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https://doi.org/10.7554/eLife.107021.3
Cryptovaranoides, a Late Triassic animal (some 230 Ma old), was originally described as a possibly anguimorph squamate, i.e., more closely related to snakes and some extant lizards than to other extant lizards, making Squamata much older than previously thought and providing a new calibration date inside it. Following a rebuttal and a defense, this fourth
contribution to the debate makes a
argument that Cryptovaranoides is not a squamate. Further comparisons to potentially closely related animals such as early lepidosauromorphs would greatly benefit this study, and parts of the text require clarification.
https://doi.org/10.7554/eLife.107021.3.sa0
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Accurate reconstruction of the timescale of organismal evolution requires placement of extinct representatives among living branches. In this way, the fossil record has the capacity to revise hypotheses of organismal evolution by producing representatives of clades that far pre-date the age of the clade inferred using phylogenies built from molecular data and previous fossil calibrations. Recently, one fossil with the potential to drastically change current understanding surrounding the timescale of reptile diversification was described from Triassic fissure-fill deposits in the United Kingdom. This taxon, †
, was originally placed deep within the squamate crown clade, suggesting that many lineages of living lizards and snakes must have appeared by the Triassic and implying long ghost lineages that paleontologists and molecular phylogeneticists have failed to detect using all other available data. Our team challenged this identification and instead suggested †
had unclear affinities to living reptiles, but a crown-squamate interpretation was later re-iterated by the team that originally described this species. Here, we again challenge the morphological character codings used to support a crown squamate affinity for †
and illustrate several empirical problems with analyses that find this taxon is a crown squamate. Our analyses emphasize the importance of stringency in constructing hypodigms of fossils, particularly when they may be key for proper time calibration of the Tree of Life.
Paleontology has found an important role in the era of widespread genome sequencing of living phylogenetic diversity: providing justification for the placement of fossil calibrations along molecular phylogenies (
). Placing fossils on the Tree of Life is common practice, and new discoveries (
) and reshuffling of hypothesized phylogenetic relationships (
) are constantly revising what fossils are best to use as prior calibration constraints. These factors make the robust placement of key fossil taxa essential for properly calibrating phylogenies in time, which themselves form a foundation for modern evolutionary biology (
based on a partially articulated skeleton and a collection of referred material from the Carnian (
; 237–201.5 million years ago) fissure fill deposits of England, UK. In a paper (
) published at the end of 2023, we joined to refute the affinities of †
to Anguimorpha, a deeply nested crown squamate clade, proposed by
. In their response to our paper,
disagree with many of our anatomical observations and restate their position on the affinities of †
referred additional Late Triassic fossils to †
and presented phylogenetic results that this taxon is a crown group squamate (squamate hereafter).
is also an impassioned rebuttal to
, who substantially revised the description of †
, and upon correction of numerous character scorings in
either an archosauromorph or an indeterminate neodiapsid
’ and not a lepidosaur, much less a crown squamate.
Here, we provide point-by-point refutations of the interpretations of both papers of
and describe what we consider to be major methodological errors in the comparative anatomical work and phylogenetic analyses they conduct. We also emphasize that both (
) papers fail to replicate the inferred position of †
across phylogenetic analyses of the same and across different morphological datasets. We also highlight here where (
) should have reported their recovered synapomorphies; they elected instead to report results from other studies as though they had been recovered in the analyses conducted by
included numerous substantive comparative anatomy errors that can broadly be grouped into two categories: (i) anatomical interpretations, and (ii) translating these interpretations into scorings in different phylogenetic datasets. In
, we identified 22 errors in the study of
) and several more of type (ii) (‘Supplementary Material’ in
claimed that there were five observational errors in
. Four of these are supposed observational errors (type (i)) and one concerned a difference in how
score a character (type (ii)). This implies that
admitted that the other 18 errors type (i) produced by their previous study were correctly identified by
discussed additional characters in sections of their study and provided different interpretations of the anatomy of †
), but without clear justification. Here we focus on the four supposed observational errors (type (i)) listed by
provided additional photographs of features on the distal ends of the humeri referred to †
that they maintained are homologous with the entepicondylar and ectepicondylar foramina observed in some, but not all, squamates. We disagree about the identity of the features that
identified as these paired distal foramina for the following reasons:
First, the features on the humeri that
figured are not foramina, but fossae on the posterodistal surface of the humerus that are filled in with sediment. Although
claimed to observe this in a third isolated and referred humerus (NHMUK R38929), they neither figured this third humeral fragment, nor did they figure the internal structure of any of the supposed humeral heads, nor the evidence for referring these isolated elements to †
, computed tomography scans provide essential information about the structure of these fossae and show that, when infill is removed, foramina are absent (Figure 4 in
interpreted to be the entepicondylar and ectepicondylar foramina on the holotype and referred humeri are also in the wrong place on the bone to be homologized as such. In all crown reptiles that possess these foramina, they are placed low on the anterior surface (entepicondylar) and high on the distal surface (ectepicondylar) of the humerus (e.g. see
for examples in turtles, and finally
for examples in rhynchocephalians) and are dissimilar in shape and size (the entepicondylar foramen is elongated along the long axis of the humerus; the ectepicondylar foramen is circular). The features that
figured on the holotype and referred humeri of †
are very similar in shape and size, are oddly both placed on the same side of the bone, and differ in placement from the foramina observed in other exemplar fossils and living species of reptiles (
). The morphology of the fossae observed on the distal end of the humeri referred to †
is, however, similar in placement, size, and shape to the fossae described on the distal ends of the humeri of some archosauromorphs, including the azendohsaurid †
We reiterate that the presence of these foramina is not an unambiguous synapomorphy of crown Squamata and is present across living