Turtle origins: Pappochelys STILL not the best candidate

Schoch and Sues 2017
bring us more details about Pappochelys, and pull a ‘Larry Martin‘ or two to force fit this taxon into a false narrative: the origin of turtles story. What little they report and show is indeed intriguing. What more they don’t report and show invalidates their hypothesis. A wider gamut phylogenetic analysis has the final say.

As a reminder,
many paleontologists try to find one, two or a dozen traits that look like they link one taxon to a clade, but avoid testing those hypotheses in a wide gamut phylogenetic analysis, like the large reptile tree (LRT, 1048 taxa). This technique of force-fitting and ignoring other candidate sisters never turns out well. It’s not pseudoscience, but it does remind one of early attempts at flying that did not include sufficient power, rudders, ailerons and horizontal stabilizers. Those attempts were all doomed to crash.

A wide gamut phylogenetic analysis
remains the only tool that always delivers a correct tree topology because  taxon exclusion is minimized. The LRT worked with Diandongosuchus. It worked with Lagerpeton. It worked with Chilesaurus. It worked with turtles, whales and seals. And it worked with pterosaurs. The LRT works!

Let’s just make this short and painful
Schoch and Sues ignored:

1. the sister of Pappochelys in the LRT, Palatodonta
2. other proximal relatives of Pappochelys in the LRT, Diandongosaurus, Anarosaurus, Palacrodon and Majiashanosaurus
3. the sister to hard shell turtles in the LRT, Elginia
4. the sister to soft shell turtles in the LRT, Sclerosaurus
5. basalmost hard shell turtles in the LRT, Niolamia and Meiolania.
6. the proximal relatives of Eunotosaurus in the LRT, Acleistorhinus, Delorhynchus, Australothyris and Feeserpeton.

Figure 1. Shoch and Sues cladogram of turtle origins. Look at that loss of resolution! Gliding kuehneosaurs nest between aquatic taxa? Really? Add about 300 taxa and let’s see if this tree resolves itself. 

Schoch and Sues employed only 29 taxa
many of which were suprageneric, compared to 1048 specimens in the LRT. Schoch and Sues lament, “the currently available data fail to support any of the three more specific hypotheses for the diapsid origins of turtles (sister group to Sauria, Lepidosauria or Archosauria, respectively). We found no support for earlier hypotheses of parareptilian relationships for turtles hypothesized by Laurin & Reisz (1997) and Lee (1997), respectively, nor for the hypothesis that captorhinid eureptiles were most closely related to turtles (Gaffney & McKenna 1979; Gauthier et al. 1988).” Schoch and Sues published a cladogram (Fig. 1)  in which the following taxa could not be resolved:

1. Acerosodontosaurus (swimming diapsid)
2. Kuehneosauridae (gliding lepidosauriforms)
3. Claudiosaurus (swimming diapsid)
4. ‘Pantestudines’ = Eunotosaurus, Pappochelys, Odontochelys, Proganochelys (turtles and turtle mimics)
5. Trilophosaurus + Rhynchosauria + Prolacerta + Archosauriformes (a paraphyletic mix)
6. Squamata + Rhynchocephalia (terrestrial lepidosaurs)
7. Placodus + Sinosaurosphargis + Eosauropterygia (swimming enaliosaurs)

In other words
Schoch and Sues have no idea how these taxa are related to each other. Their data fails to lump and separate 29 taxa completely. They report, “[Papppochelys] shares various derived features with the early Late Triassic stem-turtle Odontochelys, such as T-shaped ribs, a short trunk, and features of the girdles and limbs.” See what I mean about pulling a ‘Larry Martin’? They’re trying to save their hypothesis by listing a few to many traits. Unfortunately Schoch and Sues do not have the data that documents this suite is unique to Pappochelys and turtles. Actually these traits are found elsewhere within the Reptilia and sometimes several times by convergence.

Figure 2. Pappochelys comes to us from several specimens, all incomplete and all disarticulated. These are the pieces of the skull we will use in Photoshop to rebuild the skull. Schock and Sues made a freehand cartoon, a practice that needs to be discouraged. They had the nasals backwards and the lacrimal upside down and labeled a prefrontal. The failed to recognized the quadratojugal. And they changed the squamosal. The postorbital looks to be so fragile that the orbit might instead have been confluent with the lateral temporal fenestra.

