New ‘rodents and rabbits’ cladogram

Asher et al. 2019
bring us a new phylogenetic + genomic cladogram of rabbits + rodents (clade = Glires) that fails to include taxa recovered by the large reptile tree (LRT, 1552 taxa, subset Fig. 1).

From their abstract:
“Our results support the widely held but poorly tested intuition that fossils resemble the common ancestors shared by living species, and that fossilizable hard tissues (i.e. bones and teeth) help to reconstruct the evolutionary tree of life.”

From their results:
“Our analysis supports Glires and three major clades within crown Rodentia: Sciuromorpha (squirrels and kin), Myomorpha ((beavers + gophers) + mice and kin), and Ctenohystrica (porcupines, chinchillas and kin).”

Figure 1. Subset of the LRT focusing on Glires and subclades within.

Figure 1. Subset of the LRT focusing on Glires and subclades within. This is an older image not updated yet with the dormouse, Eliomys.

The LRT
also supports these divisions. It also supports the basal nesting of ‘Tupaiidae’ relative to Glires. It does not support the inclusion of Primates within Glires, but the two are sister clades within a single clade. The LRT supports the basal nesting of Didelphis relative to Metatheria and Eutheria.

Some oddities in the results of Asher et al. 2019.

  1. Papio, the baboon, nests between Dermoptera (flying lemurs/colugos) and Plesiadapis + lemurs. That’s way too primitive for such a derived monkey.
  2. Rodent-toothed Pleisadapis nests with baboons and lemurs. This is a traditional nesting not recovered by the wider gamut LRT where Plesiadapis nests closer to multituberculates and the aye-aye, Daubentonia.

Asher et al. 2019 included dormice
(Eliomys and kin; Fig. 2), and found them to be rather primitive, closer to squirrels. So Eliomys was added to the LRT and it nested with Mus, the mouse.

Figure 2. Eliomys, the dormouse.

Figure 2. Eliomys, the dormouse.

How to tell a mouse from a dormouse.
The skulls are similar, but different. The dormouse tail is furry, not scaly. Dormice are more arboreal. The dormouse hibernates rather than seeking warm spots. Fossil dormice are found in the Eocene, but their genesis must go back to the Early Jurassic, where multituberculates are found, according to the LRT.


References
Asher RJ, Smith MR, Rankin A and Emry RJ 2019. Congruence, fossil and the evolutionary tree of rodents and lagomorphs. Royal Society Open Science 6:190387. http://dx.doi.org/10.1098/rsos.190387

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.

A post-dentary reversal between rodents and multituberculates

Yesterday I promised a look at the new Jurassic gliding mammal, Arboroharamiya (Han et al. 2017), known from two crushed, but complete specimens (Figs. 1, 2). Originally this genus was considered a euharamiyid, close to the Jurassic squirrel-like Shenshou (Fig. 3) derived from trithelodont pre-mammals close to Haramiyavia.

Figure 1. The holotype specimen of Arboroharamiya HG-M017 in situ with DGS tracings added.

Figure 1. The holotype specimen of Arboroharamiya HG-M017 in situ with DGS tracings added. The skull in figure 5 comes from this specimen.

The two specimens are superficially distinct
due to the width of their extraordinary gliding membranes, reinforced with stiff fibers. I have not tested the paratype specimen in the LRT yet.

Figure 2. The paratype specimen of Arboroharamiya HG-M018, in situ. DGS color tracing added. The skull is in poor shape.

Figure 2. The paratype specimen of Arboroharamiya HG-M018, in situ. DGS color tracing added. The skull is in poor shape.

Contra Han et al. 2017
In the large reptile tree Arboroharamiya nests with Carpolestes, Ignacius, Plesiadapis, Daubentonia and Paulchaffatia, taxa excluded from Han et al. The extant rodents, Rattus and Mus, are also related and included in the Han et al. cladogram (Fig. 3).

Figure 1. From Han et al. 2017, a cladogram that nests Arboroharamiya close to Xianshou and Shenshou. Colors added to showing the shuffling of various clades in the LRT. Cyan = Eutheria. Red = Metatheria. Yellow = Prototheria. Gray = Trithelodontia. White are untested or basal cynodonts.

Figure 3. From Han et al. 2017, a cladogram that nests Arboroharamiya close to Xianshou and Shenshou. Colors added to showing the shuffling of various clades in the LRT. Cyan = Eutheria. Red = Metatheria. Yellow = Prototheria. Gray = Trithelodontia. White are untested or basal cynodonts. Silhouettes are gliders. The Allotheria is not recovered by the LRT.

Arboroharamiya provides an unprecedented look
at the post-dentary in taxa transitional between rodents + plesiadapiformes and multituberculates (Fig. 5). Earlier here, here and here multituberculates were shown to have pre-mammal post-dentary/ear bones, yet nested with placental and rodent taxa. This is a reversal or atavism, a neotonous development due to the backward shifting of the squamosal (another reversal) favoring the development of larger jaw muscles to power that uniquely shaped cutting tool, the lower last premolar. It has never been so clear as in Arboroharamiya, though.

Figure 4. Subset of the LRT nesting Arboroharamiya with Carpolestes within Rodentia

Figure 4. Subset of the LRT nesting Arboroharamiya with Carpolestes within Rodentia

Han et al. reported, “The lower jaws are in an occlusal position and the auditory bones are fully separated from the dentary.” In the new interpretation (Fig. 5) the neotonous articular is back in contact with the neotonous quadrate (both auditory bones in derived mammals) as the squamosal shifts posteriorly to its more primitive and neotonous position toward the back of the skull. Essentially the back of the skull in Arboroharamiya and multituberculates are embryonic relative to rodents.

