Family Tree of Mammals

- Matt Baker is developing five new Tree of Life taxonomy charts. The expanded project launched the previous month, and he had completed the plants-and-fungi and birds charts while working on the mammal chart presented in this episode.

- Audience feedback is an important part of the chart-development process. Baker invited viewers to identify missing information and errors. Comments on the earlier bird-chart video significantly influenced its final design, and he hoped the mammal chart would benefit similarly.

- The new taxonomy charts were available through Kickstarter late pledges. Although the initial funding period had ended, late pledges remained open until the end of October 2026. Baker directed interested buyers to UsefulCharts' Kickstarter page and encouraged pre-orders for delivery in time for the holidays.

- Mammary glands are the defining shared feature of mammals. They allow females to produce milk for their offspring, but not all mammals give birth to live young.

- Monotremes are the egg-laying mammals. The platypus and echidnas belong to the order Monotremata and reproduce by laying eggs, unlike the vast majority of mammals.

- Most mammals belong to the subclass Theria. These live-bearing mammals divide into two major groups: marsupials, which have short gestation periods and continue their offspring's development in an external pouch, and placentals, which generally have longer gestation periods because placentas supply developing offspring in the womb.

- Marsupials are represented in purple on the draft chart. Baker explained that the video would cover the main highlights rather than every species, with a more detailed mammal-chart video planned for the following year. The numbers beneath order names indicate the number of species in each order.

- The Americas have two major types of marsupials in this classification: opossums and shrew opossums. Each is placed in its own order, while the remaining marsupials belong to the superorder Australidelphia.

- Australidelphia contains five orders, including the familiar Australian marsupials. The order Diprotodontia includes koalas, wallabies, kangaroos, quokkas and wombats, while Dasyuromorphia includes the Tasmanian devil and the recently extinct Tasmanian tiger.

- Placental mammals divide into Boreoeutheria and Atlantogenata in the chart's evolutionary framework. Baker associated Boreoeutheria with the ancient northern continent and Atlantogenata with the southern continental landmass, using the geographic history of mammalian evolution to explain the major split.

- The historical separation of South America and Africa explains the two main branches within Atlantogenata. The southern landmass divided into western and eastern portions that became South America and Africa as the Atlantic Ocean formed.

- Xenarthra contains armadillos, sloths and anteaters. Its name means “strange joints,” referring to additional joints in the backbones of animals in this clade. The group includes the armadillo order and Pilosa, which contains sloths and anteaters.

- Afrotheria contains six orders and includes several surprisingly different kinds of mammals. Besides elephants, it encompasses hyraxes, manatees, dugongs and insect-eating mammals such as the aardvark.

- Elephants belong to Proboscidea, an order with only three living species according to the chart. Two occur in Africa and one in Asia. The name Proboscidea refers to a proboscis, meaning a long nose or tube.

- Most animal illustrations on the chart came from iNaturalist observations with public-domain photographs. Baker specifically clarified that the video was not sponsored by iNaturalist, but acknowledged the platform's important contribution to the project.

- iNaturalist allows professionals and amateurs to document and identify wildlife. Its app helps users record observations of animals, birds, insects, mushrooms, plants and other organisms. Baker actively uses the platform under the username Matt-B and invited people to contribute suitable photographs to the chart project.

- iNat Together offers opportunities to learn about nature in person. Baker directed viewers to an event finder that searches by location, explaining that participants could explore nature with others and learn to use the app. He also planned to attend an event near him.

- Boreoeutheria contains more than 85% of mammal species. Its two major branches in the chart are Laurasia Theria, shown in green, and Euarchontoglires, shown in orange and red. Their names and placement reflect the classification's evolutionary framework.

- Euarchontoglires divides into Euarchonta and Glires. Baker explained the names as meaning “true rulers” and “dormice,” respectively, before examining the groups' constituent mammals.

- Glires includes rabbits, hares and rodents. Rabbits and hares belong to Lagomorpha, while Rodentia contains more than 2,300 species, making it by far the largest mammalian order in the chart.

- Rodents encompass far more than rats and mice. The chart includes beavers and gophers; squirrels and related animals such as groundhogs, prairie dogs and chipmunks; porcupines, guinea pigs and capybaras; and rodents more closely related to rats and mice, including gerbils and hamsters.

- Euarchonta includes primates, tree shrews and flying lemurs. Primates are by far its principal group, with more than 500 species, including humans.

- Primates initially divide into Strepsirrhini and Haplorrhini. Strepsirrhini means “wet-nosed” and includes lemurs, lorises and bushbabies. Haplorrhini means “simple-nosed” or “dry-nosed” and includes tarsiers and simians.

- Simians divide into New World and Old World groups before the chart distinguishes monkeys from apes. Platyrrhini, meaning “flat-nosed,” contains the New World simians, while Catarrhini, meaning “down-nosed,” contains the Old World simians.

- New World simians have five distinct monkey families and no apes in the classification shown. Baker highlighted Cebidae, which includes capuchins and squirrel monkeys, and Atelidae, which includes spider monkeys and howler monkeys, as the two principal families.

- Old World simians contain one monkey family and two ape families. The monkey family Cercopithecidae includes baboons and rhesus monkeys, among many others. The two ape families are the gibbons and the greater apes, Hominidae.

