A partial lower jaw of a tetrapod from “Romer's Gap”

2017 ◽  
Vol 108 (1) ◽  
pp. 55-65 ◽  
Author(s):  
Donglei Chen ◽  
Yasaman Alavi ◽  
Martin D. Brazeau ◽  
Henning Blom ◽  
David Millward ◽  
...  
Keyword(s):  
Phylogenetic Analysis ◽  
Lateral Line ◽  
Early Carboniferous ◽  
Crown Group ◽  
Distinctive Character ◽  
Lower Jaw ◽  
Stem Group ◽  
Significant Step ◽  
Group Members

ABSTRACTThe first half of the Mississippian or Early Carboniferous (Tournaisian to mid- Viséan), an interval of about 20 million years, has become known as “Romer's Gap” because of its poor tetrapod record. Recent discoveries emphasise the differences between pre-“Gap” Devonian tetrapods, unambiguous stem-group members retaining numerous “fish” characters indicative of an at least partially aquatic lifestyle, and post-“Gap” Carboniferous tetrapods, which are far more diverse and include fully terrestrial representatives of the main crown-group lineages. It seems that “Romer's Gap” coincided with the cladogenetic events leading to the origin of the tetrapod crown group. Here, we describe a partial right lower jaw ramus of a tetrapod from the late Tournaisian or early Viséan of Scotland. The large and robust jaw displays a distinctive character combination, including a significant mesial lamina of the strongly sculptured angular, an open sulcus for the mandibular lateral line, a non-ossified narrow Meckelian exposure, a well-defined dorsal longitudinal denticle ridge on the prearticular, and a mesially open adductor fossa. A phylogenetic analysis places this specimen in a trichotomy withCrassigyrinusand baphetids + higher tetrapods in the upper part of the tetrapod stem group, aboveWhatcheeria, Pederpes,Ossinodus,SigourneaandGreererpeton. It represents a small but significant step in the gradual closure of “Romer's Gap”.

Lower jaws, lower tetrapods–a review based on the Devonian genus Acanthostega

1998 ◽  
Vol 89 (1) ◽  
pp. 11-46 ◽  
Author(s):  
Per Erik Ahlberg ◽  
Jennifer A. Clack
Keyword(s):  
Phylogenetic Analysis ◽  
Wide Distribution ◽  
Middle Part ◽  
Crown Group ◽  
Lower Jaw ◽  
Stem Group ◽  
Early Tetrapods ◽  
First Time

AbstractThe lower jaw of the Devonian tetrapod Acanthostega is described for the first time. Redescriptions are provided for the lower jaws of the elpistostegid Panderichthys, the Devonian tetrapods Elginerpeton, Obruchevichthys, Metaxygnathus, Ventastega and Ichthyostega, and the Carboniferous tetrapods Crassigyrinus, Megalocephalus and Gephyrostegus. The character distri- butions thus revealed differ considerably from previous accounts, particularly in the wide distribution of certain primitive characters. Meckelian ossification in the middle part of the jaw is widespread among Devonian tetrapods, being demonstrably absent only in Acanthostega. Among Carboniferous tetrapods, a tooth-bearing parasymphysial plate is shown to be present in Crassigyrinus and Megalocephalus (having already been demonstrated by other authors in Whatcheeria and Greererpeton). A phylogenetic analysis of 26 early tetrapods including all the aforementioned genera, scored for 51 lower jaw characters, produces at least 2,500 equally parsimonious trees. However, the lack of resolution lies largely in a big top end polychotomy containing anthracosaurs, temnospondyls, seymouriamorphs, microsaurs and a nectridean-amniote clade. Below this polycho- tomy, which may correspond approximately to the tetrapod crown group, there is a well-resolved stem-group containing, in descending order, Megalocephalus, Greererpeton, Crassigyrinus, (jaws associated with) Tulerpeton, Whatcheeria, Acanthostega, Metaxygnathus, Ichthyostega, Ventastega and Metaxygnathus (unresolved), an Elginerpeton-Obruchevichthys clade, and Panderichthys. This conflicts with recently published phylogenies by Coates and Lebedev & Coates, which place Tulerpeton and all post-Devonian tetrapods in the amphibian or amniote branches of the tetrapod crown group.

scholarly journals The dynamics of stem and crown groups

2019 ◽  
Author(s):  
Graham E. Budd ◽  
Richard P. Mann
Keyword(s):  
Molecular Clock ◽  
Fossil Record ◽  
Null Hypothesis ◽  
Mass Extinctions ◽  
Crown Group ◽  
Stem Group ◽  
Group Members ◽  
Evolutionary Explanations ◽  
Birth Death

