Readers will know the knives are out for this one
by Ford and Benson 2020 since the large reptile tree (LRT, 1625+ taxa) finds the Parareptilia is polyphyletic and the Varanopidae (1940) is a junior synonym for Synapsida (1903). And yes, Ford and Benson’s cladogram (Fig. 1) suffers from (altogether now): taxon exclusion. The Ford and Benson paper, like many before it, keeps perpetuating the myth of the Parareptilia and other traditional clades.
Figure 1. Cladogram by Ford and Benson 2020, with orange overlay showing taxa in the Archosauromorpha in the LRT. Massive taxon exclusion is the problem with the Ford and Benson tree.
From the abstract:
“Amniotes include mammals, reptiles and birds, representing 75% of extant vertebrate species on land. They originated around 318 million years ago in the early Late Carboniferous and their early fossil record is central to understanding the expansion of vertebrates in terrestrial ecosystems.
By contrast, in the LRT the last common ancestor of all amniotes (= reptiles) is Silvanerpeton from the Viséan (Early Carbonferous, 335mya, not listed in Fig. 1) with a likely genesis earlier since the Viséan includes several other amphibian-like reptiles, also not listed. Ford and Benson need to dip much deeper into the basal Tetrapoda to figure out which taxon is the last common ancestor of the Amniota and which taxa precede it. They make the mistake of considering Tseajaia and Limnoscelis pre-amniotes.The LRT nests them both deep within Amniota / Reptilia.
“We present a phylogenetic hypothesis that challenges the widely accepted consensus about early amniote evolution, based on parsimony analysis and Bayesian inference of a new morphological dataset.”
That would be great, so long as they include pertinent taxa, which they do not.
“We find a reduced membership of the mammalian stem lineage, which excludes varanopids.”
That’s odd because when you add pertinent taxa, the LRT finds an increased membership in the diapsid/mammal stem lineage, the new Archosauromorpha.
“This implies that evolutionary turnover of the mammalian stem lineage during the Early–Middle Permian transition (273 million years ago) was more abrupt than has previously been recognized.”
No one can make valid implications from the Ford and Benson cladogram. It is largely incomplete.
“We also find that Parareptilia are nested within Diapsida.”
This is only possible due to massive taxon exclusion. Ford and Benson omit many taxa that would change the topology of their tree. The Parareptilia include a diverse and polyphyletic assembly of taxa according to the LRT. Ford and Benson are not aware that Lepidosauria are no longer members of the archosauromorph Diapsida.
“This suggests that temporal fenestration, a key structural innovation with important functional implications, evolved fewer times than generally thought, but showed highly variable morphology among early reptiles after its initial origin.”
Just the opposite. In the LRT fenestration evolved MORE times than generally thought.
“Our phylogeny also addresses controversies over the affinities of mesosaurids, the earliest known aquatic amniotes, which we recover as early diverging parareptiles.”
That can only happen with massive taxon exclusion. We’ve known for several years that mesosaurs nest as derived pachypleurosaurs close to thalattosaurs and ichthyosaurs in the LRT. Those pertinent taxa are omitted in Ford and Benson’s paper.
From the introduction:
“The current paradigm of early amniote evolution was established in the late twentieth century. It includes a deep crown group dichotomy between Synapsida (total group mammals) and Reptilia (total group reptiles, including birds), followed by an early divergence of Parareptilia from all other reptiles (Eureptilia).”
Add taxa and the first dichotomy separates the new Archosauromorpha from the new Lepidosauromorpha. This has been online since July 2011 and represents the current paradigm. Ford and Benson are digging into old myths and traditions.
“Furthermore, both molecular and morphological studies have recovered turtles, which lack fenestrae, as diapsids.”
Since molecular studies do not replicate trait studies in deep time molecular studies must be wrong (probably due to epigenetics) and do not employ fossil taxa. So forget genomics in paleontology. Genomics delivers false positives.
“Our analysis includes 66 early fossil members of the amniote crown group, and four crownward members of the amniote stem group, giving a total of 70 operational taxonomic units.”
By contrast the LRT includes 1625+ taxa not biased by prior studies, including dozens of basal vertebrates and basal tetrapods.
“The goal of our study is to examine the deep divergences of the amniote crown group.”
If so, then Ford and Benson need to add dozens to hundreds of more taxa to their incomplete study. A suggested list is found here.
“We excluded recumbirostrans from our analysis. Recumbirostrans have generally been assigned to non-amniote microsaurs, but were recently recovered as early crown group amniotes.”
By contrast the LRT includes seven taxa listed by Wikipedia/Recumbirostra. We learned earlier that previous workers have deleted taxa that otherwise deliver unwanted results. Not sure what is happening in the Ford and Benson paper after their omission of this clade. Those seven recumbirostran taxa nest outside the Reptilia /Amniota in the LRT.
From the Results:
“All our analyses recover parareptiles and neodiapsids as a monophyletic group within Diapsida.”
These are false positive results due to taxon exclusion as shown here.
From the Discussion:
“The sister relationship between parareptiles and neodiapsids, and their relationship to Varanopidae, implies a single origin of temporal fenestration before the common ancestor of these clades.”
These are false positive results due to taxon exclusion as shown here. We’ve known the clade Diapsida is polyphyletic since July 2011 with a last common ancestor in Early Carboniferous amphibian-like reptiles.
Happy holidays, dear readers.
Ford DP and Benson RBJ 2020. The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae. Nature ecology & evolution 4:57–65. SuppData
Modesto SP 2020. Rooting about reptile relationships. Nature Ecology & Evolution 4:10–11.