General summary (pulled direct from the non-technical summary available with the paper): Researchers often use large databases to conduct their studies; however, they do not always provide credit, through citations, to the people who produced the data in the databases. In the field of paleontology, researchers use a large database called the Paleobiology Database (PBDB) to study global patterns and processes over millions of years. These studies use data from the PBDB and typically receive a greater number of citations than the original data-producing papers. This creates a situation where the hard work of collecting the data is not credited and rewarded in a fair way, even though this work is equally important to the field of paleontology. By fixing this issue and giving proper credit to data-producing papers, paleontology itself can be strengthened by increasing the incentives for producing data and at the same time creating more high-quality data for everyone to use.

Paleontology has historically been a descriptive discipline, focused on describing new fossils, which in turn may represent new species and/or new occurrences (in space and/or time). This is hardly exclusive to paleontology – all natural history disciplines (e.g., geology, other life science sub-disciplines like herpetology or ichthyology) are rooted in simply describing observations. Even today, scientists are constantly reporting new modern occurrences, from new living species (e.g., the Lady Elliott Shrimp Goby) to finding new occurrences, like the deepest known occurrence of a fish below 8,000 m. In paleontology, descriptions of new species and new occurrences are particularly common, even today, because of the incompleteness of the fossil record and the continued erosion and exposure of new fossil-bearing rocks. Such descriptive work is a great example of primary data, which are defined as being unique and novel, or data-generating in the parlance that is used in the above figure (data-provisioning for most of the rest of the paper). This is contrasted with secondary data, which are existing data that are being reused in some form, such as by downloading data from a database that has aggregated primary data from many different sources; a good summary of the distinction can be found here.

Because primary data collection involves novel data generation, it is typically (though hardly always) more time-intensive and costly (this should not be misconstrued to mean that secondary data analyses are not or cannot be time-intensive or costly). In paleontology, the official publication of a novel occurrence involves a lot more than just the examination of the fossil and writing it up; it requires someone to have found the fossil to begin with, which is often a resource-intensive process that involves identifying potential fossil-bearing areas, surveying said areas, actually finding a fossil, collecting it, and preparing it. As a result, many data-generating paleontological studies are at a very specific scale (e.g., a single fossil or a set of fossils from one site). Some examples of my primary-data-generating studies from 2023:

• Hart, L.J., Gee, B.M., Smith, P.M. and McCurry, M.R. 2023. A new chigutisaurid (Brachyopoidea, Temnospondyli) with soft tissue preservation from the Triassic Sydney Basin, New South Wales, Australia. Journal of Vertebrate Paleontology 42(6): e2232829. DOI: 10.1080/02724634.2023.2232829
• Gee, B.M., Beightol, C.V. and Sidor, C.A. 2023. A new lapillopsid from Antarctica and a reappraisal of the phylogenetic relationships of early diverging stereospondyls. Journal of Vertebrate Paleontology 42(6): e2216260. DOI: 10.1080/02724634.2023.2216260
• Kligman, B.T., Gee, B.M., Marsh, A.D., Nesbitt, S.J., Smith, M.E., Parker, W.G. and Stocker, M.R. 2023. Triassic stem caecilian supports dissorophoid origin of living amphibians. Nature 614: 102–107. DOI: 10.1038/s41586-022-05646-5

The vast majority of paleontological work has historically centered on generating primary data because that was the only thing that was really feasible until computers and other technological advancements permitted more comprehensive, and often intensive, analyses that are based on aggregating data together from many sources. Today, such studies are far more tractable and thus far more common, not just for paleontology but across all disciplines (AI being the most prominent recent development that may further expand the research horizons). We also have a variety of openly available databases that aggregate hundreds of thousands of published records, such as the Paleobiology Database (PBDB). A secondary data source could thus be generated in a matter of mere minutes but end up comprising thousands of unique records, each requiring hundreds of hours to have produced. These secondary data studies can take on a variety of forms, such as meta-analyses, bibliometric analyses, or the umbrella term of 'big data' studies; all share a commonality of collating data from many sources in order to create a larger sample size that can be used to tackle questions at larger scales. Some examples from Emma Dunne, one of the other authors on this paper:

• Dunne, E. M., Thompson, S. E., Butler, R. J., Rosindell, J., & Close, R. A. (2023). Mechanistic neutral models show that sampling biases drive the apparent explosion of early tetrapod diversity. Nature Ecology & Evolution 7(9): 1480–1489. DOI: 10.1038/s41559-023-02128-3
  
• Dunne, E. M., Farnsworth, A., Greene, S. E., Lunt, D. J., & Butler, R. J. (2021). Climatic drivers of latitudinal variation in Late Triassic tetrapod diversity. Palaeontology 64(1): 101–117. DOI: 10.1111/pala.12514
  
• Dunne, E. M., Close, R. A., Button, D. J., Brocklehurst, N., Cashmore, D. D., Lloyd, G. T., & Butler, R. J. (2018). Diversity change during the rise of tetrapods and the impact of the ‘Carboniferous rainforest collapse’. Proceedings of the Royal Society B: Biological Sciences 285(1872): 20172730. DOI: 10.1098/rspb.2017.2730
  

Academics, like many people, prefer hard numbers (quantitative) to relative assessments (qualitative). Therefore, we often rely on various imperfect numerical metrics and proxies to attempt to assess research (and researcher) quality. Two examples are impact factor (IF) and citation count. Impact factor is a journal-specific metric and is calculated as follows:

• For a time period of X years, the X-year impact factor is the ratio between the number of citations received in that year for publications in that journal that were published in the preceding X years and the total number of "citable items" published in that journal during the preceding X years. There are various common periods of 'X' (e.g., a two-year impact factor).

Journals with a higher IF are viewed as being more prestigious (selective about what they publish), and even though there are many reasons why a journal's IF does not have much of any bearing on the direct quality of a single article or the researchers who published it, remains a popular metric. For example, Nature and Science, two journals considered among the most prestigious journals across many disciplines, have two-year IFs of 64.8 and 56.9. By comparison, journals like the Journal of Paleontology and the Journal of Vertebrate Paleontology have two-year IFs below 3.0 and are thus considered much less prestigious. Because secondary data studies aggregate data, they can tackle questions that are "bigger picture" and are thus more appealing to selective journals that aren't interested in publishing a description of a new fossil (unless it's a dinosaur or something very cool). As a result, data-generating studies are often published in society journals (e.g., Journal of Paleontology, Acta Palaeontologica Polonica, Journal of Vertebrate Paleontology) that are not considered prestigious.

IF is based on citation count, but citation counts can also be used on their own (e.g., a researcher can list the citation counts for all of their articles on their CV) – this can also be used as a semi-quantitative assessment of the quality of research (on the premise that high-quality work is cited more often), but there are also many flaws with correlating citation counts with research(er) quality.

