Palaeobio Palaeoenv (2010) 90:275–282 DOI 10.1007/s12549-010-0037-x

ORIGINAL PAPER

Late Jurassic Squamata and possible Choristodera from the Junggar Basin, Xinjiang, Northwest China Annette Richter & Oliver Wings & Hans-Ulrich Pfretzschner & Thomas Martin

Received: 18 February 2010 / Revised: 19 June 2010 / Accepted: 2 July 2010 / Published online: 31 July 2010 # Senckenberg Gesellschaft für Naturforschung and Springer 2010

Abstract Screen washing at the Liuhuanggou locality, a fossiliferous bone bed within the early Late Jurassic Qigu Formation, 40 km southwest of the city of Urumqi, yielded two lizard jaw fragments with teeth and two lizard osteoderm fragments, which together reveal the presence of Paramacellodidae. The same locality also yielded four tentative choristoderan jaw and tooth fragments. This find is the first record of Mesozoic lizards and probable choristoderes from the Junggar Basin and Northwest China and expands the palaeobiodiversity known from the Qigu Formation. This article is a contribution to the special issue “Triassic–Jurassic biodiversity, ecosystems, and climate in the Junggar Basin, Xinjiang, Northwest China” A. Richter Niedersächsisches Landesmuseum Hannover, Abt. Wissenschaft und Sammlungen, Geowissenschaften, Willy-Brandt-Allee 5, 30169 Hannover, Germany e-mail: [email protected] O. Wings (*) : H.-U. Pfretzschner Institut für Geowissenschaften, Universität Tübingen, Sigwartstraße 10, 72076 Tübingen, Germany e-mail: [email protected] O. Wings Museum für Naturkunde Berlin, Leibniz-Institut für Evolutions- und Biodiversitätsforschung an der Humboldt-Universität zu Berlin, Invalidenstraße 43, 10115 Berlin, Germany T. Martin Steinmann Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Nussallee 8, 53115 Bonn, Germany

Keywords Qigu formation . Jurassic . Junggar Basin . Squamata . Choristodera

Introduction The Junggar Basin [Xinjiang Uyghur Autonomous Region, Northwest China] is a large continental basin with a succession of Mesozoic sediments up to 6 km thick (Dong 1992). Throughout the basin, several fossil sites have yielded well-preserved vertebrate remains (e.g., review in Averianov et al. 2005; Currie 1997; Dong 1992), but nothing has been published on Mesozoic lizards and choristoderes from this region. During fieldwork of the Sino-German Cooperation Project (Jilin University, Changchun, China; Geological Survey No. 1, Urumqi, China, and the University of Tübingen, Germany), several new vertebrate localities were discovered in the Junggar Basin, one of which yielded several tiny fragments of small reptiles, which are described herein. The Liuhuanggou locality (Fig. 1) is situated at the southern margin of the Junggar Basin, 40 km southwest of Urumqi. The locality consists of a bone bed within the Qigu Formation close to the boundary to the underlying Toutunhe Formation. At the locality, the Qigu Formation is 731 m thick and has been dated to the Oxfordian based on spores and palynomorphs (Ashraf et al. 2004, 2010, this issue). The area, including the nearby located TAAA (Turtle-Archosaur-Amphibian Assemblage) locality, has produced a large amount of vertebrate fossils, in particular hybodontoid sharks, actinopterygians, temnospondyls, turtles, crocodilians, mammals and several isolated dinosaur teeth (Klug et al. 2010, this issue; Maisch and Matzke 2003; Maisch et al. 2005; Martin et al. 2007, 2010, this issue; Pfretzschner et al. 2005; Skutchas et al. 2009; Wings

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Fig. 1 Map of the Junggar Basin in Xinjiang, Northwest China. The locality Liuhuanggou is marked by a square

et al. 2007, 2010, this issue). The worldwide rare documentation of Jurassic Choristodera and Squamata together with supposed climatic differences between Central Asian basins in the Jurassic (e.g., Eberth et al. 2001) as well as endemic tendencies in some Asian vertebrate groups (Averianov et al. 2005; Russell 1993) make the description and a palaeobiogeographical comparison of the new material especially interesting.

