DOLPHINS: THE “WOLVES” OF PREHISTORY
Why do dolphins need to breathe?
You will surely have asked yourself this when you studied and admired these splendid animals swimming in the waves as children; how come, although they possessed extraordinary aquatic abilities, they are forced from time to time to go up the ocean or the river to the surface of the water only to be able to breathe through the blowhole,
that “hole” on the head that allows them to breathe the air without necessarily getting out of the water. And this unusual arrangement is not unique to dolphins, in fact many of the species belonging to the cetacean family are equipped with it, such as the best known whales and porpoises.
This curious “anatomical defect” dates back, as might have been expected, to the origins of this cute animal, where many years ago, strange but true, was just another of the many creatures that populated the wild Earth.
In fact, there are many “clues” that make us understand that dolphins were first terrestrial animals, capable of walking and breathing on solid ground.
One of the first is undoubtedly the fact of being mammals, the most widespread class of vertebrates among living beings, with which it shares most of the characteristics related to being mammal such as thermoregulation through the heat produced by the metabolism, being viviparous, that is, that the development of the embryo takes place inside, the differentiation of the various types of teeth,
and many other traits that, although they may seem common and obvious to our eyes, have really made the difference between survival and extinction, not surprisingly mammals have spread and diversified in every location and shape thanks to the benefits obtained by many of these characteristics, so much so as to evolve into one of the most unnatural, ruthless and lethal creatures but also with the highest rate of evolutionary progress that ever existed: the man.
Another of the properties of mammals is that of owning a fur, which ironically “covers” many roles ranging from camouflage to thermoregulation, which we mentioned earlier.
And even though dolphins nowadays don’t have thick fur to protect them, that doesn’t mean they never had one.
In fact, in the embryonic state, it is still possible to identify small hair follicles in dolphins, which belonged to an ancient pelage presumably similar to that of seals, which regress until disappearing with the course of pregnancy.
It is also possible to see in the dolphin embryos the presence of a subdivision of hind and fore limbs, now suppressed by the evolution of the species, but which suggests a truly fascinating reality in the history of these marine animals.
THE ENIGMATIC ORIGINS OF DOLPHINS
After so many promising premises about their origins, paleontological scientists hurried to find answers that would satisfy everyone’s imagination.
But the identification of the closest descendant of the dolphin proved to be somewhat effortful, due to the absence of an effective change that distinguished itself in the fossils found in the world, but above all because the family to which the dolphins belonged, the Cetacea or cetaceans, were already present on Earth for a very long time, the oldest dated, mind you, back to 50 million years ago in the Eocene era, which made the selection of fossils that were really useful for research even more difficult.
It was only thanks to phylogenetics, the branch of science dedicated to the analysis of similarities between species at the genetic level, and to molecular biology, the study of genetic processes also at the biochemical level, that it was possible to advance on another front, that of genetics.
Thanks to the study on genes, they were able to overcome some of the main problems they had encountered in the investigation of these animals, such as the non-evolutionary accuracy of the distinctions between species, which was based only on the “visual” aspect of these and therefore extremely ambiguous considering the morphological differences that these could have regardless of the evolutionary factor in question, combined with the little information available and the inability to distinguish a change in such a wide time range, a change of direction was necessary to reach results.
And it was genetics in all its infinite fields that gave the answers they longed for.
THE HIPPOPOTAMUS: THE LIVING DESCENDANTS OF THE DOLPHINS
Numerous classifications and taxonomies later, paleontologists were able to breathe a sigh of relief, albeit narrow, for the effort to reach an order of families and classes that would satisfy all the other “nitpicking” paleontologists of the scientific community ready to deprecate and contest, which did not wait certainly to come; finally, in front of them the bases of what would later be the clade were projected, which by definition corresponds to the group composed of a single common ancestor and all its descendants, so much craved, of the Cetacea and the Artiodactyls, another group of species with ungulate legs, the two united in a vast and relatively modern clade which takes the name of, think a little, Cetartiodactyla.
It was therefore legitimate to assume that the dolphins came from species whose appearance approached that of quadruped animals with “claw hooves”, as they fell within the clade of the Cetartiodactyls and in this way even if a little “unconfirmed”, they fell for association in that of the Artiodactyla or even-toed ungulated even if they did not belong directly to it.
Obviously also on this hierarchical misdeed, the paleontologists community had to complain, and tears and rivers of ink were poured to try to remedy the equivocality…
However, from this curious diatribe resulting from the collision of these two “evolutionary families” so different from each other, that of cetaceans made up of marine beings and that of the terrestrial artiodactyls from which the dolphins originated, it can be distinguished that the foundation of that “missing link” that connects them both, lies on the passage from land to water.
