[By Chuck Almdale]

We now have only the mammal class to describe, but there’s a lot of ground to cover. As further illustration of how the clade system adds much more detail (lineage branches and nodes of division), we’ll repeat what we did in Taxonomy 6 and start at the top with Domain and use the subscript numbers to keep track of the steps. The subscript will again be on “Clade” which we’ll apply to every rank whether it already has a Linnaean rank or not, just to be uniform. Linnaean ranks (kingdom, phylum, class, order…superclass…suborder, etc.) are clades in concept, and were so long before the term “clade” was invented. But, as mentioned previously, with the discovery of molecular clocks and DNA analysis, the ability to discover the points of separation between lineages took a quantum leap forward.

The mammalian line follows the line for the previously presented chordate classes – amphibians, reptiles, snakes, crocodiles and birds through Clade₂₀ Amniota (or Class Reptilia) below. At Clade₂₁ Synapsida the line towards the mammals diverges from that towards lizards, snakes, turtles, crocodiles and birds.

Clade₁ Domain Eukaryota, Clade₂ Kingdom Animalia, Clade₃ Subkingdom Eumetazoa, Clade₄ ParaHoxozoa (Planulozoa), Clade₅ Infrakingdom Bilateria, Clade₆ Superphylum Deuterostomia, Clade₇ Phylum Chordata, Clade₈ Olfactores, Clade₉ Subphyla Craniata (Vertebrata), Clade₁₀ Infraphylum Gnathostomata, Clade₁₁ Superclass Osteichthyes, Clade₁₂ Sarcopterygii, Clade₁₃ Rhipidistia, Clade₁₄ Tetrapodomorpha, Clade₁₅ Eotetrapodiformes, Clade₁₆ Elpistostegalia, Clade₁₇ Stegocephali, Clade₁₈ Superclass Tetrapoda, Clade₁₉ Reptiliomorpha (or Pan-Amniota), Clade₂₀ Amniota (or Class Reptilia), Clade₂₁ Synapsida, Clade₂₂ Eupelycosauria (or Metopopora), Clade₂₃ Sphenacodontia, Clade₂₄ Sphenacodontoidea, Clade₂₅ Therapsida, Clade₂₆ Theriodontia, Clade₂₇ Eutheriodontia, Clade₂₈ Cynodontia, Clade₂₉ Epicynodontia, Clade₃₀ Eucynodontia, Clade₃₁ Probainognathia, Clade₃₂ Prozostrodontia, Clade₃₃ Mammaliamorpha, Clade₃₄ Mammaliaformes, and
Clade₃₅ Class Mammalia – Mammals: Translation “of the breast.”  Mammals uniquely possess: milk-producing mammary glands for feeding young, a neocortex region of the brain, fur or hair, and three middle ear bones. Their ancestors first appeared in the Carboniferous Period over 300 million years ago. There are approximately 6,400 extant described species, divided into 27 orders, give or take a few depending (as always) on who is counting. Below the level of Class Mammalia the taxonomic systems multiply incompatibly. Rather than become utterly confusing, I’ll stick with the mildly confusing and use a fairly simple system. The important Linnaean ranks and a few important clades are in blue, including all 27 orders. Important divergences get a comment, e.g. “The line towards Monotremes diverges from other mammals, then diversifies into two families.“

There is a list of all twenty-seven mammalian orders with totals for family, genera and species following the illustrated indented sequence below.

You probably skimmed the above (and mildly annoying) list. Here’s the same thing, indented. It takes up more space, but is much easier to read. It also leaves room for very short notes.

