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 barbarus | 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 clade of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates are characterised by prominent muscular limb buds (lobes) within their fins, which are supported by articulated appendicular skeletons. This is in contrast to the other clade of bony fish, the Actinopterygii, which have only skin-covered bony spines supporting the fins.
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:
Acanthostega is an extinct genus of stem-tetrapod, among the first vertebrate animals to have recognizable limbs. It appeared in the late Devonian period about 365 million years ago, and was anatomically intermediate between lobe-finned fishes and those that were fully capable of coming onto land.
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
Hynerpeton is an extinct genus of early four-limbed vertebrate that lived in the rivers and ponds of Pennsylvania during the Late Devonian period, around 365 to 363 million years ago. The only known species of Hynerpeton is H. bassetti, named after the describer's grandfather, city planner Edward Bassett. Hynerpeton is known for being the first Devonian four-limbed vertebrate discovered in the United States, as well as possibly being one of the first to have lost internal (fish-like) gills.
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 methods for land movement, such as lateral undulation, tripod-like walking, and jumping. Many of these methods of locomotion 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 of the 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.
The Fram Formation is an Upper Devonian (Frasnian) sequence of rock strata on Ellesmere Island that came into prominence in 2006 with the discovery in its rocks of examples of the transitional fossil, Tiktaalik, a sarcopterygian or lobe-finned fish showing many tetrapod characteristics. Fossils of Laccognathus embryi, a porolepiform lobe-finned fish, and Qikiqtania, a close relative of Tiktaalik, were also found in the formation. The Fram Formation is a Middle to Upper Devonian clastic wedge forming an extensive continental facies consisting of sediments derived from deposits laid down in braided stream systems that formed some 375 million years ago, at a time when the North American craton ("Laurentia") was straddling the equator.
Hemiscyllium is a genus of sharks in the family Hemiscylliidae.
The leopard epaulette shark, also known as the Milne Bay epaulette shark and Michael's 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 carpetshark, 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 (32.3 in). 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 moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only by muscles.
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.
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.
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. 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.
The evolution of fishes took place over a timeline which spans the Cambrian to the Cenozoic, including during that time in particular the Devonian, which has been dubbed the "age of fishes" for the many changes during that period.
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