Extinct Marine Research Articles

The macroevolutionary landscape of short-necked plesiosaurians

Throughout their evolution, tetrapods have repeatedly colonised a series of ecological niches in marine ecosystems, producing textbook examples of convergent evolution. However, this evolutionary phenomenon has typically been assessed qualitatively and in broad-brush frameworks that imply simplistic macroevolutionary landscapes. We establish a protocol to visualize the density of trait space occupancy and thoroughly test for the existence of macroevolutionary landscapes. We apply this protocol to a new phenotypic dataset describing the morphology of short-necked plesiosaurians, a major component of the Mesozoic marine food webs (ca. 201 to 66 Mya). Plesiosaurians evolved this body plan multiple times during their 135-million-year history, making them an ideal test case for the existence of macroevolutionary landscapes. We find ample evidence for a bimodal craniodental macroevolutionary landscape separating latirostrines from longirostrine taxa, providing the first phylogenetically-explicit quantitative assessment of trophic diversity in extinct marine reptiles. This bimodal pattern was established as early as the Middle Jurassic and was maintained in evolutionary patterns of short-necked plesiosaurians until a Late Cretaceous (Turonian) collapse to a unimodal landscape comprising longirostrine forms with novel morphologies. This study highlights the potential of severe environmental perturbations to profoundly alter the macroevolutionary dynamics of animals occupying the top of food chains.

Fossilized reproductive modes reveal a protistan affinity of Chitinozoa

Abstract Reproduction is a key aspect of evolution, but the process is rarely preserved in the fossil record. Organisms fortuitously preserved undergoing reproduction provide an exceptional window illuminating the biology of extinct taxa, especially those with unknown phylogenetic position. Here we report exceptional specimens of chitinozoans (enigmatic Paleozoic organic-walled microfossils) preserved as “test-in-test” morphology, which have previously been interpreted as teratological forms. Application of advanced imaging techniques on newly recovered and reexamined Ordovician materials enabled documentation of critical morphological details of the test’s inner ultrastructure for the first time. The results show that the newly observed spongy material and dendritic structure on or inside the chitinozoan test as well as the test wall itself are all made of clustered rounded spherical particles. Morphological details suggest that those specimens represent key stages of new asexual reproductive strategies, hitherto undescribed, which produce either one or several offspring at a time. This observation challenges the prevailing hypothesis that chitinozoans are eggs of cryptic extinct marine metazoans. Instead, it is more plausible that they represent a new isolated group of protists.

The Lost Fish of Turkey: A Recent History of Disappeared Species and Commercial Fishery Extinctions for the Turkish Marmara and Black Seas

A timeline of commercial fisheries extinctions and a list of threatened or extirpated marine species are presented to document the rapidly declining abundance of marine resources in the Turkish part of the Black Sea and Marmara Sea. Turkish nationally reported fisheries data were compared over a 50-year period from 1967 (the first year data were spatially allocated) to 2016 to assess which species are now extirpated (i.e., earlier present, and now absent from reported catch data), and which species have become commercially extinct (i.e., whose catch declined by 80.0 - 99.9%). The size of bony fish caught in Turkish waters has also strongly declined. Other important taxa, specifically big sharks and mammals, not covered by fisheries statistics, or currently under protection, but also exhibiting worrisome declining trends, are discussed based on accounts based on peer-reviewed and grey literature and personal accounts from local scientists and fishers. Overall, the Turkish parts of the Black Sea lost 17 extirpated species and 17 commercially extinct marine species, while the Sea of Marmara lost 19 extirpated species and 22 commercially extinct species. This study commemorates the many lost species of the Black and Marmara Seas, and may be seen as a warning call to prevent dozens of others species to be lost. We urge the Turkish authorities to take measures to effectively reduce fishing effort and thus to allow for a natural rebuilding of what remains of the fish stocks exploited by commercial fisheries.

Ecologically diverse clades dominate the oceans via extinction resistance.

Ecological differentiation is correlated with taxonomic diversity in many clades, and ecological divergence is often assumed to be a cause and/or consequence of high speciation rate. However, an analysis of 30,074 genera of living marine animals and 19,992 genera of fossil marine animals indicates that greater ecological differentiation in the modern oceans is actually associated with lower rates of origination over evolutionary time. Ecologically differentiated clades became taxonomically diverse over time because they were better buffered against extinction, particularly during mass extinctions, which primarily affected genus-rich, ecologically homogeneous clades. The relationship between ecological differentiation and taxonomic richness was weak early in the evolution of animals but has strengthened over geological time as successive extinction events reshaped the marine fauna.

