Opetiosaurus Bucchichi. Eine neue fossile Eidechse aus der unteren Kreide von Lesina in Dalmatien

Download 296.46 Kb.
Date conversion16.05.2018
Size296.46 Kb.
  1   2   3

A. Kornhuber Opetiosaurus Bucchichi (trans.) p.

[A translation of A. Kornhuber (30 July 1901), “Opetiosaurus Bucchichi. Eine neue fossile Eidechse aus der unteren Kreide von Lesina in Dalmatien.” Abhandlungen der kaiserlich-königlichen geologischen Reichsanstalt, Wien 17(5): 1-24, with 3 plates. As is characteristic of the time, references to the literature are contained in footnotes, all of which are provided here as sequentially numbered endnotes; to allow the reader to compare these with the original, the page number and footnote number, in that order, are provided in square brackets subsequent to the number of the endnote. All footnotes in this translation are my own. In cases of uncertainty, the original German is quoted in square brackets; my own clarifications are in italics in square brackets. Translation ©2006 by Krister T. Smith.]
Opetiosaurus Bucchichi

a new fossil lizard from the lower Chalk of Lesina in Dalmatia

A. Kornhuber.
With one photographic and two lithographic plates.
In the extensive quarries so long operational between Verbosca and Vérbanj, east of Cittavecchia on the island Lesina in Dalmatia, nearly completely preserved remains of a new fossil saurian were again unearthed in 1899.

The acquisition of the petrifactions just named we owe to the unremittingly active Mr. Gregorio Bucchich1, correspondent and friend of many years to the Royal Imperial Geological Institute, highly honored for his investigations on the natural history of said island by observation, collection and procurement [“Herbeischaffung”] of various objects from the recent and extinct animal and plant worlds.

They [the petrifactions] consist of portions of a part and of a counterpart which enclosed the remains of the animal and moved together as one in the layer of the mountain. From the size of the outline, the pieces of the part are of greater import than the pieces of the counterpart, of which only four small pieces were salvaged during the excavation of the fossil. The largest piece of the part has the form of an irregular square, nearly a trapezoid, 0.54 m in length and 0.44 m in height. It contains the head and most of the torso of the animal, that is, all presacral vertebrae with their ribs, the two sacral vertebrae, and a portion of the anterior caudal vertebrae (these mostly as impressions), as well as the forelimbs, the right hindlimb, and the conspicuously long end of the tail, which is partly an impression and partly comes to us as actual osseous vertebral tissue. The animal is resting on its back. Thus the ventral side of the vertebral column is visible, namely with the underside of the vertebral centra facing the observer. Only in the cervical section, which is strongly arched backwards and to the left, do parts of the lateral surfaces or of the front or back ends of the vertebrae become visible. As the animal was embedded in the marine calcareous mud, later hardened to stone, massive pressure of the [overlying] waters appears to have developed on the left side of the animal alone. As a result, the head, with the contiguous anterior-most three vertebrae of the neck, appears to have been violently separated from the others and shifted to the right side of the animal, up over the the tail, which is is laid out here in a rather straight stretch. It [the tail] lies on the stone about 0.22 m (measured in the anterior direction) from the 25 presacral vertebra. The ribs, lying on the left side of the vertebral column or also tightly appressed, speak further to the pressure mentioned above, whereas those of the right side stand with their distal ends free from the vertebral column. Then the right forelimb was taken from its natural position, and also the right shoulder, which was partly loosened from it, was pushed out to the right; the left forelimb was likewise displaced in this direction, so that it, with the remains of the left portion of the shoulder girdle, projects far over the midline of the vertebral column and is preserved crossing it. Three smallish pieces of the counterpart, whose broken edges partly correspond to the lower back end of the large part and partly fit one another, and which can be joined, contain an impression of the proximal end of the left femur, then its distal end, as well as the bony substance of the left lower leg and and foot, and further away, less clear impressions or even skeletal portions of the anterior third of the caudal vertebral column.

