| 1. |
- Pierce, Stephanie E., et al.
(författare)
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Vertebral architecture in the earliest stem tetrapods
- 2013
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 494:7436, s. 226-229
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Tidskriftsartikel (refereegranskat)abstract
- The construction of the vertebral column has been used as a key anatomical character in defining and diagnosing early tetrapod groups(1). Rhachitomous vertebrae(2)-in which there is a dorsally placed neural arch and spine, an anteroventially placed intercentrum and paired, posterodorsally placed pleurocentra have long been considered the ancestral morphology for tetrapods(1,3-6). Nonetheless, very little is known about vertebral anatomy in the earliest stem tetrapods, because most specimens remain trapped in surrounding matrix, obscuring Important anatomical features(7-9). Here we describe the three-dimensional vertebral architecture of the Late Devonian stem tetrapod Ichthyostega using propagation phase-contrast X-ray synchrotron. microtomography. Our scans reveal a diverse array of new morphological, and associated developmental and functional, characteristics, including a possible posterior-to-anterior vertebral ossification sequence and the first evolutionary appearance of ossified sternal elements. One of the most intriguing features relates to the positional relationships between the vertebral elements, with the pleurocentra being unexpectedly sutured or fused to the intercentra that directly succeed them, indicating a 'reverse' rhachitomous design(10). Comparison of Ichthyostega with two other stem tetrapods, Acanthostegi and Pederpess, shows that reverse rhachitomous vertebrae may be the ancestral condition for limbed vertebrates. This study fundamentally revises our current understanding' of vertebral column evolution in the earliest tetrapods and raises questions about the presumed vertebral architecture of tetrapodomorph fish(12,13) and later, more crownward, tetrapods.
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| 2. |
- Chen, Dong Lei, 1985-, et al.
(författare)
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Development of cyclic shedding teeth from semi-shedding teeth : the inner dental arcade of the stem osteichthyan Lophosteus
- 2017
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Ingår i: Royal Society Open Science. - : ROYAL SOC. - 2054-5703. ; 4:5
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Tidskriftsartikel (refereegranskat)abstract
- The numerous cushion-shaped tooth-bearing plates attributed to the stem-group osteichthyan Lophosteus superbus, which are argued here to represent the ancient form of inner dental arcade, display a unique and presumably primitive way of tooth shedding by basal hard tissue resorption. They carry regularly spaced, recumbent, gently recurved teeth arranged in transverse tooth files that diverge towards the lingual margin of the cushion. Three-dimensional (3D) reconstruction from propagation phase contrast synchrotron microtomography (PPC-SRμCT) reveals remnants of the first-generation teeth embedded in the basal plate that have never been discerned in any taxa. These teeth were shed by semi-basal resorption with the periphery of their bases retained as dentine rings. The rings are highly overlapped, which evidences tooth shedding prior to adding the next first-generation tooth. Later teeth at the same sites underwent cyclical replacing and shedding through basal resorption, producing stacks of buried resorption surfaces separated by bone of attachment. The number and spatial arrangement of resorption surfaces elucidates that basal resorption of replacement teeth had taken place at the older tooth sites before the addition of the youngest first-generation teeth at the lingual margin. Thus the replacement tooth buds cannot have been generated by a single permanent dental lamina, but must have arisen either from successional dental laminae associated with the predecessor teeth, or directly from the dental epithelium of these teeth. The virtual histological dissection of these Late Silurian microfossils broadens our understanding of the development of the gnathostome dental systems and the acquisition of the osteichthyan-type of tooth replacement.
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| 3. |
- Chen, Donglei, 1985-, et al.
(författare)
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The developmental relationship between teeth and dermal odontodes in the most primitive bony fish Lophosteus
- 2020
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Ingår i: eLIFE. - 2050-084X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The ontogenetic trajectory of a marginal jawbone of Lophosteus superbus (Late Silurian, 422 Million years old), the phylogenetically most basal stem osteichthyan, visualized by synchrotron microtomography, reveals a developmental relationship between teeth and dermal odontodes that is not evident from the adult morphology. The earliest odontodes are two longitudinal founder ridges formed at the ossification center. Subsequent odontodes that are added lingually to the ridges turn into conical teeth and undergo cyclic replacement, while those added labially achieve a stellate appearance. Stellate odontodes deposited directly on the bony plate are aligned with the alternate files of teeth, whereas new tooth positions are inserted into the files of sequential addition when a gap appears. Successive teeth and overgrowing odontodes show hybrid morphologies around the oral-dermal boundary, suggesting signal cross-communication. We propose that teeth and dermal odontodes are modifications of a single system, regulated and differentiated by the oral and dermal epithelia.
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| 4. |
- Jerve, Anna, et al.
