The endocranial anatomy of the early sarcopterygian Powichthys from Spitsbergen, based on CT scanning. more

Morphology, Phylogeny and Paleobiogeography of Fossil Fishes Honoring Meemann Chang David K. Elliott, John G. Maisey, Xiaobo Yu & Desui Miao (editors) Verlag Dr. Friedrich Pfeil • München Morphology, Phylogeny and Paleobiogeography of Fossil Fishes D. K. Elliott, J. G. Maisey, X. Yu & D. Miao (eds.): pp. 363-377, 7 figs. © 2010 by Verlag Dr. Friedrich Pfeil, München, Germany – ISBN 978-3-89937-122-2 The endocranial anatomy of the early sarcopterygian Powichthys from Spitsbergen, based on CT scanning Gaël Clément and Per E. Ahlberg Abstract A detailed description of the external and internal morphology of the neurocranium of the early sarcopterygian Powichthys spitsbergensis is presented. The study, which is based on high-resolution CT scanning and threedimensional digital reconstructions, reveals a wealth of new phylogenetically informative features. Many are shared with the Porolepiformes, such as the morphology of the nasal capsules, the separate parapineal and pineal canals, and the curved shape of the hypophysial fossa. These characters therefore favour the original assignation (Jessen 1975, 1980). However, some are autapomorphies, such as the presence of two prominent ventral processes in front of the parasphenoid, while others are shared with non-porolepiform taxa such as Youngolepis. These new anatomical data have yet to be tested within a cladistic analysis, but we predict that they will affect the position of Powichthys within the Dipnomorpha, and possibly have a broader impact on sarcopterygian phylogeny and character evolution. Introduction Jessen (1975, 1980) described the species Powichthys thorsteinssoni on the basis of skull material and assigned it to the Porolepiformes. Associated material (palatoquadrate, lachrymal, lateral extrascapular, lower jaw, submandibular and operculo-gular series, cleithrum and scales) has cautiously been referred to as Porolepiformes gen. et sp. indet. (Jessen 1980). Although these associated remains can be safely attributed to P. thorsteinssoni (Ahlberg 1991), the taxon Powichthys itself is currently interpreted either as the sister group of all other Dipnoiformes (Cloutier & Ahlberg 1996), or placed in a trichotomy with Youngolepis and the clade including Diabolepis and the Dipnoi (Ahlberg & Johanson 1998). Powichthys thorsteinssoni is restricted to the Lochkovian-Pragian (Lower Devonian) of the Canadian Arctic Archipelago. A new Powichthys species, P. spitsbergensis (Clément & Janvier 2004) has been recently defined on the basis of an anterior division of the skull and associated postorbital bone and scales. This material was found during the 1969 French expedition in the Wood Bay Formation (Lower Devonian) of Spitsbergen. Acid preparation of the anterior division of the skull has revealed most of the bones composing the palate (vomers, parasphenoid, large oral dental plates, anteromedial parts of the two palatoquadrates) and part of the ventral side of the endocranium (internasal cavities of the ethmoid and posterior part of the sphenoid). This exquisitely well preserved specimen was described in detail (Clément & Janvier 2004); however no data on internal anatomy was accessible. Powichthys is an important taxon for early vertebrate paleontology because it is one of the earliest sarcopterygians known to date, and the only Lochkovian sarcopterygian described from outside the South China microcontinent, where a rich sarcopterygian assemblage including the genera Psarolepis, Achoania, Diabolepis, Youngolepis and Styloichthys has been recovered (Chang 1995, Yu 1998, Zhu et al. 2001, Zhu & Yu 2002). Its phylogenetic position within the Dipnomorpha is still unresolved, partly due to lack of anatomical data. An exhaustive anatomical study of this Lochkovian-Pragian sarcopterygian will probably reveal some plesiomorphic con363 ditions for the Dipnomorpha, as well as for the Sarcopterygii. With this aim, an analysis of high-resolution computerized tomography scanning has been undertaken on the acid prepared anterior division of the skull of Powichthys spitsbergensis. It reveals new data on the anteromedial part of the palatoquadrates, the sensory canals, and the morphologies of the neurocranium and the endocranial cavity. Material and methods The specimen under investigation is the anterior division of the skull of the early sarcopterygian Powichthys spitsbergensis Clément & Janvier, 2004. This specimen is housed in the collection of the Laboratoire de Paléontologie, Muséum national d’Histoire naturelle, Paris, France, under the catalog number MNHN SVD 2156. It comes from the Sigurdfjellet Faunal Division, lowermost Wood Bay Formation, Late Lochkovian-Early Pragian of the Kronprinshøgda locality, Haakon VII land, northern Spitsbergen. The specimen was scanned by Matthew Colbert (Geology Department, University of Texas at Austin) on 28 October 2004. Scan parameters are as follows: 180 kV, 0.133 mA, no filter, air wedge, no offset, slice thickness 1 line (= 0.0531 mm), S.O.D. 155 mm, 2000 views, 2 samples per view, inter-slice spacing 2 lines (= 0.0531 mm), field of reconstruction 50 mm (maximum field of view 50.79406 mm), reconstruction offset 5000, reconstruction scale 1200. Acquired with 27 slices per rotation. Reconstructed with beamhardening coefficients: 0.0, 0.7, 0.2. Spike-and ring-removal processing and rotation correction processing done by S. Garlock based on correction of raw sinogram data using IDL routines “RK_SinoDeSpike” and “RK_SinoRingProcSimul” with default parameters and using IDL routine “DoRotationCorrection”. Image orientation adjusted to vertical using Photoshop. Total number of slices = 405. The scan plane was horizontal, approximately parallel with the skull roof. The resulting scan, presented as a stack of TIFF images, was rendered into 3D reconstructions using the software MIMICS (Materialise’s Interactive Medical Image Control System) from Materialise (MIMICS v10.11 2006). This is a tool for the visualization and segmentation of CT images and 3D rendering of objects, originally developed for medical use. MIMICS is well suited to reconstructing the endocranium and endocranial cavity of the specimen because it readily allows separate modeling of different parts of the scan at different density thresholds. Acid preparation of the specimen, prior to the CT scanning operation, enhanced the difference of density between the bone and the surrounding substance by removing calcareous matrix to leave either air spaces or, at most, non-calcareous matrix with low