Skull Mechanics of Capitosaurs (Amphibia: Temnospondyli)

Fortuny, J., Marcé-Nogué, J., Gil, L. and Galobart, À. 2012. Skull Mechanics and the Evolutionary Patterns of the Otic Notch Closure in Capitosaurs (Amphibia: Temnospondyli). The Anatomical Record (advance online publication) doi: 10.1002/ar.22486 http://onlinelibrary.wiley.com/doi/10.1002/ar.22486/abstract

Abstract - Capitosaurs were among the largest amphibians that have ever lived. Their members displayed an amphibious lifestyle. We provide new information on functional morphology data, using finite element analysis (FEA) which has palaeoecological implications for the group. Our analyses included 17 taxa using (2D) plate models to test four loading cases (bilateral, unilateral and lateral bitings and skull raising system simulation). Our results demonstrates that, when feeding, capitosaurs concentrated the stress at the circumorbital region of the capitosaur skull and cranial sutures probably played a key role in dissipating and absorbing the stress generated during biting. Basal members (as Wetlugasaurus) were probably less specialized forms, while during Middle- and Late Triassic the group radiated into different ecomorphotypes with closed otic notch forms (as Cyclotosaurus) resulting in the strongest skulls during biting. Previous interpretations discussed a trend from an open to closed otic notch associated with lateral repositioning of the tabular horns, but the analysis of the skull-raising system reveals that taxa exhibiting posteriorly directed tabular horns display similar results during skull raising to those of closed otic notch taxa. Our results suggest that various constraints besides otic notch morphology, such as the elongation of the tabular horns, snout length, skull width and position, and size of the orbits affect the function of the skull. On the light of our results, capitosaur skull showed a trend to reduce the stresses and deformation during biting. Capitosaurs could be considered crocodilian analogues as they were top-level predators in fluvial and brackish Triassic ecosystems.

A New Neocalamites from the Upper Triassic of China

Zan, S.-Q., Axsmith, B. J, Escapa, I., Fraser, N. C., Liu, F.-X., and D.-E. Xing. 2012. A new Neocalamites (Sphenophyta) with prickles and attached cones from the Upper Triassic of China. Palaeoworld (accepted manuscript). http://dx.doi.org/10.1016/j.palwor.2012.04.001

Abstract - Remains of the extinct sphenophyte (horsetail) Neocalamites are most widespread in the Middle–Upper Triassic and are typically represented by stem and leaf fragments. Here we report on spectacular new finds of Neocalamites from the Late Triassic Yangcaogou Formation in Liaoning Province, China that include bedding surfaces dominated by nearly complete aerial stems with attached leaf whorls and rare bractless cones. They reveal a monopodial growth habit for the stems, which are covered with downward projecting prickles that probably provided protection against herbivores. These features provide the basis for a new proposed species, Neocalamites horridus. The nodes bear whorls of very long leaves mainly free to their bases, and one specimen bears an attached cone on a long peduncle. Identical dispersed cones have also been recovered. The leaves of adjacent monopodial stems most likely interlocked to support growth in large stands akin to the role now played by branches in large modern Equisetum species. The new Chinese Neocalamites is among the most confidently reconstructed species, and indicates a greater diversity of sphenophyte morphology during the Mesozoic than previously realized.

Introducing Protome batalaria, a New Phytosaur from the Chinle Formation of Petrified Forest National Park, Arizona

In the Fall of 2004 Michelle Stocker and I were out at the Battleship NW fossil locality in Petrified Forest National Park with several researchers from Northern Arizona University. They were working on completing the geological map of the area and had noted that they could not get the current stratigraphic scheme we were using (introduced in 2002) to work out on the map.  The stratigraphic position of this quarry was an important issue behind this work as I had just collected a good skeleton of the aetosaur Calyptosuchus wellesi here just above a prominent sandstone that previous workers had correlated to the "Sonsela Sandstone Bed". If this bed correlation was correct then the specimen would be from the Revueltian biozone. This was problematic because Calyptosuchus is considered an index taxon of the Adamanian.  As we hemmed and hawed back and forth and discussed various possible correlations to work out these problems, Michelle noted some scraps of bone in unconsolidated sand at top of this bed and very near to where we were standing. She was very surprised, as was I, when she reached down and pulled up part of the skull roof of a phytosaur.

