The Sutural Pattern of Skull-Roof Bones in Lower Permian Discosauriscus Austriacus from Moravia

The sutural pattern of skull-roof bones in Lower Permian Discosauriscus austriacus from Moravia

JOZEF KLEMBARA

Klembara, J. 1994 06 15 The sutural pattern of skull-roofbones in Lower Permian DiKosauricN LETHAIA alcmiacuc &om Moravia. Lethaia, Vol. 27, pp. 85-95. Oslo. ISSN 0024-1 164. Sutures between ornamented bones of Discosaurixuc aumiacuc are mostly simple, but there are also more complicated, rarely serrated, sutures between some bones. In small individuals, the sutures are simple, but the same sutures also occur in the largest specimens. The character of the sutures and the incomplete ossification ofbones around the pineal foramen indicate the larva type of organization of DiKosauriKur The fenestra between premaxihies and nasals appears to be absent. In the majority of specimens, a squamosal-intertemporal sutural contact is present, altho~itissometimesredu~andinafewcasesintermptedbyapostorbitalandsupratemporal contact Therefore the character ‘intertmporal-squamosal suture present or absent’ cannot be used in this rigorous sense for testing the relationshipsof early tetrapods.The configuration of the suture between both parietals in osteolepiforms, Dixosaurixuc, and various early amphibians and reptiles indicates that the bones enclosing the pineal foramen in osteolepifonns are kontals. ODI~~RISCUS.Seymouriamorpha, Lower Permian mapod, skull woskLlcton, sutures. JoZqKlrmbara, Zoological Imthte, Faculty of Natural SCienceJ, Comeniuc University, Mlynskd dolina B-2,&42 15 Bratislava, Slovakia; 30th September, 1992; revised20th April, 1993.

Two localities in the Boskovice Furrow in Moravia (Czech Material, methods and localities Republic) have produced a relatively large assemblage of more or less three-dimensional skeletal material of discosau- The localities and methods have been described by Klembara riscids (Klembara & MeszAroS 1992). Despite certain Mer- & MeszAroS (1992). ences in skull proportions, there are no reliable criteria for The following specimens (skull lengths 17-52 mm) were the determination of more than one species and genus used in this paper (D - locality DrvAlovice, K - locality (Klembara & Janiga 1993). In the following account, the new Kochov): D 18, D 47, D 52, D 69, D 70, D 87, D 208, K 1, K 13, collections of discosasuriscids from Moravia are interpreted K21,K3O,K41,K52,K72,KSO,K99,K 100,K 102,K 138, as one genus and species, Discosautisnrs ausrriacus (Makow- K 139, K 177, K 285, K 323, K 329, K 333, K 334, K 336. The sky 1876). specimens are deposited at Zoological Institute, Faculty of Discosauriscids are considered by most authors to be Natural Sciences, Comenius University, Bratislava. seymouriamorph tetrapods (e.g., Romer 1947; spinar 1952; Smithson 1985; Ivakhnenko 1987; Werneburg 1989), although an unambiguous assignment is not endorsed univer- Skull-roof bones sally (Heaton 1980; Holmes 1984). Detailed descriptions of the skull and the postcranial skel- In Discosaurixus, the dermal skull roof (Fig. 1) consists of all eton will be published in several papers, because this well- the bones normally present in seymouriamorph tetrapods preserved material deserves complete documentation.Many (e.g., Seymouria, White 1939, or Karpinskiosaurus, Ivakh- structures, in particular the sutures of the dermal skull roof, nenko 1987).There is a parietakabular contact, characteris- were previously undescribed. In some respects, this paper tic for Anthracosauria (sensu Save-Mderbergh 1934; 6. also complements the preceding paper (Klembara & Janiga Smithson 1985), one of the group of the reptiliomorph 1993) dealing with the proportional differences in Disco- evolutionary line of tetrapods (muSve-Merbergh 1934, SaUrisnrs. 1935; cf. Panchen & Smithson 1988). Unlike the embolo- The term ‘Anthracosauria’ will be used to include Embo- meres, but like Seymouria and Karpinskiosaurus and prob- lomeri, Gephyrostegidae and Eoherpetontidae (cf.‘Anthra- ablyalso Gqhyrostegus(Carrolll970) and Eoherpeton (Pan- cosauroideae’ sensu Smithson 1985). chen 1975), DiscosaurisncSpossesses a septomaxiUaxy. 86 Jozefk?embara LETHAL4 27 (1994)

