A walking fish, or ambulatory fish, is a fish that is able to travel over land for extended periods of time. Some other modes of non-standard fish locomotion include "walking" along the sea floor, for example, in handfish or frogfish.
A walking fish, or ambulatory fish, is a fish that is able to travel over land for extended periods of time. Some other modes of non-standard fish locomotion include "walking" along the sea floor, for example, in handfish or frogfish.
Most commonly, walking fish are amphibious fish. Able to spend longer times out of water, these fish may use a number of means of locomotion, including springing, snake-like lateral undulation, and tripod-like walking. The mudskippers are probably the best land-adapted of contemporary fish and are able to spend days moving about out of water and can even climb mangroves, although to only modest heights. [1] The climbing gourami is often specifically referred to as a "walking fish", although it does not actually "walk", but rather moves in a jerky way by supporting itself on the extended edges of its gill plates and pushing itself by its fins and tail. Some reports indicate that it can also climb trees. [2]
The epaulette shark (Hemiscyllium ocellatum) tends to live in shallow waters where swimming is difficult, and can often be seen walking over rocks and sand by using its muscular pectoral fins. [3] It lives in areas of great variation in water depth, usually where the tide falls below its location. If it finds itself out of water, it can survive for several hours, and is capable of walking over land to get to water. This means that it is easily observed by beachgoers in its natural range.
There are a number of fish that are less adept at actual walking, such as the walking catfish. Despite being known for "walking on land", this fish usually wriggles and may use its pectoral fins to aid in its movement. Walking catfish have a respiratory system that allows them to live out of water for several days. Some are invasive species, for example, the northern snakehead in the U.S. [4] Polypterids have rudimentary lungs and can also move about on land, though rather clumsily. The mangrove rivulus can survive for months out of water and can move to places like hollow logs. [5] [6] [7]
Some species of fish can "walk" along the sea floor but not on land. One such animal is the flying gurnard (it does not actually fly, and should not be confused with flying fish). The batfishes of the family Ogcocephalidae (not to be confused with batfish of Ephippidae) are also capable of walking along the sea floor. Bathypterois grallator , also known as a "tripodfish", stands on three fins on the bottom of the ocean and hunts for food. [8] The African lungfish (P. annectens) can use its fins to "walk" along the bottom of its tank in a manner similar to the way amphibians and land vertebrates use their limbs on land. [9] [10]
Land vertebrates originate in the Devonian period and are descended from Sarcopterygian fish. [11] In 2006, a fossil, Tiktaalik roseae , was found which has many features of its wrist, elbow, and neck that resemble those of tetrapods, supporting the idea that it represents a sister group to tetrapods. [12]
A number of fish, both extant and prehistoric, have featured some characteristics related to locomotion that are typical of tetrapods.
| Species | venturing onto land | tetrapod-like spine | tetrapod-like appendages | digit-like bones | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 5 axial regions | interlocking vertebrae | fully ossified vertebrae | shoulder & skull separation | functional 'intra-fin' joints | fins adapted for walking rather than swimming | strong & muscled fins | humerus, radius & ulna bones | differentiated distal radial bones | jointed distal radial bones | ||
| Panderichthys rhombolepis † | ? | No | No | No | No | ? | No | Yes | Yes | Yes [13] | No |
| Sauripterus taylori † | ? | No | No | No | No | ? | No | Yes | Yes | Yes | Yes [14] |
| Tiktaalik roseae † | ? | No | No | No | Yes | Yes | No | Yes | Yes | No | No |
| Tarrasius problematicus † | ? | Yes [15] | No | No | No | No | No | No | No | No | No |
| Leptolepis koonwarriensis † | ? | No | No | Yes [16] | No | No | No | No | No | No | No |
| Eastmanosteus pustulosus † | ? | No | No | No | Yes [17] | No | No | No | No | No | No |
| Atractosteus spatula | No | No | Yes | Yes [18] | No | No | No | No | No | No | No |
| Periophthalmus papilio | Yes | No | No | No | No | Yes [19] [20] | No | No | No | No | No |
| Brachionichthys hirsutus | No | No | No | No | No | No | Yes | No | No | No | No |
| Ogcocephalus darwini | No | No | No | No | No | No | Yes | No | No | No | No |
| Antennarius maculatus | No | No | No | No | No | No | Yes | No | No | No | No |
| Protopterus annectens | Yes | No | No | No | No | No | ? [10] | No | No | No | No |
| Latimeria chalumnae | No | No | No | No | No | No | No | Yes | No | No | No |
| Polypterus bichir lapradei | Yes | No | No | No | No | No | No | Yes | No | No | No |
| Chelidonichthys cuculus | No | No | No | No | No | No | Yes (3 rays) | No | No | ? (3 rays) | No |
| Hemiscyllium ocellatum | Yes | No | No | No | Yes [21] | No | ? [22] | No | No | No | No |
Another usage of the term walking fish is in reference to the "Darwin fish", a bumper sticker parody of the Ichthys, a symbol of Christianity.
