Selachii, Cuvier, 1829

Ricqlès, Armand de, Taquet, Philippe & Buffrenil, Vivian de, 2009, “ Rediscovery ” of Paul Gervais’ paleohistological collection, Geodiversitas 31 (4), pp. 943-971 : 947-951

Selachii

3. “ Lamna fossil. Longitudinal section showing cellular appearance” (n.b. original label in English). Ink label: 1938-630 ( Fig. 1C ).

Description. A longitudinal section through an elongate, thin tooth-like organ, about 12 mm long and 3 mm wide at its base. The section shows two different tissue types, a and b.

Tissue a: all the periphery is formed by a homogeneous tissue of constant thickness, birefringent under crossed nicols. This tissue is itself divided in three regions. a1: the most external one is characterized by very numerous thin dark canaliculi perpendicular to the free surface. a2: the middle one is almost devoid of canaliculi and shows a faint organisation of the tissue as very thin “sheets” layered parallel to the free surface. a3: the inner one, with a complement of canaliculi similar to a1 but far less numerous. This lesser density allows observing some branching patterns of the canaliculi, several branches uniting from the periphery towards the center.

Tissue b: the internal part of the organ is made of a cone which almost reaches the surface at the tip of the tooth. This cone is formed by a highly birefringent vascularized tissue. Numerous vascular canals of small diameter are lining the limit between tissues a and b. Large and small vascular canals with irregular branching patterns are spread deeper within tissue b. Actually, there is no structural discontinuity at the limit between tissues a and b, but only a change in the orientation of canaliculi and tissue fibers, plus vascularity restricted to tissue b. The canaliculi are numerous in tissue b, but highly irregular, forming locally a very dense meshwork. They are far less numerous or almost lacking in the material immediately surrounding the vascular canals. There is nothing like a pulp cavity in the structure.

Comments. This thin section is very interesting from an historical-technological point of view. It is still technically excellent. The glass plate is not standard but very small (54 × 17mm). There is no cover slip and the section itself is only protected by a blue paper glued on both faces of the glass plate, with a circular opening around the section itself. This paper also bears the original label in English. Very likely the section was processed in Great Britain sometimes during the early development of the thin section technique.

Histologically, we interpret “tissue a ” as a kind of orthodentine, forming the so-called “manteldentin” at the periphery of a tooth. “Tissue b ” would be a so-called “circumpulpar dentin”, actually a vasodentin, with centripetal deposition of dentin around vascular canals, the denteons of Ørvig (e.g., 1967), analogous to the primary osteons of bone. There is no evidence of any enameloid.

“AMPHIBIANS” Temnospondylii

4. “ Archegosaurus latirostris de Lebach 1870 -480”. Pencil number: 1073, ink label: Anat. Comp. 1875.

According to the species name “ latirostris ” (unvalid) and the locality, “ Archegosaurus latirostris de Lebach , could be a juvenile Archegosaurus decheni (Steyer pers. comm.).

Description. Two partial cross sections of simple labyrinthodont teeth, still partially embeded in the matrix. The pulp cavity is free, with about 12 short radial expansions of dentine protruding in it. Each inward expansion roughly coincides with a slight groove at the external surface of tooth.Tooth material is monorefringent under crossed nicols. There is no distinct coating of enamel. A thin region of globular dentin forms the tooth material at a small distance from its external surface. Inside, the tooth is formed of orthodentin with very long, thin, strait canaliculi within and between the radial expansions. Overall, the material agrees well with Schultze’s (1969) illustrations of Lyrocephaliscus Wiman, 1910 ( Schultze 1969: pl. 21 fig. 3, pl. 22 fig. 2), a Trematosaur.

5. “ Archegosaurus latirostris de Lebach 1870 -480”. Pencil number: 1073, ink label: Anat. Comp. 1875 ( Fig. 1D ).

Description. One isolated tooth free of matrix. This cross section may come from a region somehow closer to the tooth tip. It shows about 20 radial expansions into the free pulp cavity. Long expansions tend to alternate with short ones, and the long ones slightly undulate. Again, no enamel could be deciphered. However the section slightly shows the radial expansions of the external dentine forming the core of the radial fences.

6. (N-1) – “Archegosaure de Lebach, crâne”. No numbers, no pencil indication.

