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[dinosaur] Pterosaurs tracks from Spain + ameghinornithid-like bird from China + bird claw shape + tetrapod hearing + more





Ben Creisler
bcreisler@gmail.com


A number of recent papers that may be of interest:

Free pdf in Spanish:

Carlos Pascual-Arribas and Nieves Hernández-Medrano (2016)
Huellas de Pteraichnus en La Muela (Soria, España):  consideraciones sobre el icnogénero y sobre la diversidad de huellas de pterosaurios en la Cuenca de Cameros. 
[Pteraichnus tracks in La Muela (Soria, Spain): considerations on the ichnogenus and diversity of pterosaur tracks in the Cameros Basin.] 
Revista de la Sociedad Geológica de España 29 (2): 89-105 
ISSN (versión impresa): 0214-2708
ISSN (Internet): 2255-1379
http://www.sociedadgeologica.es/archivos/REV/29(2)/RSGE_29(2)_art6.pdf

Pterosaurs tracks in the Cameros basin are plentiful and assorted. This fact has allowed to define several Pteraichnus ichnospecies and moreover to distinguish other morphotypes. The study of the new tracksite of La Muela (Soria, Spain) describes Pteraichnus cf. stokesi ichnites that is an unknown ichnospecies until now and that confirms the wide diversity of this type of tracks in the Cameros Basin. Their characteristics correspond to the ones of the Upper Jurassic tracksites of United States. Similar tracks have already been described in other tracksites, both inside and outside the Iberian Peninsula during the Upper Jurassic-Lower Cretaceous transit. Because of their shape and morphometrical characteristics they can be related to the pterosaurs of the Archaeopterodactyloidea clade. The analysis of this ichnogenus indicates the need for a deep review because encompasses ichnites with a big variety of shapes and morphometric characteristics.

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A revised version of a paper first posted back in 2015:

Free pdf:


David Marjanović​ and Michel Laurin (2016)
Reevaluation of the largest published morphological data matrix for phylogenetic analysis of Paleozoic limbed vertebrates. 
PeerJ Preprints 4:e1596v2
doi: https://doi.org/10.7287/peerj.preprints.1596v2
https://peerj.com/preprints/1596/

The largest published data matrix for phylogenetic analysis of Paleozoic limbed vertebrates (Ruta M, Coates MI. 2007. Journal of Systematic Palaeontology 5:69–122) supported variously controversial hypotheses; e.g., it recovered Seymouriamorpha, Diadectomorpha and (in some trees) Caudata as paraphyletic and found the “temnospondyl hypothesis” on the origin of Lissamphibia (TH) to be more parsimonious than the “lepospondyl hypothesis” (LH) – though only, as we show, by one step.

We report thousands of suboptimal scores due to typographic and similar errors and to questionable coding decisions: logically linked (redundant) characters, others with only one described state, even characters for which most taxa were scored after presumed relatives. Even continuous characters were unordered, the effects of ontogeny were not sufficiently taken into account, and data published after 2001 were mostly excluded.

After these issues are improved – we document and justify all changes to the matrix –, but no characters are removed or added, we find (Analysis R1) much longer trees with e.g. monophyletic Caudata, Diadectomorpha and (in some trees) Seymouriamorpha; Ichthyostega rootward of Acanthostega; Anthracosauria rootward of Temnospondyli which includes Caerorhachis; the LH is 9 steps shorter than the TH (R2; constrained) and 12 steps shorter the “polyphyly hypothesis” (PH – R3; constrained).

We then added 48 OTUs to the original 102. This destabilizes some parts of the tree, e.g. the positions of Anthracosauria, Temnospondyli and Caerorhachis. Yet, many added taxa have well-resolved positions, ranging from the well known Chroniosaurus (Chroniosuchia), which lies just crownward of Temnospondyli and Gephyrostegidae, to isolated lower jaws. Even though Gerobatrachus, Micropholis and Tungussogyrinus and the extremely peramorphic salamander Chelotriton are added, the difference between LH (R4) and TH (R5) rises to 12 steps, that between LH and PH (R6) to 17 steps; the TH also requires several more regains of lost bones than the LH. Brachydectes (Lysorophia) is not found next to Lissamphibia.