Paramacellodidae Estes, 1983 Genus et species indet. Description: Two different lizard fragments with teeth including jaw bone material and two osteoderm fragments were identified within the Liuhuanggou material. Only one tooth crown is preserved with striations. Teeth and jaw bones

Material and methods Several metric tons of sediment from the bone bed were screen washed at a mesh size of 0.5 mm, and the remaining concentrate was picked under stereomicroscopes. Drawings were made of all specimens using a microscope as well as technical pens and carbon wax pencils on a coquille board. Additionally, specimens were gold-coated, examined and photographed with a Camscan MV 2300 scanning electron microscope (SEM) at the Steinmann-Institut at the Universität Bonn, Germany. Digital scans of the drawings were adjusted to the same magnification and compiled together with the SEM photos to plates. The crown patterns of the paramacellodid teeth were described following the technical terminology of Richter (1994) and Evans and Searle (2002). Institutional abbreviations All specimens are deposited in the Sino-German Project collection (SGP 2007/#), which is currently housed at the Institut für Geowissenschaften (IFG), Universität Tübingen, Germany. After completion of the investigation, the material will be permanently deposited under the SGP collection numbers in the Research Center of Paleontology and Stratigraphy at the Jilin University in Changchun, China. Systematic palaeontology Diapsida Osborn, 1903 Squamata Oppel, 1811 Scincomorpha Camp, 1923

SGP 2007/1 (Figs. 2a and 3a) is a small jaw fragment with two teeth, one of which is reasonably complete, and the other has its crown broken off. Both teeth show pleurodont attachments on a very small piece of jaw bone. The complete tooth has a peg-like, slender overall morphology with a chisellike tip. Labially, the tooth appears to be convex and smooth above the lateral parapet of the jaw. Lingually, just below the inwardly bent tooth tip and its inner secondary tip, a more concave area of striae shows a typical pattern mostly used to distinguish non-paramacellodids from paramacellodids within Jurassic sediments, the latter of which always bear that character. Together with the osteoderms, this is diagnostic of Paramacellodidae. The inner tooth tip corresponds to the typical paramacellodid cuspis lingualis, and the anterior and posterior keels—both visible on the lingual side—correspond to the culmen lateris anterior and culmen lateris posterior, respectively. The cuspis lingualis is the center of two dominant “main striae”, called the stria dominans anterior and stria dominans posterior, respectively, both preserved in SGP 2007/ 1. One character of Paramacellodidae not recognizable here is the “miniature ridge” between the cuspis labialis and the already mentioned cuspis lingualis, most probably due to the preservational condition. The tooth base is diffuse and may represent a badly abraded large resorption pit. The base of the other half tooth is fully preserved and complete, showing no resorption pit at all. The internal surface of the fracture shows a lighter area of the pulp cavity. Both teeth are implanted on a subdental shelf, as can be seen in the medial aspect. Two circular nerve foramina open to the lateral side of this lower jawbone. It could supposedly be a right dentary (Gao Ke-Qin, written communication, 2010).

