#ericiolacerta

[alphynix]

The synapsids were an incredibly successful and diverse group during the Permian period, but after the devastating "Great Dying" mass extinction event 252 million years ago only three lineages survived into the Triassic – the cynodonts (close relatives and ancestors of modern mammals), the dicynodonts (beaked tusked weirdos who briefly took over the world), and the therocephalians.

Therocephalians were close relatives of cynodonts, and convergently evolved several very mammal-like anatomical features in their skulls, teeth, and limbs. But unlike their cousins this lineage never fully recovered in the Triassic, and they ultimately disappeared completely around 242 million years ago.

Ericiolacerta parva was one of these short-lived Mesozoic therocephalians, known from the early Triassic (~252-247 million years ago) of South Africa and Antarctica, in regions that were connected at the time as part of the supercontinent of Pangaea. It was a fairly small animal, about 20cm long (~8"), with small sharp teeth that indicate it mainly fed on insects, and semi-opposable thumbs and inner toes that suggest it was also a capable climber.

Holes in the bones of its snout would have carried numerous nerves and blood vessels, which may be evidence of sensitive fleshy lips and possibly whiskers. And while there's no direct evidence of fur in therocephalians, they do appear to have been active warm-blooded animals – and possible fossilized synapsid hair from the Permian period suggests fuzziness might have been ancestral to all of the "protomammal" lineages that survived into the Triassic.

———

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[extinctworld-ua]

Ericiolacerta

Ericiolacerta — монотипічний рід тероцефалів родини ериціолацертових (Ericiolacertidae), що походить з раннього тріасу Африки та Антарктики. Єдиний встановлений вид – Ericiolacerta parva. Описаний Д. Вотсоном (David Meredith Seares Watson) у 1931 році. Назва означає – «ящірка-їжак».

Повний текст на сайті "Вимерлий світ":

https://extinctworld.in.ua/ericiolacerta/

[wtf-triassic]

Thrinaxodon

By Scott Reid

Etymology: Trident tooth

First Described By: Seeley, 1894

Classification: Biota, Archaea, Proteoarchaeota, Asgardarchaeota, Eukaryota, Neokaryota, Scotokaryota, Opimoda, Podiata, Amorphea, Obazoa, Opisthokonta, Holozoa, Filozoa, Choanozoa, Animalia, Eumetazoa, Parahoxozoa, Bilateria, Nephrozoa, Deuterostomia, Chordata, Olfactores, Vertebrata, Craniata, Gnathostomata, Eugnathostomata, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiformes, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Amniota, Synapsida, Eupelycosauria, Metopophora, Haptodontiformes, Sphenacomorpha, Sphenacodontia, Pantherapsida, Sphenacodontoidea, Therapsida, Eutherapsida, Neotherapsida, Theriodontia, Eutheriodontia, Cynodontia, Epicynodontia, Thrinaxodontidae

Status: Extinct

Time and Place: Thrinaxodon lived 251 to 247 million years ago, in the Olenekian of the Early Triassic.

Thrinaxodon is known from South Africa and Antarctica.

Physical Description: If you thought Olivierosuchus was a good dog, Thrinaxodon is an even gooder dog. Like most synapsids around this area of the tree, Thrinaxodon would have been a small (~50 cm) badgery thing. Its head had whiskers, but probably didn’t have external ear pinnae (only holes in the back of the skull). The skull had a secondary palate that separated the nasal passages from the mouth, so it could continuously breathe while eating. Its teeth were divided into distinct incisors, canines, and molars, like modern mammals. The teeth were replaced continuously throuhhout its life, unlike most mammals (which get one tooth replacement, and that’s it). The inner ear still didn’t have the distinctive malleus and incus bones of mammalian middle ears, though. It held its limbs off the ground in a posture transitional between earlier semi-sprawling synapsids and straight-standing mammals. The forelimbs were not super-robust, but had features in common with modern digging mammals and reptiles. Each hand and foot had five digits each. Thrinaxodon probably had fur, although no direct fossil fur has been found yet.

Diet: Thrinaxodon’s diet likely consisted of small reptiles and invertebrates.

