Vayuraptor nongbualamphuensis, Samathi & Chanthasit & Sander, 2019

Samathi, Adun, Chanthasit, Phornphen & Sander, P. Martin, 2019, Two new basal coelurosaurian theropod dinosaurs from the Lower Cretaceous Sao Khua Formation of Thailand, Acta Palaeontologica Polonica 64 (2), pp. 239-260 : 248-255

Vayuraptor nongbualamphuensis sp. nov.

Figs. 15–17 .

Zoobank LCID: urn:lsid:zoobank.org:act:10988651-4C41-4062-A70F-13BC6DE0D722

Etymology: From Nong Bua Lamphu Province where the specimen was recovered.

Holotype: SM-NB A1-2, left tibia with associated astragalocalcaneum (collected in August 1988 by Paladej Srisuk).

Type locality: Phu Wat Site A1 Locality, Nong Sang, Nong Bua Lamphu Province, Thailand, Fig. 2 .

Type horizon: Sao Khua Formation, probably upper Barremian?, Lower Cretaceous.

Referred material.—PRC-NB A1-11, right coracoids; PRC-NB A1-4, fibula fragment; PRC-NB A1-10 rib; PRC-NB A1-3, probable pubis fragment; PRC-NB A2-20, manual phalanx, and PRC-NB A2-16, probable pedal phalanx; all from the type locality and horizon.

Diagnosis.— Vayuraptor is a basal coelurosaur and is diagnosed by the following autapomorphies: (i) astragalus has two short horizontal grooves and two foramina on the astragalar body, and two fossae at the base of the ascending process; (ii) the ascending process of the astragalus is straight laterally and straight and parallel medially at the base. In the middle of the ascending process, the medial rim slopes to the tip laterally; (iii) there is a vertical ridge starting from the tip and disappearing just above the middle of the ascending process; and (iv) extremely high and narrow ascending process of the astragalus, with a ratio of the ascending process height/ascending process width of 1.66.

Description.— General morphology: Vayuraptor was a mid to large-sized theropod with an estimated body length of 4–4.5 m. The skeletal proportions are shared by other theropods of corresponding sized such as Fukuiraptor .

Rib fragment: A rib fragment (PRC-NB A1-10) that is lacking the proximal and distal portion. There is no pneumaticity on the rib fragment.

Coracoid: The posteroventral process of the coracoid (PRC-NB A1-11) is tapering posteroventrally (the posteroventral process is broken). The ventral margin of the coracoid is expanded beyond the rim of the glenoid facet (inferred from the broken part). The coracoid is higher than long and semicircular in shape. The infraglenoid groove is absent ( Fig. 15 ).

Phalanges: Only the distal part of manual phalanx (PRC-NB A2-20) is preserved. It lacks well-defined extensor pits on the dorsal surface proximal to the distal articulation. This was pointed out to be a coelurosaurian character by Rauhut (2003) (see Novas et al. 2016). A probable pedal phalanx (PRC-NB A2-16) is very incomplete so there is not much information to be obtained from this material.

Pubis fragment: A proximal mid-portion of a left pubis PRC-NB A1-3) preserves a portion of the medial laminar of the pubic shaft. It looks similar to other theropods such as the middle portion of the pubis of Neovenator (see Brusatte et al. 2008).

Tibia and fibula: The left tibia (SM-NB A1-2; Fig. 16 ) is complete. It is long and slender. The cnemial crest is expanded. The morphology of the distal cnemial process is rounded. The anterolateral process of lateral condyle forms a horizontal projection. The tibial shaft is almost straight but the distal portion is slightly curved medially (slightly convex laterally in anterior view). The mid-shaft cross-section is sub-circular with a flattened anterior side (D-shaped cross-section at mid-shaft) as in Australovenator ( Hocknull et al. 2009) and Aerosteon (cast of MCNA-PV-3139; AS personal observations) as well as other coelurosaurs. The cnemial crest is not projected proximally. The lateral condyle is small relative to the tibial shaft and offset from the lateral side of the proximal end of the tibia by a notch (posterior cleft) posteriorly. It does not reach the same level as the medial side posteriorly. The fibular crest (the fibular flange) of the tibia is present on the proximal half as a pronounced longitudinal ridge. The fibular crest is clearly offset from the proximal lateral surface of the tibia. It does not connect with the proximal end of the tibia (the ridge continuing from the fibular flange to the proximal articular surface of the tibia is absent). The ridge emerges 85 mm from the proximal end of the tibia. The fibular crest is sheet-like. The primary nutrient foramen cannot be observed, due to bad preservation.

