The Digestive and Respiratory Cladogram depicts such a nested hierarchy of anatomical features of these animal systems.  All vertebrates posses the traits given at the node for the vertebrate ancestor (node 11).  All tetrapods possess the traits given at the node for the tetrapod ancestor (node 15).   All placental mammals possess the traits given at the node for the placental mammal ancestor (node 19).

     Apes consistently appear as a real, biological group—not a group of completely unrelated organisms which happen to share traits for no apparent reason.  Placental mammals are a real group.  Amniotes are a real group.  Deuterostomes are a real group, etc.  Biological groups are real—or at least there is an overwhelming amount of evidence that suggests that they are. 



1.        LUCA—Last common ancestor of all modern life on earth

--carbonic anhydrase (Hoar, 1983, p. 542)\


2.        Ancestor of Protists, Plants, Fungi, and Animals

--intracellular digestion which occurs after phagocytosis occurs first in an acidic environment, then in an alkaline environment (Barrington, p. 172).  

3.        Ancestor of Animals

--cutaneous respiration (which still performs some gas exchange in modern vertebrates, especially amphibians and bats but including humans) (Kardong, p.403)

Lecithin is the main phospholipid in animals and triglycerides the main energy storage. (Stevens).166

4.   Ancestor of Animals with Tissues

--mouth (Fretter)

--gastrovascular cavity(Fretter)

--digestive enzymes secreted into cavity (Fretter)

--gut lined by endoderm; glands endodermal (Fretter)

--cilia move particles which are caught in mucus (Fretter)

--muscle cells surround the gastrovascular cavity and may be present in multiple layers (Hickman 185)

--some have a pharynx and ctenophores have anal canals (Hickman 185)

--digestive enzymes include a trypsin-like digestive enzyme that functions in an alkaline environment. (Hyman, 393)


5. Ancestor Bilateran Animals (the following traits are not found in the most primitive flatworms, Order Acoela)

--muscular pharynx which performs peristalsis (Fretter)

--pharynx is ciliated, with longitudinal and circular muscle layers (Dougherty, p. 197, Beklemishev 2, p. 196)

 --microvilli increase the surface area of the intestine (Hickman)

 --many unicellular glands are present in intestine (Beklemishev 2, p. 196)

--in flatworm orders Macrostomida & Notandropora digestion is extracellular and a stable epithelial gut lining exists (Beklemishev 2, p. 192)


6.  A nemertine-like ancestor of complex bilateran animals

--a complete digestive system, with a mouth and an anus (Hickman)

--mouth is located on the anterior end of the animal (except in a few species (Hickman, p. 227)

--food is moved primarily through ciliary movement and is digested both extracellulary and intracellulary. (Hickman)

the myelin P2 superfamily of proteins includes proteins known as fatty acid-binding proteins (FABPs) (Baba, 1999). 

--peristalsis (Hoar, 1983, p. 425). 


  1. Coelomate Ancestor


--in some primitive coelomates (Phoronida), mesenteries support the intestine.  (Hickman, p. 288)

--hemoglobin dissociation curve similar to that of vertebrates (Hoar, 1983, p. 533) 

--autorhythmic neurons to control respiration and use respiratory reflexes.  (Hoar, 1983, p.  521). 


  1. Deuterostome Ancestor

--blood vessels to pharyngeal slits   (Harris)

--second embryonic opening of the digestive tract becomes the mouth, rather than the anus (Romer, p. 325)

--pharynx which possesses pouches which open to the exterior through slits (Benito, form Harrison 1997, p. 20) 

-pharynx supported with skeletal bars (Benito, form Harrison 1997, p. 20) 

--ciliate pseudostratified epithelia in the pharynx (Benito, form Harrison 1997, p. 72.)

--Goblet cells exist (Benito, form Harrison 1997, p. 26)

--microvilli in GI tract form brush border from tall epithelial cells (Benito, form Harrison 1997, p. 88)



  1. Chordate Ancestor

--(urochordates, 9A) blood vessels to pharyngeal slits more extensive; perform gas exchange  (Harris)

--internal gills around pharynx, distinct from external gills in other invertebrates (Romer, p. 348)

--multiple types of cells lining the stomach region  (Burighel, from Harrison, 1997, p. 255)

--some cells of stomach lining are endocrine cells, whose peptides include secretin, gastrin, and somatostatin. (Burighel, from Harrison, 1997, p. 255) 

--cells similar to acinar cells of the vertebrate pancreas, although they are located in the lining of the stomach (Burighel, from Harrison, 1997, p. 255) 

--cells in a pyloric gland which empties into intestine through a duct which resemble liver cells of vertebrates (especially those the most primitive fish, the hagfish) and function in the storage of glycogen and the removal of foreign substances from the blood. (Burighel, from Harrison, 1997, p. 257)

--(cephalochordates, 9B) aortic arches carry oxygenated blood to the dorsal aorta (Willey, 49)

