Palaeololigo oblonga ( Wagner, 1859 )

Donovan, D. T. & Strugnell, J. M., 2010, A redescription of the fossil coleoid cephalopod genus Palaeololigo Naef, 1921 (Decapodiformes: Palaeololiginidae) and its relationship to Recent squids, Journal of Natural History 44 (23 - 24), pp. 1475-1492 : 1478-1486

Palaeololigo oblonga ( Wagner, 1859)

( Figures 1–2 , 4A–F )

Teuthopsis oblonga Wagner, 1859 , col. 276 (Solnhofen formation, Daiting: holotype lost). Wagner, 1860 p. 798, pl. 24, fig. 2.

Palaeololigo oblonga Naef, 1921b, p. 146 . Naef 1922, p. 148. Engeser 1988, p. 75. Frickhinger 1994, fig. 139. Frickhinger 1999 fig. 42. Teuthopsis princeps Wagner, 1859 , col. 276 (Solnhofen formation, Solnhofen area: holotype lost). Wagner, 1860, p. 798, pl. 24, fig. 3

Palaeololigo princeps Naef, 1921b, p. 146 –147.

Cephalopoden-Schulp Malz, 1976 p. 42, fig. 26.

Wagner (1859, 1860) described two new species of “ Teuthopsis ”, T. oblonga and T. princeps . Naef (1922 p. 147) examined the originals of Wagner’s figured specimens, since destroyed, and concluded that they belong to the same species. His view has been accepted by subsequent authors (Engeser 1988; Engeser and Keupp 1999, 2002). A new species P. albersdoeferi was described by Engeser and Keupp (1999 p. 30). See Engeser (1988) for a full synonymy.

Types

Wagner (1859) stated that he had a single example of T. oblonga from the Solnhofen Formation at Daiting, acquired in 1848, which is, therefore, the holotype. It passed into the Bayerische Staatssammlung, Munich, where Naef examined it ( Naef 1922). It is not now in that collection and is presumed destroyed during the Second World War (Alex Nützel pers. comm.).

Wagner’s (1859) T. princeps was based on a single specimen in the Häberlein collection. Häberlein’s collection was bought by the British Museum ( Cleevely 1983), but the holotype of T. princeps remained in Wagner’s possession and was deposited at the Bayerische Staatssammlung, Munich, where Naef (1922) examined it. It is also presumed destroyed during the Second World War.

Material and figures examined

Two specimens ( AS 1968 I 62 and 1964 XXIII 147) from the Bayerische Staatssammlung, Munich. Three specimens (SOS 1323, SOS 1325 and SOS 1366) from the Jura-Museum, Eichstätt. Jura-Museum SOS 2185 is the counterpart of SOS 1323. A gladius from the Maxberg museum of the Solenhofer Aktien-Verein was figured by Malz (1976) and by Frickhinger (1994). A specimen in a private collection (Coll. Wulf, Rodelsee) illustrated by Frickhinger (1999) is the counterpart slab of AS 1968 I 62.

Gladius

Vane: pear-shaped, varying degrees of convexity but fully three-dimensional examples unknown. Split along mid-line in some examples, (e.g. holotype [ Figure 4A ]) by compression in sediment, indicating region of strongest curvature. Vane approximately two-thirds of total gladius length. Anteriorly, vane merges gradually into rachis. Side-view reconstruction, Figure 4D . Numerous growth lines on ventral surface of vane ( Figure 2E ). Only most prominent growth lines visible on dorsal surface. Vane bears ribs radiating from posterior end formed by undulations of shell. Ribs evident on dorsal surface and impression of ventral surface (e.g., SOS1366 [ Figure 2E ]). Some ribs stronger than others. Rib spacing irregular. Number of ribs varies between specimens. One pair shown in Wagner’s figure of holotype was mistaken for a lateral asymptote by Naef (1921b fig. 62). No lateral asymptote. Median asymptote is represented by line of junction of vane with rachis. No hyperbolar zone. Posterior end bluntly pointed in some gladii (e.g. AS 1968 I 62 [ Figure1 ]). Greatest width of uncrushed gladius just less than half vane length ( Table 1). Rachis narrow, increasing in width forwards, consists of rib flanked by grooves in dorsal view. Ribs and grooves are corrugations of shell so that rib is a groove in ventral view. Free rachis terminates in blunt point, incomplete in most specimens. Gladius thickness estimated 0.1 mm. Gladius composition unknown. Growth lines indicate earliest formed part of gladius triangular ( Figure 2E ). With growth, gladius rapidly assumes adult form. Gladius length 90–180 mm in most specimens ( Table 1). Gladius in Maxberg Museum stated to be 390 mm long ( Malz 1976 fig. 28; Frickhinger 1994 fig. 139).