The lateral malleolus of the distal expansion extends further distally and laterally than the medial malleolus. The lateral malleolus is overlapped by the calcaneum. The shape of the edge of lateral malleolus is a tabular notch. The distal tibia is most probably flat. The medial vertical ridge or medial bulge of the tibia anteriorly for the ascending process of the astragalus is present. This medial vertical ridge is also present in Phuwiangvenator , Australovenator , Chilantaisaurus , Aerosteon ( Benson et al. 2010) , and Juratyrant (Benson 2008; Rauhut 2012; Brussate and Benson 2013). The distal end of the tibia is triangular in outline, flattened anteroposteriorly, and strongly expanded laterally and medially.

The tibial length of Vayuraptor is more than 12 times its anteroposterior width at mid-length. This is a synapomorphy of megaraptorans and coelurosaurs ( Benson et al. 2010) or a synapomorphy of Coelurosauria, including Megaraptora ( Novas et al. 2013; Porfiri et al. 2014). In Vayuraptor this ratio is 13.9. For measurement of the tibiae see SOM: table 17. A fragment of probable fibula (PRC-NB A1-4) is preserved. It is very incomplete and does not offer much information.

Astragalocalcaneum: The left astragalus and calcaneum (SM-NB A1-2) are well preserved, only the tip of the ascending process of the astragalus is missing ( Fig. 17 ). The astragalus is 70 mm wide, the calcaneum is 18 mm wide. The astragalar width/calcaneum width ratio is 3.8. The ascending process of the astragalus is sheet-like, it is 70 mm long, 14% of the total length of the tibia. It is offset from the anterior border of the astragalar body by a shallow groove. Its shape is straight laterally and straight and parallel medially at the base before it slopes to the tip laterally. There is a vertical ridge on the ascending process, from the proximal end to the middle of the process. There are two horizonal grooves and two foramina at the base of the astragalar body. The distal side of the astragalus is strongly concave in anterior view. The trapezoidal outline of the bone in distal view looks similar to that of Australovenator and the megaraptoran astragalus NMV P150070 ( Benson et al. 2012b). It shows an extremely high and narrow ascending process of the astragalus, with a ratio of the ascending process height/ ascending process width of approximately 1.66.

The astragalar body has a concave distal surface. The ascending process of the astragalus of Fukuiraptor is 1.7 times the height of its body ( Benson et al. 2010) which is the same as in Vayuraptor (= 1.7).

The ascending process of the astragalus arises more than half of the breath of the astragalus body, and it is more than twice the height of the astragalus body (7:2.5). The astragalar condyle is significantly expanded proximally on the anterior side of the tibia and faces anterodistally.

The angle of the dorsal margin of the ascending process is almost horizontal. The articulation between the ascending process and the fibula is restricted to the lateral side. The shape of the astragalar ascending process looks similar to that of Australovenator , Fukuiraptor , Aerosteon , Qianzhousaurus ( Lü et al. 2014) , Raptorex ( Sereno et al. 2009) , and Alioramus ( Brusatte et al. 2012) . Two fossae at the base of the ascending process are present. There is an anteroproximal (= proximolateral) expansion of the astragalar lateral condyle, as in Australovenator and Fukuiraptor ( Benson et al. 2010) . The development of the articular surface for the distal end of the fibula is reduced and situated on the lateral side. The posterolateral crest and posteromedial crest are absent. The calcaneum has a well-developed facet for the tibia. Both the astragalus and calcaneum are unfused. The calcaneum transverse development is moderately wide. The width of the calcaneum is approximately 25.7% of the width of the astragalus.

Remarks.— Atlantal intercentrum: The atlantal intercentrum of Phuwiangvenator is high in proportion and looks more similar to that of Allosaurus (UMNH VP 11289; AS personal obsevations) than to Sinraptor ( Currie and Zhao 1993) , Aerosteon (cast of MCNA-PV-3137; AS personal obsevations), and Orkoraptor ( Novas et al. 2008) in which they are low dorsoventrally.