Behavior: As with the previously-featured Olivierosuchus, Thrinaxodon was able to burrow. We’ve found burrow casts with Thrinaxodon inside. Numerous Thrinaxodon specimens have been found curled up in little balls inside the burrows (it’s adorable), which suggests that it may have hibernated in these burrows during the heat of the summer. This may have helped cynodonts (as well as therocephalians) survive the Permian-Triassic extinction. In fact, one fossil burrow has both a curled-up Thrinaxodon and the temnospondyl Broomistega inside. As the Thrinaxodon was hibernating, an injured Broomistega crawled into the burrow to shelter itself and heal. It’s okay to cry at this, I’m doing so.

Thrinaxodon was a caring parent, looking out for clutches of its young until they were at least half full size. It would have laid soft-shelled eggs, like modern monotremes. Thrinaxodon is around the area of the synapsid tree where milk probably evolved into a thing that the babies drank for nutrients. Previously, “proto-milk” existed in the form of egg-moistening sweat. This said, the babies wouldn’t have suckled - instead, the milk would have been… sweated out of the mother’s skin, and they’d lick it off. 

Ecosystem: Thrinaxodon fossils have been found in what were once arid floodplains in South Africa and Antarctica. At the time these were connected by land, so many animals lived in both places at the same time. Synapsids were prevalent in the region, such as Lystrosaurus (because of course), the cynodont Galesaurus, and the therocephalians Moschorhinus, Olivierosuchus, Ericiolacerta, Scaloposaurus, and Tetracynodon. Other animals that lived in South Africa include the parareptiles Procolophon and Owenetta, the early archosauromorphs Prolacerta and Proterosuchus, and temnospondyls such as Lydekkerina, Broomistega and Micropholis. A few species are known exclusively from Thrinaxodon’s Antarctic range, like the archosauriform Antarctanax and the dicynodont Kombuisia.

Other: Histology reveals that Thrinaxodon grew very fast, suggesting that it was warm-blooded. When young, Thrinaxodon grew quickly and replaced their teeth a lot. Growth rates slowed down considerably after a certain age, which may have been the point of sexual maturity.

~ By Henry Thomas

Sources under the cut

Abdala, F., Jasinoski, S.C., Fernandez, V. 2013. Ontogeny of the Early Triassic cynodont Thrinaxodon liorhinus (Therapsida): dental morphology and replacement. Journal of Vertebrate Paleontology 33(6): 1408-1431.

Botha, J., Chinsamy, A. 2005. Growth patterns of Thrinaxodon liorhinus, a non-mammalian cynodont from the lower Triassic of South Africa. Palaeontology 48(2): 385-394.

Brink, A.S. 1954. Note on a very tiny specimen of Thrinaxodon liorhinus. Palaeontologia Africana 3: 73-76.

Brink, A.S. 1959. Note on a new skeleton of Thrinaxodon liorhinus. Palaeontologia Africana 6: 15-22.

Damiani, R., Modesto, S., Yates, A., Neveling, J. 2003. Earliest evidence of cynodont burrowing. Proceedings of the Royal Society of London B 270: 1747-1751.

Estes, R. 1961. Cranial anatomy of the cynodont reptile Thrinaxodon liorhinus. Bulletin, Museum of Comparative Zoology, Harvard University 125: 165-180.

Fernandez, V., Abdala, F., Carlson, K.J., Cook, D.C., Rubidge, B.S., Yates, A., Tafforeau, P. 2013. Synchrotron Reveals Early Triassic Odd Couple: Injured Amphibian and Aestivating Therapsid Share Burrow. PLoS ONE 8(6): e64978.

Iqbal, S. 2015. The functional morphology and internal structure of the forelimb of the Early Triassic non-mammaliaform cynodont Thrinaxodon liorhinus. Unpublished dissertation, Evolutionary Studies Institute and School of Geosciences, University of the Wiwatersrand.

Jasinoski, S.C., Abdala, F. 2017. Aggregations and parental care in the Early Triassic basal cynodonts Galesaurus planiceps and Thrinaxodon liorhinus. PeerJ 5: e2875.

