HYDROPHILIDAE WIDELY DISTRIBUTED BY THE LATE JURASSIC

Fikáček, Martin, Prokin, Alexander, Yan, Evgeny, Yue, Yanli, Wang, Bo, Ren, Dong & Beattie, Robert, 2014, Modern hydrophilid clades present and widespread in the Late Jurassic and Early Cretaceous (Coleoptera: Hydrophiloidea: Hydrophilidae), Zoological Journal of the Linnean Society 170 (4), pp. 710-734 : 729-730

HYDROPHILIDAE WIDELY DISTRIBUTED BY THE LATE JURASSIC

The second surprising result of this study besides the Mesozoic age of the whole family and its extant tribes is the wide distribution of the Hydrophilidae in the Late Jurassic and Early Cretaceous. We have documented here the occurrence in both the northern and southern hemispheres during the Late Jurassic (c. 150 Mya) for the Hydrophilidae (based on the fossils from Solnhofen, Germany, and Talbragar, Australia) and during the Early Cretaceous (c. 130–120 Mya) for the extant tribe Hydrobiusini (based on Baissalarva from Baissa, Russia, and Cretoxenus from Koonwarra, Australia).

The worldwide occurrence of the Hydrophilidae in the Late Jurassic is possibly a result of the connections between the southern and northern continental blocks that existed during the Jurassic (e.g. Sanmartín & Ronquist, 2004; Ezcurra & Agnolín, 2012). A temporal lag is expected between the origin of the clade (family Hydrophilidae in our case), origin of its synapomorphies, and its appearance in the fossil record ( Magallón, 2004). In the same way, a temporal lag may be expected between the origin of the clade, achievement of a worldwide distribution, and the appearance in the fossil record. The length of the time lag is generally impossible to estimate, but we suppose that the worldwide distribution of the family may imply its Early–Middle Jurassic origin. This is not in the conflict with the fossil-dated molecular trees of Coleoptera available at the moment, which date the origin of the Hydrophiloidea back to the Jurassic (175 ± 23 Mya; Hunt et al., 2007) or Triassic (228 Mya, McKenna & Farrell, 2009). It shouls soon be possible to compare our hypothesis with the dated Hydrophilidae tree.

Moreover, the occurrence of the extant clade Hydrobiusini in Gondwana (Koonwarra) and eastern Laurasia (Baissa) suggests that the principal extant clades may have diverged as early as the Jurassic when a worldwide distribution was easy to establish. This would explain the current worldwide distribution of most hydrophilid tribes (Short & Fikácˇek, 2013) or even of genera (e.g. Berosus , Enochrus , Helochares ; Hansen, 1999; Short & Hebauer, 2006; Short & Fikácˇek, 2011). However, this hypothesis needs to be confirmed based on a dated molecular phylogeny of the Hydrophilidae .