ABSTRACTThe fossil record of the origins of major groups is of great interests to many biologists, especially when the fossil record apparently conflicts with timings based on molecular clock estimates. Here we model the diversity of “stem” (basal) and “crown” (modern) members of groups as seen in the fossil record, using a “birth-death model”. Under background conditions, the stem group members must diversify rapidly until the modern crown group emerges, at which point their diversity rapidly collapses, followed shortly by their extinction. Mass extinctions can disturb this pattern to create very diverse stem groups such as the dinosaurs and trilobites. Understanding these null-hypothesis patterns is essential for framing ecological and evolutionary explanations for how major groups originate and subsequently evolve.

scholarly journals New mid-Cretaceous cryptic slime mold beetles and the early evolution of Sphindidae (Coleoptera: Cucujoidea)

2021 ◽  
Vol 79 ◽  
pp. 587-597
Author(s):  
Yan-Da Li ◽  
Erik Tihelka ◽  
Zhen-Hua Liu ◽  
Di-Ying Huang ◽  
Chen‑Yang Cai
Keyword(s):  
Phylogenetic Analysis ◽  
Fossil Record ◽  
Slime Mold ◽  
Early Evolution ◽  
Calibration Point ◽  
Crown Group ◽  
Slime Molds ◽  
The Family ◽  
Group Members

Abstract The cryptic slime mold beetles, Sphindidae, are a moderately diverse cucujoid beetle family, whose members are obligately tied to slime molds throughout their life. The fossil record of sphindid beetles is sparse; stem-sphindids and crown-group members of uncertain systematic placement have been reported from Cretaceous ambers. Here we review the Mesozoic fossil record of Sphindidae and report a new sphindid genus and species, Trematosphindus newtonigen. et sp. nov., from Albian/Cenomanian amber from northern Myanmar (ca. 99 Ma). Trematosphindus is set apart from all other sphindids by the presence of distinct lateral cavities on the anterior pronotal angles. Our phylogenetic analysis identifies Trematosphindus as an early-diverging genus within Sphindidae, sister to the remainder of the family except Protosphindus, or Protosphindus and Odontosphindus. The new fossils provide evidence that basal crown slime mold beetles begun to diversify by the mid-Cretaceous, providing a valuable calibration point for understanding timescale of sphindid co-evolution with slime molds.

scholarly journals Phylogeny and Biogeography of the Enigmatic Ghost Lineage Cylindrotomidae (Diptera: Nematocera)

2021 ◽  
Author(s):  
Iwona Kania-Kłosok ◽  
André Nel ◽  
Jacek Szwedo ◽  
Wiktoria Jordan-Stasiło ◽  
Wiesław Krzemiński
Keyword(s):  
Phylogenetic Analysis ◽  
New Species ◽  
Comparative Analysis ◽  
Sister Group ◽  
Phylogenetic Position ◽  
Crown Group ◽  
Extant Genus ◽  
Stem Group ◽  
Two New Species ◽  
Fossil Genus

Abstract Ghost lineages have always challenged the understanding of organism evolution. They participate in misinterpretations in phylogenetic, clade dating, biogeographic, and paleoecologic studies. They directly result from fossilization biases and organism biology. The Cylindrotomidae are a perfect example of an unexplained ghost lineage during the Mesozoic, as its sister family Tipulidae is already well diversified during the Cretaceous, while the oldest Cylindrotomidae are Paleogene representatives of the extant genus Cylindrotoma and of the enigmatic fossil genus Cyttaromyia. Here We clarify the phylogenetic position of Cyttaromyia in the stem group of the whole family, suggesting that the crown group of the Cylindrotomidae began to diversify during the Cenozoic, unlike their sister group Tipulidae. We make a comparative analysis of all species in Cyttaromyia, together with the descriptions of the two new species, C. gelhausi sp. nov. and C. freiwaldi sp. nov., and the revision of C. obdurescens. The cylindrotomid biogeography seems to be incongruent with the phylogenetic analysis, the apparently most derived subfamily Stibadocerinae having apparently a ‘Gondwanan’ distribution, with some genera only known from Australia or Chile, while the most inclusive Cylindrotominae are Holarctic.