[wtf-triassic]

Lystrosaurus

By Jack Wood / Darwin’s Door

Etymology: Shovel reptile

First Described By: Cope, 1870

Classification: Biota, Archaea, Proteoarchaeota, Asgardarchaeota, Eukaryota, Neokaryota, Scotokaryota, Opimoda, Podiata, Amorphea, Obazoa, Opisthokonta, Holozoa, Filozoa, Choanozoa, Animalia, Eumetazoa, Parahoxozoa, Bilateria, Nephrozoa, Deuterostomia, Chordata, Olfactores, Vertebrata, Craniata, Gnathostomata, Eugnathostomata, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiformes, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Amniota, Synapsida, Eupelycosauria, Sphenacodontia, Sphenacodontoidea, Therapsida, Eutherapsida, Neotherapsida, Anomodontia, Chainosauria, Dicynodontia, Therochelonia, Bidentalia, Dicynodontoidea, Lystrosauridae

Referred Species: L. curvatus, L. declivis, L. georgi, L. hedini, L. maccaigi,  L. murrayi (and several other probably invalid species)

Status: Extinct 

Time and Place: Between 253 and 247 million years ago, from the Changhsingian of the Late Permian to the Olenekian of the Early Triassic

Lystrosaurus is mostly known from the Karoo Basin in South Africa, along with the Fremouw Formation in Antarctica, the Panchet Formation in India, and probably Australia in Gondwana, while at least two or more species from Laurasia are known in Russia, China, and Mongolia, giving Lystrosaurus a very broad distribution across much of Pangaea.

Physical Description: Lystrosaurus is pretty much the quintessential dicynodont, but when you get down to it, it’s actually a pretty weird one. The skull is unusually tall and squashed looking, even by dicynodont standards, with an incredibly short snout that drops down very steeply almost right in front of the eyes to the squared-off beak and pointy tusks at the bottom, hence the resemblance to a shovel (although the face of Lystrosaurus is actually surprisingly narrow from the front). In some specimens, the snout drops down almost vertically. The eyes are placed so far forward and up on the skull that they almost look like they’re bugging out of its head, and the nostrils are sat directly below them on the front of the snout. The back region of the skull behind the eyes takes up at least half of the length of the skull and houses massive jaw muscles, giving Lystrosaurus a very strong, snapping bite. Curiously, at least some Lystrosaurus may have had a thickened cornified pad between the eyes, possibly similar to the keratin of the beak, as well as rough bosses over the eyes. These were probably used for display, and may have been surprisingly colourful for what you’d expect from a stem-mammal.

The body of Lystrosaurus is more standard, with a long, tubular trunk, stubby tail and short, squat legs. Overall it was pretty dumpy looking (this is an actual description used in a scientific paper, no joke). This shape has been compared to that of hippos, often to suggest a similar lifestyle, but the strong, semi-upright limbs suggest a more terrestrial lifestyle. The forelimbs of Lystrosaurus are very well developed, and its hands and feet are broad with spread toes and large, flat claws, well suited for digging. It was somewhere around the size of the pig, give or take how big you think a pig is, but since Lystrosaurus sizes vary between small to over a metre you’re probably in the ballpark. The integument of Lystrosaurus, and indeed almost all stem-mammals, is poorly understood, and they have been speculated to be scaley, hairy, or just covered in naked skin. However, as-yet unpublished Lystrosaurus mummies from South Africa suggest that Lystrosaurus had hairless, scaleless skin studded with bumpy tubercles. But until we know more about these specimens, we can’t be certain how this would look. Lystrosaurus may also have been sexually dimorphic, with presumed males having more prominent bosses and robuster skulls. Lystrosaurus grew fast for dicynodonts, with rapid continuous growth as juveniles, slowing down as sub-adults with periods of little to no growth, and slowing considerably as they reached adulthood.

Diet: Lystrosaurus was a herbivore, grazing mostly on tough, low-lying drought-resistant plants like horsetails and seed ferns. However, it is also possible that it ate fungi and even bits of animal matter too while rooting around in the earth. Like other dicynodonts, Lystrosaurus chewed its food with a backwards motion of the jaw using its massive jaw muscles, making it an efficient grazer, and its short skull and jaws made it extra effective at snapping through tough stems.

Behavior: Lystrosaurus has often been described as amphibious, living like a hippopotamus, based on its supposedly high set eyes and downward facing jaws. However, there is actually little evidence to support this mode of life, and in reality the evidence is more in favour of a mostly terrestrial lifestyle, no more aquatic than any other dicynodont. Bonebeds of Lystrosaurus tells us that they were social animals that at least sometimes congregated together in similar age groups, at least as juveniles and subadults, possibly for protection during extreme temperature swings. For a long time Lystrosaurus was speculated to have been a burrower, and this was confirmed later by the discovery of not only Lystrosaurus burrows, but even burrows with the skeleton of its owner still inside. Burrowing was evidently a successful strategy for surviving the Great Dying, as many other Early Triassic survivors, like Thrinaxodon and Procolophon, were also burrowers. In fact, it’s even possible that Lystrosaurus acted as a sort of ecosystem engineer, modifying the environment and providing other species with refugiums in hard times that allowed them to pull through alongside it!