What this study did is put numbers on the qualitative observation that data-generating papers tend to be undercited (undercredited). In paleontology, many of the secondary data analyses rely on aggregating data from the Paleobiology Database, but many of them do not cite the data-generating studies in a way that can be tracked and thus properly credited (I think that some of my own publications have been used in PBDB studies but frankly have no clue which ones). Studies that use the PBDB (secondary data studies) are supposed to "register" in order to receive a PBDB publication number, so these can be easily identified and have their total and per year citation counts obtained/calculated via Google Scholar (orange bar below). From those studies, the data-generating studies that were used by the PBDB studies could be identified (nearly 50,000 unique studies from just 151 PBDB studies for which data could be recovered). The total and per year citation counts for those data-generating studies could then be obtained/calculated via Google Scholar (blue bar below). However, we know that Google Scholar (and every other scholarly aggregator) isn't checking things like Supplemental Information for citaitons, if they exist in the SI to begin with. The number of missed citations (i.e. not tracked by Google Scholar) of data-generating papers could subsequently be calculated from the datasets of those 151 studies (e.g., Smith et al., 2000, was used by 5 PBDB studies) and added to the total citation count (the blue-green bar below). Because not all of the PBDB studies in the focal interval (2001-2021; n=396) had their data recovered, the hidden usage/citation rate of data-generating papers could be extrapolated from the 151 PBDB studies that did have their data recovered, assuming similar usage rates over all 396 studies (the extra blue-green bar below). These extrapolated numbers result in a mean citation rate that is nearly the same as that of PBDB studies, rather than the presently recorded rate that is only about one-third of the rate.

Predictably, if the true citation count of data-generating papers can be demonstrated to be higher than what is presently tracked across scholarly aggregators like Google Scholar, the journals in which these papers are typically published should also have higher impact factors than what is presently reported, and this is shown below (see the discussion in the paper for more context about different year-intervals in impact factor calculations and other historical conditions for publishing). Collectively, these analyses provide clear evidence that data-generating studies are systemically undercited, which can produce misleading perceptions of interest in and quality of these studies and the journals they are published in (even if that is in large part because we rely too much on flawed metrics to assess these).

A lack of proper citation of data-generating studies by data-reusing studies can and certainly does result from poor research practices around citation (I often see people remove license/copyright and citation information from database downloads in my day job), but even well-intentioned researchers can frequently have their hands tied by various other factors, mainly on the end of the journals that we publish in. For example, these are some policies found across various journals that can lead to a lack of citations of primary data:

• Page/text length limits: This is in part a holdover from the days of print-only articles where journals were naturally inclined to avoid accepting excessively long articles, as they would have to print hundreds to thousands more pages for an encapsulating volume. Even though electronic distribution now predominates, and in some cases, is the only medium through which articles are disseminated, the majority of journals retain limits on length, which can be imposed in a variety of ways, such as total page count, number of words, or other caps (e.g., limits on the number of figures). This is particularly common in high-profile journals; that guidelines from Nature are listed below as an example:
  • The typical length of a 6-page article with 4 modest display items (figures and tables) is 2500 words (summary paragraph plus body text). The typical length of an 8-page article with 5-6 modest display items is 4300 words. A ‘modest’ display item is one that, with its legend, occupies about a quarter of a page (equivalent to ~270 words). If a composite figure (with several panels) needs to occupy at least half a page in order for all the elements to be visible, the text length may need to be reduced accordingly to accommodate such figures.
• Reference limits: 'References' are the full list of scholarly items that an article cites. Some journals make implicit restrictions on references by including them in another limit (e.g., page limit); others will have an express limit. An example from Science, another high-profile journal:
  • Research Articles should not exceed 5 printed pages in the journal. This length can accommodate 2000 to 3000 words of main text, in addition to an abstract, 3 to 5 display items (figures or tables) with brief legends, about 50 main-text references, and a structured acknowledgments section.
• Restrictions on which references can be included: Numerical limits on content are highly variable across journals, but one attribute that any journal worth its salt will enforce is which references can be included in the Reference / Literature Cited section of the article, which is what is scraped to count citations on scholarly search engines like Google Scholar. All references listed in this section have to be included in the main text of the article itself, which means that any citations that are only found in the Supplemental Information (alternatively Supplementary/Supporting and Materials) cannot have its full reference listed in the formal Reference section. Especially for articles published in journals with page limits, the Supplemental Information is a valuable and often rather lengthy complement to the main text; in journals like Nature and Science, the article itself may only be a few pages, but the associated Supplemental Information can be hundreds of pages long with dozens to hundreds of citations/references that are not found in the main-text. An author who wants to properly cite potentially hundreds to thousands of primary data sources would almost certainly have to relegate this information to the Supplemental Information. This matters because...
• Scholarly indexers do not scrape Supplemental Information: In order to track citations efficiently, various scholarly indexers (e.g., Google Scholar, Web of Science) crawl the internet and look for matches to a known article. However, in order to be efficient, they only crawl certain types of pages and only certain types of content to avoid picking up casual references, such as mention in a Wikipedia page (or a blog like this one). However, this means that if a reference is only listed in the Supplemental Information of an article and not in the main text of said article, it will not be "counted" as a citation. Of course, someone could manually search for citations of an article in such supplemental documents if they really wanted a full citation count, but these documents in their entirety are also not typically indexed, so you would have to already have a good idea of which supporting documents potentially cited an article of interest.
  • To give an example, we can look at a paper I was on that was published a year ago in Nature (Kligman et al., 2023). The main text, in typeset PDF format, is just 6 pages long; the Supporting Information (SI) text, in Word format, is over 180. There are just 42 references in the main text, compared to a whopping 377 in the SI; of those 377, just 29 are also cited in the main text. In other words, there are nearly 350 unique references that were only cited in the SI (implying that they were useful for some point or another), most of which are descriptive anatomy (i.e. primary data-generating), that are not tracked as having been cited by any scholarly aggregator.

Many of these hindrances are structural at the level of a journal or publisher, so it may seem that there is little to be done to more accurately and equitably track data reuse. However, there are a variety of actions that authors can take now to try and work around these existing limitations. One example:

• Posting Supplemental Information to preprint servers like bioRxiv. Even though preprints are not peer-reviewed, they are indexed by scholarly aggregators, and thus anything that is cited in the preprint will be tracked as a citation. Although preprints by definition refer to a document that is not yet accepted for publication following peer review, preprint servers are also used to host 'post-prints,' or the accepted version of the manuscript. Sharing post-prints is a popular way of ensuring compliance with open-access publishing mandates when the journal to which an article is/will be published is not inherently open-access.  Preprint servers are free to use and can be accessed by anyone, so they offer one workaround with the current infrastructure.

