Brocklehurst 2024 ventures into the ‘mammalian stem’ without a cladogram

Brocklehurst 2024 wrote in his introduction,
“The mammal lineage separated from the reptile-line amniotes during the Paleozoic between 315 and 330 million years ago (e.g., citations).

Figure 1. Megazostrodon, an early mammal, along with Hadrocodium, a Jurassic tiny mammal. ” data-image-caption=”

Figure 1. Megazostrodon, an a Jurassic mammal, along with Hadrocodium, a Jurassic tiny mammal.

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2015/07/megazostrodon.jpg?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2015/07/megazostrodon.jpg?w=584″ class=”size-full wp-image-19487″ src=”https://pterosaurheresies.files.wordpress.com/2015/07/megazostrodon.jpg?w=584&h=330″ alt=”Figure 1. Megazostrodon, an early mammal, along with Hadrocodium, a Jurassic tiny mammal.” width=”584″ height=”330″ srcset=”https://pterosaurheresies.files.wordpress.com/2015/07/megazostrodon.jpg?w=584&h=330 584w, https://pterosaurheresies.files.wordpress.com/2015/07/megazostrodon.jpg?w=150&h=85 150w, https://pterosaurheresies.files.wordpress.com/2015/07/megazostrodon.jpg?w=300&h=169 300w, https://pterosaurheresies.files.wordpress.com/2015/07/megazostrodon.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 1. Megazostrodon, the basal-most mammal in the LRT, along with Hadrocodium, a tiny Jurassic mammal, shown full-scale on a 72-dpi monitor.

When a paper starts off this off-kilter
we can surmise the author has committed several of the most common sins in paleontology: 1) taxon exclusion and 2) arguments based on trusting the work of others.

Specific problems in the first sentence:
Amniota has been a junior synonym for Reptilia in the LRT since 2011. So there is no such thing as a reptile-line amniote. A cladogram would have recovered this to the author.

From the Early Carboniferous (Viséan, 346–330 mya) Silvanerpeton (Fig 2) is the current last common ancestor (LCA) of the Reptilia (= Archosaurmorpha + Lepidosauromorpha + Silvanerpeton). There are many Viséan archosauromorphs known, so the Reptilia likely split even earlier. A complete cladogram would have recovered this to the author.

Brocklehurst does not identify any LCA even though this is vital to this paper.

We can blame Modesto and Anderson 2004 for redefining Reptilia to exclude Synapsida, but everyone else who did not test that hypothesis is also at fault.
(More on this 2004 definition below).

Getting back to mammals and stem mammals – In the large reptile tree (LRT, 2312 taxa) late surviving Early Permian Vaughnictis (ironically renamed by Brocklehurst et al  2016) is the last common ancestor of birds and bats (i.e. when bird-line synapsids and diapsids separated from mammal-line synapsids). So synapsids and diapsids shared a long list of taxa after Silvanerpeton and before Vaughnictis. A cladogram would have showed this to the author.

Figure 2. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota. ” data-image-caption=”

Figure 2. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota.

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2014/10/silvanerpeton588.jpg?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2014/10/silvanerpeton588.jpg?w=584″ class=”size-full wp-image-16415″ src=”https://pterosaurheresies.files.wordpress.com/2014/10/silvanerpeton588.jpg?w=584&h=492″ alt=”Figure 2. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota.” width=”584″ height=”492″ srcset=”https://pterosaurheresies.files.wordpress.com/2014/10/silvanerpeton588.jpg?w=584&h=492 584w, https://pterosaurheresies.files.wordpress.com/2014/10/silvanerpeton588.jpg?w=150&h=126 150w, https://pterosaurheresies.files.wordpress.com/2014/10/silvanerpeton588.jpg?w=300&h=253 300w, https://pterosaurheresies.files.wordpress.com/2014/10/silvanerpeton588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 2. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota.

Continuing…
“For the first 100 million years of their evolutionary history, a substantial diversity of stem mammal lineages dominated terrestrial ecosystems (citations). These stem mammals include a range of clades and forms, some of which pass through the end-Permian and end-Triassic mass extinctions and persist in the fossil record throughout much of the Mesozoic (citations).

In other words, these are the traditional members of the non-mammalian Synapsida.

“The identity and age of the youngest stem mammal is uncertain; they potentially survived into the earliest Cenozoic (citations).

Here, again, a cladogram would have identified this ‘youngest stem mammal’= non-mammalian synapsid/cynodont. Googling this term only brings us back to Brocklehurst 2024. That means he was the first author to ever string these three words together.

In the LRT Early Cretaceous Repenomamus is a late-surviving non-mammal cynodont known from complete skeletons, nesting outside the Monotremata. A cladogram would have showed this to the author.

“From this point until the present day, the descendants of a single common ancestor have consistently been the sole representatives of the mammal line, remaining today as the mammalian crown.”

Brocklehurst leaves that LCA of the mammals to our imagination. In the LRT that LCA is Late Triassic Megazostrodon (Fig 2), the proximal outgroup to the Montremata + Metatheria. Wikipedia identifies Morganucodon as a non-mammal mammaliaform. It will be when a better LCA is identified, but that would be in the realm of imagination and supposition. We want current facts.

The second paragraph fares no better.
“The mammalian crown, consisting today of monotremes, marsupials and placental mammals, originated during the Mesozoic.

Again, no LCA identified. A complete cladogram would have recovered this to the author.