x-ray density. However, a zone of calcareous matrix is still present in the central part of the skull. A section of the image series (Fig. 1) shows a bright white area in the middle of the braincase. Internal structures in this area, such as the proximal part of the olfactory tracts and dorsal part of the interorbital wall, were sometimes hardly distinguishable. These hidden parts were not selected during the modeling process and do not appear on the 3D reconstructions. Anatomical description Skull roof and sensory canals. The different sections of the specimen (Fig. 1A-C) present a clear picture of the sensory canals running in the thickness of the dermal bones. The infraorbital sensory canal (along the lateral part of the premaxillae and in the postorbital bone) and supraorbital sensory canal (in the skull roof) have been three-dimensionally reconstructed. The symmetry of the sensory canals, in dorsal or lateral views, shows that the specimen has not been distorted (Fig. 2). The lyre-shape supraorbital sensory canal gives off numerous branching tubes (ssoc, Figs. 1A, 2E). Most of these secondary tubes run dorsally and pierce the cosmine cover. However, some tiny tubes are present on the ventral side of the main branch. These minute tubes are considered as nerve canals (ne.c, Fig. 2F). In contrast to Porolepis (Jarvik 1972, Ahlberg 1991), it is clear that the infraorbital sensory canal runs along the suture between the skull roof and the independent premaxillae and does not enter the premaxilla (Pmx, Fig. 2A-D). Independent premaxillae not pierced by the infraorbital sensory canal are known in Powichthys thorsteinssoni (Jessen 1975, 1980), Youngolepis (Chang 1982), Diabolepis (Chang 1995) and the basal tetrapodomorph Kenichthys (Chang & Yu 1997, Zhu & Ahlberg 2004). Palatoquadrates. It was possible from the CT data to model and isolate the broken anterior part of the palatoquadrates. Previous interpretations of the morphology of these palatoquadrates are erroneous (Clé364 ioc nca soc La Vo B Vo in.ca ‘m.s’ pr.v.et uodp soc ioc ssoc soc soc lopc mopc nca C A 10 mm pq Vo Fig. 1. Powichthys spitsbergensis (Wood Bay Formation, Lower Devonian, northern Spitsbergen). Three different CT scan slices of the specimen revealing the high quality of the image stack. A, horizontal section just below the skull roof; B, coronal section through the posterior ends of the internasal cavities; C, sagittal section at the level of the right vomer. A is a true scan slice, B and C are reconstructed image planes generated by MIMICS. Bright white areas are due to remaining calcareous matrix in the central part of the skull. Abbreviations: in.ca, internasal cavities; ioc, infraorbital sensory canal; La, lachrymal; lopc, lateral profundus nerve canal; ‘m.s’, “mushroom structure”; mopc, medial profundus nerve canal; nca, nasal capsule; pq, palatoquadrate; pr.v.et, ventral paired processes of the ethmoid; soc, supraorbital sensory canal; ssoc, secondary branches of supraorbital sensory canal; uodp, upper oral dental plates; Vo, Vomer. ment & Janvier 2004: fig. 10). This results from incomplete observations because the palatoquadrates are covered by adjacent bones and remaining matrix. The general shape of the broken left palatoquadrate and associated entopterygoid is correct, but the anterior and median processes of the pars metapterygoidea of the palatoquadrate, as well as the supposed processus paratemporalis?, (Clément & Janvier 2004: fig. 10, ant.pr, me.pr, and pat.pr?) form the distal margin of the processus ascendens (pr.as, Fig. 3E,F). The previously supposed pars metapterygoidea is the posterior slope of this processus ascendens. The authentic shape of the anterior part of the palatoquadrates of Powichthys spitsbergensis is therefore very similar to that of the palatoquadrates found associated with P. thorsteinssoni (Jessen 1980: figs. 1, 2, pl. 1). In both taxa, the lateral side of the processus ascendens presents some small rounded bumps. This region is considered by Jessen (1980) as the area of origin for mm. levator mandibularis anterior. The anteromedial articular area of the palatoquadrate (art.am, 3C,D) is well-developed. This large surface devoid of periosteal lining reveals a very close relation with the endocranium. External morphology of the endocranium. The CT scanning technique allowed us to reconstruct the endocranium without the adjacent bones (skull roof and bones of the palate), thus revealing previously hidden anatomical features. The general shape of the endocranium is similar to those of the porolepidids Porolepis and Heimenia (Jarvik 1972, Clément 2001) and, to a lesser extent, the holoptychiid Glyptolepis (Jarvik 1972, Bjerring 1991, 1995). Some differences between Powichthys and the Porolepiformes, such as the absence of a fossa autopalatina and presence of a network of grooves on the floor of the internasal cavities in Powichthys, have been discussed previously (Clément & Janvier 2004). Some new features of the endocranium are now obvious. In dorsal view, the pineal region is slightly domed and presents a single foramen (pin.c, Fig. 4E), in contrast to Glyptolepis groenlandica (Jarvik 1972: 365 Pmx A ov.int1 an.na pin.f 10 mm B ov.Po o.m C ov.La et.com ioc D soc ssoc ne.c F G E 10 mm Fig. 2. Powichthys spitsbergensis (Wood Bay Formation, Lower Devonian, northern Spitsbergen). Virtual 3D reconstructions rendered from CT scans of the skull roof and sensory canals. A, skull roof and sensory canals in dorsal view; B, same as A with skull roof rendered semi-transparent; C, skull roof and sensory canals in left lateral view; D, same as C with semi-transparent skull roof; E-G, infra- and supraorbital sensory canal in dorsal (E), left lateral (F), and anterior (G) views. Abbreviations: an.na, anterior nostril; et.com, ethmoidal commissure; ne.c, nerve canal; o.m, orbital margin; ov.int1, area overlapped by the intertemporal; ov.La, area overlapped by the lachrymal; ov.Po, area overlapped by the postorbital; pin.f, pineal foramen; Pmx, premaxilla; ssoc, secondary branches of supraorbital sensory canal. 