| 1. |
- Ahlberg, Per, et al.
(författare)
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Developmental plasticity and disparity in early dipnoan (lungfish) dentitions.
- 2006
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Ingår i: Evolution & Development. - 1520-541X .- 1525-142X. ; 8:4, s. 331-349
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Tidskriftsartikel (refereegranskat)abstract
- Although the lungfish (Dipnoi) belong within the Osteichthyes, their dentitions are radically different from other osteichthyans. Lungfish dentitions also show a uniquely high structural disparity during the early evolution of the group, partly owing to the independent variation of odontogenic and odontoclastic processes that are tightly and stereotypically coordinated in other osteichthyans. We present a phylogenetic analysis of early lungfishes incorporating a novel approach to coding these process characters in preference to the resultant adult dental morphology. The results only partially resolve the interrelationships of Devonian dipnoans, but show that the widely discussed hypothesis of separate tooth-plated, dentine-plated, and denticulated lineages is unlikely to be true. The dipnoan status of Diabolepis is corroborated. Lungfish dentitions seem to have undergone extensive and nonparsimonious evolution during the early history of the group, but much of the resulting disparity can be explained by a modest number of evolutionary steps in the underlying developmental processes, those for dental formation (odontogenic) and those for the remodeling of dentine tissue (odontoclastic). Later in lungfish evolution, this disparity was lost as the group settled to a pattern of dental development that is just as stereotypic as, but completely different from, that of other osteichthyans.
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| 2. |
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| 3. |
- Ahlberg, Per Erik, 1963-, et al.
(författare)
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Pelvic claspers confirm chondrichthyan-like internal fertilization in arthrodires
- 2009
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 460:7257, s. 888-889
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Tidskriftsartikel (refereegranskat)abstract
- Recent finds(1,2) demonstrate that internal fertilization and viviparity (live birth) were more widespread in the Placodermi, an extinct group of armoured fishes, than was previously realized. Placoderms represent the sister group of the crown group jawed vertebrates (Gnathostomata)(3,4), making their mode(s) of reproduction potentially informative about primitive gnathostome conditions. An ossified pelvic fin basipterygium discovered in the arthrodire Incisoscutum ritchiei was hypothesized to be identical in males and females, with males presumed to have an additional cartilaginous element or series forming a clasper. Here we report the discovery of a completely ossified pelvic clasper in Incisoscutum ritchiei (WAM 03.3.28) which shows that this interpretation was incorrect: the basipterygium described previously(1) is in fact unique to females. The male clasper is a slender rod attached to a square basal plate that articulates directly with the pelvis. It carries a small cap of dermal bone covered in denticles and small hooks that may be homologous with the much larger dermal component of the ptyctodont clasper.
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| 4. |
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| 5. |
- Chen, Donglei, 1985-
(författare)
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The Origin of Tooth Replacement : Three-dimensional Synchrotron Histology Visualizes the Dental Development of Silurian Stem Osteichthyans
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mechanisms of tooth replacement distribute incongruently among extant gnathostomes (jawed vertebrates): a permanent tooth-generating dental lamina exists in chondrichthyans (cartilaginous fish) and tetrapods but not teleosts, whereas tooth shedding by basal hard tissue resorption occurs in tetrapods and teleosts but not chondrichthyans. Theories about the evolution of tooth development have been biased towards the chondrichthyan conveyor-belt replacement, since there has been no fossil evidence for the origin of osteichthyan (bony fish and tetrapods) tooth replacement until now. 3D virtual dissections with submicron-scale resolution, based on propagation phase contrast synchrotron microtomography (PPC-SRµCT), reveal the growth history of the dentitions of Andreolepis and Lophosteus, 423-Myr-old Silurian stem osteichthyans close to the common ancestor of tetrapods and teleosts. Their marginal jawbones and “tooth cushions” (possible homologues of coronoids) shed teeth by in situ cyclic basal resorption, the earliest examples of osteichthyan-style tooth replacement. The replacement cycles were site-autonomic, and occurred in broad irregular multi-row tooth fields, including at sites separated from the margin of the bone by intervening teeth, showing that the production of replacement teeth did not occur in a single deep dental lamina, but in pockets associated with each tooth, as in many teleosts. It suggests that the functionally and anatomically similar laminae of chondrichthyans and tetrapods are convergent. The marginal jaw bones of both genera carry an initial non-shedding dentition arranged in alternate transverse files, labial to the shedding tooth field, overgrown by later dermal ornament and probably not belonging to the oral domain, but bearing in vivo biting damage showing that they functioned as teeth. The most lingual of these odontodes have been resorbed apically and are overlain by shedding teeth. The first-generation teeth on the tooth cushions display basal resorption in Andreolepis, but semi-basal resorption in Lophosteus. The latter leaves a basal dentine ring from each tooth, implying only odontoclasts are involved in the semi-basal resorption, which is probably the first step towards evolving a site-specific resorption. The polarized displacement of each generation of resorption surfaces reflects the fact that the cyclic replacement, as well as the sequential addition of tooth sites, is closely related to bone growth. Resorption surfaces and growth arrest surfaces also record the life history and the replacement rate. These data provide unique insights into the origin of osteichthyan tooth replacement.
