Kopidodon enters the LRT basal to pangolins

Today
another enigma taxon nests in the LRT.

The Messel pit (Eocene) assemblage
has produced some of the most incredible fossils of completely articulated skeletons of birds and mammals, often with feathers and fur. and, in this case (Fig. 1), small round ears.

Figure 1. One of five complete skeletons of Kopiodon known from the middle Eocene Messel pits. A hand, foot and pelvis are layered to extend the fingers and toes for scoring.

Figure 1. One of five complete skeletons of Kopiodon known from the middle Eocene Messel pits. A hand, foot and pelvis are layered to extend the fingers and toes for scoring.

Kopidodon macrognathus (originally Cryptopithecus macrognathus Wittich 1902; Weitzel 1933/4; Tobien 1969; Naturmuseum Senckenberg; 115cm total length; middle Eocene, 47 mya; Figs. 1, 5) is traditionally considered, “a squirrel-like mammal with large canines” and therefore, somewhat of an enigma taxon.

Here
in the large reptile tree (LRT, 1669+ taxa) Kopidodon nests at the at the base of the pangolins, a sister to Chriacus (Fig. 2) + bats. Kopidodon likely had a Late Jurassic genesis based on the presence of scaled Zhangheotherium in the Early Cretacous. The skull of Kopidodon has a convex profile, like that of another pangolin ancestor, Metachromys (Fig. 3). This helps inform the likely profile of Zhangheotherium, preserved ventrally exposed.

Figure 2. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Figure 2. Chriacus and Onychonycteris nest as sisters to the pangolin clade with Kopoidodon at its base.

Pangolins
llike Manis (Fig. 4) are slow-moving, muscular, tree climbing insectivores. Their hair coalesces to form overlapping scales. For protection pangolins are able to roll into a ball.

Figure 2. Pangolin ancestor Metacheiromys skeleton and skull.

Figure 3. Pangolin ancestor Metacheiromys skeleton and skull, less than half the size of Kopidodon.

Kopidon was a late survivor of a primitively fur covered radiation. 
Hair-scales first appear in Zhangheotherium.

Figure 2. Manis, the Chinese Tree Pangolin along with other views of other pangolins

Figure 4. Manis, the Chinese Tree Pangolin along with other views of other pangolins

Kopidodon
had 26-29 (it varies) presacral vertebrae + 3 sacrals. The foreclaws were taller than wide (similar to arboreal mammals) and larger than the hind claws. The feet were plantigrade. The limbs were heavily muscled and designed for slow movement. The tail vertebrae diminished posteriorly to tiny elongate bones. Stomach contents include fruit and seeds.

Figure 3. Kopiodon skull in situ 2x and reconstructed.

Figure 5. Kopiodon skull in situ 2x and reconstructed. Compare to figure 3.

Kopidodon is traditionally considered a member
of the Cimolesta, the Pantolestidae, and the Paroxyclaenidae, but traditional members do not form monophyletic clades in the LRT.

Wikipedia (German version) reports,
The first description of Kopidodon took place in 1933, the taxonomic position was controversial for a long time.” The original name, Cryptopithecus, reflects that uncertainty as it tentatively allied this taxon with primates. The LRT minimizes taxon exclusion problems by including a wide gamut of taxa.

If this is not a novel hypothesis of interrelationships,
let me know of the original citation so I can promote it.


References
Clemens WA and von Koenigswald W 1993. A new skeleton of Kopidodon macrognathus from the Middle Eocene of Messel and the relationship of paroxyclaenids and pantolestids based on postcranial evidence. Kaupia 3, 1993, S. 57–73.
Koenigswald W von 1983. Skelettfunde von Kopidodon (Condylarthra, Mammalia) aus dem mitteleozänen Ölschiefer der Grube Messel bei Darmstadt. N Jb Geol Paläont Abh 167:1–39.
Koenigswald W von 1992. The arboreal Kopidodon, a relative of primitive hoofed mammals. In: Schaal S, Ziegler W (eds) Messel. An insight into the history of life and of the Earth. Clarendon Press, Oxford, pp 233–237.
Tobien H 1969. Kopidodon (Condylarthra, Mammalia) aus dem Mitteleozän (Lutetium) von Messel bei Darmstadt (Hessen). Notizblätter der hessischen Landesanstalt für Bodenforschung 97, 1969, S. 7–37.
Tobien H 1988. Kopidodon (Condylarthra, Mammalia) aus dem Mitteleozän (Lutetium) von Messel bei Darmstadt (Hessen). = Kopidodon (Condylarthra, Mammalia) from the middle Eocene (Lutetian) of Messel near Darmstadt, Hesse. Notizblatt des Hessischen Landesamtes fuer Bodenforschung zu Wiesbaden 97: 7-37.
Weitzel K 1933. Kopidodon macrognathus Wittich, ein Raubtier aus dem Mitteleozän von Messel. Notizblätter des Vereins für Erdkunde der hessischen geologischen Landesanstalt Darmstadt 14, 1933, S. 81–88
Wittich E 1898, 1902. ein Raubtier aus dem Mitteleozän von Messel. Notizblatt des Vereins für. Erdkunde zu Darmstadt (5)14: 81-88.