Freehand reconstructions
Shoch and Sues created their reconstructions not by tracing bones, but freehand. That never turns out well. They created cartoon bones and modified them to be what they wanted them to be when they could have used Photoshop and real data.

Figure 3. In dorsal view Shoch and Sues compared Pappochelys to Odontochelys and Proganochelys, but deleted the more primitive Eunotosaurus. And it’s easy to see why. Eunotosaurus has wider ribs than its two purported successors. That and the LRT tell you its not a turtle, but a turtle mimic. Note the inaccuracy Schoch and Sues applied to their Odontochelys. The version from ReptileEvolution.com appears in frame 2 of this GIF animation. Since Pappochelys is know from 4 or more scattered and incomplete specimens, we really don’t know how many dorsal ribs it had.

Why didn’t they show Eunotosaurus
(in Fig. 3)? This turtle mimic has wider and more extensive dorsal ribs. That could be one reason. We’re all looking for a gradual accumulation of traits and Eunotosaurus, one of many turtle mimics, does not provide the primitive state.

Figure 4. From two years ago. Pappochelys compared to placodont sister taxa and compared to the Schoch and Sues reconstruction, which appears to have several scale bar errors and underestimated the number of dorsal vertebrae. So few ribs and vertebrae are known for Pappochelys that their order, size and number could vary from that shown here. 

The ‘Probably’ weasel word
Pappochelys is not known from any complete or articulated fossils. Even so Shoch and Sues report, “The vertebral column of Pappochelys comprises probably eight cervical, probably nine dorsal, two sacral, and more than 24 caudal vertebrae.” This is wishful thinking… They should have said ‘unknown’ not ‘probably’.

Dredging up false data to support a diapsid relationship
Schoch and Sues reference Bever et al. (2015) when they show a Eunotosaurus juvenile purportedly lacking a supratemporal and in its place, an upper temporal fenestra. Earlier that ‘missing’ supratemporal was identified as a nearby bump on the cranium of the juvenile.

Gastralia
Turtle ancestors in the LRT have no gastralia. So the origin of the plastron is still not known. According to Schoch and Sues, “The gastralia of Pappochelys are unique in their structure and arrangement.” Unfortunately Palatodonta is only known from cranial remains.    All other proximal relatives in the LRT have slender gastralia, not broad like those in Pappochelys. Some Pappochelys gastralia are laterally bifurcated, similar to the plastron elements in Odontochelys. That’s intriguing, but ultimately yet another Larry Martin trait. What we’re looking for is maximum parsimony, a larger number of traits shared by sister taxa and proximal relatives than in any other taxa.

Scapula
The Pappochochelys scapula is dorsally small and slender, like those of other placodonts and basal enaliosaurs. Shoch and Sues compared it to the basal turtle scapula, which is relatively much larger. Comparable pectoral elements are documented in the outgroups Bunostegos and Sclerosaurus, but these were ignored by Shoch and Sues. We don’t know of any post-crania for the hard shell turtle sister, Elginia, which might or might not have had a Meiolania-like carapace.

Shoch and Sues made some great observations,
but they kept their blinders on with regard to other candidates. A wide gamut analysis really is the only way to figure out how taxa are related to one another. Hand-picking traits and cherry-picking a small number of taxa is not the way to understand turtle origins. However, once relationships are established and all purported candidates are nested in a large gamut analysis, THEN it’s great to describe and compare how various parts of verified sister taxa evolved.

The LRT
nests turtles with pareiasaurs. Hardshell turtles arise from the mini-pareiasaur Elginia to Niolamia. Softshell turtles arise from the mini-pareiasaur Sclerosaurus to Odontochelys. Pappochelys nests with Palatodonta at the base of the Placodontia.

References
Bever GS, Lyson TR, Field DJ and Bhular B-A S 2015. Evolutionary origin of the turtle skull. Nature published online Sept 02. 2015.
Schoch RR and Sues H-D 2017. Osteology of the Middle Triassic stem-turtle
Pappochelys rosinae and the early evolution of the turtle skeleton. Journal of Systematic Palaeontology DOI: 10.1080/14772019.2017.1354936

Tulerpeton restoration

A reconstruction
puts the in situ bones back into their in vivo places.

A restoration
imagines the bones and soft tissues that are missing from the data. Adding scaled elements from a sister taxon is usually the best way to handle a restoration as we await further data from the field.

