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Changes in page proofs (as opposed to corrections) are very expensive. Author-generated changes in page proofs can only be made if the author agrees in advance to pay for them. THIS PUBLICATION IS PRINTED ON ACID-FREE PAPER. FTELDIANA Geology r SS- NEW SERIES, NO. 27 tf UBBANA-C GEOLOGY Status of the Pachypleurosauroid Psilotrachelosaums toeplitschi Nopcsa (Reptilia, Sauropterygia), from the Middle Triassic of Austria Olivier Rieppel Department of Geology Field Museum of Natural History Roosevelt Road at Lake Shore Drive Chicago, Illinois 60605-2496 U.S.A. Accepted March 8, 1993 Published July 30, 1993 Publication 1448 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY © 1993 Field Museum of Natural History ISSN 0096-2651 PRINTED IN THE UNITED STATES OF AMERICA Table of Contents List of Tables Abstract 1 Introduction 1 Material 2 The Geological Provenance of psilotrachelosavrus toeplitsch1 .... 2 Systematic Paleontology 4 Discussion 10 Conclusions 15 Acknowledgments 15 Literature Cited 15 1. Measurements of metatarsal and phalan- geal length in the right pes of Psilotrache- losaurus toeplitschi 9 2. Number of dorsal vertebrae and limb proportions in Psilotrachelosaurus toeplit- schi, compared to Serpianosaurus and Neusticosaurus 12 3. Data matrix for cladistic analysis of pachy- pleurosauroid interrelationships 13 List of Illustrations Map of the Kellerberg-Quarry and the Stadelbachgraben in the Gailtaler Alps ... 3 Holotype of Psilotrachelosaurus toeplit- schi 5 Pectoral girdle of Psilotrachelosaurus toep- litschi 6 Pelvic girdle of Psilotrachelosaurus toeplit- schi 7 Pubis in pachypleurosauroids 8 Appendicular skeleton of Psilotrachelo- saurus toeplitschi 8 Right humerus of Psilotrachelosaurus toep- litschi 9 Humeri of Dactylosaurus schroederi 11 Cladogram of pachypleurosauroid inter- relationships 14 in Status of the Pachypleurosauroid Psilotrachelosaurus toeplitschi Nopcsa (Reptilia, Sauropterygia), from the Middle Triassic of Austria Olivier Rieppel Abstract The redescription of the holotype and only known specimen of Psilotrachelosaurus toeplitschi Nopcsa, 1928, from the northern Alps of Austria, and its comparison with other pachypleu- rosauroids show the specimen to represent a distinct genus and species. It is the sister-taxon of the Serpianosaurus-Neusticosaurus clade from the Middle Triassic of Central and Southern Europe (German Lettenkeuper as well as Grenzbitumenzone and Meridekalke of the southern Alps in southern Switzerland and Italy). Psilotrachelosaurus is represented by a subadult (sex y) or a small but already sexually mature (sex x) individual. Diagnostic features of the specimen include body proportions (relatively short humerus as compared to standard length), ossified distal carpal and tarsal 4, and a relatively broad pubis. Introduction In 1 928, Nopcsa described a specimen of a small sauropterygian as a new genus and species, Psi- lotrachelosaurus toeplitschi. The exact locality and stratigraphical horizon of the fossil remain un- known, but the dark (blackish) and bituminous limestone surrounding the fossil led Nopcsa ( 1 928) to conclude that it came from the Alpine Muschel- kalk series (Triassic) as it crops out in the Stadel- bachgraben, 2 km west of Toplitsch in the northern Alps of Austria (Huene, 1956, p. 84, suggested a Ladinian age; see the discussion below). Nopcsa (1928) classified the new genus within his family Nothosauridae, along with Phygosaurus (a nomen dubium; Rieppel, 1989a), Lariosaurus, Macromerosaurus (a junior synonym of Lariosau- rus; see Rieppel, 1987, for a discussion), Rhaeti- conia (a problematical taxon of which the type and only known specimen is lost; Rieppel, 1987), Nothosaurus, Germanosaurus (another taxon of questionable validity, perhaps Cymatosaurus; Storrs, 1991), Cymatosaurus, and Pistosaurus. Following the discovery of abundant pachypleu- rosaur material in the Grenzbitumenzone (Ani- sian-Ladinian boundary) of Monte San Giorgio (southern Alps of Switzerland) and the redescrip- tion of the Lariosaurus and Pachypleurosaurus (a junior synonym of Neusticosaurus; see Sander, 1989, for a discussion) material from Perledo (up- per Ladinian or lower Carnian, southern Alps of northern Italy), Peyer (1934) concluded (without inspection of the original) that Psilotrachelosaurus in fact belongs to the family Pachypleurosauridae (along with Anarosaurus, Dactylosaurus, Neusti- cosaurus, "Pachypleurosaurus," and "Phygosau- rus"). This conclusion was accepted by Zangerl (1935) in his description of "Pachypleurosaurus" edwardsii from Monte San Giorgio, who added that he had, in fact, been unable to detect char- acters that separate Psilotrachelosaurus from "Pa- chypleurosaurus" at the generic level (again with- out inspection of the original). Zangerl (1935, p. 69) denied that any major taxonomic importance could be attached to limb proportions or to the number of presacral vertebrae in this group. He questioned Nopcsa's (1928) description of the di- agnostic coracoid of Psilotrachelosaurus and found Nopcsa's claim that all five metatarsals are of equal length to be refuted by Nopcsa's figure of the spec- imen (1928, pi. II fig. 1). Huene (1956) retained the genus as distinct from "Pachypleurosaurus," but Kuhn-Schnyder (1959, p. 654) once more questioned its validity, noting similarities in the FIELDIANA: GEOLOGY, N.S., NO. 27, JULY 30, 1993, PP. 1-17 structure of the carpus that Psilotrachelosaurus shares with "Pachypleurosaurus." He also indi- cated that the Monte San Giorgio material re- quired revisionary work (Kuhn-Schnyder, 1959, p. 655), since more than the one species (e.g., P. edwardsii) described by Zangerl (1935) appeared to be present. Sues and Carroll (1985) once again doubted Nopcsa's (1928) description of the cor- acoid and concluded that "[t]oo little is known about . . . Psilotrachelosaurus at present to allow a definitive phylogenetic assessment" (Sues & Car- roll, 1 985, p. 1 608). It was obvious that the proper assessment of the affinities of Psilotrachelosaurus had to be based on a revision of the abundant Monte San Giorgio material (Zapfe & Konig, 1 980, p. 78), a task that has now been completed (Carroll & Gaskill, 1985; Rieppel, 1989a; Sander, 1989). It is on the basis of this background that the type specimen of Psilotrachelosaurus toeplitschi is here redescribed. Material The holotype and only known specimen of Psi- lotrachelosaurus toeplitschi Nopcsa is housed at the Landesmuseum fur Karnten (Dept. of Min- eralogy and Geology, collection Nr. 201) in Kla- genfurt, Austria. The specimen is embedded in a dark bituminous limestone. The original hand- written label attached to the specimen reads "Sta- delbachgraben (?) bei Toplitsch." A cast of Anarosaurus pumilio, kept at the Staat- liches Museum fur Naturkunde in Stuttgart, Ger- many, was used for comparison, as well as material of Dactylosaurus cf. D. schroederi kept at the Mu- seum fur Historische Geologie und Palaontologie, University of Tubingen, Germany (GPTI 1 744/ 1-10; see fig. 8). The Geological Provenance of Psilotrachelosaurus toeplitschi The geological provenance of Psilotrachelosau- rus is difficult to reconstruct and requires some discussion. The holotype and only known speci- men was collected in 1 844, and lithological clues indicate the Stadelbachgraben, 2 km west of Top- litsch (Karnten) in the Gailtaler Alps, northern Alps of Austria (Tollmann, 1977), as the likely locality (fig. 1). The geological map of Austria (An- derle, 1977) shows the Stadelbachgraben to cut through a succession of Triassic deposits, ranging from the lower Anisian up to the Carnian (for more details on the geology of the Gailtaler Alps, see Bechstadt & Mostler, 1974; Bechstadt et al., 1976; Hauser, 1982). All indications are that Psilotrachelosaurus comes from the Partnach-Plattenkalk (Warch, 1979; also known as Partnachschichten or "Plat- tenkalk" [Zapfe & Konig, 1980]), which for its greater part is Ladinian but has been claimed to extend down into the latest Anisian (Tollmann, 1977, p. 605). Apart from Psilotrachelosaurus, the Middle Triassic of the Gailtaler Alps has produced two other, poorly preserved pachypleurosaurs, but also two specimens (one of which is rather well preserved although incomplete) of Lariosaurus cf. L. balsami (Warch, 1966, 1979; Zapfe & Konig, 1980). Both specimens of Lariosaurus were found in the Kellerberg-Quarry, located immediately east of the Stadelbachgraben and between the towns of Stadelbach and Kellerberg. Since outcrops in the Stadelbachgraben can be correlated to the se- quence of layers exposed in the Kellerberg-Quarry, the stratigraphical relations of the Lariosaurus specimens from the Kellerberg-Quarry may point to equivalent layers in the Stadelbrachgraben that have produced the Psilotrachelosaurus specimen. The Partnach-Plattenkalk lies on top of the Zwischendolomit of late Anisian age (the Zwi- schendolomit is the uppermost of three units of the Alpine Muschelkalk series [Warch, 1979; cf. Nopcsa, 1928]). A stratigraphic analysis of the Partnach-Plattenkalk in the Kellerberg-Quarry has identified three units: a lower unit of limestone, an intercalated bed of "marly shales" at the middle of the lithostratigraphical column of the Partnach- Plattenkalk (Warch, 1979, p. 36, 1984), and an upper unit of limestone. Originally believed to rep- resent the early Ladinian only (Warch, 1979), the Partnach-Plattenkalk is now thought to represent the entire suite of Ladinian deposits in the Gail- taler Alps (Bechstadt et al., 1976; Warch, 1984, and in lit. 10 Nov. 1992). According to Zapfe and Konig ( 1 980), the great- er part of the Kellerberg-Quarry is located in the upper unit of the Partnach-Plattenkalk, which to them represents the late Ladinian. This led these authors to conclude that the Lariosaurus speci- mens mentioned by Warch (1 966, 1 979) come from the late Ladinian, and the same is postulated for Psilotrachelosaurus. Zapfe and Konig (1980) sup- ported their conclusions with a comparison of the upper part of the Partnach-Plattenkalk to the Cal- FIELDIANA: GEOLOGY N Gailtaler Alps NKV %/A %//, '""///»|||, ////////%///,, <33g!*w»^^^ Villac '"""/i/i/i "milium,,, "* »miiwifijfi£i r«// % '"//. \^s~"V-. """""'„„„ '"', "tm\\\[ hi,,. ""inu\\\sv\ ^Mnttfn 10 km "',niiiiin,mmrt0 /iPH/fM/U////////, Fig. I . A map showing the location of the Kellerberg-Quarry and the Stadelbachgraben in the Gailtaler Alps. care di Perledo of the southern Alps (northern It- aly), also claimed to be of late Ladinian age, per- haps extending into the Carnian (Tintori et al., 1985; Gaetani et al., 1992). A comparison of the upper unit of the Partnach-Plattenkalk with the Calcare di Perledo (Zapfe & Konig, 1 980) had been proposed earlier on the basis of the occurrence of an actinopterygian fish, Ophiopsis lariensis, at both localities (Sieber, 1955; see also Tollmann, 1977, p. 585). The comparison of the Partnach-Platten- kalk to the Calcare di Perledo is interesting, since these are the only two localities known so far where lariosaurs and pachypleurosaurs occur together (but see the discussion below). However, the strati- graphical relations of the vertebrate fossils from the Calcare di Perledo remain uncertain, and Ophiopsis has also been found in the Prosanto Formation of the Swiss Alps, believed to be of early to middle Ladinian age (Biirgin et al., 199 1). Ophiopsis remains unknown from Monte San Giorgio (Grenzbitumenzone, Anisian-Ladinian boundary). The possibility that Psilotrachelosaurus comes from a horizon at the transition from the Zwi- schendolomit to the Partnach-Plattenkalk (Ani- sian-Ladinian boundary) can be ruled out, because RIEPPEL: PSILOTRACHELOSAURUS TOEPLITSCHI NOPCSA nowhere in the Kellerberg-Quarry nor in the Sta- delbachgraben are the corresponding layers ex- posed (Warch, in lit. 10 Nov. 1992, contra Zapfe & Konig, 1980; this transition is likewise not in- dicated in the Kellerberg profile published by Zapfe & Konig, 1980, fig. 2). Furthermore, the Lario- saurus specimens from the Kellerberg-Quarry were found immediately above the intercalated bed of marly shales within the Partnach-Plattenkalk, which indicates a middle Ladinian age (Warch, 1 984). Identical lithological and stratigraphical re- lations in the Stadelbachgraben indicate an equiv- alent age for Psilotrachelosaurus (Warch, in lit. 10 Nov. 1992). Systematic Paleontology Sauropterygia Owen, 1860 Pachypleurosauroidea Huene, 1956 Pachypleurosauridae Nopcsa, 1928 Psilotrachelosaurus Nopcsa, 1928 Type Species— Psilotrachelosaurus toeplitschi Nopcsa, 1928. Generic Diagnosis— A small-sized pachypleu- rosaur sharing with the Serpianosaurus-Neusti- cosaurus clade the surface ornamentation on the humerus but differing by the relatively short hu- merus, a more fully ossified carpus and tarsus (dis- tal carpal/tarsal 4 present), and relatively broad ventral elements in the pelvic girdle. Distribution— Middle Triassic (middle Ladin- ian), the Stadelbachgraben, Gailtaler Alps, Aus- tria. Psilotrachelosaurus toeplitschi Nopcsa, 1928 Holotype— Landesmuseum fur Karnten, Dept. of Mineralogy and Geology, Nr. 201. Diagnosis— Same as for genus, of which this is the only known species. Distribution— Same as for genus, of which this is the only known species. Morphological Description— The total length of the specimen as preserved (fig. 2) is 1 15.8 mm. It comprises most of the cervical