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| Hanyusuchus sinensis Iijima, Qiao, Lin, Peng, Yoneda & Liu, 2022 life restoration by Hikaru Amemiya twitter.com/WANIwaniamemi |
Abstract
A solid phylogenetic framework is the basis of biological studies, yet higher level relationships are still unresolved in some major vertebrate lineages. One such group is Crocodylia, where the branching pattern of three major families (Alligatoridae, Crocodylidae and Gavialidae) has been disputed over decades due to the uncertain relationship of two slender-snouted lineages, gavialines and tomistomines. Here, we report a bizarre crocodylian from the Bronze Age of China, which shows a mosaic of gavialine and tomistomine features across the skeleton, rendering support to their sister taxon relationship as molecular works have consistently postulated. Gavialine characters of the new Chinese crocodylian include a novel configuration of the pterygoid bulla, a vocal structure known in mature male Indian gharials. Extinct gavialines have repeatedly evolved potentially male-only acoustic apparatus of various shapes, illuminating the deep history of sexual selection on acoustic signalling in a slender-snouted group of crocodylians. Lastly, a cutmark analysis combined with accelerator mass spectrometry (AMS) radiocarbon dating of bone remains demonstrated that two individuals from Shang and Zhou dynasties in Guangdong, China, suffered head injuries and decapitation. Archaeological evidence together with historical accounts suggests the human-induced extinction of this unique crocodylian only a few hundred years ago.
Keywords: crocodylia, phylogeny, Holocene, extinction, sexual selection, acoustics
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| Life restoration of Hanyusuchus sinensis, gen. et sp. nov. from the Bronze Age of southern China (illustration: Hikaru Amemiya). |
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| Anatomy of Hanyusuchus sinensis, gen. et sp. nov. from the Bronze Age of southern China. (a–d) Holotype skull (XM 12-1558) in dorsal (a,b) and ventral (c,d) views. (e) Posterior skull of a paratype (XM 12-1557) in ventral view. (f) Three-dimensional reconstruction of the boxed part in (e), highlighting the pterygoid bulla (purple volume). (g) Three-dimensional reconstruction of the pterygoid bullae and nasopharyngeal duct (purple volume) in Gavialis gangeticus (UF 118998). (h–k) Holotype mandible (XM 12-1558) in dorsal (h,i) and left lateral (j,k) views. (l–n) Left femur of the holotype (XM 12-1558) in lateral (l), proximal (m) and distal (n) views. (o,p) Axis of a paratype (SM E1623) in left lateral (o) and ventral (p) views. (q,r) Third cervical vertebra of the holotype (XM 12-1558) in left lateral (q) and ventral (r) views. (s) Composite reconstruction of H. sinensis scaled to the holotype (XM 12-1558) compared with a human (1.8 m height). an, angular; ar, articular; bo, basioccipital; d, dentary; ect, ectopterygoid; emf, external mandibular fenestra; en, external naris; f, frontal; hp, hypapophysis; itf, infratemporal fenestra; j, jugal; l, lacrimal; m, maxilla; n, nasal; o, orbit; pa, parietal, pal, palatine; pf, prefrontal; pm, premaxilla; po, postorbital; pt, pterygoid, q, quadrate; qj, quadratojugal; sa, surangular; sof, soborbital fenestra; sq, squamosal; stf, supratemporal fenestra. Scale bars are 10 cm. (Online version in colour.) |
Systematics
Crocodylia Gmelin, 1789 (sensu Benton and Clark, 1988).
Gavialidae Adams, 1854 (sensu Brochu, 2003).
Hanyusuchus sinensis gen. et sp. nov.
Diagnosis: A large slender-snouted crocodylian with five premaxillary, 16 maxillary and 18 dentary teeth; seventh maxillary tooth largest in the anterior-mid maxilla; medial wall of the last three maxillary alveoli within the suborbital fenestrae swollen; dorsal half of the prefrontal pillar narrow anteroposteriorly, and the medial process of the pillar dorsoventrally tall and anteroposteriorly short; interfenestral bar wider than one half of the interorbital distance; postorbital and squamosal parts of the skull table slope laterally; a shallow fossa extending posteriorly from the supratemporal fenestra onto the dorsal squamosal surface (autapomorphy); a pair of deep depressions anterior to the internal choana associated with the expansion of the posterior chamber of the pterygoid bulla; exoccipital sending a robust process ventrally to the basioccipital tubera; a pair of knob-like hypapophyses on the ventral surface of axial and third cervical centra; anterior margin of dorsal midline osteoderms with anterior process; reduced medial condyle of the femur (figure 2a–r; see electronic supplementary material, part I and II and figures S2–S21 for full description and comparisons, and electronic supplementary material, tables S3–S5 for measurements).
Etymology: The generic name after Han Yu (a Chinese government official and poet during the Tang dynasty) + suchus (Latin for Greek soûkhos, the crocodile god Sobek), and the specific epithet after sinae (Latin for China) + ensis (Latin for ‘from’).
Distribution: Archaeological records and historical literature revealed the past occurrences of H. sinensis across Fujian, Guangdong, Guangxi, and Hainan provinces in southeastern China from the late fourth millennium BC to the mid second millennium AD (figure 1; electronic supplementary material, figure S1 and tables S1 and S2).
Masaya Iijima, Yu Qiao, Wenbin Lin, Youjie Peng, Minoru Yoneda and Jun Liu. 2022. An Intermediate Crocodylian linking Two Extant Gharials from the Bronze Age of China and Its Human-induced Extinction. Proc. R. Soc. B.. 28920220085. DOI: 10.1098/rspb.2022.0085