A large, triangular space where a piece of the rock was unfortunately lost separates the last-mentioned smallish piece of the counterpart from the lower edge of the large part. Therefore the respective piece of the caudal vertebral column is also missing and does not follow the hind part of the tail, which, as noted, lies on the largest piece of the counterpart between the head and body.

Of the the counterparts, three smaller pieces of show part of the anterior piece of the caudal vertebral column and a fourth, somewhat larger, the head, mostly preserving the substance of the bones, next to those bones of the caudal vertebral column that are preserved on the large part only as impressions. Thus the stony plates, which enclosed the bony framework on both sides, above and below, often complement one another in a desirable way and ensure the interpretation of the preserved skeletal remains.

The rock in which the the pieces were embedded has a conspicuous similarity of appearance with the lithographic shales of Solnhofen in the Frankish Jura of Bavaria2, and the type of rock has also been given precisely this name3. There are namely low-density, light yellow-gray—here and there streaked with red—, thick, matte limestones that are layered into plates mostly from 1–3 cm thick. These plates are fairly flat, or only here and there wavy, and break flatly.

This plattenkalk was for a long time known as “fish-producing calcareous shales” because of the occurrence of fossil fishes. The first notice of this was given by Fortis4. Later there were very fine specimens in the posession of Prof. Carara in Spalato and in the Chief Imperial Mineral Cabinet in Vienna. J. Heckel5 transmitted extensive descriptions of them and then added a few more to those with R. Kner6. At the encouragement of v. Hauer, Fr. Bassani, Prof. of Geology at the University of Naples, has finally treated the ichthyological fauna there in detail7; Prof. Kramberger (Agram) also presented “Paleoichthyological contributions”8.

The first reptile to become known from the quarries is Hydrosaurus lesinensis, which I described.9 Since then Prof. Dr. Karl Gorjanović-Kramberger, in the Rad of the Jugoslavian [“südslavischen”] Academy of Art and Science in Agram (v. 56, p. 96–123, Pl. I, II; translated into German in the journal of the “Societas historico-naturalis croatica”, v. 7, Agram 1892, p. 72–106), has described the well-preserved remains of a lacertilian and two other fragments, which are presently the property of the widow of Mr. J. Novak, instructor in Zara, and were discovered on the island Lesina in the quarry of the village Vrbanj by the farmer Ivan Račić. Kramberger erected for it a new genus, Aigialosaurus (, coast, shore), named the large, well-preserved species A. dalmaticus, referred vertebral fragments to another species, A. Novaki, and finally compared a piece with two whole and two half dorsal vertebrae, several rib fragments, and impressions of the humerus, radius, ulna, and metacarpals to the similar Mesoleptos Cendrini10 from the black shales of the lower Chalk of Komen in Görzi, which is reposited in the Museo civico of Milan. According to Woodward's Guide in British Museum [sic?]: Reptiles, there is there a “fine specimen” of Aigialosaurus dalmaticus from Lesina, the discovery of which was not made known to me. Prof. Dr. O. Jäkel, as Prof. V. Uhlig most kindly notified me, also claims to have collected a specimen of Carsosaurus in the calcareous shales of Lesina.

Concerning the geologic age of the plattenkalk, it is at this time not yet established with certainty. According to their stratigraphic relationships they belong to the lower Chalk, where Bassani11 also placed them on the basis of his studies of the fish fauna, and so in the Aptian level of Gaul. He compared it [the fauna] with the fauna of Komen, which he held to be contemporaneous, or—on account of a few forms—only a little older. The conclusions of Kramberger12 are also in agreement: he also drew comparisons between the few reptiles that have thus far become known from the two localities. This view is furthermore not contravened by the results of Stache's researches.13 According to these, a depression extends from Cittavecchia unto the haven of Verbosca; this trough is filled up with Terra rossa, fine sand and Gesteinstrümmern [ruins of stonesgraywacke?]. South of this is a nearly east-west trending anticline, building the spine of the mountains, to whose north- and south-dipping layers our rock belongs and on whose north slopes the quarries lie from which, again, the new fossil stems. But the uncertainty noted in the determination of the age of these fossil-producing beds of Lesina is especially grounded in the circumstance that one was unable to discover sufficiently well-preserved petrefactions in the chalks that overlie them14, although these chalks themselves occur under the rudist-producing beds of the upper Chalk which are broadly distributed and highly developed on the island.

