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Holopterygius nudus Jessen (P 7789), latest Givetian–earliest Frasnian, Bergisch-Gladbach, Germany. ( a ) Photograph of P 7789a; ( b ) composite drawing based on P7789a-c; and ( c ) reconstruction. Bones outlined in grey in ( c ) were reconstructed based on Allenypterus . Scale bar represents 10 mm. Abbreviations: ano, anocleithrum; bp, basal plate of the second dorsal fin; chy, ceratohyal; cla, calvicle; cle, cleithrum; cop, principal coronoid; ex, extracleithrum; has, haemal arch and spine; gs, indeterminate components of the gill skeleton; nas, neural arch and spine; op, opercle; ot, otolith; pal, palate; pap, parapophyses; pmx, premaxilla; psph, parasphenoid; rd, radials of the dorsal lobe of the caudal fin; rv, radials of the ventral lobe of the caudal fin; sr, skull roof; sym, symplectic; vs, ventral keel scales. 

Holopterygius nudus Jessen (P 7789), latest Givetian–earliest Frasnian, Bergisch-Gladbach, Germany. ( a ) Photograph of P 7789a; ( b ) composite drawing based on P7789a-c; and ( c ) reconstruction. Bones outlined in grey in ( c ) were reconstructed based on Allenypterus . Scale bar represents 10 mm. Abbreviations: ano, anocleithrum; bp, basal plate of the second dorsal fin; chy, ceratohyal; cla, calvicle; cle, cleithrum; cop, principal coronoid; ex, extracleithrum; has, haemal arch and spine; gs, indeterminate components of the gill skeleton; nas, neural arch and spine; op, opercle; ot, otolith; pal, palate; pap, parapophyses; pmx, premaxilla; psph, parasphenoid; rd, radials of the dorsal lobe of the caudal fin; rv, radials of the ventral lobe of the caudal fin; sr, skull roof; sym, symplectic; vs, ventral keel scales. 

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Previously considered an actinopterygian or an osteichthyan incertae sedis, the Devonian (Givetian-Frasnian) Holopterygius nudus is reinterpreted as a coelacanth. This genus is among the oldest coelacanths known from articulated remains, but its eel-like morphology marks a considerable departure from the conventional coelacanth body plan. A cladist...

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Context 1
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 2
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 3
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 4
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 5
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 6
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 7
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 8
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 9
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 10
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 11
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 12
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 13
... a long tooth-bearing fragment on the opposite side of the skull probably represents a portion of the dentary from the other mandible. The deep dorsal process of the jaw is composed of an expanded posterior coronoid ( figure 1 b , cop), which is a coelacanth synapomorphy (Forey 1998). Small teeth anterior to the principal coronoid may be the remains of additional members of the series. The posterior ramus of the jaw corresponds to the retroarticular process of other coelacanths, and is overlain by a stocky cylindrical bone that is identified as the symplectic (figure 1 b , sym), a major component of the coelacanth tandem jaw joint. The ceratohyals (figure 1 b , chy) are flared distally and proximally. Narrow endoskeletal rods represent remains of the gill skeleton (figure 1 b , gs). The cleithrum and clavicles (figure 1 b , cle, cla) are well-preserved and exhibit the slender proportions characteristic of coelacanths crownward of Miguashaia (Cloutier 1996; Forey 1998). Holopterygius also possesses an extracleithrum (figure 1 b , ex), an additional dermal ossification that is a coelacanth synapomorphy (Forey 1998). Although Jessen (1973) noted the similarities between the pectoral girdles of Holopterygius and coelacanths, he did not consider this resemblance sufficient to justify placement within the group. Fragments of the anocleithrum (figure 1 b , ano) are located dorsal to the tip of the cleithrum, and suggest this bone was of the simple unbranched morphology primitive for actinistians. The distinctive postcranium of Holopterygius is leaf- shaped, with a greatly elongated caudal region. Despite the unusual body shape of this genus, the components of its postcranial skeleton conform to the general coelacanth pattern. There are approximately 80 postcranial segments, just over 20 of which are abdominal. Vertebral centra are unossified, but small ossifications located below the abdominal neural arches may represent parapophyses (figure 