Schoch, R. R., and J. B. Desojo. 2016. Cranial anatomy of the aetosaur Paratypothorax andressorum Long & Ballew, 1985, from the Upper Triassic of Germany and its bearing on aetosaur phylogeny. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 279(1):73-95. DOI: http://dx.doi.org/10.1127/njgpa/2016/0542
http://www.ingentaconnect.com/content/schweiz/njbgeol/2016/00000279/00000001/art00008
Abstract - The large aetosaur Paratypothorax andressorum has so far been known only by its osteoderms. Here we describe for the first time the skull of a complete, articulated specimen of this taxon that was found in the type horizon at Murrhardt, southwestern Germany. Paratypothorax
andressorum has the following cranial autapomorphies: (1) upper jaw margin with deep notch between premaxilla and maxilla, (2) maxilla-lacrimal suture with finger-like projection, (3) upper
temporal fenestra triangular, and (4) first paramedian cervical osteoderms narrow and oval, much smaller than second row. Apart from these features, the skull of P. andressorum closely resembles that of the small aetosaur Aetosaurus ferratus known from the same horizons, despite major differences in the morphology of osteoderms. Both taxa share (1) the pointed, beak-shaped premaxilla which expands only gently anterior to the nasal, (2) maxilla and lacrimal excluding jugal
from margin of antorbital fenestra, (3) exclusion of squamosal from margin of infratemporal fenestra, and (4) posterior part of jugal not downturned. Phylogenetic analysis reveals poorly resolved relationships within Aetosauria, but exclusion of a problematic taxon Coahomasuchus results in a much better resolution, with Paratypothorax to nest with Rioarribasuchus, Tecovasuchus, Typothorax, and Redondasuchus within a monophyletic Typothoracinae. Interestingly, Aetosaurus and Stenomyti form successive sister taxa of this clade rather than fall within an aetosaurine grade of basal aetosaurs, as suggested by previous authors. The resemblance of Paratypothorax and Aetosaurus in many cranial features, their close relationship as suggested by the present analysis, and the immature state of all available Aetosaurus specimens suggest two new alternative hypotheses: (1) Aetosaurus is the juvenile of a close relative of Paratypothorax or (2) it is itself the juvenile of Paratypothorax.
Showing posts with label phylogenetic analysis. Show all posts
Showing posts with label phylogenetic analysis. Show all posts
Redescription of the Middle Triassic Diapsid Megachirella wachtleri, an Early Branching Lepidosauromorph
Renesto, S., and M. Bernardi. 2013. Redescription and phylogenetic relationships of Megachirella wachtleri Renesto et Posenato, 2003 (Reptilia, Diapsida). Paläontologische Zeitschrift. DOI: 10.1007/s12542-013-0194-0
Abstract - Megachirella wachtleri Renesto et Posenato, 2003, a well preserved partial reptile skeleton from the Middle Triassic of the Dolomites (N. Italy), was originally considered a lepidosauromorph, but no phylogenetic analysis was carried out. Consequently, the taxon was overlooked in later phylogenetic analyses of the Diapsida. Here, the holotype and only known specimen of M. wachtleri is redescribed, allowing an investigation of its phylogenetic relationships. Phylogenetic analyses confirm that Megachirella is a lepidosauromorph close to the crown group lepidosaurs (Squamata + Rhynchocephalia). Megachirella enhances our knowledge of the series of morphological modifications that led to the origin of the Lepidosauria, the most diverse clade of extant reptiles.
Abstract - Megachirella wachtleri Renesto et Posenato, 2003, a well preserved partial reptile skeleton from the Middle Triassic of the Dolomites (N. Italy), was originally considered a lepidosauromorph, but no phylogenetic analysis was carried out. Consequently, the taxon was overlooked in later phylogenetic analyses of the Diapsida. Here, the holotype and only known specimen of M. wachtleri is redescribed, allowing an investigation of its phylogenetic relationships. Phylogenetic analyses confirm that Megachirella is a lepidosauromorph close to the crown group lepidosaurs (Squamata + Rhynchocephalia). Megachirella enhances our knowledge of the series of morphological modifications that led to the origin of the Lepidosauria, the most diverse clade of extant reptiles.