The great difficulty that the character of the rock type that encloses our fossil causes for a detailed examination of some particulars I have already thoroughly emphasized at the time I published Hydrosaurus lesinensis15. This time I also made protracted and laborious attempts to prepare the skeleton as much as possible and to remove the calcite crust that covered many places and adhered with exquisite firmness. The first work by mechanical means with the best and keenest delicate chisels was only successful on the vertebral centra and on the proximal ends of the ribs. The method failed, however, on the larger limb bones, on the distal ends of the ribs, on the smaller elements of the caudal vertebral column and the like, because the bony parts to be prepared ran the danger of crumbling on account of their brittleness. I resorted once more to chemical agents. In this I enjoyed the expert advice and the kindly support of my friends, Mssrs. Hofr. Prof. Dr. A. Bauer and his assistent Friedrich Böck, as well as Prof. Max Bamberger. Mr. Böck was especially passionately interested in solving the problem and undertook several experiments after detailed discussions with myself. After the substances already mentioned in my previously mentioned work, namely concentrated acetic acid, hydrochloric acid and nitric acid in varying concentrations, had been applied to well-isolated bits of rock and, as before, just as little favorable results had been achieved, we experimented with more fluid carbonic acid, which we allowed by means of [“mittelst davon” + genetive] saturated wads of filter paper to react on limited places after first having surrounded them each with a small wall of beeswax. Lastly we applied, in the same way, a concentrated solution of doppelt kohlensaurem Natrium [sodium bicarbonate?], in which excess, undissolved salt remained. This last experiment proved to be the relatively most practical. Thus we succeeded, in the larger of the four counterparts, which best represents the head, in removing,

on the more fixed parts of the skull from its entire posterior portion, the not inconsiderable crust of carbonate atop the quadrate and the suspensorium, then [also] from parts of the occipital segment and the neighboring parietal with the temporal fossae, partly also from the first three cervical vertebrae attached to the head, and so enabling a close examination of the elements indicated. In the application of this procedure to smaller, flatter skeletal parts that rise only a little or not at all above the level of the stone plate, the adverse circumstance arose, that the reaction of the acid could not be well circumscribed, so that not only the crust covering the bones but also the surrounding, closely adjacent little particles of rock were attacked and lifted off in the form of small flakes. It was feared that the solution of zwiefach [sic?] kohlensauren Natriums [sodium bicarbonate?] could continue somewhat under the bone and finally cause its separation or lifting from the stone plate, which convinced me to abandon further chemical treatment of the object and content myself with the favorable result that had been achieved especially on the fixed skull and attending pieces. It is my pleasant duty to extend again here my most obliging thanks to the aforementioned Mssrs. for their gracious support and for their genial labor. It cannot be doubted that the procedure with doppelt kohlensaurem Natrium [sodium bicarbonate?] will certainly prove itself to be much more successful with rock of a different character, as seen in the plattenkalk of Lesina. This is the case when the bedding plane or splitting surface of the rock type in which the petrefaction is embedded has a more consistent, coherent structure, without the fissility of the deeper layers, so that the rock is not inclined to disintegrate surficially into thin lamellae, a peculiarity of the black, bituminous shales of Komen, among others, where Jak. Heckel16 with his fish petrefactions as well as myself with Carsosaurus Marchesettii were able to achieve better success with previously known chemical methods.

* *


I now proceed to the description of the new find; only after the conclusion of the description will comparative observations and their implications be added.

A. The Head.

The best-preserved remains of the skull, as already noted, are to be found on the counterpart of the pertinent part of the large main slab. This contains namely the osseous tissue of most of the bones of the head bestowed to us, whereas the part predominantly presents only the impressions worked in it by these very bones. By connecting both figures of the head—namely, the one in the photograph or in the Lichtdruck produced from it, where all pieces of the part are reproduced, and the one represented by a lithograph of the counterpart of the head in Pl. III, Fig. 1—, roughly like the combined sketch of the outline drawing of Pl. II strives to make sensible [“versinnlichen”], one is in the position to gain a better comprehension of the construction of the skull of our fossil.