Reversals
can be confusing because they are a form of convergence arising from neotony. The LRT separates convergent taxa by nesting them correctly with a wide suite of traits and testing them with a wide gamut of taxa.

Figure 3. Images from Han et al. Color and white labels added. Here the malleus, incus and stapes have reverted to their pre-mammal states and configurations. Note the quadrate is in contact with the articular, as in pre-mammals as the dentary and squamosal become a sliding joint, carried by larger jaw muscles. Also note the various ectotympanic bones (yellow) also present, typical of Theria.

Figure 3. Images from Han et al. Color and white labels added. Here the malleus, incus and stapes have reverted to their pre-mammal states and configurations. Note the quadrate is in contact with the articular, as in pre-mammals as the dentary and squamosal become a sliding joint, carried by larger jaw muscles. Also note the various ectotympanic bones (yellow) also present, typical of Theria.

When a few traits say: pre-mammal
and a suite of traits say: rodent descendant, go with the standard for phylogenetic analysis. Only maximum parsimony reveals reversals when they appear. If you relied on just the post-dentary traits here you’d be ‘Pulling a Larry Martin‘ and nesting Arboroharamiya with pre-mammals.

I didn’t think I’d have to
keep referring to the dear departed professor from Kansas, Dr. Larry Martin, but he did like to play that game. I’m encouraging others not to, whether they know they are doing so or not.

References
Han G, Mao F-Y, Bi-SD, Wang Y-Q and Meng J 2017. A Jurassic gliding euharamiyidan mammal with an ear of five auditory bones. Nature 551:451–457.

 

Evolution of multituberculates illustrated

Updated the next day, January 5, 2019 with new interpretations of the post-dentary bones in figure 3, detailed here.

With the addition of four taxa
to the large reptile tree (LRT, 1370 taxa), a review of the Bremer scores helped cement relationships in the Primates + Glires clade (Figs. 1, 2). Yesterday we looked at plesiadapiform taxa (within Glires, Fig. 2) leading to the aye-aye, Daubentonia. Today we’ll look at a sister clade within Glires, one that produced the clade Multituberculata.

The traditional, but invalid outgroup taxon,
Haramiyavia, is a pre-mammal trithelodontid not related to the rodent-and plesiadapiform- related members of the Multituberculata in the LRT. More on that hypothesis below.

In Figure 1
look for the gradual accumulation of traits in derived taxa. Carpolestes (Late Paleocene) is a late survivor from a Jurassic radiation. Paulchoffatia is Latest Jurassic. Megaconus is Middle Jurassic. Vilevolodon, Xianshou and Rugosodon are Late Jurassic. Kryptobaatar is Late Cretaceous. Ptilodus is Paleocene. So this radiation had its genesis in the Early Jurassic and some clades, like Carpolestes, had late survivors.

Figure 1. LRT taxa in the lineage of multituberculates arising from Carpolestes and Paulchoffatia.

Figure 1. LRT taxa in the lineage of multituberculates arising from Carpolestes and Paulchoffatia. Carpolestes is a sister to Ignacius. The new taxon, Arboroharamiya, nests with Xianshou in the Han et al. cladogram.

It’s worth noting
that the one key trait that highlights many multituberculates, the oddly enlarged last premolar of the dentary, is also a trait found in the basal taxon, Carpolestes, but not in Paulchoffatia, (Fig. 1). Paulchoffatia has the odd mandible (dentary) without a distinct retroarticular process common to multituberculates, convergent with Daubentonia. That there is also no distinct glenoid process (jaw joint) in clade members made these jaw bones even harder to understand. Then I realized the jaw joints were mobile, slung in place by muscles, as in rodents and primates, rather than a cylindrical dentary/squamosal joint, as in Carnivorans.

There is one more elephant in the room
that needs to be discussed. Earlier we looked at the splints of bone at the back of the jaws in multituberculates identified as posterior jaw bones (Fig. 3), a traditional pre-mammal trait. Multis move the squamosal to the back of the skull and reduce the ear bone coverings (ectotympanics) that nearly all other placentals use to cover the middle ear bones. This reversal to the pre-mammal condition is key to the traditional hypothesis shared by all mammal experts that multis are pre-mammals. Embryo primitive therians have posterior jaw bones, but these turn into tiny middle ear bones during ontogeny. In multis their retention in adults is yet another example of neotony.

Why lose/reverse those excellent placental middle ear bones?
‘Why’ questions get into the realm of speculation. With that proviso, here we go.

Figure 2. Jaw muscles of the Late Cretaceous multituberculate, Catopsbaatar.

Figure 2. Jaw muscles of the Late Cretaceous multituberculate, Catopsbaatar.

The over-development of the lower last premolar
indicates some sort of preference or adaptation for food requiring such a tooth. The coincident and neotonous migration of the squamosals to the back of the skull (the pre-mammal Sinoconodon condition) enlarged the temporal chewing muscles (Fig. 2). The neotonous lack of development of tiny middle ear bones was tied in to that posterior migration. Evidently Jurassic and Cretaceous arboreal multis did not need the hearing capabilities provided by the tiny middle ear bones of most therians, but they needed larger jaw muscles. Evidently they were safe in the trees because there were few to no arboreal predators of mammals back then. Multis and rodents had the trees to themselves. Evidently that changed in the Tertiary, when multis became extinct, perhaps because birds of prey (hawks and owls) became widespread and only rodents could hear them coming. That’s a lot of guesswork. Confirmation or refutation should follow.

