Purgatorius and Plesiadapis are still not primates contra Wilson et al. 2021

Short one today
on Purgatorius (Early Paleocene; Fig. 1), a mandible taxon considered by Wilson et al. 2021 to be a member of the Plesiadapiformes (Fig. x).

Figure 1. Purgatorius compared to other basal and often Paleocene mammals.

Figure 1. Purgatorius compared to other basal and often Paleocene mammals.

Wilson et all 2021 report
“Plesiadapiforms are crucial to understanding the evolutionary and ecological origins of primates and other euarchontans (treeshrews and colugos) as well as the traits that separate those groups from other mammals.”

No they are not.

Adding taxa
shifts plesiadapiformes deep into the clade Glires (Fig. x) where Plesiadapis joins Daubentonia as primate-like rodents close to Carpolestes and Ignacius.

Figure 1. Ignacius and Plesiadapis nest basal to Daubentonia in the LRT.

Figure 2. Ignacius and Plesiadapis nest basal to Daubentonia in the LRT.

Wilson et al. also reported
similarities in Purgatorius to Palaechthon, which nested in 2017 with the demopteran, Cynocelphalus in the large reptile tree (LRT, 1807+ taxa). Wilson et al. considered Palaechthon a member of the Plesiadapiformes.

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

Figure x. Subset of the LRT focusing on basal placentals, including multituberculates.

We looked at Purgatorius earlier
here in 2017.

Colleagues, expand your taxon lists.
If you don’t look in there, you won’t see what’s in there. So look. Add taxa. Sometimes traditions, professors and textbooks are not complete or incorrect. Find out for yourself.


References
Wilson MGP et al. , (9 co-aiuthors) 2021. Earliest Palaeocene purgatoriids and the initial radiation of stem primates Royal Society open science 8210050
http://doi.org/10.1098/rsos.210050

https://pterosaurheresies.wordpress.com/2019/03/07/tweaking-palaechthon-basal-volitantia/

Chilecebus: Oldest South American monkey

Flynn et al. 1995 brought us
Chilecebus carrascoensis (Early Miocene; 20mya; Fig. 1 lower left) a tiny New World monkey from Early Miocene Chile.

Figure 1. Chilcebus compared to other Western Hemisphere primates.

Figure 1. Chilcebus compared to other Western Hemisphere primates. Note the three molars in Chilecebus, as in Smilodectes and Aotus, not Alouatta. Dorsal view and CT scan view of Chilecebus on second of two frames.

When added to
the large reptile tree (LRT, 1753+ taxa) Chilecebus nested with the other South American monkeys.

Figure 1. At the start of the Eocene this is the distance monkeys would have to raft to get to South America. This hypothesis is invalidated by today's blogpost.

Figure 2. At the start of the Eocene this is the distance monkeys would have to raft to get to South America. This hypothesis is invalidated by today’s blogpost.

Worth remembering…
(since there IS this myth out there) there was no need for a monkey or two from Africa to raft over to South America (Fig. 2). The large reptile tree (LRT, 1753+ taxa) documents descent from Smilodectes (Fig. 1) an adapid living in Texas (Fig. 3).

Figure 3. The North Pole during the earliest Eocene from the CR Scotese Paleomap project with early primate skulls added, each demonstrating a gradual accumulation of traits.

Figure 3. The North Pole during the earliest Eocene from the CR Scotese Paleomap project with early primate skulls added, each demonstrating a gradual accumulation of traits.

Incrementally adding taxa to the LRT
has become less harrowing and more confident because there are no longer any large gaps, no odd enigmas, and lots of similar taxa for new specimens to nest alongside. By getting to this size the LRT has become a tool that no longer needs shaping, but can come out whenever needed to nest new specimens that others find difficult to understand. Even so, the LRT is still subject to constant scrutiny and polishing to further increase its usefullness.


