Dicynodonts Year-in-Review 2022

Hey. Been a while.

Alright, I'm going to ignore the Elephantosaurus in the room (ha, dicynodont joke*) of how long it's been since I last posted here and hopefully ease this blog back in to activity again with a nice and easy look back at dicynodont research in the past year. Compared to 2021 there's a bit less to write about and therefore easier to organise and summarise, so this should be a more manageable post all around.

(*Elephantosaurus is a large, thick-headed kannemeyeriiform from the Middle Triassic of Russia, named so because it was thought to be eponymously elephantine in size. It's known only by a chunk of skull from between the eyes 20 cm across, which although big isn't really any larger than some other wide-headed kannemeyeriiforms like Stahleckeria.)

New 'dont in a block

Only one new dicynodont was named this year, the cistecephalid Kembawacela yajuwayeyi (formerly known as the 'Malawian cistecephalid') from the Late Permian of Malawi, named in September by Araújo et al. Kembawacela itself was originally named in 2019 with the type species K. kitchingi from neighbouring Zambia, and was a member of Cistecephalidae, a highly specialised family of mole-like burrowers. Kembawacela is unique among cistecephalids for still possessing a pair of prominent tusks (which other cistecephalids lost), although K. yajuwayeyi does not preserve this part of the skull. The skull itself is encased in a block of solid matrix, so was studied using a synchrotron micro-CT scanner. K. yajuwayeyi is broadly similar to K. kitchingi superficially, mostly differing in details of how the bones of the skull attach to each other and the internal arrangement of nerves and blood vessels in the snout.

The matrix-covered specimen of K. yajuwayeyi and its synchrotron µCT-render of the skull,
viewed from above.
Modified from Araújo et al. (2022), CC-BY 4.0.

More broadly, K. yajuwayeyi highlights the level of cistecephalid endemism between even very closely associated basins in East Africa. Although there are broad similarities between the Permian faunas of South and East Africa, recent investigations have shown local species-level variations between these regions. This is particularly true of cistecephalids, where genera appear to be restricted to singular basins. This has been attributed to their mole-like lifestyles, which would have limited their dispersal. The discovery of K. yajuwayeyi in Malawi supports this idea, with two very closely related yet still distinct species from two neighbouring depositional basins.

An aside I'd also like to highlight the etymology of K. yajuwayeyi. The species is named in honour of Dr. Yusuf Juwayeyi, an accomplished friend and colleague of the authors. Usually when a species is named after someone, the suffix -i or -ae is appended to their name and Latinised (say in this case, "juwayeyii"). However, the authors describing K. yajuwayeyi didn't follow this convention, and instead combined his name with ya-, a possessive prefix in Chichewa, the Bantu language spoken locally in Malawi. It's a little detail, but I think it adds something more personal to the name it's honouring than the standard -i suffix.

This wasn't all Kembawacela yajuwayeyi got up to this year, but we'll come back to that.

Redescriptions and revisions

Specimens of Dicynodon angielczyki from Tanzania (A, B),
Zambia (C) and Mozambique (D), with D. lacerticeps (E, F).
From Kammerer et al. (2022).

Another contribution to African dicynodont biogeography this year was Kammerer et al. in April, who reported on additional specimens of Dicynodon angielczyki from both Mozambique and Zambia. D. angielczyki is the second and now only other species of Dicynodon, named in 2019 from specimens found in Tanzania.*  The discovery of D. angielczyki in the Metangula Graben and Luangwa Basin of Mozambique and Zambia, respectively, demonstrates that these East African units are both correlative to each other but collectively biogeographically distinct from the Karoo Basin of South Africa.

(*The former second species, D. huenei, was transferred to Daptocephalus in the same paper naming D. angielczyki, a story that really deserves its own post).

The overlap of Dicynodon angielczki across Tanzania, Mozambique and Zambia is interesting to contrast with the apparent endemism between the two species of Kembawacela. Now admittedly D. angielczyki isn't known from the Chiweta Beds of Malawi, and they likely represent different ages, so it's not a 1:1 comparison. Still, I think it highlights the complexities in dicynodont distribution across the various African basins, with larger species like D. angielczyki being found across (but still collectively endemic to) several neighbouring basins, while smaller and more specialised varieties like cistecephalids speciated even at this geographic scale.