vertebral column, the entire trunk region and appendicular skeleton, and proximal parts of the tail. The specimen is exposed in ventral view. The distance between glenoid and acetabulum is 56 mm; the standard length (Rieppel, 1989a; Sander, 1989), defined as the length of the last four presacral (dorsal) ver- tebrae, is 12 mm. A total of 12 cervical vertebrae (the anterior- most one incompletely preserved) can be counted (see also Nopcsa, 1928). The neural arch has sep- arated from the centrum at the neurocentral suture in the last four cervicals (in front of the pectoral girdle), such that the fossil displays the ventral (internal) view of the well-defined neural canal. The remaining eight cervical vertebrae are pre- served only as natural molds. Nopcsa (1928) con- sidered the last four cervical vertebrae to be dis- tinctly elongated (longer than broad). However, actual measurements across the length and total width of the neural arch (as preserved, in ventral view) do not corroborate this impression: the pen- ultimate (and best preserved) neural arch is 2.7 mm long and at least 2.8 mm wide (maximally 3.1 mm). Comparison of the mold and the cast of the specimen indicates a relative increase in length of the cervical vertebrae from front to back. Cer- vical ribs cannot be identified on the fossil due to poor preservation. A total of 19 dorsal vertebrae can be counted. In most of them the centrum has again separated from the neural arch at the neurocentral suture, leaving the neural arch exposed in ventral view. The lower surface of the centrum is at least par- tially preserved in the first and last dorsal vertebra. As described by Nopcsa (1928), the ventral surface of the anterior dorsal vertebra shows two slight ridges converging anteriorly. The ventral surface of the centrum of the posterior dorsal vertebra shows a vermiculate ornamentation. The dorsal ribs show very pronounced pachyostosis in their proximal part. The structure of the sacral region is obscured by the elements of the pelvic girdle, but three sacral ribs can unequivocally be identified (see below and fig. 4). The first sacral rib as well as the first sacral vertebra is exposed through the thyroid foramen between pubis and ilium. On either side, the pubis shows a well-defined obturator foramen at its pos- terior margin close to the acetabulum (see below), through which the underlying matrix is clearly identifiable. This indicates that no anterior sacral rib is covered by the pubes. Oblique light reveals two additional sacral ribs covered by the right ischium as exposed on the left side of the fossil, bringing the total number of sacral ribs up to three. On the left side of the fossil (exposed on the right side), the relation of the posterior margin of the ischium and of the third sacral rib is obscured. The second and third sacral vertebrae are partially FIELDIANA: GEOLOGY Fig. 2. Holotype and only known specimen of Psilotrachelosaurus toeplitschi Nopcsa. Approximately 1.5 times natural size. RIEPPEL: PSILOTRACHELOSAURUS TOEPLITSCHI NOPCSA FIELDIANA: GEOLOGY exposed (in ventral view) between the symphyseal edges of the ischium of either side. The sacral ribs appear to be straight and relatively robust ele- ments, pachyostotic throughout, but without sig- nificant distal expansion. Morphological details are obscured by the overlying ischia. A small number of at least six proximal caudal vertebrae are preserved, but preparation has de- stroyed all morphological detail. However, at least two pairs of caudal ribs can be clearly identified. The first caudal rib is associated with the first cau- dal vertebra, and the caudal ribs are not fused to their respective vertebrae (fig. 2). Delicate impressions between the proximal parts of the dorsal ribs, particularly in the middle and anterior part of the right body side, indicate the presence of gastral ribs. No information is avail- able on the detailed structure of the "ventral ribs," such as the number of segments in each rib. As described by Nopcsa ( 1 928), the pectoral gir- dle of Psilotrachelosaurus (figs. 3 A-D) has raised questions in regard to the apparently peculiar shape of the coracoid (Zangerl, 1935; Sues & Carroll, 1 985). The interclavicle is not preserved. The clav- icle is preserved on both sides, showing the im- pression of its tapering anterior end on the right side (more obvious in the latex mold of the fossil). The left clavicle appears to end posteriorly in a broad transverse margin, but this may be the result of breakage. Behind it, the narrow and tapering dorsal wing of the left scapula is partially exposed at the proximal end of the left humerus. On the right side, the clavicle disappears below the broken anterior end of a bone, which Nopcsa (1928) in- terpreted as the coracoid (fig. 3A). Close to the vertebral column, the broken medial head of the right coracoid can be identified. Between the latter two bone fragments, a shallow area indicates the natural mold of a bone surface; the natural bone has been torn off and lost as part and counterpart of the fossil separated (fig. 3A). According to Nopcsa (1928, p. 34), "Of the coracoids only the proximal and distal end of the right coracoid has been preserved. The middle part of the right cor- acoid broke away, but left a neat impression. To bring this part of the shoulder-girdle out more clearly, later on this impression has carefully been filled up with plaster and afterwards painted black. Fig. 4. The pelvic girdle of Psilotrachelosaurus toep- litschi Nopcsa as preserved in ventral view. Scale bar equals 5 mm. Abbreviations: fe, femur; f. obt, obturator foramen; is, ischium; pu, pubis; 1st ca, first caudal rib; 1 st sc, first sacral rib; 3rd sc, third sacral rib. Thus the general outline of the bone is well shown ..." (fig. 3B). This plaster filling has now been removed, with no indication as to when and how this happened. Removal of the plaster shows that the supposed coracoid was broken across the broad (pachyostotic) proximal portion of a dorsal rib, separating the two fragments to a degree that would add to the impression of an unduly elongated cor- acoid. Careful investigation of a latex peel of the specimen furthermore indicates that this dorsal rib separated a distal bone, the right scapula, from a proximal (medial) bone, the right coracoid (fig. 3C). Combining the drawings obtained from the type specimen and from the latex peel reveals a fragmentary preservation of the right scapula, at the proximal head of the right humerus, and a right coracoid of typical pachypleurosauroid propor- tions (fig. 3D). In the pelvic girdle (fig. 4), the ilium is not ex- posed on either side. The shape and relations of the pubis and ischium are difficult