Fig 1. Discosauriscus aumiacus (Makowsky 18761, K 13. Skull in dorsal view. Abbreviations: FR - fiond, JU- jugal, IT - intertemporal,LA - lacrimal, MX - maxihy, NA - d,PA - paridPFR - prhond, PO - postorbid,POFR - postfrontal, PP - postparid, QJ- quadratojugal, SMX- septomaxihy, SQ - squamosal, ST - supratemporal,TA - tab*, tr.f. - transverse flange of pterygoid.

Sutures position, or the orientation on a particular bone, is constant. An exception is the postparietal, in,which the median un- The sutures between the ornamented areas of the dermal ornamented area, which is overlapped by the other post- bones of the skull roof are almost always clearly visible. The parietal, is sometimes born by the left (e.g., K 177), and majority of the dermal skull-roof bones form squamose sometimes the right (e.g., D 47) postparietal. sutures, in which part of the edge of one bone overlaps the One of the simplest sutural patterns of the dermal skull unornamented part of the adjoining bone (e.g., parietals- roofofDiscosaurixusispresentinK13 (Fig. l).Theshapeof frontals, Fig. 1). In the region in front of the pineal foramen, the bone and its suture patterns are essentially bilaterally the nasals, hntals and parietals are closely attached at the symmetrical. The sutures between individual bones are midline, and the medial margin of one always fits to a certain simple. Such a ‘basic’ sutural pattern is relatively common degree into an elongated groove in the medial margin of the and does not depend on the size of the specimen. Diversity in other bone. In some skulls, however, these bones have rela- suture patterns is primarily the result ofvariations in size and tively broad unornamented areas (e.g., the left frontal of D shape of the ornamented surfaces, which is much more 87). Neither the lacrimal nor the maxillary form wider un- variable than the shape of individual bones. ornamented areas. The dorsal surface of the unornamented Because the detailed description of individual cranial areas is mostly markedly grooved (Fig. 1). Although the bones will be given in later papers, only the more pro- range of the unornamented areas can vary slightly, their nounced modifications of the relative positions of some LETHAIA 27 (1994) Skull-roof bones of DISCOSAURISCUS87

Fig. 2. Discosautiscusaustiacus (Makowdcy 1876). Skulls in dorsal view. ok K 138. OB. K 139. Abbreviations FR- frontal, IT - intertemporal,PA - parietal, PO - postorbital, POFR - postfrontal, ST - supratemporal.