The Shaanbeikannemeyeria Saga

This one comes with a little story first. For the longest time, Shaanbeikannemeyeria xilougouensis was one of the most mysterious dicynodonts to me. For starters, its Wikipedia page was the barest of bones:

"Shaanbeikannemeyeria is an extinct genus of non-mammalian synapsid known from the Middle Triassic (Anisian) of China." 

Heck, up until 2018 it had been entirely redirected to the Kannemeyeria page on the basis it was  suggested to be synonymous (again, the taxonomy here is its own whole thing probably deserving another post—if anything it should have been redirected to Rechnisaurus!). However, unlike a lot of other dicynodonts with bare-bones Wiki pages for which a bit of sleuthing and perseverance will turn up other results, I could find next to nothing accessible online for Shaanbeikannemeyeria. Papers, photos, illustrations, any more information, I was turning up blanks.

The squashed looking skull of 'S. buerdongia'
(miscaptioned here as 'Shanbeikannemeyeria').
From Li (1980).

Well, almost. There is a copy of a paper online naming a second species, S. buerdongia, which is fairly unanimously recognised as a synonym of S. xilougouensis nowadays. However, the skull of this specimen has been heavily eroded, removing most of the skull itself to leave only the lower jaw, palate and occiput. It's also been rather squashed out of shape. Tantalisingly, the whole skull of S. xilougouensis was said to be well preserved by comparison, so this just drove my curiosity further up the wall.

I don't think this was just a case of looking in the wrong places either. As far as I could tell there weren't any published reconstructions of Shaanbeikannemeyeria out there either, so it seems to me that information on this dicynodont really was just hard to come by in general, including as physical publications.

I was thrown a bone this past May when a friend shared with me a scanned copy of Paleovertebrata Sinica Volume III, a publication on China's synapsid fossil record. Naturally, I went to see what it had to say on dicynodonts, and to my surprise saw an illustration of the complete skull of Shaanbeikannemeyeria! I was compelled to make a sketchy reconstruction of it, to my knowledge still the only reconstruction of it currently online, and quite possibly the first one ever—assuming an earlier published reconstruction doesn't exist in a physical publication somewhere.

And then guess what happened.

My reconstruction of Shaanbeikannemeyeria, based off an illustration from Paleovertebrata Sinica III and pre-Liu (2022).

Only just a few days later that June, Jun Liu publishes an open-access description of numerous new specimens of Shaanbeikannemeyeria, including nearly complete postcrania and skulls from individuals of various ages, all lavishly figured with photos. Decades of next to nothing to go on, then when a single old illustration serendipitously makes its way to me, an entire paper with all the reference material I could ever ask for drops within days of reconstructing it. I'm still flabbergasted by the timing of this.*

Overnight Shaanbeikannemeyeria went from one of the least accessible and imaged kannemeyeriiforms to one of the best. If you're a palaeoartist feeling inclined to draw a dicynodont, I encourage you to give Shaanbeikannemeyeria some love. The references are all there now, so let's make up for lost time! 

(*This isn't even the first time, believe it or not—some years back I was asked to draw Hulsanpes, at the time a rarely illustrated and poorly understood paravian of uncertain affinity. A week later, Halszkaraptor is published, identifying Hulsanpes as a close relative.)

Some of the new Shaanbeikannemeyeria material. Holy cow.
From Liu (2022).

More Research

Another paper published in June was a study by Macungo et al. on the braincase and basicranium of three emydopoids; little Myosaurus and two cistecephalids, Kawingasaurus and the then-unnamed Kembawacela yajuwayeyi (told you it'd be back). This study revealed numerous new details of emydopoid brain anatomy that was informative for both their physiology and phylogeny.

A reconstruction of a burrowing cistecephalid that I can
only describe as "scrunkly".
By Luzia Soares, from Macungo et al. (2022).

Their study demonstrated the presence of prominent bony crests and hollows on the back of cistecephalid skulls that would have anchored well-developed neck muscles, as well as relatively fused and ossified braincases. This supports a previous suggestion that cistecephalids likely not only used their forelimbs to dig, but also used their heads to shovel dirt and soil out of the way. This had previously been proposed based on the highly complex and strong suturing of their skull bones (Kammerer 2021), and now there's evidence for strong neck lifting muscles and solidified braincases to protect the brain from rapid and powerful head movements.

