John Davenport

The repeated evolutionary transitions of tetrapods from terrestrial to marine environments represent one of the most remarkable examples of functional convergence among vertebrates. Despite profound specialisation for aquatic locomotion, many marine tetrapods must periodically return to land for essential activities such as reproduction, moulting, and resting, providing a unique opportunity to investigate whether convergent adaptations for swimming have been accompanied by convergent evolution of terrestrial locomotor repertoires. This study combines a comparative synthesis with original phylogenetic analyses to investigate the evolution of terrestrial locomotor repertoires in the three principal lineages of extant marine tetrapods with flippers: sea turtles, penguins, and pinnipeds. A standardised behavioural dataset compiled from published studies, publicly available videos, and original observations was used to reconstruct the evolutionary history of locomotor behaviours, test correlated evolution among locomotor modes, and evaluate the influence of body mass within a phylogenetic framework. Although these lineages exhibit remarkable convergence in appendicular adaptations for aquatic propulsion, our comparative analyses demonstrate that this convergence has not been accompanied by convergence in terrestrial locomotor repertoires. Instead, each lineage has retained or evolved distinct terrestrial locomotor strategies reflecting different combinations of phylogenetic inheritance, biomechanical constraints, and ecological specialisation. Marine turtles exhibit the most conservative terrestrial repertoire, penguins combine highly specialised underwater flight with diverse terrestrial behaviours, and pinnipeds display the greatest diversity of terrestrial locomotor strategies. These findings indicate that similar functional demands for efficient swimming have generated multiple evolutionary solutions for terrestrial locomotion rather than a single convergent strategy. More broadly, this study provides an integrative framework for understanding how behaviour, biomechanics, ecology, and evolutionary history interact to shape locomotor evolution in secondarily aquatic tetrapods and establishes a behavioural foundation for future studies linking structure, performance, behaviour, and fitness.

Diverse and extensive macrofouling of the left-hand (eyed) side has been observed in multiple films and photographs of different specimens of Eckström's topknot Zeugopterus regius. Identified foulers include macroalgae and tunicates. Photographs of unfouled specimens and preserved juveniles have also been inspected. Macrofouling is not universal in this species; unfouled fish were observed around the strongly tidal British Isles, whereas the worst-fouled topknots were seen in the eutrophic, microtidal northern Adriatic.

Sea turtle species have life cycles that have common features such as oviparity, nesting on sandy beaches, growing as juveniles in surface waters and moving to foraging grounds before migrating— often over long distances—to natal beaches to breed. They are therefore exposed to aquatic and terrestrial influences, both abiotic (e.g. temperature, weather) and biotic (e.g. food availability, predation). Humans have exploited sea turtles for millennia and pressure on their populations has increased dramatically during the ongoing Anthropocene as human influences have increased both in power and global reach. Fishing bycatches generated by powerful unselective gears have largely replaced direct fishing as an existential threat, but meat and egg poaching persist, while burgeoning global wildlife crime threatens sea turtles, especially hawksbills. Habitat loss caused by coastal development and exponential increases in beach-based tourism have reduced nesting success. Sustained losses of coral reef and seagrass habitats have removed foraging grounds for adult turtles and both habitat types are currently projected to disappear before 2100. Environmental degradation has taken several forms. Chemical pollution through the accumulation of organics and heavy metals have affected reproduction and facilitated the transmission of fibropapillomatosis. An emerging threat due to eutrophication also needs to be considered. Marine plastic pollution is already highly damaging to sea turtles; plastic fishing gears ‘ghost-fish’ indefinitely, capturing and killing all life-history stages except eggs, while ingestion of macro and microplastics blocks/damages guts. Rising global temperature has been identified as a potential existential threat for all species because of temperature-dependent sex determination and substantial sea level rise. However, climate change is also projected to cause an order of magnitude increase in the frequency of heat waves and extreme sea level highs, both of which can kill turtle embryos. This Praeger Review concludes with a description of sea turtle occurrences around the British Isles and the anthropogenic influences upon them.

