A brief run down of Meridiolestida

Meridiolestida.pngA run down of several meridiolestidans by Christopher Rigobello. Note: artist insisted on external scrotum for Leonardus, though I have my personal doubts.

Though today most mammal faunas are composed of placentals and marsupials, a variety of other groups thrived across the Late Cretaceous and even until fairly recently in the Late Cenozoic.

One of the most successful of these groups were the meridiolestidans, a group of dryolestoid mammals that became the dominant mammals of Late Cretaceous South America, ranging from small insectivores to some of the largest Mesozoic mammals. Even after the Cretaceous/Paleocene mass extinction, they managed to continue to thrive for a while longer, with the very youngest species a mere 10-17 million years ago. Some even suggested a modern presence in marsupial moles, though as we will see this is sadly likely not the case.

In any case, they are certainly an interesting bunch, with several meanderings and successes up to their extinction.

Origins at my doorstep(!)

HenkelotheriumHenkelotherium by ‘Fuzhong!’. Although not a meridiolestidan, this is just one of many dryolestoids native to the Jurassic and Early Cretaceous of the Iberian Peninsula, indicating a local radiation there.

As noted before, meridiolestidans are part of a lineage of mammals known as Dryolestoidea. Some studies have recovered Dryolestoidea as paraphyletic and with meridiolestidans slightly closer to therians than classical dryolestoids like Dryolestes itself (Averianov et al 2013), but most studies seem to recover Dryolestoidea as monophyletic and with Meridiolestidans either nested within the northern forms (Rougier et al 2011, Rougier et al 2012, Chornogubsky 2011, Rougier 2018) or as a sister-taxa outgroup (Thompson et al 2014). If the former, the north american and european genus Laolestes appears to be their closest relative (Rougier 2018).

Dryolestoids are overall similar to therian mammals and relatively closely related to them as far as most phylogenetic studies are concerned, being usually the most basal members of Cladotheria. They nonetheless differ in details of their tooth anatomy like for instance prismatic enamel, “eupantotherian” style molars* and double canines roots as well as their braincase; meridiolestidans themselves differ from other dryolestoids in lacking a parastylar hook on their molars, freeing their teeth for better grinding over piercing, most notably allowing transverse (i.e. side-to-side; imagine for instance horses or sheep) chewing. Non-meridiolestidan dryolestoids have slightly more ‘archaic’ ear and jaw bones than therian mammals, such as a well developed coronoid and splenial and the presence of a Meckelian groove, suggesting a connection of the ear bones to the jaw, but these features are independently lost in many dryolestoids, with mesungulatids and Dryolestes itself even losing the Meckelian groove, so in essence having a “modern” ear.

It’s been suggested that dryolestoids, like most cladotherians, already had erect limbs (Kielan-Jaworowska et al 2004), though personally I think we do need to rethink on how we demonstrate the limb gait in non-therian mammals, given the studies on other seemingly sprawling taxa like phytosaurs and Dimetrodon. The few full skeletons we have generally demonstrate that they lacked venomous tarsal spurs as earlier mammals such as multituberculates, symmetrodonts and gobiconodontids had, and their relatively “modern” ankle bones seem to confirm them as spur-less as far as I am concerned. Like most non-placental mammals, they have epipubic bones, suggesting that they gave birth to fetus-like undeveloped young.

They could have differed in a variety of soft tissue ways; for instance modern marsupial moles, which I regardless of its affinities see as a good functional model for at least a few species, have a true cloaca rather than separated genital and excretory holes, lack a prostate, have backwards-facing pouches and have a weird brain where the olfactory lobes are entirely in front of the cerebellum and a small neopallium. That said, as noted above some dryolestoids convergently evolved a few “modern” traits several times, and therians themselves changed their reproductive anatomy several times, with testicles dropping independently in marsupials and various boreoeutherian groups and a reversion to a true cloaca in tenrecs and marsupial moles, so it’s possible, if in my opinion not particularly likely, that some dryolestoids converged with therian mammals in these regards.

So overall, dryolestoids were similar to therians, if somewhat ‘quirky’.

