The Tyulkili [=Tjulkeli] hills (known in the paleobotanical literature as the Kankazgan locality) are located about 80 km north of Dzhusaly railway station in northeastern Kazakhstan (Fig. 1). Here the Zhirkindek Formation is exposed and is composed of sands interbedded with clays and silts (Shilin 1998; Kordikova et al. 2001). The ferruginous sandstone at the bottom of the Zhirkindek Formation section at Tyulkili hills has yielded numerous plant remains, including 36 species of fossil angiosperms (Shilin 1982, 1986, 1998). The next bed up-sequence, consisting of yellow-grey and grey clays, represents an ingression of brackish waters. It has produced fossilized wood, numerous remains of crustaceans, shark teeth (Protolamna sp., Scapanorhynchus sp.) and coprolites, the isolated bones of lindholmemydid and trionychid turtles, crocodyliforms, ornithopods (Hadrosauroidea indet.), possible sauropods, and laterally compressed teeth of theropods (Tyrannosauroidea indet.) (Nesov 1995, 1997). Indeed, in 2012 the tooth of a marine shark Cretodus longiplicatus was found at this level, a species characteristic of the Cenomanian of the Tethys region (Werner 1989; Kennedy et al. 2008; Underwood et al. 2011). According to Sokolov (1978), this species [=Semiplicatodus sulcatus in his usage] is widely distributed in late Albian – Cenomanian deposits of the Mangyshlak Peninsula and western Turkmenistan but is rare in the Turonian of Kazakhstan.

The main fossiliferous horizon at the Tyulkili locality is confined to the middle sandstone bed, about 18 m above the base of the Zhirkindek Formation (Kordikova et al. 2001). In 1982, Nesov collected the remains of plesiosaurs, crocodyliforms, pterosaurs (cf. Azhdarchidae) and dinosaurs (Ankylosauridae indet., Hadrosauroidea indet., Neoceratopsia indet., Sauropoda indet., Tyrannosauroidea indet., Ornithomimidae indet., and Therizinosauroidea indet.) at this level (Nesov 1995, 1997; Averianov 2007b, 2009; Averianov and Sues 2009). Martinson (1990b, 1997) reported six species of bivalves (Trigonioidea and Unionoidea) from unspecified levels of the Zhirkindek Formation at Tyulkili (Kankazgan). Much later, Kordikova et al. (2001) reported gastropods, bivalves, brachiopods, crustaceans, selachians, osteichthyans, amphibians, varanoid lizards, trionychid turtles, crocodyliforms (cited as “Turanosuchus aralensis” [=Kansajsuchus borealis]) and ornithomimid, tyrannosaurid, and dromaeosaurid theropods from this horizon. In 2012, we collected a microvertebrate sample from this level that included shark teeth and spines (Hybodus sp., Polyacrodus sp.), numerous gar scales and bones (Lepisosteidae indet.), rare dinosaur teeth and salamander bones (Skutschas 2013). Further up in the section, at the top part of the middle sandy bed, there are also shark teeth and spines (Hybodontidae indet., Odontaspididae indet., Scapanorhynchus sp.), holostean (Lepisosteidae indet.), teleostean bones and scales, bones of lindholmemydid and trionychid turtles, crocodyliforms, dinosaurs, and fragments of pterosaur hollow bones (Nesov 1997). The upper part of the Zhirkindek Formation at Tyulkili hills is composed of light grey clays from which abundant plant remains as well a bird feather have been collected (Shilin 1986: fig. 3; Nesov 1992a).

The flora known from the lowermost sandstone bed of the Zhirkindek Formation at Tyulkili is dominated by Platanus species and thermophilous conifers (Shilin 1998) and likely corresponds to the early Turonian thermal maximum (Nesov 1993). A similar Turonian flora has been collected from the Zhirkindek Formation at Karakumzholy at the eastern end of the Tyulkili hills (Shilin 2008). East from the Tyulkili hills, in the lower Syr Darya area below the Zhirkindek Formation, there are marine early Turonian deposits with inoceramids and fossilized wood (Geology of the USSR 1970). The lower clayey part of the Zhirkindek Formation corresponds to the early Turonian marine transgression in the region and the upper sandy part may be of the late Turonian – Coniacian age (Nesov 1997; Kordikova et al. 2001).