366 B A art.m.et art.m.et dam pr.as ap.pr E Ept Ept art.am Ept ap.pr pr.as C D 10 mm F ov.Der Ept Fig. 3. Powichthys spitsbergensis (Wood Bay Formation, Lower Devonian, northern Spitsbergen). Virtual 3D reconstructions rendered from CT scans of the endocranium and anteromedial portions of the palatoquadrates. A, endocranium and palatoquadrates in situ in ventral view (palatoquadrates have been darkened to distinguish them from the neurocranium); B, same as A without the palatoquadrates; C-D, same as A without the neurocranium; E, anteromedial portion of the right palatoquadrate in lateral view; F, anteromedial portion of the left palatoquadrate in lateral view. Abbreviations: ap.pr, apical process of the pars autopalatina of the palatoquadrate; art.am, anteromedial articular area of the palatoquadrate; art.m.et, medial ethmoidal articular area of the pars autopalatina of the palatoquadrate; dam, damaged region of the processus ascendens; Ept, entopterygoid; ov.Der, area overlapped by the dermopalatine; pr.as, processus ascendens. fig. 23) where two foramina are described. The S-shape groove for the supraorbital sensory canal (g.soc, Fig. 4B) is apparent. In ventral view, a remarkable feature is the presence of two prominent ventral processes (pr.v.et, Fig. 4) posterior to the internasal crest (in.cr, Fig. 4A). These roughly cylindrical processes point in a ventrolateral direction from a medial origin. Their distal ends have periosteal lining. They support the anteromedial corner of the large anterior upper oral dental plates (Clément & Janvier 2004: figs. 7, 9). The distal part of the broken right process is still in connection with the inner side of the upper oral dental plate due to remaining matrix (this is clearly visible on the figure 9B in Clément & Janvier 2004). As seen on the ventral view of the specimen, the upper oral dental plates are supported by the vomer, the 367 lateral margin of the parasphenoid and the entopterygoid. They form, together with the entopterygoids, a flat and horizontal denticulate dental roof. Such large oral upper dental plates were also supposed to be present in Powichthys thorsteinssoni (Clément & Janvier 2004). The anteriormost plates bend anteriorly towards the bottom of the internasal cavity. The ventral processes of the ethmoid reinforce the stability of the anterior upper oral dental plates and prevent their dorsal displacement in the internasal cavities. A small, globular structure is found between these ventral processes of the ethmoid (‘m.s’, Figs. 1, 4C,E). This is homologous with the “mushroom structure” (‘m.s’, Jessen 1980) in Powichthys thorsteinssoni. However, in contrast to the latter, its surface is not pierced by numerous small canals. It is possible that ventral processes of the ethmoid were also present in Powichthys thorsteinssoni but broken and not preserved on the holotype. The major part of the voluminous mushroom structure of P. thorsteinssoni, supposed to be penetrated by numerous canals, could well be the broken area of the ventral processes of the ethmoid, showing the lacunae of the trabecular bone. The postnasal wall is pierced by two small foramina, the lateral profundus nerve canal (lopc, Fig. 4A,D) and the orbitonasal nerve canal (orc, Fig. 4D), located dorsomedially and ventrolaterally respectively to the larger medial profundus nerve canal (mopc, Fig. 4A,D). The orbitonasal foramen is not completely closed on the left side due to the absence of closure of the postnasal wall in its ventrolateral region (orc, Fig. 4D). Contrary to the previous assumption (Clément & Janvier 2004: fig. 6), the lateral profundus nerve canal is single and in a more dorsal position. The basipterygoid process (bp.pr, Fig. 4) is well developed and its entire dorsal face lacks periosteal lining, forming a single large articular surface for the anteromedial lamina of the palatoquadrate. A fossa autopalatina is absent. A laterally directed process on the left side of the endocranium, posterior to the basipterygoid process, is identified as a descending process of the sphenoid (pr.d.sp?, Fig. 4A,D,E). Such a process is absent in Porolepis but present in Youngolepis and Powichthys thorsteinssoni. However, the process in Powichthys spitsbergensis lacks the characteristic unfinished distal end seen in Youngolepis and P. thorsteinssoni. The significance of this structure is considered further in the Discussion. The foramen for the pituitary vein (c.v.pit, Fig. 4F) is situated posterior to the dorsal end of the basipterygoid process, as in Porolepis and Glyptolepis (Jarvik 1972: figs. 20A, 21A). This condition is different in P. thorsteinssoni (Jessen 1980: fig. 5), Youngolepis (Chang 1982: pl. 15) and Holoptychius (Jarvik 1972: fig. 20B) where the foramen for the pituitary vein lies more anteriorly. The opening of the canal for the optic nerve is not obvious because the interorbital wall is partly missing but its wide groove (gr.II, Fig. 4E), which carried the optic nerve forwards to the eye, is preserved. The estimated position of the opening for the optic nerve is above the opening for the a. ophthalmica magna (c.a.om, Fig. 4E), as in P. thorsteinssoni, Porolepis, Glyptolepis, and to a lesser extent Eusthenopteron (Jarvik 1980: fig. 86). In this respect, the opening for the optic nerve is in a much more anterior position in Youngolepis (Chang 1982: pl. 15). The processus connectens (pr.conn, Fig. 4E,F) is strongly developed as in the Porolepiformes (Jarvik 1972). It is noticeable that P. thorsteinssoni does not seem to have such a strong processus connectens. A small foramen is present above a fine crest on the lateral side of the intertemporal wall. This foramen, situated anteriorly to the processus connectens, is considered as the opening for the nervus profundus (c.pro, Fig. 4E). This foramen is absent in Porolepiformes. No large foramen is present between the opening for the nervus profundus and the processus connectens in P. spitsbergensis in contrast to P. thorsteinssoni where two foramina were described (Jessen 1980: fig. 5). The posterodorsal region of the ethmosphenoid is unfortunately not preserved on the specimen. It appears to have been unossified. Cranial endocast. The shape of the cranial endocast is similar to that of the porolepiform Glyptolepis (Jarvik 1972). The nasal capsules are large and triangular, the olfactory tracts are long and slender, the anterior part of the forebrain is large and ends abruptly, and the hypophysial fossa is large and strongly curved. The nasal capsules (nca, Fig. 7) are very well preserved and not distorted. The ventral part of the right nasal sac is slightly displaced, due to a crack in the solum nasi (cr, Figs. 4A, 7E,F) along the lateral recess (re.l, Fig. 7B,E). The anterior nostril (an.na, Fig. 7) is slit-like and strongly oblique. The fenestra ventrolateralis (fe.vl, Fig. 7B) is large, especially on the left side where the closure of the canal for the orbitonasal nerve (orc, Fig. 7) is not complete. The fenestra ventrolateralis is laterally prolonged to the small and slit-like posterior nostril (post.na, Clément & Janvier 2004: figs. 2-3). The medial profundus 368 