Developmental gene expression as a phylogenetic data class: support for the monophyly of Arachnopulmonata.

Despite application of genome-scale datasets, the phylogenetic placement of scorpions within arachnids remains contentious between two different phylogenetic data classes. Paleontologists continue to recover scorpions in a basally branching position, partly owing to their morphological similarity to extinct marine orders like Eurypterida (sea scorpions). Phylogenomic datasets consistently recover scorpions in a derived position, as the sister group of Tetrapulmonata (a clade of arachnids that includes spiders). To adjudicate between these hypotheses using a rare genomic change (RGC), we leveraged the recent discovery of ancient paralogy in spiders and scorpions to assess phylogenetic placement. We identified homologs of four transcription factors required for appendage patterning (dachshund, homothorax, extradenticle, and optomotor blind) in arthropods that are known to be duplicated in spiders. Using genomic resources for a spider, a scorpion, and a harvestman, we conducted gene tree analyses and assayed expression patterns of scorpion gene duplicates. Here we show that scorpions, like spiders, retain two copies of all four transcription factors, whereas arachnid orders like mites and harvestmen bear a single copy. A survey of embryonic expression patterns of the scorpion paralogs closely matches those of their spider counterparts, with one paralog consistently retaining the putatively ancestral pattern found in the harvestman, as well as the mite, and/or other outgroups. These data comprise a rare genomic change in chelicerate phylogeny supporting the inference of a distal placement of scorpions. Beyond demonstrating the diagnostic power of developmental genetic data as a phylogenetic data class, a derived placement of scorpions within the arachnids, together with an array of stem-group Paleozoic scorpions that occupied marine habitats, effectively rules out a scenario of a single colonization of terrestrial habitat within Chelicerata, even in tree topologies contrived to recover the monophyly of Arachnida.

Euconodont hard tissue: preservation patterns of the basal body

AbstractConodont elements, consisting of crown and basal tissue are the well‐known fossilized hard parts of Conodonta (extinct marine chordates), but the taphonomic processes leading to decomposition or remineralization of the basal tissue are not well understood. Here we focus on the taphonomy of basal tissue, reviewing the published record and describing new material from Asia and Europe (248 occurrences globally). These include crown and basal tissue in conjunction, and isolated basal bodies showing different stages of preservation. Some isolated specimens resemble phosphate rings similar to those assigned to Phosphannulus universalis. High‐resolution biostratigraphy indicates that the lamellar type of conodont basal tissue is found in all facies and depositional environments. Other basal tissue types, described in the literature as tubular, mesodentine, spherulitic or lamellar with canalules, are limited to the early Palaeozoic and found exclusively in siliciclastic deposits (with the exception of spherulitic tissue). Although the stratigraphic record of basal tissue spans the range of Euconodonta (Cambrian–Triassic), this study shows that most of the isolated plate and ring‐like structures are derived from early Palaeozoic coniform conodonts. Basal tissue of platform‐type elements has a much more fragile shape and is therefore rarely preserved as a recognizable isolated unit.

Life‐history strategies indicate live‐bearing in Nothosaurus (Sauropterygia)

AbstractIn Sauropterygia, a diverse group of Mesozoic marine reptiles, fossil evidence of viviparity (live‐bearing) only exists for Pachypleurosauria and Plesiosauria, and was assumed to also be the case for nothosaurs. Previous studies have successfully applied an extant squamate model to sauropterygian life‐history traits. In extant squamates, oviparity and viviparity are associated with differences in life‐history trait combinations. We establish growth curves for Nothosaurus specimens based on their humeral histology. We then analyse life‐history traits derived from these curves and compare inferred traits to those of modern squamates and pachypleurosaurs to assess their reproduction mode. We show that birth to adult size ratios (i.e. birth size divided by the mother's size) provide good estimates of clutch sizes in extant squamates and in viviparous extinct marine reptiles, but these ratios cannot discriminate viviparous and oviparous squamates. Thus, large ratios do not indicate viviparity in fossil taxa to which the extant squamate model is applicable. Applying differences in birth size, age at maturation, and maximum longevity that are observed between extant viviparous and oviparous squamates to our Nothosaurus sample, we identified 7 out of 24 specimens as being potentially viviparous. Conversely, they suggested oviparity for many nothosaurs but also for many pachypleurosaur samples. Under the assumption that the entire clade Pachypleurosauria was viviparous, the majority of nothosaurs would also have been viviparous as they comprised trait combinations similar to those seen in pachypleurosaurs. Overall, this suggests that within nothosaurs and pachypleurosaurs both reproduction modes existed in different taxa.

