Stem sarcopterygians have primitive polybasal fin articulation

Among osteichthyans, basal actinopterygian fishes (e.g. paddlefish and bowfins) have paired fins with three endoskeletal components (pro-, meso- and metapterygia) articulating with polybasal shoulder girdles, while sarcopterygian fishes (lungfish, coelacanths and relatives) have paired fins with one endoskeletal component (metapterygium) articulating with monobasal shoulder girdles. In the fin–limb transition, the origin of the sarcopterygian paired fins triggered new possibilities of fin articulation and movement, and established the proximal segments (stylopod and zeugopod) of the presumptive tetrapod limb. Several authors have stated that the monobasal paired fins in sarcopterygians evolved from a primitive polybasal condition. However, the fossil record has been silent on whether and when the inferred transition took place. Here we describe three-dimensionally preserved shoulder girdles of two stem sarcopterygians (Psarolepis and Achoania) from the Lower Devonian of Yunnan, which demonstrate that stem sarcopterygians have polybasal pectoral fin articulation as in basal actinopterygians. This finding provides a phylogenetic and temporal constraint for studying the origin of the stylopod, which must have originated within the stem sarcopterygian lineage through the loss of the propterygium and mesopterygium.     

Distribution and variation in enamel structure in the oral teeth of sarcopterygians: Its significance for the evolution of a protoprismatic enamel

The property of tooth enamel to resist alteration during fossilization, is used to analyse the unique arrangements of biological crystallites amongst genera of Paleozoic sarcopterygians, with both polarized light and s.e.m. Previous concepts of crystallite organization in reptiles and mammal‐like reptiles are evaluated. Two of the Devonian sarcopterygians, are shown to exhibit a protoprismatic pattern, identical with that of a stem group therian. The patterns of crystallites, together with the arrangement of incremental lines establish that this tissue is solely an ectodermal product; monotypic enamel, in contrast to bitypic enamel with two cell products contributing to it as in enameloid or acrodin. Each genus examined has a different pattern, of significance in considering relationships amongst sarcopterygians. Recent information on ganoine and some new findings on enamel in extant lungfishes have led to the conclusion that types of monotypic enamel are present in both actinopterygians and sarcopterygians, and challenges the use of monotypic enamel as a synapomorphy of sarcopterygians in cladistic analyses.     

The ear region of Latimeria chalumnae: functional and evolutionary implications

The anatomy of Latimeria chalumnae has figured prominently in discussions about tetrapod origins. While the gross anatomy of Latimeria is well documented, relatively little is known about its otic anatomy and ontogeny. To examine the inner ear and the otoccipital part of the cranium, a serial-sectioned juvenile coelacanth was studied in detail and a three-dimensional reconstruction was made. The ear of Latimeria shows a derived condition compared to other basal sarcopterygians in having a connection between left and right labyrinths. This canalis communicans is perilymphatic in nature and originates at the transition point of the saccule and the lagena deep in the inner ear, where a peculiar sense end organ can be found. In most gnathostomes the inner ears are clearly separated from each other. A connection occurs in some fishes, e.g. within the Ostariophysi. In the sarcopterygian lineage no connections between the inner ears are known except in the Actinistia. Some fossil actinistians show a posteriorly directed duct lying between the foramen magnum and the notochordal canal, similar to the condition in the ear of Latimeria, so this derived character complex probably developed early in actinistian history. Because some features of the inner ear of Latimeria have been described as having tetrapod affinities, the problem of hearing and the anatomy of the otical complex in the living coelacanth has been closely connected to the question of early tetrapod evolution. It was assumed in the past that the structure found in Latimeria could exemplify a transitional stage in otic evolution between the fishlike sarcopterygians and the first tetrapods in a functional or even phylogenetic way. Here the possibility is considered that the canalis communicans does not possess any auditory function but rather is involved in sensing pressure changes during movements involving the intracranial joint. Earlier hypotheses of a putative tympanic ear are refuted.     