More broadly, proper data sharing is a precursor to proper data citation (data/clarification on data could not be obtained for 21% of sampled PBDB publications). While there is some optimism around funder/journal mandates for data sharing, similar mandates for open-access publishing of articles have not necessarily yielded the predicted or desired gains, in large part because the sheer volume and rate of growth of research output vastly exceeds the capacity of agencies to actually assess compliance and enforce policies. I have long been of the opinion that best practices have to be established, maintained, and self-policed by researchers, not by (semi-)legal apparatuses, especially in light of the volatility associated with resourcing for many national funding agencies. In many instances, even when data are shared and thus "check the boxes," they may not be sufficient (or even relevant) for reproducing the results of an associated study, and this too falls on the research community, rather than on external entities or policies, to address; if regulating bodies or publishers cannot even ensure a consistent check for a binary 'data shared/data not shared,' they certainly will not be able to assess whether the shared data are sufficient for reproducibility. Promoting healthy data sharing practices, including by according proper credit to data generators as a means of incentivizing data sharing, remains an essential part of a sustainable research ecosystem.

Finally, the biggest challenges lie in advocating for structural changes. For example, as research output rises, the incentives to perform peer review, which is practically never compensated or rewarded in any form, decline. Peer review is the primary mechanism that should be responsible for ensuring rigor of a study, which includes proper data sharing and data citation, but there is not much incentive for reviewers to even check supplemental information files if doing so would require substantial time investment. Other target areas include advocating for changes in journal policies in how citations can be provided in a format that is discoverable and indexed by the aggregators that we all rely on to track citations is the most crucial and alternative means of evaluating research quality and performance. A few journals (e.g., Global Ecology & Biogeography) do allow for references cited only in Supplemental Information to be listed in the main-text References so that they are picked up by indexers. As journal editorial boards are made up of normal (well, somewhat normal) researchers, they also have some ability to direct journal policies in a variety of ways, from formatting prescriptions to journal scope. Development and adoption of other metrics of tracking and recognizing scholarly contributions in merit-based processes, in which "normal" researchers are also directly involved, will also be critical.

General summary: The origin of modern amphibians (frogs/toads, salamanders/newts, caecilians), which are more often termed 'lissamphibians' by scientists to differentiate from the more ambiguous 'amphibians,' has long been a vexing problem. The three modern groups are remarkably morphologically disparate, which makes it hard to both confidently identify and conceive of the ancestral lissamphibian. Lissamphibians today are also relatively small, a pattern thought to have characterized much of their evolutionary history and also an attribute that predisposes their remains to not have been fossilized. Exacerbating this is the extremely poor record of caecilians, which, even today, are a rather cryptic group found only in the equatorial regions and that typically burrow, making them rather hard to observe. Burrowing animals, especially those that not only burrow but that spend much of their lives underground, also have a poor fossil record, which compounds the problems for caecilians. The first caecilian fossils were not even reported until 1972 (previous reports were a misidentifed catfish spine and a misidentified cephalopid, respectively), and to date, there are less than a dozen distinct occurrences of fossil caecilians known globally over an 180 million year interval.

In this study, led by my colleague and current Virginia Tech PhD student Ben Kligman, we report nearly 100 new specimens of the earliest known caecilian in the fossil record from a single Late Triassic site in Petrified Forest National Park, Arizona. Although no complete skulls or skeletons are known, numerous fragments preserve unequivocally diagnostic features found only in caecilians, such as a jaw comprised of largely fused elements that remain separate in other tetrapods and two rows of small teeth with a distinctive feature called pedicelly – a dividing zone at the mid-height of the tooth that often leads the tips to be lost during preservation. This occurrences pre-dates the previous oldest occurrence of caecilians by at least 35 million years and provides new insights into the early stages of the group's evolution. In particular, the new fossils appear to capture the transition toward the modern caecilian condition in which there is extensive co-ossification of multiple elements to form a more consolidated skull (good for burrowing). Their occurrence in Arizona, which was positioned close to the equator in the Late Triassic, suggests that an origin within the equatorial belt also constrained their dispersal, therein offering an explanation as to why caecilians remain tied to these regions when frogs and salamanders have nearly a global distribution except at the poles (and Australia for salamanders).

Elucidating the evolutionary origin of highly specialized organisms has been a persistent challenge for evolutionary biologists and paleontologists because the patchy fossil record often obscures the gradual transition from a generalized "ancestral" form to the observed specialized one. Fossils that fill in these gaps, often dubbed "transitional fossils," contribute substantive information by their mixture of features, but it is not as if one can simply declare, "today I will find this transitional fossil" and then actually do so. For this reason, the evolutionary origins of various groups of living tetrapods like turtles and snakes has remained contentious to even the present day; we simply lack enough transitional fossils or cannot be certain that a given fossil truly represents a transition, rather than a convergence on a similar body plan (e.g., a long body with greatly reduced or entirely absent limbs occurs across many different groups of animals, not just snakes). It's only within my parents' lifetime that the notion that birds descended from dinosaurs became the accepted consensus, which today's 5-year-olds know by heart.

One of the most vexing origin stories is that of modern amphibians, collectively termed "lissamphibians." There are three living groups of lissamphibians: the worm-like caecilians, which are poorly-known to scientists and the public alike; frogs (of which toads are a subset); and salamanders (of which newts are a subset). The simple explanation for the ongoing uncertainty is how different these three groups look – one has entirely lost its limbs, another has lost its tail and shortened its body; and the third looks like a prototypical tetrapod (salamanders are often confused for lizards because people don't think amphibians have tails). As a result, it is difficult to figure out what a transitional form to one or all three would look like – does the common ancestor of these three groups have a long or short body, a tail or no tail, etc.

Both fossil and modern amphibians are on the smaller side of the tetrapod scale; consider that the recent capture of the new recordholder for the largest living toad (who was promptly euthanized due to being an invasive species in Australia) was for a cane toad weighing just under 6 lbs, or roughly equivalent to a large chihuahua (the healthy ones, not those severely obese ones you see in kitschy Route 66 hotels sometimes). Their skeleton is rather fragile, and in early stages of life (e.g., the tadpole stage of frogs), has not even solidifed into bone. This makes them poor candidates for fossilization, which is why the fossil record of caecilians and frogs is atrocious; salamanders benefit only from apparently taking up residence in the  lakes that lended themselves to lagerstätte like in the Jurassic of China. However, whereas salamanders and frogs become increasingly well-documented towards the present-day, caecilians remain nearly invisible in the fossil record.