--(cephalochordates, 9B) gelatinous rods in walls around gill clefts (cartilage of vertebrate pharyngeal arches will compose structures such as the hyoid, trachea, and larynx) (Willey, 28)

--(cephalochordates, 9B) liver (Willey, 54)

----(cephalochordates, 9B) hepatic portal system in which blood from intestines brought to a capillary network in liver before the hepatic vein returns it to general circulation (Willey, 54)

--skeletal muscle in anal sphincter (Willey, p. 35)


  1. Craniate Ancestor

--extensions of the dorsal mesentery (mesentery, mesocolon, greater ommentum; absence of mesentery in lamprey may be secondary loss) (Romer, p. 318-9)

--pancreas (although pancreatic tissue is dispersed, similar to the multiple units of the embryonic pancreas) (Romer, p. 393-5)

--liver no longer for enzyme production and food absorption as in Amphioxus (Romer, p. 390)

-- gall bladder (Weichert, 1970, p. 194)

--only posterior portion of stomodeum (anterior embryonic invagination which unites with digestive tube) contributes to mouth (Kardong, p. 490)

--reduction of the number of pharyngeal pouches (Weichert, 1970)214

--cartilage surrounds pharynx (Weichert, 1970)214

--chitinase (Stevens

--trypsin (Stevens).172

-- aminopeptidase and carboxypeptiase (Stevens)..


  1. Vertebrate Ancestor

--(maybe hagfish as well) coelom forms from mesoderm after it separates from other tissues (it is not formed from segmented pouches from the gut as in echinoderms and lancets) (Romer, p. 315)

--oral glands; some secrete mucus (Romer, p. 329)

--reduction in the number of pharyngeal pouches (Weichert, 1970, p.214)

--amylase is secreted from pancreas (Stevens, p.160)

--pancreatic lipase is the most important enzyme in the digestion of lipids. (Stevens, p.168)


  1. Gnathostome Ancestor

--stomach (Romer, p. 378)

--dermal denticles which are homologous to teeth (Romer, p. 333)

--gills no longer involved in feeding (as in lower chordates, lamprey larvae, and fossil ostracoderms) (Romer, p. 357)

--lips (Torrey, 1979, p. 317)

there are inner circular and outer longitudinal muscle layers (Stevens).20

--hypophyseal pouch of stomodeum incorporated into mouth (Kardong, p. 490)

--pancreas units unites, exocrine and endocrine regions together (Kardong, p. 519)

--livers increase in size and are lobed.  (Weichert, 1970, p. 194)

--pepsin (Stevens).171

--elastase (Stevens). 

--stomach with  pylorus and fundus (6)

--rectum (6)

--adaptations to hypoxia include an increase in hematocrit (Hoar, 1970) 

--the medulla is responsible for rhythmic breathing 321(Hoar, 1970)


  1. Bony Fish Ancestor


--although advanced actinopterygians (teleosts) possess a swim bladder, the earliest actinopterygians possess lungs (such as Polypterus) whose texture is similar to amniote lungs.  The gar pike and Amia will suffocate without atmospheric air; as will sarcopterygian lungfish (Romer, p. 360, 364) 

--the fossil placoderm Bothriolepis possessed a pair of sacs connected to digestive tube of unknown function (Kardong, p. 403)

--lungs develop as an outpocket of digestive system (Romer, p. 362; Dutta p. 241)

--lung epithelium is endodermal (as is that of digestive tract) (Romer, p. 363)

--bilobed lungs (Polypterus) (Romer, p. 363)

--surfactant for lungs (Dutta, p. 254)

--first true enamel in teeth (Romer, p. 338)

--muscular mechanisms of gulping food which are similar to breathing (Dutta, p. 138)

--a change in the FABPs expressed in livers (Baba, 1999).

--sucrase (Stevens)

--chymotrypsin (Stevens). 


  1. Sarcopterygian Fish Ancestor

-- compact pancreas of sarcopterygians more similar to tetrapods than actinopterygians(Youson, 1999).

--pericardial cavity no longer opens into coelom around digestive organs (the early pericardial cavities were continuous with the general coelom and even in cartilaginous fish and primitive actinopterygians a connection remains) (Romer, p. 317)

--the pulmonary artery develops as a branch of aortic arch VI which also services gills before emptying into the dorsal aorta through the ductus arteriosus (amphibians have the same) (Kardong)

--pulmonary vein carries oxygenated blood from lungs to left atrium (Kardong p. 465).

--lungs paired (Romer, p. 364)

-- internal divisions and alveoli-like chambers (Johansen, Kjell from Hoar, 1970; Romer ). 

--ridges of connective tissue increase respiratory surface area (Romer, p. 366)

--internal naris (Romer, p. 325)

--nasal placodes from stomodeum incorporated into mouth (Kardong, p. 490)

--skeletal muscle and aspiratory forces help venous return (Hoar, 1970)

--both SP-A and SP-B surfactant proteins were present (Power, 1999). 

--increase of DSP (disaturated phospholipids) in surfactant (Orgeig, 1995).

-- skeletal muscle and aspiratory forces help venous return (Hoar, 1970). 


