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

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