cr fe.vl pr.v.et in.cr in.ca ov.Vo art.e mopc lopc g.soc g.a.pal g.a.ps g.a.ci b.f pin.c A in.cr nca orc g.et.com g.soc pr.d.sp? 10 mm B cr.ca nca mopc lopc ‘m.s’ pr.v.et orc orc pr.d.sp? fo.not c.pro pr.conn C bp.pr pin.c D ‘m.s’ pr.v.et c.v.pit pr.d.sp? gr.II c.a.om bp.pr pr.v.et E F bp.pr Fig. 4. Powichthys spitsbergensis (Wood Bay Formation, Lower Devonian, northern Spitsbergen). Virtual 3D reconstructions rendered from CT scans of the endocranium. A, ventral view; B, dorsal view; C, anterior view; D, posterior view; E, left lateral view; F, right lateral view. Abbreviations: art.e, area of articulation between the ethmoid and ethmoidal process of the palatoquadrate; b.f, buccohypophysial foramen; bp.pr, basipterygoid process; c.a.om, canal for ophthalmica magna artery; c.pro, canal for the profundus nerve; c.v.pit, canal for the pituitary vein; cr, crack in the solum nasi; cr.ca, cranial cavity; fe.vl, fenestra ventrolateralis; fo.not, notochord fossa; g.a.ci, groove for internal carotid artery; g.a.pal, groove for palatine artery; g.a.ps, groove for “efferent pseudobranchial” artery; g.et.com, groove for the ethmoidal commissure; g.soc, groove for the supraorbital sensory canal; gr.II, groove for the optic nerve; in.ca, internasal cavities; in.cr, internasal crest; lopc, lateral profundus nerve canal; ‘m.s’, “mushroom structure”; mopc, medial profundus nerve canal; nca, nasal capsule; orc, orbitonasal nerve canal; ov.Vo, area overlapped by the vomer; pin.c, pineal canal; pr.conn, processus connectens; pr.d.sp?, processus descendens of the sphenoid?; pr.v.et, ventral paired processes of the ethmoid. 369 in.ca fe.vl ov.Vo g.soc pin.c pr.conn g.a.pal nca pr.v.et gr.II bp.pr pr.d.sp? fo.not 10 mm pr.d.sp? g.a.ps g.a.ci b.f B A Fig. 5. Powichthys spitsbergensis (Wood Bay Formation, Lower Devonian, northern Spitsbergen). Line drawings of the endocranium. A, ventral view (corresponding to Figs. 3B, 4A, 6A); B, left lateral view (corresponding to Figs. 4E, 6B). Abbreviations: b.f, buccohypophysial foramen; bp.pr, basipterygoid process; fe.vl, fenestra ventrolateralis; fo.not, notochord fossa; g.a.ci, groove for internal carotid artery; g.a.pal, groove for palatine artery; g.a.ps, groove for “efferent pseudobranchial” artery; g.soc, groove for the supraorbital sensory canal; gr.II, groove for the optic nerve; in.ca, internasal cavities; nca, nasal capsule; ov.Vo, area overlapped by the vomer; pin.c, pineal canal; pr.conn, processus connectens; pr.d.sp?, processus descendens of the sphenoid?; pr.v.et, ventral paired processes of the ethmoid. nerve canal (mopc, Fig. 7) is as wide as the olfactory tract. The lateral profundus nerve canal (lopc, Fig. 7) is very small and located dorsally. The orbitonasal nerve canal is slightly larger than the lateral profundus nerve canal but much smaller than the medial profundus nerve canal. Some canals (c.prt, Fig. 7) emerge from the dorsomedial region of the nasal sac and run forwards with numerous bifurcations leading to a well-developed network in the more anterior part of the snout. These canals are considered homologous to the canals for twigs of medial profundus branch and vessels observed in Porolepis (Jarvik 1972: figs. 13, 14). As in Porolepis, a horizontal bulge (h.bu, Figs. 7A,F) is present on the posteromedial wall of the nasal capsule. This horizontal bulge runs forward from the medial profundus foramen, above the olfactory nerve canal, and ends in an irregularly branched ‘bush’ of smaller canals (c.prt, Fig. 7) that emerge from the mesial margin of the nasal sac; the bulge evidently represents a recess in the cavity wall that accommodated a trunk of nerves and/or blood vessels passing anteriorly from the foramen in the postnasal wall. However, Powichthys spitsbergensis does not show the large canal that emerges anteriorly from the bulge in Porolepis (c.cut, Jarvik 1972: fig. 13). This canal seems also absent in P. thorsteinssoni (Jessen 1980: pl. 9). A transverse canal (trans.c, Fig. 7B) is present in P. spitsbergensis between the distal parts of the olfactory tracts. Such a canal is not known in Porolepis (Jarvik 1972) or Youngolepis (Chang 1982) but seems to be present in Eusthenopteron (Jarvik 1980: fig. 89). A large nasobasal canal is known on the anterior side of the nasal capsule in P. thorsteinssoni (‘c.ora’, Jessen 1980: pl. 9), Porolepis (‘c.ora’, Jarvik 1972: fig. 13) and Eusthenopteron (‘nasobasal canal’, Jarvik 1980: fig. 89). Youngolepis presents the same canal which is much more reduced in size (‘c.n-b’, Chang 1982: fig. 14). Powichthys spitsbergensis presents a nasobasal canal (nb.c, Fig. 7A) similar to that of Porolepis in size and position. The dorsal part of the endocranial cavity is not preserved but the more anterior part, with the pineal and parapineal tracts, is preserved. The anterior end of the cavity is deep and its anterior margin is almost vertical. Jarvik (1972: p. 48), in his description of the pineal complex in Porolepis and Glyptolepis, defined the pineal tract as the posterior canal situated close to the right of the median line and the parapineal tract 370 A B C 10 mm Fig. 6. Powichthys spitsbergensis (Wood Bay Formation, Lower Devonian, northern Spitsbergen). Stereoscopic views of virtual 3D reconstructions rendered from CT scans of the endocranium. A, ventral view; B, left lateral view; C, same as B with anteromedial portion of the left palatoquadrate in situ. as the anterior canal emerging close to the left of the median line. Following the same determination, the parapineal canal (ppin.c, Fig. 7) of Powichthys spitsbergensis is wider and slightly shorter than the pineal canal (pin.c, Fig. 7). In section the parapineal canal is rounded whereas the pineal canal is elliptic and much wider than deep. These morphologies of the parapineal and pineal canals are virtually identical to those of Glyptolepis (Bjerring 1975). However, in contrast to Glyptolepis where both canals pierce the dorsal surface of the braincase but are closed by the skull roof (so that there is no external foramen), Powichthys spitsbergensis presents a parapineal canal piercing the endocranium and skull roof by the ‘pineal’ foramen, whereas the pineal canal terminates in a closed distal end within the braincase. 