[By Chuck Almdale]

After our brief sidestep into the wonderful world of cladistics, we’re ready to move onward into our own Phylum of Chordata; all are animals with a notochord and most of them have vertebrae like us. To make the following lengthy sequence a bit more clear, I’m using my own invention, mentioned at the end of the prior posting: each taxon begins with Clade _subnumber in bold. Each subsidiary taxon is indented and the subnumber increased; equivalent clade ranks have the same indention and same subnumber but different names. There can be significant vertical distance in the sequence between such equivalent clades [watch out for Clade₂₁] when they indicate major evolutionary splits with many descendant species. There are over sixty taxonomic ranks in this posting. To save horizontal space and avoid excessive word-wrapping, we will move the indenting back to the left margin three times (which of course interferes with the desired goal of “equivalent clade ranks have the same indentation”).

I have inserted into the sequence occasional comments indicating a major division in lineages: e.g. “The Two Crown groups of Clade₂₆ Sauria: Clade₂₇ Lepidosauromorpha (Tuatara, lizards, snakes), Clade₂₇ Archelosauria (Turtles, Crocodiles, Birds).” Those closely reading the sequence would see these divisions without this alert, but it may be helpful for the rest of us.

In the rest of this post there are a lot of clades with the comment “extinct branches….” These represent the taxon containing the crown group leading to extant species as well as all sister taxa leading only to extinct species. When you want to trace the exact lineages, including both extant and extinct species, you need all these ranks, and it is exactly these ranks which were necessitated by the development of molecular clocks. By the time we reach Class Aves we’ll be at Clade₆₂, and we will have completely overwhelmed the ability of the Linnaean Kingdom-Phylum-Class-Order sequence to encompass it all. Clade ranks may eventually number into the hundreds, perhaps thousands for the insects, as every ancestor of every living organism came into existence through the process of speciation, which begins with one lineage evolving into two differentiating branches. Even as I write there is probably someone somewhere “doing the math,” or some variant of 2¹⁰ = 1,024.

But first there’s a significant series of nesting clades (Domain Eukaryota) above our own phylum. As a reminder of how we got here, we’ll begin with all the taxonomic ranks we’ve gone through to get to Superphylum Deuterostomia and our own Phylum Chordata. As we move through the ranks following Ambulacraria we’ll mention all the closely associated phyla and classes along the way, Echinodermata (starfish, etc.), Agnatha (jawless fishes) and the like.

Clade₁ Domain Eukaryota: Have membrane-bound nucleus and organelles.
  Clade₂ Kingdom Animalia: 760 mya; multicellular, motile oxygen-breathing, sexually reproducing heterotrophs with muscle cells.
    Clade₃ Subkingdom Eumetazoa: Sister taxon to sponges, containing Comb Jellies & Planula. 
      Clade₄ ParaHoxozoa (Planulozoa): 680 mya split between Cnidaria and Bilaterians.
        Clade₅ Infrakingdom Bilateria: Left and right sides are mirror images during embryonic development, most remain bilateral into adulthood.
          Clade₆ Superphylum Deuterostomia: Translation “mouth second”. During embryonic development the anus formed before the mouth. Examples: echinoderms, hemichordates, chordates.  Wikipedia: Deuterostome 
            Clade₇ Ambulacraria: Echinodermates and Hemichordates; sister taxon to the Chordates.
              Clade₈  Phylum Echinodermata – Starfish, urchins, sea cucumbers, sea lilies. Translation: “hedgehog + skin.” All are bilaterally symmetrical as larvae, but most have a five-pointed radial symmetry as adults. Sea floor dwellers worldwide from the tidal zone to the deepest abysses. Appeared at start of Cambrian era 540 mya, 7,600 described extant species. Wikipedia: Echinoderm 
Extant and extinct echinoderms in six classes clockwise from upper left: Fromia indica (Sea Stars); Ophiocoma scolopendrina (Brittle Stars); Stomopneustes variolaris (Sea Urchins); Ctenocystoidea (extinct clade); Actinopyga echinites (Sea Cucumbers); Oxycomanthus bennetti (Crinoids ). Wikipedia: Echinoderm 