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Only a single tooth is preserved in the jawbone fragment SGP 2007/2 (Figs. 2b, 3b). The pleurodont implantation of the tooth can be deduced by the higher lateral parapet. Despite its strongly abraded state, the tooth is preserved in full original size and with its general chisel-like shape. Labially, only the smooth surface of the upper 40% can be seen. Lingually, the slightly rounded and convex base contrasts with the slightly square tip, which bears remains of the former striae system. Only the two typical paramacellodid cutting edges or keels, the culmen lateris anterior and the culmen lateris posterior are recognizable. Only a faint suggestion of the interior cusp can be seen. The tip of this cuspis lingualis is strongly rounded, similar to the main cuspis labialis. The underlying subdental shelf is exposed in small areas. In addition to the preserved tooth, there is a broken fragment of a neighbouring tooth base, showing a tiny lingual rampart. A thin fragment of the subdental shelf is visible below the complete tooth. The lateral surface of the jawbone is relatively smooth (except for many thin compaction cracks), bearing no nerve foramina at all. Two osteoderm fragments (Figs. 2c, d, 3c, d) are known to date from the Liuhuanggou locality. SGP 2007/4 (Figs. 2c, 3c) represents the posterior part of a typical paramacellodid osteoderm, the external surface being slightly eroded but also rough in comparison to the smooth internal side. The specimen shows the main paramacellodid features of a rectangular overall shape, a weak keel—located not exactly in the symmetrical middle of the bone, alluding to a lateral position on the body of the lizard—and a series of irregularly placed, small and mostly rounded to sub-oval pits on the external side, paralleled by a lesser number of internal pits. The rostral part of the osteoderm is missing. The preserved posterior part represents the so-called “free portion” of a generalized osteoderm, usually imbricating upon the rostral part of the next osteoderm. There is a weak ornamentation on the left side and a smooth margin of the right outer side of the osteoderm. Nonetheless, the ornamentation is altogether flat with no sign of tubercles. The foramina are grouped to the left and right side of the keel, and there are only irregular rows of foramina on the internal surface of the osteoderm. The mesial side is slightly concave. The thickness of the osteoderm can be estimated in Fig. 2c by the right side of the osteoderm in internal view, picturing the lateral surfaces of the bony skin element. In the classic vertical orientation of the interpretative drawing, this right flank is slightly angled and shows the homogenous surface of its lateral edge. The second osteoderm specimen (SGP 2007/5; Figs. 2d, 3d) is also broken. The rostral (=anterior) zone is lacking as in SGP 2007/4, but the posterior margin is almost complete. The rectangular main shape can be deduced by the parallel margins of the bone. The posterior margin is pointed, although enforced in its tip by a central keel, having its

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highest elevation right within the tip. Irregularly shaped, oval to rounded foramina are grouped around the keel from both sides. The internal side of the osteoderm is smooth and slightly concave. There are five foramina at the posterior end. A faint hint of a big central foramen lies around the broken anterior end of the specimen. This part of the osteoderm would have imbricated on the neighbouring anterior part. Choristodera Cope, 1884 Family incertae sedis Genus et species indet. Description: Three specimens (Figs. 2e, f, g, 3e, f, g) could be tentatively identified as belonging to Choristodera, whereas the classification of one additional specimen (Figs. 2h, 3h) is questionable. The two larger specimens have attached jaw material, each bearing two teeth. The two others are isolated single teeth, one with attached bone material. Especially the tooth tips are abraded (probably due to pre-burial transport), revealed by incompletely preserved striae, often reduced to the level of the deepest of the striae grooves. SGP 2007/6 (Figs. 2e, 3e) shows the condition of two subthecodontly implanted teeth attached to the remaining part of the jaw bone. Judging from the straight, long jawbone, it is plausibly a dentary. Dentaries are much more commonly preserved than maxillae. However, as the thin choristoderan maxillae also possess long, rod-like posterior ends, it could also be a fragment of the latter. In labial aspect, the jawbone bears a small groove, which is interpreted as one of the typical oval nerve foramina of the dentary. Medially, a part of the subdental ridge is present. The teeth are conical, with slightly broader, smooth bases and attenuated, slightly inwardly pointed tips. The latter are striated lingually. Those four to five striae seem to be the only remaining, deepest grooves of a formerly denser system of shallower striae. Due to the slightly abraded preservation, it remains unclear if there have been weak striae on the labial side of the tooth crown. The labial side of the tip appears to be smooth. Due to the abraded state, the extent of enamel cover on the teeth cannot be clearly identified. Weak, but unambiguous anterior and posterior keels are developed. SGP 2007/7 (Figs. 2g, 3g) also shows a plesiomorphic subthecodont condition, which is not only diagnostic of Choristodera but also of other reptiles. The slightly higher lateral margin contrasts with the lower medial margin. As in SGP 2007/6, it cannot be stated clearly whether the remaining jaw fragment is a dentary or a maxilla. Some elongate grooves are preserved on the lateral side, indicating that it may be part of a maxilla. Typical for lower jaws of Choristodera, two oval nerve foramina are present on the lateral side, unfortunately broken just above the zone where