Two New Temnospondyl Papers - Phylogeny of Major Clades and Suction Feeding in Gerrothorax
Schoch, R. R. 2013. The evolution of major temnospondyl clades: an inclusive phylogenetic analysis. Journal of Systematic Palaeontology DOI:10.1080/14772019.2012.699006http://www.tandfonline.com/doi/full/10.1080/14772019.2012.699006
Abstract - Phylogenetic analysis of a large dataset (72 taxa, 212 characters) focuses on the in-group relationships of temnospondyls, the largest lower tetrapod clade. Representatives of all clades and grades were considered, spanning the entire stratigraphical range of temnospondyls from the Early Carboniferous through to the Early Cretaceous. Several major groups are defined phylogenetically (node or branch-based) rather than by apomorphies. The following groups were unequivocally found to be monophyletic: Edopoidea (node), Dvinosauria (stem, excl. Brachyopidae), Dissorophoidea (node), Eryopidae (stem), and Stereospondyli (node). The latter encompass three well-defined, branch-based taxa: Rhinesuchidae, Trematosauria and Capitosauria. Trematosauria (stem) contain Trematosauroidea (node), which includes the classic trematosaurids, metoposaurids, and possibly part of the rhytidosteids (Peltostega) but their in-group relationships remain unsettled; most other short-snouted stereospondyls (chigutisaurids, brachyopids, Laidleria and the plagiosaurids) are probably monophyletic and likely nest in some form with trematosauroids. Capitosauria (stem) include the Capitosauroidea (node) spanned by Parotosuchus and Mastodonsaurus, with the successive stem taxa Edingerella, Benthosuchus, Wetlugasaurus and Watsonisuchus. In all variant analyses, edopoids form the basalmost temnospondyl clade, followed by a potential clade (or grade) of small terrestrial taxa containing Balanerpeton and Dendrerpeton (‘Dendrerpetontidae’). All taxa higher than Edopoidea are suggested to form the monophyletic stem taxon Eutemnospondyli, tax. nov. The remainder of Temnospondyli fall into four robust and undisputed clades: (1) Dvinosauria; (2) Zatracheidae plus Dissorophoidea; (3) Eryopidae; and (4) Stereospondyli. These taxa are together referred to as Rhachitomi (node). Eryopidae and Stereospondylomorpha are probably monophyletic, here referred to as Eryopiformes (tax. nov.). The position of Dissorophoidea + Zatracheidae is still ambiguous; it may either form the sister taxon of Dvinosauria, or nest between Dvinosauria and Eryopiformes, whereas there is no support for Euskelia (Dissorophoidea + Eryopidae) after basal taxa of each clade are better understood.
Witzmann, F. and R. R. Schoch. 2012. Reconstruction of cranial and hyobranchial muscles in the Triassic temnospondyl Gerrothorax provides evidence for akinetic suction feeding. Journal of Morphology DOI: 10.1002/jmor.20113 http://onlinelibrary.wiley.com/doi/10.1002/jmor.20113/abstract
Abstract - The cranial and hyobranchial muscles of the Triassic temnospondyl Gerrothorax have been reconstructed based on direct evidence (spatial limitations, ossified muscle insertion sites on skull, mandible, and hyobranchium) and on phylogenetic reasoning (with extant basal actinopterygians and caudates as bracketing taxa). The skeletal and soft-anatomical data allow the reconstruction of the feeding strike of this bottom-dwelling, aquatic temnospondyl. The orientation of the muscle scars on the postglenoid area of the mandible indicates that the depressor mandibulae was indeed used for lowering the mandible and not to raise the skull as supposed previously and implies that the skull including the mandible must have been lifted off the ground during prey capture. It can thus be assumed that Gerrothorax raised the head toward the prey with the jaws still closed. Analogous to the bracketing taxa, subsequent mouth opening was caused by action of the strong epaxial muscles (further elevation of the head) and the depressor mandibulae and rectus cervicis (lowering of the mandible). During mouth opening, the action of the rectus cervicis muscle also rotated the hyobranchial apparatus ventrally and caudally, thus expanding the buccal cavity and causing the inflow of water with the prey through the mouth opening. The strongly developed depressor mandibulae and rectus cervicis, and the well ossified, large quadrate-articular joint suggest that this action occurred rapidly and that powerful suction was generated. Also, the jaw adductors were well developed and enabled a rapid mouth closure. In contrast to extant caudate larvae and most extant actinopterygians (teleosts), no cranial kinesis was possible in the Gerrothorax skull, and therefore suction feeding was not as elaborate as in these extant forms. This reconstruction may guide future studies of feeding in extinct aquatic tetrapods with ossified hyobranchial apparatus.