to determine because of the underlying sacral ribs. The right pubis shows a broad acetabular portion, ventral (medial) to which the obturator foramen can be identified as a slit-like opening in the posterior margin of the bone. The posterior opening of the obturator foramen is narrow, but not entirely closed as it is in the left pubis (where a "suture" remains visible). The ventral part of the right pubis is bro- Fig. 3. The pectoral girdle of Psilotrachelosaurus toeplitschi Nopcsa. A, the specimen as preserved in ventral view; B, Nopcsa's (1928) interpretation of the morphology of the right coracoid bone; C, drawing of the latex mold of the right side of the pectoral girdle; D, reconstruction of the right side of the pectoral girdle in ventral view. Scale bar equals 5 mm. Abbreviations: cl, clavicle; cor, coracoid; hu, humerus; sc, scapula. RIEPPEL: PSILOTRACHELOSAURUS TOEPLITSCHI NOPCSA Fig. 5. Outlines and proportions of the pubis in pachypleurosauroids. a, Anarosaurus pumilio (original, after a cast at the Staatliches Museum fur Naturkunde, Stuttgart); b, Dactylosaurus schroederi (after Sues and Carroll, 1985); c, Neusticosaurus peyeri (after Sander, 1989); d, Neusticosaurus edwardsii (after Carroll and Gaskill, 1985); e, Serpianosaurus mirigiolensis (after Rieppel, 1989a); f, Psilotrachelosaurus toeplitschi (orig- inal). ken, but the left pubis indicates concave posterior and anterior margins that define a bone of greater relative width than is usually observed in pachy- pleurosaurs (Huene, 1956, p. 384), which show a more distinctly "waisted" appearance of the bone (fig. 5). The shape of the ischium is even harder to de- termine since the bone is broken across two sacral ribs. The anterior margin of the ischium is concave and, together with the concave posterior margin of the pubis, indicates the presence of a thyroid foramen. The posterior margin of the ischium can- not be unequivocally determined on the right side, and on the left side it is obscured by breakage caused by the sacral ribs. The posterior margin appears to lie at the level of the third sacral rib, which would again indicate a greater width of the ischium than is usually observed among pachy- pleurosaurs. The right forelimb is better preserved than the left (figs. 6A,B). The humerus is typically pachy- pleurosauroid (Peyer, 1934), with a slight curva- ture, a weakly developed deltopectoral crest, and a slight distal expansion. The entepicondyle is not pronounced, but the entepicondylar foramen is well defined, fully enclosed by bone, and separated by about 0.5 mm from the distal articular surface of the humerus. The bone surface shows a distinct ornamentation (fig. 7) of grooves and ridges on the expanded proximal and distal heads. The groove Fig. 6. The appendicular skeleton of Psilotrachelo- saurus toeplitschi Nopcsa, as preserved in ventral view. A, right forelimb; B, left forelimb; C, right hindlimb. Scale bar equals 5 mm. Abbreviations: as, astragalus; ca, calcaneum; dc4, distal carpal 4; dt4, distal tarsal 4; fe, femur; f. ent, entepicondylar foramen; fi, fibula; hu, hu- merus; in, intermedium; mcl, metacarpal 1; mc4, meta- carpal 4; mt 1 , metatarsal 1; mt4, metatarsal 4; ra, radius; ti, tibia; ul, ulna; uln, ulnare. and ridge pattern becomes more closely spaced, anastomoses become more frequent, and the sur- face ornamentation assumes a more vermiculate appearance toward the middle of the diaphysis. The total length of the right humerus is 10 mm, its proximal width is 1.5 mm, its distal width is 3 mm, and its minimum width is 1.5 mm. As in other pachypleurosaurs, the radius (6.1 mm) is somewhat longer than the ulna (5 mm). The radius is fairly slender and evenly curved, with but slightly expanded proximal and distal heads. The ulna is shorter and broader than the radius and has a more distinctly expanded proximal head. A narrow spatium interosseum is defined by the two elements. In the carpus, three ossified elements are pre- FIELDIANA: GEOLOGY Fig. 7. The right humerus of Psilotrachelosaurus toeplitschi Nopcsa, showing the ornamentation of the bone surface. Approximately 1 2 times natural size. served, namely, the intermedium, ulnare, and dis- tal carpal 4 (fig. 6A). The intermedium is a narrow but proximodistally elongated element, lying alongside the lateral side of the distal part of the radius, distal to the ulna (fig. 6B). The ulnare is a smaller, rounded element lying directly distal to the ulna. Distal carpal 4 is an even smaller ossi- fication between the ulnare and the proximal head of metacarpal 4. Distal carpal 4 appears to be miss- ing in the left carpus (fig. 6B), but this is most probably an artifact of rough preparation. The metacarpals were judged to be of equal length by Sues and Carroll (1985), but the right manus shows a continuing yet slight increase in relative length from metacarpal 1 through 4 (meta- carpal 5 is broken). This seems also to be true of the left hand, but there the metacarpals are less well exposed. The phalangeal formula cannot be established for either hand, but what is apparent on both sides is the relatively large size of the proximal phalanges as compared to the metacar- pals. The best preserved digit is the third, and it shows that the metacarpal is about 10% longer than the proximal phalanx. The right hindlimb (fig. 6C) is again better pre- served than the left. The femur is a slender and only slightly curved bone, with the proximal head more strongly expanded than the distal end. It is slightly longer than the humerus. The total length of the right femur is 10.5 mm, its maximal prox- imal width is 2.8 mm, and its distal width is 1.6 mm. In the zeugopodium, the fibula (5.8 mm) is stronger and longer than the tibia (5 mm). The fibula is a strongly curved bone, with the distal head more distinctly expanded than the proximal head, and with a strongly concave medial border, which results in a spatium interosseum (between fibula and tibia) that is wider than in the zeugo- podium of the forelimb (between radius and ulna). The well-preserved right tarsus (fig. 6C) shows three ossified proximal elements. The largest is the astragalus, which lies in an intermedium position, articulating both with the tibia (proximolaterally) and with the fibula (proximodistally); the smaller calcaneum lies directly distal to the fibula. Of the distal tarsals, only distal tarsal 4 is ossified; the bone is split horizontally (for which reason it does not show up in the photograph of the specimen; fig. 2), but it remains clearly identifiable, although it was neither figured nor described by Nopcsa (1928). Length measurements for the metatarsals and the corresponding phalanges are given in Ta- ble 1. The phalangeal formula can be reconstructed for the right foot and must have been (in agreement with Nopcsa, 1 928) 2-3-4-5^. In the fourth digit, four phalanges are preserved, of which the fourth one is so small that it must represent the penul- Table 1 . Measurements of metatarsal (mt) and pha- langeal length in the right pes of Psilotrachelosaurus toep- litschi Nopcsa. Length of corresponding Metatarsal length proximal phalange (mm) (mm) mtl approx. 