They also highlighted several novel phylogenetic relations following the inclusion of internal cranial characteristics. One of these was recovering the purported basal-bidentalian Rastodon as a basal emydopoid instead. A relationship to emydopoids had been suspected for Rastodon before, but almost every prior phylogenetic analysis still found it as a bidentalian, and none as an emdyopoid until now. Another notable shift was finding kingoriids to be more basal than emydopids, by definition removing them from Kistcephalia. This upset is accompanied by the removal of Thliptosaurus from its original home in Kingoriidae to a position between them and emydopids, alongside Digalodon. Kembawacela and Sauroscaptor have also shifted from their original placements as more derived than Cistecephalus to having diverged first among cistecephalids.

Lystrosaurus made its obligatory appearance in September with a paper testing for Bergmann's rule across Lystrosaurus populations. Bergmann's rule posits that animals grow to larger sizes at higher latitudes, usually attributed to cooler climates, and a study by Kulik & Sidor set out to test if this rule applied to the distribution of Early Triassic Lystrosaurus. Lystrosaurus body size is already an interesting subject, as it is known to show a marked decrease following the end-Permian mass extinction, albeit apparently not through dwarfism or similar mechanisms but rather seemingly by just living fast and dying younger. 

These new results found Lystrosaurus to not follow Bergmann's rule, with the maximum body sizes being much the same between high and mid-latitudes. Curiously though, the average sizes differed between high-latitude Gondwana and mid-latitude China, with Lystrosaurus more regularly reaching larger sizes in mid-latitudes. This corroborates results from a paper the year before (Kulik et al., 2021) which found Lystrosaurus from China to more often grow larger and for longer than their southern relatives. This suggests that regional environmental conditions may have been a greater factor affecting their body size and lifespans than latitude, with wetter and more favourable conditions at mid-latitudes.

Lystrosaurus would make another, very exciting appearance this year too in an August paper from Smith et al. on the taphonomy of Lystrosaurus in the earliest Triassic of South Africa. The paper itself is cool, but that's not what grabbed people's attention. What got people excited was that this was the first official publication of the long-rumoured Lystrosaurus mummies! I'm planning to discuss the paper and the mummies in their own post, so I won't go deeper into it here, but in short these mummies and how they died can tell as whole lot about the environmental conditions and behaviour of Lystrosaurus post Permo-Triassic extinction, and not just about their life appearance.

New skulls of Dinodontosaurus brevirostris,
plus D. "platygnathus" (5), with lower jaws.
From Escobar et al. (2022). 

In November, Escobar et al. (in press) released a study on the mandibular anatomy of Dinodontosaurus brevirostris from the Chañares Formation in Argentina. Like many dicynodonts, only the skull of D. brevirostris is known in detail. Escobar et al. set out to try and remedy this in Dinodontosaurus, with the description of two new, well-preserved specimens of D. brevirostris (see left) and re-analysing and scoring the characteristics of its lower jaws.

The phylogenetic results are not much different from existing analyses, strengthening the relationship between Dinodontosaurus to the Stahleckeriidae + Angonisaurus clade. Notably, the reflected lamina is well preserved in one of the new specimens, revealing it to be very large, rounded and unornamented, very much like those of Angonisaurus and stahleckeriids. On the other hand, other features like the shape and structure of the symphysis differ from stahleckeriids, affirming its position outside of Stahleckeriidae proper.

They also highlight potential taxonomic implications for the other Dinodontosaurus species, the Brazilian D. tener, too. Namely, while the mandibles of historic D. tener specimens are evidently distinct from D. brevirostris (e.g. smaller reflected lamina, more stahleckeriine-like jaw symphyses), some specimens seem more similar to those of D. brevirostris. Quite what this means taxonomically without a rigorous osteological analysis of D. tener isn't clear, but it is interesting following comments from Kammerer and Ordoñez (2021) highlighting the variation that exists in D. tener based on skulls, which now seems to also extend to the mandibles as well. Time will tell for however this shakes out in the future.

Dicynodont adjacent

In more general synapsid news, but still of great dicynodont relevance, was the first broad-scale description of the reflected lamina in therapsids by Savannah Olroyd and Christian Sidor in August. This structure, a sheet of bone attached to the angular of the lower jaw, has long been of interest to therapsid researchers and its function has been rather enigmatic. Some have regarded it as a point for muscle attachments, while others have implicated it in the evolution of hearing in therapsids. Olroyd and Sidor (2022) is a major step forward in sorting out just how the reflected lamina evolved and varied in therapsids, as most previous research has focused on specific comparisons within groups, and the broad general anatomy between therapsids as a whole has been poorly characterised. 