dermal bones and their ornamented surfaces regarding the bones is short (e.g., D 70 on the right) or fully interrupted condition in K 13 (Fig. 1) will be described here. (e.g., D 70 on the left); Fig. 4B. In some specimens (K 100, K 102, D 208), it is difficult to decide whether the contact was Region of the pineal foramen. - The size of the pineal fora- interrupted or not, because the distances involved are several men varies and does not depend on the size of the specimen. tenths of a millimetre. Moreover, the slight compression of In the majority of specimens, the pineal foramen is com- adjoining bones, often apparent at the junction of the skull pletely enclosed anteriorly by the parietal bones (Figs. 1,2A, table and cheek, may be of some importance. In K 333, 3B, 6). The length of the junction of the ornamented sur- however, a relatively long suture between the supratemporal faces of the parietals anterior to the pineal foramen varies. and postorbital (Fig. 5) completely precludes a squamosal- In some specimens this junction is relatively long (Fig. 2A), intertemporalcontact. This is due partly to a prolongation of but in others (e.g., D 18, K 139) the suture is not closed the posterior edge of the postorbital but mostly to the elon- anteriorly, and the frontal or fronds form part of its ante- gation of the anterolateral edge of the supratemporal (Figs. rior margin (Figs. 2B, 3A). Between the two extremes there 4B, 5). Although skulls show variability in relative width are many intermediate conditions (e.g., D 69, D 70, K 21, (Klembara & Janiga 1993), there is no correlation with the Figs. 3C, 4). This variation derives from the variable shape shorteningof the intertemporal-squamosal suture. A mini- of the anterior ends of the parietals and the posterior ends of mal junction ofthese bones, or its slight interruption, occurs the fiontals (on both right and left sides). As a result, differ- on ‘broad’, as well as ‘narrow’skulls (cf. specimen D 70, Fig. ent combinations of the character and length of the junc- 4B and Klembara & Janiga 1993, Fig. 1OC). It is also related tion of adjoining bones are produced, as well as variation in to the length of the postorbital bone, and/or its posterior the degree of participation of the frontal in the anterior process. It seems that individual variability is involved (cf. border of the pineal foramen. specimens D 69 and D 70, Figs. 4A and 4B). The position of the pineal foramen remains more or less constant; it varies only slightly relative to the anteroposterior Sutures beween the ornamented surfaces of bones. - The extent of the intertemporal. course of the sutures between the ornamented surfaces of individual skull-roof bones is rather variable, as is shown by Intertemporal-squamosul suture. - In the majority of skulls, theextentandshapeoftheseornamentedsurfaces.Thesecan the intertemporal has a lateral common suture with the besubstantidy different on the right and left side of the skull squamosal (Fig. 1). In some skulls the junction of these two - e.g., the parietals of D 18, K 21 (Fig. 3A, C). 88 JozefKlembara LETHAIA 27 (1994)

Fig. 3. Discosauriscus austtianrs (Makowsky 1876). Skulls in dorsal view. OA. D 18. OB. K 30. OC. K 21. Abbreviations: FR - frontal, IT - intertemporal, PA - parietal, PO - postorbital, POFR - postfrontal, ST - supratemporal, TA - tabular.

=oppositepage). DiKosauriscusaumiacus(Makowsky1876). Skulls in dorsal view. OA. D 69. OB. D 70. Abbreviations: FR- frontal, IT- intertemporal, PA - parietal, PO - postorbital, SQ - squamosal, ST - supratemporal; tr.6 - transverse flange of pterygoid. LETHAIA 27 (1994) Skull-roof bones of Dzscos~u~~scus89 90 Jozefl(lnnbara LETHAIA 27 (1994)

Fig. 5. Discosauriscuc avmiacur (Makowsky 1876), K 333. Posterior part of skull roof in dorsal view. Abbreviations: IT - intertemporal, IT, - intertemporal 1, lT2- intatrmporal2, PO - postorbital, SQ - squamosal, ST - supratemporal.