              Clade₈  Phylum Hemichordata – Acorn worms. Translation “half + string.” Solitary worm-shaped organisms; generally live in burrows (the earliest secreted tubes) in the deep sea and are deposit feeders. About 130 described species. Wikipedia: Hemichordate 
Acorn worm (or Enteropneusta).
Photo: Necrophorus. Wikipedia: Hemichordate 

            Clade₇ Phylum Chordata – Chordates: Translation “having a string (nerve chord).” Sister taxon to Ambulacraria. At some time during their larval or adult states, Chordates possess: a notochord (elastic rod-like longitudinal structure); a hollow dorsal nerve cord; either an endostyle (organ in the throat used for filter-feeding) or a thyroid (two-lobed endocrine gland in the neck); pharyngeal slits (filter-feeding organs in slits behind the mouth); and a post-anal tail. They also have a coelom (main body cavity enclosing all organs), a closed circulatory system, and exhibit metameric segmentation (a linear series of body segments fundamentally similar – but not entirely alike – in structure that often perform special functions). With over 81,000 species, Chordata is the third-largest animal phylum behind Arthropoda and Mollusca, and includes fish, amphibians, reptiles, birds and mammals. As both Class Aves (birds) and Class Primata (including humans) are in this phylum, we will briefly list the other chordate classes, our closest relatives on Planet Earth. Wikipedia: Chordate 
Cordates clockwise from upper left: Lancelet, Tunicate, Tiger, Shark. Wikipedia: Chordate 

The Three Subphyla of Clade₇ Phylum Chordata:  Cephalochordata, Tunicata, Craniata

              Clade₈ Subphylum Cephalochordata – Translation “head cords.” This small subphylum is a sister clade to the far larger clade of Olfactores.  
                Clade₉ Class Leptocardii – Lancelets: These are fish-like filter feeders first appearing during the Precambrian period more than 540 million years ago, with 30-35 species extant, burrowers in the sea floor. Their gill-slits are used only for feeding, not respiration; their blood carries nutrients but has no oxygen-carrying red blood cells. They are either male or female and breed by spawning.
Lancelet anatomy. Washington State University: Lancelet 

              Clade₈ Olfactores: Translation “smellers.” Sister taxon to Subphylum Cephalochordata. All chordates other than the Lancelets are in this clade.
                Clade₉ Subphylum Tunicata – Tunicates, 3 classes: Translation “having a tunic, (rubbery) outer coat.” 3,000 species, mostly in shallow water. Their body is a water-filled sac with two siphons (tubular openings) through which they intake and expel water for feeding and respiration. There are three Classes: 
                  Class Ascidiacea (Sea Squirts) which are sessile, 5,500  known species.
                  Class Thaliacea (Salps) which are free floating, with 72 known solitary and colonial species.
                  Class Appendicularia (Larvaceans) free-swimming filter-feeders which look like tadpoles, 0.079 to 3.9 in. long, from near surface to 2 miles deep, 70 species known. Wikipedia: Tunicate  
Bluebell Tunicate, Clavelina moluccensis, Class Ascidiacea.
Photo: Nhobgood. Wikipedia: Tunicate 

                Clade₉ Subphylum Craniata (Vertebrata) – Vertebrates: Translation “jointed spine.” Sister taxon to Subphylum Tunicata. The rest of the Chordata phylum which have internal spinal bones, 70,000 described species. Wikipedia: Craniate

The Two Infraphyla of Clade₉ Subphylum Craniata (Vertebrata): Clade₁₀ Infraphylum Agnatha, Clade₁₀ Infraphylum Gnathostomata 

                  Clade₁₀ Infraphylum (or Superclass) Agnatha – Jawless fishes. Translation “no jaw.” Sister taxon to Infraphylum Gnathostomata. The Agnatha appeared during the Cambrian Period (540-485 MYA), with two classes still extant.
                    Class (or Infraclass) Hyperoartia – Lamprey: 38 species of eel-like fish with a toothed funnel-like sucking mouth, living in temperate coastal and fresh water.
Adult pacific lamprey with sharp teeth clearly visible.
Photo: Dave Herasimtschuk, US Fish & Wildlife Service. Wikipedia: Agnatha 