Soft parts

Arm crown impressions occasionally preserved. Arms 26% of total animal length in AS 1968 I 62 ( Figures 1A–B ). Seven arms evident assuming no multiple impressions in AS 1968 I 62. Four or five arms evident in specimen from Wulf collection figured by Frickhinger (1999 fig. 41), but its identity as Palaeololigo is not clear from photograph. Impressions of suckers evident on several arms of AS 1968 I 62 ( Figure 1B ) .

Ink sac and duct 50 mm long in SOS 2185 (the counterpart of SOS 1323) of which ink sac approx. 32 mm, 25% of gladius length. Ink duct short, possibly incomplete. Ink sac of 1964 XXIII 147 25 mm long ( Figure 2B ), ink duct unclear.

Two triangular fins evident in SOS1366 ( Figure 2D ). Anterior length of fin 28 mm, posterior length of fin 23 mm.

Total length (including arms) approx. 145–150 mm.

Stratigraphic horizon and range

The holotype was from the Mörnsheim Formation of Daiting. Other specimens are from the Solnhofen Formation of the Eichstätt area (“Blumenberg”) and possibly the Solnhofen area . Both these formations belong to the Upper Jurassic, Lower Tithonian stage, zone of Hybonoticeras hybonotum ( Arkell 1956) .

Remarks

Naef’s (1921b fig. 62, 1922 fig. 55) reconstruction of the gladius shows a lateral asymptote (laterale Asymptote) (Aa). An asymptote is a deflection in the growth lines corresponding to an abrupt discontinuity in the shell outline. Naef appears to have been misled by the rib in the holotype. In fact, Wagner’s figure shows quite clearly that the growth lines are uninterrupted as is seen in other specimens. There is no lateral asymptote. There may in some cases be the appearance of one owing to distortion of the gladius during fossilization along the line of one of the ribs ( Malz 1976 fig. 42). Because of this misinterpretation Naef recognized a lateral plate marked off from the conus vane by the supposed lateral asymptote. This distinction does not exist.

Gladii comparable to that of Palaeololigo are very rarely found in the Upper Cretaceous Niobrara Formation of Kansas, USA. Several genera and species have been described, but two basic kinds can be recognized, Tusoteuthis Logan, 1898 with a leaf-shaped gladius bluntly pointed at the posterior end, and Niobrarateuthis Miller, 1957 of which the type species has an oval gladius ( Figure 4G ), both kinds have a long rachis. However, preservation may affect whether the posterior end appears rounded or pointed (see later, Recent gladii) so that this distinction may not be real. Furthermore, the bluntness may not be apparent in P. oblonga depending on the angle of view. Both Tusoteuthis and Niobrarateuthis are large gladii about half a metre long, with a rachis which is longer than the vane and is a substantial rod 1–2 cm in diameter. Green (1974) showed that the rachis does not extend to the posterior end of the gladius in Tusoteuthis , which is different in this respect from Palaeololigo . Miller indeed placed Niobrarateuthis in the Family Palaeololiginidae . Green (1977) described Niobrarateuthis walkeri ( Figure 4G, H ) from the basal Smoky Hill Member of the Niobrara (late Coniacian or early Santonian stage). This gladius appears closely similar to Bathyteuthis . The radial ribs of the Palaeololigo gladius have apparently not been reported from the American Upper Cretaceous species.