In the median plane, more or less straight or simple dermal bones of the skull roof from the inner and outer side suturesoccuronlybetweenthenasals (e.g.,K 13,Fig. l).InK in Pholiderpeton, Clack 1987, Figs. 17,19). 72 (Fig. 6) the suture deviates to form a sigmoidalpattern at The suture between the ornamented areas of the post- about the mid-length of the nasals. However, this is rare. frontal and intertemporalcan have a different shape and may Between the frontal bones a straight suture also OCCUTS rela- differ on the right and left side of the same specimen (e.g., D tively rarely, but more often it is slightly undulating or more 18, Fig. 3A). A similar irregularity occurs in the junction of sharply folded approximately in the mid-length of bone the lateral margin of the frontal with the postfrontal. In (e.g., D 18, K 138, Figs. 2A, 3A), and in one case (K 72, Fig. 6) several specimens, the frontal bears a distinct process on its is more complicated. Generally, the size and shape of the midlateral margin that fits into a notch in the ornamented ornamented surfaces of the left and right frontals are differ- surface of the postfrontal. Such a type of junction may be ent (e.g., K 30, Fig. 3B). Posterior to the pineal foramen the present on both sides of the skull (e.g., D 18, Fig. 3A) or only interparietal suture may undulate somewhat, while anterior on one side (e.g., K99, Fig. 7D).In the majority of specimens, to the pineal foramen it is mostly straight or only slightly the suture between both bones is simple. curved (Figs. 1-6). Another interestingvariation is seen in K 138 (Fig. 2A),in The variability of sutures between the ornamented sur- which the pointed anterior end of the left parietal wedges faces away from the mid-line is much greater. The sutures are into the narrow, deeply incised posterior region of the left more or less straight, broadly curved or sharply angled (Figs. frontal, the right fronto-parietal suture is of the simple, 1-5). More complex, serrated sutures may occur sporadi- transverse, ‘basic’ type (cf. Fig. 1). A similar condition also cally between two bones in some individuals (e.g., the junc- occurs in K 30 (Fig. 3B) and K 334. tion ofthe left frontalwith the pr&ontal of K 80, Fig. 7B), but A disitiformsuture occurs between the nasal and premax- onlyinK72 isthispatternhighlydevelopedthroughout (Fig. illary (e.g., K 336, Fig. 7A) and often between the nasal and 6). The serrated sutures in K 72 are not equally complicated lacrimal (e.g., D 18, K 72, Figs. 3A, 6). In some specimens, the between all the bones (e.g., between the posteromedial por- posterior portion of the median wall of the premdary tion of the omamented part of the parietal and the corre- (e.g., K 177) bears a dentate, medially projecting edge, indi- sponding margin of the postparietal, the suture is relatively cating that this type of suture is also present between the simple, Fig. 6). At several points in the skull (e.g., in the posteriormost portions of both premaxihies in the mid- region of the junction of parid and frontals or the post- line. This type of junction between premmucillaries and nasals orbitals and intertemporals, or on the right nasal) it can be and between both premaxihies indicates the absence of a seen that this complicated suture passes only between the fenma between the premaxihies and nasals in Discosau- ornamented surfaces of individd bones. In some bones rixus (contra Werneburg 1985 - ‘medianes Internasalfen- (e.g., the left postfiontal), the margins of the unomamented ’ ster’, and Ivakhnenko 1987 - ‘fontanellebetween the dorsal areas are also slightly serrated (cf. the outlines of some processes of premdaries’). LETHAIA 27 (1994) Skull-roof bones of DISCOSAURISCVS91

Fig. 6. Di~~sau~aumiacuc (Makowsky 1876), K 72. Slcull in dorsal View. Abbreviations: FR - frontal, IT - intertemporal, P - jugid, LA - hd, NA - nasal, PA - parietal, PFR - prefrontal, PO - postorbital, POFR - postfrontal, PP - postparietal, SQ - quamod, ST - supratemporal, TA - tabular.

A similar serrated suture occurs between the ornamented the exception of a degree of variabilityin the intertemporal- parts of the supratemporaland squamosal (the left side of K squamosal, and/or postorbitakupratemporal junctions. 13, the right side of D 52, Figs. 1,7C). Lehman (1967) argued that the value of the tabular-parietal It should be noted that the complexityof sutures between contact as a character defining the reptiliomorph evolution- the ornamented surfaces of individual dermal skull-roof aryline (Save-Werbergh1934,1935) isweakbecauseofthe bones does not correlate with the size of the specimen; e.g., variation in the development ofthe dermal skull-roofbones. the simple sutures are in small (e.g., K 41, K 285, D 208) and A similar opinion was expressed by Boy (1972), who de- also the largest specimens (e.g., K 52, K 323, K 329) (Klem- scribedtheparietal-tabularcontactinsomespecimensofthe bara & Janiga 1993, Fig. 11). dissorophoid amphibian Microme2erpeon In these animals Discosauriscus shows a great individual variability in the the supratemporal-postorbital contact, and/or the parietal- course and complexity of sutures, and this is reflected in the tabular contact depends on the relative widths of the tabular size and shape of the ornamented areas of the dermal skull- and postparietal. Smithson (1986) recorded the postparie- roof bones. Nevertheless, no significant changes in the mu- thl-supratemporal suture on the ventral side of the skull roof tual position of individual bones have been recorded, with of embolomere anthracosaurProterop’nwpancheni How- 92 Jozefl(lembara LETHAIA 27 (1994)