278 Fig. 2 Drawings of paramacellodid lizard and possible Choristodera remains from Liuhuanggou. a Paramacellodid jaw fragment (SGP 2007/1) with two teeth, lingual (left) and labial aspect (right); the complete tooth bears the typical paramacellodid striation b Paramacellodid tooth and jaw fragment (SGP 2007/2) in labial (left) and lingual aspect (right). c Paramacellodid osteoderm (SGP 2007/4) with weak keel, external (left) and internal aspect (right). d Paramacellodid osteoderm (SGP 2007/5) with pointed and slightly stronger keel than in specimen SGP 2007/4. e Possible Choristodera jaw fragment (SGP 2007/6) with two complete teeth, labial (left) and lingual aspect (right). f Possible Choristodera isolated tooth with a small amount of remaining jaw bone (SGP possible 2007/ 8); view onto the right flank (left) and lingual aspect (right). g Possible Choristodera jaw fragment (SGP 2007/7) with one complete and one broken tooth, lingual (left) and labial aspect (right). h Possible Choristodera jaw fragment (SGP 2007/10) with four teeth, two of which are complete; labial (left) and lingual aspect (right)

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b

a

1 mm

c

d

e

g f

h the lower row of foramina would have been situated as a true and unambiguous character of Choristodera. Two teeth are preserved, of which one is complete and the other lacks the tip. Only the complete tooth shows the typical, slightly attenuating outline around the apex. Both teeth possess a system of striae; at least nine striae can be counted on the upper third. It is plausible that these remnants of a formerly more complex system of many parallel striae are reduced due to abrasion of the tooth surface. Interestingly, some short striae have been preserved even on the labial side. A minimum of eight incomplete striae can be counted just below the tooth crown of the complete tooth. The apex is smooth, typical striae are again missing. Weak anterior and posterior keels are developed.

The isolated tooth of SGP 2007/8 (Figs. 2f, 3f) shows some characteristics expected of a slightly abraded choristoderan tooth: it is conical, has a stout, slightly broader base, attenuates towards the tooth crown and has weak, but distinct anterior and posterior keels. In addition to a few, very weak striae on the labial side, at least six more prominent striae are present on the lingual side of the tooth tip. The slightly pointed tooth tip can clearly be seen in lingual aspect. The tooth implantation of the small remaining jawbone fragment is not diagnostic, but differs markedly from the easily distinguishable pleurodont lizard fragments within the material (see above). SGP 2007/10 is tentatively interpreted as a choristoderan fragment (Figs. 2h, 3h). It consists of a relatively large

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Fig. 3 Scanning electron microscope photographs of paramacellodid lizard and possible Choristodera remains from Liuhuanggou. a Paramacellodid jaw fragment (SGP 2007/1) with two teeth, lingual (left) and labial aspect (right). b Paramacellodid tooth and jaw fragment (SGP 2007/2) in labial (left) and lingual aspect (right). c Paramacellodid osteoderm (SGP 2007/4) with weak keel, external (left) and internal aspect (right). d Paramacellodid osteoderm (SGP 2007/5) with pointed and slightly stronger keel than in specimen SGP 2007/4. e Possible Choristodera jaw fragment (SGP 2007/6) with two complete teeth, labial (left) and lingual aspect (right) f Possible Choristodera isolated tooth with a small amount of remaining jaw bone (SGP possible 2007/ 8); view onto the right flank (left) and lingual aspect (right). g Possible Choristodera jaw fragment (SGP 2007/7) with one complete and one broken tooth, lingual (left) and labial aspect (right). h Possible Choristodera jaw fragment (SGP 2007/10) with four teeth, two of which are complete; labial (left) and lingual aspect (right)

jawbone fragment with five implanted teeth. All teeth are heavily worn and abraded; only two have preserved tooth tips. Judging from their size and overall shape, they resemble the other choristoderan specimens: stout, conical teeth with slightly attenuating tips are implanted subthecodontly onto the jaw shelf. The lateral side of the latter bears three marked, elongate nerve foramina. The labial sides of the teeth show few, faint striae. However, there is a marked difference to the other specimens in lingual aspect: enamel wrinkles shaped like down-pointing arrowheads form secondary keels on the slightly obliquely oriented teeth. This feature seems to be rather unique no

matter how deeply abrasion may have altered the tooth appearance. As with all other teeth still attached to the bone, this specimen is broken just above the zone where the potential lower, second row of nerve foramina—a character of Choristodera—would have been situated.