The pterosaur specimens collected by Nesov in 1982 at Tyulkili include ZIN PH 54/43, a dorsal vertebra (Averianov 2007a: fig. 1), ZIN PH 38/43, a poorly preserved distal fragment of radius or ulna and ZIN PH 13/43, a small fragment of the first wing phalanx (?). In 2012 a well preserved distal fragment of juvenile ulna (ZIN PH 56/43; Fig. 2) was also collected from the lower part of this section. This specimen is about half the size of ZIN PH 14/44, a distal ulna fragment of Azhdarcho lancicollis from the upper Turonian Bissekty Formation of the Kyzylkum Desert, Uzbekistan (Averianov 2010: fig. 25F–J): its distal width is 25.3 mm compared with 41.0 mm in the specimen from the Bissekty Formation. ZIN PH 14/44 could be from an adult but is not the largest specimen from the Bissekty Formation as ZIN PH 86/44, an ulna lacking its distal end, is distinctly larger. In spite of these size differences, the morphology of both bones is almost identical: in each the shaft is hollow, with a maximum wall thickness around 1 mm, and is oval in cross section with a dorsoventral long axis (Fig. 2a). The shaft flares towards the distal end and is more pronounced on the ventral side compared with the dorsal side; the distal end is more than twice as expanded dorsoventrally compared with the preserved proximal end. The distal articulation surface for the proximal syncarpal is skewed towards the longitudinal axis of the shaft at an angle ~76°. This surface is composed of the dorsal articulation surface, middle tuberculum, and ventral fovea (Fig. 2). The dorsal articulation surface is slightly convex and crescentic in distal view (Fig. 2f) and has a tongue-like extension on its posterior surface. This extension occupies almost half of the distal articulation surface of the bone. The tuberculum is relatively small and similar in the area to the ventral fovea. In ZIN PH 14/44 (Averianov 2010: fig. 25G, J), this tuberculum appears larger but the ventral fovea is incompletely preserved. On the posterior side of the distal end, ventral to the ventral fovea, there is a short but prominent longitudinal groove and a deeper and longer groove is also positioned on the dorsal margin of the distal end on the anterior side (Fig. 2e), possibly for a flexor tendon (Bennett 2001). Ventrally this groove is bordered by a short prominent ridge, ventral from which the anterior surface is depressed. A similar ridge is present on the opposite posterior side that connects distally with a tongue-like extension of the dorsal articulation surface. Some parts of this ridge and dorsal articulation surface are missing in ZIN PH 56/43.

Figure 2. 

Azhdarcho sp., ZIN PH 56/43, distal fragment of a right ulna in proximal (a), ventral (b), posterior (c), dorsal (d), anterior (e), and distal (f, stereopair) views. This specimen is from the Tyulkili locality in the northeastern Aral Sea region of Kazakhstan; Zhirkindek Formation, Upper Cretaceous (upper Turonian – Coniacian). Abbreviations: das, dorsal articulation surface; ft, groove for flexor tendon; tub, tuberculum; vf, ventral fovea. Scale bar is 10 mm.

The morphology of the distal part of the ulna generally shows little variation among pterodactyloid pterosaurs (see review in Wiffen and Molnar 1988). In Ornithocheiridae, the distal articulation surface of the ulna is not skewed and the ventral portion of the distal ulna is usually wider anteroposteriorly with the ventral fovea occupying only half of this width. A pneumatic foramen can often be present on the anterior side of this element close to the distal end (Wellnhofer 1985: fig. 9a, c). In ZIN PH 56/43, common to azhdarchids, this pneumatic foramen is absent and the ventral part of the distal ulna is very narrow, with a ventral fovea occupying most of its surface (Averianov 2010). In non-azhdarchid azhdarchoids, such as “Santanadactylus spixi” [=Tupuxuara sp.] (Wellnhofer 1985: fig. 25a-c) and Tapejara wellnhoferi (SMNK PAL 1137, pers. obs. by AA) the ventral part of the distal ulna is similarly narrow, but the distal articulation surface is less skewed. Because ZIN PH 56/43 is almost undistinguishable from the distal ulna of A. lancicollis from the co-eval Bissekty Formation in the nearby Kyzylkum Desert, Uzbekistan, it is tentatively assigned here to Azhdarcho sp.

