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An Extremely Peramorphic Newt (Urodela: Salamandridae: Pleurodelini) from the Latest Oligocene of Germany, and a New Phylogenetic Analysis of Extant and Extinct Salamandrids.

Marjanović D, Witzmann F - PLoS ONE (2015)

Bottom Line: Referral to a species would require a revision of the genus, but the specimen likely does not belong to the type species.The Miocene "Triturus" roehrsi is found neither with the extant Ommatotriton nor with Lissotriton, but inside an Asian/aquatic clade or, when geographic distribution is included as a character, as the sister-group to all other European molgins.The main cause for discrepancies between the results and the molecular consensus is not heterochrony, but adaptations to a life in mountain streams; this is the most likely reason why the Paleocene Koalliella from western Europe forms the sister-group to some or all of the most aquatic extant newts in different analyses.

View Article: PubMed Central - PubMed

Affiliation: Museum für Naturkunde, Leibniz Institute for Evolutionary and Biodiversity Research, Humboldt University, Berlin, Germany.

ABSTRACT
We describe an Oligocene newt specimen from western Germany that has gone practically unnoticed in the literature despite having been housed in the Museum für Naturkunde (Berlin) for a century. It is referable to the coeval Chelotriton, but is unusually peramorphic; for many characters it is more peramorphic than all other caudates or even all other lissamphibians. Most noticeable are the position of the jaw joints far caudal to the occiput, the honeycombed sculpture on the maxilla, and the possible presence of a septomaxilla (which would be unique among salamandrids). Referral to a species would require a revision of the genus, but the specimen likely does not belong to the type species. A phylogenetic analysis of nonmolecular characters of Salamandridae, far larger than all predecessors, confirms the referral to Chelotriton. It further loosely associates the Oligocene Archaeotriton and the Miocene Carpathotriton with the extant Lissotriton, though the former may alternatively lie outside Pleurodelinae altogether. The Miocene? I. randeckensis may not belong to the extant Ichthyosaura. The Miocene "Triturus" roehrsi is found neither with the extant Ommatotriton nor with Lissotriton, but inside an Asian/aquatic clade or, when geographic distribution is included as a character, as the sister-group to all other European molgins. The main cause for discrepancies between the results and the molecular consensus is not heterochrony, but adaptations to a life in mountain streams; this is the most likely reason why the Paleocene Koalliella from western Europe forms the sister-group to some or all of the most aquatic extant newts in different analyses. We would like to urge neontologists working on salamandrids to pay renewed attention to the skeleton, not limited to the skull, as a source of diagnostic and phylogenetically informative characters.

No MeSH data available.


Right postorbital opening (supratemporal fenestra) and surroundings of MB.Am.45.Photograph of MB.Am.45.3 taken by holding a camera to an ocular of a binocular microscope, showing the diversity of sculpture around the postorbital opening. Anterior is to the left. Note how little space remains (covered by a prominent break) for an unsculptured trough on the right parietal that would have connected the posteromedial corner of the postorbital opening to the posterior margin of the skull and would have allowed jaw-closing muscles passing through the fenestra to attach to neural spines. Abbreviations: l., left; r., right; f, frontal; m, maxilla; ort, orbitotemporal fenestra; p, parietal; po, postorbital opening (supratemporal fenestra); pt?, probable pterygoid; qj-q, quadratojugal-quadrate bone; sq, squamosal.
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pone.0137068.g011: Right postorbital opening (supratemporal fenestra) and surroundings of MB.Am.45.Photograph of MB.Am.45.3 taken by holding a camera to an ocular of a binocular microscope, showing the diversity of sculpture around the postorbital opening. Anterior is to the left. Note how little space remains (covered by a prominent break) for an unsculptured trough on the right parietal that would have connected the posteromedial corner of the postorbital opening to the posterior margin of the skull and would have allowed jaw-closing muscles passing through the fenestra to attach to neural spines. Abbreviations: l., left; r., right; f, frontal; m, maxilla; ort, orbitotemporal fenestra; p, parietal; po, postorbital opening (supratemporal fenestra); pt?, probable pterygoid; qj-q, quadratojugal-quadrate bone; sq, squamosal.