Discussion and conclusions All identified fragments of small reptiles are more or less abraded. Some specimens can tentatively be referred to

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Choristodera, some others to early Squamata. The material of both groups shows a high grade of fragmentation, only limited characters are preserved and all material can thus not be identified more precisely. However, the presence of both groups has been documented within the screen-washed material with some specimens, confirming that there is a high probability of finding more complete material in the future. Due to the overall characteristic tooth implantation (pleurodonty), the tooth shape (with its rather parallel flanks and the chisel-like appearance) and especially its tip—even in an eroded state—and in one case the absolutely unmistakable striations, both jaw fragments can be assigned to the family Paramacellodidae (Estes 1983). This dominant group of Jurassic scincomorphan lizards is mostly viewed as a sister-group to the modern Cordyliformes (Estes et al. 1988). Paramacellodids were very successful, especially within the Late Jurassic and Early Cretaceous, but to date no Late Cretaceous fossil record of this group is known. Members of this group were widespread geographically, with the oldest representatives from the Middle Jurassic (Evans 1998) and very abundant remains within the Late Jurassic (e.g., Broschinski 1999; Evans and Chure 1998; Seiffert 1973) as well as Early Cretaceous localities of Laurasia (Richter 1994). There is also a sparse fossil record known from Africa (Morocco and Tanzania; Broschinski 1999; Broschinski and Sigogneau-Russell 1996) and a record within Central Asia (Alifanov 2000) from the Early Cretaceous. In spite of ongoing debates on the ecological adaptations, the use of tooth-tip morphology within lepidosauromorphs seems appropriate. Basic sets of scincomorphan characters prove very helpful operationally, especially when working with fragmentary lizard material (Evans and Searle 2002). The character set of Paramacellodidae is not unmistakable due to the lack of further skull material, but it can be utilized with a very high probability, especially when combined with the osteoderm data. Nonetheless, there are other lizards with similar tooth morphology which could potentially be mixed up with that group (e.g., the Japanese Sakurasaurus; Evans and Manabe 1999). Due to its size and slender appearance, the fragmentary status of the single tooth SGP 2007/1 does not allow the fragment to be assigned to any of the known genera. The two fragmented osteoderms (SGP 2007/4 and SGP 2007/5) can also be assigned to the Paramacellodidae, as this Mesozoic lizard group in particular is characterized by full osteodermal body coverage. Astonishingly, they represent the posterior, thinner parts of the osteoderm, although the thicker, more stable anterior part of the bone should theoretically be more abundant due to its higher taphonomic resistance against abrasion. The rectangular overall shape, the moderate thickness, more or less flat keels, small, rounded foramina on both sides of the keels and the total

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lack of any convex tubercle morphology on the external side are characters of paramacellodid osteoderms. The pits are foramina, openings of channels for blood vessels and nerves for the keratinous scutes formerly covering the bony shields. Typically, these channels (“marrow channels” sensu the German literature and Broschinski and Sigogneau-Russell 1996) diverge fan-like into the external side, resulting in a higher number of foramina on the external side than on the internal one. It appears that many of the more stable osteoderm types contrast with the smooth, thin types of, for example, British Purbeck paramacellodid osteoderms (Richter 1994). As paramacellodids had single osteoderms on the dorsal and compound osteoderms on their ventral side (Richter 1994), the margins of the osteoderms are also of importance. SGP 2007/5 is too poorly preserved, but the clearly homogenous surface of the right flank of SGP 2007/4 does not hint of the presence of a compound structure, which should have been more irregular and partly sutured. Thus, it can be interpreted tentatively that SGP 2007/4 was a single osteoderm situated on a higher part of the right or left flank of the lizard, as the keel is still very close to the midline (Richter 1994). The pointed osteoderm fragment (SGP 2007/5), however, could be tentatively assigned to a more posterior position within the lizard’s body, possibly situated between the thorax sensu stricto and the beginning of the pelvic and caudal region. Similar paramacellodid osteoderms have been found articulated in Kazakhstan (Hecht and Hecht 1984), and disarticulated specimens together with jaw and tooth material are known from Spain, Portugal (Broschinski 2000; Richter 1994), Morocco (Broschinski and Sigogneau-Russell 1996) and many other localities (i.e., Evans and Chure 1998). Interestingly, Konkasaurus from the Late Cretaceous of Madagascar has very similar looking osteoderms, but groups together with the true Cordyliformes and ?Cordylidae (Krause et al. 2003) due to different jaw and tooth morphologies. In addition to cranial characters, this is just another indication for the very close relationship of the Middle Jurassic to Lower Cretaceous Paramacellodidae with the basal Cordyliformes. Extant Gerrhosauridae, for example, still show very similar osteoderm morphology (Richter 1994). The tentative new choristoderan specimens from Liuhuanggou could possibly close another gap within the known range of Choristodera—if the subthecodonty is not doubted (Gao Ke-Qin, written communication 2010). The attachment of the teeth is indeed not very deep, and the bony basis could also be interpreted as a badly preserved (sub)dental shelf. Thus, we tentatively interpret the fragments as choristoderes, but it could well be that another, yet unknown type of reptile with rather subacrodont tooth implantation was part of the

