In honor of Mother’s Day…

We have a pregnant
plesiosaur (Fig. 1; O’Keefe and Chiappe 2011; LACM 129639; Late Cretaceous, 78 mya)…

Figure 1 Pregnant Polycotylus (LACM 129639) from O'Keefe and Chiappe 2011.

Figure 1 Pregnant Polycotylus (LACM 129639) from O’Keefe and Chiappe 2011.

and a pregnant primate (Fig. 2) very dear to my heart.

Figure 2. My daughter Stephanie one week before giving birth to grandson James (nickname: Jet).

Figure 2. My daughter Stephanie one week before giving birth to grandson James (nickname: Jet) and about three years ago.

Being a mom goes way, way back
In our lineage, first cells stuck together, flagella out (Fig. 3). Then four cells stuck together. Then eight. Ultimately hundreds stuck together creating a sphere, or blastula. And little blastulas formed inside until they were large enough to break free.

Figure 3. Blastula from the book, "From the Beginning" by Peters 1991.

Figure 3. Blastula from the book, “From the Beginning” by Peters 1991.

Plesiosaurs and primates capable of understanding prehistory
followed shortly thereafter. The basics of being a mother haven’t really changed much in the last few billion years.

References
O’Keefe FR and Chiappe LM 2011. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science. 333 (6044): 870–873. doi:10.1126/science.1205689.
Peters D 1991. From the beginning – the story of human evolution. Little Brown. 128 pp. Online here.

wiki/Polycotylus

What is Darwinius?

Franzen et al. 2009
reported on a well-preserved small primate from 50mya named Darwinius.

From the Franzen et al. 2009 conclusion:
“Darwinius masillae represents the most complete fossil primate ever found, including both skeleton, soft body outline and contents of the digestive tract. Study of all these features allows a fairly complete reconstruction of life history, locomotion, and diet. Any future study of Eocene-Oligocene primates should benefit from information preserved in the Darwinius holotype. Of particular importance to phylogenetic studies, the absence of a toilet claw and a toothcomb demonstrates that Darwinius masillae is not simply a fossil lemur, but part of a larger group of primates, Adapoidea, representative of the early haplorhine diversification.”

In a published comment Beard 2009 wrote:
“Unbridled hoopla attended the unveiling of a 47-million-year-old fossil primate skeleton at the American Museum of Natural History in New York on 19 May. Found by private collectors in 1983 in Messel, Germany, the press immediately hailed the specimen as a “missing link” and even the “eighth wonder of the world.”

“Overall proportions and anatomy resemble that of a lemur, and the same is true for other adapiform primates. A new genus and species of adapiform primate, Darwinius masillae (Franzen et al., 2009; Eocene, 50 mya ). The adapids are a branch of the primate tree that leads to modern lemurs. Ida would have to have anthropoid-like features that evolved after anthropoids split away from lemurs and other early primates. Here, alas, Ida fails miserably.” The reasons for that “fail” were not listed in the Beard note.

Taxon exclusion?
The large reptile tree, (LRT, 896 taxa), currently tests only a few primates. At this stage, Darwinius does indeed nest at the base of higher primates (simians), alongside Tarsius, the extant tarsier, but there are many dozen primate taxa that have not been included in the LRT.

Figure 1. Darwinius overall plus an X-ray showing the transition from milk teeth to adult teeth in this juvenile specimen.

Figure 1. Darwinius overall plus an X-ray showing the transition from milk teeth to adult teeth in this juvenile specimen.

In the LRT,
nesting only a few primates at present, the adapid prosimian, Notharctus, is basal to higher primates including humans (genus Homo). Tarsius, the tarsier, nests between Notharctus and Proconsul, a basal anthropoid (ape). Darwinius nests with Tarsius, but lacks the many specialized autapomorphies that characterize extant tarsiers like:

  1. oversized eyes
  2. distally fused tibiafibula
  3. elongated pedal digits 4 and 5.
  4. hyperelongated astragalus and calcaneum
  5. cervicals insert further beneath the skull
Figure 2. Tarsius, the extant tarsier. Note the several autapomorphies displayed here vs. the many plesiamorphies in Darwinius.

Figure 2. Tarsius, the extant tarsier. Note the several autapomorphies displayed here vs. the many plesiamorphies in Darwinius.

