Naked, horned and pocket gophers

Figure 1. Subset of the LRT focusing on the rabbit/rodent and kin clade where gophers nest with hedgehogs.

In the large reptile tree (LRT, 1258 taxa, Fig. 1) the naked mole rat (genus: Heterocephalus, Fig. 2) nests with the hedgehog clade, one node off from the mouse/rat/clade. So the naked mole rat should be the  naked mole gopher.

Figure 2. The naked mole rat, Heterocephalus is closer to hedgehogs than to rats.

Heterocephalus glaber (Rüppell 1842-5; 8-10cm) is the extant naked mole rat. It has a cold-blooded metabolism, lives underground, and can move backwards as fast as forward. Not the claws, but the teeth (protruding outside the lips) are used for digging. Heterocephalus is essentially hairless, lives in a colony dominated by a queen and may live up to 32 years in a low oxygen environment, or several times longer than related taxa.

Figure 2. Naked mole rat (Heterocephalus) skull in several view. The mandibles are disarticulated here, but the glenoid appears to be reduced to absent, providing great mobility to the jaws.

Ceratogaulus hatcheri is the extinct horned gopher (Fig. 3). It nests with the naked mole rat in the LRT (Fig. 1).

Figure 3. Ceratogaulus, the extinct horned gopher

Thomomys bottae (Figs. 4, 5) is the extant pocket gopher, another rodent nesting with hedgehogs.

Figure 4. Skull of Thomomys, the extant pocket gopher. No large retroarticular process here.

These taxa look like rodents
but they nest with hedgehogs. So do we expand our concept of rodents (lumping)? Or make new clades (splitting)?

Figure 5. Skeleton of Thomomys, the pocket gopher.

 

Rodentia is characterized by a single pair of continuously growing incisors in each of the jaws, as opposed to rabbits, which have two incisors.

Glires (Latin glīrēs, dormice) is a clade consisting of rodents and lagomorphs (rabbits, hares, and pikas). In the LRT many more clades of small mammals nest with rabbits and rodents.

Euarchontoglires (synonymous with Supraprimates) is a clade of mammals, the living members of which belong to one of the five following groups: rodents, lagomorphs, treeshrews, colugos and primates. In the LRT rodents nest with primates, but not colugos.

References
Rüppell E 1842-5. Säugethiere aus der Ordnung der Nager, beobachtet im nordöstlichen Africa. Museum Senckenbergianum: Abhandlungen aus dem Gebiete der beschreibenden Naturgeschichte. 3: 99–101.

wiki/Hedgehogs
wiki/Erinaceus
wiki/Echinops
wiki/Naked_mole-rat

https://blogs.scientificamerican.com/tetrapod-zoology/african-mole-rats-so-much-more-than-just-the-naked-mole-rat/

Molecules vs morphology in mammals: Beck and Baillie 2018

Some published thoughts
on traits vs. molecules just out in the last week.

Beck and Baillie 2018 titled their paper: 
“Improvements in the fossil record may largely resolve the conflict between morphological and molecular estimates of mammal phylogeny.” No. Just the opposite. But you can see exactly where they put their faith… not in what they can see and measure.

From the abstract (annotated):
“Morphological phylogenies of mammals continue to show major conflicts with the robust molecular consensus view of their relationships.” True.

“This raises doubts as to whether current morphological character sets are able to accurately resolve mammal relationships, particularly for fossil taxa for which, in most cases, molecular data is unlikely to ever become available.” Just the opposite. Doubts should have been raised about molecular data, which can be influenced by local viruses. Only physical traits, i. e. the expression of activated molecules, resolves relationships, as the large reptile tree (LRT, 1255 taxa) attests. 

“We tested this under a hypothetical ‘best case scenario’ by using ancestral state reconstruction (under both maximum parsimony and maximum likelihood) to infer the morphologies of fossil ancestors for all clades present in a recent comprehensive molecular phylogeny of mammals, and then seeing what effect inclusion of these predicted ancestors had on unconstrained analyses of morphological data. We found that this resulted in topologies that are highly congruent with the molecular consensus, even when simulating the effect of incomplete fossilisation. Most strikingly, several analyses recovered monophyly of clades that have never been found in previous morphology-only studies, such as Afrotheria and Laurasiatheria.” In other words, we used our imaginations to make molecule phylogenies work, rather than considering the possibility that molecular phylogenies did not work. 