  1. Tetrapod Ancestor

--intestine coils, as does mesentery around it (Romer, p. 318-9)

--tongue muscles from hypobranchial muscles (from gill arches) anchored to the hyoid (which is composed of the fused cartilage of several gill arches) (Romer, p. 328)

--salivary glands (Romer, p. 329)

--a short trachea in some (Romer, p. 370; Dutta, p. 246)

--esophagus more prominent (Romer, p. 378)

--loss of intestinal spiral valve (present in gnathostome fish and perhaps lampreys) (Romer, p. 387)

--ileocecal valve separating a small and large intestine (Romer, p. 388)

--duodenum (Kardong, p. 512)

--smooth muscle in esophagus (Stevens)

--lingual salivary glands (Weichert, 1970, p. 161-2)

--glandular cardiac region of the stomach(Stevens, p.16)

--villi. (Stevens, p.18)

 --lacteals in these villi (Stevens, p.18)

-- glandular crypts of Lieberkuhn in their intestines. (Stevens, p.18)

--lungs with simple squamous epithelia, collagen, and smooth muscle (Dutta, p. 248)

-- short trachea and larynx (Romer, p. 370; Dutta, p. 246) 

--sacral innervation  of GI tract (Stevens, p. 274)

-- cartilage around their nostrils and the ability to change the size of  nostril openings (Weichert, 1970)

--concha (Weichert, 1970)204, 

-- cricoid and arytenoids cartilages of the larynx (Weichert, 1970)204,  

--Maltase, isomaltase, and trehalase (Stevens)..


  1. Amniote Ancestor

--a completely separate pulmonary circuit; no ductus arteriosus connecting pulmonary and systemic circuits in adult (Kardong)

--increased internal complexity of lungs; septa further divide lungs  (Romer, p. 363; 366)

--trachea lengthens (Romer, p. 366)

--bronchi (Romer, p. 370)

--ribs attach to sternum and function in pulmonary ventilation

--in embryonic development, a large yolk sac distorts gut (even in mammals which lack yolk) (Romer, p. 374)

--cecum (Romer, p. 388)

--lactase (a small amount of lactase is present in birds) (Stevens)..

--intercostal and abdominal muscles used in breathing (Kardong, p. 421-2)

--negative pressure used to inflate lungs (9)

--pleural membranes (9)

--sublingual salivary glands (Weichert, 1970, p. 161-2)

--hyoid apparatus more closely associated with the larynx (Weichert, 1970)230-1

the hyoid is located more caudally (Webster, 1974, p. 329).

--bronchi  (Weichert, 1970)233

-- the only cholinergic excitation of the gut is parasympathetic Stevens, p. 274)

--primary bile salt is cholesterol (Stevens).167 


  1. Mammal Ancestor

--more muscular tongue  (Weichert, 1970, p. 164

--pleural cavities (also present in some reptiles) (Romer, p. 320)

--hard and soft palate (Romer, p. 327)

--fleshy, movable lips and cheeks (Romer, p. 326)

--loss of palatal teeth (Romer, p. 328)

--taste buds primarily on tongue (Romer, p. 328)

--diaphragm (Romer, p. 368)

--vocal cords and resultant voice (Romer, p. 370)

--stomach enzymes and acid are produced by two separate cell types rather than the same cell type as in reptiles (Romer, p. 382)

--intestinal villi prominent (Romer, p. 386)

--rectum derived from cloaca (Romer, p. 389)

--teeth embedded in sockets (thecodont condition) (Kardong, p. 497)

--an additional layer of teeth known as cementum anchors the root of the teeth. (Weichert, 1970, p. 169)

--teeth replaced only once

--occlusion of teeth in upper and lower jaws

--parotid and submaxillary salivary glands (Weichert, 1970, p. 161-2)

--amylase from salivary glands (Stephens)              


  1. Therian Mammal Ancestor (Marsupials and Placentals)

--thyroid cartilages which fuse (Weichert, 1970)231

--loss of possess horny egg teeth. (Weichert, 1970, p. 173)

  --sucrase (Stevens)..


  1. Placental Mammal Ancestor

--marsupial lungs are reptilian at birth ( a separate capillary in each air space, cuboidal epithelia lining alveoli); later mammal (Stonehouse, 1977)

--loss of cloaca (except in most primitive placentals such as some insectivores)


  1. Primate Ancestor


  1. Anthropoid Primate Ancestor (monkeys, apes, and humans)

--lower portion of duodenum attached by a special ligament (3)


  1. Catarrhine Primate Ancestor (Old World Monkeys, apes and humans)

--dental formula of 2133/2133


  1. Ape Ancestor

--appendix (Ankel-Simons, p. 385)


  1. African Ape Ancestor

--characteristics of spleen (Ankel-Simons, p. 385)


  1. Human Ancestor

--jaw protrudes less, affecting shape of pharynx and sound production

--in throat, pharynx lengthens which enhances sound production but makes choking a greater hazard (Kardong, p. 496)