Abstract - Phylogenetic analysis of a large dataset (72 taxa, 212 characters) focuses on the in-group relationships of temnospondyls, the largest lower tetrapod clade. Representatives of all clades and grades were considered, spanning the entire stratigraphical range of temnospondyls from the Early Carboniferous through to the Early Cretaceous. Several major groups are defined phylogenetically (node or branch-based) rather than by apomorphies. The following groups were unequivocally found to be monophyletic: Edopoidea (node), Dvinosauria (stem, excl. Brachyopidae), Dissorophoidea (node), Eryopidae (stem), and Stereospondyli (node). The latter encompass three well-defined, branch-based taxa: Rhinesuchidae, Trematosauria and Capitosauria. Trematosauria (stem) contain Trematosauroidea (node), which includes the classic trematosaurids, metoposaurids, and possibly part of the rhytidosteids (Peltostega) but their in-group relationships remain unsettled; most other short-snouted stereospondyls (chigutisaurids, brachyopids, Laidleria and the plagiosaurids) are probably monophyletic and likely nest in some form with trematosauroids. Capitosauria (stem) include the Capitosauroidea (node) spanned by Parotosuchus and Mastodonsaurus, with the successive stem taxa Edingerella, Benthosuchus, Wetlugasaurus and Watsonisuchus. In all variant analyses, edopoids form the basalmost temnospondyl clade, followed by a potential clade (or grade) of small terrestrial taxa containing Balanerpeton and Dendrerpeton (‘Dendrerpetontidae’). All taxa higher than Edopoidea are suggested to form the monophyletic stem taxon Eutemnospondyli, tax. nov. The remainder of Temnospondyli fall into four robust and undisputed clades: (1) Dvinosauria; (2) Zatracheidae plus Dissorophoidea; (3) Eryopidae; and (4) Stereospondyli. These taxa are together referred to as Rhachitomi (node). Eryopidae and Stereospondylomorpha are probably monophyletic, here referred to as Eryopiformes (tax. nov.). The position of Dissorophoidea + Zatracheidae is still ambiguous; it may either form the sister taxon of Dvinosauria, or nest between Dvinosauria and Eryopiformes, whereas there is no support for Euskelia (Dissorophoidea + Eryopidae) after basal taxa of each clade are better understood.
Witzmann, F. and R. R. Schoch. 2012. Reconstruction of cranial and hyobranchial muscles in the Triassic temnospondyl Gerrothorax provides evidence for akinetic suction feeding. Journal of Morphology DOI: 10.1002/jmor.20113 http://onlinelibrary.wiley.com/doi/10.1002/jmor.20113/abstract
Abstract - The cranial and hyobranchial muscles of the Triassic temnospondyl Gerrothorax have been reconstructed based on direct evidence (spatial limitations, ossified muscle insertion sites on skull, mandible, and hyobranchium) and on phylogenetic reasoning (with extant basal actinopterygians and caudates as bracketing taxa). The skeletal and soft-anatomical data allow the reconstruction of the feeding strike of this bottom-dwelling, aquatic temnospondyl. The orientation of the muscle scars on the postglenoid area of the mandible indicates that the depressor mandibulae was indeed used for lowering the mandible and not to raise the skull as supposed previously and implies that the skull including the mandible must have been lifted off the ground during prey capture. It can thus be assumed that Gerrothorax raised the head toward the prey with the jaws still closed. Analogous to the bracketing taxa, subsequent mouth opening was caused by action of the strong epaxial muscles (further elevation of the head) and the depressor mandibulae and rectus cervicis (lowering of the mandible). During mouth opening, the action of the rectus cervicis muscle also rotated the hyobranchial apparatus ventrally and caudally, thus expanding the buccal cavity and causing the inflow of water with the prey through the mouth opening. The strongly developed depressor mandibulae and rectus cervicis, and the well ossified, large quadrate-articular joint suggest that this action occurred rapidly and that powerful suction was generated. Also, the jaw adductors were well developed and enabled a rapid mouth closure. In contrast to extant caudate larvae and most extant actinopterygians (teleosts), no cranial kinesis was possible in the Gerrothorax skull, and therefore suction feeding was not as elaborate as in these extant forms. This reconstruction may guide future studies of feeding in extinct aquatic tetrapods with ossified hyobranchial apparatus.