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| 6. |
- Davies, Thomas G., et al.
(författare)
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Open data and digital morphology.
- 2017
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 284:1852, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Over the past two decades, the development of methods for visualizing and analysing specimens digitally, in three and even four dimensions, has transformed the study of living and fossil organisms. However, the initial promise that the widespread application of such methods would facilitate access to the underlying digital data has not been fully achieved. The underlying datasets for many published studies are not readily or freely available, introducing a barrier to verification and reproducibility, and the reuse of data. There is no current agreement or policy on the amount and type of data that should be made available alongside studies that use, and in some cases are wholly reliant on, digital morphology. Here, we propose a set of recommendations for minimum standards and additional best practice for three-dimensional digital data publication, and review the issues around data storage, management and accessibility.
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| 7. |
- Jerve, Anna, et al.
(författare)
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Embryonic development of fin spines in Callorhinchus milii (Holocephali); implications for chondrichthyan fin spine evolution
- 2014
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Ingår i: Evolution & Development. - : Wiley. - 1520-541X .- 1525-142X. ; 16:6, s. 339-353
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Tidskriftsartikel (refereegranskat)abstract
- Fin spines are commonly known from fossil gnathostomes (jawed vertebrates) and are usually associated with paired and unpaired fins. They are less common among extant gnathostomes, being restricted to the median fins of certain chondrichthyans (cartilaginous fish), including chimaerids (elephant sharks) and neoselachians (sharks, skates, and rays). Fin spine growth is of great interest and relevance but few studies have considered their evolution and development. We investigated the development of the fin spine of the chimaerid Callorhinchus milii using stained histological sections from a series of larval, hatchling, and adult individuals. The lamellar trunk dentine of the Callorhinchus spine first condenses within the mesenchyme, rather than at the contact surface between mesenchyme and epithelium, in a manner more comparable to dermal bone formation than to normal odontode development. Trabecular dentine forms a small component of the spine under the keel; it is covered externally with a thin layer of lamellar trunk dentine, which is difficult to distinguish in sectioned adult spines. We suggest that the distinctive characteristics of the trunk dentine may reflect an origin through co-option of developmental processes involved in dermal bone formation. Comparison with extant Squalus and a range of fossil chondrichthyans shows that Callorhinchus is more representative than Squalus of generalized chondrichthyan fin-spine architecture, highlighting its value as a developmental model organism.
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| 8. |
- Johanson, Zerina, et al.
(författare)
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First record of Porolepis (Sarcopterygii; Porolepiformes) from eastern Gondwana
- 2013
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Ingår i: Canadian journal of earth sciences (Print). - : Canadian Science Publishing. - 0008-4077 .- 1480-3313. ; 50:3, s. 249-253
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Tidskriftsartikel (refereegranskat)abstract
- Porolepiformes (Sarcopterygii) are poorly represented in the Devonian of Australia and eastern Gondwana as a whole. New cosmine-covered lower jaws from the Mulga Downs Group, western New South Wales (?Pragian-Emsian or Eifelian), represent the first occurrence of Porolepis in Australia, a genus formerly known exclusively from the Northern Hemisphere. This material is assigned to the new species Porolepis foxi. The wide distribution of Porolepis, demonstrated by its occurrence in New South Wales, Europe, and Spitsbergen, contrasts with the generally high endemicity of the faunas in which it is present.
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| 9. |
- Johanson, Zerina, et al.