In fact, it is precisely the Hippopotamidae, the order of the Artiodactyla, that fill the void in the evolutionary hierarchy of dolphins, at least as far as living animals of today are concerned.
The common and voluminous hippopotamus, from the Greek which means “river horse” due to the morphological similarities especially of the muzzle, is in fact a mammal (like the dolphin) belonging to the order of the Artiodactyls (also like the dolphin) and as the study on the phylogenetics of this animal tell us, the closest living ancestor of the cetaceans, much closer than it is for the artiodactyls indeed, which bears witness to the fact that we cannot really trust morphology if we are talking about the species.
Distinguished semi-aquatic creature, very imposing and apparently peaceful, the hippopotamus is able to launch fierce and merciless attacks without too many scruples. Many interesting documentaries crown them as protagonists precisely because of their not evident “temper”, much more aggressive and resolute than that of rhinos for example, which because of their pointed horns and their territorial instinct, have obtained a bad reputation which, however, should be the same as, if not inferior, to that of their neighbors the hippos, better seen instead by common opinion.
Returning to the hippos, since there is this strong relationship with the cetaceans, between the groans of the paleontologists who had to conceive another one from scratch, the need arose to create a further new specific clade that contemplated all the ramifications of these two “evolutionary families”, thus defining a clade crown group, or a clade composed of two lines still present and living today and all their ancestors and current descendants, so as to consider every possible combination, which was called Whippomorpha or with the most unknown name and graceless Cetancodonta.
The discovery of a surprisingly complete and in good condition skeleton of Indohyus (a primitive mammal similar to a raccoon) in the locality of Kashmir, connected to a now extinct family belonging to the clade Whippomorpha and therefore to that of the Artiodactyls, the Raoellidae, which for this reason were considered for some time one of the “missing pieces” in the genealogical puzzle of cetaceans and therefore of dolphins.
The careful study of the findings brought to light numerous “apparently discordant” tests that supported this thesis, such as being partially aquatic due to the bone structure designed for movement in water, and at the same time finding a food lifestyle based instead on dry land, which led to believe that it had reached a potential transition model capable of acting as a gateway between the aquatic and terrestrial world.
Unfortunately, even though there was in fact an approach to solving the riddle, there were still too many questions to which this archaic family of Raoellidae could not give concrete answers.
THE ARCHEOCETI: THE EXTINCT DESCENDANTS AND THE TRUE PRECURSORS OF THE DOLPHINS
Archaeoceti are well defined by their name as the “archaic order” of cetaceans and the true precursors of dolphins on Earth, as well as being consequently their closest extinct descendants.
These creatures, divided into 5 official families (and a sixth still disputed arduously among paleontologists for its “most appropriate” assignment, which for this reason I will avoid mentioning it), complete the evolutionary arc of cetaceans in their “amphibious” phase at Eocene epoch:
Pakicetidae : The size and physiognomy of a modern wolf, with tapered legs and even a tail. These animals moved in the water but never made it their habitat preferring instead the riparian areas, and for this reason they are supposed to not have very advanced swimming skills.
Of this family, due to the scarcity of fossils found, the assumptions are generic, based much more on correspondences than anything else. Mostly teeth and skull fragments have been recovered, so the analysis is based more on this aspect, but still sufficient to confirm the behavioral and genetic connection, finding in them many similarities with those of modern cetaceans.
These creatures in the smaller species had sharp teeth like those of today’s carnivorous fish, and in the larger and predatory versions they looked a lot like hyenas. Certainly they were carnivorous animals, with a vast assortment of species dedicated to predation or carrion eating.
Ambulocetidae: In this evolution, they had already assumed a predominant aquatic behavior, and for the bone conformation reported in the fossils and the elongated shape of the snout and nostrils, it can be assumed that they preferred the water areas for hunting based on ambushes and sudden attacks, similar to that of the crocodiles which in fact recall their appearance.
Due to their aquatic and feeding habits, the limbs had undergone an important reduction, since they could no longer support themselves on the ground, which is why they certainly increasingly adapted to aquatic life in order to survive.
Remingtonocetidae: Due to the regression of the legs, adaptation proved to be vital to balance the disadvantages due to the decrease in mobility imposed by this evolution, and probably for this reason, another part of the body of these animals began to strengthen, the tail, which allowed them to increase swimming skills above normal.
Here too, the fossils vary in species and size, which reach a varied range as for those of the two previous families, while still maintaining a similar morphology such as the large snout and an increased hearing capacity very useful for ambushes.
