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33 results for “Gnathostomes”
Figure 3 in Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters
Figure 3. Cartoons of selected characters and character states. Numbers signify characters, bracketed numbers represent character states e.g. 1(0), where 1 is the characters and (0) is the character state.
Figure 6. Most parsimonious result from a in Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters
Figure 6. Most parsimonious result from a phylogenetic analysis of discrete (1—64) and discretized continuous characters identified through gap coding (88—100). A, strict consensus of 30 most parsimonious trees with equally weighted characters (tree length 346). B, most parsimonious solution with implied weighted characters (k = 3) (tree length 27.86). Psammosteidae taxa in bold (for which quantitative characters have been treated as inapplicable, i.e. non-homologous).
Figure 2 in Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters
Figure 2. Reconstruction of a hypothetical Pteraspidiformes (adapted from Blieck 1984). A, dorsal and ventral view of Pteraspidiformes headshield with plates labelled. B, D, E, measurements used in phylogenetic analysis. C, dorsal headshield sensory canals. Anatomical abbreviations: SOC, supraorbital canal; OrbC, orbital canal; PinC, pineal canal; LDC, lateral dorsal canal; MDC, medial dorsal canal; TC, transverse commissures; MTC, median transverse commissures. Measurement abbreviations: DSL, dorsal shield length; DSW, dorsal shield width, not including the cornual plate width; DPL, dorsal plate length; DPW, dorsal plate width; RPL, rostral plate length; RPW, rostral plate width; PPL, pineal plate length; PPW, pineal plate width; BPL, brachial plate length; BOL, branchial opening distance from anterior of dorsal plate; CPL, cornual plate length; OrbPL, orbital plate length; OrbPAPL, orbital plate anterior process length; OrbPMPL, orbital plate medial process length; OrbPPPL, orbital plate posterior process length; Orb—Orb, orbital opening to orbital opening length; DSBW, dorsal spine base width; DSBL, dorsal spine base length; DPEB, dorsal plate embayment; DPEL, distance to beginning of embayment from anterior end of dorsal plate; DPEW, dorsal plate embayment narrowest width.
Figure 1. Previous Pteraspidiformes phylogenies. A in Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters
Figure 1. Previous Pteraspidiformes phylogenies. A, Blieck's (1984) Pteraspidiformes phylogeny for all the then-known taxa. B, Janvier's (1996) phylogeny for the major clades of Pteraspidiformes. C, Ilyes & Elliott's (1994) phylogeny for the Western USA taxa. D, Perǹegre's (2002) phylogeny to determine the position of Doryaspis. E, Perǹegre & Goujet's (2007) phylogeny to determine the position of Gigantaspis. F, Perǹegre & Elliott's (2008) most recent Pteraspidiformes phylogeny with the identification of major families. The Psammosteidae are highlighted when included in an analysis.
Figure 7. Pteraspidiformes phylogeny with genera plotted against their stratigraphical occurrences. A in Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters
Figure 7. Pteraspidiformes phylogeny with genera plotted against their stratigraphical occurrences. A, discrete and continuous character analysis with implied weighting (k = 3). B, discretized analysis with implied weighting (k = 3). Colours relate to palaeobiogeographical provinces.
Figure 4. Results from the phylogenetic analysis using discrete data only. A in Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters
Figure 4. Results from the phylogenetic analysis using discrete data only. A, strict consensus of 275 most parsimonious trees with equal character weights; length 276 steps, consistency index (CI) = 0.35, retention index (RI) = 0.59, and rescaled consistency index (RC) = 0.22. B, strict consensus of four most parsimonious trees with implied character weighting (k = 3) (tree length 23.11). Psammosteidae taxa in bold.
Figure 5 in Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters
Figure 5. Phylogenetic results from data sets containing discrete (1—64) and continuous (66, 68, 70, 72, 77, 80, 82, 86) characters. A, most parsimonious tree with equally weighted characters (tree length 319.36). B, most parsimonious tree with implied weighting (k = 3) (tree length 26.53). Psammosteidae taxa in bold (for which quantitative characters have been treated as inapplicable, i.e. nonhomologous).
FIGURE 1 in The oldest record of gnathostome fossils from Greece: Chondrichthyes from the Lopingian of Hydra Island
FIGURE 1. Geographical and geological context of the Hydriot chondrichthyan fossils. 1, Map of Greece showing the location of Hydra Island; 2, Outcrop map of Hydra Island showing the location of the sampled section "EP" south of the village of Episkopi. Outcrop map after Grant et al. (1991); 3, Stratigraphic section of the Episkopi Formation showing the provenance ("EP-Z") of the examined gnathostome fossils.
FIGURE 2. Chondrichthyan material from Hydra. 1-5 in The oldest record of gnathostome fossils from Greece: Chondrichthyes from the Lopingian of Hydra Island
FIGURE 2. Chondrichthyan material from Hydra. 1-5, Hybodontiformes indet. tooth (AMPG 550) in occlusal (1), basal (2), presumed lingual (3), profile (4), and presumed labial (5) views. Scale bar equals 5 mm. 6, Euselachii indet. dermal denticle (AMPG 551) in anterolateral view. Scale bar equals 100 μm.