After the NAU researchers moved on to complete their work, we examined Michelle's new "quarry" much closer.  By literally sifting our fingers through the loose sand we easily collected numerous parts of the skull including large portions of the rostrum and skull roof. We also uncovered a ramus of the mandible, but this was actually in-situ in the bedrock just underneath the loose sand. We were able to jacket this element, but it was wintertime and I distinctly remember how frozen our hands were after each application of a plaster bandage.  Luckily the truck was very nearby, so after each application we would run to the running truck to stick our hands under the heater.

Back in the lab we were able to piece back together much of the skull and it later became part of the focus of Michelle's Masters Thesis. Prior to this Randall Irmis and I mentioned (and figured) this specimen in a 2005 paper where we referred it to "Leptosuchus" adamanensis based on the overall morphology of the squamosals following work by Long and Murry. However, Michelle's detailed phylogenetic analysis in her thesis suggested something different, specifically the specimen did not form a clade with Smilosuchus adamanensis and instead was something else.

In her new paper in the Journal of Vertebrate Paleontology Michelle has described this specimen as a new taxon, which she names Protome batalaria. The name reflects the condition of the specimen, "face of an animal" and where it was found "warship" (for the Battleship Quarry). It can be diagnosed by a unique combination of characters as well as three autapomorphies of the braincase and lower jaw. Her phylogenetic analysis recovers it as a non-pseudopalatine leptosuchomorph.

Important discussion in her paper revolves around the importance of the use of apomorphies to describe and classify specimens. In this particular case past workers (myself) had focused on the generally morphology of the squamosal and robustness of the specimen to make a taxonomic assignment and ignored other discrete apomorphies of the material, which a phylogenetic analysis later determined to be of significance.  Thus the longtime practice of assigning isolated phytosaur squamosals to taxa based on general similarity and utilizing these for Late Triassic biochronology is called into question. This general squamosal morphology used to assign (fragmentary and complete) specimens to Rutiodon or Leptosuchus instead just appears to be a shared character of non-pseudopalatine leptosuchomorphs, a paraphyletic assemblage.

As recommended by Michelle it is now necessary to go back to collections such as those from the Petrified Forest and look carefully at all of the specimens assigned to "Leptosuchus" and sort them out using apomorphies. Hopefully this will provide a clear distribution pattern and biochronological signal for these specimens, testing their importance in phytosaur biochronology and biogeography.  Overall this new paper provides a great description and discussion that Michelle should be proud of and will be landmark (along with her 2010 paper) for sorting out the labyrinth that is phytosaur taxonomy.

By the way, the stratigraphic problem mentioned at the beginning of this post was finally figured out by Jeff Martz and I in 2009 when we discovered that the bed in question was definitely not the "Sonsela Sandstone Bed", but rather an isolated sandstone lens in the older Lot's Wife Beds and  Adamanian in age.

Stocker, M. R. 2012. A new phytosaur (Archosauriformes, Phytosauria) from the Lot’s Wife beds (Sonsela Member) within the Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona. Journal of Vertebrate Paleontology 32(3): 573-586 DOI:10.1080/02724634.2012.649815

Abstract - A new phytosaur taxon from Petrified Forest National Park, Arizona, is here described based on cranial material from a single individual. This specimen previously was included in an extensive phylogenetic analysis, and it was found to possess a combination of character states that differs from all known phytosaur taxa in addition to two autapomorphies within the braincase and an autapomorphy of the mandible. The new taxon adds to the taxonomic diversity recognized from the Sonsela Member of the Chinle Formation. The continued increase in phytosaur diversity emphasizes the need to more accurately characterize and identify taxa within a phylogenetic systematic context in order to produce a more refined signal for biostratigraphic correlations, biochronologic inferences, and faunal dynamics during the Late Triassic.