Dicynodonts were notable in their study for the level of variability in the shape, size, and sculpturing of the reflected lamina compared to other therapsids, which otherwise have rather stereotyped, clade-specific structures. Curiously, bidentalian dicynodonts seem to have lost much of the ridges found on the laminae of other therapsids, especially in the Triassic kannemeyeriiforms, leaving a much less complex surface. This is especially unusual considering that non-bidentalian dicynodonts have some of the more complex and variably structured reflected laminae of any therapsids. Whatever dicynodonts were using the reflected lamina for, clearly they were experimenting with it. The function of the reflected lamina is one of the most fascinating mysteries in therapsid research for me, and so I am very excited to see where this research will go in the future now that it has a standardised framework to work from.

Summary

And that about wraps up the review! A lot of cool stuff, even if it's a bit light compared to previous years. The year seems to have been fairly top heavy, having got off to a slow start but picking up from June onwards. Another new year with at least one new species, so the ball is still rolling on that count. It's always hard to make a call for any "best" discovery of the year, but I think if I had to pick a favourite that would have to go to the Shaanbeikannemeyeria redescription for being a totally unexpected but welcome surprise and also for its truly impeccable timing. 10/10 job.

The phylogenetic scope is definitely more limited this year, with only emydopoids, kannemeyeriiforms, and other dicynodontoids receiving dedicated papers this year. Nothing for basal anomodonts and dicynodonts, endothiodonts, plycaecephalids, or cryptodonts, excepting their appearances in Olroyd and Sidor (2022) with just about every other type of therapsid. Of the groups covered, it's a fairly even split with 2–3 papers each for the three groupings. Lystrosaurus, as usual, seems to be a favourite with two papers, though Kembawacela had a pretty good year too.

That about wraps up 2022, here's hoping for another exciting year of dicynodonts in 2023! I'm proud to say that I'll be taking part in this research myself, as part of my ongoing Masters degree I will be examining and describing a dicynodont specimen, and it's probable you'll be hearing more about this on here down the line.  Hopefully I'll get some exciting results from my research, and I look forward to seeing what else the new year will have in store for dicynodonts.

And maybe I'll even get some more actual posts on here too.

Scottish dicynodont Gordonia stares doubtfully at the above sentence.

References

Araújo, R., Macungo, Z., Fernandez, V., Chindebvu, E. G., & Jacobs, L. L. (2022). Kembawacela yajuwayeyi n. sp., a new cistecephalid species (Dicynodontia: Emydopoidea) from the Upper Permian of Malawi. Journal of African Earth Sciences. 196: Article 104726.

Escobar, J. A., Martinelli, A. G., Ezcurra, M. D., Fiorelli, L. E., Von Baczko, M. B., Novas, F. E., & Desojo, J. B. (2022). Reassessment of the mandibular anatomy of non-stahleckeriine kannemeyeriiforms (Synapsida, Dicynodontia) from the Ladinian-early Carnian Chañares Formation (northwestern Argentina), and its taxonomic and phylogenetic significance. Ameghiniana. In press.

Kammerer, C.F. (2021). Elevated cranial sutural complexity in burrowing dicynodonts. Frontiers in Ecology and Evolution. 9: 674151.

Kammerer, C. F., Araújo, R., Cumbane, K., MaCungo, Z., Smith, R. M. H., & Angielczyk, K. D. (2022). New material of Dicynodon angielczyki (Synapsida: Anomodontia) from Mozambique and Zambia with biostratigraphic implications for African Permo-Triassic basins. Journal of Vertebrate Paleontology. 41 (6): e2041652.

Kammerer, C. F., Ordoñez, M. D. (2021). Dicynodonts (Therapsida: Anomodontia) of South America. Journal of South American Earth Sciences. 108: 103171

Kulik, Z. T., Lungmus, J. K., Angielczyk, K. D., & Sidor, C. A. (2021). Living fast in the Triassic: New data on life history in Lystrosaurus (Therapsida: Dicynodontia) from northeastern Pangea. PLOS ONE. 16 (11): e0259369.

Kulik, Z. T., Sidor, C. A. (2022). A test of Bergmann's rule in the Early Triassic: latitude, body size, and sampling in Lystrosaurus. Paleobiology: 1–15.

Li, J-L. (1980). Kannemeyeria fossil from Inner Mongolia. Vertebrata PalAsiatica. 18 (2): 94–99.

Liu, J. (2022). On kannemeyeriiform dicynodonts from the Shaanbeikannemeyeria Assemblage Zone of the Ordos Basin, China. Vertebrata PalAsiatica: 1–38.