Figure 3. Images from Han et al. Color and white labels added. Here the malleus, incus and stapes have reverted to their pre-mammal states and configurations. Note the quadrate is in contact with the articular, as in pre-mammals as the dentary and squamosal become a sliding joint, carried by larger jaw muscles. Also note the various ectotympanic bones (yellow) also present, typical of Theria.

Figure 3. Images from Han et al. Color and white labels added. Here the malleus, incus and stapes have reverted to their pre-mammal states and configurations. Note the quadrate is in contact with the articular, as in pre-mammals as the dentary and squamosal become a sliding joint, carried by larger jaw muscles. Also note the various ectotympanic bones (yellow) also present, typical of Theria.

A recent paper by Han et al. 2017
on the Late Jurassic pre-mulltituberculate euharamiyidan, Arboroharamiya (Fig. 3), documents precisely the status of the middle ear/posteror jaw bones along with the phylogenetic reduction of the ectotympanic that frames the ear drum and forms a thin shell around the middle ear bones in more primitive members of the clade Glires (Fig. 4, evidently there is more variation in this, and I will take a look at that in the future). Han et al. report for Arboroharamiya, “The lower jaws are in an occlusal position and the auditory bones are fully separated from the dentary.” That is the mammal condition.

The Han et al cladograms
include a rabbit and a rodent, but suffer from massive taxon exclusion. As a result they mix up prototherians, metatherians and eutherians as if shuffling a deck of cards, as compared to the LRT. My first impression is that they use too many taxa known only form dental traits when they should have deleted those until a robust tree topology was created and established with a large suite of traits from more complete taxa, as in the LRT.  I will add Arboroharamiya to the LRT shortly.

Figure 2b. Subset of the LRT focusing on Primates + Glires.

Figure 4. Subset of the LRT focusing on Primates + Glires.

Unfortunately,
and I hate to report this, mammal experts have been guilty of depending on a short or long list of traits (which can and often do converge and reverse) to identify taxa and clades. As readers know, paleontologists should only depend on a phenomic phylogenetic analysis that tests a large suite of bone characters and a wide gamut of taxa. Analysis proves time and again to be the only way to confidently identify taxa and lump’n’split clades. Cladograms, when done correctly, weed out convergence. Otherwise, reversals, like the neotonous reappearance of post-dentary bones and the reotonous disappearance of ectotympanics, can be troublesome to deal with, causing massive confusion. A phylogenetic analysis quickly and confidently identifies reversals because all possible candidates are tested at one time. 

Unfortunately,
d
iscovering this little insight is yet another reason why other workers have dismissed the LRT, have attempted to discredit the LRT, and is causing confusion in yet another upcoming class of future paleontologists. Paleo students have to choose between relying on a short list of traits or performing a phenomic phylogenetic analysis. Only the latter actually works (see below) and avoids mixing in convergent traits.

If you don’t remember
‘amphibian-like reptiles,’ those are taxa, like Gephyrostegus, Eldeceeon and Silvanerpeton, that nest at the base of all reptiles in the LRT, but have no traditional reptile traits. Everyone else considers them anamniotes. In the LRT, based solely on their last common ancestor status/nesting, these taxa are known to have evolved the amniotic membrane, the one trait, by definition, that unites all reptiles (including birds and mammals) and labels the above basal taxa, ‘amphibian-lke reptiles.’

References
Han G, Mao F-Y, Bi-SD, Wang Y-Q and Meng J 2017. A Jurassic gliding euharamiyidan mammal with an ear of five auditory bones. Nature 551:451–457.
Urban et al. (6 co-authors) 2017. A new developmental mechanism for the separation of the mammalian middle ear ossicles from the jaw. Proceedings of the Royal Society B: Biological Sciences https://doi.org/10.1098/rspb.2016.2416

Ancestry of the aye-aye (Daubentonia) illustrated

Yesterday we looked at a paper that compared
the squirrel, Sciurus, to the squirrel-like aye-aye, Daubentonia (Fig. 1) using µCT scans. The authors considered this a case of convergence and nested Daubentonia (from Madagascar) with lemurs (from Madagascar) based on gene studies.

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

Figure 1. Ignacius and Plesiadapis (Paleocene) nest basal to Daubentonia (extant) in the LRT. Note the short snout in Daubentonia, a sign of neotony. 50 million years separates Daubentonia from its ancestors.

As a follow-up
I’ll show the ancestry of Daubentonia based on the large reptile tree (LRT, 1370 taxa). The short list includes Ignacius and Plesiadapis, two other taxa also previously considered basal primates, but nest in the LRT with rodents. In the LRT Ignacius is sister to the Mus/Sciurus (= mouse/squirrel) clade.

Daubentonia has a postorbital bar,
convergent with that found in primates. Don’t be guilty of ‘Pulling a Larry Martin’. One character can appear on unrelated clades. Use an unbiased suite of traits and let the taxa nest wherever they want to. Compared to Plesiadapis, Daubentonia appears to be neotonous with a shorter rostrum and mandible, along with a smaller zygomatic arch and large braincase. The mandible has a similar morphology to multituberculates.

Basal taxa in the LRT
are what they are supposed to be: generalized forms ready to evolve into wild and exotic types. In that regard, wild and exotic Daubentonia (Fig. 4) is a poor candidate as a basal primate. In the LRT it nests as a highly derived wild and exotic rodent with no known descendants.

