Alice M. Clement

The new genus and species named and described here is a dipnoan from the sandy deposits of the Ketleri Formation (upper Famennian, Upper Devonian) cropping out in the Pavāri-2 locality in the histo...

Nearly half of all living vertebrate diversity can be traced back to a single lineage of lobe‐finned fishes (piscine sarcopterygians) that radiated during the Palaeozoic Era. In recent years, the phylogenetic framework of tetrapodomorph fishes has largely stabilized, with the exception of the ‘Osteolepiformes’, the interrelationships of which are still under debate. To resolve these uncertainties, expanded taxonomic sampling and new morphological data are essential to refine our understanding of their evolutionary history. Emerging tomography imaging techniques are providing much of this new anatomical information, including that pertaining to cranial endocasts. Endocasts can serve as proxies for gross brain morphology, and thus have the added benefit of shedding light on palaeoneurological evolution in long‐extinct lineages. Here, using a combination of synchrotron, neutron and micro‐computed tomography, we generate high‐resolution 3D virtual models of ethmosphenoids and their associated cranial endocast and sensory (lateral) line canal systems in 13 stem tetrapods. Using principal components analysis for incomplete data we identify distinct patterns of morphospace occupation among the different families. While the ‘Tristichopteridae’ usually occupy a wholly distinct region, the ‘Osteolepididae’ and Megalichthyidae exhibit partial overlap, but with ‘Osteolepididae’ always showing a broader range of variation. Our findings demonstrate that ethmosphenoids and their endocasts retain morphological features of shared phylogenetic affinity that can aid in resolving phylogenetic placement of fragmentary or enigmatic taxa. Furthermore, palaeoneurobiological evidence from these ‘Osteolepiformes’ suggests that these fishes retained a more conservative sensory umwelt prior to the rapid emergence of enhanced visual acuity in the earliest tetrapods.

The Late Devonian Gogo Formation, Western Australia, preserves a diverse collection of Frasnian vertebrates, including the most diverse assemblage of lungfishes (Sarcopterygii, Dipnoi) from any geological period or locality. One enigmatic Gogo fossil known from a single specimen was originally dubbed Cainocara enigma Campbell and Barwick, 2011, interpreted as having osteichthyan affinity but otherwise considered not to belong to “any known described major systematic order”. Original interpretation of the specimen was hampered by its poor state of preservation, but thanks to increasing application of computed tomography, we can now use a more comprehensive comparative dataset, elucidating both internal and external anatomy, to study and visualise fossils more thoroughly than previously possible. Herein we show that the original orientation of the specimen was wrong, identify a kite-shaped parasphenoid and pterygoid bones that meet in their midline. We also reconstruct a partial digital cranial endocast, including portions of the inner ears, for comparison with other known endocasts from Gogo taxa, including the first cranial endocast of a holodontid lungfish ( Holodipterus gogoensis Miles, 1977). We now recognise Cainocara enigma, as a lungfish (order Dipnoi) based on anatomy revealed via CT, but concede that this enigmatic specimen most likely remains a nomen nudum and nomen dubium.

The known fossil record of crown-group amniotes begins in the late Carboniferous with the sauropsid trackmaker Notalacerta ^1,2 and the sauropsid body fossil Hylonomus ^1–4. The earliest body fossils of crown-group tetrapods are mid-Carboniferous, and the oldest trackways are early Carboniferous^5–7. This suggests that the tetrapod crown group originated in the earliest Carboniferous (early Tournaisian), with the amniote crown group appearing in the early part of the late Carboniferous. Here we present new trackway data from Australia that challenge this widely accepted timeline. A track-bearing slab from the Snowy Plains Formation of Victoria, Taungurung Country, securely dated to the early Tournaisian^8,9, shows footprints from a crown-group amniote with clawed feet, most probably a primitive sauropsid. This pushes back the likely origin of crown-group amniotes by at least 35–40 million years. We also extend the range of Notalacerta into the early Carboniferous. The Australian tracks indicate that the amniote crown-group node cannot be much younger than the Devonian/Carboniferous boundary, and that the tetrapod crown-group node must be located deep within the Devonian; an estimate based on molecular-tree branch lengths suggests an approximate age of early Frasnian for the latter. The implications for the early evolution of tetrapods are profound; all stem-tetrapod and stem-amniote lineages must have originated during the Devonian. It seems that tetrapod evolution proceeded much faster, and the Devonian tetrapod record is much less complete, than has been thought.