Dryolestoids first appear in the mid-Jurassic, with amphitheriids being the oldest and most basal representatives. Dryolestoids quickly dispersed across the northern continents, but their Jurassic-Early Cretaceous diversity is noted as being focused on Western Europe, with the Iberian Peninsula in particular being a diversity hotspot (Chimento et al 2016). Sure enough, the portuguese Jurassic mammal fauna is uniquely dominated by dryolestoids compared to other faunas such as the American Morrison Formation’s, and laurasian dryolestoids remain in the Early Cretaceous of Spain longer than in other regions.

The story of meridiolestidans likely begins here, therefore. The earliest meridiolestidans are Donodon and Thereuodon (Chornogubsky 2011), which occur in the Berriasian of North Africa. Other contemporary mammals here, typically considered symmetrodonts or early therians, may also actually be dryolestoids (Chimento et al 2016), suggesting that Meridiolestida began as an African dryolestoid radiation. Their ancestors arrived northward from a temporary connection with the Iberian Peninsula, there being also several other laurasian taxa in North Africa to back up this claim, such as gobiconodontid mammals or choristodere reptiles (Allain et al 2014).

Once isolated in Africa, the earliest meridiolestidans most likely dispersed ecologically. Donodon itself is only known from a single tooth, but it is so similar to that of Late Cretaceous mesungulatids (Bonaparte 2002) that they might indicate a similar herbivorous lifestyle; at its putative rabbit-like size, one can easily call it the hyrax of Cretaceous Morocco. This is already a far cry from the insectivore/omnivore range occupied by most laurasian dryolestoids at the time, and yet another magnificent instance of Mesozoic mammals being more diverse than typically assumed.

The ultimate fate of the African and Iberian meridiolestidans is unknown. There is sadly no mammal fossil record from the Middle and Late Cretaceous of these regions aside from a single gondwanathere jaw (and if gondwanatheres aren’t true mammals then none at all), not even in sites like the famous Kem Kem Beds. Perhaps they became extinct in the Mid-Cretaceous, alongside so many other mammal groups, or perhaps they did endure until the KT event and we simply don’t know about it. The idea of hyrax-like mammals living alongside Spinosaurus is amusing to me at least.

Still, they certainly are gone from Cenozoic deposits in Africa and in Europe, where placentals and metatherians (and, for the briefest of whiles, multituberculates) are the dominant mammals to the exclusion of all others.

*To quote Grossnickle et al 2013. In truth I don’t think I’ve ever seen “eupantotherian” used to describe a molar type anywhere else, as “eupantotherian” anything has fallen into disuse in modern literature.

Refuge in Argentina (before it was disturbing)

Photo-and-line-drawing-of-Austrotriconodon-mckennai-lower-right-premolariformAustrotriconodon mckennai tooth.

Nonetheless, we do know one place where meridiolestidans survived further: South America.

As South America was connected to Africa, its extremely easy to suspect that meridiolestidans moved to there in the Early Cretaceous. Even after the two continents split apart, however, many mammal taxa moved from Africa to South America, perhaps by rafting, such as New World monkeys and rodents; I suspect whichever method of dispersal is ultimately irrelevant, since the result is the same.

What is known is that, by the Cenomanian, meridiolestidans became the dominant mammals of the continent (Pascual 2001, Rougier 2008, Rougier 2009, Rougier et al 2011, Rougier 2012, Forasiepi 2012, Averianov 2013, Chimento et al 2016, Grossnickle et al 2016, Rougier 2018, among most other sources here), ranging in a variety of niches from small insectivores to large herbivores. Other synapsid groups are present in the Late Cretaceous as well, just as gondwanatheres, multituberculates, monotremes and even some therians (Chimento 2016, Castro 2018), but none even remotely approach both the quantity of fossils as well as morphological diversity. Some supposed representatives of other mammal groups, such as the putative eutriconodont Austrotriconodon, have turned out to be meridiolestidans as well.