1 b , pap). There are no ossified ribs. Neural arches and spines (figure 1 b , nas) and haemal arches and spines (figure 1 b , has) are co-ossified. The dorsal and ventral lobes of the diphycercal caudal fin are each supported by a single row of endoskeletal radials (figure 1 b , rd, rv). There is a one-to-one ratio between radials and neural or haemal spines and a greater than one-to-one relationship between fin rays and radials. Jessen (1973) reconstructed Holopterygius with multiple radials per body segment, but this seems to have been informed by reference to conditions in tarrasiid actinopterygians (Lund & Melton 1982; Taverne 1996). Direct comparison with Tarrasius problematicus (Natural History Museum, London, P.1167, P.18064, P.18065, P.18061) confirms the difference in spine to radial ratios. It is not possible to determine whether the fin rays were segmented in Holopterygius as in most coelacanths, or unsegmented as in Allenypterus (Lund & Lund 1985). The dorsal and ventral lobes of the caudal fin are strongly asymmetrical, with the dorsal lobe extending much further anteriorly, as in Allenypterus (Lund & Lund 1985; Forey 1998). No components of the first dorsal, pectoral, anal or pelvic fins are preserved. An irregularly shaped ossification located dorsal to the neural spines immediately anterior to the first radial of the caudal fin probably represents the basal plate of the second dorsal fin (figure 1 b , bp). No squamation is preserved on the flanks of Holopterygius , but a series of keel scales run along the ventral margin of the body from just behind the skull to approximately the midpoint of the abdominal region (figure 1 b , vs). It is possible that the absence of scales covering the body of Holopterygius is size-related, as scales are often not preserved in small fossil coelacanths (Lund & Lund 1985). There is no indication of the ossified swim bladder characteristic of derived coelacanths. Widely cited studies place coelacanths as the most basal extant sarcopterygian radiation (Cloutier & Ahlberg 1996; Forey 1998), but little is known about their early history. While the first crown-group sarcopterygians are known from Lower Devonian (Lochkovian; 411–416 Ma) depos- its (Cloutier & Ahlberg 1996), the oldest unequivocal coelacanths are of Givetian age (385–392 Ma; Forey 1998; Long 1999; Forey et al . 2000). Previously described Devonian coelacanths fall into two morphological cat- egories: primitive forms ( Gavinia , Miguashaia ) with postcrania resembling those of other plesiomorphic sarcopterygians, and more crownward taxa ( Chagrinia , Diplocercides ) whose postcranial anatomy is similar to that of stratigraphically younger and phylogenetically more derived coelacanths, including the Recent Latimeria . Holopterygius marks a considerable anatomical departure from other Devonian forms, and a cladistic analysis places it as the sister taxon of Allenypterus , another early coelacanth with unusual postcranial morphology (analysis and results are described in figure 2 a ). Two unequivocal synapomorphies link these genera: a series of ventral keel scales and an asymmetrical caudal fin in which the dorsal lobe extends far beyond the anterior extremity of the ventral lobe. Both of these fishes have unstable taxonomic histories resulting from their unconventional body profiles; like Holopterygius , Allenypterus was identified as an actinopterygian (Melton 1969) before being recognized as a coelacanth (Lund & Lund 1984). Although Holopterygius and Allenypterus are unusual among coelacanths in having greatly elongated caudal regions, they are easily distinguished. While the deep body of Allenypterus is strongly arched dorsally and compara- tively straight ventrally, the postcranium of Holopterygius is shallower with more symmetrical dorsal and ventral margins. Small specimens of Allenypterus have a less exaggerated dorsal hump than larger individuals (Lund & Lund 1985; Field Museum, Chicago, PF10942, PF 10943a,b), but they retain greatly elongated neural spines above the abdominal region, unlike the short structures in Holopterygius . Both genera share asymmetrical lobes of the caudal fin, but the ventral lobe is more extensive in Holopterygius than in Allenypterus , where it is reduced to a minor series of shortened fin rays near the tip of the tail. Additional dissimilarities are present in the skulls. The premaxillae and mandibles of Allenypterus are edentulous (Lund & Lund 1985; Forey 1998) but bear well- developed teeth in Holopterygius . Additionally, lower jaw proportions of Holopterygius are unlike those of Allenypterus , but are similar to those of other early coelacanths (Lund & Lund 1985; Forey et al . 2000), suggesting that it had a more conventional skull shape than Allenypterus , in which the cranial region is drastically ...