371 The posterior part of the endocranial cavity is not well preserved but a short canal is clearly visible on the left side. This short canal runs anterolaterally to pierce the intertemporal wall. It is here interpreted as the canal for the profundus nerve (c.pro, Fig. 7). The hypophysial fossa (hyp.f, Fig. 7) is large and curved at a right angle. The buccohypophysial canal is therefore in a much more anterior position than the proximal vertical part of the hypophysial fossa. The fossa is wide all along its length and does not seem to be constricted in its distal part, as seen in Glyptolepis (Jarvik 1972: fig. 72). The canal for the pituitary vein (c.v.pit, Fig. 7) emerges from the posterior corner of the fossa and pierces the lateral side of the intertemporal wall in a dorsal position. Its path is strongly U-shaped. Anteriorly, two parallel and straight canals join the ventral margin of the cranial cavity to the middle part of the hypophysial fossa. These short canals for cerebralis arteries (c.a.cer, Fig. 7) are known in Glyptolepis, Eusthenopteron, and Youngolepis, although reduced in the latter form (Jarvik 1972, 1980, Chang 1982). The distal part of the hypophysial fossa is connected with a complex of canals for blood vessels. A large groove for the internal carotid artery (g.a.ci, Figs. 4A, 7) runs posteriorly, a similar large groove for the palatine artery (g.a.pal, Figs. 4A, 7) runs anteriorly, and a short and slender groove for the efferent pseudobranchial artery (g.a.ps, Figs. 4A, 7) runs laterally. Powichthys spitsbergensis presents a complex of grooves for blood vessels and not of canals. It is very similar to Youngolepis and Heimenia in this respect (Chang 1982: figs. 7, 8, Clément 2001: figs. 2, 3). A short canal for ophthalmica magna artery (c.a.om, Fig. 7) emerges from the distal portion of the hypophysial fossa to run dorsolaterally. The wide buccohypophysial canal (b.c, Fig. 7) is situated anteriorly to the anterior corner of the hypophysial fossa. This canal is also short and wide in Glyptolepis but located just below the chiasma of grooves for blood vessels, whereas this canal is long and slender, moreover directed in a posterior direction, in Eusthenopteron (Jarvik 1972: fig. 72). Discussion Comparative morphology of the cranial cavity and ethmosphenoid The well-preserved cranial cavity of Powichthys spitsbergensis allows detailed comparisons with sarcopterygian taxa that have been studied by serial grinding, such as Eusthenopteron, Ectosteorhachis (“Megalichthys”) nitidus, Youngolepis and Glyptolepis (Romer 1937, Jarvik 1972, 1980, Chang 1982, Bjerring 1991, 1994, 1995). The cranial cavity of Powichthys spitsbergensis resembles those of Youngolepis and Glyptolepis, aligning itself more closely with one or the other in regard to different features but usually showing greater similarity to Glyptolepis. The phylogenetic and taxonomic significance of these patterns is considered in detail at the end of this section. The triangular shape of the nasal cavities (nca, Fig. 7) resembles Youngolepis and porolepiforms, but most of the morphological details match the porolepiform pattern. The anterior nostril (an.na, Figs. 2C, 7) faces anteriorly, rather than anteroventrally as in Youngolepis, and the groove accommodating the crista rostrocaudalis is developed exactly as in porolepiforms (cf. Jarvik 1972: figs. 13, 14). In the postnasal wall, the medial profundus canal (mopc, Fig. 7) is much larger than the orbitonasal canal (orc, Fig. 7), like in porolepiforms but contrasting with Youngolepis where the canals are similarly sized. The horizontal bulge (h.bu, Fig. 7) in the posteromesial wall of the nasal cavity resembles the condition in Porolepis (Jarvik 1942: fig. 42), although in the latter genus the horizontal bulge ends anteriorly in a single canal (“c.cut”) and small canal branches emerge directly from the nasal capsule dorsomesial surface. In Youngolepis, by contrast, the canal that extends anteriorly from the profundus foramen in the postnasal wall splits into three branches that splay out across the dorsal surface of the nasal cavity (Chang 1982: fig. 14). The orbitonasal canal in the postnasal wall of Powichthys spitsbergensis resembles Porolepis whereas the orbitonasal canal of Powichthys thorsteinssoni is larger than that of Porolepis, and approaches the condition in Youngolepis (Jessen 1980, Ahlberg 1991). Despite mutual dissimilarities, Powichthys, Youngolepis, and porolepiforms resemble each other more closely than they resemble tetrapodomorphs. In Eusthenopteron the profundus canal is very small (Jarvik 1980: fig. 89) whereas the orbitonasal canal (“fenestra endonarina posterior” of Jarvik) is large; a similar condition seems to be present in Ectosteorhachis, although Romer (1937) was not able to identify a profundus canal with confidence. These tetrapodomorphs also have a plexus of probable cutaneous vein 372 nb.c an.na trans.c re.l nca h.bu lopc b.c mopc b.c g.a.pal g.a.ps g.a.ps g.a.ps g.a.ci hyp.f c.pro fe.vl g.a.ci c.v.pit A ppin.c c.pro 10 mm B pin.c c.a.om g.a.pal c.v.pit c.a.cer C c.prt pin.c ppin.c c.prt an.na D g.a.ci ppin.c lopc g.a.ps b.c pin.c c.prt h.bu cr c.II re.l orc mopc c.v.pit c.II cr orc E F Fig. 7. Powichthys spitsbergensis (Wood Bay Formation, Lower Devonian, northern Spitsbergen). Virtual 3D reconstructions rendered from CT scans of the cranial endocast. A, dorsal view; B, ventral view; C, left lateral view; D, right lateral view; E, anterior view; F, posterior view. Hatched areas indicate truncated regions. Abbreviations: an.na, anterior nostril; b.c, buccohypophysial canal; c.a.cer, canal for cerebralis artery; c.a.om, canal for ophthalmica magna artery; c.II, canal for the optic nerve; c.pro, canal for the profundus nerve; c.prt, canals for twigs of medial profundus branch and vessels; c.v.pit, canal for the pituitary vein; cr, crack in the solum nasi; fe.vl, fenestra ventrolateralis; g.a.ci, groove for internal carotid artery; g.a.pal, groove for palatine artery; g.a.ps, groove for “efferent pseudobranchial artery”; h.bu, horizontal bulge of the nasal capsule; hyp.f, hypophysial fossa; lopc, lateral profundus nerve canal; mopc, medial profundus nerve canal; nb.c, nasobasal canal; nca, nasal capsule; orc, orbitonasal nerve canal; pin.c, pineal canal; ppin.c, parapineal canal; re.l, lateral recess of the nasal capsule; trans.c, transverse canal. 