Protocetidae: This family distinguished itself for having mastered the use of the very strong tail thanks to which they could dominate the relative low waters as avid predators.
It is precisely in this evolutionary transition, that we have a change in the nasal opening of these primitive dolphins, which to adapt to the almost aquatic environment in which they found themselves, developed a very advantageous mutation to stay longer under water, allowing them to move the nasal opening a little higher in the head than the other families, defining a prehistoric blowhole still not well developed.
Horizontal breathing was the basis of the morphological structure of the current cetaceans and dolphins, which still possess this attribute of which, however, they have lost the use and function they once assumed for these fantastic ocean hunters.
Unfortunately and consequently, a considerable reduction of the hind limbs again took place, pushing their evolution in one direction only, that of the sea.
Basilofosauridae: This is the definitive transition that assumed all the evolutionary benefits of the previous ones into a single and feared predator of the waters that has now completely stabilized, and that of Earth no longer wanted to deal with it (not that it was not even able by now, given the inability to subsist out of the water)
This family of Archaeoceti possessed the partial aspect of a modern dolphin, both for the rear part already developed in the “typical tail” with the flukes, the last remains of the hind limbs, that for the differentiation of the typical cetacean teeth. The popular Dorudon, a little better known for its cultural presence, that belongs to this family.
The extinction of these cetacean precursors was not of course total, given that the descendants are a definitive proof of their survival, but many of the species belonging to this order were severely halved, probably due to climate change or competition with other aquatic species that spread in later ages.
SOME CURIOSITIES ABOUT DOLPHINS
“Fingers” in the pectoral fins:
Among the various “evolutionary wrecks” that drag these wonderful aquatic animals, one of the most interesting ones without needing to go into detail, is that of the vestigial phalanges that are still present and visible through the x-rays in the flippers, and even if their usefulness both by division of the fin and by type of mobility has been completely neglected in evolution, they prove to be a hidden proof of their origins as quadrupeds with legs.
Aquatic peculiarities and hydroacoustics:
The unique and singular characteristics of cetaceans and dolphins are many and numerous, from the aerodynamic shape of the body, harmonized specifically for an aquatic lifestyle, up to the presence of the “uncomfortable” breather or blowhole that will disappear sooner or later to leave room for a more convenient breathing method.
In particular, dolphins have the recognizable fat structure on the forehead called melon, which for example porpoises do not have, and which is supposed to be a main component of the ability of echo-localization, as it performs a bioacoustic function for the specific substances of which is composed of such as the wax ester and the air that surrounds them, which helps them navigate the seas like a real biological sonar.
This interesting and useful attribute dates back to the Archaeoceti, who developed greater hearing underwater which gradually became more refined, so as to identify waves and echoes at a lower frequency.
For some scholars, the presence of the melon could also be one of the factors that determined the extraordinary ability to control the buoyancy that these animals possess, reasoning perhaps supported by the reports found in some species of dolphins to the increase of size of the melon and underwater performance, but it is probably more a case of correlation than causality.
The praiseworthy intelligence of the dolphin:
The well-known “intelligence” of dolphins is appreciated and recognized not only by experts but also by common opinion, considered and represented in social and cinematographic cultures.
But not everyone will know how this intelligence is calculated, and maybe they are curious about it.
First of all there are two different methods for defining the intelligence of the species, the first is that on the proportion of brain-body weight, which as the whole terminology clearly shows, it is a study relating to the ratio that exists in the calculation of the brain mass in relation to that of the body. As we can see from the scarcity of criteria analyzed, this is the least precise system, and is to be considered as a rough estimate of the intelligence of a species, which in fact leaves out many fundamental parameters such as their cognitive abilities, the metabolic factor etc.
On this scale, the most “intelligent” would be the treeshrews (Scadentia), rather agile rodents, followed by man. Dolphins are the most intelligent of all cetacean species.
The second method, on the other hand, is that of the encephalization quotient or EQ, which is more accurate because it takes into account the allometric values of the species studied, i.e. those related to shape, physiology, anatomy and other social and behavioral aspects that make it more complex and technical of the first but definitely also more complete and precise, besides being the one to which we refer when we speak of the fact that dolphins are the “most intelligent animals in the world”.
In the first place of this ranking, persists the omnipresent man (although it doesn’t seem so), while the second, third and fourth place are dedicated to the large family of Delphinidae, in particular two species of river and ocean dolphins and the famous killer whale.
Some of the photos used in this article are redirected to the wiki that indicate the author in accordance with the CC license with some rights reserved. As always, we thank their respective authors for their cordial availability and valuable contribution.
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