Flying squirrels and aye-ayes: convergent with multituberculates

For those in a hurry, a two-part summary:
1. By convergence, basal multituberculates in the Jurassic (Figs. 1, 4), had a distinct  flying squirrel (Glaucomys, Figs. 2, 3)-like patagial (= gliding membrane) morphology.
2. Also by convergence, multituberculates in the Jurassic had a short post-dentary skull length with a sliding jaw joint and a nearly absent angular process as seen in the extant aye-aye (Daubentonia, Figs. 5, 6).

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

Figure 1. The paratype specimen of Arboroharamiya HG-M018, in situ. DGS color tracing added. The skull is in poor shape.

Today’s blogpost had its genesis
when I finally noticed several basal multituberculates that preserved soft tissue had flying-squirrel-like patagia preserved in the sediment (Fig. 1)… and squirrels nested more or less close to the origin of multituberculates. So, I added a flying squirrel, Glaucomys (Fig. 1) to the large reptile tree (LRT, 1810+ taxa) to see what would happen.

It should come as no surprise
that Glaucomys nested with the extant red squirrel Sciurus, NOT any closer to multituberculates. Thus, the ability to glide in the manner of a flying squirrel turned out to be by convergence in basal multituberculates of the Jurassic.

Figure 2. Glaucomys gliding.

Figure 2. Glaucomys gliding.

Figure 2. Multituberculates to scale. Carpolestes is the proximal outgroup taxon.

Figure 3. Multituberculates to scale. Carpolestes is the proximal outgroup taxon.

Based on the phylogenetic position
of squirrels and other rodents as sisters to multituberculates, either flying squirrels were also gliding from tree-to-tree during the Mesozoic, or they took their time and only appeared after the Mesozoic. That is the current paradigm based on present evidence.

End of part 1. Scroll down for part 2.

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

Figure 4. Subset of the LRT focusing on basal placentals, including multituberculates.

Part 2.
By convergence, the aye-aye, Daubentonia

(Fig. 5) has a multituberculate-like mandible lacking an angular process along with a large circumference, sliding jaw joint and reduced post-dentary skull.

Figure 1. Taxa in the lineage of Daubentonia and multituberculates.

Figure 5. Taxa in the lineage of Daubentonia and multituberculates. Note the loss of the angular process and the sliding jaw joint.

By convergence, Carpolestes
has an enlarged posterior lower premolar, as in multituberculates. So, lots of convergence surrounds the multituberculates.

The aye-aye is a traditional basal primate,
based on gene studies (Dene et al1980; Rurnpler et al 1988; Del Pero et al 1995; Porter et al 1995).

By contrast
the large reptile tree (LRT, 1810+ taxa; subset Fig. 4) nests the aye-aye (Daubentonia) with rodents, plesiadapiformes, carpolestids and multituberculates. We’ve seen how genomic studies produce false positives. Add Daubentonia to that list of flubs. Note that both lemurs and aye-ayes are both from Madagascar, lending more evidence to the hypothesis that geography and geology (e.g. Afrotheria, Laurasiatheria) affect genomics to a greater degree than professionally realized over deep time.

Like rodents:
The aye-aye does not have mammary glands on the chest, as in primates, but along the groin, as in non-primates. The aye-aye has a large diastema between the incisors and molars, as in plesiadapiformes and rodents, distinct from primates.

Like primates:
The aye-aye has a postorbital bar, stereoscopic vision and an opposable hallux. Owen 1863 considered such traits ‘must be ordained’ in arguments for God and against Darwin’s then novel hypothesis of natural selection and evolution.

Like rodents,
Perry et al. 2014 report: “the single pair of incisors consists of continuously growing, elongate, open-rooted chisels, both upper and lower incisors.”

Based on the LRT
mutltuberculates are netonous rodents, growing to adulthood without ontogenetically incorporating post-dentary bones into the tympanic and periotic (inner ear enclosing bones), as we learned earlier here.

Figure 6. The aye-aye, Daubentonia in vivo. This is the closest living relative of multituberculates and is itself a plesiadapiform member of Glires, close to rodents, not primates.

Figure 6. The aye-aye, Daubentonia in vivo. This is the closest living relative of multituberculates and is itself a plesiadapiform member of Glires, close to rodents, not primates.

By convergence
the aye-aye (Daubentonia. Fig. 6) likewise reduces the tympanic and periotic along with the angular process of the dentary, producing a sliding joint that would have interfered with the ear bones if allowed to develop as in most placentals.

Carter 2009 notes
(while mistakenly assuming a lemur affinity for Daubentonia), “The overall dimensions of the D. madagascariensis auditory ossicles are large and they have a unique morphology.” Carter also reports on the elongate manubrium of the malleus (the former articular). This is in accord with similar structures in the neotonous (not primitive!) multituberculate auditory bone chain you can see here.

What does the angular process of the plancental dentary do?
According to Meng et al. 2003, a huge angular process was present in Rhombomylus, an extinct gerbil. Meng et al. mapped insertions for the deep masseter and superficial masseter externally. Then they mapped insertions for the medial pterygoid and superficial masseter internally. The Rhomboylus glenoid has a small diameter and rotates. It does not slide.

Meng et al. write: “As the major muscle to move the mandible forward, the superficial masseter must be long enough so that it can work to bring the jaw forward at least the minimum working distance. In general, the action line of the anterior deep masseter is nearly perpendicular to the moment arm of the mandible, while the posterior one has an acute angle to the moment arm and, therefore, less mechanical advantage. the deep masseter must have been sizable and supplies the main force for mastication as in rodents.”

The point of which is: multituberculates and the aye-aye reduce and eliminate the angular process. So we can imagine the muscles listed by Meng et al. either migrate or are lost in multituberculates and the aye-aye.

Figure 1. Maiopatagium in situ in white and UV light. The X marks an area surrounded by fur lacking proptagial data. Is the propatagium wishful thinking?

Figure 7. Maiopatagium in situ in white and UV light. The X marks an area surrounded by fur lacking proptagial data. Is the propatagium wishful thinking? Yes. Those are long guard hairs, precursors to porcupine quills. There is no patagium here.