Description. About 10 osseous fragments are scattered under the coverslip. In most fragments the bone tissue is sectioned longitudinally. Osteocyte lacunae, more or less plump or elongate in shape, are set in line with the parallel fibered bone tissue. Some vascular canals, forming primary and secondary osteons are also sectioned longitudinally. In two fragments, the structure is more complex, with several vascular canals parallel to each others or faintly converging in a fan-shaped arrangement. Sharpey’s fibers are numerous after a faint annulus. This structure is suggestive of the bone not far away from a tooth insertion.

7. “ Labyrinthodon – Wurtemberg. Os crânien”. Pencil number: 1074, ink label: 1938-613. Anat. Comp. 1875 ( Fig. 1E ).

Description. A few square millimetres probably from a horizontal (oblique) section in the external cortex of a dermal bone. The light brown bony material is mostly birefringent under crossed nicols, especially in regions around vascular canals (primary osteons).No secondary osteons (Haversian systems) are observed. Osteocytic lacunae are difficult to observe. Noticeable locally are Sharpey’s fibers and superposition of undulating dark lines strongly suggesting annuli or LAGs (= lines of arrested growth), as well known among Stegocephalians (e.g., Ricqlès 1995b).

8. “ Labyrinthodon du Wurtemberg. Écaille ? céphalique.” Pencil number: 1078, ink label: Anat.Comp. 1938-no.613.

Description. Probably a horizontal section in the external cortex of a dermal bone, broken in several small fragments, and further damaged by balsam shrinkage.Bone is strongly birefringent under crossed nicols, apparently demonstrating two orthogonal superimposed plies of bony lamellae.

9. “ Labyrinthodon de Stuttgart. Écaille ? temporale”. Pencil number: 1077, ink label: 1938-613. Charles Marchand, Préparateur à Paris. ( Fig. 1F )

Description. A good section from the free surface of a bone (with matrix) to about 3 mm deep in the cortex. No superficial ornamentation is obvious.The bone is generally birefringent under crossed nicols with a clear lamellar organisation. It contains about 16 superimposed rows of vascular canals of small diameter, sectioned longitudinally and circularly, and organized as primary osteons laid down in a “lamellar-zonal” matrix of periosteal origin. However, neither Sharpey’s fibers, nor cyclical annuli could be observed. Secondary osteons seem to be lacking.

10. “ Trimerorachis insignis . Permien du Texas ”. Pencil number: 1900. Ink label: Anat. Comp. 1878. Mr Cope.

Description. A poorly preserved bone fragment, probably sectioned vertically. What might have been the external, ornamented surface appears to have been mostly replaced by fan shaped, radiating black mineral structures which could be superficially mistaken for Sharpey’s fiber bundles. Actually, very little of the external bone is preserved. Most of the specimen is formed by thin, remodelled endosteal bone trabeculae forming a highly cancellous tissue. In many places, osteocytic lacunae appear to have experienced localized widening, probably the result of post mortem destruction.Indeed, evidence of boring canals of mycelial origin can be observed locally.

Comments. Occurrence of Trimerorachis in the collection and the presence of Professor Edward D. Cope’s name on the section label demonstrate the relationships among French and American paleontologists of the era.

11. “ Prototriton de Gaudry. Permien d’Autun”. Pencil number: 1075, ink label: 1938-613.

Description. A section containing several “ Prototriton ” (sic) bones still in their relative positions in the matrix. What can be observed suggests a complete small skeleton sectioned frontally, e.g., parallel to the bed plate in which it lies dorso-ventrally. Unfortunately the technical quality of the section is poor. It nevertheless allows deciphering occurrence of several bones and teeth. At least eight teeth can be observed in situ on teeth-bearing bones. The teeth are non labyrinthodont in structure, with a very thin dentin surrounding a relatively large pulp cavity. They appear to be pedicellate as among most Lissamphibians and a region of intensive remodelling, where a tooth base ankyloses on the dentigerous bone is visible. On the other hand neither enamel or enameloid, nor bicuspidate structure could be observed. Various parts of the skeleton, including dermal bones, and short and long endoskeletal bones, are sectioned more or less at random. Bone tissue shows little details but appears to have been poorly vascularized. Some long bones sectioned longitudinally may show sequence of endochondral ossification in the calcified cartilage of metaphyses. However the poor quality of the section and randomness of orientations preclude detailed observations.

Comments. The cover slip of this section is not round (as on most sections in the collection) but rectangular, as in modern thin sections. The endoskeletal bone structures preserved in this specimen may be compared to those of post metamorphic Urodeles ( Ricqlès 1965).

12. “ Prototriton de Gaudry. Permien d’Autun”. No numbers.