We duplicated all analyses after coding losses of bones as irreversible. The impact on the results is modest. Anthracosauria is always rootward of Temnospondyli. With 102 OTUs, the LH (R7) is 10 steps shorter than the TH (R8) and 11 steps shorter than the PH (R9); with 150, the LH (R10) is 14 steps shorter than the TH (R12) – and 13 steps shorter than the PH (R11).

Bootstrap values are mostly low, and plummet when taxa are added. Statistically, the TH (R2, R5, R8, R12) is not distinguishable from the LH or the PH, but the LH (R1, R4, R7, 53 R10) and the PH (R3, R6, R9, R11) may be distinguishable from each other under both taxon samples and both reversibility settings. A reliable test is not available.

We discuss the relationships of certain taxa, approaches to coding, some character complexes, and prospects for further improvement of this matrix.

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Free pdf:

Thomas A. STIDHAM and WANG Yuan-Qing  [2017]
An ameghinornithid-like bird (Aves: Cariamae: Ameghinornithidae?) from the Middle Eocene of Nei Mongol, China.
Vertabrata PalAsiatica (advance online publication)
http://www.ivpp.ac.cn/cbw/gjzdwxb/pressonline/201612/P020161223321522179936.pdf

Abstract   A new fossil specimen from the early Middle Eocene of an Irdin Manha Formation equivalent (Erden Obo Section) in Nei Mongol (Inner Mongolia), China appears to be derived from an ameghinornithid-like species, and may represent the first record of the Ameghinornithidae in Asia. This new specimen exhibits the subcircular lateral condyle outline, the absence of an ossified supratendinal bridge, an enlarged flattened tubercle lateral to the extensor sulcus, and other features shared among known ameghinornithid and ameghinornithid-like birds. The Nei Mongol fossil is roughly contemporaneous with the oldest records of the ameghinornithids from Europe (~48 Ma). The absence of this group of birds from North America, and their occurrence in Europe and Asia during the Eocene contrasts with the contemporaneous Nei Mongol mammalian fauna that is comprised largely of Asian taxa with a few distinct linkages to North America. Along with the record of an ameghinornithid-like bird from the early Oligocene deposits of the Fayum area in Egypt, it seems that this extinct bird group had a much larger geographic distribution than previously recognized.  

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Alexander Tiniu & Anthony Patrick Russell (2016)
Points on the curve: An analysis of methods for assessing the shape of vertebrate claws.
Journal of Morphology (advance online publication)
DOI: 10.1002/jmor.20625
http://onlinelibrary.wiley.com/doi/10.1002/jmor.20625/full


The form of amniote claws has been extensively investigated, often with inferences about ecological association being drawn from studies of their geometry. Various methods have been used to quantify differences in the geometry of claws, but rarely have the underlying assumptions of such methods been addressed. Here, we use one set of bird claws and apply six methods (five that have been previously used, and a new one) that are tasked with comparing their shape. In doing so, we compare the (1) ability of these methods to represent the shape of the claw; (2) validity of the assumptions made about underlying claw geometry; (3) their ability to be applied unambiguously; and (4) their ability to differentiate between predetermined functional clusters. We find that of the six methods considered only the geometric morphometric approach reveals differences in the shapes of bird claws. Our comparison shows that geometry-based methods can provide a general estimate of the degree of curvature of claw arcs, but are unable to differentiate between shapes. Of all of the geometry-based approaches, we conclude that the adjusted version of the Zani (2000) method is the most useful because it can be applied without ambiguity, and provides a reliable estimate of claw curvature. The three landmarks that define that method (tip and base of the claw arc, plus the intersection between said claw arc and a line drawn perpendicular from the midpoint of tip and claw base) do not all bear biological significance, but relatively clearly circumscribe the length-to-height ratio of the claw, which relates to its curvature. Overall, our comparisons reveal that the shape of avian claws does not differ significantly between climbing and perching birds, and that the utilization of preordained functional clusters in comparative data analysis can hinder the discovery of meaningful differences in claw shape. 