A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fins are also used to increase surface areas for heat transfer purposes, or simply as ornamentation.
Sarcopterygii — sometimes considered synonymous with Crossopterygii — is a taxon of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass including amphibians, sauropsids and synapsids, evolved from certain sarcopterygians; under a cladistic view, tetrapods are themselves considered a subgroup within Sarcopterygii.
Fish locomotion is the various types of animal locomotion used by fish, principally by swimming. This is achieved in different groups of fish by a variety of mechanisms of propulsion, most often by wave-like lateral flexions of the fish's body and tail in the water, and in various specialised fish by motions of the fins. The major forms of locomotion in fish are:
Panderichthys is a genus of extinct sarcopterygian from the late Devonian period, about 380 Mya. Panderichthys, which was recovered from Frasnian deposits in Latvia, is represented by two species. P. stolbovi is known only from some snout fragments and an incomplete lower jaw. P. rhombolepis is known from several more complete specimens. Although it probably belongs to a sister group of the earliest tetrapods, Panderichthys exhibits a range of features transitional between tristichopterid lobe-fin fishes and early tetrapods. It is named after the German-Baltic paleontologist Christian Heinrich Pander. Possible tetrapod tracks dating back to before the appearance of Panderichthys in the fossil record were reported in 2010, which suggests that Panderichthys is not a direct ancestor of tetrapods, but nonetheless shows the traits that evolved during the fish-tetrapod evolution
Amphibious fish are fish that are able to leave water for extended periods of time. About 11 distantly related genera of fish are considered amphibious. This suggests that many fish genera independently evolved amphibious traits, a process known as convergent evolution. These fish use a range of terrestrial locomotory modes, such as lateral undulation, tripod-like walking, and jumping. Many of these locomotory modes incorporate multiple combinations of pectoral-, pelvic-, and tail-fin movement.
Mudskippers are any of the 23 extant species of amphibious fish from the subfamily Oxudercinae of the goby family Oxudercidae. They are known for their unusual body shapes, preferences for semiaquatic habitats, limited terrestrial locomotion and jumping, and the ability to survive prolonged periods of time both in and out of water.
Tiktaalik is a monospecific genus of extinct sarcopterygian from the Late Devonian Period, about 375 Mya, having many features akin to those of tetrapods. Tiktaalik is estimated to have had a total length of 1.25–2.75 metres (4.1–9.0 ft) based on various specimens.
The epaulette shark is a species of longtailed carpet shark, family Hemiscylliidae, found in shallow, tropical waters off Australia and New Guinea. The common name of this shark comes from the very large, white-margined black spot behind each pectoral fin, which are reminiscent of military epaulettes. A small species usually under 1 m (3.3 ft) long, the epaulette shark has a slender body with a short head and broad, paddle-shaped paired fins. The caudal peduncle comprises over half the shark's length. Adults are light brown above, with scattered darker spots and indistinct saddles.
Edward B. 'Ted' Daeschler is an American vertebrate paleontologist and Associate Curator and Chair of Vertebrate Biology at the Academy of Natural Sciences in Philadelphia. He is a specialist in fish paleontology, especially in the Late Devonian, and in the development of the first limbed vertebrates. He is the discoverer of the transitional fossil tetrapod Hynerpeton bassetti, and a Devonian fish-like specimen of Sauripterus taylori with fingerlike appendages, and was also part of a team of researchers that discovered the transitional fossil Tiktaalik.
Hemiscyllium is a genus of sharks in the family Hemiscylliidae.