373 canals that arises from the dorsal surface of the olfactory tracts near their junction with the nasal cavities. No such canals are present in Powichthys, Youngolepis or (as far as we can tell) porolepiforms, though in Powichthys a single horizontal transverse canal links the two olfactory tracts. An unusual feature of the middle part of the cranial cavity of Powichthys spitsbergensis is the brevity of the forebrain division. In the porolepiform Glyptolepis (Jarvik 1972: fig. 17) the anterior margin of the forebrain cavity rises sharply above the bases of the olfactory tracts. In Powichthys, however, this margin is only slightly anterior to the level of the optic tracts, and the pineal and parapineal canals (pin.c, ppin.c, Fig. 7) arise from the top of the anterior wall of the forebrain cavity rather than from its roof as in Glyptolepis. The pineal and parapineal tracts closely resemble those of Glyptolepis, lying side by side enclosed in separate canals. The corresponding region of Youngolepis is more difficult to interpret, as it is imperfectly preserved (Chang 1982: fig. 4, slices 184-210), but it is apparent that both the pineal and parapineal organs were housed in a single cavity that was anteroposteriorly longer than wide (Chang 1982: figs. 17, 19), as in tetrapodomorphs (Romer 1937, Jarvik 1980). The endocranial cavity of Youngolepis does not appear to have risen much above the level of the olfactory tracts, unless part of it was accommodated in the pineal cavity (which seems unlikely), but it probably extended a short distance anterior to the pineal and parapineal organs. Again this resembles tetrapodomorphs, particularly Ectosteorhachis (Romer 1937); in Eusthenopteron the forebrain cavity is similarly low but proportionately longer (and the olfactory canals shorter), probably as a consequence of the proportionately longer and narrower orbitotemporal braincase region. The optic nerves (c.II, Fig. 7E) emerge ventrolaterally from the middle part of the cranial cavity, marginally posterior to the level of the pineal and parapineal, in the same way as in Glyptolepis, Eusthenopteron and Youngolepis; in Ectosteorhachis the pattern is also comparable except that the pineal eminence occupies a somewhat more posterior position. No trace of a canal for nerve III can be discerned behind the optic nerve in Powichthys spitsbergensis, so that nerve must have emerged more dorsally through the unossified part of the braincase wall. In this respect Powichthys spitsbergensis resembles Youngolepis, but differs from Glyptolepis and Eusthenopteron where nerve III emerges immediately posterior to the optic nerve. Powichthys thorsteinssoni has an external nerve III foramen located posterodorsal to the optic nerve foramen (Jessen 1980: fig. 5), suggesting that it agrees with P. spitsbergensis in this regard. The hypophysial fossa (hyp.f, Fig. 7) resembles that of Glyptolepis, and differs from those of Eusthenopteron, Youngolepis and Ectosteorhachis, as regards its relatively large size and long horizontal division. In some other respects, however, it appears to represent a rather generalized sarcopterygian morphology when compared to that of Glyptolepis. The pituitary vein (c.v.pit, Fig. 7) emerges from the posterior corner of the fossa as in Eusthenopteron and Youngolepis, and shows the same sharp change of direction from posterolateral to anterodorsolateral immediately after exiting the fossa. By contrast, the pituitary vein of Glyptolepis emerges from the side wall of the fossa and runs dorsolaterally without a sharp change of direction. The fossa of Powichthys also lacks the pair of anterior vertical canals seen in Glyptolepis and interpreted by Jarvik (1972) as housing the pars tuberalis. The ventral canal network of the fossa closely resembles that of Youngolepis but differs from the patterns seen in both Glyptolepis and Eusthenopteron. As in Youngolepis, the pattern is essentially orthogonal: the carotid arteries (g.a.ci, Fig. 7), which are oriented anteroposteriorly, run forwards on either side of the hypophysial fossa, where each is joined by a laterally directed canal interpreted by Chang (1982) as transmitting the efferent pseudobranchial artery (g.a.ps, Fig. 7). Immediately mesial to the junction between the carotid and pseudobranchial canals, the canal plexus communicates with the hypophysial fossa. The canals for the palatine arteries (g.a.pal, Fig. 7) emerge anteriorly as direct continuations of the carotid canals. The only significant difference between Powichthys spitsbergensis and Youngolepis in this regard is that the efferent pseudobranchial canal is proportionately somewhat smaller in Powichthys spitsbergensis. In both P. spitsbergensis and Youngolepis, the carotid, palatal and efferent pseudobranchial canals are external to the braincase, running between the braincase walls, parasphenoid and parasphenotic dental plates. Only the short mesially directed canal that runs from the carotid/pseudobranchial junction into the hypophysial fossa actually enters the braincase. In Glyptolepis, by contrast, the carotid arteries enter the fossa from a posterolateral direction, in a position corresponding to the efferent pseudobranchial canal. A small foramen on the posterior part of the parasphenoid (“c.a.cib”) is identified by Jarvik (1972: fig. 31) as the opening for a subsidiary branch of the carotid, and this corresponds positionally with the carotid foramen of Powichthys spitsbergensis and Youngolepis, but unfortunately the reconstruction of the hypophysial fossa (Jarvik 1972: fig. 17) does not 374 show the course of this canal or how it relates to the main carotid tract. The palatal artery of Glyptolepis also emerges anterolaterally from the hypophysial fossa itself, at approximately a 90 degree angle to the carotid canal, rather than forming an anterior continuation of the carotid canal as in Powichthys and Youngolepis. The carotid canals of Eusthenopteron and Ectosteorhachis (and indeed all tetrapodomorph fishes, as far as is known) enter the hypophysial fossa from the sides in the same manner as the main carotid canals of Glyptolepis (there are no subsidiary carotid branches in these fishes). In Ectosteorhachis the palatine artery canal emerges from the base of the fossa at an angle to the carotid canal; in Eusthenopteron it has not been identified (Jarvik 1980: fig. 87). Powichthys thorsteinssoni differs somewhat from P. spitsbergensis as regards this part of the anatomy. The posterior carotid foramen appears considerably smaller than that in P. spitsbergensis, and the “efferent pseudobranchial” foramen correspondingly bigger. Furthermore, the palatine artery emerges from a hole in the braincase wall and must thus arise from the hypophysial fossa itself rather than from the space between braincase and parasphenoid as in P. spitsbergensis and Youngolepis. P. thorsteinssoni bears greater resemblance to Glyptolepis in this respect. The most posterior part of the ethmosphenoid side wall is pierced by a cranial nerve canal that runs anterolaterally from the cavity to the exterior and which by its position and orientation must represent the exit for the profundus nerve (c.pro, Figs. 4E, 7). This matches the condition