What is the ancestor of an axolotl

Annette Bültmann
Water as a habitat for mammals and salamanders
1.Archaeoceti (primeval whales)
After life in the form of early amphibians (a well-known early fossil is Ithyostega) went ashore about 400-380 million years ago, some creatures, including whales, later returned to the water. In the case of whales, this happened in the Eocene, about 50 million years ago.
At the border between the Mesozoic Cretaceous period (135-65 million years ago) and the Cenozoic era, the great age of flowering plants, insects, birds and mammals, beginning with the Tertiary and its earliest epoch, the Paleocene (65 to 53 million years ago), the alpine mountain formation led to the folding between the ancient continents of that time, at the same time in the course of the continental drift India, which had separated from the southern primary continent Gondwana, met the land mass of Asia and the Thetys Sea , between Gondwana and Laurasia, disintegrated into individual basins; from this emerged today's Mediterranean, Lake Balaton, the Black Sea, the Caspian Sea and the Aral Sea. In this environment, the ancestors of the whales found their way back into the water.
The order of the Condylarthra, the ancestors of the ungulates, probably included the common ancestors of Cetacea (cetaceans) and Artiodactyla (artiodactyla (cloven-hoofed animals) to which today's cattle, buffalo, deer, goats, sheep, hippos, pigs and camels belong. Today's hippos and ruminants are mentioned as possible particularly close relatives of the whales among the cloven-hoofed animals.
The Mesonychidae, which became extinct about 33 million years ago, developed from the order of the condylarthra.They are described as hyena-like, were carnivorous in their teeth and had hooves, and it is not yet fully clear whether they were also the ancestors of the Whales or belonging to a side branch of development; and in the course of the Paleocene the Archaeoceti. During this time, about 50 million years ago, the Thetys Sea formed semi-closed basins and inlets in an area with tropical vegetation and swamps. The archaeocetes developed elongated bodies and snouts, the hind legs receded, possibly at some point, like the seals, they only went ashore to raise their young. It is believed that when the whales began their return to the water, they were not more attached to the water than today's tapirs, but in the course of evolution they spent increasing amounts of time in the water and adapted their physique to their watery habitat.
An example of this is Ambulocetus natans, "swimming whale", which probably waddled on land, paddled with its hind legs in the water and moved forward by moving its trunk and tail up and down, and steered with its front legs.
Earliest ancestor Pakicetus or Himalayan acetus?
For a long time the earliest known fossil whale find was Pakicetus (about 50 MJ), which has since been replaced by Himalayan acetus subathuensis (initially dated 53.5 MJ).
It is likely that Pakicetus and other early cetaceas were furry, four-legged creatures that lived mostly on land and risked their way into the water to fish. The question now arises whether the earliest whales, which probably first swam in river arms, were able to live in salt water. Pakicetus fossil remains have been found in river sediments, and the mixture of oxygen isotopes in its bones suggests fresh water. However, the Himalayan acetus subathuensis found in the Himalayas was found in marine sediments with mussel shells, which indicates that the Himalayan acetus swam in salt water, although otherwise it seems to be little adapted to aquatic life, for example in terms of hearing underwater.
The earliest fossil whales were found in Indopakistan, such as Pakicetus and Himalayan acetus, and many later whale ancestors were found in Egypt, such as Basilosaurus.
Protocetus atavus (Protocetus = primeval whale, atavus = ancestor) is 2.50 long and a link between the original land animals and the later pre-whale Basilosaurus. One of the characteristics that is pronounced in the later whale and already present in the Protocetus atavus is the detachment of the auditory bones from the rest of the skull, which enables directional hearing under water (in humans and other land mammals, the whole head vibrates under water, as a result the direction of the sound cannot be determined).
Hearing is particularly important for whales because they communicate, e.g. within groups, using various sounds, from deep grunts to high-pitched whistling tones, and their communication system is at least as sophisticated as that of dogs or even primates; the chants of some whale species can be heard over hundreds of kilometers by their fellow species.
Basilosaurus cetoides lived 40 million years ago and was already up to 20 meters long, which is why it was mistakenly mistaken for a large reptile in the course of dinosaur research around 1834, and a few years later it was found that it was a whale-like large mammal . In early whales like Basilosaurus, the cervical vertebrae had not yet grown together, so the head was still mobile. Fig. Of a reconstruction: www.pottwale.de/pottwale/historie.html
Further finds in Egypt led to the naming of the whale genera Eocetus, Dorudon and Ancalecetus.
