The Cabrières Biota in the Montagne Noire region of southern France is one of the key Early Ordovician faunas, as it represents a Lagerstätte close to the Ordovician South Pole. This biota exhibits remarkably high biodiversity, with more than 30 taxa identified to date, including algae, arthropods, brachiopods, echinoderms, bryozoans, sponges, and worms. It has fundamentally transformed our view of Early Ordovician ecosystems by preserving both characteristic Ordovician taxa and typical Cambrian animals, thereby highlighting a continuum between the Cambrian Explosion and the Great Ordovician Biodiversification Event. As one of the closest Early Ordovician Lagerstätten to the ancient South Pole, the Cabrières Biota probably served as a high-latitude biotic refuge, and shows ecological structures comparable to those of modern polar communities. Consequently, it offers invaluable insights into Early Paleozoic polar ecosystems.
Of special interest are active filter-feeding benthic organisms such as sponges. Given that sponges play a significant role in modern polar environments, the presence of Lower Ordovician polar sponges holds considerable importance for understanding early high-latitude ecosystems.
Recently, Associate Professor LI Lixia from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS), in collaboration with Professor Joachim Reitner from the University of Göttingen, Germany, conducted a systematic study of sponge fossils from the Early Ordovician Cabrières Biota in France. The findings were published in the journal Lethaia.
The studied material consists of nine specimens collected from the Cabrières Lagerstätte, located in the southern Montagne Noire, France. According to the associated trilobites, the Cabrières Lagerstätte from the Landeyran Formation corresponds to the trilobite Apatokephalus incisus biozone, indicating the late Floian age (ca. 470 Ma). Palaeogeographically, this Lagerstätte is part of Gondwana in high-latitude close to the South Pole.
A detailed study of the sponge fauna from the Cabrières Biota revealed four distinct hexactinellid morphotypes that can be assigned to the Hintzespongiidae and Protospongiidae, indicating potentially unknown groups. The discovery of two isolated root tufts with hexactinellid affinity also supports this interpretation, as these features collectively indicate the presence of previously undocumented diversity.
All currently identifiable sponges in the Cabrières Biota are hexactinellids, including two types of reticulosan sponges (hintzespongiids and protospongiids) along with root tufts attributable to two distinct hexactinellid morphotypes. Phylogenetically, hintzespongiids exhibit characteristics of both Cambrian protospongiids (regular arrangement of stauractines) and late Palaeozoic brachiospongiids (irregular hexactines in the sponge wall), potentially representing an intermediate form between these groups. Although our current specimens have yielded body fossils of only protospongiids and hintzespongiids, with no brachiospongiids identified, the isolated root tufts that have been discovered show a close similarity to those of brachiospongiids (Stioderma or Hyalostelia). Therefore, the hexactinellids in the Cabrières Biota appear to combine both Cambrian and late Palaeozoic sponge characteristics, providing a link between these two evolutionary lineages.
From an ecological perspective, the presence of long and flexible root tufts in the Cabrières Biota serves as an indicator of the palaeoenvironment. Hexactinellid sponges possessing such structures typically inhabited high-energy hydrodynamic environments, which enabled them to regulate their osculum and canal systems in adaptation to water currents, thereby enhancing their efficiency in filtering nutrients from the surrounding water. Moreover, the long root tufts probably enabled the sponges to anchor to soft bottoms in the absence of hard substrate. The evidence presented above coincides with sedimentological interpretations, which indicate that the Cabrières Biota inhabited a soft-substrate in the distal mid-shelf environment.
The sponges of the Cabrières Biota show both shared and distinct features when compared to those of other Early Ordovician polar ecosystems, such as the Fezouata and Klabava biotas. The Cabrières Biota shares hintzespongiids and protospongiids with Klabava Biota. The Fezouata Biota exhibits higher sponge diversity, is demosponge-dominated, with low-diversity monospecific populations near storm wave base. The Cabrières and Klabava biotas are reticulosan-dominated, indicating deeper, open-marine settings below normal wave base. Thus, water depth and local environmental conditions strongly shaped faunal composition across these polar ecosystems, revealing greater ecological complexity. Therefore, sponges from the Cabrières Biota offer key insights into the complexity and environmental dynamics of Early Ordovician polar ecosystems.
This research was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Strategic Priority Research Program of the Chinese Academy of Sciences (Category B).
Reference：Lixia Li* & Joachim Reitner. 2026. Hexactinellid sponges from the Early Ordovician Cabrières Biota, France: insights into Early Palaeozoic polar ecosystems. Lethaia, 59(2),1-9. https://doi.org/10.18261/let.59.2.13.
Fig.1 Hintzespongiids from the Cabrières Biota
Fig.2 Root tufts from the Cabrières Biota
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