The diversity of meridiolestidans in South America in some ways mirrors the success of their therian relatives and multituberculates in the northern continents (Grossnickle 2013). The mid-Cretaceous was a period of faunal turnovers that turned out poorly for most mammal groups, with forms like symmetrodonts and eutriconodonts dying off around this time, presumably due to their more specialised carnivorous diets. By contrast, omnivorous groups prospered, quickly expanding to occupy empty niches.

The pre-Late Cretaceous mammal fossil record of South America is extremely poor, but we know that eutriconodonts (Argentoconodon, Condorodon), australosphenidans (Henosferidae, possibly Vincelestes) and multituberculates were present at least (Chimento 216). Meridiolestidans likely moved into the vacant niches after their competitors died off, assuming they did not outcompete them directly as marsupials are sometimes said to have done to Australia’s indigenous groups.

The inner structure of the south american Meridiolestida is usually fairly consistent: a most “basal” group composed of the Cronopio + Leonardus + Necrolestes clade (for the sake of simplicity we’ll call it Necrolestidae), followed by Austrotriconodontidae, Brandoniidae and the clade Mesungulatoidea, which sensu stricto includes Mesungulatidae and a Reigitherium + Peligrotherium clade (here called Reigitheriidae for the sake of simplicity); sometimes, Mesungulatoidea can be expanded to include Austrotriconodontidae and Brandoniidae, though the general relationship between these clades remains the same.

Minor points of controversy include the genus Groebertherium, which is a Late Cretaceous dryolestoid genus sometimes recovered as a meridiolestidan but sometimes also recovered as a non-meridiolestidan dryolestoid (Rougier 2012, Rougier 2018), how Donodon and Thereuodon fit into Meridiolestida (so far, comparisons with Mesungulatidae have been most prevalent, but it is usually classified as outside the south american group) and just how extensive Brandoniidae actually is. Otherwise, however, we have a fairly consistent portrayal of this clade across the various studies, which is quite charming.


Cretaceous saberteeth or Cretaceous pigs?


Cronopio dentiacutus skull reconstruction.

By far the most famous dryolestoid is none other than Cronopio dentiacutus, the “real Scrat” due to an almost prophetic decision by Michael J. Wilson’s daughter to fuse a squirrel and a sabertooth, resulting in the mildly amusing face of the Ice Age movies. It isn’t the only Mesozoic mammal to bear long canines – another dryolestoid, the portuguese Drescheratherium acutum, also bears elongated upper canines, though they are slightly less elongated and stouter, while some deltatheroideans like Lotheridium mengi are true sabertooths, not only possessing deeper fangs but also being unambiguous predators. Still, it can’t be denied that good ol’ Cronopio has its charm as the face of the fanged fuzzballs.

Like Scrat, Cronopio dentiacutus is a fairly small mammal, at around 20 centimeters long. However, it most certainly wasn’t an acorn addict, if for no other reason that there weren’t any acorns in the patagonian Cretaceous. What it actually ate is something of a controversy: on the one hand, its teeth appear more suited to a generalist omnivorous diet (Rougier 2011; see also Chornogubsky 2011 for the closely related Leonardus, which was capable of ungulate-like transverse chewing), but on the other it ranked among insectivore species in a study documenting mammal jaw shapes (Grossnickle 2013). Given the fossorial characteristics of its relative Necrolestes, it seems likely that Cronopio probably dug for food with its snout, making it fairly akin to a miniature pig. Indeed, from an at least superficial standpoint Cronopio‘s skull strongly resembles that of a suine.

Cronopio‘s fabled fangs are rather delicate and strongly recurved, implying that it did not use them to pierce prey. Rather, they are most likely sexual ornaments like the tusks of many living mammals, though I hesitate to say that they were used in interspecific fights like they are in pigs, chevrotains and many other species. Maybe they could also have been used in foraging to some extent, digging out soft substrate.