“Our results suggest that, at least in principle, improvements in the fossil record may be sufficient to largely reconcile morphological and molecular phylogenies of mammals, even with current morphological character sets.” They used far too few taxa. And they used suprageneric taxa. They avoided fossil taxa. This is omitting available data. 

This is not the way science is supposed to work.
So why was this published?

References
Beck RMD and Baillie C 2018. Improvements in the fossil record may largely resolve the conflict between morphological and molecular estimates of mammal phylogeny. bioRxiv doi:10.1101/373191. First posted online July 20, 2018.

Click to access 373191.full.pdf

The pink fairy armadillo joins the LRT as a glyptodont…

…not an armadillo.
The pink daily ‘armadillo’ (genus: Chlamyphorus) nests with the much larger glyptodont, Holmesina in the large reptile tree (LRT, 1255 taxa, subset Fig. 4), not with Dasypus novemcinctus, the extant llong-nosed armadillo nesting on the other side of the aardvark Orycteropus. Another fairy armadillo (genus: Calyptophractos) is also described here.

The pink fairy armadillos
(genus: Chlamyphorus trunca) and the greater fairy armadillo (genus: Calyptophractos retusus) are little glyptodonts. This is not heretical news (Fig. 1).

Figure 1. When glyptodonts were nested with armadillos, the fairy armadillos nested with extinct glyptodonts. Cladogram from Delsuc et al. 2016, a DNA analysis. No aardvarks were tested here.

Using DNA
(both ancient and modern) Delsuc et al. 2016 nested the fairy armadillo with the extinct glyptodont, Doedicurus (Fig. 1). We already know not to trust DNA evidence in paleontology, but in this case trait analysis supports something like this arrangement of taxa. The distance is not great either way.

Figure 2. DNA analysis by Möller-Krull et al. 2007 omits fossil taxa and aardvarks and arrives at this tree topology of extant edentates.

Delsuc et al. 2016 nested fairy armadillos with glyptodonts
when they attempted to nest glyptodonts within the armadillo clade using DNA, omitting other fossil taxa.  I did not see LRT outgroups in their cladogram, nor did I see the aardvark.

Figure 3. Skulls of Holmesina and Calyptophractus compared. When they are together, the similarities are obvious.

Here in the LRT Calyptophractus is a phylogenetic miniature of Holmesina, with a shorter rostrum and expanded cranium (Fig. 3), along with its much smaller size and thinner scales. In lateral view the skulls are quite alike and distinct from all other edentates.

We know that aardvarks (genus: Orycteropus) nest with edentates because all the other possibilities were offered and found to be not as parsimonious (similar). Earlier we looked at the nesting of Holmesina and the phylogenetic fact that all aardvarks, armadillos and anteaters are derived from various types of glyptodonts.

Figure 4. Subset of the LRT focusing on the Edentata. Armored taxa are color tinted and their branches are thicker.

References
Delsuc F et al. 2016. The phylogenetic affinities of the extinct glyptodonts. Current Biology 26(4):R155–R156.
Harlan R 1825. Annals of the Lyceum of Natural History of New York 1:235.
Möller-Krull M et al. 2007. Retroposed Elements and Their Flanking Regions Resolve the Evolutionary History of Xenarthran Mammals (Armadillos, Anteaters, and Sloths). Mol. Biol. Evol. 24 (11): 2573–2582. PDF
Yarrell W 1828. On the osteology of the Chlamyphorus truncatus of Dr. Harlan microform; in a letter to N.A. Vigors. Zoological Journal 3:544–554.

AKA
Pink Fairy Armadillo, Lesser Fairy Armadillo, Lesser Pichi Ciego, Pichiciego
http://www.iucnredlist.org/details/4704/0

Greater Fairy Armadillo, Burmeister’s Armadillo, Chacoan Fairy Armadillo, Greater Pichi Ciego: http://www.iucnredlist.org/details/4703/0

wiki/Pink_fairy_armadillo

https://www.amnh.org/explore/news-blogs/research-posts/study-finds-relationship-between-glyptodonts-modern-armadillos/

https://www.forbes.com/sites/shaenamontanari/2016/02/23/ancient-dna-from-extinct-glyptodont-reveals-it-was-a-really-big-armadillo/#2cb057ae287d

What is Periptychus carinidens?