It is no exaggeration to say that among the various groups of living tetrapods, caecilians have one of the worst fossil records. There are fewer than a dozen definitive occurrences of fossil caecilians between the Early Jurassic and the present day, fewer than 10 of which have been published in full. Until 1972, there were no published records of fossil caecilians from even recent history. The below summary figure showing the temporal distribution of published fossil caecilian records. Six of the nine records shown here are just vertebrae, and only Eocaecilia micropodia, known from several dozen specimens on the Navajo Nation of Arizona, is represented by any appreciable number of specimens.

The fossil record of caecilians likely owes to a combination of a lot paleobiological attributes that are all disadvantageous for their preservation. As discussed above, the small size of lissamphibians reduces their odds of being preserved. Where caecilians differ from most other lissamphibians is that they are fossorial, meaning they live underground (e.g., within leaf litter or soil) by burrowing with their heads (they have no limbs to speak of). If their extinct relatives had similar ecologies, which seems likely given the many skeletal adaptations for this ecology, they would not be inhabitating areas that are frequent sites of preservation of skeletal remains, like rivers or lakes. It is no coincidence that freshwater aquatic animals like various temnospondyls and crocodilians have a pretty good fossil record. Lastly, modern caecilians are predominantly found in the tropics. These regions, while home to some of the greatest biodiversity in terrestrial environments, are also not very conducive to fossilization because humid/moist environments promote rapid decomposition of remains. Add these up and you have a recipe for a depauperate fossil record.

With nearly a hundred specimens attributed to Funcusvermis (and many more that were subsequently picked out of the sediment after we had begun finalizing this paper), we've nearly doubled the entire fossil record of caecilians based on specimen number, all from just a single remarkable site in the middle of the Arizona desert. The below figures show the relative abundance of specimens and individuals of Funcusvermis to the rest of the caecilian fossil record.

This isn't a case of many elements of a few individuals as well. The site's (published) MNI is established at a whopping 76 individuals based on lower right jaw elements (pseudodentaries), increasing the number of distinct caecilian individuals represented in the fossil record by an even greater magnitude. For some reason, nearly all of the elements are from the right side of the body, a skew that wouldn't be expected using a thorough process like screenwashing in which there's careful sorting of both fragmentary and complete elements of all taxa (this is the one time that people don't throw the temnospondyls out). We're still figuring that part out...

Perhaps the best place to start with "where does Chinlestegophis stand now" is to discuss where Chinlestegophis stood before this. Acceptance of the hypothesis of lissamphibian origins has been tepid at best and practically non-existent at worse. Per Google Scholar, Pardo et al. (2017) has been cited 62 times. When you cut out unidentified duplicate entries, theses/dissertations, preprints, and conference abstracts, the number comes down to 50 (there are a few that it misses that ResearchGate catches). Somehow, I think I am the most frequent citer of this paper actually – 13 first-authored papers that do so. Nearly all of these citations, mine included and particularly those from paleontologists, are "neutral" – they profess no personal stance on the hypothesis of Pardo et al. and do not attempt to directly tackle the question. Some examples:

• "The origin of some or all lissamphibians is hypothesized to fall among small upper Carboniferous temnospondyls, the amphibamiform dissorophoids (Bolt, 1969;Anderson et al., 2008a;Maddin et al., 2012;Pardo et al., 2017;Schoch, 2019)." – Schoch et al. (2019)
• "Nonetheless, the origin of lissamphibians remains uncertain (Pardo et al., 2017; Marjanović and Laurin, 2019)." – Dilkes (2020)
• "Despite an increase in knowledge on the fossil record of lissamphibians (e.g. Gao & Shubin, 2003; Jenkins, Walsh & Carroll, 2007; Skutschas & Martin, 2011; Ascarrunz et al., 2016), their interrelationship as well as their origin (or origins) from the vast range of early tetrapods remains a matter of debate (Laurin & Reisz, 1997; Meyer & Zardoya, 2003; Schoch & Milner, 2004; Ruta, Coates & Quicke, 2003; Ruta & Coates, 2007; Sigurdsen & Green, 2011; Marjanović & Laurin, 2013; Schoch, 2014; Pardo, Small & Huttenlocker, 2017a; Pardo et al., 2017b)." – Danto et al. (2019)

Other studies have directly challenged the results and conclusions of Pardo et al.:

• Santos et al. (2020), which presents a summary of the fossil record of gymnophionomorphs, dedicated an entire section to arguing against this hypothesis.
• Marjanović & Laurin (2019), mostly in passing, alluded to the weakness of the original results, which reported only a majority-rule consensus, as the strict consensus does not support the novel hypothesis, and the typical monophyletic origin from within dissorophoids was among a smaller subset of most parsimonious trees.
• Serra Silva & Wilkinson (2020) dedicated an entire study to demonstrating how the use of a majority-rule consensus is flawed when inferring evolutionary relationships, with the single case study being the original dataset analyzed by Pardo et al.
• Both Schoch et al. (2020) and Daza et al. (2020) independently recovered the traditional temnospondyl hypothesis when using slightly modified and slightly expanded versions of Pardo et al.'s dataset, and I (via my preprint) have shown that correcting for systemic issues in the source matrix for Pardo et al. does not recover their novel topology upon reanalysis regardless of which consensus method is used (in general though, the rest of my citations of this paper would be considered "neutral"). David Marjanović also had an SVP talk last year (see p. 233 of the abstract volume) challenging Pardo et al.'s methods and hypothesis.
  

All of this is to say that, like Anderson et al.'s (2008) polphyly hypothesis, the diphyly/new polyphyly (depending on how you want to cut it) hypothesis is not exactly causing anyone to rewrite any textbooks, and it has not gained really even marginal acceptance among workers not affiliated with the study.

With that being said, I would summarize my opinion of Chinlestegophis, which hasn't really changed over the years, as an "interesting and plausible idea that fills some notable conceptual / data gaps but that is not well-supported quantitatively or phenetically." I won't beat the proverbial horse again on the phylogenetic bits, which are re-summarized briefly in our supplemental data, but I will spend some time going through the qualitative comparisons and arguments (but read the supplement, I wrote a lot more in there).