2.9 ? mt2 3.5 1.5 mt3 4.3 2.7 mt4 4.7 3.2 mt5 3.8 2.2 RIEPPEL: PSILOTRACHELOSAURUS TOEPLITSCHI NOPCSA timate one. Without the ungual (but including metatarsal 4), the length of the fourth digit is 12.3 mm. There is no evidence for hyperphalangy. Discussion The Pachypleurosauroidea (Pachypleurosauri- dae of Peyer, 1934) are known to include the gen- era Anarosaurus, Dactylosaurus, Keichousaurus, Neusticosaurus, Psilotrachelosaurus, and Serpi- anosaurus (see Introduction, above, and Rieppel, 1987, 1989a). The genus Keichousaurus from the Middle Tri- assic of China (southwestern Keichow [Kiaochow] Province) is readily distinguished from all other pachypleurosaurs, including Psilotrachelosaurus, by a more distinctly curved humerus, a distinctly broadened ulna, and a transversally orientated in- termedium positioned distal to the broad spatium interosseum between ulna and radius (Young, 1958, 1965). For these reasons, Kuhn-Schnyder (1959, p. 655) considered Keichousaurus a mem- ber of the family Nothosauridae, closely related to the genus Lariosaurus. However, skull char- acters as well as the structure of the sacral region clearly indicate the pachypleurosauroid status of Keichousaurus (Sues & Carroll, 1985; Lin Kebang, quoted in Sues, 1987). Anarosaurus from the lower Muschelkalk of Remkersleben near Magdeburg (Germany) is readily distinguished from Psilotrachelosaurus by the lack of pachyostosis in the dorsal ribs and by its limb proportions. Originally described by Dames (1 890), the holotype and only known spec- imen of Anarosaurus pumilio was reexamined by Nopcsa (1928) but destroyed during World War II (a second species, Anarosaurus multidentatus, is known only from an isolated lower jaw; Huene, 1958). The glenoid-acetabulum length of Anaro- saurus is unknown due to incomplete preservation (following Nopcsa, 1 928, Anarosaurus had a max- imum of 2 1 dorsal vertebrae), but a cast of the original allows the measurement of the "standard length" (length of the centra of the last four pre- sacral vertebrae, approx. 23 mm), length of left humerus (29.3 mm), and length of the right femur (36.5 mm). The humerus : standard length ratio is 1.26 for Anarosaurus and 0.83 for Psilotrachelo- saurus. This indicates a smaller relative size of the humerus in Psilotrachelosaurus, which might be explained by the positive allometric growth of this bone (Rieppel, 1 989a; Sander, 1 989) and the larger overall size of Anarosaurus. However, the hu- merus: femur ratio is 0.80 in Anarosaurus (0.97 in Psilotrachelosaurus), and the femur : standard length ratio is 1.57 in Anarosaurus (0.85 in Psi- lotrachelosaurus). These values indicate a dispro- portionate large femur in Anarosaurus, the prox- imal limb bone being distinctly longer than the humerus (at a larger overall body size) as com- pared to Psilotrachelosaurus. The relative size of the femur is diagnostic of the genus Anarosaurus (see also Sues & Carroll, 1 985, p. 1 608), and (again at larger overall size) the obturator foramen is not closed in Anarosaurus (as in the left pubis of Psi- lotrachelosaurus) but is represented by a distinct notch at the posterior edge of the pubis. The genus Dactylosaurus from the lowermost Muschelkalk of Crorny Slask (Upper Silesia) was first described by Gurich (1884, Dactylosaurus gracilis), but the type and only known specimen cannot be located today. Nopcsa (1928) described a second species, Dactylosaurus schroederi, which was recently restudied by Sues and Carroll (1985). It is presently not known whether the two species represent anything but ontogenetic variation with- in a single taxon. Dactylosaurus can be distin- guished from Psilotrachelosaurus by a much more distinctly differentiated humerus (particularly in sex y sensu Rieppel, 1989a, and Sander, 1989), with a distinct deltopectoral crest, a prominent entepicondyle, and well-defined articular condyles (fig. 8). The bone lacks the surface ornamentation seen in Psilotrachelosaurus (Sander, 1989). The intermedium has rounded contours and lies distal to the spatium interosseum. Both manus and pes show a slight reduction of the phalangeal count (Sues & Carroll, 1985), which is not shared by Psilotrachelosaurus (the phalangeal count is known for the pes only). The pachypleurosaurs from the Middle Triassic of Monte San Giorgio, Switzerland, are charac- terized by an apomorphic ornamentation of the surface of endochondral bone (Sander, 1989), which is also present in Psilotrachelosaurus. In addition to the latter genus, the clade comprises Serpianosaurus and Neusticosaurus (Carroll & Gaskill, 1985; Rieppel, 1989a; Sander, 1989). Within the clade, Neusticosaurus is derived with respect to the segmentation of the gastral ribs: these are composed of five segments in Serpianosaurus (the plesiomorph condition) but of only three seg- ments in Neusticosaurus (Rieppel, 1987; Sander, 1989). Unfortunately, details of gastral rib mor- phology are unknown for Psilotrachelosaurus, but the genus differs from Serpianosaurus in the 10 FIELDIANA: GEOLOGY til lra Fig. 8. A series of humeri of Dactylosaurus schroederi Nopcsa (Institute of Geology and Paleontology of Tubingen Nr. GPTI 1744/1-10). Top row: sex y; bottom row: sex x (sensu Rieppel, 1989a; Sander, 1989). strongly pachyostotic dorsal ribs, a lower count of dorsal vertebrae (19 in Psilotrachelosaurus, 20-23 in Serpianosaurus), the presence of ossified carpal/ tarsal 4, and relatively shorter proximal limb bones (particularly a shorter femur; see table 2). Psilo- trachelosaurus differs from Neusticosaums in the broad pubis and ilium but shares with Neustico- saums the pronounced pachyostosis of dorsal ribs as well as an elongated intermedium, oriented along the long axis of the limb and situated lateral to the distal head of the radius, distal to the ulna. Among pachypleurosaurs other than Psilotrachelosaurus, this morphology of the carpus is known only for Neusticosaums (Zangerl, 1935; Kuhn-Schnyder, 1959), although variation in the shape of the in- termedium is observed within the genus and its various species (Sander, 1989). In the Middle Triassic of Monte San Giorgio, the genus Neusticosaums is represented by three species (Carroll & Gaskill, 1985; Sander, 1989), which succeed each other in time. Neusticosaurus pusillus (Fraas, 