Context 14
... probably precedes its first appearance (Harland et al . 1990). Therefore, the age of the fish beds is probably latest Givetian–earliest Frasnian ( ca 385 Ma; all dates in this article are from Gradstein et al . 2004). The skull roof of Holopterygius (figure 1 b , sr) is preserved primarily as an impression of its visceral surface, but intact areas are perforated by large, irregular pores for the supraorbital sensory canal. The premaxilla (figure 1 b , pmx) is squat and bears four large, irregularly shaped teeth. The dorsal surface of the splint-like parasphenoid (figure 1 b , psph) is exposed, and is marked by a well- developed hypophysial fossa. Much of the palate is visible (figure 1 b , pal), and it has the triangular shape characteristic of coelacanths (Forey 1998). The quadrate is preserved as a thickened region at the posteroventral corner of the palate, while a series of teeth along its ventral margin represent the remains of the ectopterygoid. A large, subspherical structure in the otic region is interpreted as an otolith (figure 1 b , ot; cf. Clack 1996). No dermal bones of the cheek can be identified. The opercle (figure 1 b , op) is a large rectangular bone with a long vertical axis, and resembles that of Allenypterus (Lund & Lund 1985; Forey 1998). The lower jaw of Holopterygius bears a long anterior ramus, a well-developed dorsal process at mid length, and another ramus posteriorly. The anterior arm of the lower jaw resembles the slender dentary of many early coelacanths (Lund & Lund 1985; Forey et al . 2000). Although the dentary of the intact jaw is preserved only as ...
Context 15
... probably precedes its first appearance (Harland et al . 1990). Therefore, the age of the fish beds is probably latest Givetian–earliest Frasnian ( ca 385 Ma; all dates in this article are from Gradstein et al . 2004). The skull roof of Holopterygius (figure 1 b , sr) is preserved primarily as an impression of its visceral surface, but intact areas are perforated by large, irregular pores for the supraorbital sensory canal. The premaxilla (figure 1 b , pmx) is squat and bears four large, irregularly shaped teeth. The dorsal surface of the splint-like parasphenoid (figure 1 b , psph) is exposed, and is marked by a well- developed hypophysial fossa. Much of the palate is visible (figure 1 b , pal), and it has the triangular shape characteristic of coelacanths (Forey 1998). The quadrate is preserved as a thickened region at the posteroventral corner of the palate, while a series of teeth along its ventral margin represent the remains of the ectopterygoid. A large, subspherical structure in the otic region is interpreted as an otolith (figure 1 b , ot; cf. Clack 1996). No dermal bones of the cheek can be identified. The opercle (figure 1 b , op) is a large rectangular bone with a long vertical axis, and resembles that of Allenypterus (Lund & Lund 1985; Forey 1998). The lower jaw of Holopterygius bears a long anterior ramus, a well-developed dorsal process at mid length, and another ramus posteriorly. The anterior arm of the lower jaw resembles the slender dentary of many early coelacanths (Lund & Lund 1985; Forey et al . 2000). Although the dentary of the intact jaw is preserved only as ...