Because the animal lies on its back, the head accordingly appears to be pressed onto the part with its upper side, that is with the skull roof [“Scheitelstirnfläche”]. With the head in this position the mandible projects its lower edge upward. After the disintegration of the soft parts, the loose connection of the suspensorium of the mandible as well as the symphysis at the anterior ends of both rami, which does not consist in a true joint, were loosened by the pressure of the mud and water masses overlying the remains of the animal. The original vertical orientation of the rami was therefore distorted by compression: indeed, the right ramus was laid flat on its inner side, the left in contrast on its outer side. One also sees them lying in this position in the stone of the small counterpart; they therefore turn their opposite lateral surfaces, namely the right mandibular ramus its outer side, the left its inner side, toward the large part [i.e., not counterpart] and accordingly leave behind impressions on it, or but pieces of the six individual bones that constitute them, as will be discussed more closely in the description of the lower jaw.

Our slabs provide clues to the more detailed depiction of the construction of the skull, particularly the occipital [“Hinterhauptsbein,” which, for Kornhuber, includes the supraoccipital, exoccipital, and basioccipital: see below], the parietal, the frontal, the pre- and postfrontal [=postorbitofrontal] and their processes, the jugal, squamosal [sic., actually supratemporal], supraorbital [palpebral?], and supratemporal [sic., actually squamosal], the quadrate and the lower jaw, less so the palatine, pterygoid, Felsenbein [opisthotic + proötic?] and ectopterygoid, the maxilla and premaxilla, and the nasal and vomer.* Of the remaining bones of the head, none is represented or even only suggested.

On the posterior-most right side of the skull roof, Pl. III, Fig. 1, next to the posterior end of the right jaw ramus, are remnants or fragments of the first three cervical vertebrae, unfortunately incompletely preserved. In front are the occipital and then parietal segments and in large part the frontal section as well, with the temporal fossa [“Schläfengruben”], then the orbits and their margins. Because of an oblique break during the excavation and extraction of the stone slabs that bear the fossil, however, the fore part of the head with the facial bones were lost. The fracture falls close to the connection of the nasal with the frontal and of the maxilla with the prefrontal and the lacrimal. Thus nearly a third of the head, circa 5 cm in length, is missing, except for the lower jaw. Only a poor mold of it on the part shows the roof of the oral cavity, specifically weak imprints of the paired vomer and the tooth rows of the maxilla and premaxilla, where especially the tooth shafts or sockets and a few remnants of the curved [“gekrümmten”], conical crowns are visible. Tiny traces of dentition can be seen encrusting most of the front third of the left mandibular ramus. The articular, at the back end of the right ramus, is well preserved in articulation with the quadrate and is followed (anteriorly) by an oblique break in the same bone and further still the impression of the remainder of the mandible with especially nicely formed negatives of seven of the hind teeth and a few less distinct ones of the front teeth. Exteriorly on the distal [anterior?] quarter of the mandible lies the imprint of a small longish, columnar bone, which comes from the broken-off columella17, and next to it traces of the tooth crowns. Both can also be perceived on the part, where they are materially present. Also appearing more or less clearly on the part (Pl. I), and for the most part well-encrusted, are impressions of the occipital complex [“Occipitale”], the parietal, and the paired frontal. A weakly raised little ridge rises from the latter, corresponding to the median suture; likewise diverging raised lines run anteriorly which correspond to the lateral fissures that the frontal suffered as a result of pressure and that are especially conspicuous on the counterpart. Good impressions of the paired prefrontal and the orbital margin [“Orbitalumrandung”], less clear ones of the postfrontal, maxilla and premaxilla, which are for the most part strongly encrusted by calcite, are also present on this plate [the counterpart]. Naturally, all impressions correspond to the upper side of the skull. On the maxilla only a few tiny traces of tooth crowns can still be recognized. The lower jaw, however, left a surprisingly beautiful impression on the part, on the basis of which the jaw will be described further below. Only with regard to its position will it be noted here that only the anterior and posterior quarters of its left ramus are visible, for the middle appears covered by the skull, whereas the right ramus lies with the exquisite dentition free and leaves a half-disc-shaped impression of the quadrate to be discerned next to it, against the occipital segment of the skull.18