Fossil whales have also been found in the northern hemisphere, such as the 27-28 million year old Eosqualodon langewieschei in Bünde and Eosqualodon latirostris in northern Italy.
In the Berlin Museum für Naturkunde you can find the 6-meter-long fossil humpback whale Megaptera hubachi, found in northern Chile, from the Lower Pliocene, i.e. around 5 million years ago.
Squalodon, a genus of the Miocene (24-5 million years old) was also first thought to be a dinosaur, it has shark-like teeth; in general, the teeth of the early whale ancestors were more like those of the sharks than those of today's toothed whales.
Classification of the early whales into families
The following families with the respective genera can be found in the subordination of the Archaeoceti (primeval whales):
Family Pakicetidae: Nalacetus, Ichthyolestes, Pakicetus, Himalyacethus (about 50 MJ ago, still rural, but already partially adapted to life in the water)
Family Ambulocetidae: Ambulocetus, Gandakasia (about 50 MJ ago, already mainly adapted to aquatic life, but could still move on land)
Family Remingtonocetidae: Attockicetus, Dalanistes, Remintonocetus, Andrewsiphius, Kutchicetus
(lived about 49-43 million years ago; smaller eyes and longer snouts than the Ambulocetidae, a certain external resemblance to platypus)
Family Protocetidae: In the past, the Protocetidae family included all particularly early and primeval primeval whales, today the genera Rodhocetus, Takracetus, Protocetus, Indocetus, Pappocetus, Babiacetus, Georgiacetus, Eocetus, Natchitochia (the first whales outside of Indo-Pakistani were found and the first whales with a fluke)
Family Dorudontidae: Zygorhiza, Dorudon (lived 41-35 million years ago, completely in the water, probably similar to today's dolphins, still had hind legs, but they were very small)
Family Basilosauridae: Basilosaurus (sometimes also known as Zeuglodon) (lived 40-35 million years ago, completely in the water, perhaps more like a sea snake, also very small hind legs)
Development of the families of today's whales
The baleen whales (Mysticeti) developed 30 million years ago; As an intermediate form there were primeval whales whose molars had several points; A grid was formed, the preliminary stage of today's beards, with which krill (small crustaceans), plankton and small schooling fish are filtered out of the water. The whales are long, flexible horn plates that grow down in two brush-like rows from the whale's upper jaw, through which the water flows back into the sea, krill and plankton remain in the whale's mail, the lower lip reaches around the whale from below.
Today there are in the order of the Cetacea (cetaceans) the two major suborders Mysticeti (baleen whales) and Odontoceti (toothed whales). In the Unterornung of the toothed whales there are the three superfamilies of the sperm whales (Physeteroidea), beaked whales (Ziphioidea) and dolphins (Delphinoidea).
The baleen whale includes the right whale and gray whale family, and the furrow whale family, including the blue whale, bowhead whale, fin whale, humpback whale and minke whale.
Links to fossil whales:
Links to whales today:
2. Axolotls
In the Carboniferous, the geological age around 360-290 million years ago, the amphibians descended from the coelaceans already had their heyday.
Ichthyostega, the first known amphibious fossil, already resembled amphibians in some features and fish in others. It has a fish-like tail with fins, but already developed limbs that could carry the body even though they are short.
The three amphibian orders known to us today developed from the group of Ichthyostega tail amphibians (Urodela), frog amphibians (Anura) and caecilians (Gymnophiona).
Based on recent finds of 150 million year old fossilized salamanders in China, it was found that the main groups of salamanders have hardly changed since that time. Even at this time there was a phenomenon in some Lurch species known as neoteny in today's axolotl.
The axolotl (Ambystoma mexicanum), which originally occurs in spotted and white forms in Mexico, has meanwhile become a popular aquarium inhabitant, especially in its white and albinotic forms.