THE ORIGIN OF TETRAPODS-PAST ANDPRESENT HYPOTHESES

HistoricalreviewoneshouldexpectthatanewtheorychangesorimprovestheunderstandingofPhylogeneticquestions.ThatdoesnotseemtobetrueoftheoriginoftetrapodsasRosenetal.(l98l)havealreadyshowninthecaseoftheapPearanceofDarwin's'ontheoriginofsPecies"inl859.Incontrast,thehistoryofthedevelopmentofhypothesesontheoriginoftetrapodsdemonstratesthatdiscoveryofnewextantorfos-silforms(Tab.l)shapesourunderstandingoftherelationshipoftetrapodstofishes.Thefrstextantlungfishwasdiscoveredinl836inSouthAmerica(Fitzinge…     

Terrestrial capture of prey by the reedfish,a model species for stem tetrapods

Due to morphological resemblance, polypterid fishes are used as extant analogues of Late Devonian lobe‐finned sarcopterygians to identify the features that allowed the evolution of a terrestrial lifestyle in early tetrapods. Previous studies using polypterids showed how terrestrial locomotion capacity can develop, and how air ventilation for breathing was possible in extinct tetrapodomorphs. Interestingly, one polypterid species, the reedfish Erpetoichthys calabaricus, has been noted being capable of capturing prey on land. We now identified the mechanism of terrestrial prey‐capture in reedfish. We showed that this species uses a lifted trunk and downward inclined head to capture ground‐based prey, remarkably similar to the mechanism described earlier for eel‐catfish. Reedfish similarly use the ground support and flexibility of their elongated body to realize the trunk elevation and dorsoventral flexion of the anterior trunk region, without a role for the pectoral fins. However, curving of the body to lift the trunk may not have been an option for the Devonian tetrapodomorphs as they are significantly less elongated than reedfish and eel‐catfish. This would imply that, in contrast to the eel‐like extant species, evolution of the capacity to capture prey on land in early tetrapods may be linked to the evolution of the pectoral system to lift the anterior part of the body.     

Considerations for the development of a terrestrial index of ecological integrity

Ecological systems are composed of complex biological and physical components that are difficult to understand and to measure. However, effective management actions and policy decisions require information on the status, condition, and trends of ecosystems. Multiple levels of information are needed to make effective decisions and the ideal indicators for measuring ecosystem integrity will incorporate information from multiple dimensions of the ecosystem. A terrestrial index of ecological integrity would be a useful tool for ecosystem managers and decision makers. The ideal requirements of the terrestrial index of ecosystem integrity (TIEI) are that it be comprehensive and multi-scale, grounded in natural history, relevant and helpful, able to integrate concerns from aquatic and terrestrial ecology, and that it be flexible and measurable.The objective of this research is to investigate if an index, or indices, could be developed that would summarize the condition of ecosystems so that changes can be tracked over time and this information utilized as a tool to support environmental decision making.     

The oldest sarcopterygian fish

The study of basal sarcopterygians is crucial to an understanding of the relationships and interrelationships of sarcopterygians, including their relationship to tetrapods. The new material from Qujing, Yunnan, southwestern China, represents the oldest known sarcopterygian fish and extends the record of sarcopterygians to the Late Silurian, or about 410 Ma. The new form is close to Youngolepis and Powichthys at the base of the Crossopterygii. Similarities among the lower jaws of onychodonts, porolepiforms, Youngolepis, Powichthys and the new form support a position of onychodonts within the Crossopterygii. Four characters in the character matrix of Cloutier & Ahlberg (1996, in Stiassny et al: Interrelationships of Fishes , Academic Press) are reviewed, and sarcopterygian interrelationships are studied on the basis of their data with minor modifications. The new scheme of sarcopterygian interrelationships differs markedly from Cloutier & Ahlberg's scheme. Neither actinistians nor onychodonts are situated at the base of Sarcopterygii, but within the Crossopterygii. Youngolepis and Powichthys are at the base of the Crossopterygii, instead of being the sister group of dipnoans plus Diabolepis.     