The Baibishe [=Baybishe] hill locality is situated about 130 km NNW from Dzhusaly railway station (Fig. 1). The vertebrate remains from this region come from the lower and middle part of the Bostobe Formation which is exposed here above the upper Albian – Cenomanian Altykuduk Formation and Turonian Zhirkindek Formation, both of which contain plants and molluscs (Martinson et al. 1966; Shilin and Romanova 1978). The first vertebrates from the Bostobe Formation at this locality were discovered by Shilin in 1979 who collected plant remains and molluscs from the lower clay bed, a nearly complete carapace of the adocid turtle Shachemys baibolatica and hadrosauroid bones from the overlying yellow-grey sandstone bed (Kuznetsov and Shilin 1983; Shilin 1983). In 1982, Nesov collected a microvertebrate sample from this locality which included brackish water chondrychthians (Polyacrodus cf. brabanticus, Polyacrodus sp., Hybodus kansaiensis, Scapanorhynchus sp., Ischyrhiza sp., Protoplatyrhina sp., Ptychotrigon sp., Myledaphus glickmani, Baibishia baibishe) and osteichthyans (Ichthyodectidae indet.), freshwater chondrosteans (Acipenseridae indet.) and holosteans (Amiidae indet.), salamanders (Eoscapherpeton sp.) and frogs, macrobaenids Anatolemys maximus, freshwater adocids Adocus bostobensis and Shachemys baibolatica and Trionychidae indet., remains of the terrestrial stem testudinoid Lindholmemys sp., crocodyliforms cf. Kansajsuchus sp., ornithopods, sauropods, small non-avian theropods, tyrannosauroids, and birds (Mertinene and Nesov 1985; Nesov and Mertinene 1986; Nesov 1988a, 1995, 1997; Syromyatnikova and Danilov 2009; Danilov et al. 2011; Skutschas 2013). Bishara backa, for example, was based on an atlas vertebra from Baibishe and was first described as an albanerpetontid (Nesov 1997) and then later considered to be an unidentifiable salamander by Gardner and Averianov (1998). This element could be the oldest record of the Proteidae (Skutschas 2013). Nesov (1995) also recorded remains of a possible ceratopsid dinosaur at this site but this cannot be confirmed. A fragmentary skull roof from Baibishe referred by Nesov (1988a) to a hadrosauroid cf. Lophorothon turns out to be a giant freshwater trionychid turtle, Khunnuchelys n. sp. (Vitek and Danilov 2010; Danilov et al. in press). Averianov (2007b) identified bones and teeth of Tyrannosauroidea indet., Therizinosauroidea indet., and Dromaeosauridae indet. from Baibishe and referred CCMGE 601/12457, a femur from this site attributed by Nesov (1995) to Tarbosaurus, to a therizinosauroid cf. Neimongosaurus sp. This latter identification has been questioned by Zanno (2010).

A rich assemblage of brackish water bivalves from Baibishe was described by Martinson (1990b): Lancedaria angustata, Psorula tasaranica, Parreysia convexa, Oxynaia baibishensis, and Rectidens asiaticus. Nesov (1988c) also reported silicified wood at this site that contains the boring traces of insect larvae, likely jewel beetles (Buprestidae) and other coleopterans, which he considered to be ichnospecies Rhombichnithes beibishensis.

In the microvertebrate sample from Baibishe there are also a number of indeterminant pterosaur hollow limb bone fragments (Nesov 1990; Averianov 2008). A single large specimen cf. ?Azhdarchidae was reported from this site by Nesov (1997: 111). ZIN PO 3475, a pedal ungual phalanx, is so far the only bird fossil reported from Baibishe (Nesov 1988b: 121, fig. 1(5); 1992b: 27; 1992a: 471, fig. 4K) although Bakhurina and Unwin (1995: 231) noted similarity with bones of Dsungaripterus and thought it instead may belong to a pterosaur.

Akkurgan [=Akkurgan-Boltyk] is an isolated hill 135 km north of Dzhusaly railway station (Fig. 1) that exposes outcrops of the Bostobe Formation. This locality has become known for the plant remains collected from the light-grey clays at the bottom of the Bostobe Formation (Martinson et al. 1966; Shilin and Romanova 1978). In 1977, Shilin collected plant remains from this level and a hadrosauroid maxilla and femur fragments from the green-grey clays above. This maxilla fragment became the type specimen of Arstanosaurus akkurganensis, which is now considered a nomen dubium (Shilin and Suslov 1982; Norman and Kurzanov 1997; Horner et al. 2004). In 1982, Nesov collected bones of the freshwater chondrostean Acipenser shilini, the adocids Adocus bostobensis and Shachemys baibolatica, an indeterminate trionychid, the stem testudinoid Lindholmemys sp., and crocodyliforms, Hadrosauroidea indet. remains and the laterally compressed teeth of Tyrannosauroidea indet. (Nesov and Kaznyshkin 1983; Nesov 1995, 1997; Syromyatnikova and Danilov 2009; Danilov et al. 2011). Much later, Godefroit et al. (2012) described the basal hadrosauroid Batyrosaurus rozhdestvenskyi based on a partial skeleton from this locality.