Dorsal vertebra: In general, the dorsal vertebra of Phuwiangvenator looks similar to that of Fukuiraptor ( AS personal observations). Based on the broken bone surface, the dorsal vertebra apparently has a camellate internal structure. There are no pleurocoels, but a lateral depression and striation on the lateral and ventral side of the centrum are present as in Fukuiraptor ( AS personal observations).

Sacral vertebrae: The proportion of the sacral centra of Phuwiangvenator is longer than high, the same as SMNS 58023, a megaraptoran from the Early Cretaceous of Brazil Aranciaga Rolando et al. 2018; AS personal observations), Gualicho ( Apesteguía et al. 2016) , MPMA 08-003-94 ( Mendez et al. 2012; AS personal observations), CPPLIP 1324 Martinelli et al. 2013; AS personal observations), Suchomimus (MNBH GAD 500 and MNBH GAD70; AS personal observations), and Spinosaurus (FSAC-KK 11888; AS personal observations). This proportion is shorter than high in Aoniraptor ( Motta et al. 2016) , Datanglong ( Mo et al. 2014) , and Megaraptor ( Porfiri et al. 2014; Aranciaga Rolando et al. 2018).

The median transverse constriction is not present in Phuwiangvenator, SMNS 58023, and Suchomimus (MNBH GAD 500 and MNBH GAD70). The constriction is present in Datanglong and Siamotyrannus .

Pleurocoels are present in SMNS 58023, Megaraptor , and Aoniraptor , but absent in Phuwiangvenator , Datanglong , and Siamotyrannus .

The flattened ventral surface of the sacrum is present in Phuwiangvenator , Aoniraptor , Falcarius ( Zanno 2010) , MPMA 08-003-94, CPPLIP 1324, and some derived coelurosaurs ( Rauhut 2003), but convex in the SMNS 58203 AS personal observations), Suchomimus MNBH GAD 500 AS personal observations), Datanglong ( Mo et al. 2014) , and Spinosaurus .

The camellate internal structure is present in SMNS 58023, Megaraptor , Aoniraptor , and Phuwiangvenator . Generally, the vertebral pneumaticity in basal theropods is camerate, where as in ceratosaurs, carcharodontosaurs, and many coelurosaurs, a camellate internal structure is present Benson et al. 2012a).

The sacral centra are ventrally less concave (in lateral view) in Phuwiangvenator , Megaraptor , Aoniraptor , and Datanglong , whereas they are concave in SMNS 58023, Suchomimus (MNBH GAD 500 and MNBH GAD70), and Spinosaurus (FSAC-KK 11888).

We note that the ventral groove on the sacral centra is present in some theropods such as Falcarius ( Zanno 2010; AS personal observations), Neovenator (Brusatte et al. 2008) , and Condorraptor (Rauhut 2005) , but there is usually one longitudinal groove instead of two sulci which is longer and wider than in Phuwiangvenator (see SOM: fig. 1).

Metacarpal: An elongate metacarpal is a coelurosaurian synapomorphy ( Novas et al. 2013) which is present in Phuwiangvenator . The metacarpal II of Phuwiangvenator looks similar to that of Kileskus and Falcarius , e.g., the shaft is straight, slender, and dorsoventrally flattened. The shaft of metacarpal II is slender in Phuwiangvenator , Megaraptor , Australovenator , Tanycolagreus , Coelurus , Gualicho , Kileskus , Guanlong , and Yutyrannus ( Carpenter et al. 2005a, b; Xu et al. 2006, 2012; Averianov et al. 2010; Apesteguía et al. 2016; Novas et al. 2016), however, it differs from that of Megaraptor in which it is more slender and straight than in Megaraptor ( Calvo et al. 2004; Novas et al. 2016). The distal end of metacarpal II is asymmetrical and divided into two condyles in Phuwiangvenator as well as in other theropods. The distal surface of the medial condyle is larger than the lateral condyle in Phuwiangvenator , Australovenator , Gualicho , and Kileskus . The medial condyle protrudes slightly more distally than the lateral condyle in Phuwiangvenator , Coelurus , and Kileskus . The pits for the collateral ligaments are not well developed on both condyles in Phuwiangvenator . There is no distinct extensor pit on the anterior surface of the shaft proximal to the distal condyle, only a small concavity is present in Phuwiangvenator and Kileskus . The shaft is straight (in dorsal view) in Phuwiangvenator , Australovenator , Tanycolagreus , Coelurus , Gualicho , Kileskus , and Guanlong .