Macungo, Z., Benoit, J., Fernandez, V., & Araújo, R. M. N. (2022). X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny. Zoological Journal of the Linnean Society.

Olroyd, S., Sidor, C. A. (2022) Nomenclature, comparative anatomy, and evolution of the reflected lamina of the angular in non-mammalian synapsids. Journal of Vertebrate Paleontology. 42 (1): e2101923.

Smith, R. M. H., Botha, J., Viglietti, P. A. (2022). Taphonomy of drought afflicted tetrapods in the Early Triassic Karoo Basin, South Africa. Palaeogeography, Palaeoclimatology, Palaeoecology. 604: Article 111207.

Dicynodont Year-in-Review 2020

Took me long enough, but here it is: the review of dicynodont research published in 2020! It simultaneously feels like I started this blog just the other day and much, much longer than over 7 months ago. And yet, the time for the annual palaeoblog tradition of an end-of-the-year roundup of discoveries has come (arguably been and gone by now). So, how did dicynodonts fare last year? 

As you'd expect, given...circumstances, 2020 has been a good bit quieter than the last year with only one newly named taxon (compared to the rather exceptional seven new taxa of 2019, but read on). However, there has still been quite a few significant discoveries published this year on them, many of which I originally intended to dedicate a post to each during the year. How many did I manage to finish this year? Two?...Oh dear.

Well without further ado, let's see just how much I managed to miss!

Research

While this year was a bit of a wash discovering and collecting new specimens, it hasn't caused dicynodont research to stop in its tracks and there's plenty of new stuff to highlight.

The bizarre Endothiodon got some much needed attention this year, with two studies on it published. The first was published by Macungo et al. (2020) in March, who described a whopping 111 new specimens from both recent and historic expeditions in the Metangula Graben in Mozambique. Curiously, collection includes specimens attributable to both E. tolani and E. bathystoma, for which the authors put forward several explanations. One possibility is that that because these species appear stratigraphically separated in the Ruhuhu Basin of Tanzania, there may be a similar, as yet unrecognised, stratigraphic separation in the Metangula Graben. Another possibility is that the two species may have coexisted after all, at least in Mozambique. Perhaps their most intriguing suggestion is that there weren't even two distinct species at all, and that they instead represent the end members of a cline of variation from the Karoo in the southwest to Tanzania and Mozambique in the northeast. The answer isn't clear, and it likely won't be solved until we have more information on the stratigraphy of Endothiodon, determine how old each species is, and sort out its taxonomy once for all.

PPN2014-11, one of many new specimens of Endothiodon from Mozambique. The presence of tusks ('tsk' in the diagram) in this specimen implies it belongs to E. tolani. From Macungo et al. (2020).

Then in June, an isotopic study of Endothiodon from the Karoo Basin was published by Rey et al. (2020). Their findings suggest that Endothiodon was more reliant on water and riparian vegetation compared to more typical dicynodonts, which may relate to its unusual distribution geographically and over time. This was actually one publication I did manage to cover last year, so I'll not repeat myself here, but with this study and the questions raised by the new specimens from Mozambique, suffice to say there is still much ado about Endothiodon.

The natural habits and habitat of Endothiodon?

In July, a new skull of Dinodontosaurus was described from the Chañares Formation by Ordoñez et al. (2020) using 3D modelling from CT scans. Dinodontosaurus returned in October with the description of a monotypic bonebed of at least six juveniles published by Ugalde et al. (2020), further supporting group-living behaviour in this genus. The taphonomy of the specimens imply that the young animals were not simply transported together during or after death, but died close by each other and lay exposed on the surface for some time before burial. They may have died of malnutrition, disease, or perhaps abandoned by their parents.

The new Dinodontosaurus bonebed while it was still alive. By Márcio L. Castro, from Ugalde et al. (2020).

Taphonomy was also the focus of another study by Kammerer et al. (2020) (open access!), who quantified the effects taphonomic deformation using the many, many known skulls of Diictodon as a case study. They found that deformation tends to overprint any sort of biological signals in Diictodon skulls, such as those attributed to sexual dimorphism or changes during growth. They also found that all the deformed Diictodon skulls cover a frighteningly broad range of the total dicynodont skull morphospace, which is bad news if you're trying to identify real variation within a species. There is some good news though, a large sample of deformed skulls can still be used to approximate the mean, undistorted morphology for higher clade-level analyses, so their utility is not all lost!