Figure 1. Subset of the LRT focusing on the nesting of Periptychus.

Updated Sept 6, 2022
as Thomashuxleya moves to the interathere marsupials with 2136 taxa in the LRT.

Short answer:
In the large reptile tree (LRT, 1253 taxa, subset Fig. 1) Periptychus (Figs, 2–4) nests between basal phenacodonts like Phenacodus, Thomashuxleya and Pleuraspidotherium, and derived phenacodonts, like Gobiatherium + Arsinoitherium and Coryphodon + Uintatherium. These are all extinct herbivores from a clade that was recovered here first. Some derived taxa had ornate skull bumps/horns.

Previously known
as a condylarth from less complete materials (Cope 1881), the latest academic paper on Periptychus (Shelley, Williamson and Brusatte 2018) was still unable to determine closest relatives based on new data. No cladogram was presented. Sisters listed above were not listed in the text. Rather, the authors called it, “A robust, ungulate-like placental mammal.” 

Figure 1. Skull of Periptychus in three views from Shelley et al. 2018. Colors added here. The prefrontal, lacrimal and nasal traits are unique to this clade. Updated February 3, 2021.

Think of Periptychus as a placental herbivore with very primitive feet…

Figure 3. Periptychus skeleton restored from Shelley, Williamson and Brusatte 2018.

… and hands (no reduced digits). This mammal is remarkable for its long list of unremarkable traits.

Of course,
this was only the ‘warm-up act’ for the big, bizarre uintatheres to follow.

Figure 4. Manus and pes of Periptychus with some bones restored.

References
Cope ED 1881. The Condylarthra (Continued). American Naturalist 84;18: 892–906.
Shelley SL, Williamson TE and Brusatte SL 2018. The osteology of Periptychus carinidens: A robust, ungulate-like placental mammal (Mammalia: Periptychidae) from the Paleocene of North America. PLoS ONE 13(7): e0200132.

https://doi.org/10.1371/journal.pone.0200132

Think of aardvarks and sloths as naked and hairy glyptodonts respectively

Because
that’s what they really are… aardvarks are naked and sloths are hairy glyptodonts. And, yes, that comes as a surprise, it breaks a paradigm, it spins your head around, it’s heretical… and it’s exactly where the data takes us.

The Edentata is an odd clade
in which the basalmost taxa, like Barylambda, Glyptodon and Holmesina are very large. On the other hand, terminal extant and derived taxa, like Peltephilus and Cyclopes, are much smaller, just the opposite of most mammal clades (in which smaller usually lead to larger, following Cope’s Rule.)

According to Wikipedia,
“Glyptodontinae (glyptodonts or glyptodontines) are an extinct subfamily of large, heavily armored armadillos which developed in South America and spread to North America.”

In the large reptile tree (LRT, 1252 taxa) the glyptodont, Glyptodon, nests between the massive Barylambda and giant sloths, followed by smaller tree sloths and small extinct horned armadillos, like Peltephilus. On another branch (Fig. 1) another large glyptodont, Holmesina, nests between the massive Barylambda and the much smaller aardvark, Orycteropus, the armadillo, Dasypus, and the anteaters, Tamandua and Cyclopes.

Such a big-to-small phylogenetic pattern,
is known as phylogenetic miniaturization or the Lilliput Effect and is often the product of neotony (adults retaining juvenile traits, including juvenile size).

Figure 2. Holmesina, the glyptodont ancestor to aardvarks, anteaters and armadillos. Those are aardvark hands (Fig. 3), glyptodont feet.

Holmesina (Fig. 2) is added to the LRT today.
Basically it is a longer-snouted glyptodont, basal to the longer snouted above-mentioned aardvarks, armadillos and anteaters.

Following a reader comment,
(suggesting ‘taxon exclusion’ was the issue that did not unite glyptodonts with armadillos) I was looking for a transitional taxon to more closely nest glyptodonts with armadillos, rather than sloths. I did so and the tree topology did not change when Holmesina was added. Armadillos are still one taxon removed from glyptodonts, but at least now we have a glyptodont on the long-nosed clade of aardvarks, etc.. As before, aardvarks nest between glyptodonts and armadillos. Looking at all the edentate taxa in detail and overall. I think this nesting and this tree topology seem very reasonable (= it produces a gradual accumulation of derived traits at all nodes and between all taxa).

Figure 3. Orycterpus, the extant aardvark, is a living sister to Barylambda from the Paleocene. Aardvarks traditionally nest alone, but in the LRT they are edentates without armor… or hair.

Other workers, like Fernicola, Vizcaíno and Fariña 2008,
described the phylogeny of glyptodonts by putting taxa like Holmesina at the base while omitting Barylambda. Thus such studies do not present the full picture due to taxon exclusion. Everyone seems to omit Barylambda and all the other edentate outgroups back to Devonian tetrapods… but not the LRT.

Goodbye ‘Xenarthra’. Goodbye ‘Pilosa’. Goodbye ‘Cingulata’.
According to Wikipedia, “The order Pilosa is a group of placental mammals, extant today only in the Americas. It includes the anteaters and sloths, including the extinct ground sloths, which became extinct about 10,000 years ago.” According to Wikipedia, “Cingulata, part of the superorder Xenarthra, is an order of armored New World placental mammals.” In the LRT ‘Xenarthra’ (Cope 1889) is a junior synonym for ‘Pilosa’ (Flower 1883) and that is a junior synonym for Edentata (Darwin 1859).

References
Darwin C 1859. On the origin of species.
Fernicola JC, Vizcaíno SF and Fariña RA 2008. The evolution of armored xenarthrans and a phylogeny of the glyptodonts. Chapter 7 in: The Biology of the Xenarthra, Eds: Vizcaíno SF and Loughry WJ. University Press of Florida.
Gaudin TJ and Croft DA 2015. Paleogene Xenarthra and the evolution of South American mammals. Journal of Mammalogy 96 (4): 622–634. https://doi.org/10.1093/jmammal/gyv073

http://www.finedictionary.com/Edentata.html

 

 

 

 

The diet of Thylacoleo, the giant sugar glider

The diet of Thylacoleo, the so-called ‘marsupial lion,’
has been a puzzle for decades. The jaws and teeth look dangerous and carnivorous, but Thylacoleo nests in the middle of an herbivorous clade of wombat-like marsupials.

That’s the problem.
Morphology and phylogeny provide the problem… and the answer to the diet of Thylacoleo. This answer could have been known decades earlier, but alas… the same taxon exclusion issue that pervades paleo was also present here.

Morphology
One look at the palate of Thylacoleo documents a very different sort of mammal palate:

1. The jawline curves laterally near the premolars
2. The molars are absent
3. There is an asymmetry in the lineup of the posterior teeth

Figure 1. The palate of Thylacoleo is unusual in several respects. See text for details. Vertical arrows point to asymmetries. Horizontal arrow lines up with parasagittal plane

Phylogeny
In the large reptile tree (LRT, 1250 taxa) the closest living sisters to Thylacoleo, the sugar gliders, like Petaurus, should provide some sort of natural guidance as to what the giant sugar glider ate. And they do.

Sugar glider diet
From the Wikipedia page on sugar gliders: “Sugar gliders are seasonally adaptive omnivores with a wide variety of foods in their diet… In summer they are primarily insectivorous, and in the winter when insects (and other arthropods) are scarce, they are mostly exudativorous (feeding on acacia gum, eucalyptus sap, manna, honeydew or lerp). Sugar gliders have an enlarged caecum to assist in digestion of complex carbohydrates obtained from gum and sap.

To obtain sap and nectar from plants, sugar gliders will strip the bark off trees or open bore holes with their teeth to access stored liquid gum. Little time is spent foraging for insects, as it is an energetically expensive process, and sugar gliders will wait until insects fly into their habitat, or stop to feed on flowers. They are opportunistic feeders and can be carnivorous, preying mostly on lizards and small birds. They eat many other foods when available, such as nectar, acacia seeds, bird eggs, pollen, fungi and native fruits. Pollen can make up a large portion of their diet, therefore sugar gliders are likely to be important pollinators of Banksia species.”

Well, there you have it. 
Little sugar gliders can be carnivorous. They can also strip bark off trees to get at the gum inside. That’s a rare diet. As sister taxa, giant sugar gliders, like Thylacoleo, were therefore likely also carnivorous and/or stripped bark off trees to get at the gum. For the latter odd reason the odd skull of Thylacoleo was likely adapted, and predation, if you insist, but predators don’t have the odd palate and teeth that Thylacoleo has.

We don’t have to provide a narrow dietary answer for Thylacoleo
because the diet of living sugar gliders is diverse. AND sugar gliders provide the long-sought carnivorous exception to this herbivorous clade.

Petaurus breviceps (Waterhouse 1839; Early Miocene to present; up to 30cm) is the extant sugar glider, a nocturnal squirrel-like marsupial able to climb trees and glide with furry membranes between the fore and hind limbs. An opposable toe is present on each hind foot. Sharp claws tip every digit.

Thylacoleo carnifex (Owen 1859; Pliocene-Pleistocene; 1.14 m long) was a giant sugar glider like Petaurus. Thylacoleo had the strongest bite of any mammal with the largest, sharpest molars of any mammal. It had fewer but larger teeth than Petaurus. The manus included retractable claws. The pes had a very large heel bone (calcaneum). This supposedly carnivorous ‘marsupial lion’ nests with herbivores. Pedal digit 1 likely had a phalanx and claw, but it has not been shown. Sugar gliders strip bark off of trees and the very odd teeth of Thylacoleo could have done the same on a larger scale.

References
Owen R 1859. On the fossil mammals of Australia. Part II. Description of a mutilated skull of the large marsupial carnivore (Thylacoleo carnifex Owen), from a calcareous conglomerate stratum, eighty miles S. W. of Melbourne, Victoria. Philosophical Transactions of the Royal Society 149, 309-322.
Waterhouse GR 1838. Observations on certain modifications observed in the dentition of the Flying Opossums (the genus Petaurus of authors). Proceedings of the Zoological Society of London. 4: 149–153.

wiki/Petaurus
wiki/Thylacoleo
NOVA | Bone Diggers | Anatomy of Thylacoleo | PBS
https://en.wikipedia.org/wiki/Sugar_glider
https://www.wired.com/2009/06/thylacoleo-herbivore-or-carnivore/

Ukhaatherium: a late-surviving Morganucodon in the LRT

Ukhaatherium nessovi (Late Cretaceous, Novacek et al. 1997) has traditionally been nested with the proto-placental, Asioryctes. Here in the large reptile tree (LRT, 1243 taxa), Ukhaatherium nests as a basal therian in the large reptile tree. Morganucodon (Latest Triassic/Earliest Jurassic, Küehne 1949) nests with Ukhaatherium, with virtually identical scores and are similar in size.

Figure 1. Morganucodon skull in several views. Compare to Ukhaatherium in figure 2.

When you see them together,
(Figs. 1,2) the similarities between Morganucodon and Ukhaatherium are strikingly obvious.

Figure 2. Skull and dentition of Ukhaatherium. Compare to Morganucodon in figure 1.

The long snout of prototheres
is retained in basal therians like Morganucodon and Ukhaatherium. The epipubic bones found in Ukhaatherium are no surprise in the LRT, where it nests in the middle of other taxa that share this trait.

Figure 3. Ukhaatherium in situ.

Rowe 1988 defined Mammaliaformes
as Morganucondontidae + Mammalia. Here Morganucodontidae nest within the Mammalia, so Mammaliaformes is a junior synonym of Mammalia.

Figure 4. Subset of the LRT with the addition of Perameles and Morganucodon. Sharp-eyed readers with good memories will not subtle changes in this tree near protorotheres.

And, by the way,
Ukhaatherium + Morganucodon is still close to Asioryctes in the LRT. If we let a little time go by from the Latest Triassic to the Latest Cretaceous, then that’s enough time for the tiny posterior jaw bones in Morganucodon to evolve into the tiny ear bones of Ukhaatherium, convergent and parallel to those of other therian and prototherian mammals (which already show distinct patterns in this regard).

References
Kuehne WG 1949. On a triconodont tooth of a new pattern from a fissure-filling in South Glamorgan. Proceedings of the Zoological Society of London 119:345-350
Novacek MJ, Rogier GW, Wible JR, McKenna MC, Dashzev g D and Horovitz I 1997. Epipubic bones in eutherian mammals from the Late Cretaceous of Mongolia Nature 389: 483-486.
Rowe TS 1988. Definition, diagnosis and origin of Mammalia. Journal of Vertebrate Paleontology 8(3):241–264.

wiki/Ukhaatherium
wiki/Morganucodon

Chaoyangodens: a transitional monotreme with big canines

Hou and Meng 2014
described a new Jehol eutriconodont mammal, Chaoyangodens lii, (Fig. 1) from the Yixian formation, Early Cretaceous. “The new species has a tooth formula I5-C1-P1-M3/i4-c1-p1-m4, unique among eutriconodonts in having only one premolar in lower and upper jaws, respectively, and a distinctive diastema between the canine and the premolar. Its simple incisors and reduced premolars show a mosaic combination of primitive and derived features.” In other words, this is a transitional taxon, as most are.

Later, Meng and Hou 2016
described ‘the earliest known mammalian stapes’ from the same specimen. “The stapes of Chaoyangodens is reduced in size compared to those of non-mammalian cynodonts and is within the size range of extant mammals.”

Figure 1. Chaoyangodens lii in situ and restored skull in lateral view. At a screen resolution of 72 dpi, this image is twice life size. This mouse-sized taxon is a monotreme basal to both the echidna and platypus.

Figure 2. Subset of the LRT focusing on monotremes and Chaoyangodens.

Here in the large reptile tree (LRT, 1137 taxa, Fig. 2) Chaoyangodens nests between Kuehneotherium and Akidolestes, basal  to the living monotremes, Ornithorhynchus and Tachyglossus.

The top of the Chaoyangodens skull is buried in the matrix. The shape of the skull in lateral view, or at least parts of it, like the position of the orbit (Fig. 1), can be surmised by phylogenetic bracketing.

Based on the nesting of Chaoyangodens
and relatives, like Brasilitherium and Kuehneotherium (Late Triassic), these taxa are all crown mammals, not stem mammals (contra traditional thinking).

Luo, Kielan-Jaworowska and Cifelli (2002)
also nested eutriconodonts within crown mammals and this was confirmed by many later workers. The LRT nests many traditional triconodonts and eutriconodonts elsewhere, both more primitive and more derived.

Recently
we looked at the echidna sister/ancestor, Cifelliodon, here. It also had fewer and bigger teeth in the jaws, though none of those erupted beyond the gum line.

References
Hou S-L and Meng J 2014. A new eutriconodont mammal from the Early Cretaceous Jehol Biota of Liaoning, China. Chinese Science Bulletin 59, 546–553.
Luo Z-X, Kielan-Jaworowska  z and Cifelli RL 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica. 47 (1): 1–78.
Meng J and Hou S-L 2016. Earliest known mammalian stapes from an early Cretaceous eutriconodontan mammal and implications for evolution of mammalian middle ear. Palaeontologica Polonica 67:181–196.

wiki/Eutriconodonta

New(?) mammal at the Eutheria-Metatheria split

Bi et al. 2018 bring us a small Virginia opossum from the early Cretaceous
“Molecular estimates of the divergence of placental and marsupial mammals and their broader clades (Eutheria and Metatheria, respectively) fall primarily in the Jurassic period. Supporting these estimates, Juramaia, the oldest purported eutherian is from the early Late Jurassic (160 million years ago) of northeastern China. Sinodelphys, the oldest purported metatherianâis from the same geographic area but is 35 million years younger, from the Jehol biota. Here we report a new Jehol eutherian, Ambolestes zhoui, with a nearly complete skeleton that preserves anatomical details that are unknown from contemporaneous mammals, including the ectotympanic and hyoid apparatus. This new fossil demonstrates that Sinodelphys is a eutherian, and that postcranial differences between Sinodelphys and the Jehol eutherian Eomaia, previously thought to indicate separate invasions of a scansorial niche by eutherians and metatherians, are instead variations among the early members of the placental lineage. The oldest known metatherians are now not from eastern Asia but are 110 million years old from western North America, which produces a 50-million-year ghost lineage for Metatheria.”

Figure 1. Ambolestes tracing from Bi et al. 2018. plate and counter plate. Note the scale bar. This taxon is one third the size of the extant opossum. Apparently and oddly no unguals were preserved.

In the large reptile tree (LRT, 1131 taxa) the new fossil at the Metatheria/ Eutheria split is phylogenetically identical to and therefore congeneric with Didelphis, the Virginia opossum. So, this is pre-marsupial in a clade at the base of the marsupial/placental split. There are also a series of pre-placentals, some of which are extant and retain a reduced pouch, like Monodelphis.

Figure 2. Ambolestes skull in situ with DGS applied.

Ambolestes zhoui gen. & sp. nov. (Bi et al. 2016, 126 mya; 25cm in length) is is one third the size of the extant opossum, but otherwise nearly identical based on tested traits. In the LRT Didelphis nests with Ambolestes and they nest with Eomaia and Agilodocodon as the last common ancestors to Metatheria and Eutheria. Bi said in an interview, “Ambolestes zhoui is an early member of the placental lineage. It also carries mixed features both placentals and marsupials”. In the LRT, Ambolestes is exactly as much in the placental lineage (Fig. 4) as Didelphis is… and Didelphis has a pouch. Both have prepubic (epipubic) bones.

Since Ambulestes is congeneric with Didelphis,
you heard it hear first when the LRT nested Didelphis as the last common ancestor of Metatheria and Eutheria. Good to see confirmation.

Figure 3. Ambolestes skull reconstructed. Jaw tips restored. Lower last molar appears to be just erupting. No retroartcular process is apparent here, which sometimes happens with Didelphis (Mohamed 2018)

The Pittsburgh Post-Gazette reported,
“The well-preserved new mammal, an ancient furry creature most similar to a modern tree shrew, is named Ambolestes zhoui.” Actually Ambolestes was a little less exotic than that.

“John Wible, curator of mammals at the Carnegie Museum of Natural History, became involved in the project about two years ago. “As soon as I saw the photographs of the fossil I was like, ‘Oh my God this is amazing,’ ” he said. “It was amazingly complete. Right off the bat I saw there were skeletal parts of the body that were not known of other animals of that time period.”

But if Dr. Wible happened upon a certain type of roadkill
or went out after midnight with a flashlight he would have seen a living version of the Early Cretaceous fossil. Rather than, “this is amazing” he could have said, “we could have predicted this.”

Figure 4. Subset of the LRT focusing on basal live-bearing mammals.

The Post-Gazette also reported, 
“The fossil was not allowed to leave China, said Mr. Wible, noting that this is the first paper he’s published where he’s been unable to actually hold the fossil, though he hopes to see it in person in the next few years. Instead, he relied on detailed photographs and scanned images.”

Figure 5. Didelphis, the extant opossum, a larger sister to the smaller and 126 million years older Ambolestes.

Now it’s important to remember 
that tooth traits can converge and reverse. Think about archaeocetes (pre-whales), which have three cusps all in a row, like cynodont. Consider odontocetes, which have simple cones, like basal reptiles. Thus, tooth only taxa must be treated separately from skeletal taxa and cladograms must be based on skeletal traits, not tooth traits, which can be dangerous based on the issues that arise from the Bi et al. cladgoram (Fig. 6).

Take another look at taxa listed in Bi et al. 2018
Maelestes, when tested with more taxa, nests at the base of the tenrec/odontoete clade. Necrolestes nests with the golden mole, Chrysochloris, a basal member of Glires. Zhangeotherium is a basal pangolin. They (Bi et al. and other basal mammal workers) are going to have to expand their taxon lists to include at least all the mammals that don’t have hooves, and that includes a few that do have quasi-hooves, like the descendants of Maelestes.

FIgure 6. Cladogram published in Bi et al. 2018 with colors added to show taxa appearing elsewhere in the LRT. As you can see, this is a mess, likely created by too much emphasis on teeth traits, which converge and reverse. Treeshrew-like Maelestes, when tested with more taxa, nests at the base of the tenrec/odontoete clade. Necrolestes nests with the golden mole, Chrysochloris, a basal member of Glires. Zhangeotherium is a basal pangolin.