Les faunes terrestres quaternaires des Îles du Japon

This paper explains a brief history of research on Quaternary terrestrial mammals in Japan and fossil occurrence of taxa at major localities of each time period at first. Based on these data, then, the changing history of Quaternary terrestrial mammals in Japan is reviewed, especially on such points as (1) importance of strait in western Japan as coming over route, (2) changing history of Plio-Pleistocene terrestrial mammals in Japan, (3) two faunas during the Late Pleistocene, (4) dates of extinctions of large mammals near the end of the Late Pleistocene. Formation process of Quaternary terrestrial mammal fauna in Japan must have been affected by condition of land connection with Asian continent at seaway west to Japan and changing history of climate and vegetation in East Asia, and it should be considered by different time period, e.g. before and after ca. 1.7 Ma. The time period after 1.7 Ma is one affected by glacial sea level fluctuations. Although a new fauna came over from the west to Japan when sea level was low, this time period is basically the age of insularization, and it is presumed that the fauna was becoming endemic during this time period. During the late Late Pleistocene, there were two faunas existed in Japan, e.g. one with Palaeoloxodon naumanni having come over from the west and another with Mammuthus primigenius having come over from the north. The former dwelled mainly in deciduous broad-leaved forest and mixed forest with conifers in temperate climate, while the latter dwelled in steppe and coniferous forest in subboreal climate. Both faunas changed their ranges to north and south repeatedly as climate changed, and the extinction of large mammals of the fauna with Palaeoloxodon naumanni occurred at the same time of the beginning of the LGM (ca. 25–16 ka). On the other hand, large mammals of the fauna with Mammuthus primigenius became extinct or moved to north as climate became warm quickly after the LGM. Thus, it is suggested that the extinction of large mammals at the late Late Pleistocene occurred by “two pulses.” The extinction process of large mammals in Japan seems likely that they went extinct finally near the end of the Pleistocene going through the reduction of habitat and fragmentation of populations caused by the repeated temperature change during the late Late Pleistocene, rather than a single drastic event.     

Ready and Waiting: Delayed Hatching and Extended Incubation of Anamniotic Vertebrate Terrestrial Eggs

Some anamniotic aquatic vertebrates lay eggs in a terrestrialhabitat that is hostile to the survival of hatchings or larvae.These terrestrial eggs are ready and able to hatch at a particulardevelopmental time, but do not hatch until presented with suitableconditions for aquatic larval survival. Beyond this time, hatchingis possible whenever aquatic conditions occur. The durationof extended terrestrial incubation is dependent on the availabilityof energy for metabolism from the yolk. Extended incubationis useful for anamniotic eggs laid in terrestrial habitats whereconditions suitable for larval survival arrive with unpredictableor variable timing. Examples of anamniotes with delayed hatchingand extended terrestrial incubation can be found among teleostfishes, anurans, and caudate amphibians. This paper characterizesthe embryonic period, compares this mode with other forms ofdevelopmental plasticity in anamniotes, evaluates the constraintsand advantages of this life history mode, and examines how somefishes and amphibians are able to obtain the benefits of terrestrialityfor their eggs when the timing of the return to aquatic conditionsis not entirely predictable.     

Historical changes in the phenology of British Odonata are related to climate

Responses of biota to climate change take a number of forms including distributional shifts, behavioural changes and life history changes. This study examined an extensive set of biological records to investigate changes in the timing of life history transitions (specifically emergence) in British Odonata between 1960 and 2004. The results show that there has been a significant, consistent advance in phenology in the taxon as a whole over the period of warming that is mediated by life history traits. British odonates significantly advanced the leading edge (first quartile date) of the flight period by a mean of 1.51 ±0.060 (SEM, n=17) days per decade or 3.08±1.16 (SEM, n=17) days per degree rise in temperature when phylogeny is controlled for. This study represents the first review of changes in odonate phenology in relation to climate change. The results suggest that the damped temperature oscillations experienced by aquatic organisms compared with terrestrial organisms are sufficient to evoke phenological responses similar to those of purely terrestrial taxa.     

