Purgatorius: What is it?

Wikipedia reports: 
“For many years, there has been a large debate as to whether Purgatorius is a primitive member of the Primates or a basal member of the Plesiadapiforms.” Here (Fig. 1) taxa from the Plesiadapiformes have giant procumbent (rat-like) incisors followed by a long diastema, followed by flat molars…completely UNLIKE Purgatorius. So what were they thinking?

Halliday et al. 2015
nested Purgatorius outside crown group placentals with Protunugulatum (Fig 1). That seems reasonable, though it is twice the size. However, the large reptile tree (LRT, 1044 taxa) was not able to replicate most of the Halliday team’s cladogram, which nested hyraxes with elephant shrews…and horses… and that clade with pre-odontocetes and an early artiodactyl. It just gets worse after that. Protunugulatum was originally allied with condylarths, large plant-eating mammals. Halliday et al. nested it outside the placentals. Wible et al. 2007 nested it with whales + artiodactyls (a clade not validated by the LRT).

Purgatorius is another one of those fossils
known from an incompleted mandible with teeth and little else. Based on a lack of other bones, this is the sort of fossil the LRT cannot successfully resolve and it does not make it onto the list. So we go to plan #2: visual comparisons.

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

Figure 1. Purgatorius compared to other basal and often Paleocene mammals. Given these choices, Purgatorius looks more like Palaechthon, the basal dermopteran, than any other taxa in the LRT. Taxa in yellow nest together in the LRT with primates. Taxa in pink nest with rats and rabbits. Maelestes is a basal tenrec.

Rat-sized Purgatorius unio
(Valen and Sloan 1965; Latest Cretaceous/Earliest Paleocene) gained some early notoriety as the earliest known primate. Ankle bones found in association with Purgatorius, but not articulation, show signs of being flexible like those of primates (Kaplan 2012).

I can describe Purgatorius in the simplest of terms
based on comparisons to related basal mammal taxa (Fig. 1) and without describing any molar cusps (except one).

  1. small in overall size (skull < 2cm in length)
  2. robust mandible with convex dorsal and ventral rims and straight in occlusal view
  3. incisors likely procumbent, but not large
  4. canine tiny
  5. three robust premolars and three robust molars with one very tall cusp
  6. Premolar #3 taller than other teeth

Based on a visual comparison
of candidate taxa (Fig. 1), Purgatorius looks more like Protungulatum and even more like Palaechthon. The latter nests with flying lemurs like Cynocephalus. So we’re close to the base of primates, but closer to their cousins, and far from plesiadapiformes.

Best I can do for now…

Halliday TJD, Upchurch P and Goswami A 2015. Resolving the relationships of Paleocene placental mammals Biological Reviews. | doi = 10.1111/brv.12242
Kaplan M 2012. Primates were always tree-dwellers. Nature. doi:10.1038/nature.2012.11423
Van Valen L and Sloan R 1965. The earliest primates. Science. 150(3697): 743–745.
Wible JR, Rougier GW, Novacek MJ and Asher RJ 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary.” Nature volume 447: 1003-1006


The aye-aye (Daubentonia) is not a primate.

More heresy:
Daubentonia is a plesiadapid, a sister to Plesiadapis, which is also not a primate. They nest with Carpolestes in the clade Glires (rabbits and rodents, etc.). And that makes the aye-aye the only living plesiadapid! And yes, it has a divergent big toe, but so does the basalmost placental, Monodelphis.

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 rabbits. It’s the only living plesiadapid. 

According to
the AMNH website on Sir Richard Owen and the Aye-Aye, “For the first 100 years after the first aye-aye was brought to Europe in the 1780s, debate swirled over whether it was a rodent, a primate, or most closely related to a kangaroo.

“The root of this confusion lay in the aye-aye’s odd collection of behavioral and morphological traits that make it appear to be composed of spare parts of other animals: continuously growing front teeth, batlike ears, a foxlike tail, abdominal mammary glands, claws on most digits, and spindly, dexterous middle fingers.

“It uses its middle finger to tap along a branch and moves its ears forward and back to help locate hollow channels within the wood created by wood-boring insect larvae. Once it detects a channel, the aye-aye uses its specialized front teeth to pry open the wood and then inserts one of its fingers to extract the larvae.”

has been wrong before. And that’s okay. This is Science. We can fix mistakes. Tradition should never trump testing. If you’re not sure where a taxon should nest, if it is constantly described as weird or autapomorphic, you simply need to test your ‘ugly duckling‘ taxon against a larger gamut of candidates. You’ll probably find your taxon is not so weird after all, when compared to its true sisters. Daubentonia has ‘rodent-like’ teeth because it is more closely related to rodents. It’s as simple as that. And convergence happens.