                    Class (or Infraclass) Myxini – Hagfish: They have narrow bodies (1.6-50 in. long) that look like worms; paddle-like tails; naked, often pinkish, skin that fits like a loose sock; cartilaginous skulls, “teeth” of keratin, unlensed eyespots, and can exude copious quantities of a milky and fibrous slime; 76 known species. Wikipedia: Agnatha 
Sixgill Hagfish (Eptatretus hexatrema), False Bay, South Africa.
Photo: Peter Southwood. Wikipedia: Agnatha 

                  Clade₁₀ Infraphylum Gnathostomata –  Translation “jaw + mouth.” Sister taxon to Infraphylum Agnatha. All remaining chordates and vertebrates have jaws. Wikipedia: Gnathostomata

The Two Clades of Clade₁₀ Infraphylum Gnathostomata (Jawed Fish): Clade₁₁ Class Chondrichtyes, Clade₁₁ Superclass Osteichthyes

                    Clade₁₁ Class Chondrichthyes – Cartilaginous Fish: Translation “cartilage + fish.” Sister taxon to Superclass Osteichthyes. Sharks, rays, skates, sawfish and ghost sharks, all have skeletons of cartilage rather than bone. They also have placoid (tooth shaped) scales and lack swim bladders. Range from 3.9 in. to 33 ft. long. Fertilization is internal, birth may be live or by egg depending on species. Worldwide over 1,280 known species. Wikipedia: Chondrichthyes 
Cartilaginous Fish clockwise from upper left: Great White Shark, Manta Ray, Spotted Ratfish, Belantsea montana (extinct 350 mya).
Photo: Prehistoricplanes. Wikipedia: Chondrichthyes

Osteichthyes (below) was long considered a class, along with Amphibia, Aves, Mammalia and Reptilia. Recently it was kicked upstairs to superclass, and the four non-fish classes were placed within it. As all these following clades evolved from that ancestral jawed bony fish, this makes sense, although most people don’t like thinking that their distant ancestor’s claim to fame consists of having bones and a jaw.

                    Clade₁₁ Superclass Osteichthyes – Bony fish: Translation “bone + fish.” Sister taxon to Class Chondrichthyes. This is the largest class of vertebrates, with endoskeletons made of bone, comprising 45 orders, over 435 families and 30,000 species. Gills filter dissolved oxygen from the water, a swim bladder controls buoyancy to keep from sinking. As superclass Osteichthyes now contains classes Amphibia, Aves, Mammalia and Reptilia, it’s a bit confusing to dwell on this superclass’s characteristics pertaining only to fish, but that’s what you’ll find when you look at more than a single website discussing this. Nevertheless, we continue. Wikipedia: Osteichthyes

The Two Clades of Clade₁₁ Superclass Osteichthyes (Bony Fish): Clade₁₂ Actinopterygii, Clade₁₂ Sarcopterygii

                      Clade₁₂ Class Actinopterygii – Ray-finned fishes: Translation “having rays + wing, fins.” Sister taxon to Sarcopterygii. Their lightly-built fins resembling folded fans are made of webbings of skin supported by radially extended thin bony spines. The fins can easily change shape and provide superior thrust; the rays attach directly to the skeleton. 99% of the over 32,000 actinopterygian fish are teleosts, which have a movable premaxilla in their jaw, which enables them to protrude their jaws outward to grab prey and pull it in. Wikipedia: Actinopterygii 
Ray-finned Fishes L-R top-bottom. Top row: Red-bellied Piranha, Spotted Lionfish, Northern Pike; Row 2: Sockeye Salmon, Humpback Anglerfish, Slender- spined Porcupine Fish; Row 3: Peacock Flounder, Japanese Pineconefish, Leafy Seadragon. Wikipedia: Actinopterygii 

                      Clade₁₂ Clade (previously Class or Subclass) Sarcopterygii – Lobe-finned fish. Translation “flesh + wing, fin.” As Osteichthyes has been raised to superclass, Sarcopterygii has been raised to Clade, as it now includes all tetrapods. [Yes, humans are now a form of four-legged lobe-finned fish. So are birds.] Sister taxon to Class Actinopterygii. These organisms – perhaps I should say “we” – are characterized by prominent muscular lobes (limb buds formed early in embryonic development within their fins, which are supported by articulated appendicular (arm and leg) skeletons. Wikipedia: Sarcopterygii

