sac-like body is supportive of Engeser's tentative conclusions, and given the weight of evidence it is here proposed as an early stem group octobrachian (Text-®g. 2). KLUESSENDORF AND DOYLE: CARBONIFEROUS `OCTOPUS' 925 Phylogenetic signi®cance of Pohlsepia Although there is much current debate over the heirarchical architecture of the Coleoidea at higher levels, most palaeontologists agree that the origins of the Coleoidea lie in the late Devonian and early Carboniferous with the development of the shelled Belemnoidea, and speci®cally the (Engeser 1990; Doyle et al. 1994; and T. Engeser's web site, the Fossil Coleoidea Page). Jeletzkya, a ten- armed coleoid from the Mazon Creek fauna is taken as an early example of this group and has ten subequal arms in its arm crown, and the presence of a shell. The development of primarily soft-bodied coleoids with modi®ed arm crowns has been taken to be primarily Mesozoic, with the ®rst, internally-shelled, representatives of the Octobrachia (the Loligosepiina) appearing in the late , the ®rst cirrate octopods in the Cretaceous, and the ®rst representatives of the Decabrachia (Loliginidae/`') appearing in the late Jurassic (Doyle et al. 1994; Text-®g. 2). Most authorities accept that some form of shell-reduction had taken place within the Coleoidea from the ®rst appearence of the group, and that this took the form of the loss of a guard or rostrum, and the progressive reduction of the phragmocone (Donovan 1977). It is likely that the simplest assignment is to the octobrachia, and speci®cally the cirrate octopods (order Cirroctopoda). This avoids the need to postulate shell reduction more than once in the decabrachian clade (Text-®g. 2). The discovery of Pohlsepia is signi®cant as it extends the range of the Octobrachia back into the Carboniferous, and therefore reopens the debate over whether the loss of the plesiomorphic shelled condition occurred earlier in the fossil record. Clearly, for the Coleoidea to be considered as a monophyletic group (Engeser 1990) its origin from a single ancestor possessing the plesiomorphic characteristics of a phragmocone and other shell material must have taken place earlier in the Palaeozoic than has previously been considered, and that diversi®cation to produce the modi®ed octobrachian (and/or decabrachian) condition must have taken place in at least the Carboniferous (Text-®g. 2). The absence of shell material would support the contention that the fossil record is selective, but the absence of more common shelled representatives of both groups further down the record is troubling.

Acknowledgments. Joanne Kluessendorf thanks Jim and Joe Pohl for their continued generosity and long-suffering patience. Desmond Donovan kindly commented on a draft of this paper.

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JOANNE KLUESSENDORF Department of Geology University of Illinois Urbana, Illinois 61801, USA e-mail [email protected]

PETER DOYLE School of Earth and Environmental Sciences University of Greenwich Pembroke, Chatham Maritime Typescript received 26 June 1999 Kent, ME4 4TB, UK Revised typescript received 20 March 2000 e-mail [email protected]