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Péter L. Pap, Orsolya Vincze, Beatrix Wekerle, Timea Daubner, Csongor I. Vágási, Robert L. Nudds, Gareth J. Dyke and Gergely Osváth (2016)
A phylogenetic comparative analysis reveals correlations between body feather structure and habitat.
Functional Ecology (advance online publication)
DOI: 10.1111/1365-2435.12820
http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12820/full

Summary

1. Body feathers ensure both waterproofing and insulation in waterbirds, but how natural variation in the morphological properties of these appendages relates to environmental constraints remains largely unexplored. Here, we test how habitat and thermal condition affect the morphology of body feathers using a phylogenetic comparative analysis of five structural traits [i.e., total feather length, the lengths of the pennaceous (distal) and plumulaceous (proximal) sections, barb density, and pennaceous barbule density] from a sample of 194 European bird species.

2. Body feather total length is shorter in aquatic than in terrestrial birds, and this difference between groups is due to the shorter plumulaceous feather section in aquatic birds. Indeed, a reduced plumulaceous section in feather length probably reflects the need to limit air trapped in the plumage to adjust the buoyancy of aquatic birds. In contrast, the high pennaceous barbule density of aquatic birds compared to their terrestrial counterparts reflects water resistance of the plumage in contact with water.

3. Our results show that birds living in environments with low ambient temperature have long plumulaceous feather lengths, low barb density, and low pennaceous barbule density. Data also suggest that plumage probably has limited function in reducing the heat absorption of species living in hot environments.

4. Our results have broad implications for understanding the suite of selection pressures driving the evolution of body feather functional morphology. It remains to be tested, however, how other feather traits, such as the density of plumage (feathers per unit area) and the relative number of different feather types, for example downy feathers, are distributed amongst birds with different water resistance and thermoinsulative needs.

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New book that may be of interest:


Jennifer A. Clack, Richard R Fay & Arthur N. Popper (eds.) (2016)
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59 2016
ISBN: 978-3-319-46659-0 (Print) 978-3-319-46661-3 (Online)
DOI: 10.1007/978-3-319-46661-3
http://link.springer.com/book/10.1007/978-3-319-46661-3

Google Books Preview:

https://books.google.com/books?id=4_3FDQAAQBAJ&printsec=frontcover#v=onepage&q&f=false


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Jennifer A. Clack, Per Erik Ahlberg (2016)
Sarcopterygians: From Lobe-Finned Fishes to the Tetrapod Stem Group.
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59: 51-70
DOI: 10.1007/978-3-319-46661-3_3
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_3

The sarcopterygians or lobe-finned fishes is the group that gave rise to tetrapods, and they were the dominant bony fishes of the Devonian period. Their otic regions were constructed similarly to those of both the actinopterygians and chondrichthyans, their structure being the common inheritance of all jawed vertebrates. One distinguishing feature of the primitive sarcopterygian braincase was that the division between the anterior ethmosphenoid and posterior otoccipital sections of the braincase was marked by a flexible hinge joint, which is seen today in the modern coelacanth, Latimeria. The hyomandibular was long and projected ventrally with an opercular process that contacted the opercular bone and with the distal end associated indirectly with the jaw joint. It was a key component of the buccal pumping mechanism for breathing and feeding. The braincases of dipnoans (lungfishes) were the most highly modified of sarcopterygian braincases with consolidated fore and aft portions and reduction or loss of the hyomandibula. The utricle was enlarged in several fossil dipnoans, although the reason for this is not clear. The braincases of tetrapodomorph sarcopterygians differed little from the primitive condition in the group. The main modifications were to the more crownward and tetrapod-like forms from the Late Devonian. In these fishes, the hyomandibula was reduced in length, its contact with the opercular bone lost and, ultimately, the opercular bone itself disappeared. The spiracular notch and associated cleft increased in width and volume respectively, possibly resulting in increased air-breathing capacity and reduced use of the gill system.