Manual phalanges: Manual phalanx I-1 of Phuwiangvenator is concave ventrally in proximal view. This character is present in Australovenator , Megaraptor, NMV P 199050 ( Benson et al. 2012b), Suchomimus (MNBH GAD 500; AS personal observations), Kileskus ( Averianov et al. 2010) , Falcarius ( Zanno 2006) , and Deinocheirus ( Osmólska and Roniewicz 1970) .

A deep and wide furrow along the ventral surface of the manual phalanx I-1 is present in Megaraptor and Australovenator ( Novas et al. 2016) . A longitudinal ventral furrow and longitudinal ridges are present in Phuwiangvenator . This furrow is also present in Suchomimus and Spinosaurus , but it is restricted to the proximal part. However, the manual phalanx I-1 of Phuwiangvenator exhibits a triangular contour at the proximal end, not a squareshaped contour as present in the megaraptorids Megaraptor and Australovenator (see Novas et al. 2016).

Manual unguals: The manual ungual I-2 of Phuwiangvenator is strongly transversely compressed, being oval with a distinct dorsoventral axis in proximal view (see Novas 1998; Porfiri et al. 2014). This character is also found in Fukuiraptor , Megaraptor , Australovenator , and Chilantaisaurus . However, the manual ungual I-2 of Phuwiangvenator , in relation to its phalanx, is proportionally smaller than in Megaraptor and Australovenator ( Calvo et al. 2004; White et al. 2012; Novas et al. 2016). The manual ungual I-2 of Phuwiangvenator has a curved flexor tubercle which is found in Fukuiraptor (FPDM-V43-11; AS personal observations) and Chilantaisaurus ( Benson and Xu 2008) , but this character is widely present among Ornithodira. The ratio of the proximal height/width of the manual ungual I-2 of Phuwiangvenator is 2.4, compared with 1.95 in Torvosaurus ( Benson et al. 2010) , 1.78 in Suchomimus (MNBH GAD 500; AS personal observations), 1.9 in Baryonyx (cast of BMNH R9951; AS personal observations), 1.9in Allosaurus (UMNH VP5676; AS personal observations), 2.7 in Chilantaisaurus ( Benson and Xu 2008) , 2.7 in Fukuiraptor (FPDM-V43-11; AS personal observations), 2.4 in Australovenator ( Benson et al. 2010) , and 2.75 in Megaraptor ( Benson et al. 2010) . The manual ungual III-4 of Phuwiangvenator is small and much smaller than the manual unguals I-2 and II-3 as in other theropods. We note that the character of the manual ungual I-2 with an asymmetrical lateral groove and well-developed ventral ridge of Megaraptor and Australovenator ( White et al. 2012; Novas et al. 2016) is not present in Phuwiangvenator and Fukuiraptor (FPDM-V43-11; AS personal observations).

Tibia: In proximal view, the lateral condyle of the tibia is level with the posterior margin of the medial condyle. This character is found in Phuwiangvenator , Vayuraptor , Australovenator ( White et al. 2013a) , Fukuiraptor ( AS personal observations), Orkoraptor ( Novas et al. 2008) , Neovenator (Brusatte et al. 2008) , Tyrannosaurus ( Brochu 2003) , Falcarius ( AS personal observations), Gualicho (Apestiguea et al. 2016) , and Murusraptor ( Coria and Currie 2016) , but not in Suchomimus (MNBH GAD 500, MNBH GAD 98, and MNBH GAD 72). In Torvosaurus ( Britt 1991) , Piatznitskysaurus, and Spinosaurus this character is independently evolved.