Ecosystem: In the earliest Triassic, Lystrosaurus was famously one of the most abundant vertebrates on the planet. It is regarded as a disaster taxon, a species that survives and proliferates in the ecological vacuum left after a mass extinction. Because the continents were joined together in Pangaea, much of the world’s fauna and flora was broadly similar. This is especially so in Gondwana, where much of the therapsid, reptile and amphibian fauna was shared. Here Lystrosaurus co-existed with various other therapsids, including two other surviving dicynodonts Myosaurus and Kombuisia, as well as the small cynodonts Thrinaxodon and Galesaurus, and various therocephalians such as Ericiolacerta, Tetracyndon, Ictidosuchus and the 1.5 metre long predatory Moschorhinus, one of the few predators that could prey upon Lystrosaurus in the Early Triassic. Archosauromorphs had also survived here, most notably the predatory proterosuchids, as well as the small Prolacerta and the larger, exclusively Antarctic Antarctax. Other reptiles includes the parareptile Procolophon, and the enigmatic diapsid Palacrodon, while the closely related (and relatively terrestrial as it turns out) temnospondyls Lydekkerina and Cryobatrachus cruised the waterways of South Africa and Antarctica, respectively. Similar fossils are known from India as well.

Prior to the P-Tr Extinction, in the time of L. maccaigi, South Africa was still relatively wet and lush with vegetated floodplains of trees and shrubs, including the famous Glossopterus seed ferns that L. maccaigi may have specialised in feeding on. However, this environment was already changing as the P-Tr Extinction took course, and was already low in biodiversity. L. maccaigi would have coexisted with other dicynodonts, including the lystrosaurid Kwazulusaurus, larger Daptocephalus, Oudenodon, Pelanomodon, and Dinanomodon, and little Thliptosaurus. Predatory therocephalians were around too, namely Promoschorhinus and Moschorhinus itself, which was another P-Tr survivor like Lystrosaurus. Most others however would be lost to the Great Dying, as the Karoo gradually dried out until it was transformed into a hot, arid plain with sprawling braided rivers, little vegetation and seasonally extreme temperatures that was prone to flash floods and cold snaps. To give a clear picture of how arid it was, it’s speculated that so many Lystrosaurus skeletons are found partially articulated and not broken apart like so many other Karoo fossils is because their carcasses were dessicated into mummies that held them together before they were eventually buried whenever it actually rained.

Lystrosaurus may have been pre-adapted to such conditions, however, as its downturned jaws would have been well-suited to grazing on low-growing drought-resistant plants, such as horsetails, as well as for Dicroidium seed ferns that would soon become the dominant Triassic flora. The Fremouw Formation in Antarctica records a more diverse range of seed ferns, cycads, horsetails and even fungi, all of which may have sustained Lystrosaurus. The climate at these high latitudes was milder, but also would mean they would have experienced months of darkness during the polar winters, even if it wasn’t cold.

Other: Lystrosaurus fossils were pivotal in proving Alfred Wegner’s theory of plate tectonics, as they had been found on various continents around the globe, along with other similarly aged fossils, indicating that the continents had once been much closer together and connected as one landmass. Their fossils are famously ludicrously abundant in the Karoo basin, making one it one of the best represented dicynodonts known, and probably of any stem-mammal. In fact, their abundance is so characteristic of the Early Triassic beds of the Karoo that they lend it its name, the Lystrosaurus Assemblage Zone. Lystrosaurus is sometimes regarded as one of the most successful tetrapods of all time, due to how widespread and populous it was. Case in point, 73% of known vertebrate fossils from the Early Triassic of South Africa are of Lystrosaurus. It’s a prime example of how a disaster taxon with the right pre-adaptations can flourish in the immediate aftermath of a mass extinction, and help to re-establish biotic communities during the recovery of global ecosystems. Not bad for a pudgy, dumpy little herbivore with a squashed up face.

