Lisowicia

History of discovery

Remains of Lisowicia have been discovered in the Lipie Śląskie clay pit in Lisowice, a village in southern Poland near the town of Lubliniec, Silesia. The fossil bearing beds of Lipie Śląskie consist mostly of green mudstones. The age of the Lipie Śląskie clay pit has been difficult to determine, with different biostratigraphic methods of dating providing varying results. The site has typically been dated to the Rhaetian, which would make Lisowicia one of the youngest dicynodonts in the world. However, palaeontologists Grzegorz Racki and Spencer Lucas have claimed the site to be older and dated to the middle Norian stage based on biostratigraphy of large vertebrates, including Lisowicia. They instead suggested Lisowicia was not significantly younger than other dicynodonts and was similar in age to the last known genera elsewhere in the world.

A sample of detrital zircons from the Lipie Śląskie clay pit was radiometrically dated to determine the maximum age of deposition for the fossil beds. The youngest zircon grain recorded an age of approximately 211 ± 3 million years old in the late Norian, however due to the discrepancy between the formation of the zircon crystals and deposition as sediment it is likely that Lipie Śląskie is younger than this, corroborating the late Norian to early Rhaetian estimates.

Remains of Lisowicia were first discovered in 2006 by palaeontologists Jerzy Dzik, Tomasz Sulej and Grzegorz Niedźwiedzki, who initially mistook them for the bones of a sauropodomorph dinosaur due to their massive size. They later recognised the fossils as those of a giant dicynodont in 2008, by then known from a partially articulated skeleton and various isolated bones from at least two individuals. Between 2007—2014, over 1,000 bones of Lisowicia were collected from the clay pit.

Lisowicia would not be officially named and published as a new taxon until January 2019, although the name and the description were released online in November 2018 prior to the official publication date. The genus is named after the village Lisowice where the original specimens were found, while the specific name bojani honours Ludwig Heinrich Bojanus (1776–1827), a German physician and naturalist who did pioneering work in comparative anatomy and paleontology. The known fossils of Lisowicia are held in the collections of the Institute of Paleobiology at the Polish Academy of Sciences and the Department of Paleobiology and Evolution at the University of Warsaw, Poland.

Classification

Lisowicia is a kannemeyeriiform, the group to which most Triassic dicynodonts belong to, and is a member of the family Stahleckeriidae, the only remaining lineage of dicynodonts present in the Late Triassic. In particular, phylogenetic analyses by Sulej & Niedźwiedzki (2019) using two separate datasets both found Lisowicia to be closely related to the well-known North American genus Placerias in the subfamily Placeriinae, together with the Moroccan Moghreberia. A similar result was recovered by Szczygielski & Sulej (2023) in their description of the Polish dicynodont Woznikella, which also recovered the South African Pentasaurus at the base of Placeriinae, while Woznikella itself was found in a more distant position outside Stahleckeriidae.

The cladogram below is modified and simplified from Szczygielski & Sulej (2023) to focus on the relationships of stahleckeriids and their closest relatives, depicting the strict consensus of the three shortest (most parsimonious) trees:

An alternative non-cladistic phylogeny for kannemeyeriiforms was proposed by Tomasz Sulej in 2024 in his osteological description of Lisowicia. Rather than determining relationships based only on morphology, as in most cladistic analyses, Sulej also used stratigraphic and biogeographic information to hypothesise ancestor-descendent relationships in space and time. This approach in palaeontology has been termed "chronophyletics" by Polish palaeontologist Jerzy Dzik. These results differ noticeably from conventional cladistics-based phylogenies, such as the tree shown above. Sulej identified Lisowicia as the last member of a Laurasian kannemeyeriiform lineage, beginning with the "kannemeyeriid" Shaanbeikannemeyeria in the Middle Triassic, through Rabidosaurus, Woznikella (in contrast to its more distant position recovered cladistically) to Placerias before culminating in Lisowicia. Unlike the cladistic tree above, he proposed that most stahleckeriines did not share close common ancestry with placeriines but instead emerged from a distinct lineage of Middle Triassic "kannemeyeriids" that migrated into Gondwana descending from the Laurasian Rhadiodromus and Parakannemeyeria.

Sulej argued that the shape of the frontals and parietals, particularly their cross-section along the midline where they surround the braincase, was one of the key distinctions separating these lines of descent. In Lisowicia and members of the Laurasian lineage, the parietals are vertically elongated and triangular, tapering down to a point. By contrast, stahleckeriines and members of their lineage have shorter parietals that have broader, more rounded bottom edges. On the surface the parietal foramen is also positioned closer to the rear of the skull in the Laurasian lineage, and the frontals are longer and participate in the margin of the orbit. A single articulation surface for the shoulder and ribs on the sternum was also identified as a characteristic of this lineage.

Dicynodont gigantism and evolution

Prior to the discovery of Lisowicia, the evolution of giant body sizes in Triassic sauropodomorphs was thought to be an exclusive trait of dinosaurs, as other large herbivores—including the dicynodonts—were not thought to have achieved similar sizes. The elephantine size of Lisowicia demonstrates that gigantism also evolved in dicynodonts, and analysis of their body size as they evolved over the course of the Late Triassic demonstrates that, like sauropodomorphs, Triassic dicynodonts were also increasing in body size, culminating in Lisowicia. In fact, dicynodonts were consistently larger than sauropodomorphs during the Carnian stage, and both achieved similar gigantic sizes in the Norian to the Rhaetian with Lisowicia. The evolution of gigantism in both sauropodomorphs and Lisowicia at similar time periods suggests that ecological factors may have allowed and encouraged both lineages to grow to giant sizes, as opposed to specific traits inherent to sauropodomorph dinosaurs as had previously been suggested.

