Evolution of the rudist bivalve Agriopleura Kühn (Radiolitidae,Hippuritida) from the Mediterranean region

The genus Agriopleura (Radiolitidae) is restricted to the Lower Cretaceous of the Mediterranean region, including the Middle East, and this rudist is apparently absent from the New World. Agriopleura underwent a size increase from late Hauterivian to mid‐late Barremian, matching Cope's rule, followed by a Lilliput phase in the early Aptian. The relative development of radial bands increased through time and represents a key evolutionary index. During its evolution, Agriopleura increased in species diversity and expanded geographically onto the European Mediterranean Tethyan margin from the late Hauterivian to Barremian, after which it disappeared from the region (pseudotermination). In the lower Aptian, after a Lazarus gap, the genus reappears in the southern Mediterranean Tethyan margin. Assuming that Archaeoradiolites is the direct descendant of Agriopleura, the disappearance of the genus in the mid‐Aptian was a pseudoextinction and this coincided with a major crisis of shallow carbonate settings and their associated biota. The definition of Agriopleura species is based on a set of qualitative and quantitative external and internal characters. Five species are recognized: three Barremian species, Agriopleura blumenbachi, the type species, A. marticensis and A. carinata; one lower Aptian species A. libanica; and a new species A. sequana restricted to the upper Hauterivian. Principal component analysis is used to test the distinctiveness of the species and the pattern of relationships of some of their key quantitative characters.     

Phylogenetic analysis of the north‐east Atlantic and Mediterranean species of the genus Stenosoma (Isopoda,Valvifera, Idoteidae)

Xavier, R., Santos, A. M., Harris, D. J., Sezgin, M., Machado, M., Branco, M. (2012). Phylogenetic analysis of the north‐east Atlantic and Mediterranean species of the genus Stenosoma (Isopoda, Valvifera, Idoteidae). —Zoologica Scripta, 41, 386–399. The marine isopod genus Stenosoma is widespread in the northern hemisphere. However, 12 of its 14 known species are found within the Mediterranean basin and adjacent regions of the north‐east Atlantic and the Black Sea. Such a high level of diversity confined to a limited region of a much larger circumglobal distribution suggests that the Mediterranean region may have played a crucial role in the evolutionary history of this genus. In the present work, the phylogeny of the genus Stenosoma was investigated on the basis of DNA sequencing data from one nuclear (28SrRNA) and two mitochondrial (COI, ND4) gene fragments obtained for nine of 12 Atlantic–Mediterranean species. Divergence time estimates point to a Tethyan origin of Stenosoma and suggest that the speciation events from which stem most of the extant species took place well before the Messinian Salinity Crisis. Stenosoma spinosum and Stenosoma appendiculatum are the only exceptions, as they apparently arose within the Mediterranean during the Pleistocene. Phylogenetic reconstruction agrees with current taxonomic status of most species. However, Stenosoma capito clustered in two distinct and well‐supported clades, one composed of eastern Mediterranean and Black Sea specimens and the other by western Mediterranean and Atlantic ones. Such polyphyly suggests the existence of a previously unrecognized species, Stenosoma sp., which so far has been confounded with S. capito.     

Neandertals,competition, and the origin of modern human behavior in the Levant

The East Mediterranean Levant is a small region, but its paleoanthropological record looms large in debates about the origin of modern humans and the fate of the Neandertals. For most of the twentieth century, the Levantine paleoanthropological record supported models of continuity and evolutionary transition between Neandertals and early modern humans. Recent advances in radiometric dating have challenged these models by reversing the chronological relationship between Levantine Neandertals and early modern humans. This revised chronostratigraphy for Levantine Middle Paleolithic human fossils raises interesting questions about the evolutionary relationship between Neandertals and early modern humans. A reconsideration of this relationship moves us closer to understanding the long delay between the origin of morphologically modern‐looking humans during the Middle Paleolithic (>130 Kyr) and the adaptive radiation of modern humans into Eurasia around the time of the transition from the Middle to Upper Paleolithic (50 to 30 Kyr).     