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

Figure 2. Notharctus, an Eocene adapid (lemur) and a basal primate. Compare to the convergent Plesiadapis in figure 3 and Daubentonia in figure 4.

Ignacius frugivorus (formerly Phenacolemur; Matthew and Granger 1921) was originally based on upper jaw with teeth. It was originally and is here considered a plesiadapiform, close to Plesiadapis.

Plesiadapis

Figure 3. Plesiadapis, formerly considered a basal primate, is here considered an aye-aye ancestor.

Plesiadapis tricuspidens (Gervais 1877) Paleocene ~55 mya. The Plesiadapiformes were widely thought to be the earliest representatives of the primate order, but here they nest wihthin Glires. Derived from a sister to IgnaciusPlesiadapis phylogenetic preceded the living aye-aye, Daubentonia. This clade nests between traditional rodents and multituberculates. Distinct from Ignacius, the skull of Plesiadapis had a deeper shorter rostrum and a higher orbit, but a smaller braincase. The jugal was more robust. The ear was raised. The mandible was more robust with deeper surfaces for muscle attachement and a more robust angular process and a longer coronoid process. The cervicals were shorter. The dorsals, ribs and lumbars were more robust along with the caudals. Chevrons developed at a likely sitting point. The limbs and girdles were more robust. The radius was anteriorly boewed and the ulna developed a large olecranon process (elbow). The unguals were large and deep. The feet were larger than the hands. The joints were nearly all transversely aligned indicating a simple extension/flexion motion for the fingers and toes.

Figure 7. Highlights of the aye-aye (Daubentonia) skeleton focusing on the small bones medial to the humerus (procoracoid + coracoid) and the lateral rotation of the ankle and pes where the astragalus still sits on top of the calcaneum, as the dorsal surface of the pes is now lateral.

Figure 4. Highlights of the aye-aye (Daubentonia) skeleton focusing on the small bones medial to the humerus (procoracoid + coracoid) and the lateral rotation of the ankle and pes where the astragalus still sits on top of the calcaneum, as the dorsal surface of the pes is now lateral.

Daubentonia madagascariensis (Gmelin 1788, Sciurus madagascariensis; Geoffrey Saint-Hilaire 1795; 40 cm snout-to-vent length) is the extant aye-aye. Originally considered a squirrel, then traditionally an odd sort of lemur-like primate with rodent-like teeth, here Daubentonia returns to Glires to nest with Plesiadapis, which has also been wrongly considered a basal primate. This nocturnal arboreal mammal has a long slender digits, particularly manual digit 3, which is used to probe for insects below tree bark. Note the hallux-like pedal digit 1. Like primates, a postorbital bar appears in this taxon, but the eyeballs are no more rotated or stereoscopic than ancestors.

An expert on mammals
(name omitted) replied to a recent query with the following note on Daubentonia“At the moment, your phylogenetic results in many ways resemble 19th century studies in which superficial similarities were interpreted as evidence of close relationship – for example, it’s striking that you find that Daubentonia is not a primate: this was debated during the early part of the 19th century, before researchers collectively reached a consensus that it is a primate, and this is overwhelmingly supported by molecular data too.”

I’m still looking for the phenomic cladogram
that includes the above taxa and others in the LRT. To my knowledge there is none as genomics has taken paleontologists to fantasyland. And, it’s not just superficial similarities… it’s a suite of 231 traits that overwhelms the few convergent traits with primates. 21st century phylogenetics should be accepted over 19th century debates. Let’s hope science and unbiased experimentation will someday triumph over tradition and ego.

References
Bloch JI, Fishe DC, Rose KD and Gingerich PD 2001. Stratocladistic analysis of Paleocene Carpolestidae (Mammalia, Plesiadapiformes) with description of a new late Tiffanian genus. Journal of Vertebrate Paleontology. 21 (1): 119–131.
Bloch JI and Boyer DM 2006. Grasping primate origins. Science 298:1606-1610.
Gervais P 1877. Enumeration de quelques ossements d’animaux vertebres recueillis aux environ de Reims par M. Lemoine. Journal de Zoologie (Paris) 6:74–79.
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).
Gingerich PD 1976. Cranial Anatomy and Evolution of Early Tertiary Plesiadapidae (Mammalia, Primates). Papers on Paleontology, Museum of Paleontology, The University of Michigan. 1-141. online pdf
Hahn G & Hahn R 2000. Multituberculates from the Guimarota mine, pp. 97-107 in Martin T & Krebs B (eds), Guimarota – A Jurassic Ecosystem, Verlag Dr Friedrich Pfeil, München.
Matthew WD and Grange W 1921. New genera of Paleocene mammals. American Museum Novitates 13:1-7
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
wiki/Plesiadapis
fossilworks/Ignacius

Origin of rodents and lagomorphs paper omits key taxa

From the Wu et al. 2012 abstract:

“The timing of the origin and diversification of rodents remains controversial, due to conflicting results from molecular clocks and paleontological data. The fossil record tends to support an early Cenozoic origin of crown-group rodents. In contrast, most molecular studies place the origin and initial diversification of crown-Rodentia deep in the Cretaceous, although some molecular analyses have recovered estimated divergence times that are more compatible with the fossil record. Here we attempt to resolve this conflict by carrying out a molecular clock investigation based on a nine-gene sequence dataset and a novel set of seven fossil constraints, including two new rodent records (the earliest known representatives of Cardiocraniinae and Dipodinae). Our results indicate that rodents originated around 61.7–62.4 Ma, shortly after the Cretaceous/ Paleogene (K/Pg) boundary, and diversified at the intraordinal level around 57.7–58.9 Ma.”

