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| ภูเวียงเวเนเตอร์ แย้มนิยมมี Phuwiangvenator yaemniyomi
วายุแรปเตอร์ หนองบัวลำภูเอนซิส Vayuraptor nongbualamphuensis
Samathi, Chanthasit & Sander, 2019
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Megaraptora is a clade of mid to large-sized theropods that are long-snouted, large-clawed, highly pneumatized, and have long and gracile metatarsals. The basal member was reported from the Barremian of Japan. A more derived clade, the Megaraptoridae, is known from the Cenomanian to Santonian of Gondwana. Here two new basal coelurosaurs from the Lower Cretaceous Sao Khua Formation of Thailand are described and named as Phuwiangvenator yaemniyomi gen. et sp. nov. and Vayuraptor nongbualamphuensis gen. et sp. nov. Phuwiangvenator is a megaraptoran coelurosaur and diagnosed by the ventrally flat sacral vertebrae with sulci in the anterior and posterior region of the centra and the anterior rim of metatarsal IV sloping proximolaterally to distomedially and being much lower than that of metatarsal III anteriorly. Vayuraptor is a basal coelurosaur and diagnosed by its astragalus which has two horizontal grooves, two fossae at the base of the ascending process, the ascending process being straight laterally and straight and parallel medially with the medial rim sloping to the tip laterally, and a long and slender astragalar ascending process. Although the position of the basal coelurosaur Vayuraptor remains unclear and must await further discovery, megaraptoran affinities are likely. The Early Cretaceous megaraptoran fossil record has been recovered from the Barremian to Aptian of Asia. All Asian megaraptorans might be a monophyletic clade or a paraphyletic series relative to the Megaraptoridae. Several specimens have been reported from the Aptian to mid-Cretaceous of Australia, and one report from the Albian of South America. These fossils show a high diversity of the Early Cretaceous megaraptorans and a wide distribution during that time. The clade then became more provincial in the Late Cretaceous.
Key words: Dinosauria, Theropoda, Coelurosauria, Megaraptora, Phuwiangvenator, Vayuraptor, Cretaceous, Thailand.
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| Map of Thailand (A) and close-up of northeastern Thailand (B) showing the location of [Phuwiangvenator yaemniyomi] Phu Wiang locality, Khon Kaen Province (square) and [Vayuraptor nongbualamphuensis] Phu Wat locality, Nong Bua Lamphu Province (star). |
Systematic palaeontology
Dinosauria Owen, 1842
Theropoda Marsh, 1881
Tetanurae Gauthier, 1986
Coelurosauria von Huene, 1920
Megaraptora Benson, Carrano, and Brusatte, 2010
Genus Phuwiangvenator nov.
Phuwiangvenator yaemniyomi gen. et sp. nov.
ภูเวียงเวเนเตอร์ แย้มนิยมมี
Etymology: Phu Wiang Mountain, Khon Kaen Province, Thailand, the place where the holotype was found, combined with Latin venator, hunter; thus “Hunter of Phu Wiang”.; and in honor of Sudham Yaemniyom, former geologist of the Department of Mineral Resources, Bangkok, who found the first dinosaur bone of Thailand in 1976 at Phu Wiang Mountain.
Diagnosis.— Phuwiangvenator is a megaraptoran diagnosed by the following autapomorphies: (i) short sulci on the sacral vertebrae ventrally along the anterior and posterior part of the centrum; (ii) the anterior rim of metatarsal IV slopes from proximolaterally to distomedially. This way, the distomedial corner of the proximal articular surface of metatarsal IV in anterior view is much lower than the articular surface of metatarsal III. In addition, the distomedial corner is lower than in any other known theropod.
Genus Vayuraptor nov.
Vayuraptor nongbualamphuensis gen. et sp. nov.
วายุแรปเตอร์ หนองบัวลำภูเอนซิส
Etymology: From Sanskrit Vayu, God of Wind and Latin raptor, thief; “Raptor of Wind or Wind raptor” in reference to its long and slender tibia, which suggest a fast running animal.; From Nong Bua Lamphu Province where the specimen was recovered.
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.
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Phuwiangvenator vs. Siamotyrannus: why are they not the same taxon?—
In Phuwiangvenator, the dorsal vertebrae are longer than high, contrary to the dorsal vertebrae of Siamotyrannus which higher than long. The sacral vertebrae of Phuwiangvenator are also longer than high. Their centra are ventrally flattened and not constricted in ventral view. There is no median transverse constriction on the sacrum, in contrast to Siamotyrannus, where the sacral vertebrae are higher than long. The centra of this taxon are ventrally convex and also have a median transverse constriction. The ventral rims of the sacral centra of Siamotyrannus are much more convex in lateral view than those of Phuwiangvenator. Phuwiangvenator also differs from Siamotyrannus in being a smaller animal.