Closely related (though depending on the studies it can be closer to the other necrolestid, Necrolestes) is Leonardus cuspidatus. Unlike Cronopio it appears to lack the formidable fangs, but otherwise seems rather similar in terms of overall anatomy and likely lifestyle; it did have three molar roots, a trait otherwise seen only in the mesungulatid Coloniatherium cilinski, but the implications in terms of diet are unclear. Assuming Leonardus isn’t specifically closer to Cronopio than to Necrolestes, this mini-pig lifestyle appears to have been the norm to necrolestids, which proceeded to shift into the mole-like lifestyle we know and love sometime after or even within the KT event.

Meat’s back on the menu, boys


Another Austrotriconodon mckennai tooth.

Austrotriconodon is a genus composed of two species, A. mckennai and A. sepulvedai, the former larger than the latter, dating to the Campanian or Maastrichtian in the Los Alamitos formation of Patagonia. Bearing triconodont teeth, it has long been assumed that these animals were relictual eutriconodonts, but it since has been revealed that they were actually meridiolestidans, their triconodont molars having evolved secondarily from an cladotherian shape (Gaetano 2013). Sure enough, you’ll easier notice more similarities to therian carnassials than to eutriconodont molars and premolars.

This dental adaptation appears to have been in response to increased carnivorous habits. Like both eutriconodont teeth and therian carnassials, Austrotriconodon‘s teeth appear to be suited for shearing, allowing a butchering action. Being weasel-to-cat sized animals, it makes sense that they were predators of small tetrapods like other mammals, amphibians, lizards, small dinosaurs, small notosuchians and even sphenodontians (Apesteguia 2003), and thus we can probably see them as the gondwanan counterpart to the contemporary deltatheroideans and stagodontids of the northern continents.

What makes austrotricononodontids particularly interesting is how they’re relatively closely related to herbivorous mesungulatoids. Either they diverged just before the development of herbivory in Meridiolestida, or they might have actually be descended of herbivorous ancestors. With the herbivorous african meridiolestidans mixed in, this becomes a question rather worth making; similar positing that insectivorous afrotheres may all descend from hyrax-like ancestors crop frequently in literature as well (Gheerbrant 2014).

Brandon’s things

CapturarBrandonia intermedia  tooth.

As mentioned before, there is some controversy in regards to how many species and genera Brandoniidae actually contains. For instance, some studies recover Barberenia and other genera as synonymous with Brandonia itself (Chornogubsky 2011, Forasiepi 2012), though given the clade’s success from the Cenomanian to Maastrichtian its diversity surely needs to be addressed further than this. Compared to other meridiolestidan clades, Brandoniidae is sadly rather underrepresented in literature.

From what can be gleaned, brandoniids were insectivores akin to modern elephant shrews (Rougier 2008), and indeed they appear to be mouse sized mammals. While their teeth are suited for transverse mastication, they have sharper cusps than most other meridiolestidans, contextualising it as grinding insect shells rather than plants. Still, as with austrotriconodontids an herbivorous ancestry can’t be denied fully.

Middle Ungulates

bd13bcef2c6598fa2533e0e73f6fb569Coloniatherium cilinski by Ceri Thomas.

Mesungulatoids are by far the most abundant meridiolestidans – and indeed, dryolestoids – in terms of remains, thanks both to their herbivorous habits and large size, being some of the largest Mesozoic mammals at 8 kg or more. Frustratingly we don’t have a complete skeleton yet, but jaws, skulls, ear bones and even hand and foot elements paint a more or less clear picture of how these animals looked in life.

As the name implies, mesungulatoids strongly converged with ungulates in terms of molar anatomy, bearing blocky, ridged molars not unlike those of a horse or an elephant. They were in fact first assumed to be Cretaceous ungulates, perhaps distant ancestors of those pesky mysterious meridiungulates, until dryolestoid hallmarks in their teeth were noticed (Pascual 2001). This offers a pretty interesting case of convergent evolution, and makes their sad demise in the Cenozoic all the more sadder to me, since there surely must be an alternate timeline where Darwin’s Toxodon was even weirder.