The Wu et al. cladogram
correctly derives placentals from marsupials, but employs Monodelphis as the outgroup rather than the Caluromys, as recovered by the large reptile tree (LRT, 1360 taxa, subset Fig. 1). The Wu et al. cladogram incorrectly nests horses with carnivores in the invalid clade, Laurasiatheria. The next split produces the clade Primates + Glires, omitting the clade Volitantia. Within the clade Glires, only two extant lagomorphs are employed, omitting 16 tree shrews, false tenrecs and many fossil taxa that preceded them as recovered by the LRT. Within the clade Rodentia, the large extant clades within the Wu et al. study matched the LRT, but the Wu et al. study omitted all fossil taxa, including plesiadapiformes, multituberculates, carpolestids and the extant aye-aye (Daubentonia).

Contra Li et al. 1987 and Wu et al. 2012,
rodents and rabbits diversified in the Early Jurassic, as we learned earlier, because their ancestors, the multituberculates and Henkelotherium (related to living pikas, Fig. 1), appear in the Middle and Late Jurassic. DNA does not work in deep time studies.

Figure 4. Mesozoic euthrerians (placentals, in black). Later taxa in light gray. All taxa more primitive than Mesozoic taxa were likely also present in the Jurassic and Cretaceous. None appear after Onychodectes. Madagascar separated from Africa 165-135 mya, deep into the Cretaceous with a population of tenrecs attached. No rafting was necessary. 

Figure 4. Mesozoic euthrerians (placentals, in black). Later taxa in light gray. All taxa more primitive than Mesozoic taxa were likely also present in the Jurassic and Cretaceous. None appear after Onychodectes. Madagascar separated from Africa 165-135 mya, deep into the Cretaceous with a population of tenrecs attached. No rafting was necessary.

References
Li C-K., Wilson RW, Dawson MR, Krishtalka L 1987. The Origin of Rodents and Lagomorphs. In: Genoways H.H. (eds) Current Mammalogy. Springer, Boston, MA
Wu S et al. (8 co-authors) 2012. Molecular and Paleontological Evidence for a Post-Cretaceous Origin of Rodents. PLoS ONE 7(10): e46445. https://doi.org/10.1371/journal.pone.0046445

SVP 2018: Rodent, plesiadapiform and multituberculate teeth similarities

You heard it here first.
Birlenbach and Fox 2018 found similarity in the rodent, multituberculate (Fig. 1) and plesiadapiform teeth. In the large reptile tree (LRT, 1038 taxa, subset Fig. 2) that is so because they are closely related to one another.

Figure 1. Animation of the mandible of the multituberculate Kryptobaatar showing the sliding of the jaw joint producing separate biting and grinding actions, just like rodents, their closest relatives in the LRT.

Figure 1. Animation of the mandible of the multituberculate Kryptobaatar showing the sliding of the jaw joint producing separate biting and grinding actions, just like rodents, their closest relatives in the LRT.

Unfortunately
Birlenback and Fox are working from older, smaller and less complete charts that tells them these three taxa are not closely related.

Figure 3. Subset of the LRT focusing on Glires, rodents and multituberculates.

Figure 2. Subset of the LRT focusing on Glires, rodents and multituberculates.

References
Birlenbach DM and Fox DL 2018. Morphological similarity in the dentition of rodents, multituberculates and plesiadapiformes during the Late Paleocene in North America.

Teeth in the shrew/rodent/rabbit/multituberculate clade

The problem:
Always ready for a review, I noticed in the rat/rabbit clade of the large reptile tree (LRT, 1272 taxa) canine teeth (and sometimes nearby others) were lost creating a diastema in seven subclades (Fig. 1). The biggest worry was the apparent reappearance of a full arcade of teeth in highly derived taxa, like Paulchaffotia and Carpolestes, after a several clades without a full arcade (including rodents and the aye-aye). Generally, that’s not supposed to happen. So I reviewed all the data and made a helpful image (Fig. 2).

Figure 1. Subset of the LRT focusing on the clade of rodents, shrews, rabbits and multituberculates. White taxa have a small or large tooth gap between the incisors and premolars.

Figure 1. Subset of the LRT focusing on the clade of rodents, shrews, rabbits and multituberculates. White taxa have a small or large tooth gap between the incisors and premolars.

The solution:
After trying and failing to force all taxa with a diastema together, the LRT recovered a cladogram in which canine teeth disappeared creating a diastema seven times by convergence in the rabbit/rodent clade (Fig. 1). Apparently unknown taxa with small canines linked the last taxa with canines (hedgehogs) with the first taxa with canines beyond rodents (multituberculates).

You might remember
that marsupials and large placental ungulates also produced taxa with a similar diastema. So it is a common convergent trait.

When charts don’t help, sometimes pictures  do.
Here (Fig. 2) are several taxa from the the subset cladogram above (Fig. 1) so you can see for yourself how evolution works in tiny steps that slowly add up to large changes. Particularly interesting here is the central place of hedgehogs (with a full arcade of teeth) basal to higher clades with a full arcade of teeth alongside yet another clade or two with lost canines (diastema).

Figure 2. A selection of taxa from figure 1 more or less to scale and in phylogenetic order (pink arrows). Hope this helps with the concept of a gradual accumulation of traits. The hedgehogs Erinaceus and Echinops are transitional to the higher taxa with teeth and without.