Exceptionally well-preserved Orsten-type phosphatocopid crustaceans from the Cambrian of Poland

Phosphatocopids are a group of small extinct marine crustaceans, which occur widespread in Cambrian dysoxic benthic lithofacies. Whereas the anatomy of the earliest ontogenetic stages of phosphatocopids, from the head larva with four pairs of appendages onward, is well documented, that of more advanced or adult growth stages has remained almost unknown (except for the external shields). Here we describe a three-dimensionally preserved specimen of a late growth stage of Cyclotron angelini from the Furongian strata (~490 Ma) of northern Poland, which possesses six pairs of appendages (2nd–7th pairs; antennula missing), much of setation, sternum with paragnath humps, and the trunk end with the putative anus. Based on comparisons with known phosphatocopids, the cephalic feeding system of this late larva comprises the antennae with their gnathobase-like median structures on their syncoxa and the mandible with a likewise strong but oblique gnathic coxal endite. Both appendages have a short, specialized endopod bearing a prominent, dentate, stout median spine on its proximal portion. The antennulae are missing but, as in other phosphatocopids, they are not expected to have contributed to the feeding and locomotory system like they do in crustacean stem-lineage representatives and the Eucrustacea, especially in the early larval phase. The lack of an antennal exopod and strong reduction in size of the mandibular exopod of C. angelini suggest that these appendages had lost their function as locomotory and sweeping devices, in contrast to other phosphatocopids (and eucrustaceans). Therefore, they may have served mainly for food gathering in the vicinity of the mouth, which may represent an autapomorphy of this phosphatocopid species. Furthermore, in this developmental stage of C. angelini the production of water currents and movement of food particles toward the median food path was likely achieved by the large, paddle-shaped setiferous exopods of the serially developed post-mandibular limbs. For comparisons, we studied additional phosphatocopid specimens from the Debki 2 borehole belonging to other taxa and representing different ontogenetic stages. This is also the first report of exceptionally preserved cuticular apodemes in phosphatocopids, extending internally and still bearing partly preserved, putative muscle bundles. As known from extant eucrustaceans, these apodemes most likely served as attachment sites for appendage muscles. (Less)

A gravid fossil turtle from the Early Cretaceous reveals a different egg development strategy to that of extant marine turtles

AbstractExtant sea turtles develop and lay pliable (flexible) eggs; however, it is unknown whether they inherited this reproductive strategy from their closer fossil relatives or if it represents an evolutionary novelty. Here, we describe the first undisputable gravid marine fossil turtle ever found, from the early Cretaceous of Colombia, belonging to Desmatochelys padillai Cadena & Parham, which constitutes a representative of the Protostegidae. Using thin sectioning of one of the eggs, as well as scanning electron microscopy coupled with elemental characterization, cathodoluminescence, and computer tomography, we established that Desmatochelys padillai produced rigid eggs similar to those associated with some extant and fossil freshwater and terrestrial turtles. At least 48 spherical eggs were preserved inside this gravid turtle. We suggest that the development of rigid eggs in the extinct marine turtle Desmatochelys padillai resulted as an adaptation for egg‐embryo requirements dictated by the physical attributes of the nesting site.

Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur.

Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to theultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.

The marine crocodile Maledictosuchus (Thalattosuchia, Metriorhynchidae) from the Kimmeridgian deposits of Tlaxiaco, Oaxaca, southern Mexico

Metriorhynchidae is a family of highly specialized, extinct marine crocodylomorphs that inhabited the Paleopacific Ocean and the Tethys Sea during the Jurassic and the Early Cretaceous. Numerous metriorhynchid fossil specimens have been recovered from European and South American localities, but North American records of this family are still scarce. Here, we describe a recently recovered Kimmeridgian metriorhynchid from the Sabinal Formation, Tlaxiaco Basin, Oaxaca, Mexico, that is attributable to the genus Maledictosuchus. This genus was known previously from a single species, M. riclaensis, from the Middle Jurassic of Spain. The characteristics of this Mexican specimen support its identification as a new species, Maledictosuchus nuyivijanan, sp. nov. The two species differ in dental and skull-roof morphology. The frontal of M. nuyivijanan, sp. nov., has a wide, rounded anterior end that extends rostrally to the same level of the anterior end of the prefrontal, whereas the frontal of M. riclaensis has a narrow anterior end that is located posterior to the anterior end of the prefrontal. Additionally, the teeth of M. nuyivijanan, sp. nov., exhibit bicarinated crowns, a smooth labial surface, and a lingual surface ornamented with longitudinal ridges, whereas those of M. riclaensis lack carinae and the labial and lingual surfaces are covered with considerably more conspicuous ridges. The North American occurrence of M. nuyivijanan, sp. nov., suggests a wider temporal and geographic distribution for the genus Maledictosuchus across the Tethys Sea than previously thought: from the Callovian in Europe to the Kimmeridgian in southern North America.http://zoobank.org/urn:lsid:zoobank.org:pub:6F6CC892-B6E1-4069-AF3A-D05792AC0F7ASUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Barrientos-Lara, J. I., J. Alvarado-Ortega, and M. S. Fernández. 2018. The marine crocodile Maledictosuchus (Thalattosuchia, Metriorhynchidae) from the Kimmeridgian deposits of Tlaxiaco, Oaxaca, southern Mexico. Journal of Vertebrate Paleontology. DOI:10.1080/02724634.2018.1478419.