The evolution of canaliculate rudists in the light of a new canaliculate polyconitid rudist from the Albian of the Central Pacific

A new polyconitid rudist, Magallanesia canaliculata gen. et sp. nov., of probably late Albian age, is described from the Pulangbato area, central Cebu Island, the Philippines in the western Central Pacific and Takuyo‐Daini Seamount, now located in the Northwest Pacific. It is similar to Praecaprotina Yabe and Nagao, 1926, a Japanese–Central Pacific endemic genus of late Aptian – early Albian age, but differs in having canals that developed by partitioning of the large ectomyophoral cavity in the posterior part of the left valve. Its discovery strengthens the evidence for Pacific endemism in Albian times. Several other clades of canaliculate rudists flourished or evolved at the same time in different regions of the Tethyan Realm, suggesting the presence of common global biological and/or environmental factors stimulating the evolution of the canals despite such endemism. Furthermore, the finding of a canaliculate polyconitid provides evidence in favour of the evolutionary hypothesis of a polyconitid origin for the Late Cretaceous canaliculate rudist family Plagioptychidae Douvillé, 1888.     

Debrunia,a new Barremian genus of petalodontid Monopleuridae (Bivalvia,Hippuritoidea) from the Mediterranean region

Abstract: Debrunia gen. nov. is characterized by asymmetric myophoral apophyses on the left valve: the posterior one a plate, the anterior a crest. The myophores on the right valve are on the shell wall. It belongs to a group of cylindro‐conical petalodontid Monopleuridae including Petalodontia and Pseudopetalodontia, and possesses some affinities with Agriopleura. Monopleura mutabilis Matheron is the type species of Debrunia gen. nov., and Monopleura (Petalodontia) bruni Douvillé is also ascribed to this genus. The two species are found in late Barremian beds from SE France. Evolutionary trends regarding the myophores of the left valve are comparable and nearly coeval with those of Agriopleura. Debrunia may be the root of the late Aptian–Albian genera Pseudopetalodontia and Mathesia. and may range throughout the Barremian‐Aptian.     

The phylogenetic systematics of blue‐tailed skinks (Plestiodon) and the family Scincidae

Blue‐tailed skinks (genus Plestiodon) are a common component of the terrestrial herpetofauna throughout their range in eastern Eurasia and North and Middle America. Plestiodon species are also frequent subjects of ecological and evolutionary research, yet a comprehensive, well‐supported phylogenetic framework does not yet exist for this genus. We construct a comprehensive molecular phylogeny of Plestiodon using Bayesian phylogenetic analyses of a nine‐locus data set comprising 8308 base pairs of DNA, sampled from 38 of the 43 species in the genus. We evaluate potential gene tree/species tree discordance by conducting phylogenetic analyses of the concatenated and individual locus data sets, as well as employing coalescent‐based methods. Specifically, we address the placement of Plestiodon within the evolutionary tree of Scincidae, as well as the phylogenetic relationships between Plestiodon species, and their taxonomy. Given our sampling of major Scincidae lineages, we also re‐evaluate ‘deep’ relationships within the family, with the goal of resolving relationships that have been ambiguous in recent molecular phylogenetic analyses. We infer strong support for several scincid relationships, including a major clade of ‘scincines’ and the inter‐relationships of major Mediterranean and southern African genera. Although we could not estimate the precise phylogenetic affinities of Plestiodon with statistically significant support, we nonetheless infer significant support for its inclusion in a large ‘scincine’ clade exclusive of Acontinae, Lygosominae, Brachymeles, and Ophiomorus. Plestiodon comprises three major geographically cohesive clades. One of these clades is composed of mostly large‐bodied species inhabiting northern Indochina, south‐eastern China (including Taiwan), and the southern Ryukyu Islands of Japan. The second clade comprises species inhabiting central China (including Taiwan) and the entire Japanese archipelago. The third clade exclusively inhabits North and Middle America and the island of Bermuda. A vast majority of interspecific relationships are strongly supported in the concatenated data analysis, but there is nonetheless significant conflict amongst the individual gene trees. Coalescent‐based gene tree/species tree analyses indicate that incongruence amongst the nuclear loci may severely obscure the phylogenetic inter‐relationships of the primarily small‐bodied Plestiodon species that inhabit the central Mexican highlands. These same analyses do support the sister relationship between Plestiodon marginatus Hallowell, 1861 and Plestiodon stimpsonii (Thompson, 1912), and differ with the mitochondrial DNA analysis that supports Plestiodon elegans (Boulenger, 1887) + P. stimpsonii. Finally, because the existing Plestiodon taxonomy is a poor representation of evolutionary relationships, we replace the existing supraspecific taxonomy with one congruent with our phylogenetic results. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 165 , 163–189.     