References
Bi S-B, Zheng X-T, X, Wang X-L, Cignetti N-E, Yang SL and Wible JR 2018.
An Early Cretaceous eutherian and the placental/marsupial dichotomy. Nature (advance online publication) DOI: https://doi.org/10.1038/s41586-018-0210-3
https://www.nature.com/articles/s41586-018-0210-3
Mohamed R. 2018. Anatomical and radiographic study on the skull and mandible of the common opossum (Didelphis marsupialis Linneaus, 1758 (in the Caribbean). Veterinary Sciences 5(44) 10 pp. doi:10.3390/vetsci5020044

https://carnegiemnh.org/press/new-mammal-fossil-provides-insights-on-early-placental-mammal-evolution/

 

Cifelliodon: new echidna ancestor from the Early Cretaceous of Utah

This one seemed pretty obvious from the first impression,
but failed to make the same impression on the original authors (Huttenlocker et al., 2018).

Usually mammal teeth are found without a skull.
Huttenlocker et al., 2018 found a skull largely without teeth (most don’t erupt beyond the rim of the very few alveoli), certainly a derived trait for mammals. And this is one more way tetrapods became toothless. They named their new taxon, Cifelliodon wahkarmoosuch (Fig. 1).

Figure 1. Early Cretaceous Cifelliodon is ancestral to the living echidna, Tachyglossus according to the LRT. The reduced number and size of teeth here led to toothlessness in the living echidna. The skull of Tachyglossus retains only a tiny lateral temporal fenestra (because the jaws don’t move much in this anteater. Compared to Cifelliodon the braincase is greatly expanded, the lateral arches are expanded and the two elements fuse, unlike most mammals.

According to Wikipedia:
“Cifelliodon is an extinct genus of haramiyid mammal from the Lower Cretaceous of North America. It is a mammaliaform, and is one of the latest surviving haramiyids yet known, belonging to the family Hahnodontidae. Its discovery led to the proposal to remove hahnodontids from the larger well-known group, the multituberculates.”

As usual the LRT recovered a different nesting.

Figure 2. Cifelliodon skull in three views, plus DGS, plus the original drawing, which is not very accurate. A mandible is restored here.

Figure 3. Subset of the LRT focusing on Monotremes, now including Cifelliodon.

Here
in the large reptile tree (LRT, 1233 taxa) Cifelliodon wahkarmoosuch from the Early Cretaceous of Utah nests strongly with Tachyglossus (Figs. 1, 4, 5), one of the extant egg-laying echidnas, currently restricted to Australia and surrounding islands. Tachyglossus was tested in the (Huttenlocker et al. analysis of basal mammal relationships, but the two taxa did not nest together.

Unfortunately Huttenlocker et al., 2018
experienced taxon exclusion problems that nested Cifelliodon with the distinctly different wombat Vintana and those two with the distinctly different multituberculates all more primitive than monotremes.

To their credit
Huttenlocker et al. linked this North American taxon with others from Gondwana which includes Australia, which broke off 99 mya, 40 million years after the appearance of Cifelliodon in Utah. In an interview for USC, Huttenlocker reported, “Most of the fossil record of early mammal relatives is based on teeth. Cifelliodon is unique in that it is one of the only near-complete skulls of a mammal relative from the basal Cretaceous of North America and is the only fossil of early mammal relatives from this time interval in Utah.”

“The fact that the skull looked so primitive compared to other known mammal groups from the Cretaceous made figuring out its relationships extremely difficult. It shows some unique dietary specializations that are seen in only a handful of groups that lived during the age of dinosaurs. Ultimately, the structure of the preserved molars showed clear similarities to some neglected fossil teeth from Northern Africa. So we think that Cifelliodon represents an archaic offshoot whose relatives may have dispersed into the southern continents and became fairly successful during the Cretaceous.”

Figure 4. Tachyglossus skeleton, manus and x-rays.

The skull of Tachyglossus
retains only a tiny lateral temporal fenestra (because the jaws don’t move much in this anteater. Compared to Cifelliodon the braincase is greatly expanded, the lateral arches are expanded and the two elements fuse, unlike most mammals.

Figure 5. The echidna (genus: Tachyglossus) in life. This slow-moving spine-covered anteater has digging claws. Many of the derived traits seen here developed during the last 100 million years since Cifelliodon.

 

References
Huttenlocker AD, 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 Letters  Link to Nature

wiki/Cifelliodon

https://news.usc.edu/143411/why-you-should-care-about-this-130-million-year-old-fossil/