Ontogenesis of the scapula in marsupial mammals, with special emphasis on perinatal stages of didelphids and remarks on the origin of the therian scapula

The development of the scapula was studied in embryonic and postnatal specimens of Monodelphis domestica and perinatal specimens of Philander opossum, Caluromys philander, and Sminthopsis virginiae using histological sections and 3D reconstructions. Additionally, macerated skeletons of postnatal M. domestica were examined. This study focused on the detachment of the scapulocoracoid from the sternum and on the acquisition of a supraspinous fossa, a supraspinatus muscle, and a scapular spine, all these events associated with the origin of the therian shoulder girdle. In none of the specimens is there a continuity of the cartilaginous scapulocoracoid with the sternum, even though the structures are in close proximity, especially in S. virginiae. At birth, the first rib laterally presents a pronounced boss that probably contacts the humerus during certain movements. Only the acromial portion of the scapular spine, which originates from the anterior margin of the scapular blade, is preformed in cartilage. The other portion is formed by appositional bone ("Zuwachsknochen"), which expands from the perichondral ossification of the scapula into an intermuscular aponeurosis between the supra- and infraspinous muscles. This intermuscular aponeurosis inserts more or less in the middle of the lateral surface of the developing scapula. Thus, the floor of the supraspinous fossa is present from the beginning of scapular development, simultaneously with the infraspinous fossa. The homology of the therian spine with the anterior border of the sauropsid and monotreme scapula is questioned. We consider the dorsal portion (as opposed to the ventral or acromial portion) of the scapular spine a neomorphic structure of therian mammals.     

Evolution of the turtle bauplan: the topological relationship of the scapula relative to the ribcage

The turtle shell and the relationship of the shoulder girdle inside or ‘deep’ to the ribcage have puzzled neontologists and developmental biologists for more than a century. Recent developmental and fossil data indicate that the shoulder girdle indeed lies inside the shell, but anterior to the ribcage. Developmental biologists compare this orientation to that found in the model organisms mice and chickens, whose scapula lies laterally on top of the ribcage. We analyse the topological relationship of the shoulder girdle relative to the ribcage within a broader phylogenetic context and determine that the condition found in turtles is also found in amphibians, monotreme mammals and lepidosaurs. A vertical scapula anterior to the thoracic ribcage is therefore inferred to be the basal amniote condition and indicates that the condition found in therian mammals and archosaurs (which includes both developmental model organisms: chickens and mice) is derived and not appropriate for studying the developmental origin of the turtle shell. Instead, among amniotes, either monotreme mammals or lepidosaurs should be used.     

Postcranial anatomy of Haldanodon exspectatus (Mammalia, Docodonta) from the Late Jurassic (Kimmeridgian) of Portugal and its bearing for mammalian evolution

The postcranium of the Late Jurassic docodont Haldanodon exspectatus Kühne & Krusat, 1972 is represented by a partial skeleton and isolated bones of other individuals from the Late Jurassic (Kimmeridgian) of the Guimarota coal mine in Portugal. Haldanodon exhibits adaptations for a fossorial lifestyle such as stout and short limb bones and humeri with greatly expanded distal joints and strong deltopectoral crests. Short first and second phalanges and moderately curved and laterally compressed terminal phalanges with lateral grooves suggest that Haldanodon was a scratch-digger. The dorso-ventrally elongated, triangular scapula has a convex transverse profile with strongly laterally reflected anterior and posterior scapula margins, enclosing a deep trough-like 'infraspinous fossa'. A supraspinous fossa is not developed. The saddle-shaped glenoid facet is mainly formed by the coracoid and orientated antero-ventrally indicating a sprawling gait. No epiphyses were detected and the wide size range of humerus and femur possibly indicate a lifelong growth. Haldanodon is more derived than Morganucodon by complete reduction of the procoracoid, absence of the procoracoid foramen, and a peg-like coracoid. It shares with monotremes a postscapular fossa that is absent in Morganucodon . A PAUP analysis based on 280 cranio-dental and postcranial characters corroborated the position of Haldanodon above morganucodontids and below Hadrocodium .  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 145 , 219–248.     