Species Differences: To be frank, and I’m sure most synapsid workers won’t mind me saying this, the majority of stem-mammal taxonomy, including Lystrosaurus, is heavily biased towards their skulls. So much so that the majority of Lystrosaurus species were named based solely on slight variations between their skulls and so consequently were massively oversplit. Thankfully this is being rectified with more thorough, dedicated examinations of Lystrosaurus specimens, and so far the Gondwanan species of Lystrosaurus in the Karoo are the best studied. Four species from there are now recognised, and by and by they’re all still pretty samey looking, superficially. These four species have been recognised as sequentially spanning across the Late Permian and into the Early Triassic, and so can also be distinguished by when they each lived.

L. maccaigi is both the largest and the oldest species, and is the only one known exclusively from the Permian (although a single skull from Antarctica may or may not bring it into the earliest Triassic, assuming the rocks weren’t really Permian all along). It’s recognised for having remarkably well-developed bosses both in front and behind the eyes, giving it very distinctive looking “brows”, and the eyes themselves are characteristically large and placed high on the skull, facing somewhat more forwards and upwards than other species. The snout also drops down especially sharply (almost vertically in some), with a straight edge and ridge down the centre. As well as being the largest species, L. maccaigi was also the rarest, and both of these factors may have contributed to its extinction in the P-Tr.

The smaller L. curvatus is also known from the Permian, but unlike L. maccaigi it is known to have actually crossed the boundary into the earliest Triassic, however it died out shortly afterwards. L. curvatus is one of the least ornamented species of Lystrosaurus, with very reduced or no ridges and bosses on the face and over the eyes, although the largest individuals may have them, including small nasal bosses. L. curvatus also has some of the proportionally largest eyes of all Lystrosaurus, as well as a more gently curved snout than the others. Probably the cutest looking.

L. declivis and L. murrayi are exclusively found in the Triassic, and interestingly they are both consistently smaller than either Permian species. This is believed to be a response to the harsh conditions of the Permian Extinction and Early Triassic, as Lystrosaurus were growing faster and reaching reproductive maturity at smaller sizes and younger ages to combat shorter life expectancies. They are both fairly similar in appearance, each with short, slightly curved, somewhat angular snouts, although L. murrayi has a shorter snout only as long as the roof of the skull, whereas L. declivis has a snout that extends further down. L. declivis also has a pair of bosses in front of the eyes and a distinct ridge running between them, as well as a ridge running down the beak, all features missing from L. murrayi. Both species have a patch of grooves between the eyes on the roof of the skull, possibly supporting a sheet of keratin not seen in L. maccaigi or L. curvatus.

However, this apparent timeline does not mean there was a linear progression between these species. In fact, L. maccaigi and L. curvatus are the most derived species of Lystrosaurus, while L. declivis and L. murrayi are each more primitive than the last! Perhaps the more primitive species were able to survive by being less specialised and growing smaller. Also, this means that their ancestors had already split off during the Permian before L. maccaigi even evolved, so Gondwanan Lystrosaurus did not survive the P-Tr Extinction in just one species, but at least three! L. curvatus and L. murrayi are also both known from Triassic Antarctica, and L. murrayi is further known from India, implying quite a broad Gondwanan distribution—although given the three continents’ close proximity in Pangaea this may not be surprising.

The differences between the Laurasian species are less clear, and while various species have been named from China, it is possible that they belong to only a single species, L. hedini. L. hedini is another species known from the Permian to have crossed into the Early Triassic, and has also been found in Mongolia.

L. georgi from the Triassic of Russia is a bit of an enigma, unlike virtually every other Lystrosaurus species its skeleton is better known than its skull. This is great for understanding how the body of Lystrosaurus functioned but less so for its taxonomy. In any case, L. georgi is still pretty biogeographically distinct from other Lystrosaurus species, so it has merit. L. georgi was initially regarded as similar to the Gondwanan L. curvatus, but preliminary analyses of other Laurasian Lystrosaurus suggest they are a taxonomically distinct grouping of Lystrosaurus species, which presumably includes L. georgi.

~ By Scott Reid

Sources under the cut

Benoit, J., Angielczyk, K.D., Miyamae, J.A., Manger, P., Fernandez, V. and Rubidge, B., 2018. Evolution of facial innervation in anomodont therapsids (Synapsida): Insights from X‐ray computerized microtomography. Journal of morphology, 279(5), pp.673-701

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