Context 16
... probably precedes its first appearance (Harland et al . 1990). Therefore, the age of the fish beds is probably latest Givetian–earliest Frasnian ( ca 385 Ma; all dates in this article are from Gradstein et al . 2004). The skull roof of Holopterygius (figure 1 b , sr) is preserved primarily as an impression of its visceral surface, but intact areas are perforated by large, irregular pores for the supraorbital sensory canal. The premaxilla (figure 1 b , pmx) is squat and bears four large, irregularly shaped teeth. The dorsal surface of the splint-like parasphenoid (figure 1 b , psph) is exposed, and is marked by a well- developed hypophysial fossa. Much of the palate is visible (figure 1 b , pal), and it has the triangular shape characteristic of coelacanths (Forey 1998). The quadrate is preserved as a thickened region at the posteroventral corner of the palate, while a series of teeth along its ventral margin represent the remains of the ectopterygoid. A large, subspherical structure in the otic region is interpreted as an otolith (figure 1 b , ot; cf. Clack 1996). No dermal bones of the cheek can be identified. The opercle (figure 1 b , op) is a large rectangular bone with a long vertical axis, and resembles that of Allenypterus (Lund & Lund 1985; Forey 1998). The lower jaw of Holopterygius bears a long anterior ramus, a well-developed dorsal process at mid length, and another ramus posteriorly. The anterior arm of the lower jaw resembles the slender dentary of many early coelacanths (Lund & Lund 1985; Forey et al . 2000). Although the dentary of the intact jaw is preserved only as ...
Context 17
... probably precedes its first appearance (Harland et al . 1990). Therefore, the age of the fish beds is probably latest Givetian–earliest Frasnian ( ca 385 Ma; all dates in this article are from Gradstein et al . 2004). The skull roof of Holopterygius (figure 1 b , sr) is preserved primarily as an impression of its visceral surface, but intact areas are perforated by large, irregular pores for the supraorbital sensory canal. The premaxilla (figure 1 b , pmx) is squat and bears four large, irregularly shaped teeth. The dorsal surface of the splint-like parasphenoid (figure 1 b , psph) is exposed, and is marked by a well- developed hypophysial fossa. Much of the palate is visible (figure 1 b , pal), and it has the triangular shape characteristic of coelacanths (Forey 1998). The quadrate is preserved as a thickened region at the posteroventral corner of the palate, while a series of teeth along its ventral margin represent the remains of the ectopterygoid. A large, subspherical structure in the otic region is interpreted as an otolith (figure 1 b , ot; cf. Clack 1996). No dermal bones of the cheek can be identified. The opercle (figure 1 b , op) is a large rectangular bone with a long vertical axis, and resembles that of Allenypterus (Lund & Lund 1985; Forey 1998). The lower jaw of Holopterygius bears a long anterior ramus, a well-developed dorsal process at mid length, and another ramus posteriorly. The anterior arm of the lower jaw resembles the slender dentary of many early coelacanths (Lund & Lund 1985; Forey et al . 2000). Although the dentary of the intact jaw is preserved only as ...
Context 18
... probably precedes its first appearance (Harland et al . 1990). Therefore, the age of the fish beds is probably latest Givetian–earliest Frasnian ( ca 385 Ma; all dates in this article are from Gradstein et al . 2004). The skull roof of Holopterygius (figure 1 b , sr) is preserved primarily as an impression of its visceral surface, but intact areas are perforated by large, irregular pores for the supraorbital sensory canal. The premaxilla (figure 1 b , pmx) is squat and bears four large, irregularly shaped teeth. The dorsal surface of the splint-like parasphenoid (figure 1 b , psph) is exposed, and is marked by a well- developed hypophysial fossa. Much of the palate is visible (figure 1 b , pal), and it has the triangular shape characteristic of coelacanths (Forey 1998). The quadrate is preserved as a thickened region at the posteroventral corner of the palate, while a series of teeth along its ventral margin represent the remains of the ectopterygoid. A large, subspherical structure in the otic region is interpreted as an otolith (figure 1 b , ot; cf. Clack 1996). No dermal bones of the cheek can be identified. The opercle (figure 1 b , op) is a large rectangular bone with a long vertical axis, and resembles that of Allenypterus (Lund & Lund 1985; Forey 1998). The lower jaw of Holopterygius bears a long anterior ramus, a well-developed dorsal process at mid length, and another ramus posteriorly. The anterior arm of the lower jaw resembles the slender dentary of many early coelacanths (Lund & Lund 1985; Forey et al . 2000). Although the dentary of the intact jaw is preserved only as ...