Most of my reservations have more to do with how Chinlestegophis is compared to other temnospondyls and caecilians, rather than the anatomical interpretation of Chinlestegophis (at least Schoch et al., 2020, dispute their identification of a lateral exposure of the palatine). I find many of the favorable comparisons made by Pardo et al. to either be oversimplifications or mischaracterizations. Let's take two examples of co-ossification that are proposed to be shared between Chinlestegophis and some other tetrapods:

• Purported to be shared with brachyopoid temnospondyls and caecilians: lacrimal coossified to maxilla
  • In Chinlestegophis, Pardo et al. (2017) identified the nasolacrimal duct passing through the top of the maxilla. In other temnospondyls, this typically passes through the lacrimal, but Chinlestegophis has no distinct lacrimal; on this basis, Pardo et al. inferred that these two bones had co-ossified. Whether this is actually shared with any other temnospondyl is debatable at best and total speculation at worst; there are a variety of non-brachyopoids that lack a lacrimal (e.g., tupilakosaurid dvinosaurs, some rhytidosteids, some trematosaurs), but it has never been demonstrated via the same nasolacrimal duct proxy, which requires either CT scanning or a really serendipitous break, that the lacrimal co-ossifies with anything in those taxa; complete loss is another option. There is no biological law that says if a distinct lacrimal is absent, it must have fused with the maxilla.
• Purported to be shared with stereospondyl temnospondyls and caecilians: opisthotics coossified to exoccipitals
  • The opisthotic is one of three bones considered to be part of the inner ear of early tetrapods; the other two are the prootic, a bone you are unlikely to ever see in full form without a CT scan, and the stapes, a rod-like bone responsible for conducting sound with whatever external ear system (e.g., a tympanic membrane) existed in these animals. The assertion by Pardo et al. that opisthotics coossified with the exoccipitals is a shared feature with stereospondyls is strange because the inner ear, and most of the braincase, is exceptionally poorly ossified in most stereospondyls on account of their paedomorphic nature. There  are many taxa in which the opisthotic is not ossified at all, and in nearly all others, it is either not co-ossified with the prootic or is not co-ossified with the exoccipital. When this does occur, again, rarely, it is only in exceptionally large stereospondyls like Mastodonsaurus, which is one of the largest known temnospondyls, and thus the co-ossification in those taxa is likely a result of large size. The more common condition, across temnospondyls and early tetrapods alike, is for the exoccipital to co-ossify with the prootic to form a joint otic but to remain separate from the exoccipital. The condition of Chinlestegophis in which the prootic is not mentioned as either a distinct or co-ossified element, is really weird in this respect and not like what we see in other temnospondyls.

I would encourage people who remain skeptical of our rebuttal of many of the original claims of Pardo et al. to read section 3 of our Supplemental Information; I spent a lot of time on that...

Today, caecilians occur within a narrow latitudinal belt (27° N and 34° S), and their fossil occurrences are bracketed between what would have been around 16° N and 27° S. This constrasts sharply with both the fossil and extant distribution of frogs and salamanders, the former of which make it nearly to the poles. Understanding the present distributions of different groups of tetrapods necessarily requires a look into the deep past to understand how the continents were arranged and how different organisms could or could not get around.

All lissamphibians are susceptible to drying out because of their wet skin and their use of it to breath (cutaneous respiration), but caecilians are particularly susceptible to dry environments, which is one reason they spend a lot of their time below ground where it's more humid/damp. Even though caecilians were already established at a time when the continents were largely still connected, allowing the dispersal of all sorts of different organisms around the world, that their fossil occurrences remain tied to this narrow equatorial belt indicates that early caecilians were also more climatically sensitive than other lissamphibians, and thus, that caecilians' present distribution has been strongly constrained by the presence or absence of humid environments. It's a strong reminder of the ways in which the past directly shapes what we observe in the present and underscores the importance of studying the deep time record of the planet and its inhabitants in order to really understand how we ended up with today's ecosystems.

Werneburg et al. (PalZ) described a new zatracheid, represented by an essentially complete skeleton, from the early Permian Chemnitz Fossil Lagerstätte in Germany, Chemnitzion richteri. This deposit records the dying moments of a terrestrial environment being buried in ashfall and the subsequent pyroclastic flow of a volcanic eruption, thus preserving a remarkable diversity of organisms (including plants and invertebrates) in 3D natural molds and casts. Despite a decent number of specimens, zatracheids remain relatively rare in the fossil record – both Acanthostomatops vorax (Germany) and Dascyeps bucklandi (England) are only known from a single site, which may reflect the lower frequency of dryland habitats recorded in the Permo-Carboniferous of Europe compared to North America. The postcranial record of the clade is also only known from Acanthostomatops, and the nearly complete skeleton of C. richteri provides further details on the variation within zatracheids.

Schoch & Sues (Journal of Paleontology) provided a long-awaited reassessment of the enigmatic early Permian temnospondyl Parioxys ferricolus. Despite being known from an appreciable sample size of specimens from Texas, the anatomy and taxonomy of this taxon have long been confusing because the original descriptions were limited to what are now grainy photographs and stylized reconstructions. The original descriptions from nearly 70 years ago were influenced by the  descriptor's (Y. Shawki Moustafa) hypothesis that Parioxys was closely related to Eryops in how comparisons and reconstructions were made, but other workers have long-suspected that the taxon might belong to a different clade. Schoch & Sues' redescription and reassessment provided more compelling evidence for dissorophid affinities, specifically with the cacopines, based on features like a transverse nuchal ridge on the postparietals, a foreshortened posterior skull table, and modified features of the palate.

Fresh off the press from last week is a revision of the Middle Triassic trematosaur Trematolestes hagdorni by Schoch & Mujal (Neues Jahrbuch für Geologie und Palaöntologie). When originally described in 2006 by Schoch, the taxon was represented by a number of essentially complete specimens, but these were interpreted as belonging to immature specimens. New material described in this study greatly expands the ontogenetic range on both sides, from highly immature individuals to demonstrably mature adults. The ontogeny of many trematosaurs (and arguably most stereospondyls) remains very poorly known due to a lack of variably sized specimens, and the new material of Trematolestes represents the most completely known ontogeny among Trematosauria.

Another hot off the press paper, Surmik et al. (BMC Ecology and Evolution) report the oldest unequivocal occurrence of osteosarcoma (bone tumor) in the vertebra of an "amphibian" (non-amniote). Given the scarcity of pathologies in the fossil record in general, it likely comes as little surprise that this osteosarcoma was identified from the extensive sample of Metoposaurus krasiejowensis from the Late Triassic Krasiejów locality in Poland. Through CT scanning and histology, the authors provided a detailed description of the tissue type and organization, which permitted their diagnosis.
   One of the interesting discussion points raised by the authors is the scarcity of identified occurrences of cancer in fossil "amphibians" given their sample size; indeed, I have never seen such a malformed intercentrum out of perhaps >1,000 that I have seen in North American collections. Modern amphibians have a relatively low rate of reported bone cancer (most occurrences of cancer are reported from the skin), and the authors speculated that temnospondyls may have been similarly resistant to cancer through a variety of developmental and genetic mechanisms.