Revised Phylogeny of Basal Turtles
Anquetin, J. 2012. Reassessment of the phylogenetic interrelationships of basal turtles (Testudinata). Journal of Systematic Palaeontology 10:3-45. doi: http://dx.doi.org/10.1080/14772019.2011.558928
Abstract - Recent discoveries from the Late Triassic and Middle Jurassic have significantly improved the fossil record of early turtles. These new forms offer a unique opportunity to test the interrelationships of basal turtles. Nineteen fossil species are added to the taxon sample of the most comprehensive morphological phylogenetic analysis of the turtle clade. Among these additional species are recently discovered forms (e.g. Odontochelys semitestacea, Eileanchelys waldmani, Condorchelys antiqua), taxa generally omitted from previous analyses (e.g. chengyuchelyids, Sichuanchelys chowi) and species included in a phylogenetic analysis for the first time (Naomichelys speciosa and Siamochelys peninsularis). The coding of several characters is reassessed in the light of recent observations, but also in order to reduce unwarranted assumptions on character and character state homologies. Additional characters from previous analyses, as well as five new ones, are also included, resulting in a data matrix of 178 characters scored for 86 turtle species and seven fossil outgroups. The dataset resolves the relationships of most newly included taxa, with the exception of S. chowi and ‘Chengyuchelys’ dashanpuensis. The phylogenetic placement of Heckerochelys romani, Condorchelys antiqua and Eileanchelys waldmani as stem turtles more derived than Kayentachelys aprix but more basal than Meiolania platyceps and Mongolochelys efremovi is corroborated. The relationships of chengyuchelyids remain unclear and they are unstable with respect to stem turtles. In contrast to previous analyses, Arundelemys dardeni is placed within pleurosternids and Siamochelys peninsularis falls within xinjiangchelyids. Perhaps the most salient conclusion of the present study is the placement of Naomichelys speciosa as a basal member of a clade uniting meiolaniids, Mongolochelys efremovi and Otwayemys cunicularius. This clade of rather large stem turtles had a worldwide spread during the Mesozoic at least, and persisted until the Pleistocene with meiolaniids.
Another Example of the Phylogenetic Utility of Osteoderms in Triassic Vertebrates
Buchwitz, M., C. Foth, I. Kogan, and S. Voigt. 2012. On the use
of osteoderm features in a phylogenetic approach on the internal relationships
of the Chroniosuchia (Tetrapoda: Reptiliomorpha). Palaeontology [Early View]. DOI: 10.1111/j.1475-4983.2012.01137.x
Abstract: Chroniosuchians are an enigmatic Permian to Triassic group of crocodile-like basal tetrapods. Their conspicuous dorsal osteoderm systems include most of the group’s yet documented postcranial morphological variability but have hardly been considered in cladistic approaches. Aiming at the clarification of the internal relationships of the Chroniosuchia, we have carried out a parsimony analysis including, among others, 23 morphological and osteohistological osteoderm characters and 12 chroniosuchian taxa. According to the most parsimonious trees, taxa usually referred to Chroniosuchidae form a paraphyletic succession with Madygenerpeton pustulatus and Chroniosaurus dongusensis as the basalmost chroniosuchians and Uralerpeton tverdochlebovae as the sister group of Bystrowianidae (hypothesis A). However, the concurrent hypothesis of a basal split into monophyletic subtaxa Chroniosuchidae and Bystrowianidae (hypothesis B) is only slightly less parsimonious and supported by an alternative analysis which includes embolomeres as the only reptiliomorph outgroup. Searching for the better hypothesis, we compare the respective order of branching to the order of first occurrences in the fossil record, demonstrating that hypothesis A provides a better stratigraphic fit than hypothesis B. Accordingly, the last common ancestor of the yet known chroniosuchians had a series of broad complexly interlocking ‘chroniosuchid’ osteoderms that served as a protection carapace apart from supporting the trunk during terrestrial locomotion. The later evolution of chroniosuchian carapaces was marked by a stepwise increase in flexibility and size reduction, which resulted in a loss of protective function and in a reduction in trunk support function. The flexibility increase is paralleled by the evolution of the Crocodylomorpha whose extant members do not possess as extensively interlocking osteoderm systems as some of their Mesozoic relatives.