We can’t leave Jurassic flying squirrels
without a quick review of Maiopatagium (Early Jurassic, Fig. 7, Meng et al. 2017), which was hailed ever since as a gliding mammal or mammaliaform.

Contra Meng et al. 2017
phylogenetic analysis nested Maiopatagium with the extant porcupine (Coendou), not with gliding multituberculates, like Vilevolodon. Maiopatagium has long straight hairs and lacks any trace of a patagium. Those long straight hairs are the precursors to porcupine quills according to the LRT.

Phyogenetic analysis puts rodents and all their precursors
(Tupaia, Henkelotherium, Nasua) squarely and clearly in the earlier part of the Early Jurassic, though not yet recovered in fossils.

The myth about the patagium surrounding Maiopatagium
seems to have had its genesis in the fact that Vilevolodon was described at the same time,  by the same authors, in the same publication. Vilevolodon (Fig. 1) has a no-doubt, flying sqirrel-like patagium. Maiopatagium (Fig. 7) was described with a misidentified patagium and a misidentified bat-like calcar. No patagium is present, but long straight hairs are. As noted above, these are precursors to porcupine quills. Getting taxa into a proper phylogenetic context is the key to understanding soft tissue and taxonomy.


References
Carter Y 2009. Monkey Hear: A morphometric analysis of the primate auditory ossicles. Master of Arts thesis, The U of Manitoba.
Del Pero M et al (4 co-authors) 1995. Phylogenetic relationships among Malagasy lemuls as revealed by mitochrondrial DNA sequence analysis. Primates 36: 43I-440.
Dene H, Goodman M and Prychodlco V 1980. Immunodiffusion systematics of the primates. Mamalia 44:27-31.
Luo Z-X, (6-co-authors) 2017. New evidence for mammaliaform ear evolution and feeding adaptation in a Jurassic ecosystem. Nature. in press (7667): 326–329. doi:10.1038/nature23483
Meng et al. 2003. The osteology of Rhombomylus (Mammalia, Glires): Implications for phylogeny and evolution of Glires. Bulletin of the American Museum of Natural History 275: 1–247.
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
Owen R 1863. On the characters of the aye-aye as a test of the Lamarckian and Darwmian hypothesis of the transmutation and origin of the species. Rep Br Assoc Adv Sci 1863: 114-116.
Perry JM et al. (4 co-authors) 2014. Anatomy and adaptations of the chewing muscles in Daubentonia (Lermuriformes). The Anatomical Record 297:308–316.
Porter CA et al (5 co-authors) 1995. Evidence on primate phylogeny from e-globin gene sequences and flanking regions. Journal of Molecular Evolution 40: 30-55.
Rurnpler Y et al (4 co-authors) 1988. Chromosomal evolution of the Malagasy lemurs. Folio Primatologica 50 124-129.
Sterling EJ 1994. Taxonomy and distribution of Daubentonia madagascariensis: a historical perspective. Folio Primatologica 62: 8-I3.

wiki/Maiopatagium
wiki/Coendou
wiki/Multituberculata

https://pterosaurheresies.wordpress.com/2019/01/06/a-post-dentary-reversal-between-rodents-and-multituberculates/

Wang et al. 2021: Vilevolodon had monotreme-like ear bones

We’ve heard this before.
Links below.

From the Wang et al. 2021 abstract:
“Recent discoveries of well-preserved Mesozoic mammals have provided glimpses into the transition from the dual (masticatory and auditory) to the single auditory function for the ossicles, which is now widely accepted to have occurred at least three times in mammal evolution.”

Wang et al. are not working from a valid phylogenetic context. They are not considering the possibility, hypothesized in the large reptile tree (LRT, 1593+ taxa) of a phylogenetic reversal in which the inner ear bones, which recapitulate phylogeny during embryonic ontogeny in placentals, could have stopped developing and stopped migrating to the typical placental position posterior to the mandible.

“Here we report a skull and postcranium that we refer to the haramiyidan Vilevolodon diplomylos (dating to the Middle Jurassic epoch (160 million years ago)) and that shows excellent preservation of the malleus, incus and ectotympanic (which supports the tympanic membrane).

See figure 1. We covered this issue earlier here, here and here.

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 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.

From the Wang et al. abstract (continued)
“After comparing this fossil with other Mesozoic and extant mammals, we propose that the overlapping incudomallear articulation found in this and other Mesozoic fossils, in extant monotremes and in early ontogeny in extant marsupials and placentals is a morphology that evolved in several groups of mammals in the transition from the dual to the single function for the ossicles.”

Unfortunately
Wang et al. are pinning all their phylogenetic hopes on the inner ear bones. Therefore they are  “Pulling a Larry Martin.” Don’t do that. When placed into a phylogenetic analysis that considers traits from the entire skeleton and a wide gamut of mammals and pre-mammals, Vilevolodon nests within the placental clade Glires (the gnawers = rodents, rabbits, shrews, aye-ayes, multituberculates, etc.) We’ve known this for several years.

Wang et al. 2021 provide four prior analyses
in their SuppData, (references below) all of which employ suprageneric taxa, none of which test pertinent members of Glires.

In summary:
When tested against more taxa Vilevolodon is recovered as a derived member of Glires (rodents, rabbits, shrews, etc.) sharing with other multituberculates a neotonous retention of the embryonic condition, prior to the migration of the inner ear bones to the base of the skull, posterior to the mandibles. Evidently in their typical adult placental position typical ear bones interfered with the long slide of the mandible during gnawing and mastication, so retained the embryonic condition. The authors noted this ‘transition” in placentals in their abstract, but did not consider the possibility of a reversal or neotony.