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

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

According to the AMNH, Owen’s 1863 description
put arguments about the aye-aye’s taxonomy to rest as it focused “attention away from the striking unusual characteristics, like the continuously growing teeth, and toward primate-like characteristics such as forward-facing eyes and an opposable thumb, providing firm evidence for why the aye-aye should be classified as a primate.”

In the large reptile tree
(LRT), we don’t focus attention toward or away from anything. We score all the traits evenly and let PAUP figure out which taxa any new taxa nests most closely to. In this test, Daubentonia (Gmelin 1788. Geoffroy Saint-Hillaire 1795; 40 cm snout-vent length; extant) nested most closely with Plesiadapis within the clade Glires. The ever-growing teeth are traits inherited from a basal member of Glires. Only the hallux has a nail. The rest of the toes bear claws. The rest of the primate-like traits are convergent, probably due to its arboreal niche.

Discovered in 1780
by French zoologist, LJM Daubenton, it was originally identified as a squirrel (Gmelin 1788) and named Sciurus madagascariensis. Geoffrey Saint-Hilaire (1795) provided a new generic name. Daubentonia was first considered a primate by Schreber 1800 who renamed it Lemur psilodactylus, a name now considered an invalid junior synonym. More taxonomic misadventures can be found here.

Figure 3. Two clades within the Mammalia from the LRT. Here Daubentonia nests with Plesiadapis, both far from primates.

Figure 3. Two clades within the Mammalia from the LRT. Here Daubentonia nests with Plesiadapis, both far from primates.

This is the yet another
‘rodent-like’ mammal that actually nests with rodents. Other similar originally mis-nested Glires we’ve already covered include:

  1. the Multituberculata – former allotheres
  2. Plesiadapids – a former basal primate
  3. Tupaia – one sort of tree shrew, the other is closer to bats, colugos, primates
  4. Macroscelides – one sort of elephant shrew, the other is closer to tenrecs.
  5. Chrysochloris – a golden mole
  6. Scutisorex – a shrew
  7. Potamogale and Echinops – two former tenrecs
  8. Apatemys – an apatemyid.
  9. Trogosus – a former tillodont
  10. Solenodon – 
  11. Nambaroo – a former kangaroo
  12. Henkelotherium – a former pantothere
  13. Erinaceus – a hedgehog
  14. Shenhou – a former allothere
  15. Carpolestes – a former basal primate
  16. Maotherium – a former symmetrodont
  17. Zalambdalestes – a former non-placental eutherian

They all have big incisors.
A few, like Daubentonia and Tupaia, have a complete postorbital ring. The wide jugals of Plesiadapis and Taeniolabis, provide forward-oriented eyes, just like their sister, Daubentonia.

More taxonomic issues
according to Yoder et al. 1996. “Morphological studies of Daubentonia have been less consistent in their conclusions, finding the aye-aye to be either a highly derived member of the Malagasy primate family Indridae (Schwartz 1986), the basal-most branch of the strepsirrhines (Groves 1990), or unclassifiable in relation to other living primates (Oxnard 1981).”

according to Picone and Sineo 2012. “Both MP and BI topologies show Daubentonia as an independent monophyletic lineage, sister group of all other Strepsirhini.” (= Prosiminiii or lemurs). You should know, BTW, they tested only lemurs with Tupaia as the outgroup and Daubentonia nested between them, just like the LRT without all the taxon exclusion. A priori taxon exclusion is… once again… the main problem here.

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).
Owen R 1863. Monograph on the Aye-Aye ((Chiromys madagascariensis, Cuvier)
Picone B and Sineo L 2012. The phylogenetic position of Daubentonia madagascariensis (Gmelin, 1788; primates, Strepsirhini) as revealed by chromosomal analysis. Caryologia: International Journal of Cytology, Cytosystematics and Cytogenetics 65(3):223-228. online here.
Geoffroy Saint-Hilaire E 1795. La décade philosophique, litteraire, et politique. Memoires d’Histoire Naturelle 4(28):193– 206.
Sterling E. 1994. Taxonomy and distribution of Daubentonia: a historical perspective.Folia Primatologica 62:8-13.
Yoder AD, Vilgalys R and Ruvolo M 1996. Molecular Evolutionary Dynamics of Cytochrome b in Strepsirrhine Primates: The Phylogenetic Significance of Third-Position Transversions. Mol. Biol. Evol. 13(10):1339-1350.

wiki/Aye-aye, Daubentonia
Mammalian species/Daubentonia

Carpolestes has a thumb, but that doesn’t make it a pre-primate.