in P. thorsteinssoni, although Jessen (1980) mistakenly described the profundus foramen as an opening for the jugular vein (Ahlberg 1991), but differs from the pattern in Glyptolepis and tetrapodomorph fishes where the profundus nerve is believed to exit through the intracranial joint. Unlike in P. thorsteinssoni we have not observed a trigeminal foramen in the ethmosphenoid of P. spitsbergensis, indicating that the trigeminal emerged either through the intracranial joint as in coelacanths (Millot & Anthony 1965) or through the otoccipital. The exterior ethmosphenoid morphology of Powichthys spitsbergensis compares well with that of P. thorsteinssoni, but there are certain minor differences. Unlike P. thorsteinssoni, P. spitsbergensis has no descending processes with unfinished tips that emerge from the posteroventral margin of the sphenoid region. Instead it has a single process (pr.d.sp?, Fig. 4) on the left side of the specimen, lacking an unfinished tip and directed laterally; its homology with the descending processes of P. thorsteinssoni must be regarded as doubtful. This feature is of considerable importance, because such similar descending processes are also present in Youngolepis (pr.d, Chang 1982: figs. 7, 10) and in the early actinopterygian Mimia (Gardiner 1984: figs. 13, 22, 23, Janvier 1996: fig. 4.66): in both genera they approach closely to the ventral end of the lateral commissure, and appear to form a synchondrotic bridge enclosing a foramen for the orbitonasal artery (Gardiner 1984, Bjerring 1994). Because it links the sphenoid region and the otic capsule, it is functionally dependent on an immobile intracranial joint. No such bridge has been described in P. thorsteinssoni, but the lateral commissure of that taxon is poorly preserved and has not been described in detail. As the intracranial joint of P. thorsteinssoni demonstrably is immobilized (the parietal and postparietal shields are sutured together) we regard it as probable that a bridge was in fact present. In P. spitsbergensis, however, that does not appear to have been the case. Other differences include the narrower parasphenoid in P. spitsbergensis, the somewhat more posterior position of the foramen for the pituitary vein, the absence of a trigeminal foramen in the ethmosphenoid, and the absence of separate arcual plates between the left and right processus connectens. Our new data from Powichthys spitsbergensis allow us to address two phylogenetic questions: firstly, are P. spitsbergensis and P. thorsteinssoni congeneric and secondly, how are these species related to other sarcopterygians? With respect to the first question, similarities include one apparent synapomorphy (the paired ventral processes/“mushroom-like area” of the ethmoid), and a number of characters that have a broader distribution. These characters include: 1) the profundus nerve exit in the side wall of the ethmosphenoid (shared with coelacanths and arguably Youngolepis), 2) the independent premaxilla which is not penetrated by the infraorbital lateral line canal (shared with a range of primitive sarcopterygians including Youngolepis, Diabolepis, Kenichthys and probably Achoania), and 3) the presence of parasphenotic dental plates (arguably shared with Youngolepis, though in that genus their proximal ends are fused with the parasphenoid) (Jarvik 1980; Chang 1982, 1995; Zhu et al. 2001; Zhu & Ahlberg 2004). Interestingly, none of these characters is shared with porolepiforms (Jarvik 1972, Ahlberg 1991). The similarities between Powichthys thorsteinssoni and P. spitsbergensis show that the two are closely related and provide some (albeit weak) evidence that they may form a clade. 375 Turning to the second question, the new endocranial data from Powichthys spitsbergensis strongly emphasize its porolepiform-like nature. Particularly significant is the observation that P. spitsbergensis in most respects resembles Glyptolepis much more closely than it does Youngolepis; the nasal capsules, pineal and parapineal organs, and hypophysis all exemplify this pattern. This favours Jessen’s original assignment of Powichthys to the Porolepiformes (Jessen 1975, 1980; Jarvik 1980), against more recent phylogenies that have placed Powichthys as the sister group of Youngolepis (Chang & Smith 1992) or Youngolepis + Dipnoi (Ahlberg 1991, Zhu et al. 2001). If Jessen was correct, it raises questions about homoplasy in the evolution of a number of structures, notably including the mobility of the intracranial joint. However, in order to provide a proper comparative context for the new Powichthys data, further endocranial morphologies need to be understood. These include a wider range of porolepiforms (most of the currently available information derives from Glyptolepis groenlandica) as well as Early Devonian taxa Psarolepis, Achoania and Styloichthys (Yu 1998, Zhu et al. 2001, Zhu & Yu 2002). Acknowledgements We are grateful to the team who operated the high-resolution CT scanning of the specimen of Powichthys spitsbergensis, i. e., Tim Rowe, Julian Humphries, Matt Colbert & Rich Ketcham (University of Texas, Austin). Thanks are due to Daniel Goujet & Philippe Janvier (MNHN, Paris) who passed the specimen on to us for study. The Materialise team efficiently supported our needs and requests concerning their software Mimics v.10.11. Didier Geffard-Kuriyama made the line drawings. We are also grateful to the editors for the invitation to contribute to this volume and we sincerely congratulate the honoree, Chang Meemann, whose outstanding work and personal qualities have been constant inspirations to both of us. This paper is a contribution to IGCP Project 491 (Middle Palaeozoic Vertebrate Biogeography, Palaeogeography and Climate). References Ahlberg, P. E. (1991): A re-examination of sarcopterygian interrelationships, with special reference to the Porolepiformes. – Zool. J. Linn. Soc. 103: 241-287. Ahlberg, P. E. & Johanson, Z. (1998): Osteolepiformes and the ancestry of Tetrapods. – Nature 395: 792-794. Bjerring, H. C. (1975): Contribution à la connaissance de la neuro-épiphyse chez les urodèles et leurs ancêtres porolépiformes avec quelques remarques sur la signification évolutive des muscles striés parfois présents dans la région neuro-épiphysaire des mammifères. – Colloques int. Cent. Natn. Rech. Scient. 218: 231-256. – (1991): Some features of the olfactory organ in a Middle Devonian porolepiform, Glyptolepis groenlandica. – Palaeontogr. A 219: 89-95. – (1994): The evolutionary origin and homologues of the supracochlear lamina: a contribution to our knowledge of mammalian ancestry. – Acta Zool., Stockholm 75: 359-369. – (1995): The question of a homology between the reptilian processus basipterygoideus and the mammalian processus alaris. – Palaeontogr. A 235: 79-96. Chang, M.