Mesungulatid molars and premolars typically number evenly, three of both in each jaw side., but some species were reducing their back teeth (Rougier 2009) so the big solitary blocks we see in elephant mouths could be an eventually had they survived. Their jaws are thick and offer a more or less blunt but vaguely dog-like profile, something comparable to hyrax snouts. Hyraxes are indeed a good ecological and morphological match among modern mammals, though unlike them mesungulatoids were not good climbers, at least the few species we have digit and ankle elements from (Rougier 2009). They were most likely fossorial, making them functionally close to wombats and marmots in these regards.

As noted before, mesungulatids lack the Meckelian groove, having thus a completely modern ear. Perhaps this was in part driven by their ungulate-like chewing mechanism; all meridiolestidans aside from austrotriconodontids have teeth adapted for transverse chewing, but mesungulatids were the most adapted for this due to their extensive herbivorous diet. Transverse chewing in general is assumed be one of the drivers in the detachment of ear bones from jaw bones in mammals (Luo 2018), so this does have precedent at least. Both Peligrotherium and Reigitherium appear to not have been as specialised to transverse mastication, however; while they could perform it, it seems they still mostly relied on vanilla chewing (Pascual 2001, Rougier 2009, Rougier 2018).

Mesungulatoids are among the most common vertebrates in some sites, with Coloniatherium cilinski actually outnumbering local dinosaur fossils (Rougier 2009, Rougier 2018). This firmly attests their hold on mid-sized herbivorous niches in their ecosystems, and combined with other herbivorous tetrapods such as gondwanatheres, sphenodontians and notosuchians it hints at a south american herbivorous guild dominated primarily by non-dinosaurian species (sauropods and large ornithopods aside).

Curiously, there are few gondwanatheres in the south american Late Cretaceous, while Madagascar and India, which still haven’t yielded dryolestoid fossils, show a much higher diversity as well as herbivorous zhelestid therians and the haramiyidan Avashishta bacharamensis.

The number of Cretaceous mesungulatoids is rather consistent. Reigitheriidae includes a single species, Reigitherium bunodontum, while Mesungulatidae has Mesungulatum houssayi, Mesungulatum lamarquensis, Quirogatherium/Mesungulatum major, Parungulatum/Mesungulatum rectangularisColoniatherium cilinski and an unnamed taxon (Forasiepi 2012); the main controversy here is whereas Quirogatherium and Parungulatum are distinct enough from Mesungulatum. Mesungulatum and Coloniatherium are the best represented, with various skull, jaw and limb elements, while other taxa are represented by teeth only, aside from the unnamed taxon which is represented by an edentulous jaw (teeth lost post-mortem).

Another controversy is whereas Groebertherium stipanicici is a mesungulatoid or not; as noted before, some studies recover it as such. However, most analyses recover it as a non-meridiolestidan dryolestoid and indeed it more closely resembles Dryolestes itself, rendering it a remarkable critter on its own.


After the dinosaurs

Capturar2Necrolestes mirabilis by Julio Lacerda.

With their Late Cretaceous success firmly set up, you might be disappointed to learn that, even immediately after the KT event, meridiolestidans are almost entirely gone from South America.

As other mammal groups were strongly affected by the KT event, it comes as no surprise that these critters were sadly mostly incapable of surviving the end of times. This no doubt helped paved the way for placentals and marsupials in South America, which quickly took over the vacant niches; in fact, direct comparisons between mesungulatoids and herbivorous south american marsupials and ungulates have been made (Rougier 2018).

In spite of this, however, at least two lineages survived: Reigitheriidae and Necrolestidae. These two lineages occupied radically different niches and are only represented by a few species, suggesting that they did not play a prominent role in South America’s Cenozoic ecosystems. Still, at least the latter survived as recently as 17 million years ago; a true ghost lineage, with a gap of at least 49 million years between Cretaceous necrolestids and Cenozoic ones.

Who knows, maybe there are more Cenozoic meridiolestidans awaiting to be discovered.

Among reigitheriids, we have Peligrotherium tropicalis, from the Palaeocene of Patagonia; its name alludes to Punta Peligro, where its holotype was discovered. It is known from a single dentary and associated molar and premolar teeth, more similar to those of Reigitherium bunodontum than those of mesungulatids. This suggests that, while reigitheriids were specialised herbivores, they clearly weren’t as much as their mesungulatid cousins, being just omnivorous enough to pass through the mass extinction event.