It is primarily the upper part of the occipital that is visible on our counterpart (Fig. 1, Pl. III), i.e., the supraoccipital (s. o.), an irregularly hexagonal small plate of bone with a shallow, median groove bounded by two weak ridges. It slopes rather steeply posteriorly and ends in a short, flat arch [“Bogen”], which probably represents the trace of the posterior skull opening, the foramen occipital [magnum]. As a result variously of pressure and crushing, which were not seldom accompanied by by breaks and displacements, the interpretation of individual elements is made difficult and sometimes also doubtful. Thus, the little indistinct pentagonal piece of bone that lies on the midline of the skull posterior to the just-described piece could be seen as the azygous basioccipital (b. o.), which participates significantly in the construction of the occipital condyle. To the side of this bone, as well as of the supraoccipital, lies then the paired exoccipital (exo.), whose posteromedially directed processes contribute to the completion of the just-mentioned occipital condyle. Laterally, violently separated from the proximal part of the exoccipital by a break into whose cleft, it appears, a part of the first cervical vertebra was pushed forward, lies the distal section of the exoccipital, which, as we will see further below, participates in the suspensorium via the quadrate. This process belongs to a separate bone in the very first developmental stages in lizards which very soon becomes fused with the exoccipital—the paroccipital of Owen, or the opisthotic of other English and German anatomists—of which it constitutes only a portion and therefore may not be taken to be the pars pro toto. It is probably most appropriate to term it the processus paroticus (p. parot.) of the exoccipital.19

The parietal (pa.) lies adjacent to the occipital anteriorly; it is an azygous rectangular bony plate that, broadening anteriorly, streches sideways with winglike processes to the postfrontal and borders the posterior edge of the frontal in a transverse suture, the fronto-parietal suture. Although it cannot be established with certainty on the slabs, this suture also appears, as in other lizards, not to be a true Zackennaht [interdigitating suture?]; rather, the furrow-like anterior edge of the parietal clasped the posterior margin of the frontal to enable a certain mobility of these bones.20 In the anterior third, 5 mm distanced from this suture on the midline, which corresponds to the fontanelle of the separated halves of the parietal at an earlier ontogenetic stage, the foramen parietal is clearly recognizable, generally known as the unossified remnant of a larger embryonic parietal hole. In its posterior half the midline is somewhat deepened; the lateral margins of the parietal run in an inwardly convex arch and constitute the upper border of the temporal fossa, on which both the squamosal [sq.] and the posterior process of the postfrontal lie. The latter [sic.] articulates posteriorly with the supratemporal (s. t.), a thin, oblong bone. From the posterior corner of the parietal diverging processes run obliquely posteriorly and laterally, the parietal process (p. p.), which, however, are cut through in our object by an oblique fracture, which also partly extends onto the adjacent squamosal. The distal end of each parietal process pushes between the parotic process of the lateral occipital, or the exoccipital, and the squamosal and serves to secure this bone in its connection with the distal end of the supratemporal. Combined, all three of these bones are in articular connection with the cephalic condyle of the quadrate. Next to the just-named bones lie smaller little pieces of bone that appear to represent parts of the proötic (petrosal) and the pterygoid. The strong posterior process of the postfrontal connects with the anterior end of the supratemporal. On our counterpart, Pl. III, Fig. 1, at the posterior upper margin of the quadrangular [“rechtseitig”] quadrate and also in impression as a mirror-image on the outline-drawing (Pl. II), the suspensory apparatus mentioned above, the suspensorium for the quadrate, is to be noted. Oblong fragments of bone, which can be discerned on the slab lateral to the parietal between the elements of the suspensorium, could derive from the posterior part of the pterygoid.