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Liuhuanggou vertebrate fauna. More complete finds will hopefully solve this question in the future. After having been neglected, misidentified and underestimated for many decades, increasing knowledge about the Choristodera since the 1970s has led to a completely new understanding. The early Late Jurassic age of Liuhuanggou further establishes the Jurassic occurrence of Choristodera within Asia, confirming the finds of fragmentary vertebral material referable to Choristodera indet. from the Middle Jurassic Balabansai Formation of the Fergana Valley, Kyrgyzstan (Averianov et al. 2006). The indeterminate possible choristodere remains from Liuhuanggou represent just another faunal element similar to the Balabansai Formation of the Fergana Valley. The two vertebrate assemblages are comparable not only in their close Jurassic age [Liuhuanggou: Oxfordian (Ashraf et al. 2010, this issue); Balabansai Formation: Callovian (Averianov et al. 2006)], but they contain many equivalent faunal elements: hybodontoid sharks (which were, however, far more abundant in the Balabansai Formation close to the Fergana Gulf, than in the intramontane Junggar Basin), the basal cryptodiran turtle Xinjiangchelys, the goniopholidid crocodylomorph Sunosuchus, pterosaurs, theropod dinosaurs and docodont mammals (Averianov 2000; Averianov et al. 2005, 2006; Martin and Averianov 2004). The great similarity in the fossil vertebrate assemblages is an indication that supposed endemic tendencies between Central Asian Basins in the Jurassic were weaker than previously thought. Acknowledgements We address our special thank to Prof. Sun Ge (Jilin University and Shenyang Normal University) for his constant help and support of our field work in Xinjiang during many years. For collaboration and field assistance, we are deeply indebted to personnel from the Geological Survey No. 1 in Urumqi and the Jilin University in Changchun. Christian Dechert, Juliane Hinz, Kristina Hippe, Li Jie, Roland Kersting, Jean Sebastian Marpmann, Rico Schellhorn, Köbi Siber, Ben Thuy, Wu Wenhao, Du Xing and Dr. Sun Yue-Wu, helped in the field during excavation. Sven Balmer, Juliane Hinz, Kristina Hippe, Kai Jäger, Roland Kersting, Franziska Kiebach, Anke Küttner, Jacqueline Langer, Leonie Lenssen, Kristina Pascher, Achim Schwermann, Nadine Siegling, Benedikt Steiner, Annika Szameitat, and Ben Thuy picked the screen-washing concentrate under the stereomicroscope. Georg Oleschinski is acknowledged for the SEM photographs. The manuscript benefitted greatly from comments and suggestions of Dr. Susan Evans and Prof. Dr. Gao Ke-Qin, and we sincerely thank both of them. Walter G. Joyce is acknowledged for a final language check. The project was funded by technical grants MA 1643/11 to TM and PF 219/21 to HUP of the Deutsche Forschungsgemeinschaft (DFG) as well as the Sino-German cooperation project.

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