Greman/wiki/Kopidodon

Resurrecting the clade ‘Volitantia’ Illiger 1811.

Volitantia
was defined by Illiger 1811 as Chiroptera (bats) + Dermoptera (colugos). Wikipedia authors consider this clade obsolete and polphyletic. The large reptile tree (LRT, 1233 taxa) nests these two taxa together in a monophyletic clade that also includes the pangolins and their closest ancestors (e.g. Zhangheotherium). We looked at their traditionally overlooked relationships a few days earlier here.

Szalay and Lucas 1996 reported, “We find support for the Volitantia in the nature of the shared derived similarities (and phyletically significant differences as well) in the elbow complex, and in Leche’s (1886) suggestion of the synapomorphus and unique presence (in non aquatic mammals) of an interdigital membrane of the hand in bats and colugos. They studied Chriacus and Mixodectes (not yet tested), not pangolins.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Like another clade traditionally considered obsolete,
Enaliosauria, that was resurrected by the LRT, Volitantia is likewise resurrected as a monophyletic clade, but it now includes the Pholidota (pangolins) according to LRT results.

Goodbye ‘Ferae’
The putative clade ‘Ferae‘ (pangolins + carnivorans) is not supported by the LRT because pangolins nest within the Volitantia.

As long-time readers know,
many traditional relationships between placental clades are not supported by the LRT, which continues to document a gradual accumulation of derived traits at every node in nearly full resolution for a wide gamut of tetrapod taxa.

Many arboreal mammals were experimenting with gliding
(e.g. Volaticotherium and  Maiopatagaium), but only one clade, bats, experimented with flapping. This was, perhaps not coincidentally, during the Middle to Late Jurassic (Oxordian, 160 mya). Remember, these membranes were all extensions of the infant nursery found in colugos and other volatantians, not far from the basalmost placental, Monodelphis. It is possible that all basalmost mammals had these membrane extensions and most of their ancestors lost them.

References
Illiger C 1811. Prodromus systematis mammalium et nivium additis terminis zoograhicis utriudque classis. Berlin: C. Salfeld.
Szalay F and Lucas SG 1996. The postcranial morphology of Paleocene Chriacus and Mixodectes and the phylogenetic  relationships of archontan mammals. Bulletin of the New Mexico Museum of Natural History and Science 7: 47 pp.

wiki/Volitantia

 

Zhangheotherium: a pangolin ancestor

Updated Sept 08, 2016 with higher resolution images of Henkelotherium.

Today we’ll look at
Zhangheotherium quinquecuspidens (Hu et al. 2009; Late Jurassic/Early Creteacous; dentary length 3 cm; IVPP V7466; Fig. 1). It was originally described as a symmetrodont mammal, an ‘archaic’ taxon typically represented by only tooth and dentary scraps. Here (Fig. 1) a complete skeleton provided new insight to the original authors. They reported Zhangheotherium did not travel in a parasagittal posture and the cochlea (an organ of the inner ear) was not fully coiled.

Figure 1. Zhangheotherium reconstructed. The tail is unknown. The high scapulae indicate great strength in the pectoral region, likely for arboreal locomotion in a taxon of this size. Zhangheotherium nests as a basal pangolin. It was preserved in ventral view. Here the epipubes are identified as pubes, which is otherwise not shown.

Figure 1. Zhangheotherium reconstructed. The tail is unknown. The high scapulae indicate great strength in the pectoral region, likely for arboreal locomotion in a taxon of this size. Zhangheotherium nests as a basal pangolin. It was preserved in ventral view. Here the epipubes are identified as pubes, which is otherwise not shown.