Fig. 7.~wu~aus~ (Makowsky 1876). OA. K 336, premaxillaries from outside. OB.K 80, serrated suture between left frontal and prefrontal. OC. D 52, junction of supratemporal and squamosal. OD.K 99, outlines of frontals, right prefiontal and postfrontal. Abbreviations: SQ - squamosal, ST - supratemporal;j.g.s. - squamosal section of jugal sensory groove. ever, in Discosaurisnrs, where abundant skull material is supinator process, and (3) expanded neural arches, argued available, no example of the interruption of the parietal- that discosauriscids should be included with gephyrostegid tabular contact has been recorded, indicating that it is a amphibians. The transverse flange on the pterygoid (tr.f,, constant and probably reliable taxonomic character. Figs. 1,4A) isverywelldevelopedinDiscosauriscus(e.g.,K 13, D 69), exactly as in Seymouria (White 1939). The humerus and the medial parts of neural arches are poorly ossified, and Comparisons and discussion it is therefore diflicult to consider unambiguously Heaton’s second and third criteria in the evaluation of the systematic The family Discosauriscidae was established by Romer position of discosauriscids. For the present, there is no justi- (1947), who placed it in the Seymouriamorpha Watson, fication in removing the discosauriscids from the Seymou- 1917, an assigment that is still generally accepted (Carroll riamorpha. Heaton (1980) also regarded the seymouria- 1988). However, Heaton (1980), on the basis of the absence morphs as a group of advanced, non-anthracosaur amphib- of: (1) a transverse flange on the pterygoid, (2) a distinct ians closely related to reptiles. Smithson ( 1985) disputed the LETHAIA 27 (1994) Skull-roof bones of DISCOSAURISCUS93 validity of the criteria that Heaton ( 1980) used to remove the acter ‘squamosal-intertemporal suture present or absent’ Discosauriscidae from the Seymouriamorpha. As noted by (Gauthier etal. 1988) cannot beapplied in this rigoroussense Smithson (1985,p. 383): ‘In members of the three families for the testing of relationships of early tetrapods. Discosauriscidae, Kotlassiidae and Seymouriidae, the squa- The type of sutures between skull-roof bones is similar mosals extend forward to contact the intertemporal, a with those in larval or neotenic tetrapods (e.g., branchio- unique condition among tetrapods’. According to Smithson saurids Boy 1978, 1987; Werneburg 1989). An intricate ( 1985), this condition and the extension of the otic capsules serrated suture such as those in K 72 (Fig. 6) also seldom to theotic tubes were probably derived characters represent- occurs in branchiosaurids (e.g., Boy 1986). The simple su- ing the synapomorphies unifying all three families as a tures are present also in the biggest specimens of Discosau- monophyletic group. rixus. This fact, as well as the incomplete ossification of Here, two remarks may be made. First, in several embolo- parietals and fiontals in the region ofthe pineal foramen (see meres (e.g., Prorerogvinus, Holmes 1984, Archeria, Holmes below), indicate the larval type of organization of Discosau- 1989; Pholiderperon, Clack 1987) or in Gephyrosrtegus (Car- riscw. roll 1970) the squamosal extends forward to the level of the White (1939)described a crenulated suture between the intertemporal but does not contact it; the postorbital joins nasals and premaxillariesin Seymouria. In Discosauriscus,the the supratemporal for a short distance, as may also occur in same basic type of suture is frequently present between these discosauriscids (Fig. 5). But if Romer’s (1963)observations bones (Figs. 3A, 7A), although the sutures between the other on the remains of the cranial skeleton of Neopreroplar cone- bones of the skull roof of the same specimen are simple. rnaughensis are correct, there was an intertemporal-squa- The participation of the posterior margins of the fiontals mosalcontact in thisembolomere. Itcannotbeexdudedthat in the border of the pineal foramen is known not only in a similar condition also occurred in some specimens of ~osauriscus,but also in branchiosaurids (e.g., Boy 1972, Gephyrosregus (Carroll 1970, Fig. 6A). Second, the squarno- PI. 21; Werneburg 1986, Figs. 2, 4). The position of the sal-intertemporal contact is not