scholarly journals Phylogeny and biogeography of the enigmatic ghost lineage Cylindrotomidae (Diptera, Nematocera)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Iwona Kania-Kłosok ◽  
André Nel ◽  
Jacek Szwedo ◽  
Wiktoria Jordan-Stasiło ◽  
Wiesław Krzemiński
Keyword(s):  
Phylogenetic Analysis ◽  
New Species ◽  
Comparative Analysis ◽  
Sister Group ◽  
Phylogenetic Position ◽  
Crown Group ◽  
Extant Genus ◽  
Stem Group ◽  
Two New Species ◽  
Fossil Genus

AbstractGhost lineages have always challenged the understanding of organism evolution. They participate in misinterpretations in phylogenetic, clade dating, biogeographic, and paleoecologic studies. They directly result from fossilization biases and organism biology. The Cylindrotomidae are a perfect example of an unexplained ghost lineage during the Mesozoic, as its sister family Tipulidae is already well diversified during the Cretaceous, while the oldest Cylindrotomidae are Paleogene representatives of the extant genus Cylindrotoma and of the enigmatic fossil genus Cyttaromyia. Here we clarify the phylogenetic position of Cyttaromyia in the stem group of the whole family, suggesting that the crown group of the Cylindrotomidae began to diversify during the Cenozoic, unlike their sister group Tipulidae. We make a comparative analysis of all species in Cyttaromyia, together with the descriptions of the two new species, C. gelhausi sp. nov. and C. freiwaldi sp. nov., and the revision of C. obdurescens. The cylindrotomid biogeography seems to be incongruent with the phylogenetic analysis, the apparently most derived subfamily Stibadocerinae having apparently a ‘Gondwanan’ distribution, with some genera only known from Australia or Chile, while the most inclusive Cylindrotominae are Holarctic.

scholarly journals A diverse assemblage of Permian echinoids (Echinodermata, Echinoidea) and implications for character evolution in early crown group echinoids

2017 ◽  
Vol 91 (4) ◽  
pp. 767-780 ◽  
Author(s):  
Jeffrey R. Thompson ◽  
Elizabeth Petsios ◽  
David J. Bottjer
Keyword(s):  
New Taxa ◽  
Character Evolution ◽  
Morphological Characterization ◽  
Crown Group ◽  
West Texas ◽  
Stem Group

AbstractThe Permian is regarded as one of the most crucial intervals during echinoid evolution because crown group echinoids are first widely known from the Permian. New faunas provide important information regarding the diversity of echinoids during this significant interval as well as the morphological characterization of the earliest crown group and latest stem group echinoids. A new fauna from the Capitanian Lamar Member of the Bell Canyon Formation in the Guadalupe Mountains of West Texas comprises at least three new taxa, includingEotiaris guadalupensisThompson n. sp. an indeterminate archaeocidarid, andPronechinus? sp. All specimens represented are silicified and known from disarticulated or semiarticulated interambulacral and ambulacral plates and spines. This assemblage is one of the most diverse echinoid assemblages known from the Permian and, as such, informs the paleoecological setting in which the earliest crown group echinoids lived. This new fauna indicates that crown group echinoids occupied the same environments as stem group echinoids of the Archaeocidaridae and Proterocidaridae. Furthermore, the echinoids described herein begin to elucidate the order of character transitions that likely took place between stem group and crown group echinoids. At least one of the morphological innovations once thought to be characteristic of early crown group echinoids, crenulate tubercles, was in fact widespread in a number of stem group taxa from the Permian as well. Crenulate tubercles are reported from two taxa, and putative cidaroid style U-shaped teeth are present in the fauna. The presence of crenulate tubercles in the archaeocidarid indicates that crenulate tubercles were present in stem group echinoids, and thus the evolution of this character likely preceded the evolution of many of the synapomorphies that define the echinoid crown group.

scholarly journals Questioning hagfish affinities of the enigmatic Devonian vertebrate Palaeospondylus

2017 ◽  
Vol 4 (7) ◽  
pp. 170214 ◽  
Author(s):  
Zerina Johanson ◽  
Moya Smith ◽  
Sophie Sanchez ◽  
Tim Senden ◽  
Kate Trinajstic ◽  
...  
Keyword(s):  
Semicircular Canals ◽  
Crown Group ◽  
Vertebral Centra ◽  
Stem Group ◽  
Tomographic Data