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Jennifer A. Clack and Jason S. Anderson (2016)
Early Tetrapods: Experimenting with Form and Function
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59: 71-105
DOI: 10.1007/978-3-319-46661-3_4
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_4



This chapter describes the ear regions of tetrapods from the Paleozoic. In the past couple of decades, understanding of their morphology has been increased by discoveries of fossils from the Late Devonian and early Carboniferous (Mississippian) periods. The primitive condition, as found in several only distantly related taxa, consisted of a bulky stapes with a large footplate and a stout wing-shaped distal portion. In some, the stapes seems to have been a strut supporting the braincase. The hearing capabilities of these taxa were probably poor, confined to low-frequency detection primarily in water but, possibly, also in air. Ichthyostega had a highly modified version probably specialized for aquatic audition. Taxa from the later Carboniferous (Pennsylvanian) and Permian show a great deal of variation, especially among more terrestrially adapted forms. These include the larger stem amniotes, such as seymouriamorphs and diadectomorphs. All these taxa have some kind of a notch or embayment at the back of the skull, which in early forms was probably part of a spiracular mechanism but, in later ones, might have housed a tympanic membrane that closed off an air-filled middle ear cavity. The small recumbirostran microsaurs and the earliest amniotes had no such notch. Microsaur stapes had large footplates and short, stubby shafts. These and the earliest amniotes probably had no middle ear cavity. The earliest amniote stapes were robust, long, and laterally or downwardly projecting. In some cases they contacted the cheek bones or the jaw joint, likely precluding good aerial sound reception.

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Tom S. Kemp (2016)
Non-Mammalian Synapsids: The Beginning of the Mammal Line.
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59: 107-137
DOI: 10.1007/978-3-319-46661-3_5
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_5
The homologies between the malleus, incus, and ectotympanic bones of the mammalian middle ear and the articular, quadrate, and angular bones of the tetrapod palatoquadrate, respectively, are well-established by embryonic evidence. The evolutionary question of how the implied transition occurred is less clear and, historically, there have been two general views. The first view is that the ancestral state was a reptile-like tympanic membrane behind the quadrate that activated the stapes, and that the jaw hinge bones were subsequently incorporated between tympanic membrane and stapes. The second view is that in the ancestor, low-frequency ground-borne sound was received by the lower jaw and transmitted via the hinge bones and stapes to the fenestra ovalis. The anatomy of the middle ear region of the known sequence of fossil stem-group mammals—pelycosaurs, basal therapsids, and several cynodonts—is reviewed in this chapter. As with almost all recent authors, the interpretation offers support for the second view. Within the cynodont grades, decreasing mass of the postdentary bones relative to the dentary is part of a complex of changes in the feeding mechanism but also implies increasing sensitivity to airborne sound. As long as the jaw hinge continued to perform a mechanical role in mandibular function, the bones were too massive to be receptive to higher frequency sound, and therefore an air-filled tympanic cavity and tympanic membrane were unlikely to have evolved. This latter stage awaited the origin of the new mammalian jaw hinge between the dentary and squamosal bones in mammaliaforms.