The character: “tibial lateral condyle of proximal end curves ventrally as a pointed process”; this character is present in Phuwiangvenator, Megaraptora , some coelurosaurs, and Neovenator , but not in Fukuiraptor and Vayuraptor .

The median prominence in the anterior surface of the distal end of the tibia(tibial vertical medial ridge or medial bulge) is present in Phuwiangvenator , Vayuraptor , Australovenator ( White et al. 2013a) , Suchomimus (MNBH GAD 500; MNBH GAD 97; and MNBH GAD 72; AS personal observations), Coelurus ( Carpenter et al. 2005b) , Chilantaisaurus ( Benson and Xu 2008) , Falcarius ( Zanno 2010; AS personal observations), Spinosaurus (cast of FSAC-KK 11888; AS personal observations), Chuandongocoelurus ( Rauhut 2012) , Juratyrant (Benson 2008; Rauhut 2012; Brussate and Benson 2013). Masiakasaurus ( Carrano et al. 2002) , theropod indet. MB.R.2351 ( AS personal observations), the abelisauroid MB.R.1750 ( AS personal observations), the abelisauroid MB.R.1751 ( AS personal observations), Aniksosaurus ( Martinez and Novas 2006) , possibly Bicentenaria ( Novas et al. 2012b) , Aerosteon , Stokesosaurus ( Rauhut 2012) , Ozraptor ( Long and Molnar 1998) , Tanycolagreus ( Carpenter et al. 2005a) , Segnosaurus ( Zanno 2010) , Erliansaurus ( Xu et al. 2002) , possibly NMV P150070 ( Benson et al. 2012b), and possibly Fukuiraptor ( AS personal observations). The posteroventral ridge of the tibia is present in Vayuraptor , Australovenator , and Tachiraptor ( Langer et al. 2014) . The tibia facet for the reception of the ascending process of the astragalus at the distal end which is flat anteriorly is an apomorphy shared by megaraptorans and coelurosaurians ( Porfiri et al. 2014).

The character:“tibia anteriorly flat at mid-length with vertical ridges anterolaterally and anteromedially” can be found in Phuwiangvenator , Vayuraptor , Neovenator (Brusatte et al. 2008) , Australovenator ( White et al. 2013a) , and Aerosteron (cast of MCNA-PV-3139; AS personal observations).

The character: “tibia anteriorly flat or slightly flat but no such vertical ridges” is present in Spinosaurus (cast of FSAC-KK11888;ASpersonalobservations), Chilantaisaurus ( Benson and Xu 2008) , a sinraptorid tibia from Thailand (SM 10; AS personal observations), Murusraptor ( Coria and Currie 2016) , and Acrocanthosaurus ( Stovall and Langston 1950; see SOM: table 18).

The character: “tibia anteriorly convex or slightly convex but ridge present” can be found in Allosaurus (UMNH VP 6402, 7145, 7926, 7936, 7939) and Fukuiraptor (FPDMV43-20).

The tibia is long and slender in the Thai theropods. The length/width ratio is more than 12 in Phuwiangvenator (13.82), Vayuraptor (13.9), Australovenator (12.53), Fukuiraptor (approximately 14.3–14.5), Aerosteon referred material (14), and Spinosaurus neotype (12.09) ( Ibrahim et al. 2014) compared with Murusraptor (11.9), the Suchomimus holotype (MNBH GAD 500, 9.6), Suchomimus “subadult” (MNBH GAD97, 10.86), and Suchomimus “juvenile” (MNBH GAD72, 11.67) (see SOM: table 17).

Astragalus: The ascending process height of astragalus being more than 0.5 times the width of the astragalar body can be found in Vayuraptor , Fukuiraptor , Australovenator , possibly in Phuwiangvenator , and all other coelurosaurs. The transverse width of the ascending process of astragalus occupies the total width of the anterior surface of distal tibia (coelurosaurian character), distinct anterior development of the lateral condyle of the astragalar body and a strong inflection in the anterior margin of the astragalar body in distal view ( Novas et al. 2013) (coelurosaurian characters) are present in Phuwiangvenator , Vayuraptor , Australovenator , Aerosteon , and other coelurosaurs. The presence of an astragalus with a prominent proximolateral extension is a megaraptoran synapomorphy ( Novas et al. 2013). This latter feature is observed in Vayuraptor and possibly Phuwiangvenator (in the latter it is small and damaged). Transverse development of the calcaneum which is moderately wide (plesiomorphic character) is present in Phuwiangvenator and Vayuraptor . The shape of the calcaneum in lateral or medial view is strongly asymmetric, with a right angle at the posterior border ( Novas et al. 2013) coelurosaurian character). This character possibly unites the Megaraptora within Coelurosauria.