In addition you can read about more new articles on Kyrgyzsaurus and Longisquama here.
Abstract: Chroniosuchians are an enigmatic Permian to Triassic group of crocodile-like basal tetrapods. Their conspicuous dorsal osteoderm systems include most of the group’s yet documented postcranial morphological variability but have hardly been considered in cladistic approaches. Aiming at the clarification of the internal relationships of the Chroniosuchia, we have carried out a parsimony analysis including, among others, 23 morphological and osteohistological osteoderm characters and 12 chroniosuchian taxa. According to the most parsimonious trees, taxa usually referred to Chroniosuchidae form a paraphyletic succession with Madygenerpeton pustulatus and Chroniosaurus dongusensis as the basalmost chroniosuchians and Uralerpeton tverdochlebovae as the sister group of Bystrowianidae (hypothesis A). However, the concurrent hypothesis of a basal split into monophyletic subtaxa Chroniosuchidae and Bystrowianidae (hypothesis B) is only slightly less parsimonious and supported by an alternative analysis which includes embolomeres as the only reptiliomorph outgroup. Searching for the better hypothesis, we compare the respective order of branching to the order of first occurrences in the fossil record, demonstrating that hypothesis A provides a better stratigraphic fit than hypothesis B. Accordingly, the last common ancestor of the yet known chroniosuchians had a series of broad complexly interlocking ‘chroniosuchid’ osteoderms that served as a protection carapace apart from supporting the trunk during terrestrial locomotion. The later evolution of chroniosuchian carapaces was marked by a stepwise increase in flexibility and size reduction, which resulted in a loss of protective function and in a reduction in trunk support function. The flexibility increase is paralleled by the evolution of the Crocodylomorpha whose extant members do not possess as extensively interlocking osteoderm systems as some of their Mesozoic relatives.
In addition you can read about more new articles on Kyrgyzsaurus and Longisquama here.
There Goes "Dicynodon" Biostratigraphy!
In the latest Journal of Vertebrate Paleontology Memoir Christian Kammerer, Kenneth Angielczyk, and Jörg Fröbisch (an allstar team of synapsid workers) readily handle the taxonomic mess more commonly known as Dicynodon. They find that the taxon is polyphyletic, is restricted to two species, and reassign all of the other material to a variety of old and new genera. Moreover, I think that their abstract sets a record for the number of included taxonomic names.
Hey guys, want to tackle "Rutiodon" next?