Figure 1. Carpolestes has a thumb-like hallux and polled (digit 1 on manus and pes). Those are primitive traits, not derived ones.

Figure 1. Carpolestes has a thumb-like hallux and polled (digit 1 on manus and pes). Those are primitive traits, not derived ones in this rabbit sister.

In their paper on primate origins, Bloch and Boyer 2006 report,
“Extant primates are distinct from other eutherian mammals in having large brains, enhanced vision brought about in part by optical convergence, the ability to leap, nails on at least the first toes, and grasping hands and feet.”

maybe not so distinct, at least in this list of traits, after phylogenetic analysis

In the LRT
the basalmost placental, Monodelphis domestics (which does not have a pouch), the forward facing eyes have a degree of optical convergence, adults pounce on their prey and they hold down with their forefeet, which, alas, do not appear to have nails. But 3 out of 4 is coming along way…

Figure 2. The basalmost placental in the LRT, Monodelphis, has a thumb-like grasping hallux and pollex.

Figure 2. The basalmost placental in the LRT, Monodelphis, has a thumb-like grasping hallux and pollex. Image © Digimorph.org and used with permission. Note the forward-facing orbits representing optical convergence.

And here’s the little cutie in vivo (Fig. 3).

Figure 1. The marsupial, Monodelphis domestica, nests as a sister to Eomaia, the oldest known placental.

Figure 3. The marsupial, Monodelphis domestica, nests as the oldest known placental. Females do not have a pouch, but epipubes are retained.

Bloch and Boyer 2006 report,
“Plesiadapiformes has long been considered an archaic radiation of primates. Evidence in favor of a plesiadapiform-euprimate link was based largely on dental and postcranial similarities, whereas the absence of a postorbital bar and other cranial features in certain plesiadapiforms provided evidence against this hypothesis. An alternative hypothesis, that Plesiadapiformes share a closer relationship to extant flying lemurs (Dermoptera) than to Euprimates, has been strongly challenged and is not followed here.”

Unfortunately, Bloch and Boyer
do not consider the third alternative, the one recovered in the LRT with a plesiadapiform relationship to rabbits, not primates. Like little kangaroos, rabbits also originated in the trees.

The large reptile tree
(LRT) nests two plesiadapiformes, Carpolestes (Fig. 1) and Plesiadapis (Fig. 2), with rabbits, like Gomphos (Fig. 3), within the clade Glires, far from primates like Nothrarctus, which developed nails by convergence. When rabbits left the trees, they lost their hallux and pollex.

In the LRT,
primates arise from a sister to the tree shrews Ptilocercus near the base of the Triassic/Jurassic placental radiation. By contrast, plesiadapidformes arise from a sister to Henkelotherium and the more rabbit-like tree shrew, Tupaia. These taxa share long, procumbent lower incisors and a long diastema. Tupaia has a circumorbital ring, but other Glires do not. 

The Bloch and Boyer published cladogram
included only 9 taxa and no rabbits.

Bloch and Boyer report,
“Several adaptive scenarios have been proposed to explain these [primate] specializations: (i) “grasp-leaping” locomotion (3), which predicts simultaneous evolution of grasping and leaping; (ii) visually directed predation (4), which predicts simultaneous evolution of forward-facing orbits and grasping; and (iii) terminal branch feeding on nectar and flowers, which allows that grasping evolved independently of other traits. The lack of well-preserved skulls and skeletons of the earliest primates has precluded testing of these hypotheses.”

Bloch and Boyer are overlooking
the living breathing, leaping and grasping basal primate, Ptilocercus (Fig. 4), or the basalmost placental, Monodelphis (Figs. 1,2) have most if not all of these morphological and behavioral traits. So… thumbs are primitive! Derived taxa, like whales and hoofed ungulates, tend to lose them.

Figure 5. Ptilocercus in vivo, holding prey with its small hands while eating it.

Figure 4. Ptilocercus in vivo, holding prey with its small hands while eating it.

Bloch JI and Boyer DM 2006. Grasping primate origins. Science 298:1606-1610.

Rats! – (or where Mickey Mouse diverged from Walt Disney)

We don’t talk about mammals much, but as reptiles they (we) do qualify as subjects to be covered by ReptileEvolution.com.

A new online study by Wu et al. (2012) finds evidence for a post-Cretaceous origin for rodents. Rodents (everything from porcupines and guinea pigs to squirrels and mice) are related to rabbits (lagomorphs) which are related to primates (including readers of this blog and lemurs) which all were derived from arboreal carnivores like Vulpavus.

The Wu et al 2012 study on rodents and their post-Cretaceous appearance.