The character: “ascending process of the astragalus which is offset from distal condyles by a pronounced groove (possible coelurosaurian character)” is present in Vayuraptor and Phuwiangvenator .

The ratio of the ascending process height/astragalar body height is high in Vayuraptor (1.7), Fukuiraptor (1.7), Aerosteron (1.9), Alioramus (2.5), and Phuwiangvenator estimated 1.73). This ratio is lower in NMV P150070 (1.43), Australovenator (1.4), Falcarius (1.3), Suchomimus (MNBH GAD97, 1.3; MNBH GAD98, 1.25), compared with Allosaurus (1.14) which has the much lower ratio (see SOM: table 19). This ratio is also low in Coelurus , Bicentenaria , and Tugulusaurus .

The ascending process of astragalus arises from the lateral side of astragalar body (not from its complete width) in Phuwiangvenator , Vayuraptor , Australovenator , Fukuiraptor, Tugurusaurus , Bicentenaria , and Coelurus . It arises from the complete width of the astragalar body in Tanycolagreus and Aerosteon . The ratio of the ascending process width at base/astragalar body width is low and the ascending process is restricted to the lateral side of the astragalar body in basal tetanurans (e.g., Novas et al. 2013) and some basal coelurosaurs. This ratio is 50% in Allosaurus , Bicentenaria ( Novas et al. 2012b) , Tugulusaurus ( Rauhut and Xu 2005) , and Coelurus ( Carpenter et al. 2005b) , 55% in NMV P150070, 56% in Suchomimus (MNBH GAD97), 63% in Vayuraptor , unknown in Fukuiraptor , 65% in Phuwiangvenator , 66% in Falcarius , 70% in Australovenator , 78% in Alioramus , and 83% in Aerosteon (see SOM: table 19).

The ratio of the astragalar ascending process height/ascending process width at base is high in Vayuraptor (approximately 1.66), compared with Alioramus (1.4), Phuwiangvenator (estimated 1.39), NMV P150070 (1.3), Fukuiraptor 1.1), Falcarius (1.1), Australovenator (1), Aerosteon (1), Allosaurus (UMNH VP11003, 1), and Suchomimus (MNBH GAD97, 0.88; MNBH GAD98, 0.8).

An anterior development of the lateral condyle of the astragalus in distal view is present in Phuwiangvenator , Vayuraptor , Australovenator , Aerosteon , probable Fukuiraptor, NMV P 150070, Appalachiosaurus ( Carr et al. 2005) , Bicentenaria ( Novas et al. 2012b) , Coelurus , Tugulusaurus , and Alioramus . The accessory posterolateral ascending process of the astragalus is present in Fukuiraptor and NMV P150070 (see Agnolin et al. 2010; see SOM: fig. 2). The prominent proximolateral extension of the astragalus ( Benson et al. 2010; Carrano et al. 2012; Porfiri et al. 2014) that projects from the anterior articular facet as a rounded triangular process is present in Australovenator , Aerosteon , Fukuiraptor (small process), Phuwiangvenator small process), and Vayuraptor . This process forms the anterior border of the fibular facet of the astragalus and the fibular facet is shallow and bordered posteriorly by the lateral margin of the ascending process ( Hocknull et al.

2009). In Fukuiraptor , the astragalus has a shallow notch for a process from the calcaneum but it is not well developed ( Azuma and Currie 2000; AS personal observations). The astragalar notch for a process from the calcaneum is present in Aerosteon , Phuwiangvenator , but not Vayuraptor . The astragalus has a distinct socket that embraced the mediodistal end of the fibula (Azuma and Corrie 2000; AS personal observations), this present in Fukuiraptor , Phuwiangvenator , and Vayuraptor . The fibular contact extending up the anterolateral margin of the ascending process of the astragalus is present in Fukuiraptor ( Azuma and Currie 2000; AS personal observations), Vayuraptor , and possibly Phuwiangvenator .