One of the distinctive features of stereospondyls is their massively enlarged pectoral elements, which form large, plate-like structures. It has often been assumed that such bones would serve as ballast to help these animals sink to the bottom of water bodies; increasing bone weight and/or density is a common feature among many aquatic animals. However, general size is not necessarily reflective of weight (although in fossilized form, it certain does) – bone compactness is the real metric that can be used to assess how a bone contributes to buoyancy. Kalita et al. (Journal of Anatomy) compared the compactness of the clavicle and interclavicle of Cyclotosaurus intermedius and Metoposaurus krasiejowensis and found a high degree of compactness in both taxa. However, differences in microanatomical structure hint at different lifestyles (Metoposaurus more benthic, Cyclotosaurus more active swimming), corroborating other research suggesting interspecific niche partitioning. At least among the several sampled specimens of Metoposaurus, there was no indication of intraspecific niche partitioning, indicating a benthic lifestyle was adopted quite early. 

Weryński & Kędzierski (Geological Quarterly) used both histology and SEM to examine the external and internal microstructure of teeth of Metoposaurus krasiejowensis (yes, it's another year filled with research on Polish metoposaurids). In addition to the typical labyrinthodont infolding that has been known for over 150 years in temnospondyls, the authors also identified directional porosity in the canals making up this structure that they interpret as an adaptation for counterbalancing stress forces during biting. Additionally, they identified what they interpret as growth marks within the teeth, equivalent to four seasonal cycles, which adds to the data used to assess the perceived biological response to any local climatic periodicity.

General summary: Frequent readers of this blog are of course familiar with my love for metoposaurids, one of the most iconic groups of North American temnospondyls. It is no secret that metoposaurids were my "gateway drug" to the world of terrifyingly large and unrecognizable amphibians, and so they always have a special place in my heart. My previous research has largely focused on two of the three species, Anaschisma browni (ex. Koskinonodon perfectus, ex. Buettneria perfecta) and Apachesaurus gregorii, which are the two most common metoposaurids that we get in the Late Triassic of North America. If you go to a museum and see a metoposaurid (most major museums in the U.S. have a metoposaurid on display), it's likely Anaschisma browni, although the label may be two or three junior synonyms out of date. The third species, known only from two sites in Texas and one site in Nova Scotia, doesn't get as much press - it was last (re)described in 1932! Ninety years later, my buddy Aaron Kufner and I are pleased to produce a full redescription of this taxon, long referred to as 'Metoposaurus' bakeri, based on a reexamination of material from the type locality that now lives at the University of Michigan Museum of Paleontology (UMMP) collections in Ann Arbor. With a thorough redescription spanning 134 print pages (probably too thorough, even by my own standards), we provide extensive documentation of the skeletal anatomy of this species (1930s-era drawings have their limitations), conducted more phylogenetics analyses to test the relationships of metoposaurids (this has gotten no better since the 1930s), and ultimately concluded that this species cannot be placed in an existing genus like Metoposaurus (otherwise only known from Europe). To that end, we created a new genus name, the mouthful Buettnererpeton, which honors a longtime fossil preparator at the UMMP, William H. Buettner, who worked extensively with E.C. Case, the museum curator who named the species in 1931. The suffix comes from -herpeton, meaning 'creeping animal' in Greek, which is a common component of names of early reptiles and amphibians. Our taxonomic act has implications for biostratigraphy (relating distantly situated rocks based on which taxa occur in them), both globally and within North America, and we discuss everything from future work needed on metoposaurids to why their phylogenetic relationships are so badly resolved. This is a 'boundary-crossing' project that originated when I was a Ph.D. student in the summer of 2019 and has only now made it to the finish line, so it is particularly memorable for me in that regard.

Most of the excessive taxonomic splitting (naming new species based on features that are not considered reliable for taxonomic differentiation, like size of the type specimens), has been historically concentrated in North America and Europe, but it's been fairly stable in North America for a few decades now, with everyone agreeing that there are three valid species. I've tackled two of these in recent years, Anaschisma browni (the one that keeps getting renamed, much to the chagrin of museum exhibit designers) and Apachesaurus gregorii, but the remaining metoposaurid is the least well-studied and thus the most taxonomically ambiguous: "Metoposaurus" bakeri (which you can find with pretty much every combination of genus + species, both with an without quotes, e.g., Koskinonodon bakeri, Buettneria bakeri).

The rationale for the updated taxonomy is entirely normal for paleontology but illustrates the subjectivity associated with how scientists differentiate at a given taxonomic scale. "Metoposaurus" bakeri was primarily allied with Metoposaurus diagnosticus because both taxa purportedly shared the condition of having a lacrimal bone that was separated from the orbit, in contrast to Anaschisma browni (then "Buettneria perfecta"), which has a lacrimal that enters the orbit (see above on right). That's it, one binary feature. "Metoposaurus" bakeri was then differentiated from M. diagnosticus by several qualitative features, like a proportionately longer lacrimal and a smaller area of radiating grooves on the clavicle. Both are (1) really continuous, not discrete, and (2) shared with A. browni. Other shared features have also been argued to separate the North American taxa from Metoposaurus proper from Europe, like the relative size of circular pitting on the interclavicle (see below). All of this is to say that an argument could have been made to unite "M." bakeri in the same genus with A. browni, and to use the lacrimal-orbit relationship as their one differentiating feature.

This convoluted history brings us to this study. Whether "Metoposaurus" bakeri really belongs in Metoposaurus or not has big implications for both metoposaurid taxonomy and biostratigraphy. If "M." bakeri was placed in Metoposaurus, this would further undermine the historical use of the lacrimal-orbit relationship as a differentiator of metoposaurids at the genus level. The reason why this is so problematic is not the undoing of precedent (a lot of historical precedent should be undone) but rather that the only reliable diagnostic cranial feature of Metoposaurus (in the sense of Brusatte et al., 2015, in which only the three European species belong to this genus) and Anaschisma is the lacrimal-orbit relationship. In other words, if "M." bakeri were placed in either genus, it would mean that a lacrimal entering the orbit would no longer be diagnostic of that given genus, and therein, that would mean that many isolated skulls from North America or Europe would essentially be unable to be referred to a particular genus, let alone to a species. This would, for many reasons, be very bad for all paleontologists, not just academics. (It also illustrates that perhaps Anaschisma should be synonymized with Metoposaurus, as it was in the 60s and 70s).

However, there are options beyond trying to squeeze "Metoposaurus" bakeri into one of these two existing genera. Although I tend to be more of a 'lumper' than a 'splitter' in casual academic parlance (I tend to prefer synonymizing taxa than to create new ones), there was really no other option given the difficulty that we already have with differentiating metoposaurid genera. Hence, Buettnererpeton was born! This admittedly very wordy name takes its inspiration from the now-defunct Buettneria, a name created in 1920 by E. C. Case to honor a longtime colleague and fossil preparator at the University of Michigan, William Buettner. Finding some way to restore Case's homage was something that the collections manager, Adam Rountrey, had suggested to us back when we first visited in 2019, and combining Buettner's name with -herpeton, a common suffix for Paleozoic tetrapods (meaning 'creeping thing' or some variation of that), was the obvious choice.