Diictodon skulls come in a variety of flavours, including but not limited to normal, squashed side-to-side, squished top-to-bottom, and many more. From Kammerer et al. (2020).

Other notable publications include a histological study of the preparietal bone in Diictodon and Lystrosaurus by Marilao et al. (2020) from July. The preparietal is an extra bone in the skull roof unique to therapsids, and seemingly independently evolved in dicynodonts, gorgonopsians and biarmosuchians, and so is about as well understood as you'd expect for a bone with no known analogue. Their findings imply that the preparietal grew rapidly to the back along the border of the pineal foramen, at least in dicynodonts, and had unusually complex sutures with the surrounding skull bones. Whether this holds true for other dicynodonts, and indeed other therapsids, is yet to be seen, but this is still an important first step in figuring out the preparietal and dicynodonts are leading the way.

Last but not least, in December, a new record referred to cf. Jachaleria candelariensis from Brazil was reported by Martinelli et al. (2020). It admittedly isn't much, just four vertebrae, but it could be the first J. candelariensis remains discovered outside of the type quarry. These remains also help to further establish correlations of the Riograndia Assemblage Zone throughout Brazil.

New 'donts on the block

In July, we saw the first and only new dicynodont named in 2020: Taoheodon baizhijuni. This was another publication I covered last year, so again I won't repeat myself much. It was a dicynodontoid, seemingly closely related to Dicynodon itself, from Northern China, part of a growing record of dicynodonts from the Late Permian of East Asia. Taoheodon may be of particular importance as it may provide a sort of link between the dicynodonts known from South Africa and Europe and those from Laos that have been known since the end of the 19th century (recently described as their own genera by Olivier et al. in 2019).

Reconstruction of Taoheodon baizhijuni.

Tangentially, Taoheodon may also be the first dicynodont known to have coexisted with an embolomere (not counting Triassic chroniosuchians). Seroherpeton was also described this year from the lower Sunjiagou Formation in China, which would place it as roughly contemporaneous with Taoheodon. While itself not a dicynodont-related discovery, it's still a bit of a novelty as to my knowledge dicynodonts and embolomeres have never been found in coeval deposits before now.

Taoheodon may be the only new name, but it may not be the only new taxon identified this year. All the way back in January, Yi and Liu (2020) described another partial dicynodont skull from the same strata as Taoheodon. They referred the specimen to Cryptodontia, which would be a first for China. Additionally, two other fossils were also described this year that may hint at even more as yet unrecognised dicynodonts. 

IVPP V 26043, also known as 'Cryptodontia indet.'. From Yi and Liu (2020).

The first of these was published by Maisch (2020) in October, who re-evaluated a partial skull roof of a large dicynodont from the Triassic Santa Maria Formation in Brazil. The specimen, GPIT RE/09622, was discovered by von Huene and Stahlecker all the way back in 1928, but remained ignored and undescribed in the near century since then. Despite its incomplete nature, Maisch concluded that the specimen is not from the two known dicynodonts of the Dinodontosaurus Assemblage Zone, Stahleckeria and the eponymous Dinodontosaurus, nor any other kannemeyeriiform for that matter. 

Maisch also raised the possibility that Stahleckeria ("Barysoma") lenzii, which has typically been lumped into S. potens, may itself also be valid after all, reiterating previous arguments for its distinction. If correct, this would raise the total number of dicynodonts in the Dinodontosaurus AZ to not just three, but four taxa.

However, and this just shows how late I am with this post, these suggestions have already been met with scepticism in a paper by Kammerer and Ordoñez (2021) published in January (I swear I'll get to this one in a timely fashion). In a review and reassessment of South American dicynodont taxa, they also evaluated the proposals made by Maisch (2020). They suggest that GPIT RE/09622 may fall within the realm of variability for Dinodontosaurus after all, with preservational complications accounting for some of the purported differences between it and the compared specimens of Dinodontosaurus. Nonetheless, they acknowledged that it is possible that there are still unrecognised dicynodonts in the Dinodontosaurus AZ, perhaps even within the many incompletely prepared specimens of "Dinodontosaurus" out there.

Likewise, they concluded that the skull characteristics used to support S./"B". lenzii  can be chalked up to taphonomy and simply the range of variation seen in other kannemeyeriiforms known from lots of specimens, and so it is likely still S. potens. So, back to square one? Maybe, but who knows, there might still be a new dicynodont taxon hidden in the Dinodontosaurus AZ yet.