The Two Clades of Clade₁₂ Sarcopterygii (Lobe-finned Fish): Clade₁₃ Actinistia, Clade₁₃ Rhipidistia

                        Clade₁₃ Class Actinistia – Crown group Coelacanthiformes and extinct branches. Sister taxon to Rhipidistia.
                          Clade₁₄ Order Coelacanthiformes –Coelacanths: Translation “hollow + spine,” referring to the tail fin. – The two lobe-fined species – recently discovered “living fossils,” thought to be extinct 66 million years ago – are located here, along with some extinct species. Wikipedia: Coelacanth 
Live coelacanth seen off coast of KwaZulu-Natal, South Africa, 2019.
Wikipedia: Coelacanth

                        Clade₁₃ Rhipidistia (Dipnotetrapodomorpha): Translation “small + bellows.” Combines the next two clades of Lungfish and Tetrapods. Sister taxon to Actinistia. Wikipedia: Rhipidistia

The Two Clades of Clade₁₃ Rhipidistia: Clade₁₄ Dipnomorpha (Lungfish), Clade₁₄ Infraclass Tetrapodomorpha

                          Clade₁₄ Dipnomorpha, Class₁₅ Dipnoi – Lungfish: Translation “double + breath.”  The six species of lungfish, found in Africa, South America and Australia, can breathe through gills or lungs. They have lobed fins and well-developed skeletons and are considered the closest living relatives to the tetrapods. Sister taxon to Tetrapodomorpha. Wikipedia: Lungfish  
Neoceratodus forsteri (Australian lungfish), Canberra, Australia.
Photo: Mitch Ames. Wikipedia: Lungfish

                          Clade₁₄ Infraclass Tetrapodomorpha – Extinct branches only 
                            Clade₁₅ Eotetrapodiformes – Extinct branches only 
                              Clade₁₆ Elpistostegalia – Extinct branches only 
                                Clade₁₇ Stegocephali – Extinct branches only 
                                  Clade₁₈ Superclass Tetrapoda – four-limbed vertebrates: Translation “four + foot.” Intervening clades 14-17 peeled off four groups of extinct fish. Evolutionary speaking, all the tetrapods evolved through the Sarcopterygii (now a clade, previously a subclass) line. It made no sense to have a superclass part of a subclass which is two ranks lower on the taxonomic scale – thus the switch to “clade” for Sarcopterygii. This classification below follows Benton 2004. There are over 35,100 described tetrapodal species in the following four classes of Amphibia, Reptilia, Aves and Mammalia. Wikipedia: Tetrapod 

The Two Clades of Clade₁₈ Superclass Tetrapoda (Four-limbed Vertebrates): Clade₁₉ Class Amphibia, Clade₁₉ Reptiliomorpha

                                    Clade₁₉ Class Amphibia – Amphibians: Translation “double + life.” Amphibians are ectothermic (“cold-blooded”), anamniotic [lack the three extraembryonic membranes: amnion (protection), chorion (gas exchange) and allantois (waste disposal)]. Most are semiaquatic, start as aquatic larvae (tadpoles) with gills, then become lung breathers. All 8,100 extant species are in subclass Lissamphibia: frogs, toads, salamanders and caecilians. Sister taxon to Reptiliomorpha.  Wikipedia: Amphibian
Gaboon Caecilian (Geotrypetes seraphini), an amphibian; reduced eyes, nostrils, small tentacles below the nostrils.
Photo: Marius Burger. Wikipedia: Caecilian 

                                    Clade₁₉ Reptiliomorpha (or Pan-Amniota): Translation “reptile + shape.” The sister taxon to Class Amphibia, defined in 2020 by Laurin and Reisz (2020) as the largest total clade that contains Homo sapiens, but not Pipa pipa (Star-fingered Toad), Caecilia tentaculata (a caecilian or serpentine amphibian), and Siren lacertina (Greater Siren amphibian). It consists of amniotes (see immediately above and below) and a few closely related extinct tetrapods. Wikipedia: Reptiliomorpha