Figure 2. A selection of taxa from figure 1 more or less to scale and in phylogenetic order (pink arrows). Hope this helps with the concept of a gradual accumulation of traits. The hedgehogs Erinaceus and Echinops are transitional to the higher taxa with teeth and without.

Note:
The rodent-like ‘primates’ Ignacius, Plesiadapis and Daubentonia (Figs. 1, 2) are more closely related to rodents in the LRT (contra Gunnell et al. 2018.) That’s heresy, still waiting to be confirmed or refuted by testing by other workers. Note how similar Ignacius is to the hedgehog, Erinaceus (Fig. 3).

Figure 3. The hedgehog, Erinanceus, compared to Ignacius from the Paleocene.

Figure 3. The hedgehog, Erinanceus, compared to Ignacius from the Paleocene. Note the reduction to loss of the canine in the latter.

References
Gunnell GF et al. (9 co-authors) 2018. Fossil lemurs from Egypt and Kenya suggest an African origin for Madagacar’s  aye-aye. Nature Communications 9(3193).

 

Vilevolodon jaw, pectoral and ankle issues

Vilevolodon diplomylos (Luo et al. 2017; Jurassic, 160 mya; Figs. 1–5) was originally considered a relative of the Jurassic porcupine, Maiopatagium and then the pre-mammal, Haramiyavia.

Figure 1. Vilevolodon in situ, plate, counterplate, original drawing, DGS color, and restored manus and pes. Note the gliding membrane (patagium) and fur.

Figure 1. Vilevolodon in situ, plate, counterplate, original drawing, DGS color, and restored manus and pes. Note the gliding membrane (patagium) and fur.

Here flying squirrel mimic Vilevolodon
nests with the Jurassic squirrel-like multituberculate, Shenshou. According to Luo et al., tiny middle ear bones fail to develop here (Fig. 2). Rather these bones remain as post-dentary jaw bones. True, but in the scheme of things, balanced against a larger suite of synapomorphies, this is an atavism (= reversal). Jaw and ankle trait misinterpretations (see below) caused Meng et al. 2017 to consider Vilevolodon a pre-mammal. Rather it is a derived mammal with an odd throw-back ear region for reasons currently unknown.

Figure 1. Basal mammals and Vilevolodon as figured by Meng et al. Note in the other taxa the two jaw joints are nearly coincident. Not so in Vilevolodon.

Figure 2. Basal mammal (Morganucodon), pre-mammal (Yanoconodon) and Vilevolodon (rodent) as figured by Meng et al. Note in the other taxa the two jaw joints are nearly coincident and side-by-side. Not so in Vilevolodon where substantial distance separates the two putative jaw joints.

Where is the jaw joint?
Most basal mammals (and many pre-mammals) have a large dentary bone that includes a 1. large coronoid process, 2. a large articular process and 3. a large retro process posteroventrally.  Vilevolodon (Fig. 1) lacks #2, but originally the huge retro process was considered the articular process. Tiny posterior jaw bones were purported to arise from a medio-ventral trough (Figs 2, 3). In all other mammals of this grade (like Morganucodon and Yanoconodon, Fig. 2) the two articular surfaces are next to each other. That’s not the case in the Vilevolodon where the two purported articulations are far apart.

No basal mammals or pre-mammals
have the same tooth count with giant incisors seen in Vilevolodon (Fig. 2. In the large reptile tree (LRT, 1269) Vilevolodon has the opportunity to nest anywhere in the Tetrapoda, and it nests within Rodentia. In many rodents the jaws are free to move on a sliding jaw joint supported by a complex sling of jaw muscles. That seems to be the case here, as well.

Many rodents with sliding jaws
have flat-topped molars and pre-molars for grinding seeds and other plant materials. These taxa have a sliding jaw joint. That’s not the case with Vilevolodon, where the teeth occlude precisely, any sort of jaw joint is absent and the articular surface angles the other way.

Figure 4. Paramys is an extinct rodent with a sliding jaw joint and flattened premolars and molars. Compare to Vilevolodon.

Figure 4. Paramys is an extinct rodent with a sliding jaw joint and flattened premolars and molars. Compare to Vilevolodon.

Paramys
(Fig. 4) is similar to modern rats and mice in having flattened teeth and sliding jaw joint. Similar to, yet distinct from those of Vilevolodon where the molars must occlude. Everything else in the mandible has to be engineered so that becomes the end point (Fig. 5).

Figure 5. Vilevolodon in CT scan from Luo et al. There is no jaw glenoid, Lacking a jaw joint the mandible was held in place by large, interweaving jaw muscles that slightly rotate the mortar and pestle molars within one another during grinding of the food. Those ‘ear’ bones are indeed former posterior jaw bones making an atavistic reappearance in this highly derived taxon.

Then there is the ankle issue.
Meng et al. interpreted a primitive ankle joint (astragalus and calcaneum side-by-side) for Vilevolodon. Reexamination indicates a fairly typical rodent ankle here (Fig. 6; astragalus on top of the calcaneum) simply lacking a large tuber for the calcaneum. We saw a similar error in Maiopatagium earlier here.

Figure 6. Original and DGS tracing of the Vilevolodon left pes, here flipped for consistency of presentation. Note the astragalus sits atop the calcaneum, as in other therian mammals and rodents.

Figure 6. Original and DGS tracing of the Vilevolodon left pes, here flipped for consistency of presentation. Note the astragalus sits atop the calcaneum, as in other therian mammals and rodents.