Mentions: The massive, broad-parabolic skull (Figs 4–8) is heavily ossified. It measures 18 mm in midline length (measured from the tip of the premaxillae to the posterior end of the parietals) and 35 mm in width (measured as the minimum distance between the lateral edges of the quadratojugal-quadrate bones). Thus, with a width-to-length ratio of 1.94, the skull is proportionally much broader than that of contemporary salamandrids like Brachycormus with a ratio of 0.96–1.07 [4] and other Chelotriton specimens with a ratio of 1.20–1.40 ([4]; 1.55 in the specimen illustrated in fig 2a5 of [29]). In Palaeopleurodeles, the type specimen has a skull which is broader than long, but this can be partially attributed to crushing and is not as pronounced as in MB.Am.45 [10], whereas the referred specimen [11] has a skull that is slightly longer than broad. Among extant pleurodelines, Pleurodeles [40], Tylototriton and Echinotriton [8] have skulls that are broader than long, but proportionally still more slender than in MB.Am.45. The quadratojugal-quadrate bones (see below) extend unusually far posteriorly and form long, slender quadrate condyles located far posterior to the skull table and the occiput (Fig 8). This character is unique among salamandrids and even among caudates, in which the quadrate condyles (forming the jaw articulation) are usually located anterior to or at the same level as the occiput [4,41]. In some specimens of Chelotriton, they lie slightly caudal to the occiput–never (to our knowledge) as far as in MB.Am.45 [24,29]. The considerably smaller Salamandra “laticeps” may come closer, but lacks the caudal projections of the quadratojugal-quadrate bones beyond the squamosals; its suspensoria are caudally rounded ([21]: plate VIII fig 2 = [4]: fig 16A). The caudal margin of the skull roof between the quadrate condyles is concave, because the caudal margins of the squamosals are inclined rostromedially to caudolaterally–the opposite is normally the case in salamanders–to connect the parietals to the quadratojugal-quadrate bones (Fig 8). On the right half of the skull, the skull-roofing bones are articulated and well discernible; on the left side, they are partially obscured by matrix. The dermal skull bones show pronounced, but regular dermal sculpture (or ornament) which is tubercular, except on the maxilla and possibly the premaxilla, where deep pits and tall ridges form “honeycombs” as seen in Palaeozoic temnospondyls [42] as well as in Chelotriton robustus [4,17]. Other Chelotriton specimens have a less regular and coarser tubercular sculpture ([13,19,32,39]; [29]: figs 2a5, 2b1). Prominent crests as in Tylototriton or Echinotriton [8] are absent. The dermal sculpture of MB.Am.45 (Figs 8–11) is described for each skull bone separately below. The external naris is a small, elongate-ovate opening, with the longitudinal axis directed anteromedially. It is bordered anteriorly by the premaxilla, posteromedially by a bone of unclear identity (see below), posteriorly by the nasal, and laterally by the alary process of the maxilla. The orbitotemporal fenestrae (or orbits) are large and directed anteromedially, measuring approximately 14 mm in length and approximately 5 mm in maximum width. They are bordered by the maxilla anterolaterally and laterally, the quadratojugal-quadrate bone posterolaterally, the squamosal posteriorly and posteromedially, the frontal medially and the prefrontal anteromedially. The frontosquamosal bar or arch (arcus frontotemporalis) is well developed and unusually broad, almost attaining the width of the orbitotemporal fenestra. Its width is at least comparable to that of the highly ossified skulls commonly referred to Chelotriton paradoxus ([22]: fig 4a; [29]: figs 2a5, 2b1), clearly surpassing Tylototriton and Echinotriton ([8]: fig 1), and much larger than in Brachycormus ([4]: fig 20; [14]). A small, squarish postorbital opening (or supratemporal fenestra) is separated from the orbitotemporal fenestra by the frontosquamosal bar; the opening is bordered anteriorly by the frontal, laterally and posterolaterally by the squamosal and posteriorly and medially by the parietal. It is proportionally smaller than in any other pleurodeline, extant or extinct. The interorbital width cannot be measured with accuracy because the outline of the left orbitotemporal fenestra is not preserved. However, the shortest distance between the medial margin of the fenestra and the interfrontal suture is approximately 7 mm, thus indicating an interorbital width of about 14 mm and a ratio of interorbital width to skull length of 0.78. In the large skull figured in fig 2a5 of [29] (referred to C. paradoxus), the ratio is 0.54, and in the Brachycormus skull illustrated as: fig 20a of [4] it is 0.51.