Clade₁ Domain Eukaryota
 Clade₂ Kingdom Animalia
  Clade₃ Subkingdom Eumetazoa
   Clade₄ ParaHoxozoa (Planulozoa)
    Clade₅ Infrakingdom Bilateria
     Clade₆ Superphylum Deuterostomia
      Clade₇ Phylum Chordata
       Clade₈ Olfactores
        Clade₉ Subphyla Craniata (Vertebrata)
         Clade₁₀ Infraphylum Gnathostomata
          Clade₁₁ Superclass Osteichthyes
           Clade₁₂ Sarcopterygii – [Link] Lobe-finned fish
            Clade₁₃ Rhipidistia
             Clade₁₄ Tetrapodomorpha
              Clade₁₅ Eotetrapodiformes
               Clade₁₆ Elpistostegalia
                Clade₁₇ Stegocephali
                 Clade₁₈ Superclass Tetrapoda – [Link] Amphibian divergence
                  Clade₁₉ Reptiliomorpha (or Pan-Amniota)
                   Clade₂₀ Amniota (or Class Reptilia) – Last common ancestor reptiles & mammals
                    Clade₂₁ Synapsida – [Link] The line to mammals line diverges from the reptilian line
                     Clade₂₂ Eupelycosauria (or Metopopora)
                      Clade₂₃  Sphenacodontia
                       Clade₂₄ Sphenacodontoidea
                        Clade₂₅ Therapsida
                         Clade₂₆ Theriodontia
                          Clade₂₇ Eutheriodontia
                           Clade₂₈ Cynodontia
                            Clade₂₉ Epicynodontia
                             Clade₃₀  Eucynodontia
                              Clade₃₁  Probainognathia
                               Clade₃₂ Prozostrodontia
                                Clade₃₃ Mammaliamorpha
                                 Clade₃₄ Mammaliaformes
                                  Clade₃₅ Class Mammalia – [Link] Mammals

Moving the line back to the left, we start with Clade₃₅ Class Mammalia – Mammals.

Clade₃₅ Class Mammalia – Mammals

The line towards Monotremes diverges from other mammals, then diversifies into two families.

 Clade₃₆ Order Monotremata – [Link] Translation “single-opening;” two families of egg-laying, live-bearing, milk-producing, furry monotremes.
  Clade₃₇ Family Tachyglossidae: [Link] four species of Echidna.
  Clade₃₇ Family Ornithorhynchidae: [Link] one species of Duck-billed Platypus.
Monotremes, clockwise from upper left: Platypus, Short-beaked Echidna, Eastern Long-beaked Echidna (replica, New Guinea), Western Long-beaked Echidna. Wikipedia: Monotreme 

 Clades_(36-42) Crown group and branches to extinct taxa. Clade₃₆ is sister taxon to Monotremata.
  Clade₄₃ Subclass Theria – [Link] Last common ancestor marsupials and placentals.

The lines into sister taxa Metatheria (Marsupials) and Eutheria (Placentals) diverge; Marsupials diversify into seven orders.

   Clade₄₄ Metatheria (Marsupialiformes) – All Marsupials. Sister taxon to Eutheria (Placental Mammals).
    Clade₄₅ Infraclass Marsupialia – [Link] Pouched animals. The young are born in a relatively undeveloped state, then nurtured within a pouch on their mother’s abdomen; primarily in Australasia. There are seven orders of Marsupials in three groups.
     Clade₄₆ Order Didelphimorphia – [Link] Opossums. Translation “two-womb-form;” 1 family, 126 species in the Americas, 1 species north of Mexico.
Female Virginia Opossum (Didelphis virginiana) with nine young, the only U.S. and Canadian marsupial species. Photo: Specialjake. Wikipedia: Opossum

     Clade₄₆ Order Paucituberculata – [Link] Shrew Opossums. Translation “few bumps (on teeth)”; 1 family, 7 species in South America.
Eastern Caenolestid (Caenolestes sangay), South America.
Photo: Jbritomolina. Wikipedia: Paucituberculata 

     Clade₄₆ Superorder Australidelphia (or Agreodontia) Originating in Gondwana, 5 orders, 266 species mostly in Australasia.
      Clade₄₇ Order Microbiotheria – [Link] Little Monkey of the Mountain. Translation “small wild animal;” 2 species in SW South America, extinct species in Australia & South America.
Monito Del Monte or Colocolo Opossum (Dromiciops gliroides).
Photo: José Luis Bartheld. Wikipedia: Microbiotheria 