New Triassic Trackway from Switzerland

Cavin, L., Avanzini, M., Bernardi, M., Piuz, A., Proz, P.-A., Meister, C., Boissonnas, J., and C. A. Meyer. 2012. New vertebrate trackway from the autochthonous cover of the Aiguilles Rouges Massif and reevaluation of the dinosaur record in the Valais, SW Switzerland. Swiss Journal of Palaeontology [online first] DOI: 10.1007/s13358-012-0040-0

Abstract - A new tracksite located in the Mesozoic autochthonous series covering the Aiguilles Rouges Massif, circa 7 km to the NNE of the tracksite of the Vieux Emosson, is briefly described. The trampled bed is most likely coeval with the outcrop in the Vieux Emosson area. Two poorly preserved quadrupedal trackways, almost parallel, measure 9.8 and 8 m in length, respectively. They are referred to the Chirotheriidae ABEL, 1835 form-family. A short and well-preserved quadrupedal trackway, composed of two manus-pes couples, is assigned to Chirotherium cf. barthii KAUP, 1835. A reinterpretation of the Vieux Emosson ichnotaxa reveals that most tracks, if not all, belong to indeterminate chirotheriid and that no clear evidence of dinosaur footprints is observed. The trampled bed of the cover of the Aiguilles Rouges Massif probably forms a megatracksite, which is Early or Middle Triassic in age.  

Could it Be? An Non-Archosaurian Archosauriform that is Actually a Dinosaur?

The past eight years have seen quite a few cases where purported Triassic dinosaurs actually turned out to be non-dinosaurian archosauriforms...Revueltosaurus, Shuvosaurus, Azendohsaurus... finally the dinosaurs get one back. Moreover there are no Jurassic or Chinese phytosaur specimens. 

Barrett, P. M., and X. Xu. 2012. The enigmatic reptile Pachysuchus imperfectus Young, 1951 from the lower Lufeng Formation (Lower Jurassic) of Yunnan, China. Vertebrata PalAsiatica 50:151-159. [Free download here]

Abstract - Phytosaurs are generally considered to have become extinct at the end of the Triassic Period, but several records have suggested that they survived into the basal Jurassic in Europe and Asia. The Asian record consists of Pachysuchus imperfectus from the lower Lufeng Formation (?Hettangian-Sinemurian) of Yunnan, China. However, this specimen differs from phytosaurs in numerous aspects and is more likely a poorly preserved, indeterminate sauropodomorph dinosaur skull. The referred specimens of this species are also regarded as indeterminate, thereby removing the post-Triassic record of phytosaurs from Asia. The European records of Jurassic phytosaurs are also shown to be doubtful, suggesting that this clade was restricted to the Late Triassic. 

Neotype Proposal for Anchisaurus polyzelus

Galton, P.M. 2012. Case 3561 Anchisaurus Marsh, 1885 (Dinosauria, Sauropodomorpha): proposed conservation of usage by designation of a neotype for its type species Megadactylus polyzelus Hitchcock, 1865. Bulletin of Zoological Nomenclature 69 (1): 44-50.



Abstract - The purpose of this application, under Article 75.5 of the Code, is to conserve the usage of the name Anchisaurus Marsh, 1885 (Lower Jurassic, Connecticut Valley, northeastern U.S.A.) that is based on Megadactylus polyzelus Hitchcock, 1865. It is proposed to replace the fragmentary and non-diagnostic holotype of M. polyzelus with a diagnostic neotype, an almost complete skull and skeleton (YPM 1883, holotype of A. colurus Marsh, 1891). This specimen has formed the basis for the concept of Anchisaurus, the first basal sauropodomorph genus from the U.S.A. and still the best represented from there since it was illustrated by Marsh (1892, 1893), and of A. polyzelus since it was illustrated by Galton (1976). Anchisaurus is the basis for ANCHISAURIDAE Marsh, 1885, the first basal sauropodomorph family to be named, and for the Anchisauria Galton & Upchurch, 2004.

First Multi-taxic Multi-component Ornithischian and Sauropodomorph Dinosaur Bonebed from the Upper Triassic of North America

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Just kidding...

Happy April 1 everyone!

Paleohistological Estimation of Bone Growth Rate in Extinct Archosaurs

Cubo, J., LeRoy, N., Martinez-Maza, C., and L. Montes. 2012. Paleohistological estimation of bone growth rate in extinct archosaurs. Paleobiology 38:335-339. doi: http://dx.doi.org/10.1666/08093.1