“The precise timing of this origin is uncertain, due to the uncertain affinity of Triassic mammal-line fossils.

In the LCA this timing is certain. It might change with future finds, but, then, that’s, again in the realm of uncertainty and imagination.

“Von Huene (1940) described a premolar from the Rhaetian (latest Triassic) of Germany, suggesting it had similarities to multituberculates (a now-extinct crown-mammal lineage). However, he did not include detailed comparison of the specimen with multituberculates, nor did he included a museum catalogue number, thus precluding further study of the specimen. The prevalence of specimens based on limited material assigned to crown mammal lineages persists into the Lower Jurassic, although many of these were more confidently assigned to species level (e.g., citations).

Late Triassic Brasilitherium (known from a complete skull) is an early platypus with teeth. Not as primitive as Morganucodon, together they point to an earlier, as yet unknown LCA. A complete cladogram would have recovered this to the author.

“But it is still unclear how reliable an identification based on such material, dominated by isolated teeth, may be (citations). Also known from the Rhaetian and Early Jurassic are haramiyidans, a lineage of mammals of uncertain affinity.

By contrast, in the LRT Haramyavia is a pre-mammal cynodont nesting certainly with Brasilodon and Sinoconodon, which continued to replace teeth throughout their lifetime. Mammals are defined by mammae (= milk producing organs) employed by toothless infants. Single-tooth replacement is evidence associated with this practice).

Many phylogenetic analyses have found them to be within the mammalian crown, as an outgroup to the clade containing marsupials and placental mammals (e.g., citations). However, others have found haramiyidans to be stem mammals.”

Try to not argue your way through a paper by citing other authors, especially if they are doing the same and doing it poorly. The blame for doing so will always fall on you… eventually. Do the necessary work. Build your own LRT.

On the plus side,
this is one of the very few single author papers I’ve seen lately.

Figure 1. Color tracings of bones moved to their in vivo positions and traced. ” data-image-caption=”

Figure 1. Color tracings of bones moved to their in vivo positions and traced.

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2016/06/vaughnictis-new-recon588.gif?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2016/06/vaughnictis-new-recon588.gif?w=584″ class=”size-full wp-image-23245″ src=”https://pterosaurheresies.files.wordpress.com/2016/06/vaughnictis-new-recon588.gif?w=584&h=560″ alt=”Figure 1. Color tracings of bones moved to their in vivo positions and traced.” width=”584″ height=”560″ srcset=”https://pterosaurheresies.files.wordpress.com/2016/06/vaughnictis-new-recon588.gif?w=584&h=560 584w, https://pterosaurheresies.files.wordpress.com/2016/06/vaughnictis-new-recon588.gif?w=150&h=144 150w, https://pterosaurheresies.files.wordpress.com/2016/06/vaughnictis-new-recon588.gif?w=300&h=288 300w, https://pterosaurheresies.files.wordpress.com/2016/06/vaughnictis-new-recon588.gif 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 3. Vaughnictis, color tracings of bones moved to their in vivo positions and traced.

Getting back to Modesto and Anderson 2004, who wrote,
“Reptilia has four definitions of which we are aware.”

So they added a fifth bogus definition ‘on the fly’ without a comprehensive, wide gamut cladogram to support their assertion.

“We offer a new stem-based definition for Reptilia: the most inclusive clade containing Lacerta agilis Linnaeus 1758 and Crocodylus niloticus Laurenti 1768, but not Homo sapiens Linnaeus 1758.”

In the LRT Homo and Crocodylus share a LCA (Vaughnictis (Fig 3), again) not shared with Lacerta. The LCA of Lacerta and Crocodylus is currently Silvanerpeton.

While a laudable attempt, Modesto and Anderson were not aware that seven years later (2011) the LRT would recover Reptilia = Archosauromorpha + Lepidosauromorpha. Silvanerpeton would be added to the LRT some time later. A complete (= wide gamut) cladogram authored by Modesto and Anderson would have recovered this result years earlier and avoided the last two decades of myth.

Creating cladograms is the duty and job of paid paleontologists.
If you want to be a paleontologist, don’t submit any phylogenetic manuscript without a wide gamut phylogenetic analysis. And don’t make up clade definitions ‘on the fly’ or with ‘careful consideration’ or based on the work of others. Provide evidence! Build your own LRT. We count on you professionals to do this.

When you don’t do the work, expect to hear from independent researchers who are not under the academic pressure to ‘publish or perish‘ and who are more than willing to change hypotheses and make corrections when mistakes are made and/or added taxa shift things around.

All the above also applies to professional editors and referees. Do the right thing.

References
Brocklehurst N, Reisz RR, Fernandez V and Fröbisch 2016. A Re-Description of ‘Mycterosaurus’ smithae, an Early Permian Eothyridid, and Its Impact on the Phylogeny of Pelycosaurian-Grade Synapsids. PLoS ONE 11(6):e0156810. doi:10.1371/journal.pone.0156810
Brocklehurst N 2024. The decline and fall of the mammalian stem. PeerJ 12:e17004 http://doi.org/10.7717/peerj.17004
Modesto SP and Anderson JS 2004. The phylogenetic definition of Reptilia. Systematic Biology. 53(5): 815–821.

wiki/Synapsid
wiki/Publish_or_perish

Vaughnictis (Brocklehurst et al. 2016): a new last common ancestor of birds and bats