(författare)
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Morphology and histology of acanthodian fin spines from the late Silurian Ramsåsa E locality, Skåne, Sweden
- 2017
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Ingår i: Palaeontologia Electronica. - : COQUINA PRESS. - 1935-3952 .- 1094-8074. ; 20:3
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Tidskriftsartikel (refereegranskat)abstract
- Comparisons of acanthodians to extant gnathostomes are often hampered by the paucity of mineralized structures in their endoskeleton, which limits the potential preservation of phylogenetically informative traits. Fin spines, mineralized dermal structures that sit anterior to fins, are found on both stem-and crown-group gnathostomes, and represent an additional potential source of comparative data for studying acanthodian relationships with the other groups of early gnathostomes. An assemblage of isolated acanthodian fin spines from the late Silurian Ramsasa site E locality (southern Sweden) has been reconstructed in 3D using propagation phase contrast synchrotron X-ray microtomography (PPC-SR mu CT). The aim is to provide morphological and taxo-nomical affinities for the spines by combining morphology and histology with the taxo-nomical framework previously established for the site mainly based on isolated scales. The high-resolution scans also enable investigations of the composition and growth of acanthodian fin spines when compared to similar studies of extinct and extant gnathostomes. In total, seven fin spine morphotypes that have affinities to both Climatiidae Berg 1940 and Ischnacanthiformes Berg 1940 are described. The majority are interpreted as median fin spines, but three possible paired spines are also identified. The spines display differences in their compositions, but generally agree with that presented for climatiids and ischnacanthiforms in previous studies. Their inferred growth modes appear to be more similar to those of fossil and extant chondrichthyan fin spines than to those described from placoderms and stem-osteichthyans, which is congruent with the emerging view of acanthodians as stem-chondrichthyans.
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| 5. |
- Qu, Qingming, et al.
(författare)
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The origin of novel features by changes in developmental mechanisms : ontogeny and three-dimensional microanatomy of polyodontode scales of two early osteichthyans
- 2017
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Ingår i: Biological Reviews. - : Wiley. - 1464-7931 .- 1469-185X. ; 92:2, s. 1189-1212
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in synchrotron imaging allow us to study the three-dimensional (3D) histology of vertebrate fossils, including microfossils (e.g. teeth and scales) of early jawed vertebrates. These microfossils can often be scanned at submicron resolution (<1 µm) because of their small size. The resulting voxel (3D pixel) stacks can be processed into virtual thin sections revealing almost every internal detail of the samples, comparable to traditional thin sections. In addition, 3D models of the internal microanatomical structures, such as embedded odontodes and vasculature, can be assembled and examined in situ. Scales of two early osteichthyans, Psarolepis romeri from the Early Devonian of China and Andreolepis hedei from the Late Silurian of Sweden, were scanned using propagation phase-contrast synchrotron X-ray microtomography (PPC-SRµCT), and 3D models of internal canal systems and buried odontodes were created from the scans. Based on these new data, we review the evolutionary origin of cosmine and its associated pore-canal system, which has been long recognized as a synapomorphy of sarcopterygians. The first odontode that appeared during growth shows almost identical morphology in the two scales, but the second odontode of the Psarolepis scale shows a distinctive morphology with several pores on the surface. It is suggested that a shift from ridge-like odontode to pore-bearing odontode was the key step in the origin of cosmine, which was then elaborated further in more-derived sarcopterygians. We perform a detailed comparison between the two scales and propose a primary homology framework to generate microanatomical characters, which can be used in the phylogenetic analysis of early osteichthyans when more 3D data become available. Our results highlight the importance of 3D data for the study of histology and ontogeny of the dermal skeleton of early jawed vertebrates, especially scales of the polyodontode type. The traditional microvertebrate collection is not only useful for biostratigraphic studies, but also preserves invaluable biological information about the growth of vertebrate hard tissues. Today, we are only beginning to understand the biological meaning of the new 3D data. The increasing availability of such data will enable, and indeed require, a complete revision of traditional palaeohistological studies on early vertebrates.
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| 6. |
- Sanchez, Sophie, et al.
(författare)
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3D Microstructural Architecture of Muscle Attachments in Extant and Fossil Vertebrates Revealed by Synchrotron Microtomography
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:2, s. e56992-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Firm attachments binding muscles to skeleton are crucial mechanical components of the vertebrate body. These attachments (entheses) are complex three-dimensional structures, containing distinctive arrangements of cells and fibre systems embedded in the bone, which can be modified during ontogeny. Until recently it has only been possible to obtain 2D surface and thin section images of entheses, leaving their 3D histology largely unstudied except by extrapolation from 2D data. Entheses are frequently preserved in fossil bones, but sectioning is inappropriate for rare or unique fossil material.Methodology/Principal Findings: Here we present the first non-destructive 3D investigation, by propagation phase contrast synchrotron microtomography (PPC-SR mu CT), of enthesis histology in extant and fossil vertebrates. We are able to identify entheses in the humerus of the salamander Desmognathus from the organization of bone-cell lacunae and extrinsic fibres. Statistical analysis of the lacunae differentiates types of attachments, and the orientation of the fibres, reflect the approximate alignment of the muscle. Similar histological structures, including ontogenetically related pattern changes, are perfectly preserved in two 380 million year old fossil vertebrates, the placoderm Compagopiscis croucheri and the sarcopterygian fish Eusthenopteron foordi.Conclusions/Significance: We are able to determine the position of entheses in fossil vertebrates, the approximate orientation of the attached muscles, and aspects of their ontogenetic histories, from PPC-SRmCT data. Sub-micron microtomography thus provides a powerful tool for studying the structure, development, evolution and palaeobiology of muscle attachments.