Description. A large thin section, obviously from the same material as above (11). Preservation is very poor (see Comments). The section is rather thick but allows deciphering a longitudinal section in a limb with the stylo-zeugopodials in articulation (no autopodial is preserved).

Comments. This section has a large oval-shaped coverslip. This has largely separated from the glass plate over time and gently curled. The balsam is badly cracked and the section will have to be intensively cured for further preservation and observation.

13. (N-2) – Plathyosaurus (?) Ink label: “fossil bone Plathyosaurus” (in English). No number.

Description. A small (4 × 4 mm) fragment of cancellous bone. This spongy bone tissue is formed by rather coarse irregular trabeculae, leaving between them irregularly elongate spaces. The bone tissue has a great cellular density and shows extensive erosion/reconstruction cycles, as well as osteon-like structures within the thick trabeculae. Some aspects within the trabeculae are suggestive of globuli ossei. If so this tissue would originate in part from previous endochondral ossification.

Comments. Another thin section of English origin, exactly similar to section 14 (N-3) (see below). It is not possible to decipher the exact label name; both “Plathyosaurus” and “Plathioposaurus” can be read. The former name does not appear to match any genus name coined to a fossil Amphibian or Reptile during the 19th century. The later name appears close to Platyposaurus, which would be a synonym given by Lydekker, 1890 to Platyops Twelvetrees, 1880 , a Permian “Rachitome” ( Lehman 1955).

“REPTILES” Ichthyosauria

14. (N-3) – Ichthyosaurus . Ink label “fossil bone Ichthyosaurus ” (in English). No number.

Description. A bone tissue fragment of 5 × 5 mm. This is a microcancellous bone tissue spatially organized along a very regular “honeycomb” pattern. The thickness of the section prevents from observing details of the tissue itself.

Comments. One of several sections probably pertaining to Paul Gervais’ collection but of English origin. The section is set on a standard (7.6 × 2.5 cm) glass plate with a round cover slip. The glass is entirely covered (and protected) by a red paper below, a red and gold paper above; with the label “C. M. TOP- PING” appearing twice into circles on top.

15. “ Ichthyosaurus communis d’Angleterre , côte.” Pencil number: 983, ink label: 1938 no. 619.

Description. A good cross section of a small bone. The section is irregularly oval, about 5 mm in its largest diameter, and with one flat, slightly concave face. The cortex merges very gently with the more cancellous central region, as usual among aquatic tetrapods ( Ricqlès & Buffrénil 2001). The outer cortex is primary in structure, containing longitudinally oriented primary osteons embedded in a woven tissue, radially oriented in the thickest par of the cortex. In the thiner (more slowly growing) regions, the cortex shows less vascularity, no radial orientation and some evidence of cyclical deposition. The medullar region is rather dense, small marrow cavities being set apart by thick, irregular secondary trabeculae of endosteal bone tissue. No remnants of cartilage are observed.

Comment. The thick convoluted trabeculae in the medullary region agree with the (non pathological) “osteosclerotic” condition often observed among aquatic tetrapods ( Ricqlès & Buffrénil 2001).

16. “Ichthyosaure du Spitzberg, vertèbre”. Pencil number: 965, ink label: 1938-619.

Description. Only cancellous bone tissue can be observed in cross section. This is a “mature” bone tissue with evidence of erosion/reconstruction cycles forming areolar secondary endosteal trabeculae. Some structures agree with the large endosteal secondary osteons lining the marrow sinuses often observed at the periphery of the medullar region in many large tetrapods.

Comments. Pollution by grinding powder hinders detailled observations. The structures are rather similar to the ones observed in an adult Plesiosaur phalanx (see Ricqlès & Buffrénil 2001: pl. 4, fig. F.).

17. “Ichthyosaure du Spitzberg, vertèbre”. Pencil number: 985, ink label: 1938-619.

Description. A large portion of cancellous bone retaining its microanatomical organisation, possibly suggesting longitudinal orientation of bone trabeculae along the section, in a vertebral centrum. Otherwise the section is too thick to show histological details.

18. “Ichthyosaure du Spitzberg, côte”. Pencil number: 984, ink label: 1938-619.

Description. A partial cross section of a bone of at least 10 mm in diameter. A central free marrow cavity (diameter 4 mm) contains a few bone trabeculae. The remains of the cortex is 5 mm thick and entirely formed by a very cancellous tissue, somewhat organized radially and longitudinally. No histological details can be deciphered because of bone opacity.

19. (N-4) – “Ichthyosaur 16 25 fofsil” (sic) (ink label on blue paper). Museum, Anatomie comparée (printed label on white paper) with pencil number: 1065 ( Fig. 2A ).