References
Flynn J et al. 1995. An Early Miocene anthropoid skull from the Chilean Andes. Nature 373, 603 – 607.

wiki/Chilecebus

https://pterosaurheresies.wordpress.com/2018/12/10/the-lrt-solves-the-south-american-monkey-puzzle/

https://www.eurekalert.org/pub_releases/2019-08/amon-2ss081919.php

https://nypost.com/2019/08/22/what-a-20-million-year-old-monkey-skull-reveals-about-the-evolution-of-human-brains/

Eric Shipton yeti snowprint revisited

So odd, so different,
it might just be real. It all started with a photograph by Eric Shipton from decades ago of a single large footprint in the snow of the Himalayan Mountains (Fig. 1). Here I simply added bones based on the apparent primate nature of the trackmaker and included gorilla pedal data for comparison.

Figure 1. Eric Shipton snowprint of Yeti with hypothetical bones and PILs applied. At top is pes of Gorilla. Ice pick for scale.

Figure 1. Eric Shipton snowprint of Yeti with hypothetical bones and PILs applied. At top is pes of Gorilla. Ice pick for scale. The impressions of digits 2 and 3 indicate logical interpretation with toe drag to avoid broken toe /#2 and nussubg toe #3 impression.

Distinct from human tracks,
the big toe of the Himalayan trackmaker is much bigger and does not extend as far as in humans. The tracks is wider than in humans. Digit 2 appears to be shorter than in humans.

Several years ago an expert of yeti and bigfoot, Dr. Jeff Meldrum,
appeared on ‘Joe Rogan Questions Everything’ #2 with Duncan Trussell (audio only, click to listen via YouTube). While Joe and Duncan tried to add levity to the discussion, Dr. Meldrum portrayed the facts as he knew them, keeping speculation to a minimum.

We touched on this subject
about a year ago earlier here.

The basalmost primate in the LRT is alive and living in Madagascar!

Now you have a choice.
Either go out looking for crumbling bits and pieces of basal primate jaws and teeth over vast stretches of badlands… Or go to Madagascar to study basal primates in the wild, and have them feeding from your hand, according to the latest addition to the LRT.

The gray mouse lemur,
(Microcebus murinus; Figs. 1, 2) nests at the base of the all the tested primates in the large reptile tree (LRT, 1692+ taxa; subset Fig. 3), basal to both larger adapid lemurs, Notharctus and Smilodectes.

Figure 1. The gray mouse lemur (Microcebus murinus) nests basal to primates in the LRT.

Figure 1. The gray mouse lemur (Microcebus murinus) nests basal to primates in the LRT.

This largest species in this smallest genus of primates
also nests between two tree shrew taxa, Tupaia (basal to Glires) and Ptilocercus (Fig. 4; basal to Volitantia).

Though living today in Madagascar forests,
Microcebus likely radiated during the Cretaceous, prior to the splitting of Madagascar from Africa 88 mya. Later it gave rise to all extinct and extant adapids and lemurs on that island.

Millions of years ago lemurs were
worldwide in distribution. Now only a few lemurs find refuge in Madagacar. and only in Madagascar.

Figure 2. The skull of Microcebus murinus from Digimorph.org and used with permission. Here colors mark bones.

Figure 2. The skull of Microcebus murinus from Digimorph.org and used with permission. Here colors mark bones.

Microcebus murinus (Miller 1777) is the extant gray mouse lemur an omnivore found only in Madagascar. This nocturnal arboreal basalmost primate in the LRT forages alone, but sleeps in groups, sharing tree holes during the day. Twin babies are typical. Offspring can reproduce after one year. Lifespan extends to ten years. The eyes are large, typical of nocturnal mammals. Relatives include Hapalodectes and Ptilocercus. Descendants include Notharctus and Smilodectes.

The newly expanded clade Scandentia (tree shrews) now unites
Volitantia (bats + pangolins + colugos), Primates and Glires (rodents, rabbits, multituberculates and kin) in the LRT, subset Fig. 3). The addition of Microcebus as the smallest lemur held the possibility that it was the most basal form or one leading to smaller galagos and tarsiers. This time Microcebus turned out to be more primitive.