Context 19
... probably precedes its first appearance (Harland et al . 1990). Therefore, the age of the fish beds is probably latest Givetian–earliest Frasnian ( ca 385 Ma; all dates in this article are from Gradstein et al . 2004). The skull roof of Holopterygius (figure 1 b , sr) is preserved primarily as an impression of its visceral surface, but intact areas are perforated by large, irregular pores for the supraorbital sensory canal. The premaxilla (figure 1 b , pmx) is squat and bears four large, irregularly shaped teeth. The dorsal surface of the splint-like parasphenoid (figure 1 b , psph) is exposed, and is marked by a well- developed hypophysial fossa. Much of the palate is visible (figure 1 b , pal), and it has the triangular shape characteristic of coelacanths (Forey 1998). The quadrate is preserved as a thickened region at the posteroventral corner of the palate, while a series of teeth along its ventral margin represent the remains of the ectopterygoid. A large, subspherical structure in the otic region is interpreted as an otolith (figure 1 b , ot; cf. Clack 1996). No dermal bones of the cheek can be identified. The opercle (figure 1 b , op) is a large rectangular bone with a long vertical axis, and resembles that of Allenypterus (Lund & Lund 1985; Forey 1998). The lower jaw of Holopterygius bears a long anterior ramus, a well-developed dorsal process at mid length, and another ramus posteriorly. The anterior arm of the lower jaw resembles the slender dentary of many early coelacanths (Lund & Lund 1985; Forey et al . 2000). Although the dentary of the intact jaw is preserved only as ...

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... 22:90 Coelacanths (Actinistia) are one of the most famous species-depauperate lineages. This clade diverged from other jawed vertebrates during the Silurian [3,29,30,43] and represents the living sister clade to all other sarcopterygians, or lobe-finned fishes [3,8,55]. Despite their historical notoriety as a species-poor, morphologically conservative lineage, the fossil record of coelacanths has shown that this clade diversified into a wide variety of morphologies in the ancient past [17,29,49]. ...
... This clade diverged from other jawed vertebrates during the Silurian [3,29,30,43] and represents the living sister clade to all other sarcopterygians, or lobe-finned fishes [3,8,55]. Despite their historical notoriety as a species-poor, morphologically conservative lineage, the fossil record of coelacanths has shown that this clade diversified into a wide variety of morphologies in the ancient past [17,29,49]. Fossil coelacanths show bursts of species diversity during the Devonian and Triassic [83] and achieved a high degree of body size variation ranging from diminutive species less than 5 cm long to 6 + m giants representing some of the largest freshwater fishes [18]. ...
... We also sampled an additional five specimens from the Old Granton Quarry in Bergen, New Jersey and examined a skull and partial skeleton of a large coelacanth collected in 1975 from the Solite Quarry site in North Carolina. Measurements made on this dataset using digital calipers were combined with measurement data from [29,70,72,76]. Together, this dataset represents the largest known collection of coelacanth material from a single region and time (Carnian-Norian, e.g., [45]). ...
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Background A major challenge to understanding how biodiversity has changed over time comes from depauperons, which are long-lived lineages with presently low species diversity. The most famous of these are the coelacanths. This clade of lobe-finned fishes occupies a pivotal position on the vertebrate tree between other fishes and tetrapods. Yet only two extant species and fewer than 100 extinct forms are known from the coelacanth fossil record, which spans over 400 million years of time. Although there is evidence for the existence of additional genetically isolated extant populations, a poor understanding of morphological disparity in this clade has made quantifying coelacanth species richness difficult. Results Here, we quantify variation in a sample of skulls and skeletons of the Triassic eastern North American coelacanth † Diplurus that represents the largest assemblage of coelacanth individuals known. Based on the results of these quantitative comparisons, we identify a diminutive new species and show that multiple lacustrine ecosystems in the Triassic rift lakes of the Atlantic coastline harbored at least three species of coelacanths spanning two orders of magnitude in size. Conclusions Conceptions about the distribution of species diversity on the tree of life may be fundamentally misguided when extant diversity is used to gauge signals of extinct diversity. Our results demonstrate how specimen-based assessments can be used to illuminate hidden biodiversity and show the utility of the fossil record for answering questions about the hidden richness of currently species-poor lineages.