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| 7. |
- Sanchez, Sophie, et al.
(författare)
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Life history of the stem tetrapod Acanthostega revealed by synchrotron microtomography
- 2016
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 537:7620, s. 408-
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Tidskriftsartikel (refereegranskat)abstract
- The transition from fish to tetrapod was arguably the most radical series of adaptive shifts in vertebrate evolutionary history. Data are accumulating rapidly for most aspects of these events(1-5), but the life histories of the earliest tetrapods remain completely unknown, leaving a major gap in our understanding of these organisms as living animals. Symptomatic of this problem is the unspoken assumption that the largest known Devonian tetrapod fossils represent adult individuals. Here we present the first, to our knowledge, life history data for a Devonian tetrapod, from the Acanthostega mass-death deposit of Stensio Bjerg, East Greenland(6,7). Using propagation phase-contrast synchrotron microtomography (PPC-SR mu CT)(8) to visualize the histology of humeri (upper arm bones) and infer their growth histories, we show that even the largest individuals from this deposit are juveniles. A long early juvenile stage with unossified limb bones, during which individuals grew to almost final size, was followed by a slow-growing late juvenile stage with ossified limbs that lasted for at least six years in some individuals. The late onset of limb ossification suggests that the juveniles were exclusively aquatic, and the predominance of juveniles in the sample suggests segregated distributions of juveniles and adults at least at certain times. The absolute size at which limb ossification began differs greatly between individuals, suggesting the possibility of sexual dimorphism, adaptive strategies or competition-related size variation.
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| 8. |
- Sanchez, Sophie, et al.
(författare)
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The humerus of Eusthenopteron : a puzzling organization presaging the establishment of tetrapod limb bone marrow
- 2014
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 281:1782, s. 20140299-
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Tidskriftsartikel (refereegranskat)abstract
- Because of its close relationship to tetrapods, Eusthenopteron is an important taxon for understanding the establishment of the tetrapod body plan. Notably, it is one of the earliest sarcopterygians in which the humerus of the pectoral fin skeleton is preserved. The microanatomical and histological organization of this humerus provides important data for understanding the evolutionary steps that built up the distinctive architecture of tetrapod limb bones. Previous histological studies showed that Eusthenopteron's long-bone organization was established through typical tetrapod ossification modalities. Based on a threedimensional reconstruction of the inner microstructure of Eusthenopteron's humerus, obtained from propagation phase-contrast X-ray synchrotron microtomography, we are now able to show that, despite ossification mechanisms and growth patterns similar to those of tetrapods, it also retains plesiomorphic characters such as a large medullary cavity, partly resulting from the perichondral ossification around a large cartilaginous bud as in actinopterygians. It also exhibits a distinctive tubular organization of bone-marrow processes. The connection between these processes and epiphyseal structures highlights their close functional relationship, suggesting that either bone marrow played a crucial role in the long-bone elongation processes or that trabecular bone resulting from the erosion of hypertrophied cartilage created a microenvironment for haematopoietic stem cell niches.
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| 9. |
- Sanchez, Sophie, et al.
(författare)
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Three-Dimensional Synchrotron Virtual Paleohistology : A New Insight into the World of Fossil Bone Microstructures
- 2012
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Ingår i: Microscopy and Microanalysis. - 1431-9276 .- 1435-8115. ; 18:5, s. 1095-1105
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Tidskriftsartikel (refereegranskat)abstract
- The recent developments of phase-contrast synchrotron imaging techniques have been of great interest for paleontologists, providing three-dimensional (3D) tomographic images of anatomical structures, thereby leading to new paleobiological insights and the discovery of new species. However, until now, it has not been used on features smaller than 57 mu m voxel size in fossil bones. Because much information is contained within the 3D histological architecture of bone, including an ontogenetic record, crucial for understanding the paleobiology of fossil species, the application of phase-contrast synchrotron tomography to bone at higher resolutions is potentially of great interest. Here we use this technique to provide new 3D insights into the submicron-scale histology of fossil and recent bones, based on the development of new pink-beam configurations, data acquisition strategies, and improved processing tools. Not only do the scans reveal by nondestructive means all of the major features of the histology at a resolution comparable to that of optical microscopy, they provide 3D information that cannot be obtained by any other method.
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| 10. |
- Trinajstic, Kate, et al.
(författare)
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Response to comment on "Exceptional preservation of organs in Devonian placoderms from the Gogo largerstätte"
- 2023
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 380:6645
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Jensen et al. (1) question evidence presented of a chambered heart within placoderms, citing its small size and apparently ventral atrium. However, they fail to note the belly-up orientation of the placoderm within one nodule, and the variability of heart morphology within extant taxa. Thus, we remain confident in our interpretation of the mineralized organ as the heart.
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