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| Natovenator polydontus Lee, Lee, Currie, Sissons, Park, Kim, Barsbold & Tsogtbaatar, 2022 (Artwork by Yusik Choi). |
Abstract
Streamlining a body is a major adaptation for aquatic animals to move efficiently in the water. Whereas diving birds are well known to have streamlined bodies, such body shapes have not been documented in non-avian dinosaurs. It is primarily because most known non-avian theropods are terrestrial, barring a few exceptions. However, clear evidence of streamlined bodies is absent even in the purported semiaquatic groups. Here we report a new theropod, Natovenator polydontus gen. et sp. nov., from the Upper Cretaceous of Mongolia. The new specimen includes a well-preserved skeleton with several articulated dorsal ribs that are posterolaterally oriented to streamline the body as in diving birds. Additionally, the widely arched proximal rib shafts reflect a dorsoventrally compressed ribcage like aquatic reptiles. Its body shape suggests that Natovenator was a potentially capable swimming predator, and the streamlined body evolved independently in separate lineages of theropod dinosaurs.
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| Skull of Natovenator polydontus (MPC-D 102/114, holotype). |
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| Body plan of Natovenator polydontus (MPC-D 102/114, holotype) and dorsal rib morphology of various diving birds and terrestrial taxa. |
Dinosauria Owen, 1842
Theropoda Marsh, 1881
Dromaeosauridae Matthew and Brown, 1922
Halszkaraptorinae Cau et al., 2017
Natovenator polydontus gen. et sp. nov.
Holotype: MPC-D 102/114 (Institute of Paleontology, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia) is a mostly articulated skeleton with a nearly complete skull (See Supplementary Table 1 for measurements).
Locality and horizon: Baruungoyot Formation (Upper Cretaceous), Hermiin Tsav, Omnogovi Province, Mongolia.
Diagnosis: A small halszkaraptorine dromaeosaurid with the following autapomorphies: wide groove delimited by a pair of ridges on the anterodorsal surface of the premaxilla, premaxilla with an elongated internarial process that overlies nasal and extends posterior to the external naris, 13 premaxillary teeth with large and incisiviform crowns, first three anteriormost maxillary teeth are greatly reduced and are clustered together with the following tooth without any separations by interdental septa, anteroposteriorly long external naris (about 30% of the preorbital skull length), paroccipital process with a anteroposteriorly broad dorsal surface, elongate maxillary process of the palatine that extends anteriorly beyond the middle of the antorbital fenestra, pterygoid with a deep fossa on the medial surface of the quadrate ramus, distinct posterolaterally oriented projection on the lateral surface of atlas, absence of pleurocoels in cervical vertebrae (not confirmed in the missing fifth cervical centrum), posterolaterally oriented and nearly horizontal proximal shafts in the dorsal ribs, hourglass-shaped metacarpal II with distinctly concave medial and lateral surfaces.
Etymology: Natovenator, from the Latin nato (swim) and venator (hunter), in reference to the hypothesized swimming behaviour and piscivorous diet of the new taxon; polydontus, from the Greek polys (many) and odous (tooth) in reference to the unusually many teeth.
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| Life reconstruction of Natovenator polydontus (Artwork by Yusik Choi). |
Sungjin Lee, Yuong-Nam Lee, Philip J. Currie, Robin Sissons, Jin-Young Park, Su-Hwan Kim, Rinchen Barsbold and Khishigjav Tsogtbaatar. 2022. A Non-avian Dinosaur with A Streamlined Body exhibits Potential Adaptations for Swimming. Communications Biology. 5, 1185. DOI: 10.1038/s42003-022-04119-9