An Extremely Peramorphic Newt (Urodela: Salamandridae: Pleurodelini) from the Latest Oligocene of Germany, and a New Phylogenetic Analysis of Extant and Extinct Salamandrids.

Marjanović D, Witzmann F - PLoS ONE (2015)

Right postorbital opening (supratemporal fenestra) and surroundings of MB.Am.45.Photograph of MB.Am.45.3 taken by holding a camera to an ocular of a binocular microscope, showing the diversity of sculpture around the postorbital opening. Anterior is to the left. Note how little space remains (covered by a prominent break) for an unsculptured trough on the right parietal that would have connected the posteromedial corner of the postorbital opening to the posterior margin of the skull and would have allowed jaw-closing muscles passing through the fenestra to attach to neural spines. Abbreviations: l., left; r., right; f, frontal; m, maxilla; ort, orbitotemporal fenestra; p, parietal; po, postorbital opening (supratemporal fenestra); pt?, probable pterygoid; qj-q, quadratojugal-quadrate bone; sq, squamosal.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4589347&req=5

pone.0137068.g011: Right postorbital opening (supratemporal fenestra) and surroundings of MB.Am.45.Photograph of MB.Am.45.3 taken by holding a camera to an ocular of a binocular microscope, showing the diversity of sculpture around the postorbital opening. Anterior is to the left. Note how little space remains (covered by a prominent break) for an unsculptured trough on the right parietal that would have connected the posteromedial corner of the postorbital opening to the posterior margin of the skull and would have allowed jaw-closing muscles passing through the fenestra to attach to neural spines. Abbreviations: l., left; r., right; f, frontal; m, maxilla; ort, orbitotemporal fenestra; p, parietal; po, postorbital opening (supratemporal fenestra); pt?, probable pterygoid; qj-q, quadratojugal-quadrate bone; sq, squamosal.
Mentions: The massive, broad-parabolic skull (Figs 4–8) is heavily ossified. It measures 18 mm in midline length (measured from the tip of the premaxillae to the posterior end of the parietals) and 35 mm in width (measured as the minimum distance between the lateral edges of the quadratojugal-quadrate bones). Thus, with a width-to-length ratio of 1.94, the skull is proportionally much broader than that of contemporary salamandrids like Brachycormus with a ratio of 0.96–1.07 [4] and other Chelotriton specimens with a ratio of 1.20–1.40 ([4]; 1.55 in the specimen illustrated in fig 2a5 of [29]). In Palaeopleurodeles, the type specimen has a skull which is broader than long, but this can be partially attributed to crushing and is not as pronounced as in MB.Am.45 [10], whereas the referred specimen [11] has a skull that is slightly longer than broad. Among extant pleurodelines, Pleurodeles [40], Tylototriton and Echinotriton [8] have skulls that are broader than long, but proportionally still more slender than in MB.Am.45. The quadratojugal-quadrate bones (see below) extend unusually far posteriorly and form long, slender quadrate condyles located far posterior to the skull table and the occiput (Fig 8). This character is unique among salamandrids and even among caudates, in which the quadrate condyles (forming the jaw articulation) are usually located anterior to or at the same level as the occiput [4,41]. In some specimens of Chelotriton, they lie slightly caudal to the occiput–never (to our knowledge) as far as in MB.Am.45 [24,29]. The considerably smaller Salamandra “laticeps” may come closer, but lacks the caudal projections of the quadratojugal-quadrate bones beyond the squamosals; its suspensoria are caudally rounded ([21]: plate VIII fig 2 = [4]: fig 16A). The caudal margin of the skull roof between the quadrate condyles is concave, because the caudal margins of the squamosals are inclined rostromedially to caudolaterally–the opposite is normally the case in salamanders–to connect the parietals to the quadratojugal-quadrate bones (Fig 8). On the right half of the skull, the skull-roofing bones are articulated and well discernible; on the left side, they are partially obscured by matrix. The dermal skull bones show pronounced, but regular dermal sculpture (or ornament) which is tubercular, except on the maxilla and possibly the premaxilla, where deep pits and tall ridges form “honeycombs” as seen in Palaeozoic temnospondyls [42] as well as in Chelotriton robustus [4,17]. Other Chelotriton specimens have a less regular and coarser tubercular sculpture ([13,19,32,39]; [29]: figs 2a5, 2b1). Prominent crests as in Tylototriton or Echinotriton [8] are absent. The dermal sculpture of MB.Am.45 (Figs 8–11) is described for each skull bone separately below. The external naris is a small, elongate-ovate opening, with the longitudinal axis directed anteromedially. It is bordered anteriorly by the premaxilla, posteromedially by a bone of unclear identity (see below), posteriorly by the nasal, and laterally by the alary process of the maxilla. The orbitotemporal fenestrae (or orbits) are large and directed anteromedially, measuring approximately 14 mm in length and approximately 5 mm in maximum width. They are bordered by the maxilla anterolaterally and laterally, the quadratojugal-quadrate bone posterolaterally, the squamosal posteriorly and posteromedially, the frontal medially and the prefrontal anteromedially. The frontosquamosal bar or arch (arcus frontotemporalis) is well developed and unusually broad, almost attaining the width of the orbitotemporal fenestra. Its width is at least comparable to that of the highly ossified skulls commonly referred to Chelotriton paradoxus ([22]: fig 4a; [29]: figs 2a5, 2b1), clearly surpassing Tylototriton and Echinotriton ([8]: fig 1), and much larger than in Brachycormus ([4]: fig 20; [14]). A small, squarish postorbital opening (or supratemporal fenestra) is separated from the orbitotemporal fenestra by the frontosquamosal bar; the opening is bordered anteriorly by the frontal, laterally and posterolaterally by the squamosal and posteriorly and medially by the parietal. It is proportionally smaller than in any other pleurodeline, extant or extinct. The interorbital width cannot be measured with accuracy because the outline of the left orbitotemporal fenestra is not preserved. However, the shortest distance between the medial margin of the fenestra and the interfrontal suture is approximately 7 mm, thus indicating an interorbital width of about 14 mm and a ratio of interorbital width to skull length of 0.78. In the large skull figured in fig 2a5 of [29] (referred to C. paradoxus), the ratio is 0.54, and in the Brachycormus skull illustrated as: fig 20a of [4] it is 0.51.