FIG. 6 in Earliest Devonian gnathostome microremains from central New South Wales (Australia)
FIG. 6. — Placoderm and palaeoniscoid scales from sample C866, middle Lochkovian (?delta CZ)?Connemarra Formation, central New South Wales, Australia; A, B, broken scale MMMC02623 from Terenolepis turnerae Burrow, 1995, in crown and antero-crown view (anterior edge to right); C, D,?petalichthyid scale MMMC02624, in crown and postero-crown view; E, F,?brindabellaspid scale MMMC02625, in crown and antero-crown view; G, H,?palaeacanthaspid scale MMMC02626, in crown and lateral view (anterior to left); I,?romundinid scale MMMC02627 in crown view. Scale bars: A-D, 1.0 mm; E-I, 0.1 mm.
FIG. 5. — Placoderm scales from sample C925 in Earliest Devonian gnathostome microremains from central New South Wales (Australia)
FIG. 5. — Placoderm scales from sample C925, Cookeys Plains Formation (early Lochkovian), central New South Wales, Australia; A, romundinid dermal bone fragment with thin base, MMMC02628; B, romundinid dermal plate fragment MMMC02629 showing edge ornament; C, romundinid scale MMMC02630, latero-crown view; D, romundinid scale MMMC02631, crown view; E, F, romundinid dermal plate fragment MMMC02632, showing thick cross-section, and close-up of ornament tubercles; G,?brindabellaspid scale MMMC02633. Scale bars: A, C, D, F, G, 0.1 mm; B, E, 1.0 mm.
FIG. 3 in Earliest Devonian gnathostome microremains from central New South Wales (Australia)
FIG. 3. — Acanthodian tooth and scales from sample C925, Cookeys Plains Formation (early Lochkovian), central New South Wales, Australia; A, B, Nostolepis sp. tooth whorl MMMC02560 in occlusal (lingual edge at top) and posterior and lingual views; C, D, Gomphonchus sandelensis (Pander, 1856) scale MMMC02561 in crown and lateral views, with anterior edge to the left (crown riddled with hyphal borings); E, Trundlelepis sp., horizontal ground thin section of scale crown MMMC02562, anterior edge to left; F, G, Gomphonchoporus hoppei (Gross, 1947) scale MMMC02563 in crown and posterior views, anterior edge at top; H, I, Radioporacanthodes porosus (Brotzen, 1934) s.s. scale MMMC02564 in antero-crown and anterior views. Abbreviation: p, pore rows. Scale bars: 0.1 mm.
FIG. 2. — Acanthodian scales from sample C925 in Earliest Devonian gnathostome microremains from central New South Wales (Australia)
FIG. 2. — Acanthodian scales from sample C925, Cookeys Plains Formation (early Lochkovian), central New South Wales, Australia; A-D, H, Nostolepis lacrima Valiukevicius, 1994; A, B, specimen MMMC02555; A, crown view; B, antero-lateral view; C, D, specimen MMMC02556; C, crown view; D, lateral view; H, vertical longitudinal ground thin section MMMC02557; remineralization has obscured histological details; E-G, Nostolepis sp.; E, F, specimen MMMC02558; E, crown view; F, anterolateral view; G,?branchial scale MMMC02559 in crown view. Anterior of scale faces to left in A-D, and to right in E-H. Scale bars: 0.1 mm.
FIG. 4. — Acanthodian scales from sample C923 in Earliest Devonian gnathostome microremains from central New South Wales (Australia)
FIG. 4. — Acanthodian scales from sample C923, Cookeys Plains Formation (early Lochkovian), central New South Wales, Australia; A, B, Nostolepis lacrima Valiukevicius, 1994 scale MMMC02551 in crown (anterior edge to right) and lateral (anterior edge to left) views; C, D, Nostolepis sp. scale of "N. applicata"-type MMMC02552 in crown and lateral views (presumed anterior edge to left); E, F, Gomphonchoporus hoppei (Gross, 1947) scale MMMC02553 in crown (anterior edge at bottom) and anterior views; G, H, Trundlelepis sp. scale MMMC02554 in crown and lateral views (anterior edge to right). Abbreviation: ms, median sulcus. Scale bars: 0.1 mm.