Comparative anatomy, homologies and evolution of the pectoral muscles of bony fish and tetrapods: a new insight

The Osteichthyes, including bony fishes and tetrapods, is a highly speciose group of vertebrates, comprising more than 42,000 living species. The anatomy of osteichthyans has been the subject of numerous comparative studies, but most of these studies concern osteological structures; much less attention has been paid to muscles. The most detailed comparative analyses of osteichthyan pectoral muscles that were actually based on a direct observation of representatives of various major actinopterygian and sarcopterygian groups were provided several decades ago by authors such as Howell and Romer. Despite the quality of their work, these authors did not have access to much information that is now available. In the present work, an updated discussion on the homologies and evolution of the osteichthyan pectoral muscles is provided, based on the authors' own analyses and on a survey of the literature, both old and recent. It is stressed that much caution should be taken when the results obtained in molecular and developmental studies concerning the pectoral muscles of model actinopterygians such as the teleostean zebrafish are discussed and compared with the results obtained in studies concerning model sarcopterygians from clades such as the Amphibia and/or the Amniota. This is because, as shown here, as a result of the different evolutionary routes followed within the actinopterygian and the sarcopterygian clades none of the individual muscles found, for example, in derived actinopterygians such as teleosts is found in derived sarcopterygians such as tetrapods. It is hoped that the information provided in the present work may help in paving the way for future analyses of the pectoral muscles in taxa from different osteichthyan groups and for a proper comparison between these muscles in those taxa.     

云南昭通早泥盆世肉鳍鱼类—新属(英文)

记述了产于云南昭通早泥盆世布拉格期基干肺鱼形动物一新属、新种——多孔弓鱼(Arquatichthys porosus gen.et sp.nov.)。新材料包括一件较为完整的下颌和鳞片若干。与基干肺鱼形动物相近的特征有:第四下齿骨水平凹线呈"L"形;下颌表面可见许多不规则排列的感觉管开孔;具三块冠状骨;冠状骨侧部为宽阔的小齿带;侧联合齿骨附着区较小;颌收肌窝大;菱形鳞片具明显的前腹突。鉴别特征包括下颌背缘明显隆起,以及后缘具加长的被覆压区。多孔弓鱼的发现为探讨肉鳍鱼类的早期分化提供了新的资料,在早期肉鳍鱼类的系统发育关系框架下讨论了鳞片的特征演化序列。     

A view of early vertebrate evolution inferred from the phylogeny of polystome parasites (Monogenea: Polystomatidae)

The Polystomatidae is the only family within the Monogenea to parasitize sarcopterygians such as the Australian lungfish Neoceratodus poisteri and freshwater tetrapods (lissamphibians and chelonians). We present a phylogeny based on partial 18S rDNA sequences of 26 species of Polystomatidae and three taxon from the infrasubclass Oligonchoinea (= Polyopisthocotylea) obtained from the gills of teleost fishes. The basal position of the polystome from lungfish within the Polystomatidae suggests that the family arose during the evolutionary transition between actinopterygians and sarcopterygians, ca. 425 million years (Myr) ago. The monophyly of the polystomatid lineages from chelonian and lissamphibian hosts, in addition to estimates of the divergence times, indicate that polystomatids from turtles radiated ca. 191 Myr ago, following a switch from an aquatic amniote presumed to be extinct to turtles, which diversified in the Upper Triassic. Within polystomatids from lissamphibians, we observe a polytomy of four lineages, namely caudatan, neobatrachian, pelobatid and pipid polystomatid lineages, which occurred ca. 246 Myr ago according to molecular divergence-time estimates. This suggests that the first polystomatids of amphibians originated during the evolution and diversification of lissamphibian orders and suborders ca. 250 Myr ago. Finally, we report a vicariance event between two major groups of neobatrachian polystomes, which is probably linked to the separation of South America from Africa ca. 100 Myr ago.     

