4. Placental mammals have now been taxonomically partitioned into two broad groups.
One, Boreoeutheria. This mammal grouping is again supported by phylogenetics. It is also hypothesized that the common ancestor of this clade and its immediate descendants lived in the Northern continent of Laurasia, which was composed of a joined Eurasia and North America. In fact, one of its component clades is named Laurasiatheria. Its other component clade is named Euarchontoglires, to which Glires (rabbits and rodents) and their sister clade Scandentia (treeshrews), Primatomorpha belong. We primates belong to the latter.
Thus funnily, our closest mammalian relatives are rabbits and rodents, and tree shrews.
Tree shrews funnily look like shrews that climb on trees.
Another fascinating hypothesis is that Laurasiatheria is composed of Eulipotyphla (most shrew-like mammals), Chiroptera (bats), and Ferungulata, which in turn is composed of Pholidota (pangolins), Carnivora, and Euungulata (ungulates or hoofed mammalian herbivores).
Thus, ungulates like horses and deer, are closely related to the Carnivorans that predate and eat them.
Surprisingly, bats and most shrews previously were thought to be closely related to the Primate common ancestor (which was shrew-like in form). But in the new phylogenetically supported taxonomy, bats and most shrews are now thought to be more closely related to horses and deer than to us Primates.
Another surprise is that most shrews are more related to horses and deer than they are to rats, mice, and other rodents to which they bear a superficial resemblance.
Still another surprise: Since the pangolins (Pholidota) that lick up ants and termites are Ferungulates, their closest relatives are Carnivorans and … Ungulates, the hoofed herbivores of the planet that munch on plants.
5. Two, the other broad placental grouping is named Atlantogenata, again supported by phylogenetics.
It is hypothesized that the common ancestor of this clade and its immediate descendants lived in the Southern continent of Gondwana, composed of Africa and South America; plus Antarctica, Australia, India, and Arabia.
Atlantogenata’s component clades are hypothesized to be Xenarthra (armadillos, anteaters, and sloths all of which live in South America) and Afrotheria. Afrotheria (mammals that mainly live in Africa) in turn is partitioned into Paenungulata (hyraxes, elephants, dugongs and manatees) and Afroinsectiphilia. Afroinsectiphilia in turn is partitioned into Tubulidentata (represented by a lone survivor – the aardvark) and Afroinsectiphilia. Afroinsectiphilia are mammals that mostly resembles shrews.
Surprise one: The elephant’s closest relative is… the dugong. Hard to believe, isn’t it? One is the planet’s largest land mammal that munches on terrestrial plants; the other resides in the world’s oceans and munches on sea plants. This however explains a longstanding phenomenon. Elephants and dugongs continually grow new teeth throughout their life, while the rest of the placentals do not.
Surprise two. Afroinsectiphilians and Eulipotyphlans used to be classified as one group – shrew-like animals. They all mostly look the same, like shrews. They also have similar behavior, especially their propensity to eat insects. Turns out they are distant relatives among Placentals. Afroinsectiphilians evolved in Africa; Eulipotyphlans evolved in Laurasia, which was composed of a joined Eurasia and North America. Yet they all look and behave like shrews.
Surprise three. Afroinsectiphilians and Eulipotyphlans are mostly shrew-like animals; and many of their members are called ‘shrews’. So are Scandentians – tree shrews. Yet tree shrews are distantly related to Eulipotyphlans within the Boreoeutherians that evolved in the ancient Northern continent; and are even more distantly related to the Afroinsectiphilians, which are Atlantogenatans that evolved in the ancient Southern continent.
Surprise four. Earlier still, both armadillos and anteaters used to be classified together with pangolins and the aardvark.
But pangolins (Pholidota) are Laurasiatherians that evolved in the ancient Northern continent, while armadillos and anteaters are Atlantogenatans that evolved in the ancient Southern continent. Very distantly related.
Meanwhile, aardvarks are also Atlantogenatans, together with the armadillos and anteaters, both evolving in the ancient Southern continent, but the two are distantly related in the Atlantogenatan magnorder.
Surprise five. Dugongs and dolphins both live in the seas and possess paddles instead of feet. But dugongs are Atlantogenatans that evolved in the ancient Southern continent; while dolphins are Boreoeutherians that evolve in the ancient Northern continent. Very distantly related.
Surprise six. Hyraxes look much like rabbits, and eat plants like rabbits. Yet they belong to clade Paenungulata, together with the dugongs and elephants. They are Atlantogenatans that evolved in the ancient Southern continent. Very distantly related.
Rabbits belong to clade Euarchontoglires, together with rodents (with whch they make up the clade Glires) and Primates. They are Boreoeutherians that evolved in the ancient Northern continent.
Looks and habits aside, hyraxes and rabbits are very distantly related.
Do you see the similarities between certain Atlantogenatans and Boreoeutherians? The following occupy the same ecological niches:
Afroinsectiphilians, and Eulipotyphlans and Scandentians, occupy the ‘shrew-like’ niche.
Armadillos and pangolins occupy the armored ant-eating niche.
Dugongs and dolphins occupy the sea mammal niche.
Hyraxes and rabbits occupy the bunny-type plant-eating niche.
What we see here are examples of convergence.
Convergence produces analogous structures with similar appearance and/or function in separate groups that were not present in the last common ancestor of those groups. More about these in future articles. (Send comments and suggestions to mabuhibisaya2017@gmail.com)/PN