The skull roof known as GPIT/RE/09622, new taxon or more Dinodontosaurus? From Maisch (2020).

The second proposed new taxon was published by Smith et al. (2020) just the next month in November, and they also described a partial skull. This time it's a chunk of the back of the skull from a kannemeyeriiform discovered in the Triassic upper Fremouw Formation in Antarctica. The Fremouw is better known for its abundant Antarctic Lystrosaurus material in its lower member, but the younger upper Fremouw has spat out fossils of kannemeyeriiforms too, albeit only fragments of maxilla, tusks and a squamosal. The partial skull described by Smith et al. is by far the most complete kannemeyeriiform remains yet recovered from the Fremouw.

Intriguingly, the specimen has a combination of characteristics unlike any known dicynodont, and may even have at least one entirely unique trait, which could mean that this Antarctic kannemeyeriiform may represent a new taxon endemic to Antarctica. Still, the specimen is too incomplete to be certain, and so it remains nameless, but the presence of a unique Antarctic Triassic dicynodont is tantalising. The specimen itself is comparable in size to Kannemeyeria, although it's less clear what type of kannemeyeriiform it belongs to.

The presence of tusks from the Fremouw would be consistent with a kannemeyeriid-esque animal, but the aforementioned squamosal shows signs of a distinctly stahleckeriid affinity. This suggests there are two kannemeyeriiforms from the upper Fremouw, and theoretically this new specimen could come from either (although it may have affinities with kannemeyeriid types). Only time will tell just what kind of dicynodont the new skull-chunk belongs too, but it's a tantalising clue of what awaits us from Antarctic dicynodonts.

LACM-DI 160748, the Antarctic kannemeyeriiform, in occipital view (from behind, in other words). From Smith et al. (2020).

Lystosaurus Galore

To cap the roundup off, special mention goes to good old Lystrosaurus, which received a fair bit of attention this year! Three studies focused on it were published this year, two from within the last two months of the year, with significant implications for its lifestyle and just how we think of this (relatively) famous dicynodont. And to top it off, they're all open access!

The first of these was a study by Whitney and Sidor (2020) on the growth of Lystrosaurus tusks from Antarctica. Compared with tusks from South African Lystrosaurus, the Antarctic specimens showed clear signs of periodic slowed growth rates, signs of stress and interrupted growth. These dark zones are consistent with these specimens entering a period of torpor or hibernation, slowing their metabolism and growth rate to sit out environmental stresses not experienced by their relatives in South Africa. Given that Antarctica was below the Antarctic circle at this time, it seems probable that polar populations of Lystrosaurus were capable of going into torpor to sit out the worst of the dark polar night, when food would have been scarce. Perhaps such metabolic flexibility shouldn't be unexpected from an animal that survived the Permo-Triassic mass extinction, but it's still a cool discovery.

Cross sections of Lystrosaurus tusks from Antarctica (a) and South Africa (b), highlighting the dark 'hiernation lines' (or lack thereof). Modified from Whitney and Sidor (2020).

The other two papers re-examine some of the stereotypical claims surrounding the genus and its survivorship of the Permo-Triassic mass extinction.

The first of these, Botha (2020), examined the growth of all four Lystrosaurus species in South Africa to test the claimed "Lilliput effect" whereby the two Triassic Lystrosaurus species were dwarfed compared to their Permo-Triassic predecessors. She found fast bone-growth in all four species, but only in L. maccaigi, the largest species, did any ever reach the stage of slower, mature growth. The case seems to be then that the smaller Triassic species could very well have reached the same large sizes as L. maccaigi and L. curvatus, but many died before reaching this size. Inconsistent growth marks in the Triassic species further imply that environmental stress was affecting their growth patterns. This builds upon previous work that proposed Triassic Lystrosaurus were breeding and dying young all while they were still growing, and weren't dwarfed adults at all (Botha-Brink et al. 2016).

Finally in December, a paper by Modesto (2020) revisited the claim that Lystrosaurus was a "disaster taxon", and concluded that whichever way you define it, Lystrosaurus probably was not a disaster taxon. Shocking, I know.