... Rapid trophic divergence in the lungfish lineage. The major lineages of crown sarcopterygians first appear in the Early Devonian fossil records, leading to inferences of rapid evolutionary change in the early history of several groups [66][67][68] , including lungfishes 69 . Our quantitative analyses reinforce this hypothesis. ...
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Innovations relating to the consumption of hard prey are implicated in ecological shifts in marine ecosystems as early as the mid-Paleozoic. Lungfishes represent the first and longest-ranging lineage of durophagous vertebrates, but how and when the various feeding specializations of this group arose remain unclear. Two exceptionally preserved fossils of the Early Devonian lobe-finned fish Youngolepis reveal the origin of the specialized lungfish feeding mechanism. Youngolepis has a radically restructured palate, reorienting jaw muscles for optimal force transition, coupled with radiating entopterygoid tooth rows like those of lungfish toothplates. This triturating surface occurs in conjunction with marginal dentition and blunt coronoid fangs, suggesting a role in crushing rather than piercing prey. Bayesian tip-dating analyses incorporating these morphological data indicate that the complete suite of lungfish feeding specializations may have arisen in as little as 7 million years, representing one of the most striking episodes of innovation during the initial evolutionary radiations of bony fishes. It is unclear how Lungfishes evolved durophagy, the consumption of hard prey, despite being the longest lineage of vertebrates with this feeding mechanism. Here, the authors describe exceptionally preserved fossils of Youngolepis from the Early Devonian, showing early adaptations to durophagy.
... Only the question of evolutionary rate is addressed here, not the question of ancestral status or other "living fossil" characteristics attributed to coelacanths. The low rate of evolution based on a lasting generalist morphological Bauplan has been confirmed by most subsequent authors who have worked on the group (Schaeffer, 1952;Cloutier, 1991;Forey, 1998;Schultze, 2004;Zhu et al., 2012;Cavin and Guinot, 2014), knowing that there are also exceptions to this general Bauplan (e.g., Friedman and Coates, 2006;Wendruff and Wilson, 2012;Cavin et al., 2017). However, part of the community of researchers working on fossil and living coelacanths avoids using this expression. ...
... Molecular data have also revealed the existence of a putative third coelacanth species in Indonesia (Kadarusman et al., 2020). However, the supposed morphological stasis of coelacanths has been challenged by new fossil discoveries (Casane & Laurenti, 2013) that highlighted important differences in the skull, axial skeleton and internal organs throughout their evolutionary history (Brito et al., 2010;Cavin et al., 2017;Cupello et al., 2017;Forey, 1998;Friedman & Coates, 2006;Lund & Lund, 1984Wendruff & Wilson, 2012). ...
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... Ray-fins of this age are rare compared with their sarcopterygian contemporaries [4] and show limited morphological and functional variety relative to both coeval lobe-finned fishes [2] and post-Devonian ray-fins [38]. The handful of known Middle Devonian actinopterygians appear conservative when contrasted with sarcopterygians of this age, which include eellike coelacanths [39], lungfishes with diverse feeding adaptations [40] and tetrapod-like elpistostegalians [41]. ...
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... Only Forey (1998), Friedman andCoates (2006), Yabumoto (2008) and Zhu et al. (2012) perform complementary analyses bringing differential weights to the characters, using a posterior weighting according to the rescaled consistency index (successive weighting, Farris 1969). Forey (op. ...
... Character 7 corrected according to Friedman & Coates (2006). Character 31 corrected according to Clément (2005) and Forey in Friedman and Coates (2006). It must be noted that Gess & Coates (2015) propose an alternative scoring combining Porolepis and Glyptolepis (only modifying the scoring of character 7). ...
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... Long, 1999;Clement, 2019), and Europe (e.g. Cavin et al., 2005Cavin et al., , 2017Cavin et al., , 2020Friedman and Coates, 2006;Zaton et al., 2017;Renesto and Stockar, 2018). They also present an important ecological diversity, with for instance moderate to deep marine water habitats for Latimeria, Macropoma, Holophagus or Coelacanthus Cupello et al., 2019), freshwater habitats for Axelrodichthys, Indocoelacanthus or Mawsonia (Jain, 1974;Patterson, 1975;Poyato-Ariza et al., 1998;Soto et al., 2012;Cavin et al., 2020) or brackish waters for Mawsonia or Axelrodichthys (Dutel et al., 2014;Cupello et al., 2019). ...