References
Han G, Mao F, Bi S., Wang Y and Meng JA2017. Jurassic gliding euharamiyidan mammal with an ear of five auditory bones. Nature 551, 451–456.
Luo Z.-X. et al. 2017. New evidence for mammaliaform ear evolution and feeding adaptation in a Jurassic ecosystem. Nature 548, 326–329.
Wang H, Meng J and Wang Y 2019. Cretaceous fossil reveals a new pattern in mammalian middle ear evolution. Nature 576, 102–105.
Wang J, Wible JR, Guo B. et al. 2021. A monotreme-like auditory apparatus in a Middle Jurassic haramiyidan. Nature. https://doi.org/10.1038/s41586-020-03137-z

The multituberculate, Barbatodon, enters the LRT with iron in its incisors

Yes, the element iron
is incorporated into the teeth of the multituberculate, Barpatodon (Fig. 1, Rãdulescu and Samson 1986; Smith and Codrea 2015), and other members of the gnawing clade, Glires to make them even stronger than ordinary enamel. That’s what gives those teeth that rusty appearance.

Figure 1. Barpatodon diagram from Smith and Codrea 2015 colorized here.

Figure 1. Barpatodon diagram from Smith and Codrea 2015 colorized here.

Barbatodon transylvanicus (Rãdulescu and Samson 1986; Late Cretaceous) is a small multituberculate preserving iron in its incisors as in several living rodents. Originally considered close to Taeniolabis, here it nests with Catopsbaatar. The premolars have been molarized. The ‘sliding jaw joint’ does not slide much.

Figure 4. Catopsbaatar greatly enlarged.

Figure 2. Catopsbaatar greatly enlarged.


References
Rãdulescu R and Samson P 1986. Précisions sur les affinités des Multituberculés du Crétacé supérieur de Roumaine. C R Acad Sci II: Mec-Phys, Chim, Sci Terre, Sci Univ 303p, p. 1825-1830.
Smith T and Codrea V 2015. Red Iron-Pigmented Tooth Enamel in a Multituberculate Mammal from the Late Cretaceous Transylvanian “Hateg Island”. PLoS ONE 10(7): e0132550. https://doi.org/10.1371/journal.pone.0132550

wiki/Barbatodon

The tiny multituberculate, Filikomys, enters the LRT

Figure 1. Ptilodus, Filikomys and Catopsbaatar to scale (at 72 dpi screen resolution).

Figure 1. Ptilodus, Filikomys and Catopsbaatar to scale (at 72 dpi screen resolution).

Filikomys primaevus 
(Weaver et al. 2020; NMC 1890; Late Cretaceous; Figs. 1, 2) is a cimolodont multituberculate found with others of its kind in a multi-season burrow/nest. Filikomys was originally nested close to Ptilodus (Figs. 1, 3), but here is more closely related to the even smaller Catopsbaatar (Fig. 1).

From the Weaver et al. abstract:
“Taphonomic and geologic evidence indicates that F. primaevus engaged in multigenerational, group-nesting and burrowing behaviour, representing the first example of social behaviour in a Mesozoic mammal. That F. primaevus was a digger is further supported by functional morphological and morphometric analyses of its postcranium.”

Figure 1. Filikomys from Weaver et al. 2020 and colorized here.

Figure 1. Filikomys from Weaver et al. 2020 and colorized here.

The Weaver et al. abstract continues:
“The social behaviour of F. primaevus suggests that the capacity for mammals to form social groups extends back to the Mesozoic and is not restricted to therians.”

By contrast, in the large reptile tree (LRT, 1754+ taxa) Filikomys is a multituberculate and they nest within the clade Glires, not far from the aye-aye (Daubentonia), rat (Rattus) and mouse (Mus), all within the clade Placentalia. Weaver’s cladogram is typical of analyses that include multituberculates where members of the clade Glires are not employed.

Figure 3. Ptilodus, an arboreal multituberculate.

Figure 3. Ptilodus, an arboreal multituberculate.

Traditional taxon exclusion problems, like this,
are minimized in the LRT, which includes a wide gamut of taxa. Colleagues, do the work you are paid to do. Don’t rest on old myths and traditions, even if they are in current textbooks and lectures.

Figure 4. Catopsbaatar greatly enlarged.

Figure 4. Catopsbaatar greatly enlarged.

The Weaver et al. paper concentrates on the subject
of sociality, first seen in basal tetrapods in the Carboniferous. Burrows go back at least to therapsids in the Permian. Filikomys was found in Late Cretaceous deposits.

Weaver et al. report,
“The material described herein includes the first associated multituberculate skeletons from the Mesozoic of North America and represents the oldest-known case of burrowing capabilities in a Mesozoic multituberculate.”

“Multiple lines of evidence thus indicate that F. primaevus was a terrestrial, scratch-digging mammal, functionally analogous to the Least Chipmunk, Neotamias minims.”

 

The above episode of “Old News”
(love that name!) features Christian Kammerer talking about multituberculates with a focus on tiny Filikomys. Click to play.


References
Weaver LN et al. 2020. Early mammalian social behaviour revealed by
multituberculates from a dinosaur nesting site. Nature ecology & evolution. https://doi.org/10.1038/s41559-020-01325-8

wiki/Kryptobaatar
wiki/Ptilodus
wiki/Catopsbaatar
wki/Filikomys
wiki/Ptilodontoidea

Célik and Phillips 2020 reshuffle basal mammal phylogeny by excluding traits (and taxa)

Célik and Phillips 2020 attempted to
understand the phylogenetic order of basal mammals by excluding traits. They wrote, “Excluding these character complexes brought agreement between anatomical regions and improved the confidence in tree topology.”

Those issues aside, taxon exclusion mars this study. 
The Célik and Phillips cladogram shuffled together unrelated taxa compared to the large reptile tree (LRT, 1737+ taxa). They cladogram (Fig. 1) mixed pre-mammals with placentals and marsupials chiefly due to taxon exclusion.

By employing so many taxa,
the LRT minimizes taxon exclusion and resolves such issues as the Multituberculata / Haramiyida problem. These taxa nest within Glires in the Placentalia in the LRT. Glires is not otherwise well represented in the Célik and Phillips cladogram.

Figure 1. Cladogram from Célik and Phillips 2020 with color overlay showing distribution of taxa in the LRT.

Figure 1. Cladogram from Célik and Phillips 2020 with color overlay showing distribution of taxa in the LRT.

