Let’s talk about mammal interrelationships

Now that a wide gamut of mammals
has been added to the large reptile tree (LRT, subset Fig. 1), the tree topology has become distinct from prior studies, many of which depend on DNA, which does well in many cases, but makes untenable sisters of several genera.

Figure 1. Mammal subset of the large reptile tree with clades named.

Figure 1. Mammal subset of the large reptile tree with clades named. This needs to be updated with Onychodectes nesting closer to Ectoconus + Pantolambda and Maelestes taking its place. See the large reptile tree for other changes due to added taxa.

Case in point: Macroscelidea
(elephant shrews, Fig. 2). Stanhope et al. (1998) proposed the clade Afrotheria based on molecular evidence. Their clade members included elephants and elephant shrews. That’s difficult to accept on the face of it, and the large reptile tree does not recover that relationship.

Figure 2. Macroscelides proboscideus, the elephant shrew or sengis is NOT more closely related to elephants with the purported 'Afrotheria.' but instead is related to Tupaia, the tree shrew.

Figure 2. Macroscelides proboscideus, the elephant shrew or sengis is NOT more closely related to elephants with the purported ‘Afrotheria.’ but instead is related to Tupaia, the tree shrew.

Rather
the large reptile tree recovers:

  1. Monotremata (Ornthorhynchus) as the most basal mammal clade.
  2. Didelphis (opossum) is basal to both Metatheria (so far only three genera) and Eutheria.
  3. The first eutherian split occurs between small carnivores and smaller insectivores
  4. Carnivora also splits into small insectivores: Chiroptera + (Dermoptera + Primates, including Manis)
  5. The two tree shrews, Tupaia and Ptilocercus, are not sister taxa.
  6. The former clade Insectivora is resurrected. It includes Tupaia + elephant shrews, Trogosus + Apatemys and Glires.
  7. Glires includes the traditional rabbits and rodents, but also shrews, moles and multituberculates
  8. Condylartha is resurrected and includes ungulates, xenarthrans and paenugulates.
  9. Maelestes gives rise to tenrecs, which give rise to giant tenrecs and whales.
  10. Onychodectes + (Pantolambda + Ectoconus) give rise to Xenarthra (sloths, anteaters), Paenungulata (elephants and kin) and Ungulata (hoover mammals).

Not only do these relationships make more sense
on their face, they provide a gradual accumulation of derived characters down to the toes. You can’t do that with ‘Afrotheria’ and other odd-bedfellow sisters that have become widely accepted within paleontology, despite the fact that they make no sense at several nodes. At other nodes, some DNA clades do match morph studies.

Once again,
we need to look at the results, put our thinking caps on, and toss out DNA results that do not make sense and cannot be supported with morphological studies.

Don’t take my word for it.
I’m reporting results, like Galieo looking through a telescope for the first time or dropping balls off the leaning tower of Pisa. Because this is Science, you can repeat the experiment and discover the mammal family tree for yourself. If you do, let us all know what you recover.

References
Stanhope MJ, Waddell VG, Madsen O, de Jong W, Hedges SB. Cleven GC, Kao D and Springer MS 1998. Molecular evidence for multiple origins of Insectivora and for a new order of endemic African insectivore mammals. Proceedings of the National Academy of Sciences 95 (17): 9967–9972. Bibcode:1998PNAS…95.9967S. doi:10.1073/pnas.95.17.9967. PMC 21445. PMID 9707584.

6 thoughts on “Let’s talk about mammal interrelationships

  1. Just out of curiosity, how many extra steps does it take to constrain the tree to match Novacek’s (1992) morphology-based hypothesis of mammal relationships?

  2. I’m looking at Novacek 1992 now. Almost apples and oranges due to suprageneric taxa (as presented, perhaps not originally) vs. specific taxa. I see his multis are basal to therians, but they are not plesiomorphic in their traits. I don’t know anything about palaeoryctoids, but a quick Google search appears to show it is not a well used term. The basal placement of Xenarthra is at odds with the present study that nests them within Condylarthra. Pholidota are now odd primates, not related to Xenarthra. Broad agreement on {Glires + Tree shrews} + {bats + primates + carnivores). Tubilidentata and Cetacea no longer are associated with Artiodactyla. The ungulates are in broad agreement. Where shifts are present, they are major. Not sure I want to get into shifting more than one or two taxa. Novacek was unsure about hyracoidea, but all workers, including yours truly, now nest them with Sirenia and Proboscidea.

    • The current consensus puts palaeoryctoids close to taeniodonts, tillodonts and/or pantodonts, with these as either basal eutherians (where Novacek put them) or stem-carnivorans (where McKenna 1975 and McKenna & Bell 1997 put them).

  3. The main reason I currently have trouble accepting your tree of mammals is the placement of multituberculata, due to the earliest multituberculata showing up ~160 million years ago (eg: Paulchoffatiidae and Rugosodon). If your tree is correct this would require mammals as a whole to evolve 10s of millions of years earlier than commonly accepted (regardless of whether you use the fossil record or DNA). The current accepted position – that multituberculata and rodents are a case of convergent evolution – seems far more convincing.

    Having said that, I find some other aspects of your tree quite interesting. The inclusion of whales with tenrecs, for example, is fascinating and makes a surprising amount of sense; I’m surprised it hasn’t been noticed before.

    https://en.wikipedia.org/wiki/Paulchoffatiidae
    http://america.pink/images/3/4/4/1/8/4/9/en/2-paulchoffatiidae.jpg . . . // an illustration of a skull

    https://en.wikipedia.org/wiki/Rugosodon
    http://science.sciencemag.org/content/sci/suppl/2013/08/15/341.6147.779.DC1/Yuan-SM.pdf . . . // starting at pg 4 has photos and tracings of Rugosodon

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