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Zhe-Xi Luo, Julia A. Schultz and Eric G. Ekdale (2016)
Evolution of the Middle and Inner Ears of Mammaliaforms: The Approach to Mammals.
Non-Mammalian Synapsids: The Beginning of the Mammal Line.
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59: 139-174
DOI: 10.1007/978-3-319-46661-3_6
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_6

Transformations of ear structures in the evolution of early mammals can be studied with the fossils of mammaliaforms. The middle ear is fully attached to the mandibles in mammaliaforms; however, in Mesozoic eutriconodont and spalacotherioid mammals, it is only connected to the mandible by an ossified Meckel’s cartilage, with the ectotympanic and malleus already displaced from the mandible. Recent morphogenetic studies have shown that the developmental potential for ossification of Meckel’s element is conserved in extant mammals. New fossils further revealed that this pattern actually evolved in mammaliaform phylogeny and that disconnection of the ear from the mandible occurred independently in monotremes, in therians, and in multituberculate mammals. The inner ear of mammaliaforms is derived in having a single petrosal bone enclosing the entire inner ear and a promontorium for an elongate cochlear canal. Mammaliaforms and most Mesozoic mammals had ancestral features of a simple cochlear canal with a single cochlear nerve foramen but no interior bony laminae nor did they have a bony canal for the cochlear ganglion. The sieve-like foramina for cochlear nerve fibers to enter the cochlear canal evolved independently three times in Mesozoic mammals. Cochlear canal curvature is homoplastic among mammaliaform groups, and a curvature beyond 270° only evolved in cladotherians, accompanied by Rosenthal’s canal for the cochlear ganglion. The homoplasies of ear structures in early mammalian evolution, although seemingly complex, are consistent with the new understanding of a labile morphogenesis of mammalian ears under a complex developmental genetic network.


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Eric G. Ekdale (2016)
The Ear of Mammals: From Monotremes to Humans.
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59:  175-206
DOI: 10.1007/978-3-319-46661-3_7
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_7


Mammals hear across a greater range of auditory frequencies than other vertebrates, which was made possible through major modifications of sound transmission and processing pathways within the middle and inner ears. The first step in the evolution of the ear of mammals is a combination of the prootic and opisthotic bones to form a single petrosal bone that fully encapsulates the organs of the inner ear. Elongation of the cochlea occurred simultaneously with the development of the petrosal. The curvature of the cochlea itself is variable among Mesozoic mammals, and extreme coiling of the cochlea is coincident with acquisition of major morphogenetic genes within the mammalian genome. A cribriform plate that is penetrated by multiple branches of the cochlear nerve in all extant mammals, internal cochlear structures such as the auditory nerve ganglion canal, and primary and secondary bony laminae for supporting the basilar membrane further broadened the bandwidth of audible frequencies in placental and marsupial mammals. Although often considered to be a major diagnostic feature of mammals, the definitive mammalian middle ear, which consists of a complete separation of middle ear elements from the mandible, appears to have evolved multiple times over the course of mammal evolution. As new important fossils are discovered, described, and included in phylogenetic analyses, the accuracy in ascertaining when and how many times the major features of the mammalian ear were acquired will increase.



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Gabriela Sobral, Robert Reisz, James M. Neenan, Johannes Müller and Torsten M. Scheyer (2016)
Basal Reptilians, Marine Diapsids, and Turtles: The Flowering of Reptile Diversity
The Ear of Mammals: From Monotremes to Humans.
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59:  207-243
DOI:  10.1007/978-3-319-46661-3_8
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_8


Reptiles form the most diverse clade of living land vertebrates. They include lizards, snakes, crocodiles, birds, and turtles, as well as many fossil groups. In this chapter we revise the otic anatomy of early reptilians, including some aquatic groups and turtles. Basal members possessed a stout stapes that still retained its ancestral bracing function, and they lacked a tympanic membrane. The acquisition of tympanic hearing did not happen until later in the evolution of the clade and occurred independently in both parareptiles and diapsids. Parareptiles also show additional otic modifications that are convergent with much later reptilians, which are potentially related to the evolution of more terrestrial habits. In contrast, in aquatic reptiles, such as ichthyosaurs, thalattosaurs, and sauropterygians, the otic anatomy and hearing capacities are adapted to an aquatic medium, resulting in many convergences in their otic anatomy. In turtles, however, there are differences in the configuration and morphology among Triassic and modern taxa.