Figure 2 in The histology and affinities of sinacanthid fishes: primitive gnathostomes from the Silurian of China
Figure 2. Histology of sinacanthid spines. A, montage of a single transverse section; B, detail showing clear boundary (arrowed) between the outer layer of atubular dentine and lamellar dentine and the inner layer of globular calcified cartilage, note also the pulp cavities beneath each ridge; C, scanning electron micrograph of HCl etched section through ridge and globular calcified cartilage showing boundary (arrowed) between the outer layer and the inner layer; D, detail of globular atubular dentine; E, cross section through presumed juvenile spine ridge showing open pulp cavity; F, globular calcified cartilage lining vascular canal. All transmitted light micrographs using Nomarski interference optics unless otherwise stated. A–D, F, Sinacanthus wuchangensis P'an (1959) from the Tataaiertage Formation, Lower Silurian, Kalpin, Xinjiang, IVPP.V14325; E, Sinacanthus sp. from the Xiushan Formation, Lower Silurian, Shiqian, Guizhou Province, NIGP 139378. Abbreviations: ad, atubular dentine; pc, pulp cavity; ld, lamellar dentine; gcc, globular calcified cartilage; vc, vascular canal. Scale bars: A = 500 Mm; B, C, E = 100 Mm; D, F = 50 Mm.
OPT data from: A novel cis-regulatory element drives early expression of Nkx3.2 in the gnathostome primary jaw joint
<p><span>The acquisition of movable jaws was a major event during vertebrate evolution. The role of NK3 homeobox 2 (Nkx3.2) transcription factor in patterning the primary jaw joint of gnathostomes (jawed vertebrates) is well known, however, knowledge about its regulatory mechanism is lacking. In this study, we report a proximal enhancer element of <em>Nkx3.2</em> that is deeply conserved in most gnathostomes but undetectable in the jawless hagfish and lamprey. This enhancer is active in the developing jaw joint region of the zebrafish <em>Danio rerio</em>, and was thus designated as <em>jaw joint regulatory sequence 1</em> (JRS1). We further show that JRS1 enhancer sequences from a range of gnathostome species, including a chondrichthyan and mammals, have the same activity in the jaw joint as the native zebrafish enhancer, indicating a high degree of functional conservation despite the divergence of cartilaginous and bony fish lineages or the transition of the primary jaw joint into the middle ear of mammals. Finally, we show that deletion of JRS1 from the zebrafish genome using CRISPR/Cas9 results in a significant reduction of early gene expression of <em>Nkx3.2</em> and leads to transient jaw joint deformation and partial fusion. The emergence of this <em>Nkx3.2 </em>enhancer in early gnathostomes may have contributed to the origin and shaping of the articulating surfaces of vertebrate jaws.</span></p>
Functional assessment of morphological homoplasy in stem-gnathostomes
<p>The Osteostraci and Galeaspida are stem gnathostomes, occupying a key phylogenetic position for resolving the nature of the jawless ancestor from which jawed vertebrates evolved more than 400 million years ago. Both groups are characterized by the presence of rigid headshields that share a number of common morphological traits, in some cases hindering the resolution of their interrelationships and the exact nature of their affinities with jawed vertebrates. Here, we explore the morphological and functional diversity of osteostracan and galeaspid headshields using an innovative approach that combines geometric morphometrics and computational fluid dynamics, thereby constraining the underlying factors that promoted the evolution of their similar morphologies and informing on the ecological scenario under which jawed vertebrates emerged. Phylomorphospace, Mantel analysis and Stayton metrics demonstrate a high degree of homoplasy. Computational fluid dynamics reveals similar hydrodynamic performance among morphologically convergent species, indicating the independent acquisition of the same morphofunctional traits and, potentially, equivalent lifestyles. This confirms that a number of the characters typically used to infer the evolutionary relationships among galeaspids, osteostracans and jawed vertebrates are convergent in nature, potentially obscuring understanding of the assembly of the gnathostome bodyplan. Ultimately, our results reveal that while the jawless relatives of the earliest jawed vertebrates were ecologically diverse, widespread convergence on the same hydrodynamic adaptations suggests they had reached the limits of their potential ecological diversity – overcome by jawed vertebrates and their later innovations.</p>
Data from: Resegmentation is an ancestral feature of the gnathostome vertebral skeleton
<p>The vertebral skeleton is a defining feature of vertebrate animals. However, the mode of vertebral segmentation varies considerably between major lineages. In tetrapods, adjacent somite halves recombine to form a single vertebra through the process of 'resegmentation'. In teleost fishes, there is considerable mixing between cells of the anterior and posterior somite halves, without clear resegmentation. To determine whether resegmentation is a tetrapod novelty, or an ancestral feature of jawed vertebrates, we tested the relationship between somites and vertebrae in a cartilaginous fish, the skate (Leucoraja erinacea). Using cell lineage tracing, we show that skate trunk vertebrae arise through tetrapod-like resegmentation, with anterior and posterior halves of each vertebra deriving from adjacent somites. We further show that tail vertebrae also arise through resegmentation, though with a duplication of the number of vertebrae per body segment. These findings resolve axial resegmentation as an ancestral feature of the jawed vertebrate body plan.</p>
Functional assessment of morphological homoplasy in stem-gnathostomes
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Data from: Resegmentation is an ancestral feature of the gnathostome vertebral skeleton
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