always present in all speci- pineal foramen does not vary in Discosaurixus only occa- mens of the family Discosauriscidae; the same is true for sionally does its anterior margin extend slightly beyond the someother representativesoftheSeymouriamorpha(Ivakh- level of the anterior margin of the intertemporal. However, nenko 1987). In teproropha and Biarmica (Ivakhnenko the degree of ossification (and hence the shape of those 1987, Figs. 9 and 12, cf. Fig. 5 here) a distinct short suture is regions of the bones bordering the pineal foramen) does present between the ornamented surfaces of the postorbital vary; the extent of the anterior regions of the parietals, or the and supratemporal. However, on the ventral side of the posterior regions of the fiontals may also vary relative to the dermal skull roof of the figured specimen of Loptotopha,the level of the anterior margin of the intertemporals (cf. condi- squamosal-intertemporal suture is present (Ivakhnenko tions in two specimens of the same size - K 138 and K 139, 1987, Fig. 9). As noted above, in the majority of Moravian Figs. 2A and 2B). Discosauriscus specimens the squamosal-intertemporal In many specimens of Discosauriscus, the suture between contact is preserved, but in some specimens this contact can the parietals in the region behind the pineal foramen is be reduced to a minimum or be fully interrupted (Figs. 1,4B, undulating to a variable degree (Figs. 1-6). This condition 5). A similar condition occurs in Utqenia shpinari; in the can be observed in various reptiliomorphs (e.g., Seymouria, smallest specimens of this species the squamosal and inter- White 1939, Fig. 1; Gqhyrosregus, Carroll 1970, Fig. 1; Ar- temporal probably only share a point contact. In larger cheria, Holmes 1989, Text-figs. 7,8; Eocuprorhinus, Heaton individuals, however, this contact is fully interrupted, and 1979); as well as in the larvae, juveniles and adults of various the postorbital joins the supratemporal in a wide suture temnospondyls(e.g., branchiosaurids, Boy 1972,1987;Scle- (Kuznetsov& Ivakhnenko 1981; Ivakhnenko 1987). In Dis- rocephahs, Boy 1988; Saurerperon, Milner 1982). In some cosauriscus, however, a well-developed squarnosal-inter- tetrapods,the opposite situation occurs, i.e. a more undulat- temporal suture, a point contact and the completeintenup- ing suture is situated in front of the pineal foramen (e.g., tion of this contact all occur in various middle-sized CoeloJtegW, Carroll & Baird 1972). In Coelosregus, however, specimens (K 13, K 102, D 70, K 333, Figs. 1,4B, 5). The thepineal foramenliesin theposterior portion oftheparietal number of small specimens is limited, but the conditions length. It may be added that, in the majority of tetrapods, seem to be the same, indicating that the variability of the only this anterior portion (approximatelyone third) of the contact of these two bones is not simply a matter of early suture between the parietals is more or less straight and is ontogenetic development. In Arieknerpeton, the squamo- situated approximately in the median plane. The posterior, sal-intertemporal contact can be relatively broad (Ivakh- longerportionofthesuture,ontheotherhand,isundulating nenko 1981, 1987, Figs. 3,5),as in Discosauriscus (Fig. 1). to a variable extent. However, this condition also exists in There is a degree of variability in this character, not only many osteolepiforms (cf. Save-Sijderbergh 1933, p. 77: ‘The within the described species of the family D~uriscidae, median suture between the parietals consists of a longer, but also throughout the entire Seymouriamorphaand prob- anterior part, always straight on the whole, and generally ably also within the Anthracosauria. Consequently,thechar- crenulated most posteriorly, and a posterior part, which is 94 Jov$K&mbara LETHAIA 27 (1994) most often bent and convex towards the left side of the head Heaton, M.J. 1979 Cranial morphology of primitive captorhinid reptiles (spec. ...), likewise bent, but convex towards the right side in from the late Pennsylvanian and early Permian, Oklahoma and Texas. Bulletin of the Oklahoma Geological Survq. 127,1-84. specimens ..., and irregularly curved in specimens ...’