Insectivore ancestors to extant odontocetes
This post should illustrate
the difficulty in recovering a single tree of 600+ extant and extinct mammals. We’ll focus today on the ancestors of odontocetes (dolphins and kin) today (Figs 1, 2). Here those ancestors extend back to Triassic marsupials, more or less apart from other placental taxa.
I trashed the earlier post
that featured the mammal subset of the LRT, because (drum roll, please) once again it changed! I was working on primates at the time when marsupial termite-eaters (Myrmecobius, Fig 3) decided on their own to move closer to placental termite-eaters (xenarthran2 taxa) and their relatives. And that’s OK. The cladogram was showing me something I needed to look at.
Perhaps this peek behind the curtain will help readers understand the fragility of some sections of the mammal subset of the LRT. Other parts remain unchanged over the last 330 days of changes.
Figure 1. Odontocete ancestors in the LRT.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors588.jpg?w=64″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors588.jpg?w=218″ class=”size-full wp-image-91920″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors588.jpg” alt=”Figure 1. Odontocete ancestors in the LRT. ” width=”584″ height=”2747″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors588.jpg?w=584&h=2747 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors588.jpg?w=32&h=150 32w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors588.jpg?w=64&h=300 64w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Odontocete ancestors in the LRT. Gray taxa are marsupials. Gold taxa are placentals.
Character #238 in the mammal subset of the LRT
is Reproduction: 1. egg-laying, 2. didelphid marsupial, 3. monodelphid marsupial, or 4. placental. The second cladogram (Fig 2) was recovered by deleting character #238. In theory this should not have resulted in much change. In practice it did result in certain changes. Given these parameters, why the two cladogram subsets differ at the top half (Figs 1, 2) is not yet understood. Certainly it goes back to scoring issues, as today’s changes and every other days’ changes historically indicate. A closer look is required.
Experiments like this are part of the scientific method.
Transparency like this is part of the scientific method.
Figure 2. Odontocete ancestors sans the reproduction mode character.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors.sans_.reproduction.jpg?w=94″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors.sans_.reproduction.jpg?w=319″ class=”size-full wp-image-91922″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors.sans_.reproduction.jpg” alt=”Figure 2. Odontocete ancestors sans the reproduction mode character. ” width=”584″ height=”1873″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors.sans_.reproduction.jpg?w=584&h=1873 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors.sans_.reproduction.jpg?w=47&h=150 47w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors.sans_.reproduction.jpg?w=94&h=300 94w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/odontocete.ancestors.sans_.reproduction.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Odontocete ancestors sans the reproduction mode character. The top half is different than the top half of figure 1.
The purple highlighted taxa
in figures 1 and 2 are shown here (Fig 3). Myrmecobius, the extant numbat, is a marsupial that lives on termites, ‘the sole member of the family Myrmecobiidae, a clade within the Dasyuromorpha’ according to Wikipedia – Numbat.
In the LRT
(Figs 1, 2) the numbat is not alone.
Numbat biography abbreviated:
Unusual for marsupials it is diurnal and the retina includes many cone cells. Females lack a pouch. Newborns crawl to one of four teats and remain attached for the next six months. Thereafter the young are carried on the mother or remain in a nest.
So numbats have placental precursor behaviors and traits.
Figure 3. Myrmecobius, Leptictis and Rhynchocyon (the purple taxa in figure 1 and 2) have similar skulls and post-crania.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/myrmecobius_leptictis588.jpg?w=136″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/myrmecobius_leptictis588.jpg?w=465″ class=”size-full wp-image-91924″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/myrmecobius_leptictis588.jpg” alt=”Figure 3. Myrmecobius, Leptictis and Rhynchocyon (the purple taxa in figure 1 and 2) have similar skulls and post-crania. ” width=”584″ height=”1287″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/myrmecobius_leptictis588.jpg?w=584&h=1287 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/myrmecobius_leptictis588.jpg?w=68&h=150 68w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/myrmecobius_leptictis588.jpg?w=136&h=300 136w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/myrmecobius_leptictis588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Myrmecobius, Leptictis and Rhynchocyon (the purple taxa in figure 1 and 2) have similar skulls and post-crania. The only two taxa in the LRT with ossified ‘eyebrows’ are Myrmecobius and Rhynchocyon. These two also share the trait of large, straight lumbar ribs, apparently by convergence at this point. Note the descending flange of the jugal (cyan) in Myrmecobius. That reappears in Holmesina (Fig 4).
Please note
Leptictis descendants include insectivorous tenrecs on one branch and similarly long-snouted insectivorous xenarthran2 taxa on the other. The resemblance of Leptictis to the much larger armadillo with a full set of teeth, Holmesina (Fig 4), was noted earlier.
The only two mammal taxa in the LRT
with ossified lateral ‘eyebrows’ are the marsupial Myrmecobius and the placental Rhynchocyon (Fig 3). Despite their phylogenetic separation, these two also share the trait of large, straight lumbar ribs, apparently by convergence.
These similar insectivorous taxa
(Figs 1–4) split from one another a few tens to hundreds of million years ago, so be aware that each one has likely evolved in its own way ever since.
Even so, shared traits link them more or less together for the first time in the LRT.
Figure 4. The armadillo with a full set of teeth, Holmesina, shown surrounded by related taxa, including Leptictis.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/holmesina_skull_mandible588.jpg?w=99″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/holmesina_skull_mandible588.jpg?w=337″ class=”size-full wp-image-91927″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/holmesina_skull_mandible588.jpg” alt=”Figure 4. The armadillo with a full set of teeth, Holmesina, shown surrounded by related taxa, including Leptictis.” width=”584″ height=”1773″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/holmesina_skull_mandible588.jpg?w=584&h=1773 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/holmesina_skull_mandible588.jpg?w=49&h=150 49w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/holmesina_skull_mandible588.jpg?w=99&h=300 99w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/holmesina_skull_mandible588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 4. The armadillo with a full set of teeth, Holmesina, shown surrounded by related taxa, including Leptictis.
Housekeeping the LRT
continues unabated. Today’s insights are progress of one sort or another. We’ll see… Hopefully these efforts will help others over time with their own 600+ taxa, trait-based mammal studies.
It’s been like herding cats. Other LRT subsets, both larger and smaller, were easier, more stable during reconstruction.
Source: https://pterosaurheresies.wordpress.com/2025/03/11/insectivore-ancestors-to-extant-odontocetes/
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