What does set Peligrotherium truly apart is its size; referred to as “dog-sized” (Rougier 2009), it is around seven times larger than the largest mesungulatids, rendering it a serious competitor to the multituberculate Taeniolabis taoensis as the largest non-therian mammal of all time at up to 100 kg (assuming typical mesungulatoid proportions it probably had a larger skull). Like many other mammals of the epoch, meridiolestidans did became giants soon after the extinction of the dinosaurs, and like the wave of multituberculate and placental giants in the northern continents they did not survive the chaotic world of the Cenozoic.

Just as interesting as Peligrotherium‘s large size is its coexistence with various early meridiungulates such as the didolodontids Raulvaccia peligrensis, Escribania chubutensis and Escribania talonicuspis and the litoptern Requisia vidmari. They were smaller than Peligrotherium, and thus the possibility that reigitheriids were competitively excluded by invading northern ungulates becomes a possibility, as this mirrors the usual pattern of specialised members of a clade being the last one standing while the competing, successful clade is represented by more generalistic species. Until further fossils are discovered, however, there is no way of knowing for sure, and it may just as likely be that reigitheriids simply did not survive the climatic changes brought by the PETM.

Flash forward 40 million years later, and two species of necrolestids, Necrolestes mirabilis and Necrolestes patagonensis, show up in Patagonia’s Miocene fossil sites, the final chapter in Meridiolestida’s story. Necrolestes patagonensis is one of the best understood dryolestoids, with most of its skeleton being known from various specimens. Necrolestes mirabilis is currently only known from a single lower jaw and associated molar teeth, depicting a slightly larger animal than its more well known cousin.

These findings depict Necrolestes as a mole-like animal, bearing massive limbs and small eyes. Its snout is long and upturned, the upperside probably ridged with a keratin shield much as in fairy armadillos and in marsupial moles as it was used to shovel earth, something further indicated by the ossification of its nasal cartilage, making it one of the very few mammals to have reverted to separate nostril holes as in earlier synapsids. The peculiar nasal cavity might have also suggest a complex organ like the tendrils of the star-nosed mole. As fitting its insectivorous diet, Necrolestes has large canines, more robust than those of its distant Cretaceous relatives, as well as zalambdodont molars, an unique feature among dryolestoids.

Necrolestes was not the first dryolestoid to be found – Dryolestes itself was described at least two decades earlier – but it was for the longest time the only dryolestoid with complete postcranial remains. As such, for most of the last two centuries it was rendered a taxonomical nightmare, with many sources putatively rendering it as a very atypical metatherian or non-placental eutherian (like most non-placental mammals, it has epipubic bones, and particularly large ones at that much like monotremes). It was only in 2012 when comparison with other dryolestoids allowed researchers to find its place among the meridiolestidan assemblage, finding many dental, ear bone, braincase and limb similarities (Rougier 2012); since then, posterior phylogenetic studies have consistently recovered it as one, with one in particular even demonstrating how its dental features evolved from the meridiolestidan norm (Rougier 2017).

Necrolestes found itself on a very cozy niche; due to the lack of available fossils, its unclear when the transition to a mole-like lifestyle took place, but the sheer rarity of necrolestid fossils in the Cenozoic seems to point out to soon after the KT event, likely outcompeted in other niches by therian mammals or perhaps even monotremes like Monotrematum sudamericanum. It co-existed with the relictual gondwanathere Patagonia peregrina, suggesting that non-therian synapsids, while rare, still endured for a long time during the Cenozoic in South America. As there are at least two contemporary Necrolestes species and no other burrowing carnivores and insectivores, it seems that necrolestids held their subterranean niches quite effectively.

Eventually, however, its good luck run out. The Late Miocene sees several cooling spells in South America, resulting in the decline of many groups from sebecids to terror birds. It’s possible that Necrolestes became extinct soon after its debut in the fossil record, not even seeing the arrival of new mammal groups from North America.

