Note added July 31, 2016:
The addition of more taxa preserves the close relationship of pangolins to primates,
At present, the large reptile tree (LRT) includes very few mammals
so keep that in mind. The LRT (now at 704 taxa) is also not fine tuned to mammal traits, like molar shapes, so keep that in mind.
Pangolins have been difficult to nest.
Recent DNA tests (Murphy et al. 2001, Beck et al. 2006) nested pangolins with carnivores, but could be no more specific than that because fossil taxa cannot be tested for DNA.
Here’s the early morphological evidence
linking Manis to Notharctus using traits that are NOT in the LRT.
- Flexible vertebral column – pangolins use to roll up, lemurs use to wind up then jump from tree to tree and land without a jolt
- Circumorbital ring in some species of pangolin
- Long, clawed fingers (toes), short opposable thumb (big toe)
- Procumbent dentary teeth at tip (some species)
- Arboreal habitat
- Prehensile tail
- One usually, but up to three infants born at a time.
- Infants ride mother’s back and tail
Manis/Notharctus synapomorphies from the LRT:
- Dorsal nasal shape: widest at mid length (here posterior to mid length, but identical in Manis and Notharctus).
- Pmx/Mx notch: > 45º
- Posterolateral Pmx not narrower than nares
- Mx ventrally convex
- Fr/Pa suture straight and > Fr/Na suture width (with Homo, too)
- Posterior parietal angle in dorsal view > 40º to transverse plane
- Suborbital fenestra (with Homo, too)
- Ectopterygoid, cheek process larger (with Homo, too)
- Ectopterygoid continues aligned along pterygoid lateral edge
- Premaxillary teeth tiny to absent
- Cervical centra taller than long (with Homo, too)
- Cervicals cerntra decrease toward skull
- Femuir < half glenoid – acetabulum length
- Pedal 3.1 > p2.1
- Longest pedal digits: 3 and 4
- Metatarsals 2 and 3 align with mt1
- Metatarsals 3 and 4 align with mt5
There are several traits
in the LRT that pangolins share with people to the exclusion of lemurs, all by convergence, so not worth going into.
Some atavisms (genetic reversals) in Manis
that most other mammals don’t have include the following:
- Low to absent coronoid process
- Elongate caudal transverse processes
What opossums and rats have on their tails, pangolins have all over their bodies.
The order of the loss of facial bones
provides clues to the chronology of evolutionary events in pangolins. The loss of the lateral temporal bar (posterior jugal + squamosal) occurred in all pangolins, but the loss of the jugal is apparent in ground forms, so this was a trees down order, with burrowing following tree climbing. The clavicle is also lost in pangolins.
Diet: ants and termites.
So this is what happens when a lemur changes diet and becomes solitary, and depends on sense of smell, rather than sight. Elongate tongue is convergent with that of chameleons, woodpeckers, anteaters and nectar bats. Some pangolins burrow. Loss of the lower temporal bar and loss of most of the jugal in some species goes along with loss of the coronoid process in this anteater. Manis doesn’t need chomping muscles. Nor does it need speed and leaping ability. Given an ant diet and solitary social life, perhaps that makes it easier to visualize how Manis could be derived from a more active, social lemur-like ancestor.
So…here’s the evolutionary scenario:
- Vicious and crafty arboreal carnivore: Vulpavus
- Frisky and social arboreal omnivore: Notharctus
- Slow and antisocial arboreal (grading to burrowing) anteater: Manis
Murphy WJ., et al. 2001-12-14. Resolution of the Early Placental Mammal Radiation Using Bayesian Phylogenetics. Science 294 (5550): 2348–2351. doi:10.1126/science.1067179. PMID 11743200.
Beck R, Bininda-Emonds ORP, Cardillo,M; Liu, F-G and Purvis A 2006. A higher-level MRP supertree of placental mammals. BMC Evolutionary Biology 6 (1): 93. doi:10.1186/1471-2148-6-93. PMC 1654192. PMID 17101039.