Palaeospondylus gunni Traquair, 1890 is an enigmatic Devonian vertebrate whose taxonomic affinities have been debated since it was first described. Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of the cartilaginous skull, a feature of jawed vertebrates. Additionally, new tomographic data reveal that the following characters of crown-group gnathostomes (chondrichthyans + osteichthyans) are present in Palaeospondylus : a longer telencephalic region of the braincase, separation of otic and occipital regions by the otico-occipital fissure, and vertebral centra. As well, a precerebral fontanelle and postorbital articulation of the palatoquadrate are characteristic of certain chondrichthyans. Similarities in the structure of the postorbital process to taxa such as Pucapampella , and possible presence of the ventral cranial fissure, both support a resolution of Pa. gunni as a stem chondrichthyan. The internally mineralized cartilaginous skeleton in Palaeospondylus may represent a stage in the loss of bone characteristic of the Chondrichthyes.

scholarly journals The putative lissamphibian stem-group: phylogeny and evolution of the dissorophoid temnospondyls

2018 ◽  
Vol 93 (1) ◽  
pp. 137-156 ◽  
Author(s):  
Rainer R. Schoch
Keyword(s):  
Phylogenetic Analysis ◽  
Large Scale ◽  
Sensu Stricto ◽  
New Taxon ◽  
Stem Group ◽  
Phylogeny And Evolution

AbstractDissorophoid temnospondyls are widely considered to have given rise to some or all modern amphibians (Lissamphibia), but their ingroup relationships still bear major unresolved questions. An inclusive phylogenetic analysis of dissorophoids gives new insights into the large-scale topology of relationships. Based on a TNT 1.5 analysis (33 taxa, 108 characters), the enigmatic taxonPerryellais found to nest just outside Dissorophoidea (phylogenetic defintion), but shares a range of synapomorphies with this clade. The dissorophoids proper are found to encompass a first dichotomy between the largely paedomorphic Micromelerpetidae and all other taxa (Xerodromes). Within the latter, there is a basal dichotomy between the large, heavily ossified Olsoniformes (Dissorophidae + Trematopidae) and the small salamander-like Amphibamiformes (new taxon), which include four clades: (1) Micropholidae (Tersomius,Pasawioops,Micropholis); (2) Amphibamidae sensu stricto (Doleserpeton,Amphibamus); (3) Branchiosauridae (Branchiosaurus,Apateon,Leptorophus,Schoenfelderpeton); and (4) Lissamphibia. The generaPlatyrhinopsandEoscopusare here found to nest at the base of Amphibamiformes. Represented by their basal-most stem-taxa (Triadobatrachus,Karaurus,Eocaecilia), lissamphibians nest withGerobatrachusrather than Amphibamidae, as repeatedly found by former analyses.UUID:http://zoobank.org/dadf36db-e003-4af7-bfa7-44d79bc04450

Protohemiphlebiidae fam. nov., a stem hemiphlebioid damselfly from Cretaceous amber in Kachin

2021 ◽  
pp. SP521-2020-249
Author(s):  
Daran Zheng ◽  
Edmund A. Jarzembowski ◽  
De Zhuo ◽  
André Nel
Keyword(s):  
Phylogenetic Analysis ◽  
Late Jurassic ◽  
New Genus ◽  
Early Evolution ◽  
Relict Species ◽  
Wing Base ◽  
New Family ◽  
Stem Group ◽  
The Family

AbstractHemiphlebiidae are the most basal lestomorphan family following the latest phylogenetic analysis of the Zygoptera: this unique damselfly family today contains one relict species found in the wetlands of Australia. It was, however, very diverse and widespread during the Mesozoic. Nevertheless, very few species were known obscuring the origination and early evolution of the family. Here we propose a new stem hemiphlebioid taxon (Protohemiphlebiidae Zheng, Jarzembowski & Nel, fam. nov.) based on a new genus and two species: Protohemiphlebia zhangi Zheng, Jarzembowski & Nel, sp. nov. and Protohemiphlebia meiyingae Zheng, Jarzembowski & Nel, sp. nov. The new family shares the characters of both Hemiphlebiidae and Coenagrionoidea, but it is more closely related to Hemiphlebiidae in having the pterostigma with a ‘star-shaped’ microsculpture, and AA originating from the wing base slightly distal of Ax0. Protohemiphlebia Zheng, Jarzembowski & Nel, gen. nov. is further considered to belong to the stem group of Hemiphlebioidea, instead of belonging to the Hemiphlebiidae, in possessing pretibial combs and a weakly kinked RP1 below the Pt-brace. The new damselflies will help to calibrate the origin of Hemiphlebiidae, which could be earlier than their current oldest records in the Kimmeridgean (Late Jurassic).

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