Figure 1. Tulerpeton restored based on the bauplan of Silvanerpeton and to the same scale.

We looked at
Tulerpeton, the Upper Devonian taxon known chiefly from its limbs, earlier. I reconstructed the limbs several ways, but did not attempt a restoration. Here (Fig. 1) that oversight is remedied based on the bauplan of Viséan sister, Silvanerpeton, also nesting at or near the base of the Reptilia (only amnion-layered eggs determine reptile status).

Among the overlapping elements,
in Tulerpeton the pectoral girdle and forelimbs are larger. An extra digit is present laterally.

References
Clack JA 1994. Silvanerpeton miripedes, a new anthracosauroid from the Visean of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (for 1993), 369–76.
Coates MI and Ruta M 2001 2002. Fins to limbs: What the fossils say. Evolution & Development 4(5): 390–401.
Lebedev OA 1984. The first find of a Devonian tetrapod in USSR. Doklady Akad. Navk. SSSR. 278: 1407–1413.
Lebedev OA and Clack JA 1993. Upper Devonian tetrapods from Andreyeva, Tula Region, Russia. Paleontology36: 721-734.
Lebedev OA and Coates MI 1995. postcranial skeleton of the Devonian tetrapod Tulerpeton curtum Lebedev. Zoological Journal of the Linnean Society. 114 (3): 307–348.
Mondéjar-Fernandez J, Clément G and Sanchez S 2014. New insights into the scales of the Devonian tetrapods Tulerpeton curtum Lebedeve, 1984. Journal of Vertebrate Paleontology 34:1454-1459.

wiki/Silvanerpeton
wiki/Tulerpeton

There’s nothing special about Henosferus

The incisors are not too big
or weird or crowded (Fig. 1), the canine just rises above the rest of the teeth, there are only 5 premolars all standard-shaped, and only three molars, all standard-shaped. The dentary definitely formed the main jaw joint and the post-dentary bones must have been tiny.

Figure 1. Henosferus mandible restored by Rougier et al. 2005 from several broken specimens.

…and that’s why
Henosferus ( Rougier et al. 2007; Middle Jurassic) makes a good candidate for basalmost mammal. There are too few traits here to add it to the large reptile tree (LRT). Frankly, I’m eyeballing this restoration. It compares well with Juramaia (Fig. 2) without the odd molars and incisors. 

Figure 2. Juramaia (Late Jurassic, 160 mya) is more completely known and nests between monotremes and therians (marsupials + placentals).

Henosferus is traditionally considered
a member of the Australosphenida, a group of mammals that include monotremes, and other taxa known chiefly from scraps. Vincelestes sometimes makes this list, but in the LRT it nests as a carnivorous marsupial.

References
Luo Z-X, Yuan C-X, Men Q-J and JiQ 2011. A Jurassic eutherian mammal and divergence of marsupials and placentals. Nature 476: 442–445. doi:10.1038/nature10291.
Rougier, GW, Martinelli AG, Forasiepi AM and Novacek M J 2007. New Jurassic mammals from Patagonia, Argentina : a reappraisal of australosphenidan morphology and interrelationships. American Museum novitates, no. 3566. online here.

wiki/Juramaia
wiki/Henosferus

You heard it here first: Chilesaurus is a basal ornithischian confirmed.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Figure 2. Look familiar? Here are the pelves of Jeholosaurus and Chilesaurus compared. As discussed earlier, this is how the ornithischian pelvis evolved from that of Eoraptor and basal saurorpodomorpha.

A new paper by Baron and Barrett 2017 confirms Chilesaurus (Fig. 1) as a basal member of the Ornithischia, not a bizarre theropod. As long time readers know, this was put online two years ago (other links below) in this blog.

Unfortunately, the authors don’t have an understanding of the interrelationships of phytodinosaurs, even though they report, “For example, Chilesauruspossesses features that appear ‘classically’ theropod-like, sauropodomorph-like and ornithischian-like…” Nor did they mention the sister taxon, Jeholosaurus (Fig. 2).

Remember,
discovery only happens once.
More on this topic later.