Most recently, Naish et al. (2012) described a posterior mandible fragment from Akkurgan which they referred to the gigantic bird Samrukia nessovi. This specimen was subsequently considered to be a pterosaur (Buffetaut 2011), a reassignment agreed with in this paper. The Samrukia mandible is similar to the mandible of Quetzalcoatlus sp. from the Maastrichtian of Texas, USA (Kellner and Langston 1996: fig. 4) in having a peculiar posterolateral process of the lateral cotyle of the mandibular glenoid, a feature absent in ornithocheirids and pteranodontids (Wellnhofer 1985; Bennett 2001). Our view is that most likely S. nessovi is an azhdarchid pterosaur and thus this name is a possible synonym of Aralazhdarcho bostobensis known from the same formation at Shakh Shakh.

Buroinak [=Boroinak] is a low ridge 110–120 km NNE of Dzhusaly railway station (Fig. 1) that exposes outcrops of the Bostobe Formation. In 1982, Nesov collected the laterally compressed teeth of Tyrannosauroidea indet. from this locality along with other remains of non-avian theropods and the bones of ankylosaurs, possible ceratopsians and hadrosauroids (Nesov 1995). Averianov (2007b) identified Tyrannosauroidea indet. and Therizinosauroidea indet. from within this sample. The other known vertebrates from this site are amiid fishes, macrobaenid, lindholmemydid, adocid, and trionychid turtles, and crocodyliforms (Nesov 1997). The adocid turtle from this locality has been recently identified as Adocus bostobensis (Syromyatnikova and Danilov 2009). Martinson (1990b) reported the presence of the brackish water bivalve Sainshandia syrdarjensis from this site and silicified wood with beetle larvae borings, Rhombichnithes boroinakensis, is also known to occur (Nesov 1988c).

A fragment of a possible pterosaur first wing phalanx has also been collected from the middle part of the Bostobe Formation in the northern part of the Buroinak Ridge (Glickman et al. 1987; Nesov 1990; Bakhurina and Unwin 1995; Nesov 1997; Unwin et al. 1997).

Shakh Shakh [=Baibolat, =Zhalmouz] was the first known and now the best sampled vertebrate locality from within the Bostobe Formation. There are two main collecting areas, Shakh Shakh I and II (Rozhdestvensky 1964), separated by about 8 km and located about 70 km north of Dzhusaly railway station (Fig. 1). The locality was discovered by geologists from the Moscow Geological Institute in 1956 (Nikiforova 1960; Rozhdestvensky 1964). In 1957 and 1961 intensive fieldwork was carried out at this locality by teams from the Paleontological Institute of the Russian Academy of Science (Rozhdestvensky 1964, 1968) and then later (1961–1967) prospecting and excavations were made by teams from the Laboratory of Paleobiology of the Kazakh Academy of Sciences (Nurumov 1964; Bazhanov 1972; Nesov and Khisarova 1988). Nesov collected vertebrates at Shakh Shakh in 1980 and 1982. In 1995 and 2002–2007 the locality was sampled by international expeditions (Kordikova et al. 2001; Dyke and Malakhov 2004; Malakhov et al. 2009; Averianov et al. 2014). Additional specimens were also collected at this site in 2012 (Syromyatnikova and Danilov 2013).

The section of the Bostobe Formation at Shakh Shakh is composed of alternating predominantly red clays and sandstones. The main fossiliferous bed is the red clay in the middle of the section (Rozhdestvensky 1964).