-M. (1982): The braincase of Youngolepis, a Lower Devonian crossopterygian from Yunnan, southwestern China. – 113 pp.; Ph.D. dissertation, University of Stockholm. – (1995): Diabolepis and its bearing on the relationships between porolepiforms and dipnoans. – Bull. Mus. Natl. Hist. Natur., Paris 17 (C): 235-268. Chang, M.-M. & Smith, M. M. (1992): Is Youngolepis a porolepiform? – J. Vert. Paleontol. 12: 294-312. Chang, M.-M. & Yu, X.-B. (1997): Reexamination of the relationship of Middle Devonian osteolepids – fossil characters and their interpretations. Am. Mus. Novitates 3189: 1-20. Clément, G. (2001): Evidence for lack of choanae in the Porolepiformes. – J. Vert. Paleontol. 21 (4): 795-802. Clément, G. & Janvier, P. (2004): Powichthys spitsbergensis sp. nov., a new member of the Dipnomorpha (Sarcopterygii, lobe-finned fishes) from the Lower Devonian of Spitsbergen, with remarks on basal dipnomorph anatomy. – Fossils and Strata 50: 92-112. Cloutier, R. & Ahlberg, P. E. (1996): Morphology, characters, and the interrelationships of the basal sarcopterygians. – In: Stiassny, M. L. J., Parenti, L. & Johnson, G. D. (eds): Interrelationships of Fishes II; p. 445-479; New York (Academic Press). Gardiner, B. C. (1984): The relationships of the palaeoniscid fishes, a review based on new specimens of Mimia and Moythomasia from the Upper Devonian of Western Australia. – Bull. Brit. Mus. Nat. Hist., Geol. 37: 173-427. 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(1965): Anatomie de Latimeria chalumnae. II. Système nerveux et organes des sens. – 130 pp.; Paris (Cent. Natn. Rech. Scient.). MIMICS, v10.11. (2006): Medical image processing software. Materialise NV, Leuven, Belgium. www.materialise.com/mimics Romer, A. S. (1937): The braincase of the Carboniferous crossopterygian Megalichthys nitidus. – Bull. Mus. Comp. Zool. Harv. 82: 1-73. Yu, X.-B. (1998): A new porolepiform-like fish, Psarolepis romeri, gen. et sp. nov. (Sarcopterygii, Osteichthyes) from the Lower Devonian of Yunnan, China. – J. Vert. Paleontol. 18: 261-274. Zhu, M. & Ahlberg, P. E. (2004): The origin of the internal nostril of tetrapods. – Nature 432: 94-97. Zhu, M. & Yu, X.-B. (2002): A primitive fish close to the common ancestor of tetrapods and lungfishes. – Nature 418: 767-770. Zhu, M., Yu, X.-B. & Ahlberg, P. E. (2001): A primitive sarcopterygian fish with an eyestalk. – Nature 410: 81-84. Authors’ addresses: Gaël Clément, Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18A, 752 36 Uppsala, Sweden. Current address: Département Histoire de la Terre, UMR 7207 du CNRS, Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements, Muséum national d’Histoire naturelle, case postale 38, 57 rue Cuvier, F-75231 Paris cedex 05, France. E-mail: gclement@mnhn.fr Per E. Ahlberg, Subdepartment of Evolution and Development, Department of Organismal Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18A, 752 36 Uppsala, Sweden. E-mail: per.ahlberg@ebc.uu.se 377 378 The study of fossil fishes has advanced significantly over the past few years, giving scientists a rare opportunity to understand the origin and early evolution of major vertebrate groups, ranging from the jawless agnathans to piscine gnathostomes (placoderms, acanthodians, chondrichthyans and osteichthyans). This book presents recent findings on the morphology, phylogeny and paleobiogeography of fossil fishes, as a tribute to Professor Meemann Chang for her contributions to paleoichthyology and to the study of early vertebrate evolution. With a foreword by Dr. Henry Gee (Senior Science Editor of Nature), an introduction, 22 research papers by leading vertebrate paleontologists from 14 countries, and 220 photos and illustrations, this book covers important fossil forms ranging from the Paleozoic to the Cenozoic and reflects research advances based on traditional paleontological methods as well as new techniques such as CT scanning. For fossil agnathans, a new heterostracan is described from the western U.S., the interrelationships and evolutionary history of anaspids are discussed, and evidence is presented showing that anaspids or anaspid-like agnathans may have had a spiral intestine similar to that of gnathostomes. One paper on acanthodians shows that the enigmatic Machaeracanthus may have had ‘paired pairs’ of pectoral fin spines and a perichondrally ossified scapulocoracoid. New placoderms from northern Siberia and western Australia are described, and the pectoral fin development in gnathostomes is reviewed based on a revision of previous hypotheses and new fossil arthrodire material. Chondrichthyans are represented by the description of a giant electric ray from the Eocene of Italy, and by new articulated material from the Early Devonian of the Northwest Territories showing that the scale- and spine-based distinctions between acanthodians and chondrichthyans do not account for the diversity that is now apparent. Nine papers on osteichthyans cover wide ranging topics from the cosmine histology of a stem sarcopterygian, to the characters of the stem tetrapod neurocranium, and to new Tertiary osteoglossid fishes. New morphological and phylogenetic information on the snout of Devonian dipnoans and the neurocranium of Powichthys is presented based on CT scanning. An uncrushed specimen of Eusthenopteron enables a revision of the ethmosphenoid morphology bearing on the choana, while a lungfish study indicates that the postcranial anatomy may be an underexploited source of characters for phylogenetic studies. The role of fossils in phylogenetic studies is also examined based on teleost phylogenies. While the link between morphology, phylogeny and paleobiogeography permeates many papers, two papers have a predominant focus on paleoecology and paleobiogeography – one reviewing the ecological connections and paleobiogeographic implications of the Jehol Biota, and the other reviewing the South American Devonian vertebrate record, demonstrating the presence of two faunal assemblages of which the earlier one equates with the “Malvinokaffric Realm” based on invertebrate communities. Professor Meemann Chang is a Research Professor at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Beijing, China. She is an honorary member of the Society of Vertebrate Paleontology, a past president of the International Paleontological Association, and a Member (Academician) of the Chinese Academy of Sciences. ISBN 978-3-89937-122-2 www.pfeil-verlag.de