The frontal (fr.) is a very elongate sheet of bone, on which the mutual suture of the paired elements that earlier comprised it is now only clear at the posterior end that borders the parietal. Additionally, the surface of this bone shows several fine, anteriorly diverging fractures, splitting of the brittle bony plate that probably resulted from the high pressure. Its posterior edge is united with the anterior margin of the parietal at a nearly straight suture in the previously disclosed manner. From this place of articulation, the frontal narrows anteriorly, or becomes embayed laterally, which concavity constitutes the upper margin of the orbit. The anterior end of the lateral edge unites with the prefrontal, the posterior end with the postfrontal. Anteriorly it appears to have been adjoined by the now-missing, paired nasal; it may have been separated from the maxilla by the highly developed prefrontal (pr. f.). This paired prefrontal is a robust, triangular bone that narrows posteriorly and adjoins the supraorbital (su. orb.) laterally. With their posterior ends, between which the inconspicuous lacrimal inserts, scarcely recognizable on our slab, both [prefrontal and supraorbital] constitute the anterior margin of the orbit. The well-developed, arch-shaped, angular (ju.) continues this [margin] laterally and posteriorly, as our counterpart shows rather very clearly. On the left it is missing entirely, and its middle or angle, around 2.5-cm-long, lies on the large part, on which, however, only an impression is present of the right jugal. The paired postfrontal (po. f.), which adjoins laterally the two bones that are united at the frontoparietal suture [i.e., frontal and parietal...], sends a process laterally and somewhat anteriorly for articulation with the posterior end of the jugal and thereby borders, as with the process that slopes anteriorly and medially and leans against the posterolateral corner of the frontal, the posterior margin of the orbit. On the floor of this [the orbit], as already mentioned, are encrusted, band-like swellings, which, according to their position, must be seen as the pterygoid, running from the posterior orbital margin, and as the ectopterygoid (tr.), [running] toward its lateral [margin], then as the palatine, directed toward the anteromedial orbital margin. A third process of the postfrontal runs straight posteriorly to unite with the supratemporal and participates indirectly in the construction of the previously described three-part suspensory arch [“Schwebebogen”], which functions to suspend the quadrate and thereby the lower jaw.

Unfortunately, on account of the transverse breaking-off of the anterior part of the skull mentioned above, only very tiny fragments of the maxilla remain. To this belong, right and left, anterior and lateral to the prefrontal, supraorbital and the anterior end of the jugal, the respective fragments [“Bruchstücken”] of this most significant of the facial bones. Mention was already made of the alveolar margin of the maxilla and that of the premaxilla, as well as of the traces of the vomer, in the treatment of the impression on the counterpart, which derive from the lost pieces of the anterior part of the head. The maxilla, as can be concluded from the preserved fragments, borders on the prefrontal, a characteristic of the Varanidae, and not on the frontal, as is the case in other saurians, Lacertidae etc.

The right quadrate, os quadratum (q.), l’os tympanic of Cuvier, is well preserved on the small counterpart of the head of our fossil, and its lateral side was entirely freed by chemical preparation; it constitutes a robust, rather thick bone of conch-like form with a laterally directed [“gekehrter”] concavity. Its upper, convex margin—somewhat thinner anteriorly, thicker posteriorly—extends as a hook-like curve posteriorly. The posterodorsal margin also bears the proximal cephalic condyle of the quadrate, which connects with the three coalescent articular surfaces found at the distal ends of the supratemporal, squamosal and processes paroticus. This joint serves primarily for the rotation of the quadrate around its horizontal axis during opening of the mouth—lowering of the jaw—but doubtlessly also afforded a certain rotation of the quadrate around its vertical axis and tehreby a slight lateral displacement of the lower jaw. The distal end of the quadrate is somewhat reduced in size and, with its mandibular condyle, provided for articulation with the articular of the lower jaw, on whose medial side, apposing the corresponding condyle, is developed the articular face [“an dessen Innenseite die dem gennanten Condylus entsprechende Facies articularis angebracht ist”]. On our slab on the posterior fifth of the right ramus of the lower jaw, whose osseous tissue was preserved, one sees this joint indicated by a conspicuous emargination of its dorsal margin vis-à-vis the distal end of the quadrate.