      Clade₄₇ Order Diprotodontia – [Link] Kangaroos, Wallabies, Possums, Koalas, Wombats. Translation “two forward teeth;” mostly carnivorous (or insectivorous); 11 families, 151 species in Australia and New Guinea. 
Kangaroo Island Kangaroo (Macropus fuliginosus fuliginosus) displaying his or her two forward teeth, Kangaroo Island, South Australia.
Photo: DiverDave. Wikipedia: Diprotodontia 

      Clade₄₇ Grandorder Agreodontia
       Clade₄₈ Order Dasyuromorphia – [Link] Numbat, Quoll, Marsupial Mice, Tasmanian Devil. Translation “hairy tail;” mostly carnivorous (or insectivorous); 3 families, 88 species in Australia and New Guinea. 
Numbat (Myrmecobius fasciatus), Dryandra Woodland, Western Australia.
Photo: JJ Harrison. Wikipedia: Dasyuromorphia 

       Clade₄₈ Order Notoryctemorphia – [Link] Marsupial Moles. Translation “southern-digger-form;” specialized to forage through loose sand; 1 family, 2 species in Australian interior.

Northern Marsupial Mole (Notoryctes caurinus) eating a gecko in the Tanami Desert,  Northern Territory, Australia. Source: Australian Geographic.
Photo: Auscape Int’l Pty Ltd via Alamy.  Wikipedia: Notoryctidae 

       Clade₄₈ Order Peramelemorphia – [Link] Bandicoots and Bilbies. Translation “pouched badger;” 3 families, 23 species in Australian interior.
Greater Bilby (Macrotis lagotis), Australia.
Photo: Kevin503. Wikipedia: Peramelemorphia 

Following are the remaining mammals, nineteen orders of placentals. 

   Clade₄₄ Eutheria – [Link] Placental Mammals. Sister taxon to Infraclass Marsupialia. Translation “true beasts;” all placental mammals, numerous differences in skeletal and tooth structure. There are eleven clades (as of 12 Aug 2024) between Clade Eutheria and Infraclass Placentalia which branch off only to extinct species. We’ll omit listing them (I could not find their names, if any) and go directly to Infraclass Placentalia which contains all extant placental mammals.
     Clade₅₆ Infraclass Placentalia – [Link] All extant placental mammals. Two groups: Atlantogenata and Boreoeutheria.
      Clade₅₇ Atlantogenata: [Link] Two radiations: Xenarthra (So. American) & Afrotheria (African).
       Clade₅₈ Superorder Xenarthra – [Link] So. American placentals. Two orders: Cingulata and Pilosa.
        Clade₅₉ Order Cingulata – [Link] Armadillos. Translation “belted;” 2 families, 22 species.
Glyptodont (Glyptodon asper),(Vienna Museum), lived throughout the New World until c. 10,000 BCE; Nine-banded Armadillo (Dasypus novemcinctus), lives throughout the New World.
Photo: Hunadam, Tomfriedel. Wikipedia: Cingulata 

        Clade₅₉ Order Pilosa – [Link] Anteaters and sloths. Translation “hairy;” 4 families, 17 species.
Giant anteater (Myrmecophaga tridactyla) Mato Grosso, Brazil.
Photo: Nortondefeis. Wikipedia: Pilosa 

       Clade₅₈ Superorder Afrotheria – [Link] African origin placentals. Sister taxon to Xenarthra. Two groups: Paenungulata and Afroinsectiphilia.
        Clade₅₉ Grandorder Paenungulata: [Link] Two groups: Hyracoidea and Tethytheria.
         Clade₆₀ Order Hyracoidea – [Link] Hyraxes. Translation “Greek for shrew-mouse;” 1 family, 6 species.
Young Hyrax on Mount Kenya, widespread in Africa.
Photo: Josski at Dutch Wikipedia. Wikipedia: Hyrax 

         Clade₆₀ Mirorder Tethytheria – [Link] Sister taxon to: Hyracoidea. Two groups: Sirenia and Proboscidia.
          Clade₆₁ Order Sirenia – [Link] Sea Cow & Dugong. Translation “of the Sirens (Greek mythical creatures);” 2 families, 4 species.