At the very least, Meridiolestida went out with a bang. Or did it?

Obligatory marsupial mole discussion

Southern-marsupial-mole-eating-a-geckoMarsupial moles are considered peaceful animals by the Pitjantjatjara people. Geckoes politely disagree.

No discussion on meridiolestidans, or indeed dryolestoids as a whole, is complete without the highly controversial 2014 paper that found these odd pouched morlocks to not be marsupials after all, but actually surviving meridiolestidans closely related to Necrolestes, Leonardus and Cronopio. Thus, not only does the dryolestoid story not have an end yet, but there are also two lineages of non-therian mammals living in Australia.

This hypothesis certainly has its appeal, to put it lightly, and it even parallels the story of Necrolestes (as well as the gondwanathere Patagonia peregrina) as going from an oddball shoved into Marsupialia because there is nowhere else to put it to a fairly normal member of a older mammal lineage.

Sadly, however, genetic studies are very much against this interpretation, having recovered marsupial moles as true marsupials closely related to dasyuromorphs and bandicoots. Not only that, but other studies have effectively demonstrated how the supposed similarities between marsupial moles and necrolestids are purely convergent; in particular, necrolestid zalambdodont teeth evolved from a typical dryolestoid mold, while the marsupial mole’s evolved from a therian one (Rougier 2017). Furthermore, the extinct marsupial Naraboryctes offers a clear bridge between a more normal marsupial anatomy and the bizarre mess that modern marsupial moles have now.

Plus, while marsupial mole anatomy does strongly resemble that of necrolestids, I do have to question their short canines and vestigial epipubic bones, the polar opposite of the situation seen in Necrolestes. This just further screams “different ancestry” to me.

That said, marsupial moles overall do offer a good model for not only necrolestid anatomy and lifestyle, but likely also for the soft tissue anatomy of dryolestoids as a whole. That said, just as one shouldn’t mistake the marsupial mole’s “primitive” anatomy as ancestral, neither should one assume that some dryolestoids didn’t converge with therian mammals, particularly at more active niches like in austrotriconodontids and brandoniids.

Final Thoughts

Sem TítuloI’m not the only one who noticed this, right?

Hopefully I have given you insight towards this majestic but underrated mammal clade.


Alexander O. Averianov, Thomas Martin and Alexey V. Lopatin (2013). “A new phylogeny for basal Trechnotheria and Cladotheria and affinities of South American endemic Late Cretaceous mammals”. Naturwissenschaften. 100 (4): 311–326. doi:10.1007/s00114-013-1028-3.

Guillermo W. Rougier, John R. Wible, Robin M. D. Beck and Sebastian Apesteguía (2012). “The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America”. Proceedings of the National Academy of Sciences of the United States of America109 (49): 20053–20058. doi:10.1073/pnas.1212997109. PMC 3523863.

Laura Chornogubsky, New remains of the dryolestoid mammal Leonardus cuspidatus from the Los Alamitos Formation (Late Cretaceous, Argentina), Article in Paläontologische Zeitschrift 85(3):343-350 · September 2011 DOI: 10.1007/s12542-010-0095-4

Richard Stephen Thompson, Rachel O’Meara, Were There Miocene Meridiolestidans? Assessing the Phylogenetic Placement of Necrolestes patagonensis and the Presence of a 40 Million Year Meridiolestidan Ghost Lineage, Article in Journal of Mammalian Evolution · September 2014 DOI: 10.1007/s10914-013-9252-3

Zofia Kielan-Jaworowska, Richard L. Cifelli, and Zhe-Xi Luo, Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure (New York: Columbia University Press, 2004), 14, 531.