The long and sheet-liked ascending process of the astragalus with a slope or convex medially and straight laterally can be found in Vayuraptor , Australovenator , Fukuiraptor , Qianzhousaurus ( Lü et al. 2014) , Raptorex ( Sereno et al. 2009) , and Appalachiosaurus ( Carr et al. 2005) . However, the shape of the ascending process of Vayuraptor is different from the other theropods mentioned above. The ascending process with vertical ridge proximally which ends in the middle is present in Vayuraptor and Qianzhousaurus ( Lü et al. 2014) . Two fossae at the base of the ascending process of the astragalus can be found in Vayuraptor and Appalachiosaurus ( Carr et al. 2005) . One fossa is present in Qianzhousaurus , Alioramus , Raptorex , and other tyrannosauroids and ornithomimosaurs (e.g., White et al. 2013a; Lü et al. 2014; Sereno et al. 2009; Brusatte et al. 2012; Choiniere et al. 2012), whereas there is no fossa in Coelurus, Tugurusaurus , and Bicentenaria . There is a cranio-proximal process at the base of the astragalus in Vayuraptor , Australovenator , Aerosteon , and Coelurus , small in Fukuiraptor and Phuwiangvenator .

Calcaneum: In Phuwiangvenator , the facet for the fibula of the calcaneum is small and smaller than in the allosauroid Allosaurus (UMNH VP 9965). The area for astragalocalcaneum attachment in Allosaurus is small and restricted to the anteroventral part, clearly different from Phuwiangvenator . The calcaneum of Phuwiangvenator is wider anteroposteriorly than high dorsoventrally. This is in contrast to the tyrannosauroid Appalachiosaurus ( Carr et al. 2005) . The facet for the fibula of the calcaneum is larger and not restricted to the dorsal part as in Appalachiosaurus . In Phuwiangvenator and Vayuraptor , the calcaneum is thick and differed from Falcarius (UMNH VP 12365), which has a disk-like calcaneum.

The calcaneum of Phuwiangvenator looks more similar to that of Murusraptor than to Baryonyx and Allosaurus in the shape and ratio of the fibular facet of the calcaneum. In Baryonyx and Allosaurus , there are large fibular facets dorsal to the calcaneum, the tibia facets is situated on the medial side. In Phuwiangvenator and Murusraptor , lateral view, the fibular facet is almost the same size as the tibia facet, and the tibia facet is situated on the mediodorsal side of the calcaneum. In the evolution from basal theropods to moderately derived coelurosaurs, there is a trend of enlargement of the tibial facet of the calcaneum and a concurrent reduction of the fibular facet. As a result, the tibial facet is much larger than the fibular facet in moderately derived coelurosaurs. The calcaneum is relatively wide transversely in Phuwiangvenator , Vayuraptor , Murusraptor , Aerosteon , and Tugulusaurus . It is strongly compressed in Tanycolagreus , Alioramus , and derived coelurosaurs. The calcaneum is roughly symmetrical with a wide angle on the posterior border in Murusraptor and Aerosteon . It is asymmetrical with a right angle on the posterior border in Phuwiangvenator , Vayuraptor , and Tanycolagreus ( Novas et al. 2013) . The ratio of the width of the calcaneum/the width of the astragalus is 25.7% in Vayuraptor , 24% (left) and 23% (right) in Phuwiangvenator , and whereas the ratio of the width of the calcaneum/astragalus is less than 20% in coelurosaurs ( Rauhut and Pol 2017).

Metatarsals: In proximal view, the lateral margin of metatarsal II is straight in Australovenator , Fukuiraptor ( White et al. 2013a) , and Tanycolagreus ( Carpenter et al. 2005a) , but the lateral margin is convex or slightly convex in Phuwiangvenator , Ornitholestes , and Allosaurus .

In proximal view, the metatarsal III is slightly concave medially in Phuwiangvenator , Torvosaurus , Ornitholestes , and possibly Fukuiraptor . It is straight in Australovenator , Afrovenator , possibly Neovenator , Tanycolagreus , Mapusaurus , and almost straight in Zuolong and Allosaurus (UMNH VP 16038). It is concave in Chilantaisaurus and Sinraptor .