 

Finally
I present a possible solution to the procoracoid/coracoid issue, almost following the reconstruction of Meng et al. with modification. In Vilevolodon the procoracoid and coracoid are loose (Fig. 7) and reconstructed like the same bones in a juvenile platypus, many nodes distant.  No other related taxa back to prototheres have a procoracoid and coracoid. These few traits appear to be atavisms or reversals because they do not tip the balance enough to nest Vilevolodon in or around prototheres. On that note, no prototheres have a suite of rodent-like traits to match those of rodents.

Figure 7. The pectoral girdle of BMNH 3258, fossil lacking a skull and any post lumbar data. Here a tentative reconstruction is presented that locates the procoracoid and coracoid anterior to the humerus with concave coracoid curves matching convex humerus curves. 

Figure 7. The pectoral girdle of BMNH 3258, fossil lacking a skull and any post lumbar data. Here a tentative reconstruction is presented that locates the procoracoid and coracoid anterior to the humerus with concave coracoid curves matching convex humerus curves.

Reversals like this are real problems for paleontologists.
Without the rest of the skeleton to tip the scores toward rodents, the presence of a procoracoid and coracoid would have been protothere indicators, which is what traditional paleontologists have thought for decades. Don’t pull a Larry Martin! One, two or a dozen traits do not nest taxa. Only a suite of 200+ traits can be trusted to correctly nest taxa, overcoming the phylogenetic problems of convergence, reversal and ‘eyeballing’ phylogeny based on a short list of cherry-picked traits.

Whenever Maiopatagium and Vilevolodon
are someday tested with squirrels and porcupines by other workers,  then we’ll see if those two nest basal to Theria or within Rodentia. At present, taxon exclusion, the use of suprageneric taxa and some misinterpretations appear to be problems with prior studies.

We’re all learning as we go.
I better understand things today than yesterday, then sharing those new thoughts with you.

Added six hours later:
The extant aye-aye (genus: Daubentonia), the closest living relative of Vilevolodon, seems to provide insight into the derived/atavistic rodent pectoral girdle and ankle described above. The precise drawing of Daubentonia (Fig. 8) seems to show a procoracoid and coracoid medial to the humerus, as shown above. It also shows an astragalus side-by-side with the calcaneum, except that the tibia and fibula are rotated medially (= dorsal pes rotated laterally), so the astragalus, relative to the tibia, still sits atop the calcaneum. Such solutions must be acknowledged when they appear in nature— or is this just artistic liberty?

Figure 7. Highlights of the aye-aye (Daubentonia) skeleton focusing on the small bones medial to the humerus (procoracoid + coracoid) and the lateral rotation of the ankle and pes where the astragalus still sits on top of the calcaneum, as the dorsal surface of the pes is now lateral.

Figure 7. Highlights of the aye-aye (Daubentonia) skeleton focusing on the small bones medial to the humerus (procoracoid + coracoid) and the lateral rotation of the ankle and pes where the astragalus still sits on top of the calcaneum, as the dorsal surface of the pes is now lateral.

References
Luo Z-X, Meng Q-J, Grossnickle DM, Neander AI, Zhang Y-G and Ji Q 2017. New evidence for mammaliaform ear evolution and feeding adaptation in a Jurassic ecosystem. doi:101.1038/nature 23483\
Meng Q-J, Grossnickle DM, Liu D, Zhang Y-G, Neander AI, Ji Q and Luo Z-X 2017.
New gliding mammaliaforms from the Jurassic. Nature (advance online publication)
doi:10.1038/nature23476

wiki/Shenshou
wiki/Vilevolodon

Reassessing Maiopatagium: now it’s a Jurassic porcupine!

Modified August 21, 2018 with the note that a procoracoid and coracoid were likely present in Jurassic rodents. These traits appear to be atavisms since taxa between prototheres and Jurassic rodents do not have these bones. 

Another case of taxon exclusion…remedied.
Earlier we looked at the Jurassic mammal, Maiopatagium, a putative glider, surrounded by a deep halo of long, straight hair. Meng et al. 2017 nested Maiopatagium between Sinoconodon and Haldanodon, taxa more primitive than mammals.

By contrast
the large reptile tree (LRT, 1235 taxa) nested Maiopatagium with Vilevolodon and Shenshou, two Jurassic arboreal rodents.

Now with 24 more taxa,
and several new ones from the rodent clade, the LRT nests Maiopatagium with the only tested porcupine, the small arboreal Coendou.

Figure 1. Subset of the LRT focusing on Scandentia + Glires. Yellow-green taxa are Jurassic in age.

Figure 1. Subset of the LRT focusing on Scandentia + Glires. Yellow-green taxa are Jurassic in age.

With this nesting
that halo of long straight hair on Maiopatagium
(Fig. 4) takes on a new identity as a pelage of still soft pre-quills, similar to a closely related taxon, Chinchillanesting with a former enigma taxon, Neoreomys

To no one’s surprise,
the guinea pig (genus: Cavia) nests with the pig-sized capybara (genus: Hydrochoerus). All but Maiopatagium are widely recognized members of the Hystricomorpha clade of rodents. The presence of Maiopatagium in this rodent clade supports the previously reported Jurassic radiation and dispersal of rodents (Fig. 1) currently represented by  a few specimens not widely recognized as rodents, nor tested against rodents. Porcupines and chinchillas were not in the Meng et al. taxon list.