From the abstract
“The evolutionary history of Mesozoic mammaliaformes is well studied. Although the backbone of their phylogeny is well resolved, the placement of ecologically specialized groups has remained uncertain. Functional and developmental covariation has long been identified as an important source of phylogenetic error, yet combining incongruent morphological characters altogether is currently a common practice when reconstructing phylogenetic relationships.”

“Ignoring incongruence may inflate the confidence in reconstructing relationships, particularly for the placement of highly derived and ecologically specialized taxa, such as among australosphenidans (particularly, crown monotremes), haramiyidans, and multituberculates. The alternative placement of these highly derived clades can alter the taxonomic constituency and temporal origin of the mammalian crown group.”

“Based on prior hypotheses and correlated homoplasy analyses, we identified cheek teeth and shoulder girdle character complexes as having a high potential to introduce phylogenetic error.

“We showed that incongruence among mandibulodental, cranial, and postcranial anatomical partitions for the placement of the australosphenidans, haramiyids, and multituberculates could largely be explained by apparently non-phylogenetic covariance from cheek teeth and shoulder girdle characters.”

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

Figure 3. Subset of the LRT focusing on basal placentals, including multituberculates.

Figure 3. Comparing multituberculate origins: Cziki-Sava et al. vs. LRT.

Figure 4. Comparing multituberculate origins: Cziki-Sava et al. vs. LRT.

Based on results recovered in the LRT,
I encourage Célik and Phillips to rerun their analysis with a far larger taxon list. A gradual accumulation of derived traits that mirrors evolutionary events will appear whenever taxon exclusion is minimized.


References
Célik MA and Phillips MJ 2020. Conflict Resolution for Mesozoic Mammals: Reconciling Phylogenetic Incongruence Among Anatomical Regions. Frontiers in Genetics 11: 0651
doi: 10.3389/fgene.2020.00651
https://www.frontiersin.org/articles/10.3389/fgene.2020.00651/full

Mao et al. 2020 “Pull a Larry Martin” with the multituberculate, Sinobaatar

Mao et al. 2020 report on a
crushed and articulated Early Cretaceous multituberculate specimen of Sinobaatar (Fig. 1). Presently several species are known. This one was µCT scanned.

From the abstract
“We report a new Cretaceous multituberculate mammal with 3D auditory bones preserved. Along with other fossil and extant mammals, the unequivocal auditory bones display features potentially representing ancestral phenotypes of the mammalian middle ear.”

The authors made several basic mistakes with Sinobaatar.

  1. By concentrating on one set of traits (the middle ear), rather than the entire skeleton, the authors ‘Pulled a Larry Mrartin“.
  2. By not including derived members of Glires (gnawing placentals) in their phylogenetic analysis, their cladogram (Fig. 2) suffers from taxon exclusion and inappropriate taxon inclusion (e.g. Liaoconodon and Origolestes are mammal-mimics living in the Early Cretaceous alongside real mammals).
  3. The authors did not consider the possibility of convergence brought about by a reversal. When members of Glires are added to analysis (Fig. 3), the reversal becomes obvious (Fig. 4).

The takeaway:
Not matter what the configuration of the middle ear in Sinobaatar, if the rest of the skeleton nests it in Glires, maximum parsimony says: Sinobaatar and all multituberculates nest in Glires.

Figure 1. Sinobaatar skull in two views. DGS colors added.

Figure 1. Sinobaatar skull in two views. DGS colors added. The skull was crushed from side to side.

The authors report in the SuppData:
“Given several recent efforts of higher-level phylogenies of mammaliaforms [1-3] and the relatively stable position of multituberculates (Sinobaatar in particular) within mammals in all these studies, we consider it redundant to run another phylogenetic analysis.”

Redundant, yes, if using the same taxon list. But adding members of Glires to that taxon list changes everything.

Figure 2. Cladogram from Mao et al. 2020 with the wrong phylogenetic order, repaired on frame 2.

Figure 2. Cladogram from Mao et al. 2020 with the wrong phylogenetic order, repaired on frame 2 in which Origolestes and Liaoconodon are late-surviving mammal mimics, not mammals.

The wide gamut of the taxon list
in the large reptile tree (LRT, 1729+ taxa; subset Fig. 3) minimizes taxon exclusion. When taxa that have never been tested together before get tested together, sometimes they nest together. You just have to let the software do what it does best and keep shoveling in more taxa.

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

Figure 3. Subset of the LRT focusing on basal placentals, including multituberculates.

The authors report,
“While the auditory bones already detached from the dentary in the three phenotypes, the transitional middle ear of Liaoconodon is most primitive in that the malleus and ectotympanic have long anterior processes that are still in contact with the ossified Meckel’s cartilage; thus, hearing and chewing functions were not completely separated. Origolestes is more derived in having lost the bony contact of the auditory bones to the ossified Meckel’s cartilage so that hearing and chewing functions were decoupled.” 

Without a valid cladogram the authors assume the order of evolution without really knowing. In the LRT Origolestes is not a mammal and the more primitive of the two, hinting at an earlier stage in a reversal. The LRT lumps and separates taxa to reveal such reversals.

Figure 3. Comparing multituberculate origins: Cziki-Sava et al. vs. LRT.

Figure 4. Comparing multituberculate origins: Cziki-Sava et al. vs. LRT.

The authors report, 
“With the assumption that the DMME evolved independently in monotremes, therians, and multituberculates, there should be no common ancestral phenotype of the middle ear for these clades.”

That is incorrect. The LRT nests multituberculates within the gnawing clade, Glires (Fig. 3). The LRT indicates the primitive nature of the middle ear of multituberculates is a reversal likely caused by the great propalinal movement of the gnawing jaw interfering with and preventing normal maturation of the placental middle ear and leaving it at a more primitive state. You can have more confidence in this hypothesis because more taxa are tested, ‘leaving no stone unturned.’

Every description you’ll ever see
of multituberculates, plesiadapiformes, carpolestids and the aye-aye, Daubentonia, includes the phrase, “rodent-like” for a very good reason. That’s because they are closely related, something Mao et al. 2020 and other multituberculate experts do not yet realize. Adding taxa always resolves problems. Just do it. Don’t “Pull a Larry Martin.”