Abstract - The clade Archosauria contains two very different sister groups in terms of diversity (number of species) and disparity (phenotypic variation): Crurotarsi (taxa more closely related to crocodiles than to birds) and Ornithodira (pterosaurs and dinosaurs including birds). The extant species of Crurotarsi may constitute a biased sample of past biodiversity regarding growth patterns and metabolic rates. Bone histological characters can be conserved over hundreds of millions of years in the fossil record and potentially contain information about individual age at death, age at sexual maturity, bone growth rates, and basal metabolic rates of extinct vertebrates. Using a sample of extant amniotes, we have constructed a paleobiological model to estimate bone growth rate from bone histological traits. Cross-validation tests show that this model is reliable. We then used it to estimate bone growth rates in a sample of extinct archosaurs including Crurotarsi and Ornithodira. After testing for phylogenetic signal, optimization of femoral growth rates through squared change parsimony onto a time-calibrated tree of amniotes shows two divergent evolutionary trends: whereas bone growth rates increase from the last common ancestor of Ornithodira to extant birds, they decrease from the last common ancestor of Crurotarsi to extant crocodiles. However, we conclude, on the basis of recent evidence for unidirectional airflow in the lungs of alligators, that crocodiles may have retained the capacity of growing at high rates.

Vegetation History and Climate Change Across the Tr/J Boundary

Bonis, N. R., and W. M. Kürschner. 2012. Vegetation history, diversity patterns, and climate change across the Triassic/Jurassic boundary. Paleobiology 38:240-264. doi: http://dx.doi.org/10.1666/09071.1

Abstract - High-resolution palynological data sets from shallow marine Triassic-Jurassic (Tr/J) boundary beds of two principal sections in Europe (Hochalplgraben in Austria and St. Audrie's Bay in the United Kingdom) were analyzed to reconstruct changes in vegetation, biodiversity, and climate. In Hochalplgraben, a hardwood gymnosperm forest with conifers and seed ferns is replaced by vegetation with dominant ferns, club mosses and liverworts, which concurs with an increased diversification of spore types during the latest Rhaetian. Multivariate statistical analysis reveals a trend to warmer and wetter conditions across the Tr/J boundary in Hochalplgraben. The vegetation changes in St. Audrie's Bay are markedly different. Here, a mixed gymnosperm forest is replaced by monotonous vegetation consisting mainly of Cheirolepidiaceae (80–100%). This change is caused by a transition to a warmer and more arid climate. The observed diversity decrease in St. Audrie's Bay affirms this interpretation. Although both sections show major vegetation changes, neither of them demonstrates a distinctive floral mass extinction. A compilation of Tr/J boundary sections across the world demonstrates the presence of Cheirolepidiaceae-dominated forests in the Pangaean interior and increases in abundance of spore-producing plants adjacent to the Tethys Ocean. We propose that the non-uniform vegetation changes reflected in the Tr/J palynological records are the result of environmental changes caused by Central Atlantic Magmatic Province volcanism. The increase in greenhouse gases caused a warmer climate and an enhanced thermal contrast between the continent and the seas. Consequently, the monsoon system got stronger and induced a drier continental interior and more intensive rainfall near the margins of the Tethys Ocean.

Postcranial Skeletal Pneumaticity in Triassic Archosaurs

Butler, R. J., Barrett, P. M., and D. J. Gower. 2012. Reassessment of the evidence for postcranial skeletal pneumaticity in Triassic archosaurs, and the early evolution of the avian respiratory system. PLoS ONE 7(3): e34094. doi:10.1371/journal.pone.0034094


Abstract - Uniquely among extant vertebrates, birds possess complex respiratory systems characterised by the combination of small, rigid lungs, extensive pulmonary air sacs that possess diverticula that invade (pneumatise) the postcranial skeleton, unidirectional ventilation of the lungs, and efficient crosscurrent gas exchange. Crocodilians, the only other living archosaurs, also possess unidirectional lung ventilation, but lack true air sacs and postcranial skeletal pneumaticity (PSP). PSP can be used to infer the presence of avian-like pulmonary air sacs in several extinct archosaur clades (non-avian theropod dinosaurs, sauropod dinosaurs and pterosaurs). However, the evolution of respiratory systems in other archosaurs, especially in the lineage leading to crocodilians, is poorly documented. Here, we use mCT-scanning to investigate the vertebral anatomy of Triassic archosaur taxa, from both the avian and crocodilian lineages as well as non-archosaurian diapsid outgroups. Our results confirm previous suggestions that unambiguous evidence of PSP (presence of internal pneumatic cavities linked to the exterior by foramina) is found only in bird-line (ornithodiran) archosaurs. We propose that pulmonary air sacs were present in the common ancestor of Ornithodira and may have been subsequently lost or reduced in some members of the clade (notably in ornithischian dinosaurs). The development of these avian-like respiratory features might have been linked to inferred increases in activity levels among ornithodirans. By contrast, no crocodile-line archosaur (pseudosuchian) exhibits evidence for unambiguous PSP, but many of these taxa possess the complex array of vertebral laminae and fossae that always accompany the presence of air sacs in ornithodirans. These laminae and fossae are likely homologous with those in ornithodirans, which suggests the need for further investigation of the hypothesis that a reduced, or non-invasive, system of pulmonary air sacs may be have been present in these taxa (and secondarily lost in extant crocodilians) and was potentially primitive for Archosauria as a whole.