The Crown Group Clade of Clade Reptiliomorpha: Amniotes

                                      Clade₂₀ Amniota (or Class Reptilia) – Amniotes: They have three extraembryonic membranes: amnion (protection), chorion (gas exchange) and allantois (waste disposal); this clade includes reptiles, birds and mammals. Wikipedia: Amniote

The Two Clades of Clade₂₀ Amniota (Crown Group Amniotes): Clade₂₁ Sauropsida, Clade₂₁ Synapsida

Following Clade₂₀ Amniota (or Class Reptilia) there is a major lineage division.
                                        Clade₂₁ Synapsida heads towards the mammals. 
                                        Clade₂₁ Sauropsida heads towards lizards, snakes, crocodiles and birds. For the rest of this posting we’ll follow the Sauropsida line. In the next posting we’ll begin again at this juncture and follow the Synapsida line towards the mammals.

It took us twenty-one taxonomic ranks from Clade₁ Domain Eukaryota to sister taxon Clades₂₁ Sauropsida and Clade₂₁ Synapsida. It will take another forty-one steps to get to Clade₆₂ Class Aves. In this posting we won’t be counting how much farther it is to get to an individual bird species such as Passer domesticus; we’ll leave that for later. If nothing else, you’ll have a good understanding why cladistics has caught on so quickly. Notice that following this point we’re re-starting the indentation of taxonomic ranks back at the left margin.

Clade₂₁ Sauropsida – Lizards, snakes, turtles, crocodiles, tyrannosaurs, pterosaurs, birds. Translation “lizard + face.” A clade broadly equivalent to Class Reptilia, used to include extinct stem-group relatives of modern reptiles and birds (which, as theropod dinosaurs, are nested within reptiles as they are more closely related to crocodilians than to lizards or turtles). Wikipedia: Sauropsida
  Clade₂₂ Eureptilia – Crown group reptiles & extinct branches.  
    Clade₂₃ Romeriida – Crown group reptiles & extinct branches.
      Clade₂₄ Diapsida – Crown group reptiles & extinct branches.
        Clade₂₅ Neodiapsida – Crown group reptiles & extinct branches.
          Clade₂₆ Sauria (or Ankylopoda) – Extinct branches and last common ancestor of lizards, turtles, crocodiles and birds. Wikipedia: Sauria 
Saurian Crown Group: Clockwise from top left: Copperhead Snake, White-faced Buffalo-Weaver, various extinct ornithischian dinosaurs, Green Sea Turtle, Anurognathus (an extinct pterosaur), American Alligator.
Collage: Kiwi Rex. Wikipedia: Sauria

The Two Crown groups of Clade₂₆ Sauria: Clade₂₇ Lepidosauromorpha (Tuatara, lizards, snakes), Clade₂₇ Archelosauria (Turtles, Crocodiles, Birds)

            Clade₂₇ Lepidosauromorpha (or Pan-Lepidosauria) – Crown group lizards & extinct branches. Sister taxon to Archelosauria.
              Clade₂₈ Superorder Lepidosauria – Translation “scaled + lizard.” Within Superorder Lepidosauria are two clade-orders.
                Clade₂₉ Order Rhynchocephalia – Translation “beak + heads.” This order was very diverse a mere 240 mya but now contains only one species, the Tuatara of New Zealand, which has a functioning 3^rd eye on the top of its head, not for vision, probably for endocrine system daylight sensing.  
 Henry, at 111 the world’s oldest Tuatara in captivity and still reproductively active, at Invercargill, New Zealand. Photo: KeresH. Wikipedia: Tuatara

                Clade₂₉ Order Squamata – Lizards & Snakes. Contains all other lizards (over 7,100 known species) and snakes. Skin of horny scales which periodically molt. Movable quadrate bones allows both jaws to move relative to the rest of the skull. Sister taxon to Rhynchocephalia. Wikipedia: Squamata
Veiled Chameleon (Chamaeleo calyptratus) from Yemen.
Photo: Kupos. Wikipedia: Chameleon 

                  Clade₃₀ Suborder Serpentes – Snakes. (over 3,900 known species). Schema follows Lee 2013. 
Coast Garter Snake (Thamnophis elegans terrestris), California.
Photo: Steve Jurvetson. Wikipedia: Ophidia 

            Clade₂₇ Clade Archelosauria (or Archosauromorpha) Sister taxon to Lepidosauromorpha.