Frequency of decompression illness among recent and extinct mammals and "reptiles": a review.

The frequency of decompression illness was high among the extinct marine "reptiles" and very low among the marine mammals. Signs of decompression illness are still found among turtles but whales and seals are unaffected. In humans, the risk of decompression illness is five times increased in individuals with Patent Foramen Ovale; this condition allows blood shunting from the venous circuit to the systemic circuit. This right-left shunt is characteristic of the "reptile" heart, and it is suggested that this could contribute to the high frequency of decompression illness in the extinct reptiles.

Live birth in a new lineage.

Vertebrate Paleontology Live birth has evolved multiple times among vertebrates, most notably in mammals. Although live birth also occurs in some reptiles, including several extinct marine reptiles, it has appeared convincingly to be absent in the Archosauromorphs, the lineage leading to dinosaurs, birds, and crocodiles. Liu et al. describe a previously unknown marine Archosauromorph from the middle Triassic in China, Dinocephalosaurus , which shows evidence of an embryo within the body cavity. Viviparity in marine animals has clear functional advantages, but the lack of evidence for live birth across millions of years in this large group has caused some to question whether its evolution was impossible because of some genetic or developmental constraint. This new evidence suggests that, at least initially, this was not the case. Nat. Commun. 1038/ncomms14445 (2017).

Habitat preferences of the enigmatic Miocene tethythere Desmostylus and Paleoparadoxia (Desmostylia; Mammalia) inferred from the depositional depth of fossil occurrences in the Northwestern Pacific realm

Desmostylus and Paleoparadoxia are extinct marine mammals belonging to the order Desmostylia that existed in the period between the late Oligocene and middle Miocene. All occurrences of their fossils are limited to marine strata along the coasts of the North Pacific Ocean. Although these two genera have similar body form, their paleoecologies including habitat preferences are thought to be different because their cranial structures are distinctive as well as they have been known separately in different localities. We estimated the depositional depths of their fossil occurrences on the basis of the associated mollusks and benthic foraminiferal assemblages from 45 desmostylian localities. Only data on complete or partial skeletal specimens were considered in order to exclude cases of reworking and pre-burial drift of carcasses that would confound our inference.Our results indicate that the depositional environment of Desmostylus specimens was restricted to the inner sublittoral zone shallower than 30m in depth whereas that of Paleoparadoxia specimens ranged from the inner sublittoral (0–50m) to upper bathyal zone (between 150 and 400 and 500m). This finding indicates that Desmostylus lived in nearshore water while Paleoparadoxia foraged in a relatively deep, offshore water. The depositional segregation of these two genera most likely reflects their different habitat preferences.

Distributional patterns of enchodontoid fishes in the Late Cretaceous

Enchodontoidei are extinct marine teleost fishes with a long temporal range and a wide geographic distribution. We propose here to apply Parsimony Analysis of Endemicity (PAE), Track Analysis and Brooks Parsimony Analysis (BPA) to analyze the distributional patterns of these fishes during the Late Cretaceous. Matrices were built according to their respective geological age in the Late Cretaceous. The occurrence data of enchodontoids produced consistent results for the Cenomanian, Turonian, and Santonian. The generalized track found for the Cenomanian (GT 1) can be associated to oceanic currents, whereas for the Turonian the generalized tracks (GT 2, GT 3 and GT 4) were associated with eutrophication/sedimentation effects. During the Santonian, the third Oceanic Anoxic Event (OAE 3) promoted vicariant events that could explain the generalized track found therein (GT 5). The BPA recovered the area formed by Middle East and Europe, which is congruent with GT 1 and GT 5.