One of the prominent regional patterns in the distribution of metoposaurids within North America is that there are very few on the eastern half of the continent, owing in large part of the much more limited exposures of Late Triassic rocks. Essentially all of the ones on display are from Arizona, New Mexico, or Texas (even the ones housed in east coast museums like the Smithsonian, American Museum of Natural History, and the Museum of Comparative Zoology). Most metoposaurid material from the eastern seaboard was collected during the construction of tunnels, which as you might imagine, was less than conducive for the collection of delicate fossils. As a result, practically none of it is diagnostic to a certain species, and it requires a fair bit of circular logic to even assert metoposaurid identity at all.

The one exception to this is a very nice natural mold of Buettnererpeton bakeri from Nova Scotia, also one of the few nice Mesozoic temnospondyl fossils from Canada. This specimen was first collected several decades ago (and now lives at Yale) and has long been the only occurrence of B. bakeri from outside of Texas. Although its identity hasn't been particularly controversial, Hans kindly gave us a good photograph, from which we reproduced an interpretive line drawing (not previously done), to corroborate its conspecificity with the Texas material. Its isn't that surprising that metoposaurids would have lived there - they are found in Morocco and western Europe, which would have been much closer to the eastern seaboard in the Late Triassic - but it does demonstrate the geographic range of one species. Really broad geographic ranges are only something that we observe in North America, likely due to a combination of the large size of North America compared to Europe, the heterogenous geography of the Late Triassic, and the heterogenous distribution of Late Triassic exposures today. But it's nonetheless important for indicating that metoposaurids were likely distributed across much of North America and are only unknown from many parts because of lack of Late Triassic exposures. Quite possibly, they were as widely distributed as common living fauna like raccoons.

One of the longstanding practices in paleontology was naming new species when something was found in a new region. Of course, perceptions of geographic distance can be greatly exaggerated by the modern configuration, when in fact what are now disparate regions could have been closely situated in the geologic past. The general amalgamation of the continents into Pangea was largely consistent throughout the Triassic, as seen below.

As a result, most of the metoposaurid-bearing regions are actually quite close to each other. Nova Scotia was very close to the Argana Basin of Morocco, from which many metoposaurids have been collected, closer in fact than it was to the southwestern United States. At the time, Nova Scotia was about as close to Germany as it was (is) to Arizona. The below figure from Brusatte et al. (2015) illustrates this well, demonstrating that there was a strong latitudinal constraint on the distribution of metoposaurids, which have yet to turn up in the well-explored Late Triassic of South America.

"Metoposaurus" bakeri figured somewhat prominently in the attempts of some workers to make correlations in relative age between geographically disparate regions around the world. Dating back to the old framework of Hunt (1993) in which Metoposaurus was found in both North America (viz. "M." bakeri) and Germany (viz. M. diagnosticus), certain workers honed in on Metoposaurus as a possible index taxon, a species or genus that is sufficiently common and widespread to serve as one of the markers used to correlate rocks deposited in disparate regions. At the time, no other genus and no species was found on more than one continent; most are actually quite restricted. However, old-school taxonomy is often conceptually suspect, and as a result, a lot of these index taxa have been diminished in biostratigraphic value. Sometimes it's shown that the occurrence in one region is not actually that taxon, so there is no direct correlation. Other times, original identifications were somewhat circular in logic or based on very fragmentary material, leaving a lot of doubt. This is not exclusive to metoposaurids, which has led to a stark bifurcation in utilized taxonomic frameworks of all sorts of Triassic tetrapods, with proponents of an ability to use terrestrial tetrapods for global biostratigraphy preferring older (outdated) frameworks that maintain the utility of this global system. This is likely an unstated rationale behind certain workers preference to maintain "M." bakeri in Metoposaurus, even after studies demonstrating that they do not actually share the lacrimal excluded from the orbit.

Our formalization of a new genus for "M." bakeri puts the final nail in the coffin for the use of metoposaurids for global biostratigraphy (although I'm sure that proponents of this scheme will continue to push the old framework). With this, no metoposaurid genus or species is definitively found on more than one continent, and most are restricted to a single depositional basin. Although metoposaurids were clearly widely spread globally thanks to the formation of Pangea, it's not surprising that taxonomic divisions along some of the modern continental boundaries as the supercontinent started to break up. Metoposaurids have never been shown to have saltwater tolerance or to be particularly capable of much terrestrial locomotion (i.e. they were limited to dispersal in freshwater). Consequently, even a narrow separation induced by, say geography, could easily result in allopatric speciation along contemporary continental bounds, kind of like the famed Grand Canyon squirrel speciation example that is often cited in high school biology books. Of course, it is important to note that the time intervals preserved on each continent or within a given depositional basin are rarely the same, so we don't always have a precise apples-to-apples comparison, but as of right now, metoposaurids are no longer viable for global biostratigraphy.

Despite an impressive surge in metoposaurid work within the past decade (more than 20 papers focusing exclusively on metoposaurids, with many others including them in a broader sample), there remains a lot of work on all fronts for metoposaurids. We outline many of these in the paper, and I'll list a few of them below.

Phylogenetic grass
The phylogeny of metoposaurids remains utterly unresolved, which is not really that surprising when considering the limitations of morphology-based phylogenetic inference for any clade and the stark conservatism in metoposaurid morphology. Through a series of differnet analyses, we demonstrated that resolution is highly sensitive to minor differences in algorithms, analytical methods, and scoring philosophy such that it's quite hard to be confident in most nodes. Certainly I think that people could do more testing (there are a million different combinations of settings), after the first set of computer-assisted phylogenies from Chakravorti & Sengupta (2018); Buffa et al. (2019); and Gee et al. (2019), this one has pretty clearly demonstrated that we are going to need a lot more data (i.e. more fossils) to even have a chance of producing any topology with measurable support for recovered nodes.

Apples and oranges
One of the often unstated limitations to the metoposaurid record is that most taxa are only known from what are probably already adult individuals. We know nothing of whether there was a larval stage in metoposaurids or of what ontogeny looked like at skull lengths less than 10 cm (metoposaurids could reach at least 65 cm or so in skull length). One of the intriguing yet oft-overlooked aspects of this incomplete record, which we illustrate below, is that one of the lesser known metoposaurids, Arganasaurus lyazidi from Morocco, is only known from small specimens. This attribute is much better known and discussed for Apachesaurus gregorii, but although the describer of Ar. lyazidi, Jean-Michel Dutuit, speculated (in French) that it might be a dwarfed taxon, this has never been adopted by other workers, let alone tested. It's interesting to juxatpose this against the growing acceptance of my proposal that Apachesaurus is also not a dwarf taxon, although certain workers continue to advocate this while ignoring all of my previous studies (likely because they have no way to refute the histological data and related arguments). How the disparity in distribution of known specimens might in general affect our interpretations of metoposaurid taxonomy (are some purportedly diagnostic features really ontogenetic features) remains to be well-explored and arguably requires someone to get lucky and find some breeding pond or something of the sort.