This isn't to say that Lystrosaurus wasn't an especially abundant animal in the wake of the P-Tr extinction event, it certainly was. But according to Modesto Lystrosaurus just doesn't fit the criteria for any of the definitions of disaster taxa in palaeontology. It lived about as long as could be expected of any fossil tetrapod genus, it evolved prior to the extinction, not during and/or immediately after, and its great abundance is not associated with the immediate aftermath either. Rather than a disaster taxon in the strict sense that flourished in the wake of an environmental crisis, Lystrosaurus was a genus that simply managed to whether the P-Tr extinction and was able to recover afterwards, exploiting a vacuum left behind by the extinction of most other large herbivores. I suspect that this is what some of you picture as a disaster taxon anyway, but hey, that's semantics.

Summary

Overall, I think it's fair to say it's been a busy year for Lystrosaurus for one, but there's certainly been no shortage of other dicynodont research across the board either. One new named species isn't bad for a group like dicynodonts, but raising the prospect of others definitely counts for something too. The phylogenetic scope hasn't been that bad either, though there was a clear bias to the dicynodontoids. Endothiodon takes the cake for non-dicynodontoids, although only Diictodon of the pylaecephalids provides much competition, with little to say for the cryptodonts and let alone anything for the emydopoids. To say nothing of other amomodonts, which were conspicuously lacking this year.

That wraps it up for 2020, hopefully 2021 will deliver just as many exciting new discoveries! The year's already off to a strong start with a review of South American dicynodonts (Kammerer and Ordoñez), including coining two new taxa, so let's hope the momentum keeps up.

And if not, it means I've got plenty of time to play catch-up.

A smiley Galeops wishes you all a long overdue happy 2021.

References

Botha, J. (2020). The paleobiology and paleoecology of South African Lystrosaurus. PeerJ, 8, e10408.

Botha-Brink, J., Huttenlocker, A., Angielczyk, K. D., Codron, D., Ruta, M. (2016). Breeding young as a survival strategy during Earth’s greatest mass extinction. Scientific Reports 6, 24053.

Kammerer, C. F., Deutsch, M., Lungmus, J. K., & Angielczyk, K. D. (2020). Effects of taphonomic deformation on geometric morphometric analysis of fossils: a study using the dicynodont Diictodon feliceps (Therapsida, Anomodontia). PeerJ, 8, e9925.

Kammerer, C. F., Ordoñez, M. D. (2021). Dicynodonts (Therapsida: Anomodontia) of South America. Journal of South American Earth Sciences. In press.

Liu, J. (2020). Taoheodon baizhijuni, gen. et sp. nov. (Anomodontia, Dicynodontoidea), from the upper Permian Sunjiagou Formation of China and its implications. Journal of Vertebrate Paleontology, 40 (1), e1762088.

Maisch, M. W. (2020). An unusual historic dicynodont specimen (Therapsida: Dicynodontia) from the Dinodontosaurus Assemblage Zone of the Santa Maria Formation (Middle Triassic) of Rio Grande do Sul, Brazil. PalZ, 1-16.

Marilao, L. M., Kulik, Z. T., & Sidor, C. A. (2020). Histology of the preparietal: a neomorphic cranial element in dicynodont therapsids. Journal of Vertebrate Paleontology, 40 (2), e1770775.

Modesto, S. P. (2020). The disaster taxon Lystrosaurus: a paleontological myth. Frontiers in Earth Science, 8, 617.

Ordoñez, M., Marsicano, C. A., & Mancuso, A. C. (2020). New specimen of Dinodontosaurus (Therapsida, Anomodontia) from west-central Argentina (Chañares Formation) and a reassessment of the Triassic Dinodontosaurus Assemblage Zone of southern South America. Journal of South American Earth Sciences, 102597.

Smith, N. D., Makovicky, P. J., Sidor, C. A., & Hammer, W. R. (2020). A kannemeyeriiform (Synapsida: Dicynodontia) occipital plate from the Middle Triassic upper Fremouw Formation of Antarctica. Journal of Vertebrate Paleontology, e1829634.

Ugalde, G. D., Müller, R. T., de Araújo-Júnior, H. I., Dias-da-Silva, S., & Pinheiro, F. L. (2020). A peculiar bonebed reinforces gregarious behaviour for the Triassic dicynodont Dinodontosaurus. Historical Biology, 32 (6), 764-772.

Whitney, M. R., & Sidor, C. A. (2020). Evidence of torpor in the tusks of Lystrosaurus from the Early Triassic of Antarctica. Communications biology, 3 (1), 1-6.

Yi, J. & Liu, J. (2020). Pareiasaur and dicynodont fossils from upper Permian of Shouyang, Shanxi, China. Vertebrata PalAsiatica. 51 (8): 16–23.