Reptilia exploit a large diversity of food resources from plant materials to living mobile prey. They are among the first tetrapods that needed to drink to maintain their water homeostasis. Here were compare the feeding and drinking mechanisms in Reptilia through an empirical approach based on the available data to open perspectives in our understanding of the evolution of the various mechanisms determined in these Tetrapoda for exploiting solid and liquid food resources. This article is part of the theme issue ‘Food processing and nutritional assimilation in animals’.

Common topknots (Zeugopterus punctatus) attach to vertical rock surfaces and overhangs. It has been speculated that attachment is by a suction cup, with the median (anal, dorsal) fins providing a peripheral seal. Here the authors propose that the attachment is actually based on a Venturi effect. The rear portions of the median fins continually move in a fan‐like fashion (atc. 4 cycles per second). This movement produces a tailward fluid flow that ventilates the shallow underbody space between the fish and its rocky substratum. The anterior portions of the median fins seal the space laterally, but the space is open anterior (beneath the raised head) and posterior to the sea. The mid‐underbody space likely has a lower cross‐sectional area than does the front intake or rear exit, so flow should be faster (and pressure lower) within it than outside, thus providing pressure gradient suction. Topknots attach to rough and heavily biofouled surfaces, presumably because the high numbers of fin rays and their associated membranes plus fine muscle control allow effective sealing. The attachment ability is shared by all members of the flatfish tribe Phrynorhombini; it can be related to anatomical peculiarities and constitutes a probable synapomorphy for this clade.

Videofilms of a foraging flying gurnard (Dactylopterus volitans) were collected at Itaipu, Niterói, RJ, Brazil. Analysis revealed details of the use of anterior parts of the pectoral fins which act as digging ‘hands’ to access infaunal prey items that are subsequently captured by oral suction feeding. Each pectoral fin has two distinct sections articulated separately on the pectoral girdle. The digging ‘anterior pectoral fin’ mainly consists of segmented and flexible fin rays but has an anterior robust unsegmented ray that provides an edge to the ‘hand’, allowing penetration of the substratum. The huge ‘posterior pectoral fins’ are supported by unsegmented rays. Most digging episodes involved one ‘hand’ and consisted of 1–7 cycles of movement with frequencies 1.15–3.74 cycles s⁻¹. During a cycle, the ‘hand’ is moved forwards and medially above the substratum, then is twisted medially and simultaneously depressed so that the anterior unsegmented ray impacts and enters the substratum. The hand is then drawn backwards and laterally to disturb the substratum. To prevent upward pitching of the head during digging, the ‘posterior pectoral fins’ are both moved anteriorly and laterally to shift the centre of gravity forwards while the caudal and second dorsal fins continue to provide propulsive force.

Adult ocean sunfish are the heaviest living teleosts. They have no axial musculature or caudal fin. Propulsion is by unpaired dorsal and anal fins; a pseudocaudal fin (‘clavus’) acts as a rudder. Despite common perception, young sunfish are active predators that swim quickly, beating their vertical fins in unison to generate lift‐based propulsion and attain cruising speeds similar to salmon and marlin. Here we show that the thick subcutaneous layer (or ‘capsule’), already known to provide positive buoyancy, is also crucial to locomotion. It provides two compartments, one for dorsal fin musculature and one for anal fin muscles, separated by a thick, fibrous, elastic horizontal septum that is bound to the capsule itself, the roof of the skull and the dorsal surface of the short vertebral column. The compartments are braced sagittally by bony haemal and neural spines. Both fins are powered by white muscles distributed laterally and red muscles located medially. The anal fin muscles are mostly aligned dorso‐ventrally and have origins on the septum and haemal spines. Dorsal fin muscles vary in orientation; many have origins on the capsule above the skull and run near‐horizontally and some bipennate muscles have origins on both capsule and septum. Such bipennate muscle arrangements have not been described previously in fishes. Fin muscles have hinged tendons that pass through capsular channels and radial cartilages to insertions on fin rays. The capsule is gelatinous (89.8% water) with a collagen and elastin meshwork. Greasy in texture, calculations indicate capsular buoyancy is partly provided by lipid. Capsule, septum and tendons provide elastic structures likely to enhance muscle action and support fast cruising.