1881; Seeley, 1882) comes from the Cava inferiore horizon of the lower Meridekal- ke, Ladinian, Monte San Giorgio, and equivalent deposits in northern Italy (also known from the Prosanto Formation, Ladinian, eastern Switzer- land [Burgin et al., 1991] and from the Dolomite of the Lettenkeuper, southwest Germany). Neus- ticosaurus peyeri Sander, 1989, comes from the Cava superiore horizon of the lower Meridekalke, Ladinian, Monte San Giorgio, and equivalent de- posits in northern Italy. Neusticosaurus edwardsii (Cornalia, 1854) is from the Alia Cascina horizon of the lower Meridekalke, Ladinian, Monte San Giorgio, and northern Italy. Comparison of Psi- lotrachelosaurus to the three known species of Neusticosaurus raises the question as to whether the only known specimen of the first genus rep- resents a juvenile or an adult individual. Sander (1989) was able to study the postembryonic on- togeny of N. pusillus and N. peyeri in great detail, in particular as it relates to the differentiation of sexual dimorphism and the attainment of sexual maturity. The carpal and tarsal bones do not ossify in Neusticosaurus until late in size class B (juveniles; Sander, 1989); in Psilotrachelosaurus, carpus and tarsus are well ossified, including a distal carpal/ tarsal 4. The entepicondylar foramen is distally open in juvenile specimens of Serpianosaurus or Neusticosaurus. In Psilotrachelosaurus, the entepi- condylar foramen is fully enclosed by bone and has retracted from the ossified distal margin of the humerus. This condition compares to a subadult (size class E of Sander, 1989) of Neusticosaurus peyeri, with a humerus length of about 9-10 mm. Presumed sexual maturity as indicated by the pro- portions and differentiation of the humerus is RIEPPEL: PSILOTRACHELOSAURUS TOEPLITSCHI NOPCSA 11 Table 2. Number of dorsal vertebrae and limb proportions in Psilotrachelosaurus toeplitschi Nopcsa compared to the genera Serpianosaurus and Nensticosaurus. N. pusillus Psilotrache- Serpiano- (Monte N. pusillus losaurus saurus San Giorgio) (Lettenkeuper) N. peyeri N. edwardsii Number of dorsal vertebrae 19 20-23 22-24 23-24 19-20 19-20 gle-ac : stand 4.66 3.91^1.80 3.79-5.46 4.21-5.44 3.45^1.48 3.66-4.58 hu:fe 0.97 0.75-1.23 0.88-1.15 0.87-1.03 0.90-1.30 1.24-1.84 hu : gle-ac 0.18 0.19-0.36 0.20-0.33 0.18-0.24 0.20-0.33 0.24-0.35 hu : stand 0.83 0.80-1.47 0.95-1.50 0.89-1.25 0.86-1.25 1.18-1.39 fe : gle-ac 0.18 0.21-0.32 0.22-0.30 0.20-0.29 0.21-0.25 0.16-0.21 fe : stand 0.86 0.97-1.20 0.97-1.40 0.91-1.50 0.79-1.06 0.65-O.96 Abbreviations: fe, femur length; gle-ac, glenoid-acetabulum length; hu, humerus length; stand, standard length. reached in size class E (Sander, 1 989). The smallest available individual of Neusticosaurus peyeri hav- ing reached apparent sexual maturity in sex y (as judged by the beginning differentiation of sexual dimorphism) has a standard length of 13.2 mm and a glenoid-acetabulum length of ca. 55 mm (Sander, 1 989) and, hence, compares well with the size class of Psilotrachelosaurus; similar values ob- tain for Neusticosaurus pusillus (Sander, 1989). Sex x, however, remains closer to the juvenile con- dition in both proportions and morphology of the humerus (Rieppel, 1989a,b; Sander, 1989) and falls into size class E (subadults; Sander, 1989) as it reaches maturity. The conclusion therefore must be that, on the basis of humerus morphology and proportions, Psilotrachelosaurus represents a sub- adult (sex y) or a small but already sexually mature (sex x) individual. Among the species of Neusticosaurus, N. pusillus (sample from Monte San Giorgio) differs from Psi- lotrachelosaurus by a higher vertebral count (22- 24 dorsal vertebrae) and by relatively longer prox- imal limb bones (in both sexes; see table 2). The limb proportions of Psilotrachelosaurus more closely approach the proportions of a sample of Neusticosaurus pusillus from the German Letten- keuper (Sander, 1 989; table 2), but vertebral counts are again distinctly higher in the Neusticosaurus from Germany. As far as is known, distal carpal/ tarsal 4 always fail to ossify in Neusticosaurus pu- sillus (Sander, 1989). Sander (1989) recognized a subpopulation of Neusticosaurus pusillus which shows a reduction in number of presacral verte- brae, reflected by a lower glenoid-acetabulum length : standard length ratio. However, although the values obtained for this subpopulation of N. pusillus (Sander, 1989, fig. 42) overlap with the value obtained in Psilotrachelosaurus, the relative limb proportions remain different (for the sub- population of N. pusillus, the humerus : femur ra- tio is 1.0-1.25, the humerus : glenoid-acetabulum length is 0.26-0.32, and the femur : glenoid-ace- tabulum length is 0.24-0.28; for Psilotrachelosau- rus, see table 2). Neusticosaurus peyeri shares with Psilotrache- losaurus a lower count of dorsal vertebrae ( 1 9-20), and the proportions of the humerus and femur (as related to standard length) closely approach each other in the two species: the relative humerus length of Psilotrachelosaurus is at the lower end of the range of variation within N. peyeri, but the values for the relative length of the femur are closely comparable. However, Neusticosaurus peyeri shows a distinctly shortened trunk, as indicated by the glenoid-acetabulum length : standard length ratio (see table 2; the mean values for all specimens measured by Sander [1989] are N. pusillus, 4.62; N peyeri, 3.89; N. edwardsii, 4.10; and Psilotra- chelosaurus, 4.66). Neusticosaurus edwardsii grows to larger overall size than can be extrapolated for Psilotrachelosau- rus. Although the two taxa share a similar count of dorsal vertebrae ( 1 9-20) and a relatively short femur (see table 2), Psilotrachelosaurus differs from N. edwardsii (as also from N. pusillus) by a rela- tively short humerus. The smallest available spec- imen of Neusticosaurus edwardsii happens to be the holotype of this species (Carroll & Gaskill, 1 985), with a glenoid-acetabulum length of 59 mm. Its proximal limb bones (humerus and femur) are relatively longer (as related both to standard length and to glenoid-acetabulum length) compared to Psilotrachelosaurus (for the type of TV. edwardsii, the humerus : femur ratio is 1.13, the humerus: glenoid-acetabulum length is 0.28, the humerus : standard length is 1.3, the femur : glenoid-acetab- ulum length is 0.25, the femur: standard length is 1.15, and the glenoid-acetabulum : standard length 12 FIELDIANA: GEOLOGY Table 3. Data matrix for the cladistic analysis of pachypleurosauroid interrelationships. Character definitions are given in the text. 1 2 3 4 5 6 7 8 9 10 11 Petrolacosaurus 0 0 0 0 0 0 0 0 0 7 0 Claudiosaurus 0 0 0 0 0 0 0 0 0 0 0 Youngina 0 0 0 0 0 0 0 0 0 ? 