Pulmonary arteries in coelacanths shed light on the vasculature evolution of air-breathing organs in vertebrates.

To date, the presence of pulmonary organs in the fossil record is extremely rare. Among extant vertebrates, lungs are described in actinopterygian polypterids and in all sarcopterygians, including coelacanths and lungfish. However, vasculature of pulmonary arteries has never been accurately identified neither in fossil nor extant coelacanths due to the paucity of fossil preservation of pulmonary organs and limitations of invasive studies in extant specimens. Here we present the first description of the pulmonary vasculature in both fossil and extant actinistian, a non-tetrapod sarcopterygian clade, contributing to a more in-depth discussion on the morphology of these structures and on the possible homology between vertebrate air-filled organs (lungs of sarcopterygians, lungs of actinopterygians, and gas bladders of actinopterygians).

Taxonomical use of scale ornamentation: Challenges by intraspecific and intra-individual variations in four adult specimens of Polypterus bichir.

Many actinopterygian fish groups, including fossil and extant polypteriforms and lepisosteiforms, fossil halecomorphs, and some basal teleosts, have stout bony scales covered by layers of ganoin-an enamel layer ornamented with minute tubercles. Ganoid scales preserve well as disarticulated remains and notably constitute most of the fossil record for polypteriform in both South America and Africa. Based on two variables (tubercle size and distance between tubercles), some authors reported that the ganoin tubercle ornamentation in these scales is constant within a species and differs between species and allows distinguishing species or at least groups of species. However, despite its promising potential for assessing polypteriform paleodiversity, this tool has remained unused, probably because the variables are not well defined, and intraspecific variation does not seem to have been considered. To address this gap, we aimed to test the intraspecific and intra-individual variation in the ornamentation of ganoid scales in the type species Polypterus bichir. We propose three different parameters to describe the tubercle ornamentation: the distance between contiguous tubercles centers, their density, and their relative spatial organization. With these parameters, we investigate the variation in ganoin ornamentation among four specimens and across different regions of the body. Our results show that the distribution of the tubercles is highly variable within a same species, regardless of the body region, and sometimes even between different sectors of a same scale. Moreover, the variation observed in P. bichir overlaps with the distribution described in the literature for several extant and fossil species. Thus far, the ornamentation of ganoid scales is not a reliable diagnostical feature for polypterids.

Lung evolution in vertebrates and the water-to-land transition.

A crucial evolutionary change in vertebrate history was the Palaeozoic (Devonian 419-359 million years ago) water-to-land transition, allowed by key morphological and physiological modifications including the acquisition of lungs. Nonetheless, the origin and early evolution of vertebrate lungs remain highly controversial, particularly whether the ancestral state was paired or unpaired. Due to the rarity of fossil soft tissue preservation, lung evolution can only be traced based on the extant phylogenetic bracket. Here we investigate, for the first time, lung morphology in extensive developmental series of key living lunged osteichthyans using synchrotron x-ray microtomography and histology. Our results shed light on the primitive state of vertebrate lungs as unpaired, evolving to be truly paired in the lineage towards the tetrapods. The water-to-land transition confronted profound physiological challenges and paired lungs were decisive for increasing the surface area and the pulmonary compliance and volume, especially during the air-breathing on land.

All life on Earth started out under water. However, around 400 million years ago some vertebrates, such as fish, started developing limbs and other characteristics that allowed them to explore life on land. One of the most pivotal features to evolve was the lungs, which gave vertebrates the ability to breathe above water. Most land-living vertebrates, including humans, have two lungs which sit on either side of their chest. The lungs extract oxygen from the atmosphere and transfer it to the bloodstream in exchange for carbon dioxide which then gets exhaled out in to the atmosphere. How this important organ first evolved is a hotly debated topic. This is largely because lung tissue does not preserve well in fossils, making it difficult to trace how the lungs of vertebrates changed over the course of evolution. To overcome this barrier, Cupello et al. compared the lungs of living species which are crucial to understand the early stages of the water-to-land transition. This included four species of lunged bony fish which breathe air at the water surface, and a four-legged salamander that lives on land. Cupello et al. used a range of techniques to examine how the lungs of the bony fish and salamander changed shape during development. The results suggested that the lungs of vertebrates started out as a single organ, which became truly paired later in evolution once vertebrates started developing limbs. This anatomical shift increased the surface area available for exchanging oxygen and carbon dioxide so that vertebrates could breathe more easily on land. These findings provide new insights in to how the lung evolved into the paired structure found in most vertebrates alive today. It likely that this transition allowed vertebrates to fully adapt to breathing above water, which may explain why this event only happened once over the course of evolution.