Figure 3. Subset of the LRT focusing on the clade Scandentia (tree shrews) and the three arboreal clades that arise from it.

Figure 3. Subset of the LRT focusing on the clade Scandentia (tree shrews) and the three arboreal clades that arise from it.

With the addition of Microcebus to the LRT,
the extant pen-tailed tree shrew, Ptilocercus (Fig. 4) nests basal to colugos, which also lack upper incisors. That means an older, more plesiomorphic fossil taxon with a complete set of upper incisors is out there waiting to be discovered somewhere in Early Jurassic fossil beds.

Figure 4. Ptilocercus is a sister to Microcebus nesting with colugos.

Figure 4. Ptilocercus is a sister to Microcebus nesting with colugos.

Paleontologists have been looking for the ancestor of primates,
colugos and bats for ages. They find fewer and smaller bony scraps the deeper they look.

Here’s a solution:
Add extant taxa. Phylogenetic analyses that includes extant taxa can sometimes help by nesting late survivors at basal nodes. Sure the fossil taxa are the real ancestors. Sure, living lemurs are late survivors, radiating into new morphologies and niches, but the soft, cuddly, active chatterboxes (Fig. 1) are still worth studying and scoring.


References
Miller JF 1777. Cimelia Physica p.25

wiki/Microcebus

Restoring Plagiomene (incomplete basal placental)

Wikipedia reports,
Plagiomene multicuspis (Fig. 1; Matthew 1918; MacPhee et al. 1989; YPM VP 030624; Wyoming; Paleocene) is an extinct genus of early flying lemur like mammal from North America that lived during the Paleogene.”

Here
using imagination (Fig. 1) to restore the missing parts, scrappy Plagiomene data turns into a more complete skull. Plagiomene had four small molars and a narrow snout between wide robust cheekbones. Those facts and phylogenetic bracketing suggest forward-pointed eyes sitting atop wide cheekbones for bifocal vision.

Figure 1. What little is known of Plagiomene seems to agree with the North American adapid, Smilodectes, among tested taxa.

Figure 1. What little is known of Plagiomene seems to agree with the North American adapid, Smilodectes, among tested taxa. Plagiomene was not added to the LRT.

Here an attempt at restoring the rest of the skull
(Fig. 1) results in a short-snouted taxon with robust cheekbones, more or less similar to Smilodectes (Fig. 1), which has not four, but only three molars and lived during the middle Eocene. An extremely tall coronoid process requires a similarly tall skull. If valid, Plagiomene would be a basal primate, or basal to Primates + Volantia (where dermopterans are a basal taxa).

Possible outgroups,
such as basal Carnivora and Cheiroptera, do not have a similar mandible or molars.

The basal dermopterans,
Palaechthon
(Fig. 1) and Cynocephalus, both have 4 molars, but do not have a tall coronoid process on the mandible.

Earlier we looked at the evidence for
the clade that includes Smilodectes (Adapidae) nesting at the base of the clade of New World monkeys (Platyrrhini). Plagiomene is also from North America.

The last upper premolar
of Plagiomene extends further toward the midline than the molars do. That is unusual in basal mammals. When I find this trait in another basal mammal palate, I will let you know.


References
MacPhee RDE, Cartmill M and Rose KD 1989. Craniodental morphology and relationships of the supposed Eocene dermopterans Plagiomene (Mammalia). Journal of Vertebrate Paleontology 9(3):329–349.
Matthew WD 1918. A revision of the Lower Eocene Wasatch and Wind River faunas. Part V. Insectivora (Continued), Glires, Edentata. Bulletin of the American Museum of Natural History 38(16):429-483.

wiki/Plagiomene
wiki/Smilodectes

New yeti tracks?

Photos from Mountaineers in the Indian Army
show several long (32″) prints in the snow, one directly in front of the other. The New York Times covered the story (see citation below).

Figure 1. 2019 yeti tracks found in Nepal and posted online.

Figure 1. 2019 yeti tracks found in Nepal and posted online. That’s an ice pick alongside for scale. Is this a combo track? See text.