Taphonomy of an Upper Triassic Rhynchosaur Bonebed From India

Mukherje, D. and  & S. Ray. 2012. Taphonomy of an Upper Triassic vertebrate bonebed: A new rhynchosaur (Reptilia; Archosauromorpha) accumulation from India. Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication) http://dx.doi.org/10.1016/j.palaeo.2012.03.010


Abstract - The Upper Triassic Tiki Formation of India is a rich storehouse of varied vertebrate fossil assemblages. So far, there is no information on taphonomic signatures of the Tiki vertebrate assemblages in comparison to that of other fossiliferous horizons of India. We report a new, low diversity, mono-dominant, multitaxic vertebrate accumulation where rhynchosaurs constitute the dominant component. The formation of the rhynchosaur bonebed is attributed to biological aggregation with a hydraulic overprint resulting in a mixed-origin concentration. Other taxa include rauisuchid, phytosaur, small indeterminate archosaur and cynodonts. Taphonomic study based on 617 skeletal specimens of rhynchosaurs collected from nine sites within an area of about 250x217 sq m shows that most of the specimens are disarticulated and disassociated but in close spatial proximity to one another; some are associated specimens and few are articulated. About 13 to 20 individuals of rhynchosaur at different ontogenetic stages are estimated from the specimens collected, suggesting gregarious behaviour, possibly herding. These specimens show varying degree of weathering, breakage, encrustation, abrasion and deformation. The bonebed is preserved within the Tiki red mudstone unit and is found in association with paleosol profiles, suggesting prolonged subaerial exposure. Spatial distribution and relative bone frequencies show differential susceptibility of the skeletal specimens to fluvial transport. 55.4% of the collected skeletal specimens belonged to Voorhies Group I, whereas 12.4% and 24% constituted Voorhies Group II and III respectively, and 8.2% of the collected specimens belonged to the intermediate group I and II. It appears that the animals concentrated in the vicinity of the water sources during prolonged period of aridity and died possibly during high seasonal rainfall that resulted in a major flood event. Subsequently, the soft tissues decomposed, and the skeletons suffered prolonged subaerial exposure when the water receded leading to disarticulation and fragmentation followed by minor dispersion by low velocity water currents. This resulted in segregation of skeletal specimens, which were gradually covered by mud deposited during later flooding events. Based on the known flora and fauna, the Tiki Upper Triassic ecosystem is reconstructed for the first time. In the aquatic ecosystem, the metoposaurid labyrinthodonts occupied the top of the food pyramid together with the semi-aquatic parasuchids, which occupied an ecological niche similar to that of the present day crocodilians. The abundance of herbivorous rhynchosaurs at the base with few large and carnivorous rauisuchids and parasuchids at the top suggest a trophic structure similar to that of a modern day terrestrial ecosystem.

Revised Phylogeny of Basal Turtles

Anquetin, J. 2012. Reassessment of the phylogenetic interrelationships of basal turtles (Testudinata). Journal of Systematic Palaeontology 10:3-45. doi: http://dx.doi.org/10.1080/14772019.2011.558928