The outline [“Grundrisse”] of the lower jaw, or mandible (md.), corresponding to the wedge-shaped skull, has the form of an isosceles triangle at whose apex a symphysis unites the two halves of the jaw. This symphysis, in the living animal, consisted of fibrous connective tissue, for all signs of a well-developed bony suture are lacking.21 Each half of the lower jaw, also called a ramus, is composed, as in other Sauria, of six pieces of bone, connected to one another by sutures, viz., the tooth-bearing piece, or dentary (d.), the covering piece, or opercular (op.) (splenial of Owen), the angular (an.), the sur- or supraangular (su. an.), the articular (ar.) and the crown-piece, or coronoid (co.). On our stony slab the lower jaw, with its two rami, presents itself in the following manner:

On the counterpart that contains the skull, Pl. III, Fig. 1, the symphysis, which in consequence of the progressive decay saw its fibrous matter gradually soften and loosen, is shown to be separated. At the same time the halves of the jaw were turned onto their sides by the pressure of the water, and thereby their anterior ends were somewhat displaced, so that the left end came to lie somewhat atop that of the right half. Their lateral surfaces were pressed against the enclosing and later hardening mass of rock, so delicately [“zart”] that now, on the counterpart, the lateral surface of the right ramus appears in correspondence to the natural position of the animal in those places where its bony matter was preserved, whereas in places where the bone is missing, deepened impressions of the medial surface of the ramus are seen. Thus there appears on the counterpart the proximal end of the right jaw ramus with the articular, and namely, its lateral surface, and one recognizes also the place where this piece of bone articulated with the distal end of the quadrate, as mentioned above. The bone is then transversely broken off, and anteriorly the impressions of the medial surface of the supraangular, and below this also those of the missing part of the articular and the angular and over both the triangular impression of the coronoid, as well as the angled suture at which the above-named pieces of bone join with the two elements that compose the anterior part of the jaw ramus, namely the opercular and the dentary, are seen more or less clearly. Posteriorly on the dentary, six rather distinct impressions of the tooth row [“Zahnreihe”] are present; anteriorly there are equally numerous but less distinct impressions. When one compares the area of contact of the just-described surface on the part, then one sees there the impressions of the lateral surface of the articular, which extends far anteriorly, then above it the supraangular and under it the angular, farther along the aforementioned suture that runs in an angled groove, farther still and above the medial surface of the coronoid, the bone of which is present, whereupon the opercular, whose matter is only partly preserved, and the dentary, crowned by the beautiful, well-preserved tooth row, seen medially, follow anteriorly.

Only the anterior third of the left mandibular ramus is preserved on the counterpart—on the part one also sees, in part, the posterior third—whereas the middle is covered by the skull, and in particular is shut in by the mass of stone lying on its [the skull’s] side, and so is not observable. This anterior third one sees medially on the counterpart, the bony matter present, with a few poor traces of attachment sites for the teeth, pseudoalvoeli, whereas its lateral surface adheres to the rock. Its [the lateral surface’s] impression on the part, however, which is somewhat encrusted below, permits recognition dorsally of several not especially distinct tooth bases and depressions from the cone-shaped tooth crowns, whose tips appear posteriorly curved. The hard parts that left behind these impressions, however, were lost and can no longer be found on the counterpart.

The length of one mandibular ramus comes to 15 cm, the distance between the knobs at the posterior end of each ramus 7.5 cm.