(författare)
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Fish fingers : digit homologues in sarcopterygian fish fins
- 2007
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Ingår i: Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. - : Wiley. - 1552-5007 .- 1552-5015. ; 308B:6, s. 757-768
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Tidskriftsartikel (refereegranskat)abstract
- A defining feature of tetrapod evolutionary origins is the transition from fish fins to tetrapod limbs. A major change during this transition is the appearance of the autopod (hands, feet), which comprises two distinct regions, the wrist/ankle and the digits. When the autopod first appeared in Late Devonian fossil tetrapods, it was incomplete: digits evolved before the full complement of wrist/ankle bones. Early tetrapod wrists/ankles, including those with a full complement of bones, also show a sharp pattern discontinuity between proximal elements and distal elements. This suggests the presence of a discontinuity in the proximal-distal sequence of development. Such a discontinuity occurs in living urodeles, where digits form before completion of the wrist/ankle, implying developmental independence of the digits from wrist/ankle elements. We have observed comparable independent development of pectoral fin radials in the lungfish Neoceratodus (Osteichthyes: Sareopterygii), relative to homologues of the tetrapod limb and proximal wrist elements in the main fin axis. Moreover, in the Neoceratodus fin, expression of Hoxd13 closely matches late expression patterns observed in the tetrapod autopod. This evidence suggests that Neoceratodus fin radials and tetrapod digits may be patterned by shared mechanisms distinct from those patterning the proximal fin/limb elements, and in that sense are homologous. The presence of independently developing radials in the distal part of the pectoral (and pelvic) fin may be a general feature of the Sarcopterygii.
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| 10. |
- Johanson, Zerina, et al.
(författare)
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Phylogeny of lungfishes
- 2010
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Ingår i: The Biology of Lungfishes. - Enfield, N.H. : Science Publishers. - 1578084318 - 9781578084319 ; , s. 43-60
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 11. |
- Johanson, Zerina, et al.
(författare)
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Questioning hagfish affinities of the enigmatic Devonian vertebrate Palaeospondylus
- 2017
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Ingår i: Royal Society Open Science. - : ROYAL SOC. - 2054-5703. ; 4:7
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Tidskriftsartikel (refereegranskat)abstract
- Palaeospondylus gunni Traquair, 1890 is an enigmatic Devonian vertebrate whose taxonomic affinities have been debated since it was first described. Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of the cartilaginous skull, a feature of jawed vertebrates. Additionally, new tomographic data reveal that the following characters of crown-group gnathostomes (chondrichthyans + osteichthyans) are present in Palaeospondylus: a longer telencephalic region of the braincase, separation of otic and occipital regions by the otico-occipital fissure, and vertebral centra. As well, a precerebral fontanelle and postorbital articulation of the palatoquadrate are characteristic of certain chondrichthyans. Similarities in the structure of the postorbital process to taxa such as Pucapampella, and possible presence of the ventral cranial fissure, both support a resolution of Pa. gunni as a stem chondrichthyan. The internally mineralized cartilaginous skeleton in Palaeospondylus may represent a stage in the loss of bone characteristic of the Chondrichthyes.
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| 12. |
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| 13. |
- Johanson, Zerina, et al.
(författare)
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The braincase and palate of the tetrapodomorph sarcopterygian Mandageria fairfaxi: morphological variability near the fish-tetrapod transition
- 2003
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 46:2, s. 271-293
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Tidskriftsartikel (refereegranskat)abstract
- The braincase of the Late Devonian tristichopterid sarcopterygian Mandageria fairfaxi, from Canowindra, NSW, Australia, differs radically from the conservative pattern present in other 'osteolepiforms' (stem–group tetrapodomorph fishes) and non–dipnoan sarcopterygian fishes in general. The basioccipital region is short, displaced anteriorly, and either unossified or loosely articulated to the exoccipital, leaving most or all of the notochordal tunnel open ventrally. The exoccipital complex, which is developed into a large saddle that would have rested on top of the notochord, carries large, triangular articular facets on its posterior face and appears to have formed part of a functional neck joint, a synovial articulation between the skull and vertebral column that allows the former to rotate against the latter. Such a joint is characteristic of post–Devonian tetrapods, but unknown in other sarcopterygians. We infer that the ventrally open notochordal tunnel allowed gentle flexion of the cranial notochord during (predominantly vertical) rotational movement at the occiput; this is a mechanically unique solution to the problem of creating a mobile neck. Other unusual features of Mandageria include a posteriorly located lateral commissure, and structures on the entopterygoid and lateral commissure that may have been associated with an elaborate spiracular tract.