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Susan E. Evans (2016)
The Lepidosaurian Ear: Variations on a Theme.
The Ear of Mammals: From Monotremes to Humans.
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59:  245-284
DOI: 10.1007/978-3-319-46661-3_9
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_9

Today, Lepidosauria encompasses more than 9,000 species of lizards, snakes, and amphisbaenians (Squamata), as well as the New Zealand Tuatara, Sphenodon (Rhynchocephalia). In many lizards, an efficient tympanic middle ear and an effective inner-ear compensatory mechanism permit acute hearing across a range of frequencies. Sphenodon lacks a tympanic membrane, but this is the result of secondary loss. Fossils of stem lepidosaurs and early rhynchocephalians indicate that the ancestral lepidosaurian middle ear was tympanic, although the compensatory mechanism was probably rudimentary. Derived rhynchocephalians like Sphenodon lost the tympanic ear, possibly in association with feeding specializations, whereas squamates improved it by developing a more efficient compensatory window. However, the timing of this change is uncertain as the earliest lizard fossils are uninformative in this respect. Lizards from the Early Cretaceous onward show the derived condition. Squamates are morphologically and ecologically diverse, and some specialized lifestyles have affected ear anatomy. Among extant squamates, the only obligate marine swimmers are sea snakes, but in the Cretaceous, mosasaurs dominated the marine niche. These aquatic lizards show a middle ear morphology analogous to that of extant marine turtles (bulla-like quadrate, expanded extrastapes, loss of the tympanum?). Loss of the tympanum also occurs in squamate burrowers but in conjunction with the possession of a robust stapes with an enlarged footplate and, frequently, reduction or modification of the compensatory mechanism. Ears of this type are found in the enigmatic Cretaceous Sineoamphisbaena and in amphisbaenians from the Eocene to the present day. Where known, the ears of early snakes more closely resemble those of burrowers than swimmers.

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Gabriela Sobral and Johannes Müller (2016)
Archosaurs and Their Kin: The Ruling Reptiles.
The Ear of Mammals: From Monotremes to Humans.
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59:  285-326
DOI: 10.1007/978-3-319-46661-3_10
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_10

Archosauria includes birds, crocodylians, and a number of fossil groups such as dinosaurs and pterosaurs. They first appeared in the Early Triassic and since then have dominated terrestrial ecosystems. This chapter is a compilation of the available information on the inner ear morphology of archosaur crown groups and stem groups and an exploration of different aspects of the evolution of their otic anatomy. It is still not clear whether tympanic hearing was present in the basalmost members of stem archosaur clades. However, more derived taxa show a number of modifications that certainly improved their hearing sense, such as a larger metotic foramen and a more elongate cochlea. Impedance-matching hearing appeared many times independently in archosaurs, although it is currently problematic to know at which point this happened. In theropods, impedance-matching hearing appeared before the origin of birds and was retained in the crown-group. Pneumatization must play an important role in directional hearing and is likely to have influenced skull pneumatization in crocodylians. Exquisite sound production capacities were present not only in hadrosaurids but also in ankylosaurids. Elongation of the semicircular canals seems to be linked to the acquisition of a more upright posture and a more active lifestyle in archosaurs. Many crown groups show further elongation of the canals, with birds representing an extreme condition.