This note went out this morning:
Thank you, Matthew,
for the confirmation on Chilesaurus.
In this case, it would have been appropriate to include me as a co-author since I put this online two years ago.

https://pterosaurheresies.wordpress.com/2015/04/28/chilesaurus-new-dinosaur-not-so-enigmatic-after-all/
http://www.reptileevolution.com/reptile-tree.htm
http://www.reptileevolution.com/chilesaurus.htm

References
Baron MG, Barrett PM 2017. A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs. Biol. Lett. 13: 20170220. http://dx.doi.org/10.1098/rsbl.2017.0220 pdf online

Best regards,

Azhdarchid pterosaur flight issues

Pterosaurs,
as fenestrasaur tritosaur lepidosaurs matured isometrically. That’s a widely overlooked fact, even by pterosaur workers. Hatchlings had adult proportions with small eyes and long rostra — if their 8x larger parents had small eyes and long rostra. Hatchlings also had adult-proportioned wings. So presumably they were able to fly shortly after hatching (and drying out a bit) — if their parents were able to fly. But not all adult pterosaurs were able to fly…

Figure 1. GIF animation, 4 frames, showing three pterosaurs specimens in 3 sizes (see scale bars) with short, medium and long wings, drawn to the same torso length. The question is: did Quetzalcoatlus fly?

Flightless pterosaurs
Earlier we looked at two related pterosaurs, the no. 57 specimen (Sos 2482) and the no. 42 specimen in the Wellnhofer 1970 catalog (Fig. 1). Both are adults. Both are in the azhdarchid lineage that arose from a tiny pterodactyloid-grade dorygnathid, the no. 1 specimen (TM 10341) in the Wellnhofer 1970 catalog and ultimately gave rise to the giant pterosaur, Quetzalcoatlus (also in Fig. 1). A magnitude or more greater in size and with wings only half as long as the flying no. 42 specimen,

Quetzalcoatlus is widely considered a flying pterosaur.
Can that be verified? Other clades of large (larger than a pelican) pterosaurs all have elongate wings, ideal for soaring. Azhdarchids, apparently deep shoreline waders, did not. The distal two long phalanges (sans the ungual) were shorter in azhdarchids, but the wing was not otherwise reduced, as in the flightless pterosaur, no. 57 (Fig. 1). Witton and Naish 2008 provide a history of workers pondering this question. Unfortunately they provided a bat-wing membrane attached to the ankles or shins with anteriorly oriented pteroids, ignoring key references for pterosaur wing shape (Peters 2002, 2009 and references therein) while ignoring fossilized evidence of pterosaur wing tissue, as others have done.

As anything gets larger,
either ontogenetically or phylogenetically, they generally put on weight at the cube of their length. Air-filled pterosaurs were not as solid, so that ratio was undoubtedly lower.  Even so longer, larger wings on larger pterosaurs makes sense, as in living large birds that fly and are also air-filled.

But that is countered by the isometric growth of individual pterosaurs as they mature to adulthood. Whatever works for hatchlings and tiny pterosaurs, is working just as well for giant adults. Could that mean that all ontogenetic stages of Quetzalcoatlus could fly? Or none of them? Or only half-sized juveniles at about ten percent of the adult weight? With flight, it’s always a balancing act: thrust, lift, drag, weight.

Wings can still provide great thrust
for terrestrial excursions even if they cannot get a big pterosaur off the ground (Fig. 2). So that’s a possibility under consideration, too. After all, why not use all the thrust available?

Figure 10. Quetzalcoatlus running like a lizard prior to takeoff.

To prevent an extant flying bird, like a cockatiel, from flying, or flying well,
it’s surprising how little of the tips of the feathers need to be clipped. Link here. Basically its the difference between no. 42 and Quetzalcoatlus above (Fig. 1). With this in mind, I cannot join those who say giant Quetzalcoatlus could fly or fly between continents, until supporting evidence comes alone. Rather, giant azhdarchids become hippo analogs in this respect: they were probably constant deep waders (Fig. 3) capable of charging or running from danger. Storks, which azhdarchids otherwise resemble, tend to fly away because they have long, not truncated wings and can do so.

Figure 3. In my opinion this saddle-bill stork wading in water appears to be the bird closest to azhdarchid morphology and, for that matter, niche. It can fly from danger on elongate wings. Not so sure that Q could do the same. 

References
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing—with a twist. Historical Biology 15:277-301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
Witton M and Naish D 2008.  A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. https://doi.org/10.1371/journal.pone.0002271. online here.

What is Fruitafossor? A xenarthran close to Peltephilus.