Bottom Line: Referral to a species would require a revision of the genus, but the specimen likely does not belong to the type species.The Miocene "Triturus" roehrsi is found neither with the extant Ommatotriton nor with Lissotriton, but inside an Asian/aquatic clade or, when geographic distribution is included as a character, as the sister-group to all other European molgins.The main cause for discrepancies between the results and the molecular consensus is not heterochrony, but adaptations to a life in mountain streams; this is the most likely reason why the Paleocene Koalliella from western Europe forms the sister-group to some or all of the most aquatic extant newts in different analyses.

View Article: PubMed Central - PubMed

Affiliation: Museum für Naturkunde, Leibniz Institute for Evolutionary and Biodiversity Research, Humboldt University, Berlin, Germany.

ABSTRACT
We describe an Oligocene newt specimen from western Germany that has gone practically unnoticed in the literature despite having been housed in the Museum für Naturkunde (Berlin) for a century. It is referable to the coeval Chelotriton, but is unusually peramorphic; for many characters it is more peramorphic than all other caudates or even all other lissamphibians. Most noticeable are the position of the jaw joints far caudal to the occiput, the honeycombed sculpture on the maxilla, and the possible presence of a septomaxilla (which would be unique among salamandrids). Referral to a species would require a revision of the genus, but the specimen likely does not belong to the type species. A phylogenetic analysis of nonmolecular characters of Salamandridae, far larger than all predecessors, confirms the referral to Chelotriton. It further loosely associates the Oligocene Archaeotriton and the Miocene Carpathotriton with the extant Lissotriton, though the former may alternatively lie outside Pleurodelinae altogether. The Miocene? I. randeckensis may not belong to the extant Ichthyosaura. The Miocene "Triturus" roehrsi is found neither with the extant Ommatotriton nor with Lissotriton, but inside an Asian/aquatic clade or, when geographic distribution is included as a character, as the sister-group to all other European molgins. The main cause for discrepancies between the results and the molecular consensus is not heterochrony, but adaptations to a life in mountain streams; this is the most likely reason why the Paleocene Koalliella from western Europe forms the sister-group to some or all of the most aquatic extant newts in different analyses. We would like to urge neontologists working on salamandrids to pay renewed attention to the skeleton, not limited to the skull, as a source of diagnostic and phylogenetically informative characters.

No MeSH data available.