The year after he proposed the genus Palaeololigo, Naef (1922) pointed out the “marked similarity” of its gladius to that of Recent squids. He was probably referring to the projecting rachis because he cited a figure of the Loligo Lamarck, 1798 gladius in comparison. This is a feature of several Recent genera, and the closest similarity is not to Loligo , but to the extant squids Bathyteuthis (family Bathyteuthidae ) and Chtenopteryx (family Chtenopterygidae ); both superfamily Bathyteuthoidea ) (Figure 5 A–G), the Bathyteuthis gladius being narrower and the rachis longer ( Table 1).

The gladius of Bathyteuthis has been illustrated by several authors. Roper (1969) in his comprehensive treatment of the genus figured gladii, all essentially similar, of three species. Toll (1982) illustrated gladii of several species including one or two unnamed. All these pictures show similar forms, a pear-shaped vane with rounded posterior end and a rachis longer than the vane. However Bizikov (1996 fig. 34C; 2008 fig. 69) shows a gladius with a pointed posterior margin and a true conus (Figure 5G). The explanation of the difference may lie in the curvature of the gladius. Conventional diagrams of gladii show them as seen in dorsal or ventral view. The Bathyteuthis gladius, in side view, curves through almost 90º as shown by Toll (1982 pl. 32, figs. C–D) reproduced here (Figure 5E). The side-to-side curvature of the vane may make the posterior margin appear rounded in this conventional view. But seen obliquely, or if the gladius is flattened, the posterior end may be angular as shown by Bizikov. This is the case with Chtenopteryx , discussed later. The gladii of Bathyteuthis seen by us do not resolve the matter as the vanes have become distorted after removal from the animal. A small true conus is shown by both Toll and Bizikov.

The distinctive Chtenopteryx , the Comb Fin Squid, is the sister taxon to Bathyteuthis ( Young and Vecchione 1996) . Gladii have been figured by Toll (1982, 1998 fig. 39) and by Bizikov (1996 fig. 34A; 2008 fig. 68). A gladius of Chtenopteryx is shown in Figures 3 and 5A–D. The vane is strongly curved in lateral view which may account for the rounded posterior end shown by Toll. Bizikov (1996, 2008), who does not give a lateral view, shows the pointed posterior end as it appears in oblique view. Our specimen has a small secondary conus. Roper (1969) wrote: “A conus is lacking, but the postero-lateral edge of the vane folds under to form a shallow, cup-shaped terminus of the gladius”. This does not exactly describe our specimen but it may be a different species from Roper’s.

It will be clear from the preceding paragraphs that while the resemblance of the gladius of Palaeololigo to conventional illustrations of the gladii of Bathyteuthis and Chtenopteryx is close, differences being mainly in proportions, it may differ depending Figure 5. Gladii of Recent squids. (A–D) Chtenopteryx : (A–B) un-named species, new drawing; (C) C. canariensis Salcedo-Vargas & Guerrero-Kommritz , after Salcedo-Vargas & Young, website; (D) C. sicula (Verany) after Bizikov (1996 fig. 34A). The sides of the vane are folded in giving a more pointed appearance; (E–G) Bathyteuthis , not to scale: (E) Bathyteuthis sp. after Toll (1982 pl. 32, figs. C, D); (F) B. sp. after Toll (1982 pl. 31, fig. B); (G) B. abyssicola (Hoyle) after Bizikov (1996 fig. 34C). Note: Scale bars, 10 mm.

on the details of the posterior ends of the Recent gladii, which are inadequately known. It is interesting that Naef’s reconstruction of the Palaeololigo gladius, based on the now destroyed specimens from the Munich collection, does show a very small, shallow, bluntly pointed conus ( Naef 1922 fig. 55).