This appears to be
yet another case of pertinent taxon exclusion. Today’s fossorial digger has several universally acknowledged xenarthran (edentate) traits. For reasons unknown it was not tested against another fossorial xenarthran, Peltephilus. Rather the authors compared their digger to an arboreal sloth, Bradypus, among several other taxa, including distinctly different anteaters and armadillos.

ºªº Figure 1. Scapula of Fruitafossor compared to several candidate sisters. Luo and Wible made things a bit more difficult by presenting left and right scapulae. In frame 2 they are all left scapulae for ready comparison. There is no doubt that the Fruitafossor scapula was illustrated to look more like that of Ornithorhynchus. Unfortunately the photo data (Fig. 2) does not clearly support that shape. That shape is so important, it needed to be better documented.

Luo and Wible 2005
brought us a small, mostly articulated, rather crushed and incomplete Late Jurassic mammal with simple blunt teeth and digging forelimbs. Fruitafossor windscheffeli (Figs. 1–6) is best represented by a CT scan (Figs. 2–4) and original drawings (Figs. 5, 6) created by the Luo and Wible team.

Figure 2. Fruitafossor in situ from Digimorph.org and used with permission and here colorized to an uncertain extent. All those little white dots could be scattered osteoderms.

The original analysis
nested Fruitafossor between extremely tiny Hadrocodium + Shuotherium and Gobiconodon in a tree topology that does not resemble the topology of the large reptile tree (LRT, 1048 taxa). The authors noted Fruitafossor is “not a eutherian, let alone a xenarthran” despite noting Fruitafossor had tubular molars and xenarthran intervertebral articulations, traits otherwise found only in xenarthrans.

Figure 3. Same specimen from Digimorph.org and rotated to show the teeth better. See figure 3 for a closeup. All those little white dots could be scattered osteoderms. Some of this flatness is due to crushing. Some of it is due to this being a wider than deep armored mammal.

Wider than deep
Yes, the Fruitafossor specimen is crushed, but what is shown here indicates a low, wide mammal just getting some armor in the Late Jurassic. And we all know why armor might have been helpful! And this may explain the lateral sprawl of the forelimbs and giant wide humerus, another atavism!

Figure 4. Closeup of figure 2 showing maxilla and dentary in occlusion. If there is a convex ventral dentary it must be imagined because it is not preserved.

By contrast,
the LRT nested Fruitafossor with the horned, armored digging ‘armadillo’ more closely related to Bradypus: Peltephilus (Fig. 5).

Figure 5. The xenarthran, Peltephilus, compared to Fruitafossor, not to scale, but to similar jaw lengths. Note the drawing from Luo and Wible does not exactly match what one can see in the photo (Fig. 3). This data needs to be clear and it is not.

Luo and Wible compared
Fruitafossor to the arboreal and extant Bradypus, but not to the fossorial and extinct Peltephilius (Fig. 5). I would consider that a mistake or an oversight that here overturns their hypothesis of a relationship of Fruitafossor to basalmost mammals.

Figure 6. Several drawings from Luo and Wible that one must trust for accuracy. The verification data is too fuzzy to validate. As in other xenarthrans, the ilia actually form a pair of horizontal plates on either side of the long fused and eroded sacrals. Four fingers is a trait shared with Peltephilus. Imagine that rib cage wider and not so deep.

Scattered osteoderms
(Fig. 3) were not mentioned in the text. That’s one more trait shared with the armored xenarthran, Peltephilus. This overlooked relationship of derived xenarthrans moves them into the Jurassic, an era they have never been in before in phylogenetic and chronological analyses. Here placental arboreal and fossorial mammals (prior to condylarths) shared time and space with dinosaurs during the Jurassic and Cretaceous, but have, so far, been underrepresented in the fossil record. That’s changing with re-examination of the data applied to a larger gamut taxon list.

Although the illustrated scapula
(Fig. 1) looks like that of an egg-laying mammal, I will wait for better data to validate that illustration. In the meantime, Fruitafossor has blunt, tubular molars and xenarthran vertebral articulations (among many other xenarthran traits) because it is a xenarthran, not an egg-layer with convergent traits.

References
Luo Z-X and Wible JR 2005. A late Jurassic digging mammal and early mammal diversification. Science 308:103–107.