Keep in mind, for the moment,
that neither bats nor pangolins travel in a parasagittal posture. Pangolins are bipedal (video here). Bats are inverted bipeds. Both fold their fingers posteriorly when not using them. That’s why the forelimbs are lifted here (Fig.1) even though neither Zhangheotherium nor Manis would be reconstructed as a biped if not known from in vivo behavior.

Figure 2. Hu et al. nested Zhangheotherium basal to the Placental/Marsupial split, contra the results of the large reptile tree.

Figure 2. Hu et al. nested Zhangheotherium basal to the Placental/Marsupial split, contra the results of the large reptile tree.

Unfortunately, 
Hu et al. thought Zhangheotherium radiated before the divergence of living marsupials and placentals. Here, in the large reptile tree (LRT) Zhangheotherium nests at the base of the Ernanodon + pangolins clade, close to Chriacus and the bats and not far from the dermopterans. Clearly this was originally or principally an arboreal clade. Ernanodon is the exception that got big as it left the trees for the ground, something other pangolins did, too.

Figure 3. Subset of the large reptile tree showing the nesting Zhangheotherium basal to pangolins.

Figure 3. Subset of the large reptile tree showing the nesting Zhangheotherium basal to pangolins.

Hu et al note:
“A mobile clavicle–interclavicle joint that allows a wide range of movement of the forelimb has an ancient origin in the mammalian phylogeny.” This is quite visible in the fossil and interesting with regard to Zhangheotherium’s relation to bat ancestors. Bats and Didelphis likewise have a large floating pectoral girdle. Pangolins have a large scapula more closely associated with the rib cage.

In Zhangheotherium, Hu et all note [my remarks follow in brackets]:

  1. The cervical ribs were unfused.[have not gotten close enough to pangolins to check this out]
  2. The caudal transverse processes were wide [as in pangolins].
  3. Three or four sacrals were present [suggesting stress in this area, perhaps for balance].
  4. The pisiform is very large [as in Ptilocercus and Manis].
  5. Only the dorsal acetabulum is preserved [open ventrally as in pangolins]
  6. Zhangheotherium has an external pedal spur, as in Ornithorhynchus [not sure about this disarticulated bone, perhaps not a spur, but a simple spindle-shaped ankle bone similar to one seen in Manis, see Fig. 4]
  7. The interclavicle is triangular and the sternal manubria are only three in number. [Could not find com parables here]
  8. It is more primitive than Henkelotherium and Vincelestes in retaining the interclavicle in its pectoral girdle/sternal manubrium [no comparables found]
  9. These new data suggest that the mobility of the clavicle and scapula has a more ancient origin than the more parasagittal posture of the forelimbs [or… this type of arboreal locomotion loosens the girdles]
  10. The mobile and pivotal clavicle evolved before the divergence of multituberculates and therians. [in the LRT multituberculates are therians and placentals, and so is Zhangheotherium].
Figure 4. The pes of Zhangheotherium with spine in orange. The same bone shrinks in Cryptomanis and further in Manis.

Figure 4. The pes of Zhangheotherium with identified spine in orange. The same bone shrinks in Cryptomanis and further in Manis.

Hu et al. report, “It has been argued that dental characters are as homoplasic as non-dental characters and the reliability of dental characters for inferring the relationships of major lineages of mammals has been questioned. Zhangheotherium has provided more extensive basicranial and postcranial evidence to corroborate the traditional hypothesis that symmetrodonts represent a part of the basal therian radiation.” [Zhangheotherium nests in a basal placental position in the LRT.

Figure 1. Henkelotherium, a traditional pantothere, nests as a Late Jurassic pre-rabbit in the LRT.

Figure 5. Henkelotherium, a traditional pantothere, nests as a Late Jurassic pre-rabbit in the LRT. Note how tiny it is.

Hu et al. link
Zhangheotherium to Henkelotherium (Krebs 1991; Late Jurassic, Kimmeridgian; Figs. 5, 6). So let’s look at Henkelotherium while we’re here.

Figure 2. Henkelotherium reconstructed from DGS tracings in figure 1. Note the tiny manus and large pes, traits that continue into extant rabbits.

Figure 6. Henkelotherium reconstructed from DGS tracings in figure 1. Note the tiny manus and large pes, traits that continue into extant rabbits. The purported epipubes may in fact be displaced pubes.