Genetic groups and endosymbiotic microbiota of the Bemisia tabaci species complex in Japanese agricultural sites

The whitefly Bemisia tabaci is a cryptic species complex of at least 24 genetically distinct species. Thus far, one obligate and seven facultative symbiotic bacteria have been reported from the B. tabaci species complex. Both genetic groups and infected symbionts are extremely important to estimate the pest status of B. tabaci. In this study, we collected 340 whiteflies from 39 agricultural sites, covering an entire region of the B. tabaci habitat in Japan, and examined the genotypes and symbiont community composition at subspecies level. Use of the cleaved amplified polymorphic sequence technique and mitochondrial cytochrome oxidase subunit I gene sequencing detected five genetic groups: indigenous species JpL and Asia II 6, invasive species Middle East‐Asia Minor 1 (MEAM1) and Mediterranean Subclade Q1 (MED Q1), and a genetic group previously undetected in Asia, Mediterranean Subclade Q2 (MED Q2). The genetic groups exhibited characteristic infection statuses with regard to their facultative symbionts, as observed in other countries. The endosymbiotic microbiota of the Japanese MED Q1 was different from that in neighbouring countries, but similar to that in the French or Uruguayan MED Q1. These results may indicate that Japanese MED Q1 species have not invaded from neighbouring countries, but from distant countries by international transportation. All Japanese MED Q2 species were infected with Rickettsia, some of which are regarded as conferring a female‐biased sex ratio and fitness benefit on B. tabaci. The results suggest that MED Q2 may be prevalent in Japan and neighbouring countries.     

Craniid brachiopods: aspects of clade structure and distribution reflect continental drift (Brachiopoda: Craniiformea)

