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- Clément, Gaël, et al.
(författare)
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A new tristichopterid (Sarcopterygii, Tetrapodomorpha) from the Upper Famennian Evieux Formation (Upper Devonian) of Belgium
- 2009
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 52, s. 823-836
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Tidskriftsartikel (refereegranskat)abstract
- Additional material of a large specimen of tristichopterid fish from the Upper Famennian Evieux Formation of Belgium is described. This large fish was previously assigned to Tristichopteridae gen. et sp. indet. due to the lack of diagnostic anatomical data. New available material consists of the internal surface of the parietal shield, vomers and anterior part of the parasphenoid, subopercular and submandibulo-branchiostegal bones, and an internal view of the anterior part of the mandible. A possible autapomorphy of the new form from Belgium, Langlieria socqueti gen. nov. et sp. nov., is the absence of marginal teeth on the vomer except on its most lateral part. Apart from these features, it only differs from the genus Mandageria from Australia in the absence of marginal teeth between the dentary fang and the mandibular symphysis, in the presence of a raised marginal crest lateral to the anterior coronoid fang, and in the presence of numerous small marginal teeth on the premaxilla. It differs from the cosmopolitan genus Eusthenodon in a number of respects: the supratemporal, tabular, and postparietal bones are superficially fused, as are the intertemporal and parietal bones, the dermal ornament is proportionally very fine, and the denticulated field of the parasphenoid stands proud rather than being recessed into the body of the bone.
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- Habicher, Judith, et al.
(författare)
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Chondroitin/dermatan sulfate glycosyltransferase genes are essential for craniofacial development
- 2022
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Ingår i: PLOS Genetics. - : Public Library of Science (PLoS). - 1553-7390 .- 1553-7404. ; 18:2
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Tidskriftsartikel (refereegranskat)abstract
- Chondroitin/dermatan sulfate (CS/DS) proteoglycans are indispensable for animal development and homeostasis but the large number of enzymes involved in their biosynthesis have made CS/DS function a challenging problem to study genetically. In our study, we generated loss-of-function alleles in zebrafish genes encoding CS/DS biosynthetic enzymes and characterized the effect on development in single and double mutants. Homozygous mutants in chsy1, csgalnact1a, csgalnat2, chpfa, ust and chst7, respectively, develop to adults. However, csgalnact1a-/- fish develop distinct craniofacial defects while the chsy1-/- skeletal phenotype is milder and the remaining mutants display no gross morphological abnormalities. These results suggest a high redundancy for the CS/DS biosynthetic enzymes and to further reduce CS/DS biosynthesis we combined mutant alleles. The craniofacial phenotype is further enhanced in csgalnact1a-/-;chsy1-/- adults and csgalnact1a-/-;csgalnact2-/- larvae. While csgalnact1a-/-;csgalnact2-/- was the most affected allele combination in our study, CS/DS is still not completely abolished. Transcriptome analysis of chsy1-/-, csgalnact1a-/- and csgalnact1a-/-;csgalnact2-/- larvae revealed that the expression had changed in a similar way in the three mutant lines but no differential expression was found in any of fifty GAG biosynthesis enzymes identified. Thus, zebrafish larvae do not increase transcription of GAG biosynthesis genes as a consequence of decreased CS/DS biosynthesis. The new zebrafish lines develop phenotypes similar to clinical characteristics of several human congenital disorders making the mutants potentially useful to study disease mechanisms and treatment.
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- Holland, Timothy, et al.
(författare)
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New information on the enigmatic tetrapodomorph fish Marsdenichthys longioccipitus (Long, 1985)
- 2010
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Ingår i: Journal of Vertebrate Paleontology. - : Informa UK Limited. - 0272-4634 .- 1937-2809. ; 30:1, s. 68-77
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Tidskriftsartikel (refereegranskat)abstract
- The tetrapodomorph fish Marsdenichthys longioccipitus from the Givetian-Frasnian of Mt. Howitt, Victoria, Australia, occupies an uncertain phylogenetic position. Marsdenichthys has been linked to the base of the Tristichopteridae, as well as to the poorly known Northern Hemisphere form Rhizodopsis, based on the presence of rounded scales bearing a median boss on the internal surface. However, its affinities to these taxa are ambiguous, due to the incomplete preservation of the two Marsdenichthys specimens initially described. For the first time, we present significant information regarding the cheek and palate of Marsdenichthys, based on the descriptions of two new specimens from Mt. Howitt. New autapomorphies for Marsdenichthys are proposed, including the presence of a bar-like maxilla being approximately equal in depth to the dentary, and a rectangular anterior termination of the lacrimal. Several plesiomorphic features are described from the palate, including rounded vomer morphology lacking a posterior process, a relatively short, broad parasphenoid, and a dermopalatine approximately equal in length to the ectopterygoid. No synapomorphies are shared between Marsdenichthys and tristichopterids. Scale morphology is redescribed, and shown to exhibit concentric rings on the external surface, as in Rhizodopsis. However, differences in skull morphology, such as the lack of an external opening for the pineal foramen in Rhizodopsis, suggest that this scale morphology may have evolved independently.