References
Mao F-G, Liu C, Chase MH, Smith AK, Meng J 2020.
 Exploring ancestral phenotypes and evolutionary development of the mammalian middle ear based on Early Cretaceous Jehol mammals. Research Article Earth Sciences. National Science Review, nwaa188, https://doi.org/10.1093/nsr/nwaa188

wiki/Multituberculata
wiki/Sinobaatar

Two papers in one: Haramiyidans and Juramaia

Part 1: King and Beck 2020
bring us their views (again), on ‘early mammal relationships‘. Let’s see how they stack up (again) against the validated (thanks to taxon inclusion) results of the large reptile tree (LRT, 1697+ taxa).

From their abstract:
“Many phylogenetic analyses have placed haramiyidans in a clade with multituberculates within crown Mammalia, thus extending the minimum divergence date for the crown group deep into the Triassic. Here, we apply Bayesian tip-dated phylogenetic methods [definition below] to investigate these issues. Tip dating firmly rejects a monophyletic Allotheria (multituberculates and haramiyidans), which are split into three separate clades, a result not found in any previous analysis. Most notably, the Late Triassic Haramiyavia and Thomasia are separate from the Middle Jurassic euharamiyidans.”

Bayesian tip-dated phylogenetic methods = online definition here.

You heard it here first
Earlier (2016) the LRT rejected a monophyletic Allotheria (separating Haramiavia (Fig. 1) and Thomasia), from Megaconus and all the multituberculates (Fig. 2). Haramiavia and Thomasia nest as pre-mammal synapsids (tritylodontids), not far from Pachygenelus. Several dozen nodes away, Megaconus and the multis nest within the placental clade Glires, at a node more highly derived than tree shrews, rodents and rabbits. So far that hypothesis of relationships has not been tested by other workers, despite several invitations to expand their taxon lists.

Figure 4. Haramiyava dentary showing what a more typical stem mammal dentary and teeth look like. Earlier studies linked this clade to multituberculates, but this dentary was cause to reject that association.

Figure 1. Haramiyava dentary showing what a more typical stem mammal dentary and teeth look like. Earlier studies linked this clade to multituberculates, but this dentary was cause to reject that association.

According to King and Beck 2020,
“Our analysis places Haramiyavia and Thomasia in a clade with tritylodontids, a result that may be the result of insufficient sampling of non-mammaliaform cynodont characters and taxa, and which we consider in need of further testing (see detailed discussion in the electronic supplementary material).” This confirms relationships first recovered by the LRT.

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

Figure 2. LRT taxa in the lineage of multituberculates arising from Carpolestes and Paulchoffatia.

The authors continue,
“Our focal dataset was taken from Huttenlocker et al. 2018, which comprises 538 morphological characters scored for 125 mammaliaforms and non-mammaliaform cynodonts.

Unfortunately,
as I mentioned earlier, King and Beck still need to include extant mammals, like montoremes, marsupials, rodents and Daubentonia, rather than rely on fossil taxa exclusively. (See below).

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

Figure 3. Subset of the LRT focusing on Glires and subclades within.

Part 2: King and Beck 2020 report:
“A second taxon of interest is the eutherian Juramaia (Fig. 4) from the Middle–Late Jurassic Yanliao Biota, which is morphologically very similar to eutherians from the Early Cretaceous Jehol Biota and implies a very early origin for therian mammals. We also test whether the Middle– Late Jurassic age of Juramaia is ‘expected’ given its known morphology by assigning an age prior without hard bounds. Strikingly, this analysis supports an Early Cretaceous age for Juramaia, but similar analyses on 12 other mammaliaforms from the Yanliao Biota return the correct, Jurassic age.”

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

Figure 4. Juramaia (Late Jurassic, 160 mya) is more completely known and nests between monotremes and therians (marsupials + placentals).

By contrast In the LRT,
Juramaia is a basal protorothere, nesting between Megazostrodon + Sinodelphys and Chaoyangodens, all basal to the extant platypus and echidna in the LRT. Beck and King omit so many key taxa that they do not recover Prototheria, Metatheria and Eutheria.

The same authors publishing on a similar topic in 2019
were reviewed here. The following is one paragraph from that review: King and Beck 2019 bring us a new phylogenetic analysis restricted to Mesozoic mammals. This represents a massive case of taxon exclusion of basal mammals as demonstrated earlier here, because so many basal mammals are still alive! Think of all the tree shrews, arboreal didelphids, and nearly every little creeping taxon in Glires that nest basal to known Mesozoic mammals. You cannot restrict the taxon list to just those extremely rare Mesozoic mammals.

Colleagues: Please use extant mammals in your analyses!
They are guaranteed complete and articulated with soft tissues and gut contents. Figure out your cladogram with as many of these complete specimens as possible. Then… start adding crushed, incomplete and disarticulated fossil taxa. In other words, give yourself a basic education first. Establish a valid tree topology first. Don’t muddle through your studies with questionable traits based on fractured mandibles missing several teeth. As longtime readers know, a valid phylogenetic context is paramount for all further studies.


References
Huttenlocker AK, Grossnickle DM, Kirkland JI, Schultz JA and Luo Z-X 2018. Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana. Nature 558, 108–112. 8. (doi:10.1038/s41586-018-0126-y);
King B and Beck R 2019. Bayesian Tip-dated Phylogenetics: Topological Effects, Stratigraphic Fit and the Early Evolution of Mammals. PeerJ
doi: http://dx.doi.org/10.1101/533885.
King B and Beck RMD 2020.
Tip dating supports novel resolutions of controversial relationships among early mammals. Proceedings of the Royal Society B 287: 20200943. http://dx.doi.org/10.1098/rspb.2020.0943

https://pterosaurheresies.wordpress.com/2019/02/07/taxon-exclusion-mars-mesozoic-mammal-study/

Adalatherium: this ‘crazy beast’ suffers from taxon exclusion… and hyperbole

Figure x. Adalatherium diagram, added later.