... The main synapomorphy of Actinistia is the presence of an extracleithrum, a supernumerary dermal bone on the pectoral girdle Arratia and Schultze, 2015). In their early history, coelacanths had a rapid diversification (Friedman and Coates, 2006). Devonian coelacanths as Miguashaia, Gavinia and Styloichthys possess plesiomorphic characters for sarcopterygians such as a heterocercal tail or an elongate post-orbital portion of the skull Zhu et al., 2012). ...
... Coelacanths are well represented in the fossil record, with about 40 described genera and more than 130 species . The clade also presents an important diversity of form, size and ecology Friedman and Coates, 2006;Casane and Laurenti, 2013;Cavin et al., 2017), and was considered to have gone extinct at the end of the Mesozoic Era . ...
Thesis
Among the sarcopterygians, the clade of coelacanths (Actinistia) is today only represented by the coelacanth genus Latimeria, and is the sister-taxa of the clade lungfish + tetrapods. Based on their phylogenetic position and their ecology, they are considered as a good model to study the fin-to-limb transition. However, it is necessary to have a good understanding of the skeletal and muscular anatomy of their paired fins before to infer their role in the fin-to-limb transition. As in other jawed vertebrates, we showed that the development of the pectoral fins occurs earlier than that of the paired fins. The development of the radial elements around the metapterygial axis of the fin occurs by the fragmentation of the associated mesomere, as observe in lungfish. We also highlighted by the development of a superficial ossification of the anterior part of the pelvic girdle, associated with a trabecular system in the adult. This trabecular system and this ossification permit to resist to the important constraints developed by the muscles inserted on this part of the girdle. The study of the muscular anatomy showed a more complex anatomy than previously known, with that of the pelvic fin that seems more plesiomorphic than that of the pectoral fin. Indeed, the muscles of the pelvic fin run from the girdle to the fin rays, whereas on the pectoral fin, majority of the muscles insert on the endoskeletal elements, as in lungfish and tetrapods. Moreover, the pectoral fin is stronger than the pelvic fin, that indicates a more important role for the locomotion. The joint mobility of the pectoral and pelvic fins was also studied, after complete dissections of the fins. We showed that the pectoral fin has a greater mobility than the pelvic fin. This difference of mobility is due to the morphology of the mesomeres on the pelvic fin, with pre-axial radial element on a more proximo-lateral position than that of the pectoral fin. Finally, we made a preliminary study on the evolution of the muscle architecture during the fin-to-limb transition. It appears that the muscle mass and force are more important in tetrapod than in fish, relative to the body size. The limbs need to produce more force than fins, since they are the principal locomotor force generator. In fishes however, the propulsion is mainly produced by the lateral undulation of the body and the caudal fin. Thus the paired fins don’t need to produce a large amount of force. The hind limbs of tetrapods are also more powerful than the pelvic fins of fishes, relative to the pectoral appendages, what supports the hypothesis of a locomotor shift during the fin-to-limb transition.
... Coelacanths are well represented in the fossil record, with about 40 described genera and more than 130 species (Forey, 1998). The clade also presents an important diversity of form, size and ecology (Forey, 1998;Friedman & Coates, 2006;Casane & Laurenti, 2013;Cavin & Guinot, 2014;Cavin et al., 2017), and was considered to have become extinct at the end of the Mesozoic era (Smith, 1939). Today, there are two known species: Latimeria chalumnae (Smith, 1939) in the western Indian Ocean and L. menadoensis (Erdmann et al., 1998;Pouyaud et al., 1999), discovered offshore of Sulawesi, Indonesia. ...
