Into Africa via docked India: a fossil climbing perch from the Oligocene of Tibet helps solve the anabantid biogeographical puzzle

Terrestrial locomotion characteristics of climbing perch (Anabas testudineus)

The evolution and utilization of limbs facilitated terrestrial vertebrate movement on land, but little is known about how other lateral structures enhance terrestrial locomotion in amphibian fishes without terrestrialized limb structures. Climbing perch (Anabas testudineus) exhibit sustained terrestrial locomotion using uniaxial rotating gill covers instead of appendages. To investigate the role of such simple lateral structures in terrestrial locomotion and the motion-generating mechanism of the corresponding locomotor structure configuration (gill covers and body undulation), we measured the terrestrial kinematics of climbing perch and quantitatively analysed its motion characteristics. The digitized locomotor kinematics showed a unique body postural adjustment ability that enables the regulation of the posture of the caudal peduncle for converting lateral bending force into propulsion. An analysis of the coordination characteristics demonstrated that the motion of the gill cover is kinematically independent of axial undulation, suggesting that the gill cover functions as an anchored simple support pole while axial undulation actively mediates body posture and produces propulsive force. The two identified feature shapes explained more than 87% of the complex lateral undulation in multistage locomotion. The kinematic characteristics enhance our understanding of the underlying coordinating mechanism corresponding to locomotor configurations. Our work provides quantitative insight into the terrestrial locomotor adaptation of climbing perch and sheds light on terrestrial motion potential of locomotor configurations containing a typical aquatic body and restricted lateral structure.

Cenozoic topography, monsoons and biodiversity conservation within the Tibetan Region: An evolving story

The biodiversity of the Himalaya, Hengduan Mountains and Tibet, here collectively termed the Tibetan Region, is exceptional in a global context. To contextualize and understand the origins of this biotic richness, and its conservation value, we examine recent fossil finds and review progress in understanding the orogeny of the Tibetan Region. We examine the deep-time origins of monsoons affecting Asia, climate variation over different timescales, and the establishment of environmental niche heterogeneity linked to topographic development. The origins of the modern biodiversity were established in the Eocene, concurrent with the formation of pronounced topographic relief across the Tibetan Region. High (>4 km) mountains to the north and south of what is now the Tibetan Plateau bounded a Paleogene central lowland (<2.5 km) hosting moist subtropical vegetation influenced by an intensifying monsoon. In mid Miocene times, before the Himalaya reached their current elevation, sediment infilling and compressional tectonics raised the floor of the central valley to above 3000 m, but central Tibet was still moist enough, and low enough, to host a warm temperate angiosperm-dominated woodland. After 15 Ma, global cooling, the further rise of central Tibet, and the rain shadow cast by the growing Himalaya, progressively led to more open, herb-rich vegetation as the modern high plateau formed with its cool, dry climate. In the moist monsoonal Hengduan Mountains, high and spatially extensive since the Eocene but subsequently deeply dissected by river incision, Neogene cooling depressed the tree line, compressed altitudinal zonation, and created strong environmental heterogeneity. This served as a cradle for the then newly-evolving alpine biota and favoured diversity within more thermophilic vegetation at lower elevations. This diversity has survived through a combination of minimal Quaternary glaciation, and complex relief-related environmental niche heterogeneity. The great antiquity and diversity of the Tibetan Region biota argues for its conservation, and the importance of that biota is demonstrated through our insights into its long temporal gestation provided by fossil archives and information written in surviving genomes. These data sources are worthy of conservation in their own right, but for the living biotic inventory we need to ask what it is we want to conserve. Is it 1) individual taxa for their intrinsic properties, 2) their services in functioning ecosystems, or 3) their capacity to generate future new biodiversity? If 2 or 3 are our goal then landscape conservation at scale is required, and not just seed banks or botanical/zoological gardens.

Origins of Afrotropical freshwater fishes

The Afrotropics house a diverse freshwater ichthyofauna with > 3000 species, almost all of which are endemic. Recent progress in dated phylogenetics and palaeontology of several groups of Afrotropical freshwater fishes (AFFs) has allowed the testing of palaeoecology- and palaeogeography-based hypotheses explaining their early presence in Africa. Seven hypotheses were tested for 37 most-inclusive monophyletic groups of AFFs. Results indicated that ten lineages originated from direct, but asynchronous, marine-to-freshwater shifts. These lineages contribute < 2% to the current AFF species richness. Eleven lineages colonized the Afrotropics from the Orient after the Afro-Arabian plate collided with Eurasia in the early Oligocene. These lineages contribute ~20% to the total diversity. There are seven sister relationships between Afrotropical and Neotropical taxa. For only three of them (4% of the species diversity), the continental drift vicariance hypothesis was not rejected. Distributions of the other four younger trans-Atlantic lineages are better explained by post-drifting long-distance dispersal. In those cases, I discuss the possibility of dispersal through the Northern Hemisphere as an alternative to direct trans-Atlantic dispersal. The origins of ten AFF lineages, including the most species-rich Pseudocrenilabrinae (> 1100 species), are not yet established with confidence.