The Two Crown groups of Clade₂₇ Archelosauria: Clade₂₈ Pantestudines (Turtles), Clade₂₈ Pan-Archosauria (Crocodiles, Birds)

              Clade₂₈ Pantestudines – Crown group turtles and extinct branches; sister taxon to Pan-Archosauria. 
                Clade₂₉ Testudinata – Crown group turtles and extinct branches.  
                  Clade₃₀ Mesochelydia – Crown group turtles and extinct branches.
                    Clade₃₁ Perichelydia – Crown group turtles and extinct branches.
                      Order₃₂ Testudines – Turtles. Turtle shells, made mostly of bone, grow from their ribs, their outer surface is covered with scales made of keratin (as with hair, horns and claws). There are two divisions:  
                         Clade₃₃ Suborder Cryptodira –Found worldwide, 246 extant species which pull their neck straight back between their front legs. Wikipedia: Cryptodira 
Indian Flapshell Turtle, Lissemys punctata, Bangalore; a highly advanced eucryptodire. Photo: L. Shyamal.  Wikipedia: Cryptodira 

                         Clade₃₃ Suborder Pleurodira – 43 extant species found in the southern hemisphere which bend their head sideways into a space in front of one of the front legs. This schema follows Lee 2013. Wikipedia: Pleurodira 
Yellow-spotted Amazon River Turtle (Podocnemis unifilis), showing Pleurodira head retraction. Photo: Pierre Fidenci. Wikipedia: Pleurodira 

At this point the clades are excessively word-wrapping, so we’re moving back to the left margin again and reducing indenting to one space per rank change.

Clade₂₈ Pan-Archosauria – Crown group crocodiles & birds, extinct branches. Sister taxon to Pantestudines.
 Clade₂₉ Archosauromorpha (may be = Crocopoda) Crown group crocodiles & birds, extinct branches.
  Clade₃₀ Crocopoda – Crown group crocodiles & birds, extinct branches.
   Clade₃₁ Archosauriformes – Crown group crocodiles & birds, extinct branches.
    Clade₃₂ Eucrocopoda – Crown group crocodiles & birds, extinct branches.
     Clade₃₃ Crurotarsi – Crown group crocodiles & birds, extinct branches. 
      Clade₃₄ Archosauria – Last common ancestor of crocodiles & birds. Wikipedia: Archosaur 

The Two Crown groups of Clade₃₄ Archosauria: Clade₃₅ Pseudosuchia (Crocodiles), Clade₃₅ Avemetatarsalia (Flying Dinosaurs, Bird-like Dinosaurs, Birds)

       Clade₃₅ Pseudosuchia – Crown group crocodiles, extinct branches; sister taxon to Avemetatarsalia.
        Clade₃₆ Suchia – Crown group crocodiles, extinct branches.
         Clade₃₇ Paracrocodylomorpha – Crown group crocodiles, extinct branches. 
          Clade₃₈ Loricata – Crown group crocodiles, extinct branches. 
           Clade₃₉ Crocodylomorpha – Crown group crocodiles, extinct branches.
            Clade₄₀ Solidocrania – Crown group crocodiles, extinct branches.
             Clade₄₁ Crocodyliformes – Crown group crocodiles, extinct branches.
              Clade₄₂ Mesoeucrocodylia – Crown group crocodiles, extinct branches.
               Clade₄₃ Metasuchia – Crown group crocodiles, extinct branches.
                Clade₄₄ Neosuchia – Crown group crocodiles, extinct branches.
                 Clade₄₅ Eusuchia – Crown group crocodiles, extinct branches.
                  Clade₄₆ Order Crocodilia – Crocodiles. Translation “stone + worm.” Egg-laying, semiaquatic predatory reptiles, first appearing during the Late Cretaceous (100-66 mya) and are the closest living relatives of birds. Their Archosauria ancestors appeared 235 mya and were the only survivors of the Triassic-Jurassic Extinction Event 201.4 mya. Wikipedia: Sauropsida Lee 2013;  Wikipedia: Crocodilia 
The Gharial (Gavialis gangeticus) of India,formerly common, now nearly extinct. Photo: Clpramod. Wikipedia: Gharial 

We just came to a major clade break, so we’re returning back to the left margin.