Neoteny is a special type of development into an adult animal in which features of the tadpole stage persist into adulthood. It is associated with a low-iodine environment in which neotenic salamanders develop; i.e. with decreased thyroid function and a deficiency of the thyroid hormone thyroxine. In addition to the axolotl, neoteny also occurs, for example, in the Yugoslav cave olm (Proteus anguineus) or in the European low mountain range in the mountain newt (Triturus alpestris). A close relative of the axolotls, the north-western salamander, Ambystoma gracile, native to the Pacific coast of North America, sometimes grows into a neotenic salamander that lives in the water, sometimes, in contrast to the axolotl, which specializes in water, but also to the land salamander, which seems to be largely dependent of the altitude, at low and medium altitudes mostly land-dwelling salamanders live, at higher altitudes neotenic forms.
In the axolotls, the larval features are clearly visible: bushy outer gills, which they keep for life, and broad skin seams on the back; in addition, a particularly good regenerative capacity of severed gills or limbs has been observed.
Neoteny is not a completely genetically determined condition, it can happen that animals, when they come into an environment containing iodine, still achieve metamorphosis, whereby the gills shrink and the legs grow so that the axolotls can then go ashore, and resemble the tiger salamander (Ambystoma tigrinum), to which they are also closely related. Warmer temperatures and lower air humidity are also named as factors that promote metamorphosis, so that it can be assumed that the axolotl may go ashore when water dries up in order to survive.
Axolotls grow up to 30 cm long and can live up to 25 years. They are native to a few lakes south of Mexico City, most notably Lake Xochimilco.
They belong to the Ambystomatidea family, cross-toothed salamanders, have external gills and a not fully developed lung, the gills are branched, well-perfused tufts on the side of the neck that shimmer reddish in the white axolotls. The water is absorbed through the mouth and pushed laterally outwards through the gill slits. In addition, axolotls swim to the surface of the water from time to time to gasp for air. They prefer water temperatures of 15-22ºC, can also live with 10-25ºC, at less than 10ºC they fall into a cold rigidity similar to amphibians in our latitudes in winter. They are active during the day and at twilight, live with loose contact with their fellow species, and eat smaller aquatic creatures of all kinds. The colors are varied, the wild type is speckled and looks overall washed out gray to blackish gray, possibly with a few light spots, the belly is lighter. The brown axolotl is marbled in various shades of brown, the albino is white with red eyes, the white axolotl is white with dark eyes, the gold albino is yellowish-white, and there are also black axolotls.
The genotypic prerequisites for the color phenomena in Axoltls are somewhat complicated because they are generated by combining several genes, pigment genes for dark, yellow and shimmering pigment, and an additional development gene that influences the expression of the color genes present in each case.
The neoteny of the axolotl can also be viewed as a way back into the water, because presumably there was first the land-living form of the animal, an ancestor of the tiger salamander (Ambystoma tigrinum) or the tiger salamander itself, and due to environmental influences, e.g. a change in living conditions in the area south of Mexico City, the neotenic form of the axolotl, the species Ambystoma mexicanum, arose, which was able to survive under these conditions. It is conceivable, for example, that the salamanders, whose skin must be kept moist at all times, colonized the remaining lakes and rivers as a neotenic form due to the partial drying up of former swamps.
Neoteny is thus one of the evolutionary processes that enable change and bring about the emergence of new species, in the course of evolution it has probably come to the formation of species several times in this way.
Many animal species have made their way back into the water:
Manatees, sea lions and walruses, fur seals, elephant seals, harbor seals and other seals, sea and river otters, aquatic birds (penguin), insectivores (water shrew, muskrat weevil), ungulates (hippopotamus), marsupials (water opossum), rodents (beavers) and water voles Reptiles (crocodile, sea snake), more on this, for example, at http://www.marine-mammals.de.
Some scientists also suspect a neotenic development in the origin of the human species, because humans show some characteristics of young chimpanzees and have a comparatively longer development time to adulthood and also a longer lifespan. In addition, there are theories that are not generally scientifically recognized, that see a connection between water as a habitat and human development, i.e. humans as descendants of apes or early humans, the marine primates or water monkeys, aquarian or aquatic apes.
The name "Axolotl" comes from the ancient Aztec language Nahuatl, and is made up of Atl, which means water, and the name of the god Xolotl. There are various translations of the second part of the name, the god Xolotl also has several epithets, the attentive, the twin (of the god Quetzalquoatl), god of wind, rain and lightning, god of the evening star, companion of the sun in the underworld, god of shape transformation, the singing dog, god of games.
Hence it is that for axolotl one finds the translations water dog, water game, water elf, water monster, water sports, water puppet, water spirit and some more.
Links to axolotls: