Labidolemur enters the LRT as a ‘freakish dead-end’ taxon

Labidolemur kayi
(Matthew and Granger 1921; Eocene, 55mya; Fig. 1) was re-described by Silcox et al. 2010 with µCT scans that provided cranial cavity and other never-before-seen details. The several skeletons analyzed in the publication were recovered from freshwater limestone in the Bighorn Basin by co-author Peter Houde of New Mexico State University.

Figure 1. Co-author Jonathan Block holding up the rather complete and articulated skeleton of Labidolemur still encased in a bit of reddish matrix.

Figure 1. Co-author Jonathan Block holding up the rather complete and articulated skeleton of Labidolemur still encased in a bit of reddish matrix.

According to a publicity release
(link below) “Researchers said the new information will aide future studies to better understand the origin of primates. Scientists have disputed the relationships of Apatemyidae, the family that includes L. kayi, for more than a century because of their unusual physical characteristics. With can opener-shaped upper front teeth and two unusually long fingers, apatemyids have been compared to a variety of animals, from opossums to woodpeckers.”

When added to
the large reptile tree (LRT, 1698+ taxa) Labidolemur unsurprisingly nests with Apatemys, within Glires (gnawing placentals). Labidolemur and Apatemys are virtually identical according to the LRT scores, but proportional differences can still be discerned when the two skulls are side-by-side.

So Labidolemur will not help us,
“better understand the origin of primates.”

Silcox et al. 2010 wrote:
“To test all of the hypotheses that have been suggested, it is necessary to include a very broad range of eutherians, including other apatemyids, eulipotyphlans, ‘proteutherians’ (leptictids and palaeoryctids), primates and other euarchontans, and any other groups that might be relevant for accurately reconstructing basal states for larger clades that include those taxa (e.g. carnivorans and gliroids). To this end we have assembled a matrix of 33 in-group taxa and one out-group (Ukhaatherium nessovi) that were assessed for 240 morphological characters (68 postcranial, 45 cranial, and 127 dental.”

Figure 2. Cladoram from and Bloch 2020 lacking many pertinent taxa.

Figure 2. Cladoram from Silcox et sl. 2020 lacking many pertinent taxa. See text for list.

A broad range, indeed, but not broad enough
according to the LRT. Missing taxa include:

  1. All three shrew opossums, which surround Microsyops and Trogosus. Labidolemur correctly nests with Apatemys.
  2. Any metatherians (marsupials), including Caluromys, the proximal outgroup to the Eutheria (placentals) of which Carnivora is the basalmost clade.
  3. Leptictidae are not basalmost placentals, but basal to tenrecs + odontocetes when more taxa are added
  4. Vulpavus and other arboreal, wooly opossum-like Carnivora nest at the base of the Eutheria apart from Erinaceus (hedgehog) and Sorex (shrew) both members of Glires. Missing basal shrew: Uropsilus.
  5. Tupaia is basal to Glires in the LRT. Missing relatives include Macroscelides, Chrysochloris and Necrolestes.
  6. All the rodents and multituberculates are missing. They attract carpolestids and plesiadiformes away from Primates in the LRT.
  7. Altanius requires study, but is represented by teeth and jaw fragments described as plesiadapiform-like.
Figure 2. Apatemys nests as a proximal sister to bats in the Halliday et al. tree. But it shares very few traits with bats. Note the very odd dentition.

Figure 2. Apatemys nests as a proximal sister to bats in the Halliday et al. tree. But it shares very few traits with bats. Note the very odd dentition, largely matched to Labidolemur.

John Wible, is curator of mammals
at the Carnegie Museum of Natural History. After reviewing the Silcox et al. 2010b study, he reported, “It is now clear that any assessment of the origins of primates in the future will have to include apatemyids. Apatemyids are not some freakish dead-end, but significant members of our own history.”

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

Figure 3. Subset of the LRT focusing on Glires and subclades within. Slightly out of date, Ptilocercus now nests basal to colugos, but the nesting of Apatemys has not changed.

The LRT invalidates Wible’s statement.
Instead, apatemyids are indeed ‘some freakish-dead taxa’, nesting in Glires, far from Primates. The myth of a plesiadapid-primate interrelationship (that includes the aye-aye, Daubentonia) is not supported when more taxa are added. In the LRT plesiadapiformes, like Daubentonia, are primate-mimics nesting within Glires close to multituberculates and carpolestids. Simply adding taxa recovers this topology. That’s all it takes.


References
Matthew WD and Granger W 1921. New genera of Paleocene mammals. American Museum Novitates 13:1-7
Silcox MT, Bloch JI, Boyer DM and Houde P 2010. Cranial anatomy of Paleocene and Eocene Labidolemur kayi (Mammalia: Apatotheria), and the relationships of the Apatemyidae to other mammals. Zoological Journal of the Linnean Society160: 773–825.

https://www.floridamuseum.ufl.edu/science/labidolemur-kayi-bizarre-extinct-mammal/https://www.eurekalert.org/pub_releases/2010-10/w-uof101110.php

Heterohyus enters the LRT

Figure 1. Two of several Heterohyus specimens from the Messel Pit of Germany.

Figure 1. Two of several Heterohyus specimens from the Messel Pit of Germany.

Heterohyus nanus (Gervais 1848, late Eocene) from the Messel Pit in Germany nests with Apatemys in the large reptile tree (LRT, 1563 taxa). Relatively few traits differentiate the two. The lumbar region is shorter. The skull is larger. The naris is smaller and higher on the rostrum.

According to Wikipedia members of the Apatemyidae were
“small and presumably insectivorous. Size ranged from that of a dormouse to a large rat. The toes were slender and well clawed, and the family were probably mainly arboreal.[2] The skull was fairly massive compared to the otherwise slender skeleton, and the front teeth were long and hooked, resembling those of the modern aye-aye and marsupial Dactylopsila, both whom make their living by gnawing off bark with their front teeth to get at grubs and maggots beneath.”

The LRT nests apatemyids
as basal members of Glires, not related to other so-called cimolestids, a polyphyletic assembly of placental taxa. according to the LRT. Rather apatemyids are a clade of gnawing tree shrews, now extinct.


References
Gervais P 1848–52. Primates, Microchoeridae? Zoologie et Paléontologie Françaises. Paris, Arthrus Bertrand, text, 2 vols; atlas, 80 pls.

wiki/Heterohyus
wiki/Apatemyidae

 

Dactylopsila, the striped possum, enters the LRT

Dactylopsila trivirgata (Gray 1858) is the extant striped possum (Fig. 1), closely related to the sugar glider, Petaurus and the marsupial lion, Thylacoleo (below), according to the large reptile tree (LRT, 1412 taxa). Dactylopsila is an arboreal marsupial with a prehensile tail the size and proportions of a placental squirrel. The fourth finger is elongated and used to extract beetles and caterpillars from tree bark, analogous to the extant aye-aye, Daubentonia. Dactylopsila, also eats leaves, fruit and small vertebrates.

By convergence
Dactylopsila has similar teeth and overall proportions to the extinct arboreal placental Apatemys (Fig. 2).

Figure 1. Dactylopsila skull in 3 views, plus in vivo. Comparisons to the extinct arboreal placental Apatemys (figure 2) are intriguing, showing convergence.

Figure 1. Dactylopsila skull in 3 views, plus in vivo. Comparisons to the extinct arboreal placental Apatemys (figure 2) are intriguing, showing convergence.

For comparison, we recently looked at Apatemys
here as it relates to the extant shrew opossums Caenolestes and Rhyncholestes, now nesting as apatemyid placentals in the LRT, rather than as traditional didelphid marsupials. The convergence is powerful here. Despite the phylogenetic distance, only 12 extra steps are needed to nest caenolestids with basal didelphids.

Figure 3. Apatemys skull in situ and reconstructed shares several similar traits with the extant striped opossum, Dactylopsila, including a squirrel-like size, elongate fingers and similar teeth.

Figure 2. Apatemys skull in situ and reconstructed shares several similar traits with the extant striped opossum, Dactylopsila, including a squirrel-like size, elongate fingers and similar teeth.

The nesting of Dactylopsila
close to Petaurus (Fig. 3) is not controversial.

Figure 1. Subset of the LRT showing the nesting of Dactylopsila, the striped opossum.

Figure 3. Subset of the LRT showing the nesting of Dactylopsila, the striped opossum, with Petaurus the sugar glider and Thylacoleo, the marsupial lion.

The problem continues to be
the traditional nesting of the marsupial lion, Thylacoleo (Fig. 4), as a member of the wombats (Vombatiiformes), rather than the Phalangeriformes and Petauroidea, as recovered by the LRT (Fig. 3), which points to a bigger problem…

Nowhere in traditional taxon lists
will you find interatheres, toxodontids and creodonts. All these taxa need to be tested in traditional metathere trees because the LRT has tested them and they nest with metatheres. It’s a good time for a confirmation or a refutation. PhD students… are you looking for a good subject to write about for your dissertation?

Figure 2. Thylacoleo skeleton compared to Petaurus skeleton to scale.

Figure 4. Large Thylacoleo skeleton compared to small Petaurus skeleton to scale. Dactylopsila is similar in size to Petaurus.

Here, again,
is where tradition, opinion and bias have, so far, trumped testing. Taxon exclusion needs to be tested with taxon inclusion. The list of taxa needing testing is provided by the LRT.


References
Gray JE 1858. List of species of Mammalia sent from the Aru Islands by Mr A.R. Wallace to the British Museum. Proceedings of the Zoological Society of London. 26: 106–113.

wiki/Striped_possum – Dactylopsia trivirgata

Shrew opossums (caenolestids) are supposed to be marsupials

According to Wikipedia,
“The family Caenolestidae contains the seven surviving species of shrew opossum: small, shrew-like marsupials that are confined to the Andes mountains of South America.”

Figure 1. Caenolestes skull and in vivo.

Figure 1. Caenolestes skull and in vivo. It sure looks more like a shrew than an opossum. Skull images from Digimorph.org and used with permission. Colors added.

The trouble is
tested caenolestids, Caenolestes (Fig. 1) and Rhyncholestes (Fig. 2), do not have a pouch. Nor do they nest with marsupials in the large reptile tree (LRT, 1412 taxa, subset Fig. 3). But female caenolestids do have a marsupial-like double vagina (see below).

On the traditional side,
Dr. Darren Naish reported online for Tetrapod Zoology/Scientific American in 2015, “Incidentally, the most frequently used name for the group – shrew-opossums – might not be a particularly good one, seeing as they don’t look much like shrews, don’t live like shrews, and don’t act like shrews. And they’re not technically opossums, either, but perhaps we can let that go.”

Contra Dr. Naish’s amusing musings,
shrew opossums nest with placental shrews alongside the otherwise extinct Apatamys (Fig. 3) + Trogosus (Fig. 4) in the Glires clade. All are derived from a tree shrew taxon close to Tupaia. It’s unfortunate that Dr. Naish did not test these taxa while they were on his mind in 2015. That’s how initial errors become perpetuated as long-standing traditions.

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

Figure 2. Skull of Rhyncholestes along with in vivo photo.

Rhyncholestes raphanurus (Osgood, 1924; long-nosed shrew-opossum, Chilean shrew opossum, extant; snout-vent length 20cm), nests in the large reptile tree between the shrew-mole, Uropsilus, and the tree shrew, Tupaia at the base of the Apatemys clade. 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).

Figure 2. Apatemys nests as a proximal sister to bats in the Halliday et al. tree. But it shares very few traits with bats. Note the very odd dentition.

Figure 3. Apatemys nests as a proximal sister to bats in the Halliday et al. tree. But it shares very few traits with bats. Note the shrew-opposum/rodent-like dentition.

Genetically
Wikipedia reports. “Genetic studies indicate that they are the second most basal order of marsupials, after the didelphimorphs” (Nilsson et al. 2010). That’s exactly where the LRT documents the splitting of eutherian mammals from the phytometatherians and carnimetatherians.  Even so, we’re talking about deep time here. Don’t trust genes. Test traits.

Figure 3. Subset of the LRT focusing on primates and basal glires, including the caenolestids, Caenolestes and Rhyncholestes.

Figure 4. Subset of the LRT focusing on primates and basal glires, including the caenolestids, Caenolestes and Rhyncholestes.

According to AnimalDiversity.org, “In general, members of family Caenolestidae can be distinguished from other marsupial groups by their unique dentition. Their lower middle incisors are large and have a forward slope; likewise, they have a reduced number of incisors. The dental formula for genus Caenolestes is: I 4/3, C 1/1, P 3/3, M 4/4, 46 teeth total. Shrew opossums have short robust limbs, each containing 5 digits; their middle 3 digits are shorter than the outside two. Their humeri are extremely heavy; in comparison, their femurs are relatively slender. Members of family Caenolestidae have unusual lip flaps, they may function as a method of preventing debris from interfering with their whiskers or they may help prevent ingestion of unwanted debris. Similar to other marsupials, Caenolestid females have 2 uteri and 2 vaginas. Members of genus Caenolestes lack a pouch but do have 4 mammae, 2 on either side of their abdomen.”

Unfortunately
the LRT tests only skeletal material, not for ‘number of uteri and vaginas’. While Larry Martin and Darren Naish might wave this trait about in support of a marsupial affinity, the LRT documents the emergence of placentals from marsupials. So the reappearance of a long-lost trait, like a long tail, a sixth digit, or double vaginas is well within the realm of possibilities in placentals.

As a matter of fact,
a double vagina sometimes occurs in humans.

Here, as elsewhere in paleontology,
maximum parsimony is the only yardstick. PAUP is free to nest taxa wherever 231 unbiased scores indicate it should. Moving the two caenolestids to the Metatheria adds 12 steps to the MPT.

The Apatamyidae is a clade that was long considered extinct.
Now it joins several other clades that are no longer extinct, thanks to the LRT.

Rhyncholestes raphanurus (Osgood, 1924; long-nosed shrew-opossum, Chilean shrew opossum, extant; snout-vent length 20cm), nests in the LRT between the shrew-mole, Uropsilus, 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).

Caenolestes fuliginosus (originally Hyracodon fuliginosus Tomes 1863)

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


References
Marsh OC 1872. Preliminary description of new Tertiary mammals. Part II. American Journal of Science 4(21):202-224.
Nilsson MA, et al. (6 co-authors) 2010. Tracking Marsupial Evolution Using Archaic Genomic Retroposon Insertions”. PLoS Biology. 8 (7): e1000436. doi:10.1371/journal.pbio.1000436
Osgood WH 1924. Field Mus. Nat. Hist. Publ., Zool. Ser. 14:170.

tetrapod-zoology/you-never-hear-much-about-shrew-opossums/
wiki/Shrew_opossum = Caenolestidae
animaldiversity.org/accounts/Caenolestes_fuliginosus/
wiki/Apatemyidae
wiki/Rhyncholestes
wiki/Caenolestes
wiki/Paucituberculata
wiki/Uterus_didelphys

Click here for Glires skulls compared.

Newsflash: Shrews evolved from Apatemyidae! (or vice versa)

Wikipedia reports,
“A shrew (Figs. 2, 3) or shrew mouse (family Soricidae) is a small mole-like mammal classified in the order Eulipotyphla.”

“Apatemyidae is an extinct family of placental mammals that took part in the first placental evolutionary radiation together with other early mammals such as the leptictids.” 

Figure 3. Apatemys skull in situ and reconstructed shares several similar traits with the extant striped opossum, Dactylopsila, including a squirrel-like size, elongate fingers and similar teeth.

Figure 1a. Apatemys skull in situ and reconstructed shares several similar traits with the extant striped opossum, Dactylopsila, including a squirrel-like size, elongate fingers and similar teeth. Note the stronger similarities recovered by the LRT with the shrew, Scutisorex (figure 2).

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

Figure 1b. Apatemys, only complete fossil skeleton of an apatemyid, turns out to be an Eocene sister to the shrew. So this clade is not completely extinct.

As it turns out
shrews are less like moles in the large reptile tree and more like members of the Apatemyidae, like Apatemys (Marsh 1872; Fig. 1),  thought to have originated in the Paleocene and disappeared in the Eocene. Both are derived. At present they nest as sisters. Neither can be shown, at present, to be more primitive than the other.

Apatemys chardini (Eocene, 50-33 mya; Fig. 2) was a squirrel-lke arboreal herbivore with a massive skull. It had long slender fingers, a long flexible lumbar region, and a long gracile tail. From head to tail, the matrix scores for apatemyids and shrews are quite similar. It’s not just the dentition, which remains amazingly conservative in living shrews.

By contrast
moles have a set of small procumbent anterior dentary teeth and the posterolateral premaxillary teeth are large and canine-like while the medial premaxillary teeth are small like typical incisors. Moles nest closer to Solenodon and rodents [and I need to update that webpage].

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 and unique to themselves. Note sure how this was overlooked. The resemblance is remarkable.

Wikipedia reports,
“Like most Paleocene mammals, the Apatemyids were small and presumably insectivorous. Size ranged from that of a dormouse to a large rat. The toes were slender and well clawed, and the family were probably mainly arboreal.The skull was fairly massive compared to the otherwise slender skeleton, and the front teeth were long and hooked, resembling those of the modern aye-aye and marsupial Dactylopsila, both whom make their living by gnawing off bark with their front teeth to get at grubs and maggots beneath.”

Evidently others have missed the shrew connection. Let me know of any literature that predates this blogpost. I’d like to promote it, if it’s out there.

Figure 2. Scutisorex (below) and Crocidura (above) are extant shrews.

Figure 3. Scutisorex (below) and Crocidura (above) are extant shrews.

The book ‘Evolution of Shrews’ reports,
“Shrews are among the most ancient of all living mammals. They are small and have rather unspecialized body plans, retained almost unchanged since they evolved about 45 million years ago. They appear to be extremely successful as a group in comparison to all other families of Insectivora: the living species of shrews represent approximately 80% of all insectivorans, which in turn make up some 10% of all mammmalian species extant today.”

The apatemyid connection described here
pushes the origin of shrews back another 5-10 million years. True shrews are not to be confused with elephant shrews. They are more closely related now, then what was recovered earlier, but more work needs to be done to figure this out precisely. Then I’ll update the cladogram.

Afterthought
Earlier I posted on Hyopsodus, the pre-dog, former condylarth. One the images appeared in editing, but did not appear in publication. I was not aware of this until today. The JPEG had a ‘bad marker’, whatever that is. Please let me know if you see a technical problem here. That Hyopsodus image has been repaired and is visible now.

References
Churchfield S 1990. The Natural History of Shrews online. Comstock Publishing; 1st edition (January 1990) Amazon link.
Multiple Authors 1998. Evolution of Shrews. Edited By: JM Wójcik and M Wolsan. Cornell Paperbacks. 458 pp.  online.
Gingerich PD and Rose KD 1982. 1. Dentition of Clarkforkian Labidolemur kayiGingerich PD 1982. 2. Labidolemur and Apatemys from the early Wasatchian of the Clark’s Fork Basin, Wyoming. Studies on Paleocene and Early Eocene Apatemyidae (Mammalia, Insectivora). Contributions from the Museum of Paleontology. The University of Michigan. 26(4):49-69.
v. Koenigswald W, Schierning H-P 1987. The ecological niche of an extinct group of mammals, the early Tertiary apatemyids. Nature. 326 (6113): 595–597. doi:10.1038/326595a0.
Marsh OC 1872. 
Preliminary description of new Tertiary mammals. Part II. American Journal of Science 4(21):202-224.

wiki/Apatemyidae