SINCE the 1990s, phylogenetics has ushered in several surprising hypotheses on mammalian classification. Herein, we limit ourselves mostly to placental mammals.
A quick word on phylogenetics. Phylogenetics is the study of the evolutionary history of organisms deducing, using genes, protein amino acid sequences, and morphology, the relationships among them.
Note that before the 1990s, biologists were limited mostly to morphology, the study of the visible form of an organism, that is to say its outside shape and the shape of internal organs and bones. Then in the 1990s, extensive studies began on genes and protein amino acid sequences.
Some surprising things, and the confirmation of some of the traditional classifications as well:
1. Cetaceans, which are whales, dolphin and porpoises, are most closely related to hippopotamuses, forming the clade Whippomorpha. The Whippomorpha are in turn closely related to Ruminantia, the often-seen ruminants such as cattle, goats, carabaos, deer, antelopes, and so on. The Whippomorpha (whales, dolphin and porpoises, and hippopotamuses) and Ruminantia (ruminants) in turn form the clade Cetruminantia. Cetrumninants are mainly herbivores that have multiple stomachs that aid in digesting the cellulose and hemicelluloses of plant material. Cetruminantia’s closest relative in turn is Suina, which are non-ruminating pigs and peccaries. Cetruminantia and Suina in turn form the clade Artiofabula. Artiofabula in turn is related to the clade Tylopoda which are the camelids (camels and llamas).
All of the above form the order Artiodactyla, which are the even hoofed ungulates.
It can be seen from the above that Cetaceans, the which are the whales, dolphin and porpoises, are even hoofed ungulates (Artiodactyls) that went to live in the sea. Consequently, Artiodactyla is also referred to as Cetartiodactyla.
In so doing, the Cetaceans shifted their mostly herbivore plant-eating diet to a hypercarnivore all-meat diet (fish and crustaceans, such as krill, copepods, and so on).
Artiodactyls have multiple stomachs. This explains a long-standing puzzle. While the other main group of marine mammals, which are the seals, have only one stomach (being members of the single stomached order Carnivora), Cetaceans have multiple stomachs.
Not only that. The Cetaceans also have a microbial community in their stomachs that resembles those of land-based (terrestrials) Artiodactyls. These microbes can break down cellulose, hemicelluloses, and of import to crustaceans-eating Cetaceans, chitin, which consists 10% of arthropods (including crustaceans) by weight. Chitin has a chemical formula similar to cellulose, and consequently most animals cannot thoroughly digest it.
The Cetaceans’ multiple stomachs, which have a microbial community that can digest chitin, give them and advantage over the single stomached seals. This could be the main reason why seals never evolved a form that is completely oceanic, living and giving birth in the seas and never coming on land. The Cetaceans, with their chitin digesting ability, competitively excluded them. (On the other hand, Carnivorans, with their carnassial teeth that can act like scissors to shear flesh and bone, had an advantage over terrestrial Cetaceans that had already turned to predating and scavenging on animals. The original mostly land-based carnivorous Cetaceans such as Pakicetus lacked carnassial teeth. Thus, ancestral carnivorous Carnivoran seals may eventually have had competitively excluded ancestral carnivorous Cetaceans from the land.)
Just imagine that Cetaceans once had actual hooves and ate plants.
Funnily, when an orca (an Artiodactyl Cetacean) predates and eats a seal (a Carnivoran closely related to Mustelid weasels and Ursid bears), you have an Artiodactyl predating on a Carnivoran. It’s like a deer eating a lion.
Of great import is also the unearthing of fossils of the family Raoellidae. A typical Raoellid such as Indohyus looked and lived like a mouse deer, also called chevrotain, which are Ruminantia (ruminants). Paleontologists know that Raoellids were Cetaceans because of a unique middle ear set of bones that can be found only in whales, dolphin and porpoises. And not in extant terrestrial ruminants like the mouse deer.
In addition, phylogenetic studies confirm the traditional view that Artiodactyla (even hoofed ungulates) and Perissodactyla (odd toed ungulates such as horses, tapirs, and rhinoceroses) are most closely related to each other, forming the clade Euungulata, which are the ungulates or hoofed mammals.
2. The clade Euungulata, which are the ungulates or hoofed mammals, are most closely related to the order Carnivora – dogs and cats, and other Carnivorans that resemble them. Thus funnily, the larger canids (dog-like form) and felids (cat-like form) predate and scavenge mostly their closest relatives among mammals.
3. Glires, the clade that encompasses the orders Lagomorpha (rabbits, hares, and pikas) and Rodentia {rodents}, are most closely related to Primatomorpha (Dermoptera or colugos) and Primates. And humans are Primates. Thus funnily, we are more closely related to say the rats and mice (which are rodents) than to dogs and cats, bats, cattle, carabaos, and all other mammals.
More about these in future articles. (Send comments and suggestions to mabuhibisaya2017@gmail.com)/PN