Vilevolodon: the atavistic reappearance of post-dentary bones

Preface
I’ve been wondering about the traditional nesting of Multituberculata and kin outside of the Mammalia for years. All have a dentary jaw joint, but some have post-dentary bones. given the opportunity multituberculates nest with rodents and plesiadapiformes in the large reptile tree (LRT, 1047 taxa).  No other pre-mammals resemble them. Traditionally Haramiyava (Fig. 1) has been considered a pre-mammal link to Haramiyida + Multituberculata. In the LRT Haramiyava nests with the mammaliaforms Brasilodon, Sinoconodon and Therioherpeton – far from any other taxa considered Haramiyida + Multituberculata currently and provisionally nesting deep within the Mammalia.

Figure 1. Haramiyavia reconstructed and restored. Missing parts are ghosted. The fourth maxillary tooth appears to be a small canine. The post-dentary bones are imagined from Vilevolodon (figure 4).

Vilevolodon diplomylos
(Luo et al. 2017; Jurassic, 160 mya; BMNH2942A, B; Figs. 2-4) was originally considered a stem mammal (= mammaliaform), a eleutherodontid in the clade Haramiyida AND it had clearly defined gliding membranes (Fig. 2). By contrast the LRT nests Vilevolodon with the Late Jurassic para-rodent Shenshou and the extant rodents, Rattus and Mus, not far from members of the Multituberculata.

Figure 2. Vilevolodon in situ, plate, counterplate, original drawing, DGS color, and restored manus and pes. Note the gliding membrane (patagium) and fur.

But there’s a big problem
Vilevolodon doesn’t have tiny ear bones, like mammals do. It has post-dentary bones, like pre-mammals do (Figs. 3, 4).

Figure 3. Vilevolodont skull in situ, without color, DGS color tracing, that tracing reconstructed and a CT scan form Luo et al. 2017.

The ear problem in Jurassic rodents
Luo et al. report, “a mandibular middle ear with a unique character combination previously unknown in mammaliaforms.” Pre-mammals have post-dentary bones (articular, angular, surangular). Therian mammals shrink and migrate those bones to the base of the skull where they become middle ear bones with new names (malleus, incus, ectotympanic). The stapes remains the stapes in all tetrapods. So what is happening with Vilevolodon and its sisters? Why don’t the pre-mammal post-dentary bones define it as a pre-mammal? After all, that’s the current paradigm.

Figure 3. There is no doubt that Vilevolodon has pre-mammal type post-dentary bones. There is also no doubt that the dentary formed the main jaw joint with the squamosal. How does one reconcile both sets of traits? In the LRT Vilevolodon nests with rodents. This appears to be a mammal with an atavism, a reversal. These elements simply stopped developing as in other mammals.

Mammals are defined by
the evolution and migration of their posterior jaw bones into middle ear bones with a jaw joint switch from quadrate/articular to dentary/squamosal. Multituberculates and haramiyids appear to bend or break that rule because they have cynodont-like posterior jaw bones, not tiny middle ear bones, and yet otherwise they nest with rodents and plesiadapiformes. This is one reason why you don’t want to pull a Larry Martin with post-dentary bones. You want to nest a taxon based on a long list of traits, not just one, two or a dozen.

The massive jaw joint
Mammals, such as Vilevolodon, with atavistic post-dentary bones also have a massive jaw joint with a long articulating surface on the dentary contacting the squamosal. All mammals have such a jaw joint. Pre-mammals don’t. While Vilevolodon has a large dentary/squamosal jaw joint, the post-dentary articular, still contacts the quadrate. It’s clearly not the main jaw joint.

Filan 1991
traced the development of post-dentary bones in embryonic Monodelphis specimens. She reported, “Neonates of Monodelphis possess neither mammalian (dentarysquamosal) nor reptilian (quadrate-articular) jaw articulations, nor does the contact between the incus and crista parotica offer a joint surface. Elasticity in Meckel’s cartilage allows minimal deflection of the lower jaw.” After all, those neonates are just sucking milk, not biting, and the embryos don’t even do that. Does that make neonates like this not mammals? No. The evidence indicates that in multituberculates and haramiyds the embryological transformation of posterior jaw bones stopped before development transformed them into middle ear bones. This is an atavism, a phylogenetic reversal. The timing of development changed. In the case of Vilevolodon, the middle ear bones stop evolving during embryological development and the post-dentary bones they would have evolved from continue to appear in adults. What was a rare mutation probably spread throughout an isolated population. Perhaps this had something to do with the increase in size of the dentary jaw joint.