Description. A partial cross section from a large tooth (partial diameter 14 mm), close to its base. The tooth has a complex, “folded” structure, showing 9-10 partly preserved folds of dentine circling a large pulp cavity entirely filled by finely cancellous bony tissue.Each individual fold is a U-shaped mass of orthodentine of about one millimetre thick, the top of the U opens towards a small pulp cavity. The orthodentine has typical dentinal tubules, oriented from the periphery to the pulp cavity along radial curves, crossed by several (6 to 8) “growth lines” parallel to the external surface of the folds. Close to the surface, a thin coating of very dark dentine appears to be globular and is capped by a very thin sheet of a strongly birefringent hard tissue with a slightly irregular surface. Between the folds a distinct bone-like tissue contains cell spaces and vascular canals, apparently in structural continuity with the highly birefringent thin sheet mentioned above. This osseous tissue (topologically located outside the dentine) is in continuity with the finely trabecular bone filling the pulp cavity. The dentine folds are isolated from each others at the level of this cross section.

Comments. This section is of a rather good quality. It is mounted on a tiny glass plate, with original label on blue paper, as section no. 3 “ Lamna ” fossil (see above) but better prepared. There is no coverslip and the section is thus technically very similar to section no. 3 and may have the same British origin. The tissue between the dentine folds may be interpreted either as a cellular cementum (as suggested by its specialized fibre systems) or as bone of attachment, nevertheless it merges with the regular bone inside the pulp cavity. There is no clear indication of enamel.

These structures agree with later descriptions of ichthyosaurian teeth by Schultze (1969: 111-115, text fig. 18 and pl. XVI figs 1, 2) and Schmidt & Kiel (1971).

Figures

FIG. 1. — A, General aspect of the ground sections in Paul Gervais’ collection; above: section 76 x 26 mm (a format still in use today) from a dinosaur bone (so called “reptile de la Nerthe”) made in Paris by E. Bourgogne (section 27 [N-10]), below: section from an Iguanodon Mantell, 1809 bone made in Great Britain (section 23 [N-7]). The latter section is protected by a cover of strong paper; B, detail of the kind of information written on the labels.This section (section 28 [N-11]) is supposed to be from a dinosaur;C, tooth-like organ of Lamna Cuvier, 1816 (section no. 3), longitudinal section in ordinary transmitted light, a1-3 and b refer to the two main tissue types observed in this section (see description in text); D, Archegosaurus latirostris Jordan, 1849 (i.e. juvenile Archegosaurus decheni Goldfuss, 1847) tooth (section no. 4), cross section in ordinary transmitted light, globular dentine (gd, dark peripheral layer) is close to the tooth surface; E, section of a “cranial bone” of Labyrinthodon Owen, 1842, a synonym of Mastodonsaurus Jaeger, 1828 from Wurtemberg (section no. 7), ordinary transmitted light, a few vascular canals and lignes of arrested growths (arrows, lines of arrested growth) can be observed;F, section of the “temporal scale” of Labyrinthodon from Stuttgart (section no. 9), polarized transmitted light (crossed nicols), the tissue is finely lamellar. Scale bars: A, 26 mm; B, 13 mm; C, 0.55 mm; D, 0.32 mm; E, 1 mm; F, 1.2 mm.

FIG. 2. — A, Ichthyosaur tooth (section no. 19), cross section in ordinary transmitted light, conspicious growth marks (arrow heads) are present in the dentine; B, neural spine of a plesiosaur (section no. 20), cross section in ordinary transmitted light, the cores of the trabeculae still contain remnants of calcified cartilage matrix (arrow); C, Iguanodon Mantell, 1809 femur (section no. 25), cross section in ordinary transmitted light, the bone tissue is of the laminar type (lb); D, section of an undetermined bone from Rhabdodon Matheron, 1869. (section no. 26), the deep cortex (at the lower right corner of the photo) is extensively eroded and broad resorption bays (asterisk) are created; E, Megatherium Cuvier, 1796 tooth (section no. 36), a and b designate respectively tissues a and b, as described in the text, the sparse remants of tissue c are not visible on this picture, cementing line (cl), vascular canals (vc); F, humerus of a bradypoid (section no. 38), cross section in ordinary transmitted light, primary grossly lamellar cortex (plc), Haversian bone (hb). Scale bars: A, 0.55 mm; B, 0.36 mm; C, 0.85 mm; D, 1 mm; E, 0.20 mm; F, 0.60 mm.