Nicholas Chimento, Frederico Agnolin, Agustin Martinelli, Mesozoic Mammals from South America: Implications for understanding early mammalian faunas from Gondwana, May 2016

Hamid Haddoumi, Ronan Allain, Said Meslouh, Grégoire Metais, Michel Monbaron, Denise Pons, Jean-Claude Rage, Romain Vullo, Samir Zouhri, Emmanuel Gheerbrant, Guelb el Ahmar (Bathonian, Anoual Syncline, eastern Morocco): First continental flora and fauna including mammals from the Middle Jurassic of Africa, doi:10.1016/j.gr.2014.12.004

Bonaparte, J.F. 2002. New Dryolestida (Theria) from the Late Cretaceous of Los Alamitos, Argentina, and paleogeographical comments. Neues Jahrbuch fu ̈r Geologie und Pala ̈ontologie, Abhandlungen224(3): 339–371.

G. W. Rougier, S. Apesteguía, and L. C. Gaetano. 2011. Highly specialized mammalian skulls from the Late Cretaceous of South America. Nature 479:98-102

David M. Grossnickle, P. David Polly, Mammal disparity decreases during the Cretaceous angiosperm radiation, Published 2 October 2013.DOI: 10.1098/rspb.2013.2110

Mariela C. Castro; Francisco J. Goin; Edgardo Ortiz-Jaureguizar; E. Carolina Vieytes; Kaori Tsukui; Jahandar Ramezani; Alessandro Batezelli; Júlio C. A. Marsola; Max C. Langer (2018). “A Late Cretaceous mammal from Brazil and the first radioisotopic age for the Bauru Group”. Royal Society Open Science5 (5): 180482. doi:10.1098/rsos.180482. PMC 5990825. PMID 29892465.

Harper T, Parras A, Rougier GW. 2018. Reigitherium (Meridiolestida, Mesungulatoidea) an enigmatic Late Cretaceous mammal from Patagonia, Argentina: morphology, affinities, and dental evolution. Journal of Mammalian Evolution.

L. C. Gaetano, C. A. Marsicano, and G. W. Roughier. 2013. A revision of the putative Late Cretaceous triconodonts from South America. Cretaceous Research 46:90-100

Apesteguia, Sebatian; Novas, Fernando E. (2003). “Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana”. Letters to Nature425: 609–612. doi:10.1038/nature01995.

Gheerbrant, E.; Amaghzaz, M.; Bouya, B.; Goussard, F.; Letenneur, C. (2014). “Ocepeia (Middle Paleocene of Morocco): The Oldest Skull of an Afrotherian Mammal”. PLoS ONE9 (2): e89739. doi:10.1371/journal.pone.0089739. PMC 3935939. PMID 24587000.

Analia M Forasiepi Rodolfo A. Coria Rodolfo A. Coria Jørn Hurum Philip J. Currie Philip J. Currie, First Dryolestoid (Mammalia, Dryolestoidea, Meridiolestida) from the Coniacian of Patagonia and New Evidence on their Early Radiation in South America, December 2012 AMEGHINIANA 49(4):497-504 DOI: 10.5710/AMGH.8.8.2012.581

Guillermo W. Rougier, Laura Chornogubsky, Silvio Casadio, Natalia Paéz Arangoa, Andres Giallombardo, Mammals from the Allen Formation, Late Cretaceous, Argentina, Cretaceous Research Volume 30, Issue 1, February 2009, Pages 223-238, doi.org/10.1016/j.cretres.2008.07.006

J. N. Gelfo and R. Pascual. 2001. Peligrotherium tropicalis (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation. Geodiversitas 23(3):369-379

Stephan Lautenschlager; Pamela G. Gill; Zhe-Xi Luo; Michael J. Fagan; Emily J. Rayfield (2018). “The role of miniaturization in the evolution of the mammalian jaw and middle ear”. Nature561 (7724): 533–537. doi:10.1038/s41586-018-0521-4. PMID 30224748.

John R. Wible, Guillermo Rougier, Craniomandibular Anatomy of the Subterranean Meridiolestidan Necrolestes patagonensis Ameghino, 1891 (Mammalia, Cladotheria) from the Early Miocene of Patagonia, June 2017 Annals of Carnegie Museum 84(3):183-252 DOI: 10.2992/007.084.0302

Author: Carlos Albuquerque

Bisexual and proud. Interested in paleobiology, esoterism/occultism and other stuff.

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