Department of Geology and Palaeontology, Natural History Muesum, Geneva, Switzerland.
Laboratoire de Géologie de l'Ecole Normale Supérieure, CNRS (UMR 8538), PSL Research University, Paris, France.
PLoS One. 2020 Jun 5;15(6):e0234183. doi: 10.1371/journal.pone.0234183. eCollection 2020.
Coelacanths are iconic fishes represented today by a single marine genus. The group was a little bit more diversified in the Mesozoic, with representatives in marine and continental environments in the Late Cretaceous. Here we describe isolated skull bones of the last know freshwater coelacanths found in several fossil sites from the Early Campanian to the Early Maastrichtian of Southern France (in the Departments of Aude, Bouches-du-Rhône, Hérault, and Var). The sample does not allow distinguishing different species, and all material is referred to Axelrodichthys megadromos Cavin, Valentin, Garcia originally described from the locality of Ventabren in Southern France. A reconstruction of the skull is proposed. Previously unrecognized features are described, including parts of the postparietal portion of the skull, of the suspensorium and of the mandible. The new data confirm the assignation of the species to the mawsoniids, and more specifically to Axelrodichthys. A cladistic analysis scoring new character states provides a similar topology than a previous analysis, i.e. A. megadromos is placed in a polytomy with Axelrodichthys araripensis and Lualabaea lerichei, two species from the Early Cretaceous of Brazil and from the Late Jurassic of the Democratic Republic of the Congo, respectively. A. megadromos appears to have been restricted to freshwater environments, to the contrary of oldest Western Gondwanan representatives of the family that were able to live in brackish and marine waters. A. megadromos is the last representative of the mawsoniids and its occurrence in Europe is probably the result of a dispersal event from Western Gondwana that happened somewhen in the Cretaceous. Based on the available data, the mawsoniids went extinct in the mid-Maastrichthian, i.e. before the end-Cretaceous mass extinction. But it is possible that the fossil record of this family, which has been only recently recognized in Late Cretaceous European deposits, will geographically and stratigraphically widen with further discoveries.
腔棘鱼是标志性的鱼类，现今仅由一个海洋属代表。该群体在中生代略有多样化，在晚白垩世有代表生活在海洋和大陆环境中。本文描述了法国南部早坎潘期至早马斯特里赫特期几个化石点发现的最后一批已知淡水腔棘鱼的孤立头骨骨骼。该样本无法区分不同的物种，所有材料均指 Axelrodichthys megadromos Cavin、Valentin、Garcia，最初是在法国南部的文塔布伦（Ventabren）地区描述的。提出了头骨的重建。描述了以前未被识别的特征，包括头骨后顶骨部分、悬挂系统和下颌骨的一部分。新数据证实了该物种属于矛尾鱼科，更具体地说是 Axelrodichthys。对新特征状态进行的系统发育分析提供了与之前分析相似的拓扑结构，即 A. megadromos 与 Axelrodichthys araripensis 和 Lualabaea lerichei 处于多系群中，这两个物种分别来自巴西的早白垩世和刚果民主共和国的晚侏罗世。A. megadromos 似乎仅限于淡水环境，与该科最早的西部冈瓦纳代表相反，后者能够生活在半咸水和海水中。A. megadromos 是矛尾鱼科的最后一个代表，它在欧洲的出现可能是白垩纪时期从西部冈瓦纳发生的扩散事件的结果。基于现有数据，矛尾鱼科在中马斯特里赫特期灭绝，即在白垩纪末期大灭绝之前。但该科的化石记录可能会随着进一步的发现，在地理和地层上扩大。
