Megasternini

Mulsant, 1844

Megasternini is the largest tribe of terrestrial (: ), with approximately 600 described worldwide. The tribe is divided into two subtribes—Megasternina and Oosternina—distinguished by male and surrounding . Molecular phylogenetic studies reveal a complex biogeographic involving multiple intercontinental events during the Paleocene-Eocene Thermal Maximum. The tribe exhibits its highest in tropical regions across all continents.

Megasternum concinnum by (c) janet graham, some rights reserved (CC BY). Used under a CC-BY license.

Cercyon setulosus by (c) Trevor Van Loon, some rights reserved (CC BY), uploaded by Trevor Van Loon. Used under a CC-BY license.

Pronunciation

How to pronounce Megasternini: /ˌmɛɡəˈstɜrnɪnaɪ/

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Identification

Megasternini can be distinguished from other tribes by the combination of terrestrial habits and specific male . Within the tribe, two subtribes are recognized: Megasternina and Oosternina, separated by the structure of male genitalia and surrounding . The metaventrite with complete femoral crossing arcuate ridges serves as a diagnostic character for certain such as Peltocercyon. Many genera within Megasternini—including Cercyon, Oosternum, Cetiocyon, Australocyon, and Pelosoma—are not based on current molecular evidence, complicating identification at the genus level.

Images

Habitat

Members of Megasternini are primarily terrestrial, inhabiting decaying material. Some occur in cave environments with underground rivers and pools, though their status as truly aquatic or subterranean remains uncertain. The tribe shows to moist microhabitats associated with decomposition.

Distribution

Worldwide distribution with highest in tropical areas of all continents. Documented from Asia (China, Laos, Indonesia, Philippines, Malaysia, Vietnam, India, Cambodia, Myanmar, Japan), the Americas, Australia, Africa, and Europe including Turkey. Historical biogeographic analyses indicate of South America from Australia approximately 90 million years ago and at least five events between Asia and North America via the Beringia land bridge during the Paleocene-Eocene (63–55 million years ago).

Similar Taxa

Other Hydrophilidae tribesMegasternini is distinguished from other tribes in the by its primarily terrestrial habits, whereas most are aquatic. The subtribal division (Megasternina vs. Oosternina) is unique to this tribe and based on male .

More Details

Phylogenetic structure

reveals 12 principal clades within Megasternini: three in Oosternina and nine in Megasternina. These clades group largely by geographic distribution rather than , indicating of morphological characters across lineages. The Cercyon, the most diverse in the tribe, is distributed across all principal clades in both subtribes, necessitating future reorganization of generic concepts.

Historical biogeography

The tribe's evolutionary includes repeated continental interchange during warm climate periods. The Asia-America faunal interchange (63–55 mya) coincided with the Paleocene-Eocene Thermal Maximum, when tropical and subtropical expanded toward polar regions. Diversification analyses show no effect of intercontinental on speciation or extinction rates, but suggest possible influence of declining global temperatures over the last 20 million years.