Climbing,brachiation, and terrestrial quadrupedalism: Historical precursors of hominid bipedalism

The vertical-climbing account of the evolution of locomotor behavior and morphology in hominid ancestry is reexamined in light of recent behavioral, anatomical, and paleontological findings and a more firmly established phylogeny for the living apes. The behavioral record shows that African apes, when arboreal, are good vertical climbers, and that locomotion during traveling best separates the living apes into brachiators (gibbons), scrambling/climbing/brachiators (orangutans), and terrestrial quadrupeds (gorillas and chimpanzees). The paleontological record documents frequent climbing as an ancestral catarrhine ability, while a reassessment of the morphology of the torso and forelimb in living apes and Atelini suggests that their shared unique morphological pattern is best explained by brachiation and forelimb suspensory positional behavior. Further, evidence from the hand and foot points to a terrestrial quadrupedal phase in hominoid evolution prior to the adoption of bipedalism. The evolution of positional behavior from early hominoids to hominids appears to have begun with an arboreal quadrupedal-climbing phase and proceeded though an orthograde, brachiating, forelimb-suspensory phase, which was in turn followed by arboreal and terrestrial quadrupedal phases prior to the advent of hominid bipedality. The thesis that protohominids climbed down from the trees to become terrestrial bipeds needs to be reexamined in light of a potentially long history of terrestriality in the ancestral protohominid. © 1996 Wiley-Liss, Inc.     

Genomic legacy of migration in endangered caribou

Wide-ranging animals, including migratory species, are significantly threatened by the effects of habitat fragmentation and habitat loss. In the case of terrestrial mammals, this results in nearly a quarter of species being at risk of extinction. Caribou are one such example of a wide-ranging, migratory, terrestrial, and endangered mammal. In populations of caribou, the proportion of individuals considered as “migrants” can vary dramatically. There is therefore a possibility that, under the condition that migratory behavior is genetically determined, those individuals or populations that are migratory will be further impacted by humans, and this impact could result in the permanent loss of the migratory trait in some populations. However, genetic determination of migration has not previously been studied in an endangered terrestrial mammal. We examined migratory behavior of 139 GPS-collared endangered caribou in western North America and carried out genomic scans for the same individuals. Here we determine a genetic subdivision of caribou into a Northern and a Southern genetic cluster. We also detect >50 SNPs associated with migratory behavior, which are in genes with hypothesized roles in determining migration in other organisms. Furthermore, we determine that propensity to migrate depends upon the proportion of ancestry in individual caribou, and thus on the evolutionary history of its migratory and sedentary subspecies. If, as we report, migratory behavior is influenced by genes, caribou could be further impacted by the loss of the migratory trait in some isolated populations already at low numbers. Our results indicating an ancestral genetic component also suggest that the migratory trait and their associated genetic mutations could not be easily re-established when lost in a population.     

The fossil record of fish ontogenies: Insights into developmental patterns and processes

One of the properties of fossils is to provide unique ontogenies that have the potential to inform us of developmental patterns and processes in the past. Although fossilized ontogenies are fairly rare, size series of relatively complete specimens for more than 90 fish species have been documented in the literature. These fossilized ontogenies are known for most major phylogenetic groups of fishes and have a broad stratigraphic range extending from the Silurian to the Quaternary with a good representation during the Devonian. Classically, size series have been studied in terms of size and shape differences, where subsequently allometric changes were used as indicators of heterochronic changes in Paleozoic placoderms and sarcopterygians. Quantitative analyses of fossilized ontogenies of dipnoans have been interpreted in terms of morphological integration and fluctuating asymmetry. Recently, reconstructed sequences of ossification have been used to identify recurrent patterns of similar development in actinopterygians and sarcopterygians in order to infer phenotypic developmental modularity and saltatory pattern of development. Phylogenetic and temporal landmarks are put forward for some of the major developmental patterns in the evolution of fishes.     

Evolutionary origin of the Otx2 enhancer for its expression in visceral endoderm

In the mouse, the Otx2 gene has been shown to play essential roles in the visceral endoderm during anterior-posterior axis formation and head induction. While these are primary processes in vertebrate embryogenesis, the visceral endoderm is a tissue unique to mammals. Two enhancers (VE and CM) have been previously found to direct Otx2 expression during early embryogenesis. This study demonstrates that in anterior visceral endoderm the CM enhancer does not have an activity by itself, but enhances the activity of the VE enhancer. These two enhancers also cooperate for the activities in anterior mesendoderm and cephalic mesenchyme. Comparative studies suggest that VE enhancer function was most likely established before the divergence of sarcopterygians into Actinistia, Dipnoi and tetrapods, while the nucleotide sequence corresponding to the VE enhancer was already present in the last common ancestor of bony fishes. The CM enhancer sequence and function would have been also established in ancestral sarcopterygians. The VE/CM enhancers and their gene cascades in the ancestral sarcopterygian head organizer would then have been co-opted by amphibian deep endoderm cells and mammalian visceral endoderm cells for the head development.     

