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| Palaemon aestuarius
Du, Chen, Li, et al., 2019.
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Abstract
The aquatic and semiaquatic invertebrates in fossiliferous amber have been reported, including taxa in a wide range of the subphylum Crustacea of Arthropoda. However, no caridean shrimp has been discovered so far in the world. The shrimp Palaemon aestuarius sp. nov. (Palaemonidae) preserved in amber from Chiapas, Mexico during Early Miocene (ca. 22.8 Ma) represents the first and the oldest amber caridean species. This finding suggests that the genus Palaemon has occupied Mexico at least since Early Miocene. In addition, the coexistence of the shrimp, a beetle larva, and a piece of residual leaf in the same amber supports the previous explanations for the Mexican amber depositional environment, in the tide-influenced mangrove estuary region.
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| Figure 1: Morphological photographs of Palaemon aestuarius sp. nov. (a) Detail of cephalothorax in lateral view. (b) General view in ateral view.
Fl, flagellum; Ro, rostrum; Ey, eyestalk; Co, cornea; Bg, branchiostegal groove; Bs, branchiostegal spine; Sc, scaphocerite; Mp3, third maxillipede; P1, first pereiopod; P3, third pereiopod; P4, forth pereiopod; P5, fifth pereiopod; Pm1, first pleomere; Pm2, second pleomere; Pm3, third pleomere; Pm4, forth pleomere; Pm5, fifth pleomere; Pm6, sixth pleomere; Te, telson; Ur, uropod. Scale bar, 2 mm.
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Systematic palaeontology
Order Decapoda Latreille, 1802
Suborder Dendrobranchiata Bate, 1888
Infrorder Caridea Dana, 1852
Superfamily Palaemonoidea Rafinesque, 1815
Family Palaemonidae Rafinesque, 1815
Subfamily Palaemoninae Rafinesque, 1815
Genus Palaemon Weber, 1795
Palaemon aestuarius sp. nov.
Holotype: STJ172. All length measurements are recorded in mm. Total length: 10.3, carapace length: 2.6, rostrum length: 2.2, abdomen length: 4.77, telson length: 1.28 (Figs 1a, b, 2 and S1). The materal deposited in the the Paleo-diary Museum of Natural History, Beijing, China.
Type locality/horizon: Campo La Granja mine, Simojovel de Allende town, Chiapas, southeastern Mexico (Early Miocene, c. 22.8 Ma)16,19.
Diagnosis: Rostrum without elevated basal crest, faintly convex in the middle, dorsal margin with nine teeth including one postorbital tooth, basal four teeth evenly distributed, the distance between them greater than the intervals of other teeth. Carapace smooth, branchiostegal groove extended longitudinally backward; branchiostegal spine sharp, situated on anterior margin of cephalon; hepatic spine absent. Length of non-chelate pereiopods increasing gradually from third to fifth; ischium slightly longer than the length of propodus, about 2–3 times as long as carpus, merus longest, dactylus the shortest, apices inwardly hooklike.
Etymology: The specific name comes from the Latinization “estuary” where the shrimp inhabited.
Remarks: P. aestuarius sp. nov. resembles Palaemon vesolensis Bravi, Coppa, Garassino & Patricelli, 1999, the difference between them in: P. aestuarius sp. nov. with nine teeth on the dorsal margin, carapace bearing prominent branchiostegal groove; but the P. vesolensis with seven dorsal teeth, carapace without traces of grooves.
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| Figure 2: Reconstruction of habitus of Palaemon aestuarius sp. nov. (lateral view). The abbreviations represent the same morphological characteristics as the Fig. 1. Scale bar, 2 mm. |
Bao-Jie Du, Rui Chen, Xin-Zheng Li, Wen-Tao Tao, Wen-Jun Bu, Jin-Hua Xiao and Da-Wei Huang. 2019. The First Amber Caridean Shrimp from Mexico Reveals the Ancient Adaptation of the Palaemon to the Mangrove Estuary Environment. Scientific Reports. 9; 14782. nature.com/articles/s41598-019-51218-5