Article
The monobasal pectoral fins of living coelacanths and lungfishes are homologous to the forelimbs of tetrapods and are thus critical to investigate the origin thereof. However, it remains unclear whether the similarity in the asymmetrical endoskeletal arrangement of the pectoral fins of coelacanths reflects the evolution of the pectoral appendages in sarcopterygians. Here, we describe for the first time the development of the pectoral fin and shoulder girdle in the extant coelacanth Latimeria chalumnae, based on the tomographic acquisition of a growth series. The pectoral girdle and pectoral fin endoskeleton are formed early in development with a radially outward growth of the endoskeletal elements. The visualization of the pectoral girdle during development shows a reorientation of the girdle between the fetus and pup 1 stages, creating a contact between the scapulocoracoids and the clavicles in the ventro-medial region. Moreover, we observed a splitting of the pre- and post-axial cartilaginous plates in respectively pre-axial radials and accessory elements on one hand, and in post-axial accessory elements on the other hand. However, the mechanisms involved in the splitting of the cartilaginous plates appear different from those involved in the formation of radials in actinopterygians. Our results show a proportional reduction of the proximal pre-axial radial of the fin, rendering the external morphology of the fin more lobe-shaped, and a spatial reorganization of elements resulting from the fragmentation of the two cartilaginous plates. Latimeria development hence supports previous interpretations of the asymmetrical pectoral fin skeleton as being plesiomorphic for coelacanths and sarcopterygians.
... Morphological disparity of post-Devonian actinistians is considered as comparatively low compared to other clades (SCHAEFFER, 1952;CLOUTIER, 1991;FOREY, 1998;SCHULTZE, 2004;FRIEDMAN and COATES, 2006;CAVIN and GUINOT, 2014). Moreover, it has been suggested that intraspecific polymorphism is high in mawsoniid species. ...
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Mawsoniids is a well-defined family of Mesozoic coelacanths ranging from the Late Triassic to the Late Cretaceous. They dwelled in marine and freshwater environments, and most species are characterized by the presence of ossified ribs, coarse rugosities of the dermatocranium and cheek bones, spiracular and suboperculum usually absent, and reduction or loss of the descending process of the supratemporal, as well as by a large body size. Although relatively abundant in some localities in South America and Africa, the phylogenetic relationships among the species are still poorly understood. Here, we propose for the first time a species-level phylogeny of the mawsoniids, and we discuss its implications on the evolutionary history of the clade. This evolutionary history can be divided into two main episodes: a Triassic episode that occurred mostly in North America and a Western Gondwanan early Cretaceous episode that occurred mostly on Western Gondwana with a Late Cretaceous European extension. The Jurassic has yielded few mawsoniid remains, except the marine Trachymetopon, whose place in this evolutionary history remains to be understood. Other problematic taxa in this scheme, either for their age or for their phylogenetic relationships, are Parnaibaia and “Mawsonia” lavocati. Lualabaea is closely related, or possibly co-generic with Axelrodichthys. This analysis highlights the rich evolutionary history of this clade, and proposes some biogeographic patterns composed of both vicariant and dispersal events.
... Recently, the slow evolutionary pace of actinistians was questioned by Casane and Laurenti (2013), who found no evidence of slowly evolving genome and morphology compared to other groups of vertebrates. The latter statement contradicts studies, which have shown that the rate of morphological evolution of the actinistians is comparatively slow (Schaeffer, 1952;Cloutier, 1991;Forey, 1998;Schultze, 2004;Friedman and Coates, 2006;Cavin and Guinot, 2014). Does this lineage evolve more slowly than others? ...
Article
Latimeria chalumnae (Actinistia) was regarded as the ‘ancestor of the four-legged vertebrates’ and rapidly became the iconic example of a ‘living fossil’. Although its evolutionary position close to the origin of tetrapods is now dismissed, the question of its evolutionary pace is still a matter of debate. The UNESCOs’ World Heritage Monte San Giorgio Triassic site, spanning the border between Italy and Switzerland in the Southern Alps, has yielded one of the major marine vertebrate assemblages of the Middle Triassic worldwide. This general overview of the Middle Triassic coelacanths from Switzerland heralds a project that will be conducted in the following years. The project consists firstly to prepare, describe and compare the coelacanth material from the Besano Formation housed in the collection of the University of Zurich.