These are definitely not bear tracks.
The large digit 1 tells us they were made by a primate… if this is a single impression.

The only question is…
did the primate use its own feet to make foot tracks, or was it wearing yeti shoes? Or is this a combination track?

Unfortunately
only one footprint is shown. It would have been more useful to see a complete set, to see if there was a right foot also, and what variation there might be as the trackmaker navigated the terrain, its own weight shifts, etc.

It’s a nice first step.
To its credit, the trackmaker had parallel interphalangeal lines (PILs). Cheap knock-offs and fakes generally overlook this detail. The NY Times.com story suggests it is a combination track from a mama bear and her cub. We should consider all possibilities.


References
NY Times.com story

Hapalodectes: when primates split from dolphins

Back when placental mammals were first diversifying in the Jurassic
they all looked like small arboreal marsupial didelophids, like Caluromys, and small arboreal placental tree shrews, like the extant Ptilocercus and Tupaia. Two distinct specimens, both given the genus name Hapalodectes (Fig. 1), are among these basal placental taxa in the large reptile tree (LRT, 1378 taxa).

The slightly smaller
IVPP V5235 specimen attributed to Hapalodectes (Ting and Li 1987) nests at the base of the primate clade. It had already taken on the appearance of a little basal lemur or adapid (Fig. 1).

Figure 1. Two Hapalodectes specimens. The smaller one nests at the base of the Primates. The larger one nests as the base of the anagalid-tenrec-odontocete clade.

Figure 1. Two Hapalodectes specimens. The smaller one nests at the base of the Primates. The larger one nests as the base of the anagalid-tenrec-odontocete clade.

The slightly larger
IVPP V12385 specimen attributed to Hapalodectes (Ting et al. 2004; Fig. 1) nests at the base of the anagalid-tenrec-odontocete clade and it had already taken on the appearance of a little anagalid or elephant shrew.

Other than size, the differences are subtle:

  1. The basal primate has a postorbital ring. The basal anagalid does not.
  2. The basal primate has three upper molars. The basal anagalid has four.
  3. The basal primate cranium has no crest. The basal anagalid has a nuchal and parasagittal crest.
  4. The basal primate anchors the squamosal further back, with a smaller ectotympanic (middle ear container bones below the cranium). The basal anagalid anchors the squamosal further forward, with a larger ectotympanic (for better hearing).

Hapalodectes hetangensis (Ting and Li 1987; 4.5cm skull length; Paleocene, 55 mya; IVPP V 5235) This skull was originally wrongly applied to the Mesonychidae, but here nests at the base of the primates, including Notharctus.  Note the transverse premaxilla, the large canine, and the encircled orbits rotated anteriorly.

?Hapalodectes ?hetangensis (Ting et al. 2004; 7 cm skull length; Early Eocene 50 mya; IVPP V 12385) was originally considered a tiny mesonychid. This species nests at the base of the anagale-tenrec-odontocete clade, between Ptilocercus and Onychodectes. The large nuchal crest is a key trait found in later taxa. The premaxilla is largely missing, but likely was transverse in orientation.

Figure 2. Ptilocercus (pen-tailed tree shrew) compared to Caluromys (wooly-opossum) young juvenile from Flores, Abdala and Giannini 2010.

Figure 2. Ptilocercus (pen-tailed tree shrew) compared to Caluromys (wooly-opossum) young juvenile from Flores, Abdala and Giannini 2010.

References
Ting S and Li C 1987. The skull of Hapalodectes (?Acreodi, Mammalia), with notes on some Chinese Paleocene mesonychids.
Ting SY, Wang Y, Schiebout JA, Koch PL, Clyde WC, Bowen GJ and Wang Y 2004. New Early Eocene mammalian fossils from the Hengyang Basin, Hunan China. Bulletin of Carnegie Museum of Natural History 36: 291-301.

wiki/Hapalodectes

The bushbaby (genus: Galago), a tarsier-mimic

Figure 1. Galago skeleton. Note the elongate tarsals and large orbits, both convergent with Tarsius.