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- Kundrát, Martin, 1969-, et al.
(författare)
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Specialized Craniofacial Anatomy of a Titanosaurian Embryo from Argentina
- 2020
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 30:21, s. 4263-4269.e2
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Tidskriftsartikel (refereegranskat)abstract
- The first dinosaur embryos found inside megaloolithid eggs from Auca Mahuevo, Patagonia, were assigned to sauropod dinosaurs that lived approximately 80 million years ago. Discovered some 25 years ago, these considerably flattened specimens still remain the only unquestionable embryonic remains of a sauropod dinosaur providing an initial glimpse into titanosaurian in ovo ontogeny. Here we describe an almost intact embryonic skull, which indicates the early development of stereoscopic vision, and an unusual monocerotic face for a sauropod. The new fossil also reveals a neurovascular sensory system in the premaxilla and a partly calcified braincase, which potentially refines estimates of its prenatal stage. The embryo was found in an egg with thicker eggshell and a partly different geochemical signature than those from the egg-bearing layers described in Auca Mahuevo. The cranial bones are comparably ossified as in previously described specimens but differ in facial anatomy and size. The new specimen reveals significant heterochrony in cranial ossifications when compared with non-sauropod sauropodomorph embryos, and demonstrates that the specialized craniofacial morphology preceded the postnatal transformation of the skull anatomy in adults of related titanosaurians.
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- Moczydlowska-Vidal, Malgorzata, 1951-, et al.
(författare)
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Ediacaran metazoan fossils with siliceous skeletons from the Digermulen Peninsula of Arctic Norway
- 2021
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Ingår i: Journal of Paleontology. - : Cambridge University Press. - 0022-3360 .- 1937-2337. ; 95:3, s. 440-475
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a new assemblage of Ediacaran metazoan fossils is reported from the basal Stahpogieddi Formation on the Digermulen Peninsula of Arctic Norway, including Anulitubus n. gen. Moczydlowska in Moczydlowska et al., Anulitubus formosus n. gen. n. sp. Moczydlowska in Moczydlowska et al., Coniculus n. gen. Moczydlowska in Moczydlowska et al., Coniculus elegantis n. gen. n. sp. Moczydlowska in Moczydlowska et al., Fistula n. gen. Moczydlowska in Moczydlowska et al., and Fistula crenulata n. gen. n. sp. Moczydlowska in Moczydlowska et al. The specimens are three-dimensionally preserved and include tubular and conical skeletons that are morphologically distinguished by their body-wall constructions, radial symmetry, polarity, segmentation, and annulation. The skeletons are interpreted to be biomineralized by primary silica based on computed micro-tomographic, petrographic, geochemical, and spectroscopic evidence of originally rigid body wall with layers of constant thicknesses, composed of opal, microcrystalline quartz, and an admixture of carbonaceous material, which differ from the host sediment mineralogy and do not show replacement or encrustation. The fossil-bearing interval immediately overlies strata of Gaskiers age and can be bracketed within 580-541 Ma, but it is estimated to be ca. 575 Ma on the basis of averaged sedimentation rates and biostratigraphic correlations with Ediacaran biota found in up-section deposits of ca. 558-555 Ma. Future new findings of such fossils in different preservation modes and further multi-collector inductively coupled plasma mass spectrometry, which shows the silicon fractionation and traces its biogenic origin versus inorganic mineralization, may corroborate the interpretation of biogenic silicification of these earliest skeletal fossils.
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- Snitting, Daniel
(författare)
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A Redescription of the Anatomy of the Late Devonian Spodichthys Buetleri Jarvik, 1985 (Sarcopterygii, Tetrapodomorpha) from East Greenland
- 2008
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Ingår i: Journal of Vertebrate Paleontology. - 0272-4634 .- 1937-2809. ; 28:3, s. 637-655
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Tidskriftsartikel (refereegranskat)abstract
- The tetrapodomorph fish Spodichthys buetleri from the Upper Devonian of East Greenland is redescribed from computed tomography scans of material originally studied by Erik Jarvik. A wealth of new anatomical data was revealed by scanning the nearly perfectly three-dimensional specimens, including detailed information on the shape of the brain cavity and the internal structure of the lower jaws. Spodichthys displays an interesting mix of generalized “osteolepidid,” or primitive tetrapodomorph, and tristichopterid features. Derived characters shared by Spodichthys, tristichopterids and (Panderichthys + Tetrapoda) include the loss of cosmine, a small kite-shaped parasymphysial plate, and a long commissural lamina of the entopterygoid. The presence of an extratemporal lateral to the tabular and a single fang position on the posterior coronoid and ectopterygoid are examples of basal tetrapodomorph characters retained in Spodichthys. Spodichthys is unique in having coronoid fangs positioned lateral to the corresponding replacement pit rather than having an anterior-posterior alternation between developed fang and replacement pit, which is the normal tetrapodomorph condition. Jarvik's original conclusion that Spodichthys is closely related to the tristichopterids is confirmed by a phylogenetic analysis, which places Spodichthys as the sister taxon of the Tristichopteridae.
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