A revision of Laeliichthys ancestralis Santos, 1985 (Teleostei: Osteoglossomorpha) from the Lower Cretaceous of Brazil: Phylogenetic relationships and biogeographical implications.

A re-description of the freshwater, Early Cretaceous osteoglossomorph Laeliichthys ancestralis Santos, 1985, from the Sanfranciscana Basin of Brazil, is provided. New anatomical details and a revised diagnosis, as well as a new phylogeny are presented. A phylogenetic analysis places this taxon within the Osteoglossomorpha most likely as a member of the Notopteroidei. Within this clade Laeliichthys is the sister-taxon of the Notopteridae. The subfamily Laeliichthyinae is elevated to family rank. The revised phylogenetic position revealed in this study has important consequences on the biogeography of Notopteroidei as it extends their distribution to western Gondwana, prior to the separation of South America and Africa, and extends the evolutionary origins of notopteroid lineages by at least ~27 Myr before their first appearance in the fossil record.

Visualizing mineralization processes and fossil anatomy using synchronous synchrotron X-ray fluorescence and X-ray diffraction mapping.

Fossils, including those that occasionally preserve decay-prone soft tissues, are mostly made of minerals. Accessing their chemical composition provides unique insight into their past biology and/or the mechanisms by which they preserve, leading to a series of developments in chemical and elemental imaging. However, the mineral composition of fossils, particularly where soft tissues are preserved, is often only inferred indirectly from elemental data, while X-ray diffraction that specifically provides phase identification received little attention. Here, we show the use of synchrotron radiation to generate not only X-ray fluorescence elemental maps of a fossil, but also mineralogical maps in transmission geometry using a two-dimensional area detector placed behind the fossil. This innovative approach was applied to millimetre-thick cross-sections prepared through three-dimensionally preserved fossils, as well as to compressed fossils. It identifies and maps mineral phases and their distribution at the microscale over centimetre-sized areas, benefitting from the elemental information collected synchronously, and further informs on texture (preferential orientation), crystallite size and local strain. Probing such crystallographic information is instrumental in defining mineralization sequences, reconstructing the fossilization environment and constraining preservation biases. Similarly, this approach could potentially provide new knowledge on other (bio)mineralization processes in environmental sciences. We also illustrate that mineralogical contrasts between fossil tissues and/or the encasing sedimentary matrix can be used to visualize hidden anatomies in fossils.

-Morphological variations in the dorsal fin finlets of extant polypterids raise questions about their taxonomical validity.

Fossil polypterids are mainly represented by disarticulated material, most of them pinnules. However, there is no study that proves the taxonomical validity of these structures. Here we describe the pinnules of four species of extant polypterids and report for the first time intraindividual variations in the pinnules according to their position in the dorsal fin. Nevertheless, when comparing two different specimens of one species there is little or no interindividual variation, suggesting that pinnule morphology may have taxonomical validity. As the fossil polypterid record is based mainly on the articular head of the pinnules, we suggest caution when describing new taxa, especially if different fragments corresponding to specific positions in the dorsal fin occur in the same locality.

Earliest known lepisosteoid extends the range of anatomically modern gars to the Late Jurassic.

Lepisosteoids are known for their evolutionary conservatism, and their body plan can be traced at least as far back as the Early Cretaceous, by which point two families had diverged: Lepisosteidae, known since the Late Cretaceous and including all living species and various fossils from all continents, except Antarctica and Australia, and Obaichthyidae, restricted to the Cretaceous of northeastern Brazil and Morocco. Until now, the oldest known lepisosteoids were the obaichthyids, which show general neopterygian features lost or transformed in lepisosteids. Here we describe the earliest known lepisosteoid (Nhanulepisosteus mexicanus gen. and sp. nov.) from the Upper Jurassic (Kimmeridgian - about 157 Myr), of the Tlaxiaco Basin, Mexico. The new taxon is based on disarticulated cranial pieces, preserved three-dimensionally, as well as on scales. Nhanulepisosteus is recovered as the sister taxon of the rest of the Lepisosteidae. This extends the chronological range of lepisosteoids by about 46 Myr and of the lepisosteids by about 57 Myr, and fills a major morphological gap in current understanding the early diversification of this group.