.). The Heaton, M.J. 1980 The Cotytosauria: a reconsideration of a group of bones which Save-saderbergh (1933)calls parietals, Westoll archaic tetrapods. In Panchen, A.L. (ed.):The Terrestrial Environment (1938,1943) and Romer (1941) call the postparietals. and the Origin ofhnd Vertebratts, 497-551. Academic Press, London. However, the above comparisons are only possible if one Holmes, R 1984: The Carboniferous amphibian Proterogyrinuc scheclei Romer, and the early evolution of tetrapods. Philosophical Transactions accepts the terminology of the dermal skull-roof bones in of the Royal Society of London B 3@5,431-527. osteolepiforms, used by Sve-siiderbergh (1933), Jarvik Holmes, R 1989 The skull and axial skeleton of the Lower Permian (1944 and in litt.), Jessen (1966), Long (1985, 1989) and anthracosauroid amphibian Archetia massidisca Cope. Palaeonrogm- others. According to these authors, the bones situated imme- phicn A 207,161-206. Irakhnenko. M.F. (Mnamiemo M.Q.) 1981: Dhsauriscidae from the diately anteriorly to the exhascapular bones in osteolepi- Permian of Tadzhikjstan. Paleontologicheskij Zhurnal1981:1,114-128. forms are parietals, not postparietals (as suggested by (In Russian.) Westoll 1938, 1943 and Romer 1941). In many osteolepi- Ivakhnenko, M.F. (MnaxnemoMD.) 1987: PermianparareptilesofUSSR form fishes, the suture between the parietals, approximately TrudyPalcontologicheskogoIm’rumANSSSR223,1-160.(In Russian.) Jarvik, E. 1944: On the dermal bones, sensory canals and pit-lines of the in the portion of the posterior two-thirds, is more or less skull in Euctttenopetronfoordiwhiteaves, with some remarks on E slive- undulating, as in early tetrapock, while the anterior third of s(kiertnrgfiiJarvik. Kungliga Svenska VetenskapsakademiensHandlingar its course remains straight (Siive-sijderbergh 1933, Pls. 4; 21:3, 1-48. 101;Jarvikl948,Pls. 1:1;3:4;9;27;29;30; 1950,P1.5:1; 1985, Jarvik,E. 1948 On the morphology and taxonomy of the Middle Devonian osteolepid fishes of Scotland. Kungliga Svmka Vetmkapsakademiens Fig. 29A; Jessen 1966, Figs. 1,2;PL 52; Schultze 1984, Fig. 4; Handlingar 253, 1-301. Long 1985, Fig. 1; 1989, Fig. 1,4D). Although this character Jarvik. E. 1950 On some osteolepiform CrossopterYgianS from the Upper is not decisive, it supports theview that these dermal bones in Old Red Sandstone of Scotland. Kungliga Svmka Vetmkapdde- osteolepiforms are parietals, despite the absence of a pineal miens Handlingar 2:2, 1-35. Jarvik,E. 1967: The homologies of frontal and parietal bones in fishes and foramen between them (Jarvik 1967; Klembara 1992). tetrapods. Colloqucc internationaux du Centre National de la Reherche AcknowLdgementr - For reading and linguistic correction of the manu- Scienti$qu~163,181-213. saipt, I am indebted to Dr. AR Milner (Birkbecl~College, London). For Jarvik,E. 1985 Devonian osteolepiform tishes from East Greenland. Med- the making of the photographs and the typing of the manuscript I thank delelser om Grlcnland, Geoscience 13,l-52. Mrs Z ~ulavhvi(Faculty of Natural Sciences, Bratislava). Jessen,H. 1% DieCrossopterygierdesOberenPlattenkalkes(Devon)der Bergisch-Gladbach-PafhtherMulde (Rheinisches schiefergebirge) unter BerUcksichtigung von amerikanischem und europWem Ony- References ChodUcMateriaJ. Arkivfllr Zoologi 18:14,305-389. Klernbara, J. 1992 The first record of pit-lines and foraminal pits in Boy, JA 1972: Die Branchiosaurier (Amphibia) des SaarpFdlziSchen Rot- tetrapods and the problem of the skull roof bones homology between Iicgenh (Perm, SW-htschland). Hasiwha hndesamtfir Boden- teCrapods and fishes. Geolopa Capthicn 43:4,24!%252. fmUhung65,1-137. Klernbara, J. & Janiga, M. 1993 Variation in Dixosaurisncc aumiaw Boy, JA 1978 Die Tetrapodcnfa~~(Amphibia, Reptilia) des ~aarpW- (Maltowsky 1876) from the Lower Permian of the Boskovice Furrow denRotliegenden (Unter-Pem, SW-Deutschland). 1. Branchiosau- (Czechoslovakia). Zoological Journal of the Linnean Society 108, nu. Mainzrpwhtdafliche Mittdungen 7,27-76. 247-270. Boy, JA 1986 Studien Uber die Branchiosauridae (Amphiba Temno- Klernbara, J. & MWoJ, s. 1992 New finds of Discosaurisncc audaus spondyii) 1. 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Lethaia Seminar Lethaia, Vol. 27, pp. 95%. Oslo, 1994 06 15