In the large reptile tree
Henkelotherium and Zhangheotherium do not nest together. Rather Henkelotherium nests with Nambaroo and Plesiadapis + rabbits.  Wikipedia considers Henkelotherium a paurodontid dryolestid (formerly considered a eupantothere) and similar in locomotion patterns to tree shrews and opossums. Key to Henkelotherium are the enlarged dentary incisors (premaxilla remains unknown). This represents the first step toward the larger incisors found in plesiadapiformes, Tupaia-like tree shrews, apatemyids and rodents + multituberculates.

Back to Zhangheotherium, you’ll note
the dentary condylar process curves dorsally and no post-dentary bones are present (all had become middle ear bones enclosed within the petrosal). That dorsal curve removes most of the ability to resist jaw dislocation often caused by struggling large prey and or small pieces of even larger prey are working against large canines, which were also not present in Zhangheotherium. These traits point to a tiny prey diet, likely of insects, just like pangolins.

References
Hu Y-M, Wang YQ, Luo Z and Li CK 1997. A new symmetrodont mammal from China and its implications for mammalian evolution. Nature 390:137-142.
Krebs B 1991. Skelett von Henkelotherium guimarotae gen. et sp. nov. (Eupantotheria, Mammalia) aus dem Oberen Jura von Portugal. Berl Geowiss Abh A.: 133:1–110.

wiki/Zhangheotherium

Pangolins nest as bat sisters in the LRT

Note added July 31, 2016:
The addition of more taxa preserves the close relationship of pangolins to primates, 

Note added June 20, 2018
The reevaluation of Zhangheotherium as a basal pangolin nests this clade between dermopterans and bats. Click here for more details.

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.

So here it is:
the large reptile tree nests the pangolin, Manis, with the basal lemur, Notharctus. And Notharctus is derived from basal carnivores like Vulpavus.

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.

Figure 1. Therapsida includes the pangolin, Manis, which nests here with Notharctus. one of only a few mammals tested so far.

Here’s the early morphological evidence
linking Manis to Notharctus using traits that are NOT in the LRT.

  1. Flexible vertebral column – pangolins use to roll up, lemurs use to wind up then jump from tree to tree and land without a jolt
  2. Circumorbital ring in some species of pangolin
  3. Long, clawed fingers (toes), short opposable thumb (big toe)
  4. Procumbent dentary teeth at tip (some species)
  5. Arboreal habitat
  6. Prehensile tail
  7. One usually, but up to three infants born at a time.
  8. Infants ride mother’s back and tail
Figure 1. Notharctus, an Eocene adapid (lemur) and likely sister to Manis.

Figure 1. Notharctus, an Eocene adapid (lemur) and likely sister to Manis.

Figure 2. Manis, the Chinese Tree Pangolin along with other views of other pangolins

Figure 2. Manis, the Chinese Tree Pangolin along with other views of other pangolins

Manis/Notharctus synapomorphies from the LRT:

  1. Dorsal nasal shape: widest at mid length (here posterior to mid length, but identical in Manis and Notharctus).
  2. Pmx/Mx notch: > 45º
  3. Posterolateral Pmx not narrower than nares
  4. Mx ventrally convex
  5. Fr/Pa suture straight and > Fr/Na suture width (with Homo, too)
  6. Posterior parietal angle in dorsal view > 40º to transverse plane
  7. Suborbital fenestra (with Homo, too)
  8. Ectopterygoid, cheek process larger (with Homo, too)
  9. Ectopterygoid continues aligned along pterygoid lateral edge
  10. Premaxillary teeth tiny to absent
  11. Cervical centra taller than long (with Homo, too)
  12. Cervicals cerntra decrease toward skull
  13. Femuir < half glenoid – acetabulum length
  14. Pedal 3.1 > p2.1
  15. Longest pedal digits: 3 and 4
  16. Metatarsals 2 and 3 align with mt1
  17. 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:

  1. Chevrons
  2. Scales
  3. Low to absent coronoid process
  4. Elongate caudal transverse processes

The important thing here
is that given the opportunity to nest with the basal carnivores, Vulpavus, Nandinia and Chriacus, Manis nested instead with Notharctus.

Keratin scales
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:

  1. Vicious and crafty arboreal carnivore: Vulpavus
  2. Frisky and social arboreal omnivore: Notharctus
  3. Slow and antisocial arboreal (grading to burrowing) anteater: Manis

New data:

Figure 1. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins.

Figure 1. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

References
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.

wiki/Pangolin