Figure 1. Galago skeleton. Note the elongate tarsals and large orbits, both convergent with Tarsius (Fig. 5).

The Senegal bushbaby,
Galago senegalensis (Figs. 1, 2) is a small primate in the Lemur lineage, most closely related to Perodicticus potto (Fig. 3) in the large reptile tree (LRT, 1373 taxa), despite sharing a long tail, elongate tarsals and large orbits with the tarsier, Tarsius (Fig. 5). These relationships follow traditional cladograms.

Figure 2. Galago skull in three views.

Figure 2. Galago skull in three views.

Galago senegalensis (É. Geoffroy, 1796) is the Senegal bushbaby, a small nocturnal lemur close to Lemur catta and the potto, Perodicticus. Convergent to Tarsius, the proximal tarsals are elongated. The anterior upper incisors are missing. The medial incisors are appressed to the canines.\

Figure 4. Perodicticus potto, the extant potto, has a typical lemur dentition, lacking giant incisors.

Figure 4. Perodicticus potto, the extant potto, has a typical lemur dentition, lacking giant incisors.

Some skulls attributed to Galago
have 4 molars rather than the 3 shown here (Fig. 2).

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

Figure 5 Tarsius, the extant tarsier. Note the elongate calcaneum and astragalus, as in Galago.

References
Geoffroy Saint-Hilaire E 1796. Mémoire sur les rapports naturels des Makis Lemur, L. et description d’une espèce nouvelle de mammifère. Magasin Encyclopédique, ou Journal des Sciences, des Lettres et des Arts 7: 20-50.

wiki/Galago

Another flawed aye-aye origin paper: Gunnell et al. 2018

Earlier we looked at µCT scans of the aye-aye (Figs. 1, 4), Daubentonia made by Morris, Cobb and Cox 2018 and comparisons to Lemur catta (Fig. 2), a taxon often considered a sister to Daubentonia.

Figure 1. Daubentonia was considered a primate for over 150 years. Here it nests with Plesiadapis, rodents and rabbits.

Figure 1. Daubentonia was considered a primate for over 150 years. Here it nests with Plesiadapis, rodents and multituberculates + carpolestids.

 

Figure 2. Lemur catta in vivo and skeleton.

Figure 2a. Lemur catta in vivo and skeleton.

Figure 2. Lemur catta skull in 3 views.

Figure 2b. Lemur catta skull in 3 views. Compare this skull to Daubentonia in figure 4. Note the large canines missing in Daubentonia, replaced by giant incisors and no canines.

Gunnell et al. 2018
reidentified the fossil jaw bone of Propotto leaky (Simpson 1967, 20mya; Fig. 3). “In a study published August 21 in the journal Nature Communications, researchers have re-examined Propotto’s fossilized remains and suggest that the strange creature wasn’t a bat, but an ancient relative of the aye-aye, the bucktoothed nocturnal primate that represents one of the earliest branches of the lemur family tree.” 

Figure 1. Propotto and Plesiopithecus nest with Daubentonia in Gunnell et al. 2018, which does not test many rodents, despite the rodent-like teeth shown here.

Figure 3. Propotto and Plesiopithecus nest with Daubentonia in Gunnell et al. 2018, which does not test many rodents, despite the rodent-like teeth shown here.

Unfortunately
when I ran the Gunnell et al. matrix the clade of rodent-toothed taxa (Daubentonia, Propotto and Pleisopithecus) nested with the primate-toothed Lemur catta. All primates in the large reptile tree (LRT, 1372 taxa) have large canines and two small incisors (except humans and kin where the canines are not fangs). Rodents have the opposite, small to absent canines together with single giant incisors. Rodent-toothed Carpolestes and Plesiadapis (Fig. 6) were tested by Morris, Cobb and Cox 2018, but nested far from the Daubentonia clade. That is strange. No other rodents were tested to eliminate the possibility that rodent-toothed taxa might actually be closer to rodents than primates or that Carpolestes and Pleisadapis might be rodents themselves. In the LRT they are primate-like rodents, not rodent-like primates.

