Convergent anterior shifts of the zygomatic arch in Glires

Something  a little strange in the course of mammal evolution here.
The temporal region of rodents (Fig. 1) appears to ‘break the rules’, but on further examination merely bends them.

We’re used to seeing
the orbit separate from the temporal fenestra, as in most reptiles, but it is a little disconcerting to see them confluent, as in most mammals, knowing that the eyeball and temporal muscle share the same opening without division.

In some rodents,
like the capybara (genus: Hydrochoerus) (Fig. 1), the lateral temporal arch (aka: zygomatic arch) drifts/shifts so far forward that it moves anterior to the temporal region and just borders the orbit (or so it seems).

Actually
the temporal jaw muscle continues to dive inside the temporal arch to the coronoid process of the dentary (= mandible). The difference is the temporal muscle in capybaras pulls at an angle over the valley created by the squamosal (Fig. 1, lower right).

FIgure 3. Hydrochoerus the capybara. At lower right, large jaw muscles are illustrated.

FIgure1. Hydrochoerus the capybara. At lower right, large jaw muscles are illustrated. The temporalis muscle (light red) anchors on the temple and inserts on the coronoid process as usual, just angled much closer to the eyeball to maintain these contacts. In dorsal view the zygomatic arch is located anterior to the temporal region of the skull here.

In other words,
the zygomatic arch (maxilla + jugal + squamosal bar) in the capybara and several other rodents and their allies (Fig. 3) does not extend to the posterior skull, as it does in basal tetrapods and most mammals, including multituberculates (Fig. 3). Even so, the temporalis muscle (Fig. 1, light red) always anchors on the temple and inserts on the coronoid process. In the capybara the temporal muscle inserts much closer to the eyeball.

Rodents have a loose jaw joint
(Fig. 2) that permits the mandible to move freely (not restricted by an axle and shaft as in Carnivora) within a muscular sling to alternately gnaw with incisors in one position, then grind with the molars in another. Primates, including humans, are similar in this regard. The alignment of the teeth can shift because the axis of rotation is loose.

Figure 3. Xianshou animation showing the loose jaw joint permitting both gnawing and grinding.

Figure 2. Xianshou animation showing the loose jaw joint permitting both gnawing and grinding. The zygomatic arch is shifted slightly anteriorly here, distinct from sister taxa (Fig. 3). If the jugal is still present, it is located as a vestigial patch on the inner rim of the zygomatic arch, as in sister taxa. This is obviously a highly derived skull and it nests at a highly derived node, contra the present paradigm and despite its early Late Jurassic appearance in the fossil record.

Cox et al. 2012 report,
“The masticatory musculature of rodents has evolved to enable both gnawing at the incisors and chewing at the molars. In particular, the masseter muscle is highly specialised, having extended anteriorly to originate from the rostrum. All living rodents have achieved this masseteric expansion in one of three ways, known as the sciuromorph, hystricomorph and myomorph conditions. Our results show that the morphology of the skull and masticatory muscles have allowed squirrels to specialise as gnawers and guinea pigs as chewers, but that rats are high-performance generalists, which helps explain their overwhelming success as a group.”

Other groups not traditionally associated with rodents,
but nest with rodents in the large reptile tree (LRT, 1281 taxa) include:

  1. The aye-aye (genus: Daubentonia) possesses large, ever-growing incisors, which it uses to gnaw wood and to access the subsurface larvae it locates through tapping. This feature of ever-growing teeth was once considered unique among primates (Simons 1995), but the aye-aye is not a primate in the LRT. Daubentonia also uses its rodent-like teeth to gnaw at nuts and hard-shelled fruits (Sterling et al. 1994, Sterling 1994b). In the LRT, Daubentonia is not a primate, but a rodent, explaining all of the above issues.
  2. The Multituberculata and Haramiyida, also posses large presumably ever-growing incisors, which they presumably use as rodents use these teeth.
  3. Maiopatagium was originally considered a haramiyid, but here nests with porcupines.

Typically the auditory bulla becomes larger
as the zygomatic arch advances forward, thus filling the vacated space below the temples. This happened several times by convergence. I wonder if that was the driving force: improved hearing for predator avoidance and/or prey detection, that made this happen in the following taxa and their kin.

  1. Scutisorex (shrews)
  2. Chrysochloris (golden moles)
  3. Macroscelides (one type of elephant shrew not related to the other type.)
  4. Solenodon 
  5. Gomphos (rabbits)
  6. Coendou (porcupines) and maybe Maiopatagium (back of skull missing)
  7. Heterocephalus (naked mole rats)
Figure 2. A selection of taxa from figure 1 more or less to scale and in phylogenetic order (pink arrows). Hope this helps with the concept of a gradual accumulation of traits. The hedgehogs Erinaceus and Echinops are transitional to the higher taxa with teeth and without.

Figure 3. A selection of taxa from figure 1 more or less to scale and in phylogenetic order (pink arrows). The hedgehogs Erinaceus and Echinops are transitional to the higher taxa with a complete arcade of teeth and without. Today, please note the posterior anchor of the squamosal (zygomatic arch).

I wonder if multituberculates are no longer with us
because they could not hear as well, based on their smaller auditory apparatus? Good question…

References
Cox et al. 2012. Functional evolution of the feeding system in rodents. PloS One 7(4): e36299. Online here.
Simons EL 1995. History, anatomy, subfossil record and management of Daubentonia Madagascariensis. In: Alterman L, Doyle GA, Izard MK. Creatures of the dark: the nocturnal prosimians. New York: Plenum Pr. p133-140.
Sterling EJ, Dierenfeld ES, Ashbourne CJ, Feistner ATC 1994. Dietary intake, food composition and nutrient intake in wild and captive populations of Daubentonia madagascariensis. Folia Primatol 62(1-3):115-24.
Sterling E 1994b. Ayes-ayes: Specialists on structurally defended resources. Folia Primatologica 62:142-154.

http://pin.primate.wisc.edu/factsheets/entry/aye-aye

Teeth in the shrew/rodent/rabbit/multituberculate clade

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

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

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

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

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

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

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

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

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

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

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

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

 

More evidence that euharamyidans are mislabeled Jurassic rodents

Figure 1. The Jurassic mammal Shenshou, which nests within Allotheria (Haramiyida + Mutituberculata) within the Mammalia, as I proposed based on the LRT without knowledge of this paper.

Figure 1. The Jurassic mammal Shenshou, which nests within Allotheria (Haramiyida + Mutituberculata) within the Mammalia, as I proposed based on the LRT without knowledge of this paper.

Euharamyidans include the squirrel-like Jurassic gliders
Shenshou (Figs. 1,2 ), Vilevolodon and Maiopatagium in the large reptile tree (LRT, 1265 taxa). These are sisters to the squirrel, Ratufa, the squirrel-like Paramys and two living rodents, Rattus and Mus (rat and mouse).

Mao et al. 2018 report, “The new evidence suggests presence of diphyodonty in euharamiyidans. While it will take time to amass data to resolve the discrepancy between competing phylogenetic hypotheses about ‘haramiyidans’, multituberculates, and/or allotherians, it is helpful to continue deepening our knowledge about the morphology of euharamiyidans. Our finding of potential diphyodonty in euharamiyidans provides an additional piece of evidence for mammalness of the peculiar group.”

Figure 2. Shenshou skull traced in colors.

Figure 2. Shenshou skull traced in colors.

Above:
The skull of Shenshou (Fig. 2), close to living squirrels. Evidently the molar cusps are convergent with those of Haramiyavia, but there are few other similarities.

Below:
Haramiyavia (Fig. 3), a pre-mammal cynodont with a small canine and large incisors not related to Shenshou. Note the dual articular/dentary jaw joint in Haramiyavia, missing (actually evolved into ear bones) in Shenshou. Such a jaw joint marks this taxon as a pre-mammal synapsid.

Figure 1. Haramiyavia reconstructed and restored. Missing parts are ghosted. Three slightly different originals are used for the base here. The last appears to be the least manipulated and it appears to fit the premaxilla better.  The fourth maxillary tooth appears to be a small canine. The groove on the dorsal premaxillary appears to be for the nasal, not the septomaxilla. Parts are taken from both mandibles

Figure 3. Haramiyavia reconstructed and restored. Missing parts are ghosted. Three slightly different originals are used for the base here. The last appears to be the least manipulated and it appears to fit the premaxilla better.  The fourth maxillary tooth appears to be a small canine. The groove on the dorsal premaxillary appears to be for the nasal, not the septomaxilla. Parts are taken from both mandibles

In the LRT, Haramyavia, a basal member of the Haramiyida
nests with other pre-mammals like Brasiliodon and Sinoconodon, hence: not related to euharamiyidans. Determining the clade based on traits (no matter what these traits may be) is the cause of the phylogenetic confusion based on tooth shape and replacement patterns, which can converge. Only a taxon’s placement on a cladogram can tell you what an animal really is. Sadly, that’s a current heresy, not widely appreciated.

According to Wikipedia
(ref below): Haramiyidans are a long lived lineage of mammaliaform cynodonts. Their teeth, which are by far the most common remains, resemble those of the multituberculates. However, based on Haramiyavia, the jaw is less derived; and at the level of evolution of earlier basal mammals like Morganucodon and Kuehneotherium, with a groove for ear ossicles on the dentary.[1] They are the longest lived mammalian clade of all time.”

As the LRT showed several years ago
the rodent-like Euharamiyidans (Fig. 1) nest with placental rodents in the clade Glires, not with the much more primitive pre-mammals like Haramiyavia (Fig. 3).

Mao et al. 2018 report, “presence of the diphyodont dentition alone is not diagnostic for mammals. This is because a diphyodont dentition exists not only in mammals but also in stem mammaliaforms, such as Morganucodon and docodonts, although there may be more than one replacement for the upper canine of Haldanodon (Martin et al., 2010b).”

By contrast, in the LRT
Morganucodon is a basal metatherian, not a stem mammaliaform. Which is one more reason why it has diphyodont dentition (milk teeth + permanent teeth). The late-surviving docodonts, Haldanodon and Castorocauda nest between the synapsids, Probainognathus and Pachygenelus in the LRT. Those four should be replacing all their teeth all the time. All four had a dual jaw joint that was not quite mammalian, but getting there!

Diphyodont dentition alone is diagnostic for mammals
because it implies toothless, milk-lapping/sucking hatchlings, (but be careful not to pull a Larry Martin here, because the LRT uses 231 traits and diphyodont dentition is not among them).

Among mammals
Mao et al. 2018 report, “tooth replacement is also complex among mammals. For instance, the molariform teeth of eutriconodonts show replacement and some species have the entire dentition replaced and show at least three tooth generations. Cheek tooth replacement is uncertain in “symmetrodontans”. In North American spalacotheriids deciduous canine and premolars were retained late in life and may never have been replaced; thus, their dentitions perhaps were monophyodont. This has been supported by the spalacolestine Lactodon from the Early Cretaceous Jehol Biota, in which there is no sign of cheek tooth replacement even though this taxon possesses deciduous-like antemolars. New CT scan data (unpublished) further confirmed that there is no tooth germ at any tooth locus, including incisors and canines, of Lactodon [= Lactodens”?]. Thus, presence of the diphyodonty in euharamiyidans, does not constitute a sufficient evidence for the group’s mammalian affinity.”

Let’s examine those arguments
in new light shed by the LRT.

  1. Eutriconodonts (Spinolestes, Gobiconodon and kin): These taxa do not nest within Mammalia in the LRT (contra Martin et al. 2015).
  2. Symmetrodontans (Zhangheotherium and kin): Zhangheotherium is a basal pangolin, hence the atavistic teeth, as in another placental clade, the archaeocete ‘whales’.
  3. Spalacotherids (Lactodon = Lactodens): Taxa like Lactodens nest within the prototheria in the LRT.

It always comes back down to phylogenetic analysis.
And the LRT answesr all such problems within its ken. The radiation of placental mammals was in the Early Jurassic based on the appearance of derived placental mammals in the Late Jurassic. Non-mammalian synapsids survived into the Middle Jurassic, so there was plenty of overlap.

Figure 4. Lactodens in situ. This Early Cretaceous protothere has tooth-lined jaws. At 72 dpi this is about 3x larger than life size.

Figure 4. Lactodens in situ. This Early Cretaceous protothere has tooth-lined jaws. At 72 dpi this is about 3x larger than life size.

PS. If you’re wondering about
Lactodens (= Lactodon; Fig. 4; Han and Meng 2018; Early Cretaceous) here it nests at the base of the echidna + platypus clade, two toothless (as adults) taxa. Perhaps that’s why the diphyodont dental rules start breaking down with this taxon, as described by Mao et al.

References
Mao F-Y et al. (5 co-authors) 2018. Evidence of diphyodonty and heterochrony for dental development in euharamiyidan mammals from Jurassic Yanliao Biota. Vertebrata PalAsiatica DOI: 10.19615/j.cnki.1000-3118.180803

https://en.wikipedia.org/wiki/Haramiyida

Rhyncholestes: it’s supposed to be a marsupial…

…but Rhyncholestes raphanurus (Osgood, 1924; long-nosed shrew-opossum, Chilean shrew opossum, extant; snout-vent length 20cm), nests in the large reptile tree (LRT, 1259 taxa) between the squirrel-like tree shrew, Apatemys, and a large living shrew, Scutisorex, all within the placental clade, Glires. Wikipedia and other sources consider this shrew-like South American mammal a marsupial, but Wiki also notes that Rhyncholestes lacks a marsupium (pouch). Females have seven nipples.

Figure 1. Skull of Rhyncholestes along with in vivo photo.

Figure 1. Skull of Rhyncholestes along with in vivo photo.

Rhyncholestes appears to be terrestrial,
nocturnal and an omnivore with a very restricted range (central Chile). Unlike the common shrew, Scutisorex, Rhyncholestes has a complete zygomatic arch and 3 large molars + a fourth vestige molar. That may be why it was considered a marsupial… but that would be pulling a Larry Martin in the LRT, where you need hundreds of traits to determine where a taxon nests.

 

Figure 1. The shrew Scutisorex compared to the apatemyid, Labidolemur from the early Eocene. Despite the difference in time, the teeth are still quite comparable.

Figure 2. The shrew Scutisorex compared to the apatemyid, Labidolemur from the early Eocene. Despite the difference in time, the teeth are still quite comparable. More to the point of today’s blogpost, fewer teeth on a shorter rostrum here than on Rhyncholestes, but otherwise, scores about the same in the LRT.

References
Osgood WH 1924. Review of living caenolestids with description of a new genus from Chile. Field Museum of Natural History Zoological Series 14, 165–173.

wiki/Long-nosed_caenolestid
https://sib.gob.ar/ficha/ANIMALIA*rhyncholestes*raphanurus

Apatemys revisited with DGS

Another short one today
in which the skull elements of Apatemys chardini (Marsh 1872, Eocene, Figs. 1, 2) are restored to their in vivo positions as determined by molar occlusion and jaw glenoid insertion.

Figure 1. Apatemys skull traced and reconstructed using color overlays (DGS). Yes, quite a bit of the mandible appears to be hidden beneath the broken coronoid process.

Figure 1. Apatemys skull traced and reconstructed using color overlays (DGS).

Apatemys chardini (Marsh 1872, Eocene, 50-33 mya) was a squirrel-lke arboreal herbivore with a massive skull. Here it nests between the much larger Trogosus and the more plesiomorphic, Tupaia, a tree shrew. Apatemys had long slender fingers, a long flexible lumbar region, and a long gracile tail.

This taxon also gives rise to the shrew Scutisorex (check out the similar teeth, for instance), and the former tenrecs, Limnogale and Potamogale. All three are extant.

Figure 1. Apatemys, only complete fossil skeleton of an apatemyid, turns out to be a basal shrew. So this clade is not extinct.

Figure 2. Apatemys, only complete fossil skeleton of an apatemyid, turns out to be a squirrel-like  basal shrew. So this clade is not extinct.

References
Marsh OC 1872. Preliminary description of new Tertiary mammals. Part II. American Journal of Science 4(21):202-224.

wiki/Apatemyidae

 

Naked, horned and pocket gophers

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

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

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.

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

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.

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.

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 glīrēsdormice) 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: rodentslagomorphstreeshrewscolugos 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/

Necrolestes: 125 year-old assessment beats recent analysis.

As usual
I had second hand (academic papers and figures) rather than firsthand access to the specimens. It doesn’t matter how good your players are if you don’t show up on the right field at the proper hour. Here you’ll see, once again, how excluding the actual sister to an enigma taxon is the major problem, solvable by second-hand phylogenetic analysis in a large gamut study, the large reptile tree (LRT) that minimizes the problem of taxon exclusion.

Figure 1. Necrolestes skull. Note the scale bar problems. DGS colors the bones here.

Figure 1. Necrolestes skull. Note the scale bar problems. DGS colors the bones here. The lacrimal and infraorbital are enlarged here, providing a large opening for large facial nerves. Note the larger lower incisors as compared to the drawing above.

Necrolestes patagonensis  (Ameghino 1891; early Miocene, 16mya; Fig. 1; YPM PU 15065, 15384, and 15699) has been argued about for over a hundred years. Originally (Ameghino 1891) it was described as the only known extinct placental “insectivore” from South America and allied to Chrysochloris (Fig. 2), the extant golden mole.

Well done Ameghino!

Unfortunately, as time went on…
Saban 1954 considered Necrolestes a palaeanodont (Ernanodon was previously considered one). Patterson 1958 considered it a borhyaenoid metatherian. Asher et al. 2007 looked at several candidates and could not make a firm conclusion. Ladevèze et al. 2008 supported metatherian affinities. Goin et al. 2008 also could not be specific with regard to a closest known sister taxon.

The latest paper on the subject
Rougier et al. 2012 reported, “earlier studies leaned toward placental affinities and more recent ones endorsed either therian or specifically metatherian relationships.” Ultimately they nested Necrolestes with Cronopio (Fig. 4) which they considered a non-therian mammal. That is correct. They considered an earlier Van Valen 1988 statement  inspired, “…the enigmatic Miocene genus Necrolestes, usually thought to be a marsupial, is [conceivably] a late surviving Gondwantherian pantothere.” That is incorrect.

Figure 2. Chrysochloris skull lateral view. Note the many similarities to Necrolestes, including a ventral naris, expanded bulla, and similar shapes for the other bones.

Figure 2. Chrysochloris skull lateral view. Note the many similarities to Necrolestes, including a ventral naris, dorsally expanded bulla, and similar shapes for the other bones. Note the orbit is very tiny in this burrowing taxon. I don’t see an infraorbital foramen. here, distinct from Necrolestes.

Asher et al. 2007 report,
“Characters that support [Necrolestes] status as a therian mammal include a coiled cochlear housing of the inner ear. Necrolestes shows similarities to eutherian mammals, such as small incisive foramina and possibly three molars. Consistent with its status as a metatherian is the presence of five upper incisors, transverse canal foramina, and a broad proximal fibula. However, we cannot confirm other characters claimed by previous researchers as evidence for affinity with marsupial or nonplacental mammals, such as the presence of an inflected mandibular angle and epipubic bones.”

Asher et al. report,
“The external digital flexor in Chrysochloris ossifies along nearly the entire forearm, from the humeral medial epicondyle to the carpus. Necrolestes shows a similarly elongate element stretching proximally from the carpus.”

Asher et al. report,
“The idea that [Necrolestes] is related to golden moles was favored in the first two publications describing its anatomy (Ameghino, 1891; Scott, 1905). We do not believe Patterson’s contention that the status of Necrolestes as a marsupial is ‘‘virtually assured’’. We admit that the list of possible taxonomic affiliations for this animal still remains long.”

Figure 1. The Golden Mole (Chrysocloris asiaticus) nests with the tree shrew and elephant shrew in the large reptile tree, not the common mole. Image copyright Digimorph.org and used with permission.

Figure 3. The Golden Mole (Chrysochloris asiaticus) nests with the tree shrew and elephant shrew in the large reptile tree, not the common mole. Image copyright Digimorph.org and used with permission.

 

 

The large reptile tree
(920 taxa) tested Necrolestes against a wide gamut of mammal candidates and nested it securely with the golden mole, Chrysochloris. To shift Necrolestes next to Cronopio adds 22 steps.

Distinct from sister taxa
Necrolestes had five upper incisors and four lowers. That is closer to the primitive numbers for mammals and two more than in Chrysochloris. The molars are also primitive in having fewer cusps, but that also happens in whales and armadillos… and golden moles… with their simplified zalambdodont teeth… so let’s focus on other traits. Dental traits are plastic and can lead analysis astray.

Rougier et al. report,
“the first upper and lower premolars are double rooted and the following five molariform elements are single rooted, a condition shared only with the recently described meridiolestidan mammal Cronopio.” Convergent dental traits might be leading these workers so far afield the neglected to add Chrysochloris to their analysis, which seems odd and dangerous based on the long list of shared traits and overall similarity, not by convergence.

Figure 4. Cronopio nests between Juramaia and Didelphis + Ukhaatherium in the LRT. Rogier et al. nest this taxon with Necrolestes, contra the LRT. This taxon has an anterior naris, not a ventral one.

Figure 4. Cronopio nests between Juramaia and Didelphis + Ukhaatherium in the LRT. Rogier et al. nest this taxon with Necrolestes, contra the LRT. This taxon has an anterior naris, not a ventral one.

Rougier et al. gave us straw dogs
when they compared the basicrania of several sister candidates, but NOT that of Chrysochloris, to that of Necrolestes. Here I add a basicranium Rougier et al. chose to not show. Chrysochloris more closely matches the morphology of Necrolestes than any of the other three candidates. I don’t see Chrysochloris listed in the Supplemental Information for Rougier et al. which appears to test non-placental mammals only. So this is what I mean by another case of taxon exclusion. Ameghino (1891) got it right originally. Rougier Wible, Beck and Apesteguía 2012, for some reason, dropped the ball.

Figure 3. Necrolestes basicrania compared to three candidates by Rougier 2012. Here I add the basicranium for Chrysochloris for comparison and it's a better match.

Figure 3. Necrolestes basicrania compared to three candidates by Rougier 2012. Here I add the basicranium for Chrysochloris for comparison and it’s a better match. The blue element is the posterior mandible, which is not shown on the Rougier et al. drawings. Not how the lower (posterior) element curls over the basicranial element in only two candidates here. This is a placental trait. The LRT uses no petrosal traits, but image speaks for itself. Excluding the actual sister taxon was done for reasons unknown in this flawed study.

 

Deleting Chrysochloris from the LRT
nests Necrolestes with the remaining basal Glires, but resolution is lost. Not sure why, but Necrolestes has a history (see above) of being a confusing taxon when not nested with Chrysochloris.

Deleting all placentals from the LRT,
except Necrolestes, nests it between Didelphis and Asioryctes a node apart from Cronopio. So taxon exclusion doesn’t recover what Rougier et al. recovered.

Now that we have golden moles in Africa and South America
this is evidence that golden moles first appeared before those continents split apart 118 to 115 mya, long before the end of the Cretaceous. Video link here. Naish reports, “Golden moles and tenrecs appear to be close relatives, forming a clade usually termed Afrosoricida Stanhope et al., 1998 (though this is essentially synonymous with Tenrecoidea McDowell, 1958, see Asher (2001)“. That relationship is not supported by the LRT. Golden moles probably first appeared in the Early Jurassic, given that other Glires, multituberculates, split from rodents about the same time and are found as early as Middle Jurassic strata.

Rougier et al. tested earlier studies and found them flawed
Similarly, I tested Rougier et al. and found it flawed. Perhaps someday someone will likewise test this test and present additional insight into this former enigma taxon.

References
Ameghino F 1891. Nuevos restos de mamíferos fósiles descubiertos por Carlos Ameghino en el Eoceno inferior de la Patagonia austral. Especies nuevas, adiciones y correciones [New remains of fossil mammals discovered by Carlos Ameghino in the lower Eocene of southern Patagonia. New species, additions and corrections]. Rev Arg Hist Nat 1:289–328. Spanish.
Asher RJ, Horovitz I, Martin T and Sanchez-Villagra MR 2007. Neither a Rodent nor a Platypus: a Reexamination of Necrolestes patagonensis Ameghino. American Museum Novitates 3546:1-40.
Ladevèze S, Asher RJ, Sánchez-Villagra MR 2008. Petrosal anatomy in the fossil mammal Necrolestes: evidence for metatherian affinities and comparisons with the extant marsupial mole. J Anat 213(6):686–697.
Patterson B 1958. Affinities of the Patagonian fossil mammal Necrolestes. Breviora Mus Comp Zool 94:1–14.
Rougier GW, Wible JR,  Beck RMD and Apesteguía S 2012. The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America.
Saban R 1954. Phylogénie des insectivores [Phylogeny of the insectivores]. Bull Mus Natl d’Hist Nat. Ser 2 26:419–432. in French
Van Valen L 1988. Faunas of a southern world. Nature 333(6152):113.

Tetrapod Zoology on golden moles

http://www.sci-news.com/paleontology/article00737.html

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

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

Figure 1. Daubentonia was considered a primate for over 150 years. Here it nests with Plesiadapis, rodents and rabbits.

Figure 1. Daubentonia was considered a primate for over 150 years. Here it nests with Plesiadapis, rodents and rabbits. It’s the only living plesiadapid. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

References
Gmelin JF 1788. Caroli a Linné systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima tertia, aucta, reformata. – pp. [1-12], 1-500. Lipsiae. (Beer).
Owen R 1863. Monograph on the Aye-Aye ((Chiromys madagascariensis, Cuvier)
Picone B and Sineo L 2012. The phylogenetic position of Daubentonia madagascariensis (Gmelin, 1788; primates, Strepsirhini) as revealed by chromosomal analysis. Caryologia: International Journal of Cytology, Cytosystematics and Cytogenetics 65(3):223-228. online here.
Geoffroy Saint-Hilaire E 1795. La décade philosophique, litteraire, et politique. Memoires d’Histoire Naturelle 4(28):193– 206.
Sterling E. 1994. Taxonomy and distribution of Daubentonia: a historical perspective.Folia Primatologica 62:8-13.
Yoder AD, Vilgalys R and Ruvolo M 1996. Molecular Evolutionary Dynamics of Cytochrome b in Strepsirrhine Primates: The Phylogenetic Significance of Third-Position Transversions. Mol. Biol. Evol. 13(10):1339-1350.

wiki/Aye-aye, Daubentonia
Primates.com/Daubentoniidae
Mammalian species/Daubentonia

The ‘hedgehog’ tenrecs: they nest with hedgehogs

This is a think piece.
You’re going to be faced with

  1. a geographically inspired return of the cloaca (proposed heresy) or
  2. MASSIVE convergence involving everything but the cloaca (current and traditional paradigm)

Arguments will be presented.
You decide which is more parsimonious. We may need to bring in the DNA guys here, and I would welcome them! I don’t think such a study involving a wide range of purported and actual tenrecs has been proposed or done yet. Let me know as I am unaware of published work on this subject.

The present problem had its genesis in whale phylogenetic studies.
Earlier, from skeletal data, the the large reptile tree (LRT) nested odontocete (toothed) whales with tenrecs and mysticete (baleen) whales with hippos and desmostylians.

However
current DNA studies do not support the tenrec – odontocete relationship — perhaps because workers used the lesser hedgehog tenrec (Echinops telfairi, Martin 1838, Figs. 2, 3) in their DNA studies. Echinops is traditionally considered a tenrec, but it may not be one based on bones (Fig. 3) and massive homology/convergence with the European hedgehog, Erinaceus (Figs. 1, 3).

Figure 4. European hedgehog, a member of Glires.

Figure 1. European hedgehog, Erinaceus, a member of Glires.

It’s the cloaca that seems to matter most
in tenrec studies. Plus the location: Madagascar.

Figur3 5. Madagascar hedgehog, is not a tenrec, but another member of Glires.

Figure 2. Madagascar hedgehog tenrec, Echinops, perhaps not a tenrec, but another member of hedgehog family within Glires.

There are two extant hedgehog tenrecs (HHTs):
the greater HHT (Setifer = Ericulus setosus) and the lesser HHT (Echinops telfari). Their skulls are not that different from each other, except in size. They have similar skeletons and spines coats. So we’ll focus on the lesser HHT as other workers have done before.

The problem is
the large reptile tree (LRT) nests Echinops rather convincingly with hedgehogs, like Erinaceus, within Glires, not with tenrecs like Tenrec (Fig. 1). Shifting Echinops to the tenrecs adds 30 steps to the LRT. Shifting the entire tenrec clade (ncluding the odontocetes) to the hedgehogs adds only 12 steps.

We’ve seen something like this before
when the purported tenrec, Potamogale (Du Chaillu 1860, Nicoll 1985; extant), the giant otter shrew that was supposed to be a tenrec, instead nested rather convincingly with shrews, far from tenrecs. It, too, has a cloaca.

Maybe it’s because they’re all from Madagascar.
Not sure what it is about that island that takes a perfectly good set of genital and anal openings and reverts them back into a single primitive cloaca. But that appears to be happening here among unrelated taxa, by convergence.

Among mammals
monotremes have a cloaca and that is most likely the primitive condition, as a cloaca is found in all other reptiles. Most marsupials separate the anus and genitals, so no cloaca is present — except in the very derived marsupial moles. Marsupials are basal to placentals according to the LRT, so any appearance of a cloaca in placentals is a reversal. Thus the Madagascar hedgehogs, the African golden moles and giant otter shrews (Potamogale) that redevelop a cloaca are examples of phylogenetic reversals.

So you  have a choice in nesting these purported tenrecs:

  1. Do you follow the bones and other soft (and prickly, Fig. 2) tissue with the exception of the cloaca?
  2. Or do you follow the cloaca alone? Current taxonomy and experts for over a century favor this choice.

To my knowledge,
mtDNA studies have not been conducted yet to resolve interrelationships among tenrecs and other mammals. If Echinops is indeed a hedgehog, then tenrecs have not been genetically tested against odontocetes. In fact, tell me if I’m wrong, but this may be the first time such a study has been conducted on morphology alone. Asher and Hofreiter 2006 stated at the time: “Due in part to scarcity of material, no published study has yet cladistically addressed the systematics of living and fossil Tenrecidae (Mammalia, Afrotheria).”

Echinops was employed by Mouchaty et al. 2000. Echinops might have been used by Meredith 2011 and Song 2012 to nest tenrecs with golden moles (Chrysocloris) as Afrotheres, related to elephants (Elephas) and hyraxes (Procavia). I don’t see any other tenrecs being used in molecular studies.

Echinops was recently employed by
Suarez 2009 in a study of the vomernasal system (VNS). The distribution of both vomernasal pathways in Eutheria was found to be present in rodents and Echinops, but not in other tested eutherians, none of which included other tenrecs. Of course, hedgehogs nest with rodents in the LRT.

Figure 1. The skulls of Erinaceus (above), Echinops (middle) and Tenrec (below), compared. Note the large premaxillary teeth common to all members of the Glires to the exclusion of other clades, including Tenrecidae.

Figure 3. The skulls of Erinaceus (above), Echinops (middle) and Tenrec (below), compared. Note the large premaxillary teeth common to all members of the Glires to the exclusion of other clades, including Tenrecidae. The anterior maxillary tooth of Erinaceus might be a canine, but it is not at the anterior rim of the maxilla, where one expects a canine.

Let’s compare
a hedgehog, a tenrec and the lesser hedgehog tenrec and perhaps you’ll see that a mistake was made over 100 years ago that continues to adversely affect phylogenetic analyses today. Perhaps a member of Glires has been long considered a member of Tenrecidae by virtue of its location, Madagascar, and its cloaca.

The European hedgehog
Erinaceus europaeus (Linneaus 1758; 20-30cm; extant) this omnivore can roll itself into a ball, erecting its spines for defence. Unlike most Glires, the hedgehog does not have a diastema. The jugal is very tiny in this clade.

The lesser hedgehog tenrec
Echinops telfairi (Martin 1838; extant, 13-17 cm) the lesser or pygmy hedgehog tenrec is widely considered a tenrec, but here it nests with hedgehogs and other Glires including rodents. This omnivore is restricted to Madagascar, home of severalt tenrecs. Note the large canines, like tenrecs and unlike hedgehogs. Note the large premaxillary teeth, like hedgehogs and unlike tenrecs. Unlike tenrecs, the ears are prominent. Like tenrecs, the jugal is absent.

Given that the Madagascar mammals with a cloaca
all do some burrowing, I wonder if the genitals and anus retreated beneath the cover of a single opening in order to keep dirt out? If that’s not the answer, I wonder what the common thread is that these unrelated taxa have that caused that primitive trait to reappear? And I wonder if there are any analyses based on morphology that include several tenrecs and other eutherians for comparison? So far I have found none, so the LRT is shedding light where it may be needed.

If Echinops is indeed a hedgehog with a cloaca
then we have to go get some mtDNA from Tenrec to see if it is a good match for odontocete mtDNA. At present, Tenrec has not been tested for its mtDNA, that I know of, so the whale connection question remains open.

While we’re at it it
count the stomachs in Tenrec. Even odontocetes have subdivided stomachs. Let’s find out when that trait appeared.

References
Asher RJ 2007. A web-database of mammalian morphology and a reanalysis of placental phylogeny. BMC Evol Biol. 7: 108-10 online
Asher  RJ and Helgen KM 2010. Nomenclature and placental mammal phylogeny. BMC Evolutionary Biology 10:102 online
Du Chaillu P 1860. Descriptions of mammals from equatorial Africa. Proceedings of the Boston Society of Natural History, 7, 358–369.
Eisenberg JF and Gould E 1970. The tenrecs: a study in mammalian behavior and evolution. Smithsonian Institution Press, Washington, DC. 138 pp. PDF online
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Martin WCL 1838. On a new genus of insectivorous mammalia. Proceedings of the Zoological Socieety, London, 6:17.
Mouchaty SK, Gullberg A, Janke A, Arnason U 2000. Phylogenetic position of the Tenrecs (Mammalia: Tenrecidae) of Madagascar based on analysis of the complete mitochondrial genome sequence of Echinops telfairi. Zoologica Scripta. 2000, 29 (4): 307-317. 10.1046/j.1463-6409.2000.00045.x.
Nicoll M 1985. The biology of the giant otter shrew *Potamogale velox*. National Geographic Society Research Reports, 21: 331-337.
O’Leary, MA et al. 2013. The placental mammal ancestor and the post-K-Pg radiation of  placentals. Science 339:662-667. abstract
Suárez R, Villalón A, Künzle H and Mpodozis J 2009. Transposition and Intermingling of Gαi2 and Gαo Afferences into Single Vomeronasal Glomeruli in the Madagascan Lesser Tenrec Echinops telfairi. PLoS ONE 4(11): e8005. doi:10.1371/journal.pone.0008005

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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