The homology and function of the lung plates in extant and fossil coelacanths.

The presence of a pulmonary organ that is entirely covered by true bone tissue and fills most of the abdominal cavity is hitherto unique to fossil actinistians. Although small hard plates have been recently reported in the lung of the extant coelacanth Latimeria chalumnae, the homology between these hard structures in fossil and extant forms remained to be demonstrated. Here, we resolve this question by reporting the presence of a similar histological pattern-true cellular bone with star-shaped osteocytes, and a globular mineralisation with radiating arrangement-in the lung plates of two fossil coelacanths (Swenzia latimerae and Axelrodichthys araripensis) and the plates that surround the lung of the most extensively studied extant coelacanth species, L. chalumnae. The point-for-point structural similarity of the plates in extant and fossil coelacanths supports their probable homology and, consequently, that of the organ they surround. Thus, this evidence questions the previous interpretations of the fatty organ as a component of the pulmonary complex of Latimeria.

†Sorbinicharax verraesi: An unexpected case of a benthic fish outside Acanthomorpha in the Upper Cretaceous of the Tethyan Sea.

†Sorbinicharax verraesi is a marine teleostean fish from the Upper Cretaceous of Nardò (Italy). It was first attributed to the otophysan order Characiformes, which represents potential evidence for the controversial marine origin of the clade. Through a review of all the available material, we demonstrate that this species is not an otophysan since it lacks key structures that would allow for its inclusion in this group. †Sorbinicharax has a body shape that recalls ground fishes classically assigned to Acanthomorpha. However, no unambiguous feature allows us to relate it to this clade. In fact, the presence of cellular bony tissue supports its exclusion from Eurypterygii. Since no feature permits the definitive attribution of †Sorbinicharax to any teleost group, it remains as Teleostei incertae sedis. We infer that the morphology of †Sorbinicharax indicates a benthic ecology. It displays: an anteriorly wide body with enlarged ribs; large pectoral fins, while anal and dorsal fins are reduced; a large head measuring » of the total body length; and a mouth opening dorsally in a high position. Such morphology was so far undescribed in Nardo. It is surprisingly displayed by a non-eurypterygian teleost fish which means by a fish which does not belong to the clades that diversify since the upper Cretaceous and include the extant families that show ground ecomorphologies.

Lung anatomy and histology of the extant coelacanth shed light on the loss of air-breathing during deep-water adaptation in actinistians.

Lungs are specialized organs originated from the posterior pharyngeal cavity and considered as plesiomorphic for osteichthyans, as they are found in extant basal actinopterygians (i.e. Polypterus) and in all major groups of extant sarcopterygians. The presence of a vestigial lung in adult stages of the extant coelacanth Latimeria chalumnae is the result of allometric growth during ontogeny, in relation with long-time adaptation to deep water. Here, we present the first detailed histological and anatomical description of the lung of Latimeria chalumnae, providing new insights into its arrested differentiation in an air-breathing complex, mainly represented by the absence of pneumocytes and of compartmentalization in the latest ontogenetic stages.

Allometric growth in the extant coelacanth lung during ontogenetic development.

Coelacanths are lobe-finned fishes known from the Devonian to Recent that were long considered extinct, until the discovery of two living species in deep marine waters of the Mozambique Channel and Sulawesi. Despite extensive studies, the pulmonary system of extant coelacanths has not been fully investigated. Here we confirm the presence of a lung and discuss its allometric growth in Latimeria chalumnae, based on a unique ontogenetic series. Our results demonstrate the presence of a potentially functional, well-developed lung in the earliest known coelacanth embryo, and its arrested growth at later ontogenetic stages, when the lung is clearly vestigial. The parallel development of a fatty organ for buoyancy control suggests a unique adaptation to deep-water environments. Furthermore, we provide the first evidence for the presence of small, hard, flexible plates around the lung in L. chalumnae, and consider them homologous to the plates of the 'calcified lung' of fossil coelacanths.