We present maximum likelihood and Bayesian inference relative time‐tree analyses of aligned gene sequences from a worldwide collection of craniiform brachiopods belonging to two genera, Novocrania and Neoancistrocrania. Sequences were obtained from one mitochondrial and three nuclear‐encoded ribosomal RNA genes from varying numbers of specimens. Data‐exploration by network (splits) analyses indicates that each gene identifies the same divergent clades and (with one minor exception) the same inter‐clade relationships. Neoancistrocrania specimens were found only in the Pacific Ocean, near Japan, on the Norfolk and Chesterfield Ridges, and near the Solomon Islands. The Novocrania clades, in approximate order of increasing distance from the root comprise 1. a ‘Northern’ clade of animals collected in the NE. Atlantic, W. Mediterranean and Adriatic; 2. a ‘Tethyan’ clade comprising animals from the E. Mediterranean, Cape Verde islands and the Caribbean (Belize and Jamaica); 3. a ‘NE. Pacific’ clade containing animals from Vancouver Island and from localities near Japan and south of Taiwan; 4. a ‘Southern’ clade that contains two widely separated subclades, one from New Zealand and the other with an extraordinarily wide distribution, ranging from near Japan in the north to the Chesterfield Ridge and Solomon Islands in the West, and in the East to the Galapagos Islands, the coast of South America (Chile) and Richardson seamount (off South Africa) in the South Atlantic. To the South, members of this clade were found in the Weddell, Scotia and Bellinghausen Antarctic Seas. The root of the extant craniid radiation was previously found (by relaxed‐clock analysis) to lie on the branch connecting the two genera so that, in effect, the one clade of Neoancistrocrania serves to polarise evolutionary relationships within the several clades of Novocrania. As previously suggested, all results confirm that Neoancistrocrania is sister to the ‘Northern’ Novocrania clade, and this leads to a proposal that Neoancistrocrania represents one extreme of a wide range of variation in ancestral ventral valve mineralisation, speciation (～90 Ma) resulting from competitive exclusion in rapidly‐growing reef environments. To the extent possible, the identified molecular clades are correlated with named species of Novocrania. The reproductive and population biology of craniid brachiopods is not well known, but from available evidence they are considered to have low‐dispersal potential and, except in enclosed localities such as cold‐water fjords, to have small effective population sizes, features which are consistent with the observed divergent populations in well‐separated localities. Exceptionally slow craniid molecular (rDNA) evolution is suggested by the short branch of Novocrania where it has been used as an outgroup for large‐scale analyses of metazoans. Slow molecular evolution is also indicated by the existence of a distinct Tethyan clade, reflecting restricted dispersal at former times, and by the uniform, short, genetic distances and exceptionally wide geographical distribution of the Southern clade. Thus, the geographical distribution and phylogenetic divergence of craniid brachiopods is an example of phylotectonics, in which relationships revealed by phylogenetic analyses reflect opportunities for dispersal and settlement that were created by tectonic plate movements associated, in this case, with opening and closure of Tethys and the breakup of Gondwana. Molecular dating of craniid divergences and radiochemical dating of tectonic events thus illuminate one another. © 2014 The Linnean Society of London     

First fossil record of an East Asian endemic genus Sladenia (Sladeniaceae) from its modern range: Implications for floristic evolution and conservation biology

Fossil records of endemic plants play an important role in recognizing the floristic history of East Asia and thereby facilitate the conservation of plant diversity in the region. However, the fossil record of many extant East Asian endemic genera remains poorly documented thus far. Here, we report an infructescence fossil of an East Asian endemic genus, Sladenia (Sladeniaceae), from the early Miocene of southeastern Yunnan, China. The fossil is characterized by: (i) dichasial cymes; and (ii) flask‐shaped ovary with dense subparallel ribs on the surface extending from the base to the distal end of the united style. It represents the first fossil record of Sladenia in Asia, showing that the genus was established in the region at least by the early Miocene. Given that a much older fossil record of Sladeniaceae has been reported from Africa and the sister group of Sladenia is distributed only in Africa, Sladenia is not likely of East Asian origin. The present endemic status of Sladenia was possibly achieved by regional extirpation in Africa and taking refuge in East Asia. This case thus supports the “Museum” rather than “Cradle” hypothesis for the genesis of high plant species in the flora of East Asia. A comparison of the present fossil with extant Sladenia infructescence shows morphological stasis from the early Miocene to present. Such evolutionary tardiness might have resulted in the reduced fitness of the genus, which further caused its current endangered situation.     

Taxonomic revision of the genus Stauropoctonus Brauns, 1889 (Hymenoptera: Ichneumonidae: Ophioninae) in Japan

The Japanese species of the ichneumonid genus Stauropoctonus Brauns, 1889 are revised. As a result, three species are recognized. Stauropoctonus infuscus (Uchida, 1928 ) stat. rev. , previously synonymized with S. bombycivorus (Gravenhorst, 1829 ), is recognized as a valid species and re‐described. Stauropoctonus bombycivorus, which has already been recorded in Japan, is also recognized and re‐described based on Japanese specimens. Stauropoctonus aurantiacus sp. nov. is described based on a single male specimen from Yakushima Island, Kagoshima Prefecture, Japan. Stauropoctonus nigrithorax Lee & Kim, 2002 syn. nov. is newly synonymized with S. bombycivorus. Additionally, a key to the Stauropoctonus species and discussions on their phenology and collection methods are provided.     