The revised vertebrate fauna known from Shakh Shakh includes the euryhaline chondrychthians Polyacrodus cf. brabanticus, Hybodus kansaiensis and Myledaphus glickmani, chondrosteans (Acipenseridae indet.), holosteans (Amiidae indet.), teleosteans (Aspidorhynchiformes indet., Ichthyodectidae indet.), cryptobranchids (Eoscapherpeton sp.), the possible proteid Bishara backa, anurans (Discoglossidae indet.), the macrobaenid Anatolemys maximus, the adocids Shachemys baibolatica, Adocus bostobensis, trionychids (Aspideretoides riabinini and “Trionyx” kansaiensis), the stem testudinoid Lindholmemys gravis, squamates (Scincomorpha indet.), crocodyliforms cf. Kansajsuchus sp. and Eusuchia indet., Ankylosauridae indet., the lambeosaurine Aralosaurus tuberiferus, Sauropoda indet., Ornithomimidae indet., Tyrannosauroidea indet., Therizinosauroidea indet., Caenagnathidae (?) indet., birds and eutherian mammals (Beleutinus orlovi and Zhalmouzia bazhanovi) (Rozhdestvensky 1964; Rozhdestvensky and Khozatsky 1967; Rozhdestvensky 1968, 1970, 1973; Kuznetsov 1976, 1977; Glickman 1980; Suslov 1982; Mertinene and Nesov 1985; Nesov 1986; Kuznetsov and Chkhikvadze 1987; Efimov 1988; Nesov and Khisarova 1988; Nesov 1995; Storrs and Efimov 2000; Kordikova et al. 2001; Dyke and Malakhov 2004; Godefroit et al. 2004; Averianov 2007b; Danilov et al. 2007; Syromyatnikova and Danilov 2009; Vitek and Danilov 2010; Danilov et al. 2011; Averianov and Sues 2012; Skutschas 2013; Syromyatnikova and Danilov 2013; Averianov et al. 2014).

The first pterosaur bones reported from Shakh Shakh were collected by Rozhdestvensky but not recognized as such at the time (Averianov 2004: fig. 8). The first reported pterosaur bone from this locality is a jugal fragment (CCMGE 41/11915) collected by Nesov in 1982 (Nesov 1984: pl. 7, fig. 13, 1990, 1997: pl. 15, fig. 13; Averianov 2004: fig. 7c-e). All identifiable pterosaur specimens from Shakh Shakh likely belong to an azhdarchid which was subsequently described as Aralazhdarcho bostobensis (Averianov 2007a: pl. 9). Described referred specimens include an edentulous jaw fragment (ZIN PH 37/43), an anterior fragment of a mid-cervical vertebra (ZIN PH 9/43), an atlas–axis centrum (ZIN PH 44/43), a posterior dorsal vertebral centrum (ZIN PH 46/43), a distal fragment of a scapula (ZIN PH 45/43), the proximal end of a wing phalanx 2 (ZIN PH 16/43), and a proximal fragment of femur (ZIN PH 43/43). In 2007 and 2012 some additional but poorly preserved pterosaur bones were also collected by our field teams. Of these remains, the best preserved new specimen is a proximal humerus fragment (ZIN PH 57/43) that was collected in 2012 (Fig. 3). The humeral head is incompletely preserved; it is crescentic in proximal view, with broadly concave anterior and pointed convex posterior sides (Fig. 3a). The most striking feature of this specimen is that the humeral head is not saddle-shaped, as in other azhdarchids (Averianov 2010); it is convex in anteroposterior section and almost flat in dorsoventral section as opposed to the concave shape seen in other azhdarchids (and an elevated dorsal ridge might be present on the missing dorsal part of the head) (Fig. 3a). The dorsal side of the proximal humerus extends anteriorly beyond the level of the humeral head but the base of the deltopectoral crest is missing on this specimen. This basal region should be distal to a huge pneumatic foramen on the anterior side (length 10.0 mm, width 5.5 mm; Fig. 3a, c) but only the base of the ulnar crest is preserved and directed ventrally, as in other pterodactyloids. Bennett (1989) considered the ventral (=posterior in non-flight position) orientation of the ulnar crest to be a synapomorphy for Ornithocheiroidea (Pteranodontidae + Ornithocheiridae) but this is based on comparison with the holotype of Bennettazhia oregonensis, where the ulnar crest is actually missing. The anterior side of this bone is deeply concave between the pneumatic foramen and the base of ulnar crest in dorsoventral section and sinusoidal anteroposteriorly. The opposite posterior side is convex in dorsoventral section and concave anteroposteriorly. The humeral neck is inclined posteriorly to the long axis of the shaft at an angle of ~40° while the articular surface of the humeral head overhangs the neck along the posterior side, so it is exposed posteriorly much more than anteriorly (Fig. 3e).

Figure 3. 

Aralazhdarcho bostobensis, ZIN PH 57/43, a proximal fragment of a left humerus in proximal (a), ventral (b), anterior (c), dorsal (d), and posterior (e) views. This specimen is from the Shakh Shakh II locality in the northeasten Aral Sea region of Kazakhstan; Bostobe Formation, Upper Cretaceous (Santonian – lower Campanian). Abbreviations: h, humeral head; pf, pneumatic foramen; uc, ulnar crest. Scale bar is 10 mm.