Extraordinarily noteworthy is the dentition of our fossil. The teeth all have the same form—only slightly wider in the middle of the jaw—on average 4 mm, measured from front to back. A tooth count can be made with fair certainty on the right mandibular ramus on the large part and comes to 17. They either stand closely appressed to one another or show uneven interdental spaces, up to more than 1.5 mm. Because, as is known, the number of teeth in one and the same species of lizard often differs, being lower in youth than in the adult and increasing with progressing age, this point also has little significance in our animal. Most striking, however, is the form of the teeth, which does not otherwise occur in any lacertilian known thus far, nor in any saurian from the post-Cretaceous time. Each tooth crown is namely borne by a base, i.e., a bony little column or a support, 5 mm in height, on average, on which it sits, sharply demarcated and surrounded by a delicate, wall-like ridge [“Erhöhung”]. The base is cylindrical and, diminishing apically, terminates blunt and bevelled [“conisch”] at the circular place of apposition of the little crown. The side of the base is weakly striated and in the middle provided with a conspicuous, channel-like longitudinal depression that takes up nearly the fourth part of the width of the base. The tooth crowns are on average 2 mm in diameter at their base and over 3 mm in height; they are somewhat posteriorly curved with their conical tip and encased by a shiny, brownish enamel on which is seen no Zähnelung but rather only weak striae. In the left jaw on this slab, only six robust tooth crowns are clearly preserved; their bases cannot be discerned well, and the crowns are not directed in the same way, but rather are somewhat out of sight [“verdrückt”] and in part more posteriorly inclined than in the other ramus. Individual little crowns were also separated from their base and dispersed, as one sees such a crown lying, for instance, in the region of the columella. A kind of differentiation of the teeth, such as would cause [“veranlasste”] a division in some Sauria into incisors, canines and molars, is not found here. The described bases grow from the wall of the jaw [“sind dem Kieferrande aufgewachsen”] and appear to be somewhat sunken into the subdental lamella. The dentition can therefore, according to Wagler’s distinction, be termed acrodont. Teeth of this kind are also present among Sauria in each giant, elongated, snakelike sea-lizards, the Pythonomorpha, whose remains were first found in the chalk tuff [“Kreidetuff”] of Mastricht [sic]—Mosasaurus Hoffmanni (1780) Cuv.22—and later in the chalk of North America—Liodon, Clidastes et al.23 Similar teeth, of course, were even described in the most remarkable birds with toothed jaws from the Chalk formation of Kansas.24

The teeth of our fossil, in form in complete agreement and in exterior characteristics exactly the same as those of the large Pythonomorpha, in which a study could more easily be conducted, entitles one to assume that, between them, agreement in the most important features would also obtain in the histological construction of the teeth [“dass auch im histologischen Aufbau der Zähne zwischen ihnen eine Uebereinstimmung der wichtigeren Eigenthümlichkeiten obwalte”]. We can therefore accept without compunction the results of the study of the formidable teeth of Mosasaurus by Cuvier25, as well as those achieved by Leidy26 and Cope27 on American species. According to Cuvier’s interpretation the bases of such teeth are only hollow, so long as they grow. They become filled, then, gradually and length-wise, until at last they are for the most part completely solid. They adhere to the jaw by connective tissue matter, which ossifies by degrees and merges profoundly with them [the teeth] [“mit ihrer eigenen innig verschmilzt”]. According to Leidy’s observations the dentin does not continue as a root from the enamel-covered crown, but rather ends at a place in line with the alveolar margin and does not enter into the crypt of the tooth, the tooth-cavity or the so-called alveolus. The base is thus no root covered with cement, as Owen28 says, but rather is composed of a variety of bony matter that is close to cement.29

In the premaxilla and maxilla, unfortunately, only tiny traces of the dentition are present. On the small counterpart of the skull, where the nasal part of the skull is broken away, there is only their impression, that is, from the roof of the mouth or the hard palate, and even this is hardly clear on account of the calcite veneer [“Calcitüberrindung”]. Yet one can recognize approximately the location of the bases of the teeth by the gleaming markings [“der strahligen Zeichnung”], but little of the hook-like [“hakig”] tips or the crowns, which so clearly cap the the bases of the mandibular rami on the part. On this large part, there remains little to see of the tooth tips or the bases on the margin of the impression that derives from the upper jaw. From the features of the dentition in other Sauria, where its form in the two jaws is generally in agreement, one can conclude that hook-teeth sitting on bases were doubtlessly present in the maxilla and premaxilla of our animal as well. Of their number one can probably only express the hunch that they could have differed only scarcely or a little from those of the mandible.


  1   2   3

The database is protected by copyright ©dentisty.org 2016
send message

    Main page