Origin and spatio‐temporal diversification of a fishfly lineage endemic to the islands of East Asia (Megaloptera: Corydalidae)

Chauliodinae (fishflies), with their low capacity of long‐distance dispersal represent a suitable model insect group to investigate the biogeographical history. The genus Parachauliodes van der Weele, including the herein synonymized genus Sinochauliodes Liu & Yang, is endemic to East Asia. Here, we reconstruct the interspecific phylogeny of Parachauliodes based on mitochondrial DNA sequence data. Sinochauliodes syn.n. was recovered with a group of Parachauliodes species and not the sister group; we therefore treat it as the junior synonym of Parachauliodes. Species delimitation was performed combining the molecular identification with morphological evidence, with Parachauliodes inopinatus syn.n. treated as the junior synonym of Parachauliodes asahinai. The spatio‐temporal divergence pattern of Parachauliodes indicates that the genus might have originated from Eurasian continent no later than the early Miocene and the initial divergence within genus was likely to be correlated to the split of southwestern Japanese Islands from the continent. There likely was a southward dispersal in the Parachauliodes japonicus clade from southwestern Japan via the Ryukyus to Taiwan by the end of the Miocene. The present species diversity of the insular lineage of Parachauliodes was possibly shaped by island isolations and sympatric distribution.     

Late Jurassic decapod crustaceans from northeast Japan

Abstract: Astacidean and thalassinidean macrurans (Glyphea sp., ?Eryma sp. and Protaxius sp.) and a new longodromitid crab, Planoprosopon kashimaensis, are recorded from the Upper Jurassic (upper Kimmeridgian to lower Tithonian) of Fukushima Prefecture, northeast Japan. Material was collected from the Tatenosawa Sandstone Member of the Nakanosawa Formation, Somanakamura Group, from which abundant Tethyan‐type marine invertebrates are known. Planoprosopon kashimaensis sp. nov. closely resembles P. heydeni (von Meyer), a common form in the Upper Jurassic of the Tethyan realm in Europe, and represents the oldest record of a brachyuran from the circum‐Pacific region. Similarities to contemporaneous decapod assemblages in southern Germany indicate that closely comparable, parallel decapod faunas in the Tethyan realm, inclusive of brachyurans, had already been established in the western circum‐Pacific region by the Late Jurassic.     

A new record for Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) species complex of Turkey

In this study, species complex of Turkish Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) populations was determined by PCR‐based DNA analysis. According to phylogenetic analyses, the B. tabaci samples have been identified within three generic groups. A major part of the samples belonged to two invasive species, either Middle East–Asia Minor 1 (MEAM1) or Mediterranean (MED). In addition to these two invasive species, several samples collected from greenhouses and cotton fields have been found to be related to Middle East–Asia Minor 2 (MEAM2), which is the first record of Turkish B. tabaci species complex.     

First partial face and upper dentition of the Middle Miocene hominoid Dryopithecus fontani from Abocador de Can Mata (Vallès‐Penedès Basin,Catalonia, NE Spain): Taxonomic and phylogenetic implications

A well‐preserved 11.8‐million‐years‐old lower face attributed to the seminal taxon Dryopithecus fontani (Primates, Hominidae) from the Catalan site ACM/C3‐Ae of the Hostalets de Pierola area (Vallès‐Penedès Basin, Catalonia, NE Spain) is described. The new data indicate that D. fontani is distinct at the genus level from Late Miocene European taxa previously attributed to Dryopithecus, which are here reassigned to Hispanopithecus. The new facial specimen also suggests that D. fontani and the Middle Miocene Pierolapithecus catalaunicus are not synonymous. Anatomical and morphometric analyses further indicate that the new specimen shows a combination of lower facial features—hitherto unknown in Miocene hominoids—that resembles the facial pattern of Gorilla, thus providing the first nondental evidence of gorilla‐like lower facial morphology in the fossil record. Considering the current evidence, the gorilla‐like facial pattern of D. fontani is inferred to be derived relative to previously known stem hominids, and might indicate that this taxon is either an early member of the Homininae or, alternatively, a stem hominid convergent with the lower facial pattern of Gorilla. The biogeographic implications of both alternatives are discussed. This new finding in the Hostalets de Pierola section reinforces the importance of this area for understanding the elusive question of the Middle Miocene origin and early radiation of great apes. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