Shifting Maiopatagium in the LRT to Sinoconodon adds 49 steps. Shifting to the more primitive Haldanodon adds 58 steps.

Distinct from all extant and extinct rodents Maiopatagium was reported to have a small coracoid and pro-coracoid, traits that disappear in therian mammals. This could be an atavism (= reversal) or it could be a misinterpretation of a crushed process of the scapula that appears in other hystricomorphs (Fig. 2). Vilevolodon has a protothere-like pro-coracoid and coracoid and it is medial to the scapula, not lateral as shown below. Interesting that similar structures appeared medial and lateral to the shoulder joint by convergence.

Figure 2. Possible source for the coracoid and procoracoid in Maiopatagium as crushed parts of the acromion process on other hystricomorphs.

Figure 2. Possible source for the coracoid and procoracoid in Maiopatagium as crushed parts of the acromion process on other hystricomorphs. At left is Hydrochoerus, the capybara. Above right is Cavia, the guinea pig. Lower right is Maiopatagium from Meng et al. 2017. Crushing would tend to break this fragile process. 

When the skull of Maiopatagium
nests with rodents we should consider the possibility that it may have included a large braincase (Fig. 3) not figured or restored by Meng et al. 2017 (Fig. 4).

Figure 3. Maiopatagium skull revised with extended, rodent-like cranium. Compared to figure 4. The anterodorsal naris is a hystricomorph trait. So is the premaxilla-frontal contact overlooked by Meng et al. 

Figure 3. Maiopatagium skull revised with extended, rodent-like cranium. Compared to figure 4. The anterodorsal naris is a hystricomorph trait. So is the premaxilla-frontal contact overlooked by Meng et al.

I was never able to see the gliding membrane
distinct from the halo of long hairs on Maiopatagium (Fig. 4) as described by Meng et al. 2017. No related taxa in the LRT are gliders.

Figure 2. Maiopatagium images from Meng et al. with the addition of a braincase restored here.

Figure 4. Maiopatagium images from Meng et al. with the addition of a braincase restored here. The pes has a new reconstruction (Fig. 5) than shown here.

The porcupine Coendou prehensilis
(Fig. 5) is the closest living relative to Maiopatagium in the LRT. Yes, the tooth shapes are distinctly different, but tooth shapes are highly variable and these taxa are separated by 160 million years. The limbs are longer in the Jurassic taxon and the hair has not yet turned into quills. The LRT does not test every trait. However, traits in the LRT nest Maiopatagium as a primitive porcupine and less likely to glide than originally figured.

Figure 4. Coendou, the extant prehensile-tailed porcupine, nests with the Jurassic Maiopatagium in the LRT. No other taxon nests closer among the 1268 tested.

Figure 5. Coendou, the extant prehensile-tailed porcupine, nests with the Jurassic Maiopatagium in the LRT. No other taxon nests closer among the 1268 tested.

The side-by-side alignment of the calcaneum and astragalus
figured by Meng et al. (Fig. 4) is yet another pre-therian trait (see Eomaia for the first shift to the therian state). Rodents don’t have this type of ankle (Fig. 5), so when you see it in the rodent clade we might count this as an atavism… possibly because Maiopatagium could have been hanging from branches or descending tree trunks head first and rotating the ankle, as squirrels do. The other possibility is a misinterpretation of the tarsals by Meng et al. An alternate reconstruction is shown here (Fig. 6).

In the porcupine pes,
please note the large flat bone arising from the medial tarsals (Fig. 5). The chinchilla does not have this disk, but Maiopatagium does (Fig. 6). It is an atavism arising from digit zero on the pes. Atavisms like this form the spur on the screamers.

Figure 6. The pes and tarsus of Maiopatagium traced and reconstructed with DGS methods compared to original art by Meng et al. 2017 (drawing).

Figure 6. The pes and tarsus of Maiopatagium traced and reconstructed with DGS methods compared to original art by Meng et al. 2017 (drawing). The porcupine, Coendou, also has a small digit 1 and a medial disk (tarsal zero) arising from the tarsus. The calcaneum appears to be crushed into several pieces, so the ‘calcar’ may be a broken artifact. No sister taxa have the Meng et al. ankle. Tarsal 5 and the lateral centrale (cuboid) are also separate.

Added almost a day later:
the pes of another specimen, BMNH1133 (from Meng et al. 2017, Fig. 7) compared to Rattus the rat. Pretty similar when reconstructed, aren’t they?

Figure 7. Another pes from Meng et al. 2017, this time reconstructed and compared to Rattus the rat. All the bones are there in just about the same shape and interrelation.

Figure 7. Another pes from Meng et al. 2017, this time reconstructed and compared to Rattus the rat. All the bones of the tarsus are there in just about the same shape and interrelation. The digits differ in proportion. Note the matching of the tibia-fibula width to a typical narrowly stacked astragalus and calcaneum.

 

References
Kermack KA, Kermack DM, Lees PM and Mills JRE 1998. New multituberculate-like teeth from the Middle Jurassic of England. Acta Palaeontologica Polonica 43(4):581-606.
Meng Q-J, Grossnickle DM, Liu D, Zhang Y-G, Neander AI, Ji Q and Luo Z-X 2017.
New gliding mammaliaforms from the Jurassic. Nature (advance online publication)
doi:10.1038/nature23476

wiki/Hydrochoerus
wiki/Maiopatagium
wiki/Coendou
raftingmonkey.com/Neoreomys
wiki/Brazilian_guinea_pig
wiki/Chinchilla