Wikipedia reports
“Most experts hold that the higher primates (simians) evolved from Tarsiidae, branching off the Strepsirrhini before the appearance of the Adapiformes.” If true, Darwinius is close to the lineage of humans. “A smaller group agrees with Franzen et al. that the higher primates descend from Adapiformes (Adapoidea). The view of paleontologist Tim White is that Darwinius is unlikely to end the argument.” 

NBC news reports,
here that “Ida is as far removed from the monkey-ape-human ancestry as a primate could be, says Erik Seiffert of Stony Brook University in New York. The new analysis says Darwinius does not belong in the same primate category as monkeys, apes and humans. Instead, the analysis concluded, it falls into the other major grouping, which includes lemurs.”

Nature reports on the “media frenzy”
here in a paper entitled: A hyped-up fossil find highlights the potential dangers of publicity machines.  To be fair, the authors’ claims at the press conference were appropriately measured. Nonetheless, the researchers were fully involved in the documentaries and the media campaign, which associate them with a drastic misrepresentation of their research.”

“Another damaging aspect of the events was the unavailability of the paper ahead of the press conference and initial media coverage. This prevented scientists other than those in the team from assessing the work and thereby ensuring that journalists could give a balanced account of the research.

“There is no reason to think that PLoS ONE’s editors and reviewers did less than their duty to the paper. Nonetheless, the clock was ticking at the time of submission.”

“In principle, there is no reason why science should not be accompanied by highly proactive publicity machines. But in practice, such arrangements introduce conflicting incentives that can all too easily undermine the process of the assessment and communication of science.”

The primate experts can hash this out.
At present, with so few primates tested, Darwinius is still a candidate to be at the transition from prosimian to simian in the LRT, as it presently nests… until additional taxa knock it out.

Added within minutes of posting
I ran across this reference:
Gingerich PD et al. 2010. Darwinius masillae is a Haplorhine — Reply to  Williams et al. (2010). Journal of Human Evolution. 59(5)574-576 where they report, “Williams et al. (2010) imply that ‘total evidence’ means study of hundreds of characters in a great many taxa. However, total evidence is about combining data before analysis and not about the size of the resulting matrix. “We agree with Seiffert et al., 2009 and Williams et al., 2010, and others that there is a strepsirrhine–haplorhine dichotomy in primate evolution. We employ the same cladistic methods. We accept that total evidence drawn from many sources is advantageous. Why then do we reach such a different conclusion about the systematic position of Darwinius? Given that our methods are the same, then our contrasting results can only be explained by differences in the number and balance of taxa chosen for study, the character matrix used to analyze higher-level primate phylogeny, the outgroup chosen to root a phylogenetic network, or some combination of these.”
More details on their arguments are found here.

References
Beard C 2009. Why Ida is fossil is not the missing link. Comment, NewScientist.
Online here.
Franzen JL, Gingerich PD, Habersetzer J, Hurum JH, Von Koenigswald W and Smith BH 2009. Complete primate skeleton from the Middle Eocene of Messel in Germany: morphology and paleobiology PLoS ONE. 4 (5): e5723.

wiki/Darwinius

nature.com article that touches on Darwinius

 

Pangolins nest as lemur sisters in the LRT

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.

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.

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

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

The foot of Archicebus – an early primate

We haven’t looked at mammals or synapsids for awhile.
If you want to check the large reptile tree, they’re still reptiles — just hairier. Todays let’s look at Archicebus (Early Eocene, 55 mya, Ni et al. 2013),  the oldest primate known from a skeleton. Notharctus is 5 million years younger, but more primitive, just as living lemurs are more primitive than modern apes and humans are. Ipso facto, the discovery of Archicebus pushes the origin of lemurs back even further. The younger lemuroid, Smilodectes, had a similar short-snout skull.

Figure 1. Archicebus is close the ancestry of tarsiers and monkeys. It retained a lemur-like foot,

Figure 1. Archicebus is close the ancestry of tarsiers and monkeys. It retained a lemur-like foot, but with distinctly tarsier-like proportions starting to show. Here in a published illustration pedal digit 1 is not illustrated as more robust and the metatarsals are inaccurately similar in length. The size was about that of the smallest living lemur, the pygmy mouse lemur. Moderate size eye sockets are distinct from the giant eye sockets of living nocturnal tarsiers.

My interest in feet
and PILs (parallel interphalangeal lines) goes back a long way (Peters 2000a, 2010, 2011). Pterosaur PILs are instructive, helping flatten or elevate plantigrade and digitigrade pedes. Cats put an interesting twist on PILs due to their retractable claws. Primates do too, because they are adapted to cylindrical substrates (branches), not flat (the ground).