Figure x. Adalatherium diagram, added later.

Figure 1. Adalatherium mount.

Figure 1. Adalatherium mount. Compare to Paedotherium in figure 2. Both have large, rodent-like incisors, lack an thumb and share a high presacral count, among many hundred other synapomorphies. Note: the prepubes here are epipubes in the paper.

Krause et al. bring us a complete and articulated skeleton
from the latest Cretaceous of Madagascar they call Adalatherium hui (=”crazy beast”, Fig. 1). Added to the large reptile tree (LRT, 1678+ taxa; subset Fig. 3), Adalatherium nests with Miocene Paedotherium (Fig. 2), a metatherian taxon known since 1888 with homologous large rodent-like incisors and retained coracoids. Regrettably this taxon was omitted from the Krause et al. cladogram (Fig. 4).

Figure 2. Miocene Paedotherium was excluded by Krause et al. It nests with Late Cretaceous Adalatherium in the LRT.

Figure 2. Miocene Paedotherium was excluded by Krause et al. It nests with Late Cretaceous Adalatherium in the LRT.

Paedotherium typicum (Burmeister 1888, Cerdeño E and Bond M 1998; Miocene-Pleistocene) was originally considered a rabbit-like typothere notoungulate, but here nests between Dasyuroides and Phalanger among the marsupials. The Cretaceous taxa, Vintana and Groeberia are more closey related, hinting at the probable Jurassic origin of Paedotherium.

Figure 7. Subset of the LRT focusing on Metatheria (marsupials) including Paedotherium and Adalatherium.

Figure 3. Subset of the LRT focusing on Metatheria (marsupials) including Paedotherium and Adalatherium. Red taxa are known from too few traits to enter the LRT, but tests show they nest as shown.

By contrast with the LRT, 
Krause et al. considered their discovery a member of the ‘Gondwanatheria’ and therefore a basal mammal between Prototheria (duckbills and echidnas) and Metatheria (marsupials) (Fig. 4), still close to Vintana, the closest included taxon known from more than teeth.

Figure 5. Cladogram from Krause et al. 2020 nests Adalatherium with several paedotheres, but omits Paedotherium.

Figure 4. Cladogram from Krause et al. 2020 nests Adalatherium with several paedotheres, but omits Paedotherium.

From the abstract:
“To our knowledge, the specimen is the most complete skeleton of a Gondwanan Mesozoic mammaliaform that has been found, and includes the only postcranial material and ascending ramus of the dentary known for any gondwanatherian. A phylogenetic analysis including the new taxon recovers Gondwanatheria as the sister group to Multituberculata.”

This is a red flag. In the LRT multituberculates are members of the clade Glires a placental clade that includes tree shrews and rodents. Krause et al. omitted the closest taxa in the LRT to the multituberculates.

Figure 2. From Krause et al. 2020, Adalatherium in situ sans matrix.

Figure 5 From Krause et al. 2020, Adalatherium in situ sans matrix.

Large rodent-like incisors, coupled with procoracoids, coupled with epipubes,
narrowed the taxonomic focus for the Krause team, but narrowed it a little too far. Overlooked Paedotherium (Fig. 2) shares those traits and hundreds more. The LRT minimizes exactly this type of taxon exclusion by including such a wide gamut of taxa that keeps getting wider and deeper with every new taxon. The similarities are obvious.

Figure 4. Adalatherium skull in 3 views from Krause et al. 2020.

Figure 6. Adalatherium skull in 3 views from CT µscans in Krause et al. 2020.  Compare to Paedotherium in figure 2.

From the abstract:
“The skeleton, which represents one of the largest of the Gondwanan Mesozoic mammaliaforms, is particularly notable for exhibiting many unique features in combination with features that are convergent on those of therian mammals. This uniqueness is consistent with a lineage history for A. hui of isolation on Madagascar for more than 20 million years.”

Not ‘unique’ and not ‘convergent’ with those of therian mammals—Adalatherium IS a therian mammal… with a procoracoid and epipubes.

Don’t rely on a short list of traits.
That would be like ‘Pulling a Larry Martin.” Don’t rely on dental traits. Don’t rely on genes. Just expand your taxon list and let the software decide where to nest new taxa. Omitting pertinent taxa is a common issue in paleontology. Not sure what drives it other than headlines in this case.

After all the work involved in discovering
and recovering Adalatherium, expanding the taxon list would have been the easiest thing to do… and, as usual, the most important. Simply omitting taxa too often produces erroneous conclusions, turning a wonderful discovery, kept under wraps and studied for twenty years in prestigious institutions into an embarrassing error published in Nature and widely publicized around the world (links below).

Earlier we talked about the origin of major mammal clades
in the Jurassic and Cretaceous (Fig. 7). Adalatherium is just one of many already known and many to come.

Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Figure 7. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Is Adalatherium the oldest mammal found in the Southern Hemisphere?
No. Brasilitherium and Brasilodon (Fig. 7) both from Brazil, are known from the Norian (Late Triassic) more than twice as old as Adalatherium. We also have seven placentals (Fig. 7) from the Late Jurassic of China and older marsupials from China and England.

According to Science Alert (link below):
“Exactly what factors induced the craziness of the crazy beast isn’t fully clear, but a 20-year-long analysis of the remains (the fossil was first discovered in 1999) indicates it is indeed a strange creature. Knowing what we know about the skeletal anatomy of all living and extinct mammals, it is difficult to imagine that a mammal like Adalatherium could have evolved,” says vertebrate palaeontologist David Krause from the Denver Museum of Nature & Science, who helped find the skeleton during a field expedition in Madagascar in 1999. “It bends and even breaks a lot of rules.”

“Strange… crazy… difficult to imagine…”
this is all hyperbole. When Paedotherium is added to the taxon list, none of this is strange… and there goes the headline… and the generic name…

Continuing from Science Alert
“Part of the weirdness is the primitive septomaxilla bone in its snout region – a feature that disappeared 100 million years earlier in the ancestors of living modern mammals.” 