Why did the invasive walking catfish cross the road? Terrestrial chemoreception described for the first time in a fish

Clarias batrachus (walking catfish) is an invasive species in Florida, renowned for its air-breathing and terrestrial locomotor capabilities. However, it is unknown how this species orients in terrestrial environments. Furthermore, while anecdotal life history information is widespread for this species in its nonnative range, little of this information exists in the literature. The goals of this study were to identify sensory modalities that C. batrachus use to orient on land, and to describe the natural history of this species in its nonnative range. Fish (n = 150) were collected from around Ruskin, FL, and housed in a greenhouse, where experiments took place. Individual catfish were placed in the center of a terrestrial arena and were exposed to nine treatments: two controls, L-alanine, quinine, allyl isothiocynate, sucrose, volatile hydrogen sulphide, pond water and aluminium foil. These fish exhibited significantly positive chemotaxis toward alanine and pond water, and negative chemotaxis away from volatile hydrogen sulphide, suggesting chemoreception – both through direct contact and through the air – is important to their terrestrial orientation. Additionally, 88 people from Florida wildlife-related Facebook groups who have personal observations of C. batrachus on land were interviewed for information regarding their terrestrial natural history. These data were combined with observations from 38 YouTube videos. C. batrachus appear to emerge most frequently during or just after heavy summer rains, particularly from stormwater drains in urban areas, where they may feed on terrestrial invertebrates. By better understanding the full life history of C. batrachus, we can improve management of this species.     

The Gut Bacterial Community of Mammals from Marine and Terrestrial Habitats

After birth, mammals acquire a community of bacteria in their gastro-intestinal tract, which harvests energy and provides nutrients for the host. Comparative studies of numerous terrestrial mammal hosts have identified host phylogeny, diet and gut morphology as primary drivers of the gut bacterial community composition. To date, marine mammals have been excluded from these comparative studies, yet they represent distinct examples of evolutionary history, diet and lifestyle traits. To provide an updated understanding of the gut bacterial community of mammals, we compared bacterial 16S rRNA gene sequence data generated from faecal material of 151 marine and terrestrial mammal hosts. This included 42 hosts from a marine habitat. When compared to terrestrial mammals, marine mammals clustered separately and displayed a significantly greater average relative abundance of the phylum Fusobacteria. The marine carnivores (Antarctic and Arctic seals) and the marine herbivore (dugong) possessed significantly richer gut bacterial community than terrestrial carnivores and terrestrial herbivores, respectively. This suggests that evolutionary history and dietary items specific to the marine environment may have resulted in a gut bacterial community distinct to that identified in terrestrial mammals. Finally we hypothesize that reduced marine trophic webs, whereby marine carnivores (and herbivores) feed directly on lower trophic levels, may expose this group to high levels of secondary metabolites and influence gut microbial community richness.     

HETEROCOCCUS ENDOLITHICUS SP. NOV. (XANTHOPHYCEAE) AND OTHER TERRESTRIAL HETEROCOCCUS SPECIES FROM ANTARCTICA: MORPHOLOGICAL CHANGES DURING LIFE HISTORY AND RESPONSE TO TEMPERATURE1

Strains of Heterococcus endolithicus sp. nov., H. pleurococcoides Pitschmann, H. caespitosus Vischer, and H. protonematoides Vischer isolated from terrestrial habitats in Antarctica were studied in culture. Morphology of the algae changes with stage in life history. The characteristic branching patterns are not present in very young or old cultures. Filament formation is suppressed when cultures are grown outside their optimal temperature range.