Clade₃₅ Avemetatarsalia – Crown group dinosaurs, extinct branches; sister taxon to Pseudosuchia. 
 Clade₃₆ Ornithodira – Crown group dinosaurs, extinct branches.
  Clade₃₇ Pterosauromorpha – Flying Pterosaurs; sister taxon to Dinosauromorpha.
Sordes (Sordes pilosus) evidences the possibility that pterosaurs had a cruropatagium – a membrane connecting the legs that leaves the tail free.
Artist: Dmitry Bogdanov . Wikipedia: Pterosaur 

  Clade₃₇ Dinosauromorpha – Crown group dinosaurs, extinct branches; sister taxon to Pterosauromorpha.
   Clade₃₈ Dinosauriformes – Crown group dinosaurs, extinct branches.
    Clade₃₉ Dracohors – Crown group dinosaurs, extinct branches. 
     Clade₄₀ Dinosauria – Crown group dinosaurs, extinct branches. 
      Clade₄₁ Saurischia – Crown group dinosaurs, extinct branches. 
       Clade₄₂ Eusaurischia – Crown group dinosaurs, extinct branches. 
        Clade₄₃ Theropoda – upright carnivorous dinosaurs 231-66 mya. 
         Clade₄₄ Neotheropoda – Crown group theropods, extinct branches. 
          Clade₄₅ Averostra – Crown group theropods, extinct branches.
           Clade₄₆ Tetanurae – Crown group theropods, extinct branches.
            Clade₄₇ Orionides – Crown group theropods, extinct branches.
             Clade₄₈ Avetheropoda – Crown group theropods, extinct branches.
              Clade₄₉ Coelurosauria – Crown group theropods, extinct branches.
               Clade₅₀ Tyrannoraptora – Tyrannosaurs and Coelurosaurs (includes birds).
                Clade₅₁ Tyrannosauroidea – Tyrannosaurs and kin. 
                Clade₅₁ Maniraptoriformes – Coelurosaurians closer to birds than tyrannosaurs. 
                 Clade₅₂ Maniraptora – Crown group coelurosaurs, extinct branches. 
                  Clade₅₃ Pennaraptora – Crown group coelurosaurs, extinct branches.
                   Clade₅₄ Paraves – Extinct branches, bird-like dinosaurs.
                    Clade₅₅ Avialae – Bird-like dinosaurs, Archaeopteryx 150mya. 
                     Clade₅₆ Avebrevicauda – Bird-like dinosaurs.
                      Clade₅₇ Pygostylia – Avialans with stubby tails, Confuciusornis.
                       Clade₅₈ Ornithothoraces – Advanced thorax for better flight.
Sinornis restoration.  Author: Pavel.Riha.CB.  Wikipedia: Sinornis  

                        Clade₅₉ Euornithes – “True birds” excludes Sinornis.
                         Clade₆₀ Ornithuromorpha – Crown group Aves, extinct branches.
                          Clade₆₁ Ornithurae – Modern birds plus Ichthyornis, Hesperornis, and Vegavis. 
Vegavis (Vegavis iaai) of Antarctica during the Maastrichtian stage (72.1-66 mya) of the Late Cretaceous. Author: El fosilmaníaco. Wikipedia: Vegavis

                           Clade₆₂ Class Aves – Appeared during early-to-middle Cretaceous 146-110 mya.
                            Clade₆₃ Subclass Neornithes – Modern birds   
                             Clade₆₄ Infraclass Paleognathae  – Ratites
                             Clade₆₄ Neognathae – all other birds
Yellow-faced Honeyeater (Caligavis chrysops) raises three chicks in a garden nest, SE Australia. Photo:  Benjamint444. Wikipedia: Yellow-faced Honeyeater

Clade₂₁ Synapsida – The line to mammals, sister taxon to Clade₂₁ Sauropsida. 
Nearly all mammals, including humans (Homo sapiens), care for their young for a significant period following birth.
YouTube: Toddler sees world clearly for first time

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.