The evolution of gigantism in dicynodonts was a gradual process, occurring over approximately 20 million years, and acquired major restructuring of the musculo-skeletal system to achieve the size and posture of Lisowicia. It's possible that gigantism in Lisowicia was driven by increasing body size in predators, or as a metabolic adaptation for getting more nutrition out of their food by increasing the size of their gut. It also highlights that dicynodont evolution in the Late Triassic is still poorly understood. Previously considered to be geographically restricted and in decline, Lisowicia demonstrates that dicynodonts were both still geographically widespread and continuing to diversify in the Late Triassic, particularly evolving traits to support massive body sizes.

Palaeobiology

Feeding and diet

Lisowicia was a herbivore, like most other dicynodonts, using its relatively long beak to crop and chew, although its large size implies it was feeding on higher levels of vegetation than was typical for the group. On the other hand, Sulej (2024) proposed that Lisowicia was a "grazer" that fed on low-lying vegetation. This suggestion was based on the orientation of the orbits and the low position of the occipital condyles (where the skull joins the neck), interpreted as indicating that its head was habitually held tilted down towards the ground. In this position, the slightly upward-directed orbits would now face the eyes forwards towards the horizon as it fed.

Coprolites attributed to Lisowicia indicate that it mostly ate soft vegetation and conifers. However, some coprolites contain large portions of woody material, a trait observed in some other dicynodont coprolites. This has been suggested to represent seasonal variation in its diet, possibly when their preferred diet of soft vegetation was out of season.

Predation

Numerous bite marks have been found on the bones of juvenile dicynodonts from the same locality where the dicynodont Lisowicia and the predatory archosaur Smok were found, indicating that juvenile dicynodonts were preferentially and actively hunted by Smok. Dicynodont bone fragments have also been identified in the proposed coprolites of Smok, implying that dicynodonts like Lisowicia were a major component in the predator's diet. Based on the absence of nasals and rarity of other snout bones, Sulej (2024) suggested that the snout of Lisowicia may have been structurally weak, and so preferentially targeted by predators like Smok either during predation or by disarticulating the snout first from the carcass.

Growth

Histological studies from the limb bones of Lisowicia showed features characteristic of a rapid growth rate as juveniles, similar to other large dicynodonts. However, while the growth rate of other dicynodonts slowed down as they grew, the studied bones of Lisowicia showed no such signs of slowing their growth. The possibility that the bones belonged to juveniles with an even larger adult body size than estimated was ruled out partly on the basis of their already massive size, but also because the bones were well ossified and developmentally mature. Instead, it's more likely that Lisowicia grew very rapidly without any interruptions until reaching their adult body size, as there were no clear lines of arrested growth (LAGs) that otherwise indicate periods of slower, reduced growth. LAGs may have been truly absent, or were possibly erased by extensive remodelling of the bone into adulthood, both of which would support permanently rapid growth in Lisowicia, similar to mammals and some dinosaurs.

Latrines

Coprolites attributed to Lisowicia have been discovered in abundant accumulations in areas believed to have been around standing water. These assemblages are similar to discoveries in Brazil believed to represent communal latrines made by the dicynodont Dinodontosaurus, and it's possible that Lisowicia may have performed a similar behaviour. Communal latrines are documented in modern gregarious mammals, and support the idea that dicynodonts like Lisowicia lived in herds and even suggest that they had complex social behaviours like modern large mammals.

Palaeoecology

Lisowicia coexisted with a broad variety of Late Triassic animals in Lipie Śląskie. The majority of these animals were archosaurs, including the large predatory archosaur Smok, small dinosauromorphs including a silesaurid and a Coelophysis-like neotheropod, pterosaurs, and a small crocodylomorph (previously believed to be a poposauroid). Other small reptiles include a sphenodont, an indeterminate archosauromorph and a possible choristodere. The only other synapsid known to coexist with Lisowicia was Hallautherium, a small morganucodont mammaliaform closely related to modern mammals and many orders of magnitude smaller than Lisowicia. The wet, freshwater environment supported temnospondyl amphibians (a capitosaur and smaller plagiosaurid) as well as an abundance of fish including lungfish, coelacanths and hybodontid sharks.

The environment at Lipie Śląskie was wet and swampy, comparable to the modern-day everglades, with slow-moving meandering rivers and oxbow lakes, surrounded by abundant vegetation that included Cheirolepidiaceae conifers and ginkgoales, seed ferns such as Lepidopteris and the cycads Androstrobus and Beania. By contrast, neighbouring environments may have been dry and arid, suggested by remains of the possibly xerophytic conifer Hirmeriella and charcoal fragments from fires being transported by rivers to the locality.

The absence of any large sauropodomorph herbivores is curious, as they are present in many other Late Triassic ecosystems, including in nearby localities in Europe, such as Plateosaurus in Germany. It's possible that giant dicynodonts like Lisowicia competed directly with sauropodomorphs, however, it was also possible that their absence was unrelated, and instead Lisowicia grew to its massive size to fill the ecological role of large browsing herbivores otherwise occupied by sauropodomorphs in other ecosystems.