0 Keichousaurus 0 0 0 1 1 0 0 0 1 ? 0 Dactylosaurus 0 0 0 0 0 0 1 0 0 0 Anarosaurus 0 7 ? 7 7 1 0 0 0 Psilotrachelosaurus ? 0 0 7 1 1 7 Serpianosaurus 0& 1 0& 1 1 0 1 0 0 N. pusillus 0& 1 1 1 0 1 1 1 N. peyeri 2 0& 1 0 1 1 1 1 1 N. edwardsii 2 1 0 1 1 1 1 1 is 4.53; for Psilotrachelosaurus, see table 2). Again, distal carpal/tarsal 4 never ossify in Neusticosau- rus edwardsii (Sander, 1 989; contra Carroll & Gas- kill, 1985). Sander (1989) also distinguished the bone ornamentation in Neusticosaurus edwardsii (his "orange peel" pattern) from that of other spe- cies (his "fingerprint pattern"). As indicated in the description of the humerus of Psilotrachelosaurus, the ornamentation of the endochondral bone sur- face may vary on different elements and in differ- ent locations of the same element. A systematic analysis of the variation of the ornamentation pat- tern throughout the skeleton of pachypleurosaur taxa is not yet available. On Sander's (1989) cri- teria, the ornamentation pattern of Psilotrache- losaurus compares better to the one observed in Neusticosaurus pusillus and N. peyeri (as well as Serpianosaurus), than to that of Neusticosaurus edwardsii. In 1 959, Kuhn-Schnyder ( 1 959) described a new pachypleurosaur, Neusticosaurus "staubi," from the Prosanto Formation (Ladinian) of the eastern Alps of Switzerland. A comparison of the speci- men to the abundant material from Monte San Giorgio (Sander, 1989; Burgin et al., 1991, p. 970) revealed no taxonomically significant differences from Neusticosaurus pusillus. Neusticosaurus "staubi" must therefore be considered a species inquirenda and should at this time be referred to as Neusticosaurus sp. Peyer ( 1 934) described poor- ly preserved specimens of " Pachypleurosaurus" (Neusticosaurus) from Perledo, northern Italy, but stratigraphical control on these early findings (dat- ing back to the last century) is poor (A. Tintori, pers. comm.). Crude measurements taken from Peyer's (1934) monograph for the best preserved specimen ("Bergamo" specimen) show relative limb proportions that fall into the range of vari- ability of the Monte San Giorgio species and, hence, differ from Psilotrachelosaurus by the characters outlined above. To assess the phylogenetic relationships of Psi- lotrachelosaurus within the Pachypleurosauroi- dea, a phylogenetic analysis was carried out based on D. L. Swofford's software package PAUP (Phy- logenetic Analysis Using Parsimony), version 3.0c (Swofford, 1989). Youngina, Claudiosaurus, and Petrolacosaurus were used as successive out- groups, based on an earlier analysis of sauropteryg- ian interrelationships within diapsid reptiles (Rieppel, 1993). Character definition for the char- acters listed in the data matrix (table 3) is as fol- lows. 1. Upper temporal fossa: Except for Keichou- saurus (Young, 1958, 1965), pachypleurosaurs are characterized by a reduction of the size of the up- per temporal fossa ( 1 ). The upper temporal fenes- tra is very small and slit-like or keyhole-shaped (2) in Neusticosaurus peyeri and iV. edwardsii (Car- roll & Gaskill, 1985; Sander, 1989), which may be correlated with the relatively great width of the skull table discussed by Carroll and Gaskill (1985) and Sander (1989). 2. In the plesiomorphic condition, the postor- bital enters the margin of the upper temporal fossa (0) but is excluded therefrom in the apomorphic state (1). 3. The number of dorsal vertebrae is variable within taxa, and the range of variations overlap to some slight extent (Serpianosaurus, Anarosau- rus). Twenty or fewer dorsal vertebrae are consid- ered the plesiomorphic condition (1), 20 or more dorsal vertebrae the apomorphic condition. 4. A distinct and well-developed entepicondyle on the humerus is considered the plesiomorphic condition (0); its reduction is derived (1) within RIEPPEL: PSILOTRACHELOSAURUS TOEPLITSCHI NOPCSA 13 1(2), 7 Fig. 9. Cladogram of pachypleurosauroid interrela- tionships. The characters are discussed in the text; their distribution among the taxa analyzed is coded in Table 3. pachypleurosauroids. Other characters of the hu- merus are not used in this analysis because of sex- ual dimorphism (degree of development of the deltopectoral crest) or ontogenetic variation (clo- sure of the entepicondylar foramen). 5. The pisiform may be present (0) or absent (1). Other characters of the forelimb were omitted from the analysis because of extensive variation, such as the shape and position of the intermedium. The distinctly broadened ulna is an autapomorphy of Keichousaurus, and hence uninformative in the analysis of interrelationships. 6. Distal carpal 4 may be ossified (0) or may fail to do so (1). The presence or absence of an ossified distal tarsal 4 is not coded separately, be- cause the two characters generally show a congru- ent distribution. 7. The plesiomorphic number of phalanges in the manus is 2-3-4-5-3 (0); reduction of the pha- langeal formula of the manus below 2-3 4—4-3 is coded as the derived condition (1). The formula 2-3-4-4-3 itself is still coded as plesiomorphic, because it may be accounted for by incomplete or problematical preservation {Keichousaurus [Young, 1958]; Dactylosaurus [Sues & Carroll, 1 985]) or by ontogenetic variation {Neusticosaurus [Sander, 1989]). The reduction of the phalangeal count in the pes (beyond 2-3-4-4-3) is autapo- morphic for Neusticosaurus edwardsii (Sander, 1989). 8. The plesiomorphic number of sacral ribs is two (0); three or more sacral ribs represent the derived condition (1). 9. Distinct pachyostosis of dorsal ribs is coded as the derived condition ( 1 ). The degree of pachy- ostosis may vary ontogenetically, being weakly ex- pressed in juveniles (Sander, 1989). However, dis- tinct pachyostosis is absent in Anarosaurus and Dactylosaurus, two genera represented by speci- mens of adult age. 10. Gastral ribs composed of five segments rep- resent the plesiomorphic condition; three seg- ments per gastral rib is the derived character state (1). 