A new cryptic species of South American freshwater pufferfish of the genus Colomesus (Tetraodontidae), based on both morphology and DNA data.

The Tetraodontidae are an Acantomorpha fish family with circumglobal distribution composed of 189 species grouped in 19 genera, occurring in seas, estuaries, and rivers between the tropical and temperate regions. Of these, the genus Colomesus is confined to South America, with what have been up to now considered only two species. C. asellus is spread over the entire Amazon, Tocantins-Araguaia drainages, and coastal environments from the Amazon mouth to Venezuela, and is the only freshwater puffers on that continent. C. psittacus is found in coastal marine and brackish water environments from Cuba to the northern coast of South America as far south as to Sergipe in Brazil. In the present contribution we used morphological data along with molecular systematics techniques to investigate the phylogeny and phylogeography of the freshwater pufferfishes of the genus Colomesus. The molecular part is based on a cytochrome C oxidase subunit I dataset constructed from both previously published and newly determined sequences, obtained from specimens collected from three distinct localities in South America. Our results from both molecular and morphological approaches enable us to identify and describe a new Colomesus species from the Tocantins River. We also discuss aspects of the historical biogeography and phylogeography of the South American freshwater pufferfishes, suggesting that it could be more recent than previously expected.

Cipactlichthys scutatus, gen. nov., sp. nov. a new Halecomorph (Neopterygii, Holostei) from the Lower Cretaceous Tlayua Formation of Mexico.

Based on specimens from the Lower Cretaceous Tlayua Formation of Mexico, we describe a new genus and species of Halecomorphi, Cipactlichthysscutatus gen. et sp. nov, which exhibits several diagnostic characters such as the dermal bones and the scales with ganoin and highly ornamented by numerous tubercles and ridges; parietal slightly longer than wide with approximately the same length as the frontal; jaws extending far, below the posterior orbital margin, reaching the posterior third of the postorbital plate; maxilla with a convexly rounded posterior margin; pectoral fin margins slightly convex; first ray of pectoral fin very long, reaching the posterior edge of the pelvic fin; about 37 preural vertebrae and 7 Ural centra; a series of hypertrophied scales just posterior to the cleithrum; arrangement of flank scales with two rows of deep scales; a series of dorsal and ventral scutes forming the dorsal and ventral midline, between the dorsal and anal fins and the caudal fin. A phylogenetic analysis including two outgroups and eleven neopterygians confirmed the monophyly of the Holostei as well as the monophyly of the Halecomorphi, although this last clade is weakly supported. Cipactlichthysscutatus was hypothesised as the sister-group of the (Ionoscopiformes + Amiiformes).

A new Chanidae (Ostariophysii: Gonorynchiformes) from the Cretaceous of Brazil with affinities to Laurasian gonorynchiforms from Spain.

Based on specimens originally referred to as "Dastilbe minor", a nomem-nudum, we describe a new genus of Chanidae †Nanaichthys longipinnus nov. gen. and sp. which exhibits several diagnostic characters such as the absence of orbitosphenoid and basisphenoid, anteriorly displaced quadrate-mandibular articulation, laterally expanded supraneurals, an acute angle between the preopercular limbs, expansion at the angle between the preopercular limbs, and a curved maxillary articular process. Its occurrence and supposed relationship within the Chanidae reinforce the influence of the Mediterranean Tethys over the Gondwanan main rift system prior to the Aptian/Albian highstands.

On the type material of Lepidosiren paradoxa Fitzinger, 1837 (Sarcopterygii, Dipnoi).

Lepidosiren paradoxa, the first living dipnoan to be discovered, was first described from two specimens collected by Johann Natterer during his 18-year expedition in Brazil. Those specimens were first studied by Fitzinger and Bischoff, but few data are available to identify the syntypes of L. paradoxa. A reevaluation of Bischoff's original description permits one to clearly identify one of four lots--NMW-50270 pt.a--currently housed in the Naturhistorisches Museum Wien as part of one of the syntypes of this species, based mostly on the reported measurements and marks on the skull, and putatively attribute another lot--NMW-50270 pt.b--to the same specimen. Two lots could be definitely ruled out as part of the type series. The second type specimen could not be found.