Haramiyavia and the Haramiyida clade
Seems at this point that only Haramiyavia is a haramiyid, unless Brasilodon is one as well. Members traditionally assigned to the clade Eleutherodontidae also nest in various locations in the LRT, not all in one clade.

Meng et al. 2017 report,
“Stem mammaliaforms are morphologically disparate and ecologically diverse in their own right, and they developed versatile locomotor modes that include arboreal, semiaquatic, and subterranean specializations, which are all distinct from generalized mammaliaforms.” Unfortunately, the LRT nests a long list of mammaliaforms at various nodes within the Mammalia. They are not from a single diverse clade.

Contra Meng et al. 2017
the LRT reduces the niches and body shapes of stem mammals down to a few small, generalized taxa like Sinoconodon and Megazostrodon. Derived taxa nest at derived nodes.

The LRT nests rodents close to Plesidapiformes,
including the extant aye-aye, Daubentonia as first reported here. So it comes as no surprise when Luo et al. report, “Eleutherodontids show a marked similarity to the primate Daubentonia in the ventrally bent rostrum and deep mandible, and both features are interpreted to be reinforcement for incisor gnawing.” That’s the case only with Vilevolodon this time. Others may be by convergence.

Molars
The jaw joint of the rodent allows for rostral-caudal and dorsal-ventral motion of the jaws. Luo et al. report, in Villevolodon it is not possible for the mandible to move posteriorly or horizontally, but their images show a continuous anteroposterior trough/furrow in the three molars, though not to the extent seen in sister taxon Shenshou. Molars with a long and continuous trough for rostral-caudal grinding appear by convergence in several reptile/mammal clades.

Incisor replacement
Luo et al. report, “Incisor replacement is prolonged until well after molars are fully erupted, a timing pattern unique to most other mammaliaforms.“ In rodents incisors never stop growing. The growth pattern in Vilevolodon may be the first step toward that. Not sure why Luo et al. are missing all these strong rodent clues.

Gliding?
Meng et al. 2017 note: “They [Vilevolodon and kin] are the most primitive known gliders in mammal evolution, evolving approximately 100 million years before the earliest known therian gliders.” Earlier, with the appearance of the stem pangolin, Zhangheotherium at the start of the Cretaceous, the ghost lineage for primates, flying lemurs and bats was also set to that time or earlier. Before the advent of flying birds, but after the advent of predatory theropods, many mammals had evidently taken to the trees. And one way to get from tree to tree without descending to the dangerous turf is to jump, glide and fly. I predict we’ll find the big-handed ancestors of bats in Jurassic and Cretaceous strata someday. They are already volant shortly after the K-T extinction event.

Hearing in Vilevolodon
With the reappearance of post-dentary bones in taxa like Vilevolodon, the auditory acuity that was more highly developed in its ancestors must have suffered a setback. By the evidence provided, the massive jaw joint must have been more important for its survival.

Figure 4. Multituberculate Kryobaatar mandible in lateral and medial views. Here post-dentary bones are absent here. The malleus (quadrate) and ectotympanic are on the skull.

Getting back to the purported patagium of Maiopatagium
which we looked at yesterday. It is not apparent and the authors do not describe it. Rather, Meng et al. 2017 sidestep this by reporting, “Furthermore, we report a second eleutherodont specimen (BMNH2942) preserved with a halo of carbonized fur and patagial membranes, similar to those of Maiopatagium.” The patagial taxon remains unnamed in the Maiopatagium paper (Meng et al. 2017), but is named in a second paper appearing on the same day. It is today’s subject, Vilevolodon (Fig. 1)

References
Filan SL 1991. Development of the middle ear region in Monodelphis domestica (Marsupialia, Didelphidae): marsupial solutions to an early birth. Journal of Zoology 225(4): 577–588 DOI: 10.1111/j.1469-7998.1991.tb04326.x
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
Jenkins FA, Jr, Gatesy SM, Shubin NH and Amaral WW 1997. Haramiyids and Triassic mammalian evolution. Nature 385(6618):715–718.
Luo Z-X, Gatesy SM, Jenkins FA, Jr, Amaralc WW and Shubin NH 2015. Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution. PNAS 112 (51) E7101–E7109.

wiki/Haramiyavia
wiki/Vilevolodon
wiki/Maiopatagium