Endothermic mosasaurs? Possible thermoregulation of Late Cretaceous mosasaurs (Reptilia, Squamata) indicated by stable oxygen isotopes in fossil bioapatite in comparison with coeval marine fish and pelagic seabirds

AbstractThe thermoregulatory style of Late Cretaceous mosasaurs has become a highly controversial subject in vertebrate palaeontology. These extinct marine reptiles have previously been described as poikilothermic, endothermic or gigantothermic. Here we analyse three genera of mosasaurs from the Mooreville Chalk in Alabama (USA) of differing body mass, and compare their δ18OPO4 derived body temperatures (Tb) with those of coeval poikilothermic fish (Enchodus) and endothermic pelagic seabirds (Ichthyornis). Results show that all mosasaurs, Clidastes (Tb = 33.1°C), Platecarpus (Tb = 36.3°C), and Tylosaurus (Tb = 34.3°C), had elevated average body temperatures in relation to those of the fish (Tb = 28.3°C) and were closer to those of Ichthyornis (Tb = 38.6°C). The temperatures calculated for Enchodus compare well with previously reported temperature estimates for the Mooreville Chalk and the Tb of Ichthyornis compares well with temperatures that have been reported for modern seabirds, suggesting that this method provides accurate results. Finally, although there are small differences of body temperature among mosasaur genera, these are independent of size, and thus inferred body mass, suggesting that mosasaurs were not gigantotherms, but rather endotherms.

A unique feeding strategy of the extinct marine mammal Kolponomos: convergence on sabretooths and sea otters.

Mammalian molluscivores feed mainly by shell-crushing or suction-feeding. The extinct marine arctoid, Kolponomos, has been interpreted as an otter-like shell-crusher based on similar dentitions. However, neither the masticatory biomechanics of the shell-crushing adaptation nor the way Kolponomos may have captured hard-shelled prey have been tested. Based on mandibular symphyseal morphology shared by Kolponomos and sabre-toothed carnivores, we hypothesize a sabretooth-like mechanism for Kolponomos prey-capture, whereby the mandible functioned as an anchor. Torque generated from jaw closure and head flexion was used to dislodge prey by prying, with prey then crushed using cheek teeth. We test this hypothesized feeding sequence using phylogenetically informed biomechanical simulations and shape analyses, and find a strongly supported, shared high mandibular stiffness in simulated prey-capture bites and mandibular shape in Kolponomos and the sabre-toothed cat Smilodon. These two distantly related taxa converged on using mandibles to anchor cranial torqueing forces when prying substrate-bound prey in the former and sabre-driving forces during prey-killing in the latter. Simulated prey-crushing bites indicate that Kolponomos and sea otters exhibit alternative structural stiffness-bite efficiency combinations in mandibular biomechanical adaptation for shell-crushing. This unique feeding system of Kolponomos exemplifies a mosaic of form-function convergence relative to other Carnivora.

Ontogenetic Tooth Reduction in Stenopterygius quadriscissus (Reptilia: Ichthyosauria): Negative Allometry, Changes in Growth Rate, and Early Senescence of the Dental Lamina.

We explore the functional, developmental, and evolutionary processes which are argued to produce tooth reduction in the extinct marine reptile Stenopterygius quadriscissus (Reptilia: Ichthyosauria). We analyze the relationship between mandible growth and tooth size, shape, and count, to establish an ontogenetic trend. The pattern in S. quadriscissus is consistent with hypotheses of tooth size reduction by neutral selection, and this unusual morphology (a functionally edentulous rostrum) was produced by a series of different evolutionary developmental changes that are known for other taxa showing tooth reduction and loss. Specifically, this species evolved functional edentulism by evolutionary changes in the growth allometry of the dentition and by altering growth rates through ontogeny. This observation supports previous hypotheses that S. quadriscissus underwent ontogenetic tooth reduction. Tooth reduction in S. quadriscissus may be caused by unique selective pressures resulting from prey choice and feeding behavior, expanding our current understanding of the mechanisms producing tooth reduction.

On the age of fossil diatoms

Abstract The finding of fossil freshwater diatoms in late Cretaceous chert in Mexico suggests - together with all the discoveries of fossil freshwater diatoms known from positions older than the Cretaceous - that the extinct marine Cretaceous diatom taxa cannot be considered to be the oldest.

Making a molecular fossil lookalike

Molecular Physics Atoms are generally compact objects. However, if one of the electrons orbiting the nucleus is given an extra boost of energy so that it's barely still attached, you get a much larger Rydberg atom. Booth et al. created an even more exotic species: a giant molecule consisting of a regular cesium atom bound within a Rydberg atom of the same element. The molecules are named “trilobites” because their electronic density visually resembles fossils of these extinct marine creatures. Science , this issue p. [99][1] [1]: /lookup/volpage/348/99?iss=6230