In the proximal view, the shape of the medial margin of metatarsal IV is sigmoidal in Phuwiangvenator , Mapusaurus , Chilantaisaurus , Allosaurus , and Tanycolagreus . It is steplike in Australovenator , Megaraptor , Ornitholestes , and Coelurus , whereas there is a convex medial margin in Zuolong . The shape of the posterolateral margin of metatarsal IV is slightly concave in Phuwiangvenator , Australovenator , and Zuolong , whereas it is almost straight in Megaraptor , Mapusaurus , Chilantaisaurus , and Ornitholestes .

In Phuwiangvenator , metatarsal III is anteriorposteriorly oriented in proximal view, which is similar to Australovenator ( White et al. 2013a) , Chilantaisaurus ( Benson and Xu 2008) , Neovenator (Brusatte et al. 2008) , Falcarius ( Zanno 2010) , Garudimimus ( Kobayashi and Barsbold 2005) , and Acrocanthosaurus ( Stovall and Langston 1950; Currie and Carpenter 2000), but differs from Suchomimus (MNBH GAD70; AS personal observations), Sinraptor (cast of holotype in FPDM; AS personal observations), Tanycolagreus ( Carpenter et al. 2005a) , Allosaurus (UMNH VP 9892, 16038, 9877; AS personal observations), Majungasaurus ( Carrano 2007) , Afrovenator ( Sereno et al. 1994) , and Dilophosaurus ( Welles 1984) in which the metatarsal III is anterolaterally-posteromedially oriented in proximal view.

In Phuwiangvenator , the low anterior rim of the metatarsal IV, which is its autapomorphy, is independently present in Pandoravenator (a basal tetanuran from the Late Jurassic of Argentina, Rauhut and Pol 2017), but in Pandoravenator the anterior rim of the metatarsal IV, which

A

B

is much lower than metatarsal III, does not slope proximolaterally to distomedially.

Pedal and ungual phalanges: The pedal phalanges of Phuwiangvenator are clearly different from Suchomimus (MNBH GAD70) and Spinosaurus (FSAC-KK 11888) because in spinosaurids, their pedal phalanges are strongly dorsoventrally flattened. Ventrally flattened unguals are present in Phuwiangvenator , Australovenator , Spinosaurus , and ornithomimosaurs. However, the unguals of Spinosaurus are extremely dorsoventrally flattened and less curved than in other theropods (FSAC-KK 11888, MSNM V6897; see Maganuco and Dal Sasso 2018).

Figures

Fig. 15. Coelurosaurian theropod Vayuraptor nongbualamphuensis gen. et sp. nov. from the Early Cretaceous Sao Khua Formation of Phu Wat, Nong Bua Lamphu Province, Thailand. PRC-NB A1-11, right coracoid in lateral (A1) and medial (A2) views. Dashed lines are the reconstruction of the posteroventral process of the coracoid.

Fig. 16. Coelurosaurian theropod Vayuraptor nongbualamphuensis gen. et sp. nov. from the Early Cretaceous Sao Khua Formation of Phu Wat, Nong Bua Lamphu Province, Thailand. SM-NB A1-2, left tibia with associated astragalocalcaneum in anterior (A1), lateral (A2), posterior (A3), medial (A4), proximal (A5), and distal (A6) view. Arrow indicates vertical ridge on the tibia.

Fig. 17. Coelurosaurian theropod Vayuraptor nongbualamphuensis gen. et sp. nov. from the Early Cretaceous Sao Khua Formation of Phu Wat, Nong Bua Lamphu Province, Thailand. SM-NB A1-2, left astragalocalcaneum in anterior (A2), medial (A3), lateral (A4), and distal (A5) views; line drawing in anterior view (A1).

Fig. 2. Map of Thailand (A) and close-up of northeastern Thailand (B) showing the location of Phu Wiang locality, Khon Kaen Province (square) and Phu Wat locality, Nong Bua Lamphu Province (star). Dark gray, Sao Khua Formation outcrops, light gey, Phu Kradung and Khok Kruat formations.