Strangely, but traditionally,
the outgroup taxa for primates in the Morris, Cobb and Cox 2018 study were Tupaia and Ptilocercus, two taxa that nest not with primates, but with Glires (shrews + rodents + multituberculates and kin) in the LRT, which includes more taxa.

A toothless diastema
occurs between the one to two premolars and the giant dentary incisors of Daubentonia, Plesiadapis, Ignacius and most rodents. I don’t see that morphology in figure 3 where three premolars fill the space between the molars and incisors of Propotto and Plesiopithecus. Such a mandible morphology is found in more basal members of Glires, like the hedgehog (Echinops), Apatemys and some shrews, like Scutisorex. None of these taxa were tested by the Gunnell team in their study of Propotto and Plesiopithecus.

The Gunnell et al. cladogram may have suffered from
too many dental traits and too few Glires taxa. It did not deliver the expected ‘gradual accumulation of traits’ that mark every good cladogram (because that’s how evolution works). Rather, like too many cladograms we’ve looked at over the years, sister taxa just don’t look like each other and the enigma taxon looks too much like something else in the cladogram.

Quote mining from the Duke U PR online article:
Propotto: “In 1967, paleontologist George Gaylord Simpson inspected the fragments and classified the specimen as a previously unknown member of the loris family, nocturnal primates with enormous eyes. But a colleague named Alan Walker took a look and thought otherwise, eventually convincing Simpson that the bones belonged to a bat.

For nearly half a century the creature’s identity appeared to have been settled, until 2016, when another paleontologist, the late Gregg Gunnell of Duke University, began taking a fresh look at the fossil. To Gunnell’s eye, the creature’s hind teeth were more reminiscent of a primate than a bat. He also noted the stump of a broken front tooth, just visible in cross section, which would have jutted out from its mouth like a dagger — a trait only known in aye-ayes, the only living primates with rodent-like teeth.

“Gregg wrote to us and said, ‘Tell me I’m crazy,’” Seiffert said.

The researchers found that Propotto shared a number of features with a similarly buck-toothed primate that lived 34 million years ago in Egypt called Plesiopithecus, and that both were ancient relatives of the aye-aye.

In the new study, Seiffert, Gunnell and colleagues propose that the ancestors of aye-ayes split from the rest of the lemur family tree roughly 40 million years ago, while still on the African continent, and the resulting two lineages didn’t make their separate ways to Madagascar until later.

The findings suggest they arrived around the same time as other mammals, such as rodents, Malagasy mongooses and hedgehog- and shrew-like animals called tenrecs. Frogs, snakes and lizards may have made the trip around the same time.”

In the LRT, all these taxa were already on Madagascar in the Mesozoic and did not have to raft over after the split from Africa. 

“Lemurs can’t swim, so some scientists hypothesize that the small-bodied creatures crossed the 250-mile-wide channel that lies between Africa and Madagascar after being swept out to sea in a storm, by holding on to tree limbs or floating mats of vegetation before finally washing ashore.

Figure 2. Skeleton of Daubentonia (aye-aye). Like other plesiadapids, it convergences with the lemuroid primates.

Figure 4. Skeleton of Daubentonia (aye-aye). Like other plesiadapids, it convergences with the lemuroid primates. Consider it a primate-like rodent, not a rodent-like primate. Compare this skull to figure 5.

“But if the arrival were more recent, they might have had a shorter distance to travel, thanks to lower sea levels when the Antarctic ice sheet was much larger. “It’s possible that lemurs weren’t in Madagascar at all until maybe the Miocene,” as recently as 23 million years ago, Boyer said. Some of the lowest sea levels were also during this time,” Heritage said.

Figure 4. Perodicticus potto, the extant potto, has a typical lemur dentition, lacking giant incisors.