- Hominidae is presented as containing eight living species across four genera. Homo represents humans; Pan includes chimpanzees and bonobos; Gorilla contains the eastern and western gorilla species; and Pongo contains three orangutan species.

- The orangutan species P. tapanoeliensis is highlighted as a comparatively recent discovery. Baker noted that it was discovered in the late 1990s, illustrating how research continues to refine knowledge of the greater apes.

- The chart deliberately limits its treatment of prehistoric extinct mammals. Baker said at least 20 additional extinct species could potentially be added to the Hominidae family based on the extensive research into its evolutionary history. However, because the chart primarily focuses on living species, he chose not to include that wider range of prehistoric relatives, while retaining a few species that became extinct during historical times.

- Laurasiatheria contains several major mammalian groups, beginning with Eulipotyphla. This order includes shrews, hedgehogs and moles, which Baker described as true insectivores because they form the largest group of insect-eating mammals. The remaining major branch is called Scrotifera.

- DNA comparisons have substantially changed the classification of insectivorous mammals. Eulipotyphla was formerly called Insectivora and included several additional shrew-like species. Those species have since been reassigned to other groups based on genetic evidence.

- Bats are the only mammals capable of powered flight and the second-largest mammalian order. They are surpassed in species numbers only by rodents. The older division into macrobats and microbats has been replaced by the groups Yinpterochiroptera and Yangochiroptera.

- Yinpterochiroptera includes all macrobats and some smaller bat families. Flying foxes belong to this group, as do certain microbat families, including horseshoe bats and roundleaf bats. Most microbats, however, belong to Yangochiroptera.

- Vespertilionidae is identified as the largest bat family within Yangochiroptera. Its name is associated with bats and night-flying. Baker mentioned the big brown bat and little brown bat as two common North American species and highlighted vampire bats, which feed exclusively on blood.

- Ferungulata brings together the wild-beast and hoofed-mammal branches. Baker explained the name through Ferae, meaning wild beasts, and ungulates, meaning hoofed animals. The ungulates divide into Perissodactyla, the odd-toed group, and Artiodactyla, the even-toed group.

- Perissodactyla includes rhinos, tapirs and equines. The equines include horses, donkeys and zebras, which are grouped with the odd-toed hoofed mammals.

- Artiodactyla contains most hoofed mammals and includes pigs and camelids. Its members include the pig family and the camel family, with the latter encompassing camels, llamas and alpacas.

- The classification places whales within Artiodactyla because of their evolutionary ancestry. The group Cetuminantia combines a reference to cetaceans, or whales, with ruminants. Within it, Whippomorpha includes both hippos and cetaceans, reflecting the shared ancestry of whales and even-toed hoofed mammals.

- Whales receive a distinct colour on the chart despite their placement among even-toed mammals. Baker explained that their evolutionary relationship justifies the classification, but their substantial differences from other hoofed mammals warranted a separate visual treatment.

- Whales divide into toothed whales and baleen whales. Baleen whales possess rows of fibrous baleen plates instead of teeth for filtering food. This group includes gray whales, humpback whales and blue whales, the largest animals on Earth.

- Toothed whales include sperm whales, belugas, narwhals and all dolphins. The distinction between toothed and baleen whales provides a major subdivision within the cetacean branch of the chart.

- Ruminants share the ability to chew their cud. This is part of a multistep digestive process. Ruminants include giraffes, as well as the two principal families highlighted by Baker: Cervidae and Bovidae.

- Cervidae includes deer and several familiar related animals. Its members include moose, caribou and elk, alongside deer.

- Bovidae includes both familiar livestock and numerous wild hoofed mammals. Cows, bison and buffaloes belong to this family, as do wildebeests, impalas, gazelles, sheep and goats.

- The wild-beast branch is dominated by Carnivora, with pangolins shown in a separate small order. Carnivora is coloured yellow on the chart and divides into Feliformia, the cat-like group, and Caniformia, the dog-like group.

- Feliformia includes civets, hyenas, mongooses and cats. The cat family, Felidae, contains 14 genera, of which Baker chose to illustrate five to provide a representative selection.

- The five illustrated cat genera connect familiar animals to their taxonomic groups. Lynx includes bobcats; Felis includes domestic cats; Puma includes cougars or mountain lions; Acinonyx includes cheetahs; and Panthera contains the largest cats shown. Baker used his own cat, Ketzel, to represent the domestic cat genus Felis.

- Panthera is represented by all five species identified in the chart. These are the jaguar, tiger, lion, leopard and snow leopard, illustrating the diversity within this major cat genus.

- Caniformia includes dogs, bears, pinnipeds and several other mammalian families. Canidae, the principal dog family, encompasses foxes, jackals, coyotes and wolves, from which the domestic dog descended.

- Pinnipeds are part of the dog-like carnivore branch. This group includes walruses, sea lions and seals, placing these marine mammals within the wider carnivore classification.

- Musteloids encompass several familiar small and medium-sized mammals. The chart includes skunks, raccoons, red pandas and members of Mustelidae, a family containing wolverines, badgers, minks, weasels and otters.

- The mammal chart remains a draft open to public revision. Baker ended by asking viewers to suggest missing information or corrections so he could incorporate useful feedback into the final design, while continuing to invite pre-orders through the Kickstarter campaign.