Kammerer, C. F., Angielczyk, K. D., and J. Fröbisch. 2011. A comprehensive taxonomic revision of Dicynodon (Therapsida, Anomodontia) and its implications for dicynodont phylogeny, biogeography, and biostratigraphy. Journal of Vertebrate Paleontology 31, Supplement 1: 1-158 DOI:10.1080/02724634.2011.627074
Abstract - The dicynodont wastebasket genus Dicynodon is revised following a comprehensive review of nominal species. Most nominal species of Dicynodon pertain to other well-known dicynodont genera, especially Oudenodon and Diictodon. Of the Karoo Permian species that are referable to "Dicynodon" sensu lato, we recognize four common, valid morphospecies: Dicynodon lacerticeps, D. leoniceps, D. woodwardi, and Dinanomodon gilli, comb. nov. Eleven additional species of "Dicynodon" are recognized worldwide: D. alticeps, D. amalitzkii, D. bathyrhynchus, D. benjamini, D. bogdaensis, D. huenei, D. limbus, D. sinkianensis, D. traquairi, D. trautscholdi, and D. vanhoepeni. Morphometric analysis of D. lacerticeps and D. leoniceps specimens recovers statistically significant separation between these species in snout profile and squamosal shape, supporting their distinction. A new phylogenetic analysis of Anomodontia reveals that "Dicynodon" is polyphyletic, necessitating taxonomic revision at the generic level. D. benjamini and D. limbus are basal cryptodonts, whereas the other valid "Dicynodon" species are basal dicynodontoids. The genus Dicynodon is restricted to D. lacerticeps and D. huenei. We reinstate use of Daptocephalus, Sintocephalus, Turfanodon, Daqingshanodon, Jimusaria, and Gordonia for other species. We synonymize Vivaxosaurus permirus and Dicynodon trautscholdi (as V. trautscholdi, comb. nov.) We establish new generic names for several species formerly included in Dicynodon: Peramodon amalitzkii, comb. nov., Keyseria benjamini, comb. nov., Euptychognathus bathyrhynchus, comb. nov., Syops vanhoepeni, comb. nov., and Basilodon woodwardi, comb. nov. Of the main Karoo Permian taxa, Dicynodon, Basilodon, and Dinanomodon range throughout the Cistecephalus and Dicynodon assemblage zones, but Daptocephalus is restricted to the Dicynodon Assemblage Zone.
Hey guys, want to tackle "Rutiodon" next?
Kammerer, C. F., Angielczyk, K. D., and J. Fröbisch. 2011. A comprehensive taxonomic revision of Dicynodon (Therapsida, Anomodontia) and its implications for dicynodont phylogeny, biogeography, and biostratigraphy. Journal of Vertebrate Paleontology 31, Supplement 1: 1-158 DOI:10.1080/02724634.2011.627074
Abstract - The dicynodont wastebasket genus Dicynodon is revised following a comprehensive review of nominal species. Most nominal species of Dicynodon pertain to other well-known dicynodont genera, especially Oudenodon and Diictodon. Of the Karoo Permian species that are referable to "Dicynodon" sensu lato, we recognize four common, valid morphospecies: Dicynodon lacerticeps, D. leoniceps, D. woodwardi, and Dinanomodon gilli, comb. nov. Eleven additional species of "Dicynodon" are recognized worldwide: D. alticeps, D. amalitzkii, D. bathyrhynchus, D. benjamini, D. bogdaensis, D. huenei, D. limbus, D. sinkianensis, D. traquairi, D. trautscholdi, and D. vanhoepeni. Morphometric analysis of D. lacerticeps and D. leoniceps specimens recovers statistically significant separation between these species in snout profile and squamosal shape, supporting their distinction. A new phylogenetic analysis of Anomodontia reveals that "Dicynodon" is polyphyletic, necessitating taxonomic revision at the generic level. D. benjamini and D. limbus are basal cryptodonts, whereas the other valid "Dicynodon" species are basal dicynodontoids. The genus Dicynodon is restricted to D. lacerticeps and D. huenei. We reinstate use of Daptocephalus, Sintocephalus, Turfanodon, Daqingshanodon, Jimusaria, and Gordonia for other species. We synonymize Vivaxosaurus permirus and Dicynodon trautscholdi (as V. trautscholdi, comb. nov.) We establish new generic names for several species formerly included in Dicynodon: Peramodon amalitzkii, comb. nov., Keyseria benjamini, comb. nov., Euptychognathus bathyrhynchus, comb. nov., Syops vanhoepeni, comb. nov., and Basilodon woodwardi, comb. nov. Of the main Karoo Permian taxa, Dicynodon, Basilodon, and Dinanomodon range throughout the Cistecephalus and Dicynodon assemblage zones, but Daptocephalus is restricted to the Dicynodon Assemblage Zone.
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