Figure 5. Perodicticus potto, the extant potto, has a typical lemur dentition, lacking giant incisors. Compare this skull to figure 4. Note the large canines missing in Daubentonia. 

What about the extant potto, Perodicticus potto?
Perodicticus potto (Bosman 1704, Fig. 5) does not have large rodent-like lower incisors. Rather it has a skull somewhat midway between the lemurs and tarsioids (Fig. 3) with large canines.

Figure 1. Ignacius and Plesiadapis nest basal to Daubentonia in the LRT.

Figure 6.  Ignacius and Plesiadapis nest basal to Daubentonia in the LRT.

This brings up the unfortunate habit
of naming taxa that are not related to the taxa they are purportedly related to, like Propotto and Plesiopithecus (Fig. 3).

And yet another example of ‘Pulling a Larry Martin’:

Figure 7. How Gunnell et al. 'Pulled a Larry Martin'. They cherry-picked taxa. They focused on just a few traits in the mandible. They hope that four tiny incisors might evolve into two giant incisors.

Figure 7. How Gunnell et al. ‘Pulled a Larry Martin’. They cherry-picked taxa. They focused on just a few traits in the mandible. They hope that four tiny incisors might evolve into two giant incisors.

For those who don’t read captions.
How Gunnell et al. ‘Pulled a Larry Martin‘. (Fig. 7).

  1. They cherry-picked taxa, (= taxon exclusion, where is Lemur catta in figure 7?).
  2. They focused on just a few traits in the mandible.
  3. They hoped that four tiny incisors might evolve into two giant incisors.
  4. They did not recognize the convergence that the LRT recovered.

References
Gunnell GF et al. (9 co-authors) 2018. Fossil lemurs from Egypt and Kenya suggest an African origin for Madagascar’s aye-aye. Nature Communications. PDF
Simpson GG 1967. The tertiary lorisiform primates of Africa. Bull. Mus. Comp. Zool. 136, 39–62.

The aye-aye and squirrel revisited in µCT scans

Morris, Cobbb and Cox 2018
used µCT scans to compare the traditional ‘unusual primate’ from Madagascar, Daubentonia (the aye-aye, Fig. 1) to the grey squirrel, Sciurus. In the large reptile tree (LRT) these two both nest within the larger clade Glires and the smaller clade, Rodentia, not close to Primates. Daubentonia could have nested with any one of several included primates, but did not do so, although other putative primates with rodent-like teeth, Ignacius and Plesiadapis, also nests within Rodentia in the Daubentonia clade.

Figure 1. From Morris, Cobb and Cox 2018, µCT images of Daubentonia and Sciurus.

Figure 1. From Morris, Cobb and Cox 2018, µCT images of Daubentonia and Sciurus.

The Morris, Cobb and Cox study labeled the obvious similariities
of the aye-aye and squirrel “Convergence—the independent evolution of similar phenotypes in distantly related clades”.

Unfortunately,
the Morris, Cobb and Cox cladogram, compiled from three earlier genomic studies, did not include any fossil taxa. In their study, Daubentonia nests with other taxa from the island of Madagascar, adding evidence to the curious notion that placental mammals fall into genomic clades determined by land masses, like Afrotheria.

According to Sterling and McCreless 2007 (citations deleted), “Owen’s definitive study of aye-aye anatomy (Owen, 1866) finally quelled the debate over the species’ taxonomic position, focusing attention away from the animal’s rodentlike anterior teeth and towards its primatelike characteristics, such as a postorbital bar, stereoscopic vision, and an opposable hallux. Although its placement within the primates is still being debated, Daubentonia is considered a member of the family Indridae; as a sister taxon to the other Malagasy primates; and as the most basal branch of the strepsirrhines.”

Owen 1866 had no idea
of the fossil taxa that now surround Daubentonia in the LRT, attracting it away from primates and toward fossil rodents, none of which have a postorbital bar, but all of which have an opposable hallux and rodent-like dentition. In the LRT a postorbital bar is retained in taxa basal to Glires (Ptilocercus and Tupaia), but lost in all derived taxa, except Daubentonia. A postorbital process appears in the Late Cretaceous multituberculate, Catopsbaatar. A pseudo-postorbital bar created by the anteriorly displaced squamosal appears in the clade that includes Pectinator, Chinchilla and Allactaga.