Dugong near Marsa Alam, Egypt. Range E. Africa to West Pacific.
Photo: Thomas Breuer. Wikipedia: Sirenia 

          Clade₆₁ Order Proboscidea – [Link] Elephants. Translation “nose, esp. if long;” 1 family, 3 species.
Forest elephants (Loxodonta cyclotis), Nouabalé-Ndoki National Park, Congo. Photo: Thomas Breuer. Wikipedia: Proboscidea 

        Clade₅₉ Grandorder Afroinsectiphilia: [Link] Sister taxon to: Paenungulata. Two groups: Tubulidentata and Afroinsectivora.
         Clade₆₀ Order Tubulidentata – [Link] Aardvark. Translation “tube-tooth;” 1 family, 6 species.
Aardvark (Orycteropus afer), sub-Saharan Africa.
Photo: Kelly Abram. Wikipedia: Aardvark 

         Clade₆₀ Mirorder Afroinsectivora: [Link] Sister taxon to Tubulidentata. Two orders: Macroscelidea and Afrosoricida.
          Clade₆₁ Order Macroscelidea – [Link] Elephant shrews. Translation “long-leg;” 1 family, 20 species.
Black and rufous elephant shrew (Rhynchocyon petersi), non-Saharan Africa.
Photo: Joey Makalintal. Wikipedia: Elephant Shrew 

          Clade₆₁ Order Afrosoricida – [Link] Shrews & Tenrecs. Translation “African shrew-like;” 3 families, 55 species.
Lesser Hedgehog Tenrec (Echinops telfairi), Central Africa & Madagascar.
Photo: Wilfried Berns. Wikipedia: Afrosoricida 

      Clade₅₇ Magorder Boreoeutheria – [Link] Most males have a scrotum. Sister taxon to Atlantogenata. Two groups: Euarchontoglires and Laurasiatheria.
       Clade₅₈ Superorder Euarchontoglires: [Link] Two groups: Glires and Euarchonta.
        Clade₅₉ Grandorder Glires: [Link] Two groups: Rodentia and Lagomorpha.
         Clade₆₀ Order Rodentia – [Link] Rodents. Translation “gnawer;” continuously growing incisors; 35 families, 2,680 species.
Capybara (Hydrochoerus hydrochaeris) with Cattle Tyrant (Machetornis rixosa), both feeding; largest rodent in the world, up to 4.5 ft. & 150 lbs. South America. Photo: Fidel León Darder. Wikipedia: Rodent 

         Clade₆₀ Order Lagomorpha – [Link] Rabbits & Picas. Translation “hare-shape;” 3 families, 111 species.
Large-eared Pika (Ochotona macrotis) in Ladakh.
Photo: Karunakar Rayker. Wikipedia: Lagomorpha 

        Clade₅₉ Grandorder Euarchonta: [Link] Sister taxon to Glires. Two groups: Scandentia and Primatomorpha.
         Clade₆₀ Order Scandentia – [Link] Treeshrews. Translation “climber;” 2 families, 23 species.
Pygmy Treeshrew (Tupaia minor), native to SE Asia.
Photo: Paul J. Morris. Wikipedia: Treeshrew 

         Clade₆₀ Mirorder Primatomorpha: [Link] Sister taxon to Scandentia. Two orders: Dermoptera and Primata.
          Clade₆₁ Order Dermoptera – [Link] Colugos. Translation “skin-wing;” 2 families, 2 species.
Sunda Flying Lemur (Galeopterus variegatus). Colugos (which are not lemurs and cannot fly) are arboreal gliding mammals found in SE Asia.
Photo: Lip Kee Yap. Wikipedia: Colugo 