“It also had more openings (called foramina) in its cranium than any known mammal, the researchers say, which may have enhanced the sensitivity of its snout and whiskers, by enabling passage for nerves and blood vessels through the skull.”

“The animal had strangely bowed leg bones, too, and researchers aren’t sure whether it used its limbs for digging, or running, or even other kinds of locomotion. Then there are the teeth. The strangeness of the animal is clearly apparent in the teeth – they are backwards compared to all other mammals, and must have evolved afresh from a remote ancestor,” Evans explains.

Backwards? Does that mean more primitive?
Let’s assume the latter. On that point, the teeth of Paedotherium are similar.

Bottom line:
Adalatherium is just a minor variation on a traditionally overlooked taxon known for over 100 years. Chronologically it’s not that old. Phylogenetically it’s not that crazy, strange or bizarre. Omitting taxa remains THE MOST COMMON error in academic papers. Let’s fix that.


References
Krause DW et al. (12 co-authors) 2020. Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity. Nature (advance online publication DOI: https://doi.org/10.1038/s41586-020-2234-8
https://www.nature.com/articles/s41586-020-2234-8

wiki/Adalatherium

News:

https://www.macalester.edu/news/2020/04/geology-professors-rare-fossil-discovery-in-madagascar-featured-in-scientific-journal-nature

https://phys.org/news/2020-04-marooned-mesozoic-madagascar-million-year-old-crazy.html

https://www.washingtonpost.com/science/2020/04/29/mammal-skeleton-adalatherium-hui/

https://www.nytimes.com/reuters/2020/04/29/world/africa/29reuters-science-crazybeast.html

https://www.livescience.com/ancient-bizarre-mammal-madagascar.html

https://www.sciencealert.com/crazy-beast-of-gondwana-may-be-oldest-mammal-skeleton-found-in-southern-hemisphere

Early Cretaceous Jeholbaatar kielanae: middle ear origin or reversal?

FIgure 1. Tiny Jeholbaatar in situ, full scale.

FIgure 1. Tiny Jeholbaatar in situ, full scale.

Wang, Meng  and Wang 2019 introduce us 
to a tiny new multituberculate, Jeholbaatar kielanae (Figs. 1, 2), in which the much tinier and displaced middle ear bones are found in articulation (Figs. 3, 4) along with a displaced surangular!

Figure 2. Jeholbaatar with certain bones colorized using DGS methods.

Figure 2. Jeholbaatar with certain bones colorized using DGS methods.

Figure 5. Jeholobaatar images from Wang, Meng and Weng 2019. Rat ear bones photo from Li, Gao, Ding and Salvi 2015. Correction label added here. The rat middle ear, no surprise, is phylogenetically similar to that of the multituberculates, Jeholbaatar and Arboroharamiya.

Figure 3. Jeholobaatar images from Wang, Meng and Weng 2019. Rat ear bones photo from Li, Gao, Ding and Salvi 2015. Correction label added here. The rat middle ear, no surprise, is phylogenetically similar to that of the multituberculates, Jeholbaatar and Arboroharamiya.

Figure 4. The tiny displaced middle ear bones of Jeholbaatar colorized

Figure 4. The tiny displaced middle ear bones of Jeholbaatar colorized

Wang, Meng and Wang present two cladograms
(Fig. 3) of multituberculate relationships. The LRT agrees with the ‘a’ oversimplified cladogram, the one that does not split Arboroharamiya from Jeholobaatar. 

In similar fashion,
the large reptile tree (LRT, 1612+ taxa) nests multituberculates as derived rodents, despite what appears to be, in this phylogenetic context, a more primitive middle ear morphology than found in extant rats (Rattus, Fig. 4), mice (Mus) and their closest living relatives, the aye-aye (Daubentonia). In the LRT Jeholbaatar nests at the base of the Villevolodon + Shenshou clade.

Tradition continues in Wang, Meng and Wang
as they omit rodents from multituberculate studies while force fitting multis into a dissimilar nesting with basal mammals, including prototheres, the egg-laying mammals.

It is worthwhile comparing the skulls
of the rodent, Rattus (Fig. 6), and the multituberculate, Kryptobaatar (Fig. 5). This is much more than convergence. That is why they nest close to one another in the LRT, but not as sisters.

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 5. 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. In multis the middle ear bones remain attached to the posterior dentary and ride along with jaws as they slide distinct from most placental taxa. Note the lack of a middle ear (tympanic) bulla. Compare to figure 1.

Figure . Skull of Rattus, the rat. Note the similarities to Megaconus. Not identical but similar.

Figure 6 The brown rat (Rattus norvegicus) skull has a mandible glenoid separate from the retroarticular process. Whenever the jaw slides back and forth, these two processes slide above and below the middle ear (tympanic) bulla without interfering with the ear canal. Compare to figure 2.

From the Wang, Meng and Wang 2019 abstract:
“The evolution of the mammalian middle ear is thought to provide an example of ‘recapitulation’—the theory that the present embryological development of a species reflects its evolutionary history.”

This has been documented in embryo dissections.

“Accumulating data from both developmental biology and palaeontology have suggested that the transformation of post-dentary jaw elements into cranial ear bones occurred several times in mammals.”

In the LRT this happened once in crown mammals, and once again in Repenomamus, a pre-mammal, Cretaceous mammal-mimic

“In addition, well-preserved fossils have revealed transitional stages in the evolution of the mammalian middle ear. But questions remain concerning middle-ear evolution, such as how and why the post-dentary unit became completely detached from the dentary bone in different clades of mammaliaforms.”

The LRT does not recognize the clade Mammaliaformes, defined as, “the clade originating from the most recent common ancestor of Morganucodonta and the crown group mammals.” Morganucodon is a basal metatherian in the LRT.

“Here we report a definitive mammalian middle ear preserved in an eobaatarid multituberculate mammal, with complete post-dentary elements that are well-preserved and detached from the dentary bones. The specimen reveals the transformation of the surangular jaw bone from an independent element into part of the malleus of the middle ear, and the presence of a restricted contact between the columelliform stapes and the flat incus.”

Congratulations to the preparator. The middle ear bones are microscopic.