Evolutionary distinctiveness and conservation priority of the endangered Najas ancistrocarpa (Hydrocharitaceae)

Phylogeny is vitally important to evaluate evolutionary distinctiveness and conservation priorities of species. Najas ancistrocarpa is one of the rarest and least known East Asian species of the c. 30–40 species of the aquatic plant genus Najas (Hydrocharitaceae). We used a recently discovered collection of this nationally and regionally endangered species in Japan and East Asia to assess whether N. ancistrocarpa is a distinct species or an untypical form of other Najas species and to evaluate its conservation priority in a phylogenetic context. The sample set of our previous study, exploring worldwide phylogeny of the genus was used with N. ancistrocarpa to delimit species boundaries in Najas and obtain conservation priority scores, calculated by multiplying evolutionary distinctiveness and global extinction risks converted from Red List categories. We performed molecular phylogenetic analyses of plastid (ptDNA) and nuclear (ITS) DNA datasets, STACEY species delimitation analysis using the multilocus dataset and a measurement of conservation priority with Tuatara. Najas ancistrocarpa was consistently placed in ptDNA and ITS trees. Species delimitation analysis objectively assessed that N. ancistrocarpa is phylogenetically distinct. Phylogenetic conservation prioritization ranked N. ancistrocarpa the second highest priority species of the genus Najas. Overall, in terms of biodiversity conservation, N. ancistrocarpa represents an important Najas species in Japan and probably the world.     

A pre‐Miocene Irano‐Turanian cradle: Origin and diversification of the species‐rich monocot genus Gagea (Liliaceae)

The Irano‐Turanian (IT) floristic region is considered an important center of origin for many taxa. However, there is a lack of studies dealing with typical IT genera that also occur in neighboring areas. The species‐rich monocot genus Gagea Salisb. shows a center of diversity in IT region and a distribution in adjacent regions, therefore representing a good study object to investigate spatial and temporal relationships among IT region and its neighboring areas (East Asia, Euro‐Siberia, Himalaya, and Mediterranean). We aimed at (a) testing the origin of the genus and of its major lineages in the IT region, (b) reconstructing divergence times, and (c) reconstructing colonization events. To address these problems, sequences of the ribosomal DNA internal transcribed spacer (ITS) region of 418 individuals and chloroplast intergenic spacers sequences (psbA‐trnH, trnL‐trnF) of 497 individuals, representing 116 species from all sections of the genus and nearly its entire distribution area were analyzed. Divergence times were estimated under a random molecular clock based on nrITS phylogeny, which was the most complete data set regarding the representation of species and distribution areas. Ancestral distribution ranges were estimated for the nrITS data set as well as for a combined data set, revealing that Gagea most likely originated in southwestern Asia. This genus first diversified there starting in the Early Miocene. In the Middle Miocene, Gagea migrated to the Mediterranean and to East Asia, while migration into Euro‐Siberia took place in the Late Miocene. During the Pleistocene, the Arctic was colonized and Gagea serotina, the most widespread species, reached North America. The Mediterranean basin was colonized multiple times from southwestern Asia or Euro‐Siberia. Most of the currently existing species originated during the last 3 Ma.     