          Clade₆₁ Order Primata – [Link] Sister taxon to Dermoptera. Lemurs, Tarsiers, Simians. Translation “first, prime;” 19 families, 517 species.
Female Pygmy Slow Loris (Nycticebus pygmaeus) of SE Asia, clinging to a human arm. Photo: Lionel Mauritson. Wikipedia: Primate 

       Clade₅₈ Superorder Laurasiatheria: [Link] Sister taxon to Euarchontoglires. Two groups: Eulipotyphla and Scrotifera.
        Clade₅₉ Order Eulipotyphla – [Link] Hedgehogs, moles, true shrews, soledons. Translation “truly fat and blind;” 5 families, 584 species.

Young European hedgehog (Erinaceus europaeus).
Photo: Michael Gäbler. Wikipedia: Eulipotyphla 

        Clade₅₉ Scrotifera: [Link] Sister taxon to: Eulipotyphla.Two groups: Chiroptera and Ferungulata.
         Clade₆₀ Order Chiroptera – [Link] Bats. Translation “hand-wing;” 21 families, 1466 species.

Newborn foundling Common Pipistrelle (Pipistrellus pipistrellus), 3 cm., on the back of a hand. Photo: Mnolf. Wikipedia: Bat 

         Clade₆₀ Grandorder Ferungulata: [Link] Translation “wild-beasts & ungulates.” Sister taxon to: Chiroptera. Two groups: Pan-Euungulata and Ferae.
          Clade₆₁ Pan-Euungulata Sister taxon to: Ferae.
           Clade₆₂ Mirorder Euungulata: [Link] Two groups: Pan-perissodactyla and Paraxonia.
            Clade₆₃ Pan-perissodactyla Sister taxon to Paraxonia.
             Clade₆₄ Perissodactylamorpha
              Clade₆₅ Order Perissodactyla – [Link] Odd-toed ungulates. Translation “odd-toe;” includes horses, zebras, rhinoceroses, tapirs; digest cellulose in their intestines; 3 families, 18 species.  

Quagga, extinct subspecies of zebra.
Photo: Frederick York (d. 1903). Wikipedia: Perissodactyl 

            Clade₆₃ Paraxonia Sister taxon to: Pan-perissodactyla
             Clade₆₄ Order Artiodactyla – [Link] Even-toed ungulates. Translation “even-toe;” includes cetaceans, hippopotamuses, antelopes, deer, giraffes, camels, llamas, sheep, goats and cattle; digest cellulose in their stomachs; 23 families, 360 species.

Artiodactyls, clockwise from upper left: Giraffe, American Bison, Dromedary Camel, Wild Boar, Orca, Red Dear. Wikipedia: Artiodactyl 

          Clade₆₁ Mirorder Ferae – [Link] Sister taxon to: Pan-Euungulata. Two groups: Pan-carnivora and Pholidotamorpha.
           Clade₆₂ Pan-Carnivora Sister taxon to Pholidotamorpha.
            Clade₆₃ Carnivoramorpha (Carnivoriformes)
             Clade₆₄ Order Carnivora – [Link] Carnivores. Translation “flesh-devour;” 16 families, 310 species.  
Carnivores, clockwise from upper left: Binturong (SE Asia), Raccoon, American Mink, Walrus, Fossa (Madagascar), Indian Grey Mongoose.
Wikipedia: Carnivora 

           Clade₆₂ Pholidotamorpha Sister taxon to Pan-carnivora.
            Clade₆₃ Order Pholidota – [Link] Pangolins or Scaly Anteaters. Translation “horny-scale;” 1 family, 8 species. Wikipedia – Pangolin Philippine Pangolin (Manis culionensis), curled-up mother and pup.
Photo: Shukran888. Wikipedia: Pangolin 

According to a self-described “mammalogist who works on mammal taxonomy and systematics” the Mammal Diversity Database is the “best and most up-to-date source for mammal taxonomy,” as it “gets regularly updated based on reviews of taxonomic changes in the primary literature.” Although the sequence of Orders on their website was different from what I have been following, I used their data for the following chart of 27 Orders of mammals while – for the sake of internal consistency – following the sequence I had already adopted. There are plenty of clades between Infraclass Placentalia and these orders which I shall not mention. Judging by the numbers below, rodents are the most important mammals, well ahead of the second-place bats. Primates are in forth place, edged out by shrews.