1 1 . The presence of surface ornamentation on the humerus is considered to represent the derived condition (1), as opposed to a smooth bone sur- face. This character is used here with the proviso that future studies may indicate ontogenetic vari- ation or preservational bias in its distribution. With the branch-and-bound search option im- plemented, and all characters treated as unweight- ed and unordered (character 1), the analysis yield- ed a single most parsimonious and fully resolved tree (fig. 9) with a tree length of 15 steps and a consistency index of 0.8 (rescaled consistency in- dex 0.711). The Pachypleurosauroidea are diag- nosed by a reduced upper temporal fossa (char- acter 1), a feature carried to a greater extreme in the sister-taxa Neusticosaurus peyeri and N. ed- wardsii; the relatively large upper temporal fossa of Keichousaurus is best interpreted as a reversal (based on ACCTRAN and DELTRAN character optimization strategies). The presence of three sa- cral ribs (character 8) is a second synapomorphy of the Pachypleurosauroidea, again reversed in Keichousaurus (see below). Within the Pachypleurosauroidea, Dactylosau- rus is shown as sister-taxon of all other genera, which share the derived absence of a well-devel- oped entepicondyle on the humerus (character 4) and of a pisiform in the carpus (character 5; this character is not known in Anarosaurus). Keichou- saurus groups with Psilotrachelosaurus, Serpiano- saurus, and Neusticosaurus on the basis of rib pachyostosis (character 9), which implies that the presence of two sacral ribs (Lin Kebang, cited in Sues, 1987) is to be treated as a reversal in this genus, whereas absence of rib pachyostosis in Ser- pianosaurus is also a reversal. Psilotrachelosaurus finally is shown to be the sister-taxon of the Serpianosaurus-Neusticosaurus clade, a relationship supported by the shared pres- ence of surface ornamentation on the humerus (character 11). The Serpianosaurus-Neusticosau- rus clade shares the (variable) exclusion of the postorbital from the upper temporal fossa (char- acter 2), a character that is unknown in Psilotra- chelosaurus. Another derived character shared by 14 FIELDIANA: GEOLOGY the Serpianosaurus-Neusticosaurus clade is the lack of an ossified distal carpal/tarsal 4 (character 6). Neusticosaurus finally is diagnosed by gastral ribs composed of three segments (character 8), and, within this genus, the species peyeri and edwardsii form sister-taxa on the basis of a reduced phalan- geal count in the manus (character 7). Neustico- saurus pusillus is diagnosed by a high number of dorsal vertebrae (overlapping to some degree with Serpianosaurus). Conclusions Psilotrachelosaurus is redescribed and recog- nized as a distinct taxon, closely related to the Serpianosaurus-Neusticosaurus clade of the Mid- dle Triassic from the southern Alps and the Ger- man Muschelkalk. It shares with this clade the derived surface ornamentation on endoskeletal el- ements but differs from it in the retention of an ossified distal carpal/tarsal 4, the relatively broad ventral elements in the pelvic girdle (pubis and ischium), and body proportions, in particular a proportionately short humerus (as related to stan- dard length). Serpianosaurus is so far known only from the Grenzbitumenzone (Anisian-Ladinian bound- ary), followed by species of the genus Neustico- saurus in stratigraphical succession (Sander, 1989). As discussed above, a late Anisian or early Ladin- ian age can be ruled out for Psilotrachelosaurus. However, as Psilotrachelosaurus is the sister-group of the Serpianosaurus-Neusticosaurus clade, the conclusion must be that Psilotrachelosaurus and Serpianosaurus share the same minimal geological age, i.e., that the clade of pachypleurosauroids rep- resented by Psilotrachelosaurus must date back to the Anisian-Ladinian boundary (Rieppel, 1986; Norell & Novacek, 1992). Zapfe and Konig ( 1 980, p. 70) describe the tran- sition between the late Anisian Zwischendolomit and the basal layers of the lower unit of the Part- nach-Plattenkalk in the Kellerberg profile as being very similar to the Grenzbitumenzone of Monte San Giorgio (which comprises the Anisian-Ladin- ian boundary) in terms of both lithology and facies (Bechstadt & Mostler, 1974, p. 50). Psilotrachelo- saurus as well as Lariosaurus come from geolog- ically younger deposits (middle Ladinian) of the Gailtaler Alps, stratigraphically equivalent to de- posits at Monte San Giorgio (lower Meridekalke) that have yielded hundreds of specimens of Neus- ticosaurus but, for some unknown reason, not a single lariosaur. Depositional conditions again seem to have been rather similar at both localities (Rieber, 1968, 1973; Zorn, 1971; Warch, 1979, 1984). And whereas a coexistence of Lariosaurus and pachypleurosaurs may have occurred during the deposition of the Grenzbitumenzone (Lario- saurus buzzi Tschanz, 1979, represented by a sin- gle specimen of controversial generic identity; see Kuhn-Schnyder, 1990; Rieppel, in press), Lario- saurus is otherwise known at Monte San Giorgio only from the upper Meridekalke (upper Ladinian [Kuhn-Schnyder, 1987]; Lariosaurus lavizzarii is a junior synonym of L. balsami [see Tschanz, 1989]), deposits, which have not yielded any pachypleurosaur material. Other than in the Gail- taler Alps, a coexistence of Lariosaurus and pachy- pleurosaurs is known from the Calcare di Perledo, most probably of late Ladinian age (see discussion under Geological Provenance). Further analysis of the temporal as well as geographical distribution of lariosaurs and pachypleurosaurs might provide important insights into the synecological relation- ships between these morphologically quite similar, but only distantly related taxa. Acknowledgments I thank Dr. F. H. Ucik, Curator for Geology and Mineralogy at the Landesmuseum fur Karnten in Klagenfurt, Austria, for his hospitality and help during my visit. He and his staff also provided the photograph of Psilotrachelosaurus toeplitschi shown in Figure 2. Dr. P. M. Sander kindly let me use his original morphometric data for the genus Neusticosaurus from Monte San Giorgio. Dr. F. H. Ucik and Dr. A. Warch kindly provided in- formation on the geology and stratigraphy of the Gailtaler Alps where Psilotrachelosaurus toeplit- schi was found. Drs. T. Biirgin, R. L. Carroll, P. M. Sander, G. W. Storrs, H.-D. Sues, K. Tschanz, A. 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On the new nothosaurs from Hupeh and Keichow, southwest China. Vertebrata PalAsiatica, 9: 315-356. Zangerl, R. 1935. Die Triasfauna der Tessiner Kal- kalpen. IX. Pachypleurosaurus edwardsi Cornalia sp. Osteologie-Variationsbreite-Biologie. Abhandlungen der Schweizerischen Palaontologischen Gesellschaft, 56: 1-80. Zapfe, H., and H. Konig. 1980. Neue Reptilienfunde aus der Mitteltrias der Gailtaler Alpen (Kamten, Os- terreich). Sitzungsberichte der Osterreichischen Aka- demie der Wissenschaften, mathematisch-naturwis- senschaftliche Klasse, Abt. I, 189: 65-82. Zorn, H. 1971. Die Triasfauna der Tessiner Kalkal- pen. XXI. Palaontologische, stratigraphische und se- dimentologische Untersuchungen des Salvatoredo- lomites (Mitteltrias) der Tessiner Kalkalpen. Abhandlungen der Schweizerischen Palaontologi- schen Gesellschaft, 91: 1-90. RIEPPEL: PSILOTRACHELOSAURUS TOEPLITSCHI NOPCSA 17 A Selected Listing of Other Fieldiana: Geology Titles Available The Mammalian Fauna of Madura Cave. 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