Pholidota

Pholidota (commonly known as pangolins or scaly anteaters, from the Ancient Greek pholis / pholidos, "horny scale," and the Malay word pengguling, "one that rolls up") is an order of placental mammals comprising eight extant species in a single living family (Manidae) distributed across tropical and subtropical Asia (Manis) and sub-Saharan Africa (Phataginus and Smutsia). Pangolins are the only known mammals in Earth's history whose bodies are covered in large, overlapping, sharp-edged epidermal scales made of α- and β-like keratin.

Although pangolins were historically grouped with South American anteaters, sloths, and armadillos (Xenarthra) and African aardvarks (Orycteropus afer in Afrotheria) inside the obsolete taxon "Edentata" due to their striking convergent adaptations for eating ants and termites (myrmecophagy), molecular phylogenomics establishes that Pholidota is not related to Xenarthra at all. Instead, Pholidota lies inside the superorder Laurasiatheria as the direct sister order to Carnivora (cats, dogs, bears, and seals), together forming the clade Ferae (which diverged during the Paleocene, ~60 million years ago).

Fossil pangolins (Eomanis waldi and Eurotamandua from the 47-million-year-old Middle Eocene Messel Pit in Germany, and the giant Miocene–Pleistocene Manis paleojavanica, which reached 2.5 meters in length) demonstrate that Pholidota originated in Europe/Eurasia before dispersing into Asia and Africa:

Unlike the armor of armadillos (Xenarthra), crocodiles (Crocodylia), and turtles (Testudines)—which consists of vascularized dermal bone plates (osteoderms) covered by a thin keratin film—pangolin scales contain zero bone and zero calcium mineralization. Instead, they are pure cornified epidermal appendages (homologous to mammalian fingernails and primate hair, growing continuously from dermal papillae to replace distal wear) that account for ~20% of the pangolin's total body weight (~900 to 1,000 overlapping scales per adult):

1. Tri-Layered Crossed-Lamellar Microarchitecture: Materials-science indentation and synchrotron X-ray diffraction studies (Wang et al., 2016) reveal why a 2–4 mm thick pangolin scale can withstand the >3,000-Newton crushing bite of an African lion (Panthera leo) or leopard (Panthera pardus) without shattering:
   • Dorsal Outer Layer: Flattened, parallel keratinized corneocytes rich in hard α-keratin intermediate filaments that resist localized tooth penetration.
   • Thick Middle Layer (Crossed-Lamellar / Bouligand-Like Tilt): Flattened keratinized cell sheets stacked in alternating orthogonal and oblique orientations (45°–90°) linked by nanoscale interlocking cell-membrane sutures (~50–100 nm wavelength) and dense disulfide (–S–S–) cross-links.
   • Ventral Inner Layer: Coaligned fibers running parallel to the scale axis to absorb tensile bending strain.
2. Strain-Rate-Dependent Energy Dissipation: When a predator's canine tooth impacts a rolled-up pangolin (whose powerful cutaneous panniculus carnosus muscle locks the overlapping scales into an impenetrable sphere while swinging the sharp-edged tail scales sideways like a serrated scissor), propagating microcracks are deflected through 90° twists along the crossed-lamellar cell boundaries—increasing fracture toughness by an order of magnitude over homogeneous keratin.

Every anatomically specialized trait of the pangolin feeding apparatus evolved independently of South American anteaters (Xenarthra) and African aardvarks:

• Complete Loss of Teeth and Enamel Genes (ENAM, AMELX, AMBN): Adult pangolins are 100% edentulous (toothless), having pseudogenized all tooth-enamel and dentin-sialophosphoprotein (DSPP) genes in the Paleocene. Their jaws are reduced to slender, splint-like bony rods lacking a coronoid process, angular process, and zygomatic arch, with chewed mastication eliminated fully.
• The Pelvic-Anchored Xiphisternal Tongue: A pangolin's cylindrical, muscular-hydrostat tongue is longer than its head and body combined (extending up to 40 cm past the snout in Smutsia gigantea). Because no throat or thoracic cavity could house a tongue of this length, the pangolin's xiphisternum (posterior sternum) is elongated into two extraordinary cartilaginous/bony rods that run backward through the entire abdominal cavity, turn upward near the pelvis, and anchor near the last ribs, enclosing a lubricated sheath (glossal tube) inside which the retractor muscles pull the resting tongue deep into the lower abdomen!
• Keratinous Pyloric Gizzard Spines and Swallowed Stones: Coated in sticky glycoprotein saliva from large-scale submandibular glands (which fill the upper chest), the tongue flicks in and out of ant nests and termite mounds to harvest 150,000 to 200,000 insects per night. Inside the stomach, whose lumen is lined with stratified squamous keratinized epithelium rather than acid-secreting glands over most of its surface, a muscular pyloric gizzard armed with cornified keratinous "gastric teeth" (spines) grinds whole ants and termites against swallowed quartz pebbles (gastroliths).

Whole-genome sequencing of Malayan (Manis javanica) and Chinese (Manis pentadactyla) pangolins (Choo et al., 2016; Fischer et al., 2020) uncovered two surprising evolutionary deletions in the pangolin innate immune repertoire:

1. Deletion of Interferon-Epsilon (IFNE): Unlike nearly all other placental mammals, which express IFNE constitutively in skin and mucosal epithelia as a first-line antiviral barrier, IFNE is pseudogenized in all sequenced pangolins (correlating with the replacement of sweat-gland-bearing furred skin with avascular keratin scales).
2. Pseudogenization of Cytosolic Viral Sensors IFIH1 (MDA5) and ZBP1: Pangolins have fully inactivated both IFIH1 (which encodes MDA5, the primary cytosolic RIG-I-like receptor that senses long double-stranded RNA of coronaviruses and picornaviruses) and ZBP1 (which senses Z-form viral RNA/DNA to trigger necroptosis and pyroptosis), as well as dampening the cGAS–STING pathway!
   • Evolutionary immunologists hypothesize that just as bats evolved dampened interferon/inflammasome responses to tolerate viral infection without lethal immunopathology, pangolins lost IFIH1/MDA5 and ZBP1 as an evolutionary tolerance adaptation—preventing hyper-inflammatory cytokine storms when exposed to soil- and arthropod-borne viruses, while making trafficked pangolins permissive hosts for Sendai virus, pestiviruses, and SARS-CoV-2-related sarbecoviruses.

Because pangolin evolutionary defense against lions, tigers, and hyenas consists of curling into a passive immobile ball, pangolins are uniquely defenseless against human poachers, who simply pick them up from the forest floor. Driven by illegal international demand for pangolin meat and dried scales (which are chemically identical to human fingernails and carry zero pharmacological activity, yet are consumed in illicit traditional medicine markets), more than 1 million wild pangolins were poached between 2000 and 2020—leading CITES in 2016 to transfer all eight extant species to Appendix I (prohibiting all international commercial trade).

1. Gaudin, T. J., Emry, R. J., & Wible, J. R. (2009). The phylogeny of living and extinct pangolins (Mammalia, Pholidota) and associated taxa: a morphology based analysis. Journal of Mammalian Evolution, 16(4), 235–305. Google Scholar
2. Wang, B., Yang, W., Sherman, V. R., & Meyers, M. A. (2016). Pangolin armor: overlapping, structure, and mechanical properties of the keratinous scales. Acta Biomaterialia, 41, 60–74. Google Scholar
3. Choo, S. W., et al. (2016). Pangolin genomes and the evolution of mammalian scales and immunity. Genome Research, 26(10), 1312–1322. Google Scholar
4. Fischer, H., Tschachler, E., & Eckhart, L. (2020). Pangolins lack IFIH1/MDA5, a cytoplasmic RNA sensor that initiates innate immune defense upon coronavirus infection. Frontiers in Immunology, 11, 939. Google Scholar

• Carnivora
• Mammalia
• Xenarthra
• Biomaterials
• Innate Immunity