Figure 2. Lemur catta skull in 3 views.

Figure 2. Lemur catta skull in 3 views. Compare this skull to that of Daubentonia in figure 1.

A little backstory
Gmelin 1788 and Cuvier 1797 assigned Daubentonia to the Rodentia, under the genus and species: Sciurus madagascariensis. Geoffroy 1795 coined the present genus name, in honor of his professor L-J-M Daubenton. Shaw 1800 called Daubentonia a “long-fingered lemur” perhaps because it lived in the land of lemurs, Madagascar. Wikipedia provides no references for phylogenetic studies that include Daubentonia and fossil taxa nesting as sisters and near-sisters in the LRT. So… taxon exclusion once again appears to have unnecessarily created an enigma.

Oxnard 1981 reported,
“The differences that have been found are large enough that it can be confidently asserted that in its postcranial skeleton, Daubentonia is more different from the primates as a whole than is any other primate genus. paralleling the enormous differences of Daubentonia from other primates in its dentition, skull and cheiridia, that we may prefer to keep open minds about its taxonomic placement.”

No other primates
have the ever-growing rodent-like incisors that Daubentonia has. But all rodents do.

There is one family of rodents native to Madagascar,
the Nesomyinae. Genera include:

  1. Brachytarsomys
  2. Brachyuromys
  3. Eliurus
  4. Gymnuromys
  5. Hypogeomys
  6. Macrotarsomys
  7. Monticolomys
  8. Nesomys
  9. Voalavo

None of these taxa
are currently included in the LRT. None appear to be more closely related to Daubentonia that to Mus and Rattus.

Sciurus was recently added to the LRT
and, not surprisingly, it nested with Ratufa, the giant squirrel, within the clade Rodentia.

Lemur catta was also recently added to the LRT
just to be fair, because Morris, Cobb and Cox 2018 nested Daubentonia with Lemur catta. Not surprisingly Lemur nested at the base of the Notharctus clade, derived from the IVPP V 5235 specimen of Hapalodectes.

The worldwide dispersion of post-Cretaceous basal primates
actually signals a radiation preceding the splitting of Madagascar and South America from Africa in the Early Cretaceous (rather than lemurs rafting to Madagascar and New World monkey to South America), as discussed earlier here. Madagascar provided a refuge for lemurs and lemur-like rodents, like Daubentonia.

References
Cuvier G 1797. Tableau e´lementaire de l’histoire naturelle des animaux. Paris, France: Baudouin.
Gmelin JF 1788. Caroli a Linné systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima tertia, aucta, reformata. – pp. [1-12], 1-500. Lipsiae. (Beer).
Groves CP 2005. Order Primates. pp. 111–184 In Wilson, D. E.; Reeder, D. M. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press.
Morris PJR, Cobb SNF and Cox PG 2018. Convergent evolution in the Euarchontoglires. Biology Letters 14: 20180366. http://dx.doi.org/10.1098/rsbl.2018.0366
Owen R 1866. On the aye-aye (Chiromys, Cuvier: Chiromys madagascariensis, Desm.; Sciurus madagascariensis, Gmelin, Sonnerat; Lemur psilodactylus, Schreber, Shaw). Transactions of the Zoological Society of London 5:33–101.
Oxnard CE 1981. The uniqueness of Daubentonia. American Journal of Physical Anthropology 54(1):1–21.
Sterling EJ and McCreless 2007. Adaptations in the Aye-Aye: A review. Chapter 8 (pp. 159–184) in Lemurs, Ecology and Adaptation. Gould L and Sauther ML Eds. Part of the 47 volume Developments in Primatology: Progress and Prospect book series. Springer Nature Switzerland.

PR on Morris, Cobb and Cox 2018
wiki/Aye-aye