Well-preserved specimens of a new species of arthrodiran placoderm, Groenlandaspis howittensis sp. nov. (Middle Devonian of Victoria, Australia), reveals previously unknown information on the dermal skeleton, body-shape and dentition of the wide-spread genus Groenlandaspis. The new material includes dual pineal plates, extrascapular plates, and cheek bones showing the presence of cutaneous sensory organs. The anterior supragnathal, usually a paired element in arthrodires, is a fused median bone in G. howittensis sp. nov. It is positioned anterior to the occlusion of the mouth between the lower jaw (infragnathals) and upper jaw (posterior supragnathals) bones, indicating a specialised feeding mechanism and broadening the known diversity of placoderm dental morphologies. G. howittensis sp. nov. differs from all other groenlandaspidids by a less pronounced posterior expansion of the nuchal plate; the shape of the posterior dorsolateral plate and the presence of a short accessory canal on the anterior dorsolateral plate. A new phylogenetic analysis positions Groenlandaspididae in a monophyly with the phlyctaeniid families Arctolepidae and Arctaspididae, however, the specific intrarelationships of groenlandaspidids remain poorly resolved.

Well-preserved specimens of an undescribed species of arthrodiran placoderm, Groenlandaspis howittensis sp. nov. (Middle Devonian of Victoria, Australia), reveals previously unknown information on the dermal skeleton, body-shape and tooth arcade of the wide-spread genus Groenlandaspis . The new material includes, dual pineal plates, extrascapular plates, and cheek bones cheek bones showing the presence of cutaneous sensory organs. The anterior supragnathal, usually a paired element in arthrodires, is a fused medial bone in G. howittensis sp. nov. It is positioned anterior to the occlusion of the mouth between the lower jaw (infragnathals) and upper jaw (posterior supragnathals) bones, indicating a specialised feeding mechanism and broadening the known diversity of placoderm dental morphologies. G. howittensis sp. nov. differs from all other groenlandaspidids by a less pronounced posterior expansion of the nuchal plate; the shape of the posterior dorsolateral plate and the presence of a short accessory canal on the anterior dorsolateral plate. A new phylogenetic analysis positions Groenlandaspididae in a monophyly with the phlyctaeniid families Arctolepidae and Arctaspdidae, however, the specific intrarelationships of groenlandaspidids remain poorly resolved.

The living coelacanth Latimeria (Sarcopterygii: Actinistia) is an iconic, so-called ‘living fossil’ within one of the most apparently morphologically conservative vertebrate groups. We describe a new, 3-D preserved coelacanth from the Late Devonian Gogo Formation in Western Australia. We assemble a comprehensive analysis of the group to assess the phylogeny, evolutionary rates, and morphological disparity of all coelacanths. We reveal a major shift in morphological disparity between Devonian and post-Devonian coelacanths. The newly described fossil fish fills a critical transitional stage in coelacanth disparity and evolution. Since the mid-Cretaceous, discrete character changes (representing major morphological innovations) have essentially ceased, while meristic and continuous characters have continued to evolve within coelacanths. Considering a range of putative environmental drivers, tectonic activity best explains variation in the rates of coelacanth evolution.

The diversity and distribution of species’ traits in an ecological community determine how it functions. While modern fish communities conse rve trait space across similar habitats, little is known about trait-space variation through deep time or across different habitats. We examined how fish trait diversity varies through space and time by comparing three Late Devonian fish communities — a tropical reef (Gogo, Australia), a tropical estuary (Miguasha, Canada), and a temperate freshwater system (Canowindra, Australia) — with six modern communities from diverse habitats. Trait-space metrics reflecting within-community diversity (functional richness) and species similarity (functional nearest-neighbour distance) indicated Late Devonian communities had scores similar to modern communities. However, they were less functionally rich than their closest modern analogues, and their species tended to be more functionally distinct from one another. Metrics describing location in trait space (centroid distances and hypervolume overlap) showed modern communities were similar to each other, Gogo and Miguasha were similar but distinct from modern communities, and Canowindra was distinct from all others. This pattern suggests period-associated differentiation and substantial heterogeneity among some Late Devonian communities. In addition to temporal changes, we found consistent differences associated with habitat type and climate zone. Reef and tropical communities were the most functionally rich, whereas functional nearest-neighbour scores were highest in estuarine and temperate communities. These results indicate fish community trait space varies with time, habitat and climate, suggesting ( i ) lability in fish trait space and ( ii ) that evolutionary history, environmental filtering, and stochasticity influence community assembly.