Old horizons
One of the downsides of being an extremely common taxon is that people rarely collect your fossils. Metoposaurids are so abundant that there is an unspoken predisposition against spending a lot of time collecting metoposaurids, which are on the larger side of the Late Triassic tetrapod scale and definitely on the upper end of the most abundant group known from the Late Triassic of North America. One of the problems is that this leads to a lot of poorly documented reported occurrences, which get dodgier as you work down to a particular genus or species. Most reports of North American metoposaurids are asides in faunal lists or review papers, and they don't provide photographs, description, or even specimen numbers. As a result, a lot of these "reports" are not reproducible. Particularly in North America, this translates into irreproducible stratigraphic ranges - what are the highest and lowest occurrences of the given taxa. In some instances, there is good documentation of the fossils, and it's the sites that are just not well-constrained stratigraphically (this is the case for B. bakeri's three localities), but for Anaschisma browni and Apachesaurus gregorii, which have thousands of specimens referred to each of them, it's more often that the stratigraphy is reasonably well-resolved, and the taxonomy is suspect (or at least not demonstrated). The North American taxa are particularly susceptible to circular logic where both size and stratigraphic position are used as identifying features in the absence of any actually diagnostic anatomical features.

The outcome of this is extreme uncertainty in what are the actual stratigraphic ranges of these two taxa, indicated above by dashed lines. The debate over Apachesaurus and whether small, elongate intercentra are really diagnostic for the taxon or just a hallmark of early ontogeny in North American metoposaurids has a huge impact on both the total abundance of specimens and the stratigraphic range of this taxon. Therefore, establishing the true range of these taxa will require a huge undertaking that involves both revisiting of specimens thought to be near the upper and lower bounds to determine whether they are diagnostic and revisiting of the sites that they come from to determine whether they are actually where previous workers have situated them.

General summary: The Middle Triassic captures a diverse global record of temnospondyls, which is also when we start to see the pinnacle of the evolution of large body size, with many taxa routinely exceeding skull lengths of half a meter and body lengths of probably 2m or greater. A variety of different groups are present at this time, all of which appeared in the Early Triassic and which would also continue through the Late Triassic, and many ecosystems were host to several different species of no close relatedness. However, the Antarctic record of Middle Triassic temnospondyls has only comprised members of a single clade, the capitosaurs. Dated and brief historical notes suggested the possible presence of another clade, the long-snouted crocodilian-like trematosaurs, but this was never substantiated, and thus the Antarctic record, despite preserving at least three different species, captures an overall much lower diversity of temnospondyls than found elsewhere around the world. In this study, we took a look at some of this more ambiguous historical material, combined with more recently collected material of some very large lower jaws. While every single one of these lower jaws belongs to a capitosaur, there is a partial interclavicle (part of the shoulder girdle) that is very clearly not that of a capitosaur but instead that of a plagiosaurid, a peculiar short-snouted clade that has hundreds of records from the northern hemisphere but a mere two others from the southern hemisphere (both of those are from the Early Triassic). We speculate on some of the reasons why the Antarctic record, which is undoubtedly undersampled, might reflect real patterns of differing ecologies among large-bodied temnospondyls (i.e. 'big crocodile analogue' is a gross oversimplication).

Globally, the Middle Triassic record of temnospondyls is quite diverse, with extensive records of many of the large-bodied taxa that people often associate with the Mesozoic. This includes the short-snouted brachyopids and plagiosaurids and the long-snouted capitosaurs and trematosaurs. Often, we find localities with multiple species, if not multiple families, of different temnospondyls, indicating that they were flourishing during this time period. The Antarctic record is therefore interesting because to date, there are only capitosaurs! Previous records mostly include brief reports of fragmentary material (e.g., Hammer, 1990), but more recently, three different genera, two of them entirely new, have been documented by Chris and colleagues (Sidor et al., 2007, 2008, 2014; see below). Some of these newer fossils are traveling around the U.S. right now as part of the traveling Antarctic Dinosaurs exhibit (currently in Buffalo at the Buffalo Museum of Science).

We also looked at more recently collected material from approximately the same localities/horizons as the historical material. This material also only included lower jaws that appear to be capitosaur in nature. Some are also remarkably large - the scale bars below are 5 cm, and conservative estimates indicate that some of these lower jaws would have been more than 90 cm long, which ranks among the largest temnospondyl specimens known from the Triassic (most capitosaurs aren't known to exceed about 60 cm in skull length). So not only do we only have capitosaurs, we have only very mature individuals, which makes sense given that these remains come from a coarse sandstone that represents a high-energy setting that would have been less conducive to preserving the remains of juveniles.

This specimen isn't just notable for being the first plagiosaurid from Antarctica, but also for being the first plagiosaurid from anywhere in the southern hemisphere in the Middle Triassic. One of the ideas that we advance here is the notion that plagiosaurids were pioneer species, something previously postulated based on bone histology (e.g., Witzmann & Soler-Gijón, 2010; Sanchez & Schoch, 2013). In this scenario, plagiosaurids would have been well-adapted for more unstable environments that could have seen fluctuations in oxygen content, salinity, and other aspects of water chemistry, and these habitats may not have been so great for other temnospondyls. Conversely, plagiosaurids may thus not have been as common in more stable habitats that were frequented by other temnospondyls, like floodplains or high-energy rivers. There is some evidence for this in the temnospondyl-rich Late Triassic deposits of Germany, where plagiosaurids tend to be common in oxygen-poor environments where remains of other temnospondyls are rare but are rare in more stable environments where there is a greater diversity of other temnospondyls.

This still leaves the question of where are the trematosaurs? This clade is found throughout the world, including in the Arctic Circle, yet there is no trace of them in the Fremouw Formation, either the Early or the Middle Triassic exposures. One idea is that trematosaurs have often been cited as being euryhaline, as they are often (but not always) found in marine deposits. If so, it's possible that trematosaurs didn't inhabit the freshwater ecosystems in Antarctica (as they do in Germany, for example), and that the marine settings that they did inhabit around the south pole weren't preserved or haven't been discovered yet. If this were true, it would indicate that the Middle Triassic clades had settled into different niches, not only with respect to what they ate, but also what type of aquatic habitats they preferred.