Nautilus - model or muddle?

DAVID K. JACOBS AND NEIL H. LANDMAN

Paleontologistshave dominated research on modem Naurihcz Samdem & exits well below the center of mass, causing rotation. Lack of stability has Ward (1994)appear to argue that these studies were not intended to thereforebeen mvoliedas a constrainton ammonoid swimming (Mutvei & develop NautiZus as a ‘model’for fossil cephalopods, and that they howof Reyment 1973; Ebel1990; Chamberlain 1981). However, in long-bodied no ‘instance where NautiZus has served as a strict analogue for infaring Mesozoic ammonoids the force of the jet may not have exited the shell biological function in any group of ammonoids’. We use the term model in below the cente-r of gravity, and the stability argument need not apply. We ourdiscussioninthesthat‘model’or‘m~o~~come~be also present arguments countering interpretations of ammonoid func- usedinbiology,asanexemplar~loredindetailinthehopeofdiscovering tional morphology based on the function of Nautilus musculature. generalitiesthat may apply to a broader range of taxa (e.g., Kdog &,%a& Students of modem cephalopods have also used NautiZus as a proxy for 1993). Previous work (e.g., Mutvei & Reyment 1973; Reyment 1973,1980; thelocomotorypropertiesofanaent or primitive (read fossil) cephalopods Ebel 1990, Chamberlain 1981) that appkd results generated &om the (e.g., O’Dor & Wells 1990, Wells & O’Dor 1991). The first lines of a paper study of NautiZus to the interpretation of locomotion in ammonoids by Wells &Wells (1985)read ‘Because it is the only surviving cephalopod provided the impetus for our paper. In large part, our &rtwas direaed at with an extend shell, representingmore than two thousand extinct genera thesestudieswheretheredoesappeartobeadear,andweargueincorrect, of Nautiloids and Ammonoids, Nautilus has long been of peculiar interest interpretation of ammonoid function based on data generated &om the to zoologistf and paleontologists [italics added].’ In one of the more telling study of modem NautiZus. Many of these works appear to be internally examples of this approach, a Nautilus was dressed up as an ammonoid. A inconsistent. For example, stability is important in Naurilurbecausethejet rubber covering acoutered with ornament thought to be typical of at least