The Leopard Epaulette Shark, also known as the Milne Bay Epaulette Shark, is a species of bamboo shark in the genus Hemiscyllium. It is a tropical shark known from the shallow ocean in the Milne Bay region of eastern Papua New Guinea. The epaulette sharks of this region have long been confused with the Indonesian Speckled Catpetshark, and it was only in 2010 that H. michaeli was described as a separate species by Gerald R. Allen and Christine L. Dudgeon. It can reach a maximum length of 82 cm. Confusingly, some books with illustrations and photos labelled as H. freycineti actually show H. michaeli.
The Atlantic mudskipper is a species of mudskipper native to fresh, marine, and brackish waters of the tropical Atlantic coasts of Africa, including most offshore islands, through the Indian Ocean and into the western Pacific Ocean to Guam. The Greek scientific name Periophthalmus barbarus is named after the eyes that provide the Atlantic mudskipper with a wide field of vision. The Atlantic mudskipper is a member of the genus Periophthalmus, which includes oxudercine gobies that have one row of canine-like teeth.
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of Actinopterygii and Chondrichthyes fishes. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as seen in sharks. Apart from the tail or caudal fin, fish fins have no direct connection with the spine and are supported only by muscles. Their principal function is to help the fish swim.
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish. Early examples include Haikouichthys. During the late Cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. Most jawless fish are now extinct; but the extant lampreys may approximate ancient pre-jawed fish. Lampreys belong to the Cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. Tetrapods are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals. While most species today are terrestrial, little evidence supports the idea that any of the earliest tetrapods could move about on land, as their limbs could not have held their midsections off the ground and the known trackways do not indicate they dragged their bellies around. Presumably, the tracks were made by animals walking along the bottoms of shallow bodies of water. The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear. They are areas of active research and debate among palaeontologists at present.
Innovations conventionally associated with terrestrially first appeared in aquatic elpistostegalians such as Panderichthys rhombolepis, Elpistostege watsoni, and Tiktaalik roseae. Phylogenetic analyses distribute the features that developed along the tetrapod stem and display a stepwise process of character acquisition, rather than abrupt. The complete transition occurred over a period of 30 million years beginning with the tetrapodomorph diversification in the Middle Devonian.
The vertebrate land invasion refers to the aquatic-to-terrestrial transition of vertebrate organisms in the Late Devonian period. This transition allowed animals to escape competitive pressure from the water and explore niche opportunities on land. Fossils from this period have allowed scientists to identify some of the species that existed during this transition, such as Tiktaalik and Acanthostega. Many of these species were also the first to develop adaptations suited to terrestrial over aquatic life, such as neck mobility and hindlimb locomotion.
There are several cases of reported trackways of the earliest land-going vertebrates, also known as tetrapods. These trackways provide crucial insights to the study of the transition of aquatic to terrestrial lifestyles in vertebrate evolution. Such fossils help to illuminate not only the timing of this keystone transition of evolutionary history but also what the earliest forms of tetrapod locomotion may have entailed.
Qikiqtania is an extinct genus of elpistostegalian tetrapodomorph from the Late Devonian Fram Formation of Nunavut, Canada. The genus contains a single species, Q. wakei, known from a partial skeleton. Analysis of the fin bones suggests that Qikiqtania was well-suited to swimming, and likely incapable of walking or supporting itself out of the water, as has been suggested for the closely related Tiktaalik.
The Zachelmie trackways are a series of Middle Devonian-age trace fossils in Poland, purportedly the oldest evidence of terrestrial vertebrates (tetrapods) in the fossil record. These trackways were discovered in the Wojciechowice Formation, an Eifelian-age carbonate unit exposed in the Zachełmie Quarry of the Świętokrzyskie Mountains (Holy Cross Mountains]. The discovery of these tracks has complicated the study of tetrapod evolution. Morphological studies suggest that four-limbed vertebrates are descended from a specialized type of tetrapodomorph fish, the epistostegalians. This hypothesis was supported further by the discovery and 2006 description of Tiktaalik, a well-preserved epistostegalian from the Frasnian of Nunavut. Crucial to this idea is the assumption that tetrapods originated in the Late Devonian, after elpistostegalians appear in the fossil record near the start of the Frasnian. The Zachelmie trackways, however, appear to demonstrate that tetrapods were present prior to the Late Devonian. The implications of this find has led to several different perspectives on the sequence of events involved in tetrapod evolution.
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