Figure 2. Click to enlarge. The two pedes of Archicebus, bottom sides flipped to match top sides. Toes colorized for reconstruction (Fig. 3).

Figure 2. Click to enlarge. The two pedes of Archicebus, bottom sides flipped to match top sides. Toes colorized for reconstruction (Fig. 3). The talus/astragalus is missing from both pedes.  Note the massive proximal articulation of the big toe.

Nature reports, “By analyzing almost 1,200 morphological aspects of the fossil and comparing them to those of 156 other extant and extinct mammals, the team put the ancient primate near the base of the tarsier family tree.” I haven’t repeated that experiment, buy it looks to me that pedal characters alone would tell the tale Figs. 3,4).

Figure 3. The reconstructed foot of Archicebus alongside that of the basal lemur, Notharctus. Note the gathering of metatarsals 2-4, as in tarsiers.

Figure 3. The reconstructed foot of Archicebus alongside that of the basal lemur, Notharctus. Note the gathering of metatarsals 2-4, as in tarsiers. The missing astragalus/talus sits on top of the calcaneum, a trait first appearing on cynodonts like Probelesodon. I suppose this is an example of modular evolution: first the toes, then the ankle.

Nature reports, “The mammal sports an odd blend of features, with its skull, teeth and limb bones having proportions resembling those of tarsiers, but its heel and foot bones more like anthropoids.” Actually the Archicebus foot is also an “odd blend.” The ankle is short, like that of most other primates (Fig. 3, not just anthropoids). But digit 2 is short and digit 4 is long, like those of tarsiers (Fig. 4). Really it comes down to just these two traits for an accurate nesting of Archicebus. Perhaps an accurate reconstruction would have helped. I took my data (Fig. 1) from online photos of Ni et al. 2014, but I have not seen the paper.

Figure 4. Archicebus pes compared to a living tarsier  pes. Note the elongated proximal tarsals in the tarsier. Archicebus has the elongate digit 3 retained by tarsiers.

Figure 4. Archicebus pes compared to a living tarsier pes. Note the elongated proximal tarsals and shorter metatarsals in the tarsier. Archicebus has the elongate digit 4 and short digit 2 retained by tarsiers. Both of these reconstructions are flattened, which is not the way tarsiers hold their toes (Fig. 5). The lengthening of the ankle makes tarsiers excellent leapers.

PIL continuity
The foot of Archicebus appears to lose the continuity of many PILs (Fig. 4) when laid flat. But that’s not the way tarsiers hold their toes in vivo (Fig. 5). Similarly in the human hand the PILs become more continuous in use, like when you grasp a golf club, hold a baseball bat or make a fist. And, of course, the opposable thumb does not work as part of the lateral four digit sets. It goes its own way.

The elongation of the proximal ankle elements in tarsiers enables them to leap tremendous distances. Archicebus did not have that ability. I suppose Archicebus is an example of modular evolution: first the toes, then the ankle, but, of course, it’s never as simple as that.

Figure 6. The tarsier foot and PILs are shown in action at right angles to the tree cylinder and parallel to the long axis. The use of pads appears to change the way the foot operates, without the strong PILs a grasping or walking foot has.

Figure 5. The tarsier foot and PILs are shown in action at right angles to the tree cylinder and parallel to the long axis. The use of pads appears to change the way the foot operates, without the strong PILs a grasping or walking foot has. The fingers and toes don’t lie flat, but strongly flex at the interphalangeal joints. This messes with PILs that are applied to flat reconstructions (Fig. 3, 4)

Archicebus is well-deserving of its celebrity.
According to Nature, “Because A. achilles sits near the base of the tarsier family tree, scientists say it probably resembles the yet-to-be-discovered creatures that lie at the base of most primate groups — including the anthropoid lineage that ultimately gave rise to humans. “If you retrace primate evolution to its beginning, [A. achilles] is what our ancestors most likely looked like,” says Luo.”

References
Ni X, Gebo DL, Dagosto M, Meng J, Tafforeau P, Flynn JJ, Beard KC 2013. The oldest known primate skeleton and early haplorhine evolution. Nature 498 (7452):60–64.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos, 7: 11-41.
Peters D 2010. In defence of parallel interphalangeal lines. Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605

wiki/Archicebus