Abstract - Recent discoveries from the Late Triassic and Middle Jurassic have significantly improved the fossil record of early turtles. These new forms offer a unique opportunity to test the interrelationships of basal turtles. Nineteen fossil species are added to the taxon sample of the most comprehensive morphological phylogenetic analysis of the turtle clade. Among these additional species are recently discovered forms (e.g. Odontochelys semitestacea, Eileanchelys waldmani, Condorchelys antiqua), taxa generally omitted from previous analyses (e.g. chengyuchelyids, Sichuanchelys chowi) and species included in a phylogenetic analysis for the first time (Naomichelys speciosa and Siamochelys peninsularis). The coding of several characters is reassessed in the light of recent observations, but also in order to reduce unwarranted assumptions on character and character state homologies. Additional characters from previous analyses, as well as five new ones, are also included, resulting in a data matrix of 178 characters scored for 86 turtle species and seven fossil outgroups. The dataset resolves the relationships of most newly included taxa, with the exception of S. chowi and ‘Chengyuchelys’ dashanpuensis. The phylogenetic placement of Heckerochelys romani, Condorchelys antiqua and Eileanchelys waldmani as stem turtles more derived than Kayentachelys aprix but more basal than Meiolania platyceps and Mongolochelys efremovi is corroborated. The relationships of chengyuchelyids remain unclear and they are unstable with respect to stem turtles. In contrast to previous analyses, Arundelemys dardeni is placed within pleurosternids and Siamochelys peninsularis falls within xinjiangchelyids. Perhaps the most salient conclusion of the present study is the placement of Naomichelys speciosa as a basal member of a clade uniting meiolaniids, Mongolochelys efremovi and Otwayemys cunicularius. This clade of rather large stem turtles had a worldwide spread during the Mesozoic at least, and persisted until the Pleistocene with meiolaniids.

Further Evidence of Burrowing in Procolophonid Parareptiles

MacDougall, M. J., Modesto, S. P., and J. Botha-Brink. 2012. The postcranial skeleton of the Early Triassic parareptile Sauropareion anoplus, with a discussion of possible life history. Acta Palaeontologica Polonica in press. Available online 27 Feb 2012 doi: http://dx.doi.org/10.4202/app.2011.0099.

Abstract - The skeletal anatomy of the Early Triassic (Induan) procolophonid reptile Sauropareion anoplus is described on the basis of three partial skeletons from Vangfontein, Middelburg District, South Africa. Together these three specimens preserve the large majority of the pectoral and pelvic girdles, articulated forelimbs and hindlimbs, and all but the caudal portion of the vertebral column, elements hitherto undescribed. Our phylogenetic analysis of the Procolophonoidea is consonant with previous work, positing S. anoplus as the sister taxon to a clade composed of all other procolophonids exclusive of Coletta seca. Previous studies have suggested that procolophonids were burrowers, and this seems to have been the case for S. anoplus, based on comparisons with characteristic skeletal anatomy of living digging animals, such as the presence of a spade-shaped skull, robust phalanges, and large unguals.

Earliest Evidence of Ovoviviparity in Coelocanths

Wen, W., Zhang, Q.-Y., Hu, S.-X., Benton, M. J., Zhou, C.-Y., Tao, X., Yuan, H.-J., and Z.-Q., Chen. 2012. Coelacanths from the Middle Triassic Luoping Biota, Yunnan, South China, with the earliest evidence of ovoviviparity. Acta Palaeontologica Polonica in press. Available online 08 Mar 2012 doi: http://dx.doi.org/10.4202/app.2011.0066

Abstract - The fossil record of coelacanths is patchy, with very few taxa known from the Triassic of Asia. We report here two new genera and species of coelacanths from the Luoping Biota, a recently found site of exceptional fossil preservation from Yunnan, South China. The first new taxon, Luopingcoelacanthus eurylacrimalis, is based on four specimens, which together show most aspects of the anatomy. One specimen shows two small coelacanths inside the ventral portion of the abdominal cavity, and these are interpreted as intrauterine embryos, close to birth size, based on comparisons with previously reported embryos of the fossil coelacanths Rhabdoderma and Undina, and the extant genus Latimeria. Our new find extends the evidence for ovoviviparity in coelacanths back from the Late Jurassic to the Middle Triassic. The second new taxon, Yunnancoelacanthus acrotuberculatus, is based on one specimen, and differs from Luopingcoelacanthus in the dentary, lachrymojugal, number of rays of the first dorsal fin, and especially in the ornament on dermal bones and scales. A cladistic analysis shows that the new taxa are closest relatives to the derived clade Latimerioidei. The relatively high diversity of coelacanths in the Early Triassic, and adaptations of living Latimeria to low-oxygen conditions, suggests that the group may have included ‘disaster taxa’ that benefited from anoxic and dysoxic ocean conditions in the aftermath of the end-Permian mass extinction.