Vayuraptor vs. Phuwiangvenator: why are they not the same taxon?—
These two new theropods belong to the basal Coelurosauria, based on their morphologies as described above. Because the fossils were recovered from the same rock formation within approximately 40 km of each other, careful comparison is needed to determine whether they belong to the same taxon or not. The overlapping materials of these two theropods are the tibia and astragalocalcaneum. Phuwiangvenator is larger than Vayuraptor (tibial length 615 vs. 515 mm, respectively). Although the cranioproximal process of the astragalus is present in Vayuraptor and Phuwiangvenator, it is more prominent in Vayuraptor than in Phuwiangvenator. Two short horizontal grooves on the astragalar body are present in Vayuraptor, whereas only one horizontal groove is present in Phuwiangvenator. There are two fossae at the base of the ascending process of the astragalus in Vayuraptor whereas there is only one fossa in Phuwiangvenator. The calcaneum of Vayuraptor is narrower mediolaterally proximally than that of Phuwiangvenator in anterior view. A shallow notch of the astragalus for the calcaneum process is present in Phuwiangvenator. This notch is not present in Vayuraptor. The character “tibia anterolateral process of the lateral condyle curves as a pointed process” is present in Phuwiangvenator, not in Vayuraptor. This character has been compared with various ontogenetic stages of Allosaurus (UMNH VP 7148, 7922, 7932, 7938, 7939, 7940), and this process was found in all observed specimens (AS personal observations), so we conclude that the differences between Phuwiangvenator and Vayuraptor are not due to ontogeny. The shape of the fibular crest is different as well (e.g., the fibular crest is expanded proximolaterally in Phuwiangvenator vs. being expanded distolaterally in Vayuraptor). The shape of the proximal end of the tibia is different, the proximal articular surface of the medial condyle being more convex in Phuwiangvenator than Vayuraptor.
Vayuraptor vs. Siamotyrannus: why are they not the same taxon?—
Vayuraptor and Siamotyrannus are represented by skeletally mature animals based on the fusion of their bones (e.g., astragalocalcaneum in Vayuraptor, and pelvis, dorsal and caudal vertebrae in Siamotyrannus). There is no overlapping material, so anatomical comparison is impossible. Vayuraptor is found here to be a basal coelurosaur. Siamotyrannus is an avetheropod, possibly a basal coelurosaur (Samathi 2013; Samathi and Chanthasit 2017; present work) or basal allosauroid (e.g., Rauhut 2003; Carrano et al. 2012). Vayuraptor differs from Siamotyrannus in being a much smaller animal. Vayuraptor is approximately 4–4.5 m in length (similar to Fukuiraptor), whereas Siamotyrannus is approximately 6.5–7 m in length (Buffetaut et al. 1996). Based on the above information, it is reasonable to conclude that Vayuraptor represents a different taxon from Siamotyrannus.
Conclusions:
The present study describes the anatomy of the two new basal coelurosaurs from Southeast Asia in detail. One of them, Phuwiangvenator, is here referred to the Megaraptora. These findings extend the diversity of basal megaraptorans and support the origin of Megaraptora in Asia. The Asian megaraptorans might be a monophyletic clade or a paraphyletic series relative to the Megaraptoridae. Recently, Early Cretaceous fossils of megaraptorans have been recovered from the Barremian to Aptian of Asia. Several materials have been reported from the Aptian to mid-Cretaceous of Australia, whereas there is only one report from the Albian of South America. These show a high diversity and wide distribution during the Early Cretaceous which became more provincial in the Late Cretaceous. However, the phylogenetic position of the basal coelurosaur Vayuraptor must await further discovery of additional material and remains open to future analyses.
Adun Samathi, Phornphen Chanthasit and P. Martin Sander. 2019. Two New Basal Coelurosaurian Theropod Dinosaurs from the Lower Cretaceous Sao Khua Formation of Thailand. Acta Palaeontologica Polonica. in press. DOI: 10.4202/app.00540.2018
Thai dinosaur is a cousin of T. rex phys.org/news/2019-05-thai-dinosaur-cousin-rex.html via @physorg_com
Mega-raptors were top predators in Thailand 100 million years ago | PLOS Paleo Community blogs.plos.org/paleocomm/2019/05/28/mega-raptors-were-top-predators-in-thailand-100-million-years-ago/