“We propose that the malleus–incus joint is dichotomic [= classification based upon two opposites] in mammaliaforms, with the two bones connecting in either an abutting or an interlocking arrangement, reflecting the evolutionary divergence of the dentary–squamosal joint. In our phylogenetic analysis, acquisition of the definitive mammalian middle ear in allotherians such as this specimen was independent of that in monotremes and therians.”

The LRT does not recover the clade Allotheria. Rather multituberculates nest within Glires, within Rodentia close to Rattus (Fig. 4), Carpolestes and the aye-aye, Daubentonia.

“Our findings suggest that the co-evolution of the primary and secondary jaw joints in allotherians was an evolutionary adaptation allowing feeding with unique palinal (longitudinal and backwards) chewing. Thus, the evolution of the allotherian auditory apparatus was probably triggered by the functional requirements of the feeding apparatus.”

Unfortunately,
the authors do not compare their find to rodents. Note the similarity of the middle ear bones in Rattus (Fig. 3) to those of multituberculates. So, once again: taxon exclusion spoils a perfectly grand discovery and description.

Figure 4. Evolution of the tetrapod mandible and ear bones leading to humans.

Figure 7. Evolution of the tetrapod mandible and ear bones leading to humans.

A little backstory:
As mentioned by Wang, Meng and Wang, a mammal embryo develops ontogenetically it more or less recapitulates its entire phylogenetic development, from one cell, to a ball of cells, to an embryo with gills, to an embryo with several primordial jaw bones. Three of these detach from the dentary in placentals, migrate posteriorly and become middle ear bones.

Multis are different.
Multis appear to have large, attached, more primitive middle ear bones, like those found in egg-laying pre-mammals. The question few appear to have asked is: why would this happen?

Multis are renown
for losing (or never developing in the tradition model) their cylinder and socket jaw joint to develop a sliding jaw joint, harnessed by large muscles. A sliding jaw joint is also present in rodents.

Here’s a thought:
Perhaps nature found it more important for the jaw joint to slide posteriorly in multis, over the spot where tiny ear bones are found in rodents, so the middle ear bones remained in a state of arrested development, more or less attached to the posterior dentary, moving along with the sliding jaw, never attaching themselves to the base of the braincase, as in other placental mammals. This can happen by a simple matter of stopping the development of primitive large ear bones to tiny ear bones. Evidently this reversal was a successful gambit, as multis survived from the Jurassic deep into the Tertiary before finally going extinct for reasons unknown.

For the general public (popular press),
the following online article describes the specimen and its authors.

“Researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences and the American Museum of Natural History (AMNH) have reported a new species of multituberculate – a type of extinct Mesozoic “rodent” – with well-preserved middle ear bones from the Cretaceous Jehol Biota of China. The findings were published in Nature on November 27.”

Note the use of quotation marks around the word “rodent” indicate their understanding that Jeholbaatar was not a rodent, but looked like one.

“The new mammal, Jeholbaatar kielanae, has a middle ear that is distinct from those of its relatives. WANG Yuanqing and WANG Haibing from IVPP, along with MENG Jin from AMNH, proposed that the evolution of its auditory apparatus might have been driven by specialization for feeding.”

According to the LRT, it is not the evolution of an auditory apparatus, but the reversal to to a more primitive state, because sisters all have tiny middle ear bones.

“Fossil evidence shows that postdentary bones were either embedded in the postdentary trough on the medial side of the dentary or connected to the dentary via an ossified Meckel’s cartilage in early mammals, prior to their migration into the cranium as seen in extant mammals.”

See figure 7 for an illustration of this trough and migration in several taxa.

“Detachment of the mammalian middle ear bones from the dentary occurred independently at least three times. But how and why this process took place in different clades of mammals remains unclear.”

It remains unclear in the Wang, Meng and Wang paper due to taxon exclusion, leading to an invalid tree topology. They why was likely due to the nocturnal and arboreal displacement of surviving mammals, requiring better hearing abilities, during the age of dinosaurs, which were their chief predators during the day.

“The Jeholbaatar kielanae specimen was discovered in the Jiufotang Formation in China’s Liaoning Province. It displays the first well-preserved middle-ear bones in multituberculates, providing solid evidence of the morphology and articulation of these bony elements, which are fully detached from the dentary.”

Fully detached and displaced, between the teeth.

“It reveals a unique configuration with more complete components than those previously reported in multituberculates. The new fossil reveals a transitional stage in the evolution of the surangular – a “reptilian” jawbone.”

Remember, ontogeny recapitulates phylogeny, and Jeholbaatar is a tiny specimen (Fig. 1), a precocial and phylogenetically miniaturized taxon, retaining juvenile traits, including a middle ear in an arrested state of development.

“In light of current evidence, scientists argue that the primary (malleus-incus) and secondary (squamosal-dentary) jaw joints co-evolved in allotherians, allowing a distinct palinal (anteroposterior) jaw movement while chewing.” 

In the LRT anteroposterior jaw movement was well established in more primitive taxa (Figs, 3, 4). The LRT does not recognize the traditional clade, ‘Allotheria’.

“Selective pressure to detach the middle ear bones could have been stronger in order to increase feeding efficiency, suggesting that evolution of the middle ear was probably triggered by functional constraints on the feeding apparatus in allotherians.”

Actually, just the opposite, according to the LRT.  Primitive placentals already had, for millions of generations, tiny middle ear bones. In multis alone neotony + phylogenetic miniaturization led to the arrested development of the middle ear bones, which moved along with the dentary during palinal (anteroposterior) jaw movement. I suggest workers add more taxa to their phylogenetic analyses. Test rodents and their relatives along with multituberculates and see what pops out.


References
Li P, Gao K, Ding D and Salvi R 2015. Characteristic anatomical structures of rat temporal bone. ScienceDirect Journal of Otology 10:118–124.
Wang H, Meng J and Wang Y-Q 2019. Cretaceous fossil reveals a new pattern in mammalian middle ear evolution. Nature  online

http://english.cas.cn/newsroom/research_news/life/201911/t20191127_226412.shtml

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.