Phylogeography of Asparagopsis taxiformis revisited: Combined mtDNA data provide novel insights into population structure in Japan

Six intraspecific lineages (Lineages 1–6) of Asparagopsis taxiformis have been previously established based on mitochondrial cox2‐cox3 intergenic spacer and a partial cox1 sequences. ‘Lineage 2’ (L2) was suggested to be a recent introduction to the Mediterranean Sea, but its source population has not yet been identified. In order to clarify the nature of northwestern Pacific populations, we performed extensive sampling in Japan (60 individuals from 16 locations) and molecular phylogenetic analyses based on mitochondrial sequences. Sixteen additional individuals, collected from eight locations in the Indo‐Pacific, Caribbean, and Mediterranean regions, were also analyzed. Combined sequence analyses revealed that the Japanese populations only consisted of L2. Out of 19 combined haplotypes identified within L2, two are shared between Japan and the Mediterranean Sea and the Hawaiian Islands, and 12 were identified as endemic to Japan. Genetic analyses of population differentiation suggested that Japanese populations are genetically isolated from the Mediterranean and the Hawaiian populations. A genetic disjunction appears to separate two subpopulations within Japan: one between Toi and Kagoshima and the other between Ojikajima Island and Kagoshima in the Kyushu area.     

Phylogenetic analyses of Gammaridae crustacean reveal different diversification patterns among sister lineages in the Tethyan region

The Gammaridae shows the greatest disparity in species diversity and distribution pattern in the Amphipoda, with some genera ranging from the Palearctic to Nearctic, while others are limited to the Mediterranean region or ancient Tethyan margins. Here we present the first molecular phylogenetic analysis of the Gammaridae to investigate its evolutionary history using four genetic markers and a comprehensive set of taxa representing 198 species. The phylogenetic results revealed that the Gammaridae originated from the Tethyan region in the Cretaceous, and split into three morphologically and geographically distinct lineages by the end of the Paleocene. Diversification analysis combined with paleogeological evidence suggested that the Tethyan changes induced by sea‐level fluctuation and tectonic uplift triggered different diversification modes and range expansions for the three lineages. The Gammarus lineage underwent an early rapid radiation across Eurasia and North America, then declined towards modern species. Pontogammarids maintained stable diversification with restricted distributions around the Tethyan basin, whereas sarothrogammarids experienced evolutionary stasis by stranding on the ancient Tethyan margins. Our findings suggest that environmental changes have played an important role in the diversification of Gammaridae lineages, which could be an opportunity to promote adaptive radiations in new habitats, or constraints resulting in evolutionary relicts.     

A lower jaw of Palaeoxonodon from the Middle Jurassic of the Isle of Skye,Scotland, sheds new light on the diversity of British stem therians

The Middle Jurassic was a key interval of mammalian evolutionary history that witnessed the diversification of the therian stem group. Great Britain has yielded a significant record of mammalian fossils from this interval, represented by numerous isolated jaws and teeth from the Bathonian of Oxfordshire and the Isle of Skye. This record captures a key period in early cladotherian evolution, with amphitheriids, peramurans and ‘stem zatherians’ displaying intermediate talonid morphologies that document the evolutionary assembly of tribosphenic molars. We present a mandible with near‐complete dentition from the late Bathonian (c. 167.4–166.5 Ma) Kilmaluag Formation, near Elgol, Skye, representing the amphitheriid Palaeoxonodon ooliticus, previously known only from isolated teeth. The specimen sheds new light on the taxonomic diversity of British Middle Jurassic stem therians, as the morphological variation within the preserved tooth row encompasses that previously ascribed to three distinct species within two genera: Palaeoxonodon ooliticus, P. freemani and Kennetheridium leesi. Thus, both P. freemani and K. leesi are subjective junior synonyms of P. ooliticus. The dental formula of P. ooliticus (i4:c1:p5:m5) is intermediate between the primitively larger postcanine count (p5:m6–7) of Amphitherium and the reduced number in peramurans and tribosphenidans (p5:m3). Phylogenetic analyses of P. ooliticus generally confirm a close affinity with Amphitherium, but highlight the lack of strong empirical support for hypothesized patterns of divergences among early cladotherians.