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| 14. |
- Long, John A., et al.
(författare)
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Copulation in antiarch placoderms and the origin of gnathostome internal fertilization
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 517:7533, s. 196-199
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Tidskriftsartikel (refereegranskat)abstract
- Reproduction in jawed vertebrates (gnathostomes) involves either external or internal fertilization. It is commonly argued that internal fertilization can evolve from external, but not the reverse. Male copulatoryclaspers are present in certain placoderms, fossil jawed vertebrates retrieved as a paraphyletic segment of the gnathostome stem group in recent studies. This suggests that internal fertilization could be primitive for gnathostomes, but such a conclusion depends on demonstrating that copulation was not just a specialized feature of certain placoderm subgroups. The reproductive biology of antiarchs, consistently identified as the least crownward placoderms and thus of great interest in this context, has until now remained unknown. Here we show that certain antiarchs possessed dermal claspers in the males, while females bore paired dermal plates inferred to have facilitated copulation. These structures are not associated with pelvic fins. The clasper morphology resembles that of ptyctodonts, a more crownward placoderm group, suggesting that all placoderm claspers are homologous and that internal fertilization characterized all placoderms. This implies that external fertilization and spawning, which characterize most extant aquatic gnathostomes, must be derived from internal fertilization, even though this transformation has been thought implausible. Alternatively, the substantial morphological evidence for placoderm paraphyly must be rejected.
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| 15. |
- Snitting, Daniel, 1977-
(författare)
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Morphology, Taxonomy and Interrelationships of Tristichopterid Fishes (Sarcopterygii, Tetrapodomorpha)
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tristichopterids (Sarcopterygii, Tetrapodomorpha) form a monophyletic group of exclusively Devonian fishes. This thesis consists of descriptions of new material of tristichopterids and closely related taxa, as well as new interpretations and descriptions of previously figured material. Redescribed specimens were originally figured as far back as 1861, and publications as old as this are almost always of limited use as anatomical and systematical references, in addition to being difficult to acquire. The possibility of using new techniques and new theoretical frameworks also provides good justification for taking a second look at such specimens. In the case of this thesis, this includes the use of computed tomography scanning methods, and the cladistic approach to describing the interrelationships of taxa. The thesis includes a complete taxonomy of valid tristichopterid taxa, in addition to two new phylogenetic analyses incorporating the taxa that were described or redescribed. One of the analyses deals with the interrelationships of taxa along the entire tetrapod stem, and establishes the monophyly of the Tristichopteridae. The other analysis focuses on tristichopterid interrelationships. An account is given of evolutionary trends within Tristichopteridae, and instances of parallel evolution between tristichopterids and other tetrapodomorph groups are discussed. The biogeographical implications of tristichopterid occurences world-wide seem to corroborate the picture provided by other vertebrate groups, and give further support to one of two main hypotheses concerning the relative positions of Gondwana and Laurussia, the two major palaeocontinents during the Late Devonian. The supported hypothesis proposes a close proximity between southern Laurussia and northwestern Gondwana, as evidenced by the wide dispersal of derived tristichopterids by the Late Devonian. A Laurussian origin of tristichopterids is proposed.
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| 16. |
- Vaskaninova, Valeria, et al.
(författare)
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Marginal dentition and multiple dermal jawbones as the ancestral condition of jawed vertebrates
- 2020
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Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 369:6500, s. 211-
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Tidskriftsartikel (refereegranskat)abstract
- The dentitions of extant fishes and land vertebrates vary in both pattern and type of tooth replacement. It has been argued that the common ancestral condition likely resembles the nonmarginal, radially arranged tooth files of arthrodires, an early group of armoured fishes. We used synchrotron microtomography to describe the fossil dentitions of so-called acanthothoracids, the most phylogenetically basal jawed vertebrates with teeth, belonging to the genera Radotina, Kosoraspis, and Tlamaspis (from the Early Devonian of the Czech Republic). Their dentitions differ fundamentally from those of arthrodires; they are marginal, carried by a cheekbone or a series of short dermal bones along the jaw edges, and teeth are added lingually as is the case in many chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). We propose these characteristics as ancestral for all jawed vertebrates.
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