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Rainer R. Schoch and Jason S. Anderson (2016)
Amphibia: A Case of Diversity and Convergence in the Auditory Region.
The Ear of Mammals: From Monotremes to Humans.
Evolution of the Vertebrate Ear: Evidence from the Fossil Record. 
Springer Handbook of Auditory Research 59:  327-355
DOI: 10.1007/978-3-319-46661-3_11
http://link.springer.com/chapter/10.1007/978-3-319-46661-3_11

The ears of extant amphibians are remarkably diverse and when fossil taxa are considered, the picture becomes even more complicated. Anurans have a differentiated stapes inside a middle ear cavity associated with a eustachian tube and tympanum. Instead, salamanders and caecilians have rudimentary stapes connected to the cheek or jaw articulation, and they lack the tympanum and middle ear cavity. At the same time, batrachians (salamanders and frogs) share a second ear ossicle, the batrachian operculum, whereas all lissamphibians have a second receptor in the inner ear, the amphibian papilla. The largest fossil clade and probable stem group of Lissamphibia, the temnospondyls, had a stapes similar to that of anurans, consistent in the possession of a ventral process and an elongate and slender distal shaft that probably attached to a tympanum. The evolutionary sequence of ear types forms a puzzle with several of the major groups each sharing features that others lack. The primitive condition is exemplified by the temnospondyl ear, especially that of dissorophoids. We argue that the loss of the tympanic system was an evolutionary option only available after the batrachian operculum had evolved.


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Also, from a few months back:



Bruce S. Rubidge , Michael O. Day, Natasha Barbolini, P. John Hancox, Jonah N. Choiniere, Marion K. Bamford, Pia A. Viglietti, Blair W. McPhee &  Sifelani Jirah (2016)
Advances in Nonmarine Karoo Biostratigraphy: Significance for Understanding Basin Development.
Origin and Evolution of the Cape Mountains and Karoo Basin.
Regional Geology Reviews: 141-149
DOI: 10.1007/978-3-319-40859-0_14
http://link.springer.com/chapter/10.1007/978-3-319-40859-0_14


The nonmarine Permo-Jurassic deposits of the Karoo Supergroup of South Africa have long been a world standard for tetrapod biostratigraphy. Recent and ongoing research is revising the palaeoflora and palaeofauna of these sedimentary strata with an unprecedented level of stratigraphic precision. This work has shown that: Permian palynomorphs are useful for correlating time-equivalent lithostratigraphic units in different sectors of the basin; that there is a marked end-Guadalupian diversity drop in tetrapods; that the Dicynodon Assemblage Zone can be subdivided, and should be renamed as the Daptocephalus Assemblage Zone; that the Cynognathus Assemblage Zone has a robust threefold subdivision; and that the name Euskelosaurus for the Euskelosaurus Range Zone is invalid and should be replaced. This work, together with new radiometric dates from the Karoo Supergroup, has dramatically enhanced our understanding of the timing of major evolutionary events in terrestrial ecosystems and provides strong evidence for tectonic controls on accommodation and sedimentation in the Karoo Basin during the Permo-Jurassic, within an overall flexural basinal setting.

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Johann Neveling , Robert A. Gastaldo, Sandra L. Kamo, John W. Geissman, Cindy V. Looy, Marion K. Bamford (2016)
A Review of Stratigraphic, Geochemical, and Paleontologic Data of the Terrestrial End-Permian Record in the Karoo Basin, South Africa.
Origin and Evolution of the Cape Mountains and Karoo Basin.
Regional Geology Reviews: 151-157
DOI: 10.1007/978-3-319-40859-0_15
http://link.springer.com/chapter/10.1007/978-3-319-40859-0_15

The Karoo Basin has long been considered to contain the type stratigraphic succession for the terrestrial _expression_ of the end-Permian mass extinction. A detailed extinction model, based on biostratigraphic and geologic data, has proposed rapid environmental change that coincides with a vertebrate biozone boundary, which was postulated to have been caused by increased aridity. Our sedimentologic, geochronologic, palaeomagnetic, and geochemical data collected from reported boundary sections, show that the link between the floral and faunal turnover and marine end-Permian event is tenuous. A review of existing, as well as our own palaeontological data, interpreted within a robust stratigraphic and sedimentologic framework, further indicate that ecological change was more subtle and protracted than currently modeled, and reflects the complex way in which the ancient Karoo landscape responded to changes in several extrinsic factors.