BY DR. JOSE PALU-AY DACUDAO
IT’S ALMOST instinctive to classify such mammals as camels, pigs, hippopotamuses, and ruminants (deer and bovids such as cows, carabaos, goats) as belonging together. Indeed, they do, in the biological order artiodactyla. They are all even-toed ungulates. In other words, they are hoofed mammals that walk on an even number of toes. They walk and run on two toes. This is an adaptation to running fast as almost all of them are dedicated herbivores and are often prey to carnivores.
(Think of it this way. When walk normally, we do so on our tarsal bones meaning our heel and ankles. When we run, we do so mostly on our metatarsal bones, our ‘midfoot’. We can’t run on our phalanges, our toes, but ungulates do. That allows them to run even faster in order to escape carnivores.)
Most artiodactyls are foregut fermenters. Mammals never evolved cellulase enzymes that degrade cellulose, the most common plant component. Thus, artiodactyls have multiple stomachs (multichambered) that allow them to host the bacteria needed to ferment hard-to-digest plant material such as cellulose. Except pigs, which have one stomach, but then again pigs are omnivores, and will also eat lots of meat if available. Meat is a lot easier to digest than plants, and so you need only one stomach for it.
Other ungulates walk and run on an odd number of toes, the order perissodactyla. This includes rhinoceroses and tapirs, which walk on three toes; and horses which walk on one toe. Perissodactyls are hindgut fermenters. They mostly have a huge cecum, an extension of the large intestine, which houses bacteria that can hydrolyze cellulose.
Both artiodactyla and perissodactyla are grouped under the same clade, the ungulates (ungulata). No surprise there. These are mainly hoofed dedicated herbivores; whose diets are almost all plants.
Note however that foregut fermenters with multichambered stomachs digest food more efficiently than hindgut fermenters. Why? The degradation of plant matter occurs in the proximal part of the gastro-intestinal tract (GIT), the stomach, in foregut fermenters; thus, food can still get further digested in the intestines. While in hindgut fermenters, the abundant cellulose of plants starts getting seriously degraded only in the distal part of the GIT, the cecum and large intestine.
Commonsensically, for an embryo it’s harder developmentally to make multiple stomachs compared to only one. But as we can see from the above, once the resulting herbivore starts eating plants, the ones with multiple stomachs will have a decided advantage over those with only one stomach.
Do ecosystems bear this out? Yes. The large herbivore niche in terrestrial ecosystems is dominated by artiodactyls with multiple stomachs rather than perissodactyls. In other words, there are a lot more deer, antelopes, goats and other artiodactyls than horses, tapirs, and rhinos. Both in species and numbers. (To be continued)/PN