The Wu et al 2012 study on rodents and their post-Cretaceous appearance.

How are they all related? 
Near (but not at) the base of the primates is an interesting set of taxa known as tree shrews. Essentially they are micro lemurs with shifted teeth.

Tupaia, the large tree shrew,

Figure 1. Tupaia, the large tree shrew, a living taxon close to the base of rabbits and rodents with origins in the Paleocene, just following the Cretaceous. Click to learn more.

The most common one, Tupaia (Raffles 1821) was found to be basal to the equally arboreal Plesiadapis (Fig. 3) and by extension to the terrestrial rabbits, and by further extension to rodents (keeping on topic), like the porcupine. It’s worthwhile to see the porcupine skull and how close it resembles that of Plesiadapis.


Figure 3. Plesiadapis, formerly considered a basal primate, is here considered a basal arboreal lagomorph (rabbit ancestor).

The other arboreal tree shrew, Ptilocercus, was found to be basal to bats and colugos (flying lemurs), all three with relatives extending back to the Paleocene (post-Cretaceous).

Ptilocercus, pen-tailed tree shrew

Figure 2. Ptilocercus, pen-tailed tree shrew, a living relative to the ancestor of bats and colugos.

I don’t know much about rodents, but given what I do know about the initial appearance of their outgroups, the Wu et al. (2012) study makes perfect sense in the present context!

Wu S, Wu W, Zhang Z, Ye J, Ni X, Sun J, Edwards SV, Meng J and Organ CL 2012. Molecular and Paleontological Evidence for a Post-Cretaceous Origin of Rodents. PLoS ONE 7(10): e46445. doi:10.1371/journal.pone.0046445

The Evolution and Origin of Man

The Latest List of Human Ancestors
The evolution of humans from australopithecines and beyond has been well chronicled. We know the beginning and we know the end. That list of what happened in between keeps growing as more transitional taxa are added to fill in the present gaps, which keep getting smaller and smaller.

The best represented lineage hasn’t changed much since the publication of From The Beginning, a book I wrote that was published by Little Brown in 1991. At the time it was a first of its kind. FTB illustrated 36 steps in the evolution of humans: from raw chemicals, through bacteria, worms, fish, and the rest of our clade. Every turn of the page introduced the reader to a new taxon that added, modified and/or subtracted various body parts, abilities and behaviors. That list of 36 has held up pretty well in the last twenty years, with only a few exceptions. Now Ophiacodon and Nikkasaurus would replace Haptodus. Tree shrews would be dropped in favor of a primitive carnivore, Vulpavus.

Human evolution.

Figure 1. Human evolution back to the cynodonts — and beyond. Click to enlarge. From “From the Beginning” (Peters 1991).

Bush or Ladder?
As in From the Beginning, this blog and reptileevolution.com seek to provide the latest insight into the origin and evolution of various animals (including humans). Everyone knows the process of evolution produces a branching bush, but if you want to focus on just one lineage, to see how your own body parts were modified by evolution over time and generations, it’s an unbroken ladder. By that I mean, every one of our ancestors, in an unbroken chain, successfully grew to maturity, mated and reproduced. They weren’t eaten, killed while hatching or destroyed by an asteroid impact. Our ancestors always found safe haven. Some of their offspring were a little taller, a little shorter, a little more aggressive, a little less able to breathe with gills, etc. They evolved a little bit at a time. Over time all those little bits added up.

Of the millions of ancestors we all share in common, here’s an abbreviated and clickable list that will provide more information about each step in the process of human evolution going back to the first of our ancestors to walk on land. It’s like the book From the Beginning, only its on the web.

1. Ichthyostega, Acanthostega and Pederpes. 2. Proterogyrinus.  3. Seymouria.
4. Silvanerpeton. 5. Gephyrostegus.

6. Cephalerpeton. 7. Casineria. 8. Paleothyris. 9. Coelostegus. 10. Hylonomus.

11. Elliotsmithia 11a. Apsisaurus 12. Archaeothyris. 13. Ophiacodon 14. Nikkasaurus. 15. Biarmosuchus. 16. Stenocybus. 17. Eotitanosuchus and Scymnognathus. 18. Aelurognathus. 19. Procynosuchus. 20. Thrinaxodon. 21. Chiniquodon. 22. Pachygenelus.

23.  Megazostrodon. 24. Amphitherium. 25. Asioryctes and Eomaia. 26. Vulpavus. 27. Notharctus. 28. Aegyptopithecus. 29. Proconsul. 30. Ardipithecus. 31. Australopithecus. 32. Homo.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

No references this time.

>> Returning visitors will note a small edit based on updated data at positions 10 and 11.