Another difference between the fossil and Recent gladii may be the presence of radial ribs in Palaeololigo , which are not seen in Bathyteuthis gladius, whether in illustrations or direct observations. Possibly similar structures are shown in illustrations of the Chtenopteryx gladius ( Bizikov 1996 fig. 34A; Bizikov 2008 fig. 68; Salcedo-Vargas and Guerrero-Kommritz 2000; Figure 5C), but they are not apparent in the Recent gladii examined.

The fact that the vane in Palaeololigo bears numerous growth lines which are evident ventrally, but only vaguely dorsally, shows that the vane increases in size by the addition of larger and larger increments to the dorsal surface. This contrasts to the assumed site of secretion in the Recent Loligo ( Hopkins and Boletzky 1994) , which is on the ventral side of the shell sac.

Niobrarateuthis walkeri ( Figure 4G–H ) appears to be even more similar to the Recent Bathyteuthis than to Palaeololigo due to the narrow vane and long rachis. Presumably preserved in a flattened state, N. walkeri has a pointed posterior end (“apex” of Green, 1977) which may be an additional similarity to Bathyteuthis , as discussed previously.

Furthermore, the triangular fins evident in Figure 2D of Palaeololigo appear to be subterminal (i.e., not contiguous at end, but remaining distinctly separated). Similarly, the fins in Bathyteuthis and Chtenopteryx are also subterminal and appear similar in shape and proportion to the entire body size in Bathyteuthis and in juvenile Chtenopteryx , although with maturity the fins extend in Chtenopteryx so that in adults they are nearly as long as the mantle ( Roper 1969). The relationships of these genera are discussed later.

Figures

Figure 1. Palaeololigo oblonga (Wagner). Paläontologisches Museum Munich AS 1968 I 62. (A) Note that the end of the rachis is broken and bent backwards; (B) detail of arm crown. Note: Photos supplied by Georg Janssen with permission.

Figure 2. Palaeololigo oblonga (Wagner). (A) Paläontologisches Museum Munich AS 1968 I 62. Posterior part to show vane of gladius; (B) Paläontologisches Museum Munich 1964 XXIII 147. Gladius, dorsal view with outline of ink sac; (C) Jura-Museum, Eichstätt SOS 1325. Gladius; (D) Jura-Museum, Eichstätt SOS 1366. Posterior end of gladius and impression of fin; (E) Jura-Museum, Eichstätt SOS 1366. Posterior part of right side of vane. Area where gladius is missing shows clear impression of growth lines and radial folds. Notes: Photos, (A–B) Georg Janssen; (C) Martin Ebert; (D–E) D.T. Donovan.

Figure 3. Chtenopteryx sp. Gladius. (Top) right lateral view; (bottom) oblique ventral view. Note: Photo, D.T. Donovan.

Figure 4. (A) Palaeololigo oblonga (Wagner), holotype. Formerly in Paläontologisches Museum Munich, from Wagner 1860; (B) holotype of Teuthopsis princeps Wagner. Formerly in Paläontologisches Museum Munich, from Wagner 1860; (C) P. oblonga (Wagner), dorsal view of gladius, based mainly on the holotype, restored to original shape, as for illustrations of Recent gladii; (D) P. oblonga (Wagner), left lateral views of gladius, based mainly on the holotype, restored to original shape; (E) P. oblonga (Wagner), gladius of Paläontologisches Museum Munich AS 1968 I 62, natural size; (F) P. oblonga (Wagner), gladius of Jura-Museum, Eichstätt SOS 1325, natural size; (G) Niobrarateuthis walkeri Green, dorsal view of gladius.Upper Cretaceous (Coniacian or Santonian), Kansas, USA. Actual length of specimen about 60 cm, after Green (1977); (H) N. walkeri Green, right lateral view (details as for Fig. 4G).