Another way of looking at Class Mammalia is the round phylogenetic tree below (the common ancestor root is not identified, so it’s not a cladogram). This one shows a sample of 126 mammal species, or a whopping 1.9% of the complete 6,611 species. Still, it’s enough to build a tree as it averages almost 6 species per order. The relationships are shown, but the length of lines do not  represent dates or elapsed time, as all the smallest “steps” are of equal length, something that doesn’t happen in the real world of evolution.

The major clades are colored: Marsupials (magenta), Xenarthrans (orange), afrotherians (red), laurasiatherians (green), and euarchontoglires (blue). To get you started, Ornithorhynchus is the Platypus in order Monotremata,  and the Xenarthrans (below) are members of the above orders of Cingulata and Pilosa. The rest is straightforward.

Here’s a question that we’ll address in a future posting.
Find the three species of horses (Equus) at about 5 o’clock, the cats (Felis) at about 6 o’clock, and cattle (Bos) at 9 o’clock. Which, if any, of these three is most closely related to the Armadillo (Dasypus) at about 4 o’clock? And why? Answer is at the very bottom.

Genus-level molecular phylogeny of 116 extant mammals inferred from the gene tree information of 14,509 coding DNA sequences.
Produced by OrthoMaM team, Institute of Evolutionary Sciences of Montpellier & University of Montpellier.  Original paper – OrthoMaM: A database of orthologous genomic markers for placental mammal phylogenetics. Ranwez V., Delsuc F., Ranwez S., Belkhir K., Tilak M. & Douzery E. J. P. BMC Evolutionary Biology, 2007, 7 : 241.
WEBLINK: https://en.wikipedia.org/wiki/Mammal#Molecular_classification_of_placentals

The Taxonomy Series

Installments post ever other day; installments will not open until posted.

Taxonomy One:  A brief survey of the history and wherefores of taxonomy: Aristotle, Linnaeus and his binomial system of nomenclature, taxonomic ranks and the discovery and application of biological clocks.
Taxonomy Two:  Introduces the higher levels of current taxonomy: the three Domains and the four Kingdoms. We briefly discuss Kingdom Protista, then the seven phyla of Kingdom Fungi.
Taxonomy Three:  Kingdom Plantae.
Taxonomy Four:  Kingdom Animalia to Phylum Annelida.
Taxonomy Five:  A discussion of Cladistics, how it works and why it is becoming ever more important.
Taxonomy Six:  Phylum Chordata, stopping at Class Mammalia.
Taxonomy Seven:  Class Mammalia.
Taxonomy Eight:  Class Aves, beginning with a comparison of five different avian checklists of the past 50 years.
Taxonomy Nine:  A cladogram and discussion of Subclass Neornithes (modern birds) of the past 110 million years, reaching down to the current forty-one orders of birds.
Taxonomy Ten:  A checklist of Neornithes including all ranks and clades down to the rank of the current 251 families of birds (plus a few probable new arrivals) with totals of the current 11,017 species of birds.

Mammal question: They’re all equally related to the Armadillos. Horses, cats and cattle are descended from an unnamed common ancestor which is more closely related to the Armadillos than are any of it’s descendants. This is why checklists that don’t show relationships in a branching tree are inherently deceptive whenever one “branch” abuts another.
Now figure out – according to the same phylogenetic tree – if the cats and cattle are equally related to the horses, or if one is closer than the other.