滇东中泥盆统的节甲鱼类化石

本文记述了节甲鱼类中称为北极鱼类的三个新属种:Exutaspis megista,Kunmingolepislucaowanensis,Yangaspis jinningensis,化石分别采自武定海口组(广义),海口和晋宁的海口组。代表我国中泥盆世该类化石鱼类的首次记述。     

On the phylogenetic position of monotremes (Mammalia,Monotremata)

Henosferida from the Middle-Upper Jurassic of Western Gondwana is the most probable sister group for monotremes. They share the derived pretribosphenic structure of lower molars combined with the presumably absent protocone on the upper molars and the plesiomorphic retention of postdentary bones and pseudangular process of the lower jaw. In addition, the two groups share the dental formula with three molars and the position of the Meckel’s groove, which passes ventral to the mandibular foramen. In the course of subsequent evolution, monotremes acquired the mammalian middle ear with three auditory ossicles independently of therian mammals and multituberculates. Jurassic Laurasian Shuotheriidae are probably a sister group of the Gondwanian clade Henosferida + Monotremata. The Jurassic shuotheriid Pseudotribos shows a great plesiomorphic similarity to monotremes in the structure of the pectoral girdle, with a large interclavicle immovably connected to the clavicle. In the lineages leading to therian mammals and multituberculates, the pectoral girdle changed probably independently and in parallel in connection with the establishment of the parasagittal posture of the forelimbs (reduction of the interclavicle, mobile articulation of the interclavicle with clavicle, reduction of the procoracoid, and development of a supraspinous fossa of the scapula) and formation of the mammalian middle ear with three auditory ossicles.     

Terrestrial locomotion in monotremes (Mammalia: Monotremata)

Cineradiographic analysis of the limb movements of Ornithorhynchus reveals that the proximal limb bones undergo horizontal retraction, long-axis rotation and distal elevation (humerus) or depression (femur) during the propulsive phase of walking. Cinematographic records show that the locomotor movements of Ornithorhynchus differ in several respects from those of Tachyglossus and Zaglossus which are essentially similar. Comparison of the propulsive phase limb movements of Ornithorhynchus with those previously established radiographically for Tachyglossus reveals that the humerus is on average less laterally but more dorsally directed, and that the femur is on average more dorsally and slightly more laterally directed in Ornithorhynchus . Comparison of the limb orientations of monotremes with those empirically determined in therian mammals and lepidosaurian reptiles indicates that monotremes are most similar to therians. Consideration of several evidently derived features of the appendicular skeleton of monotremes leads to the conclusion that the limb orientations used by early mammals were probably similar to those used by locomotively generalized living therians, and that monotremes show modifications of this.     

Load transfer across the scapula during humeral abduction

Stress analysis in the individual parts of the scapula under normal physiological conditions is necessary to understand the load transfer mechanism, its relation with morphology of bone and to analyse the deviations in stress patterns due to implantation of the glenoid. The purpose of this study was to obtain stress distribution in the scapula during abduction of the arm and to obtain a qualitative estimate of the function of coracoacromial ligament. An accurate three-dimensional (3D) finite element (FE) model of the natural scapula has been developed for this purpose, using computed tomography data and shell-solid modelling approach. The model was experimentally validated. A musculoskeletal shoulder model of forces that calculates all muscle, ligament and joint reaction forces, in six load cases (30-180 degrees) during unloaded humeral abduction was used as applied loading conditions for the 3D FE model. High tensile and compressive stresses (15-60 MPa) were generated in the thick bony ridges of the scapula, like the scapular spine, lateral border, glenoid and acromion. High compressive stresses (45-58 MPa) were evoked in the glenoid and at the connection of glenoid-scapular spine-infraspinous fossa. The stresses in the infraspinous fossa and supraspinous fossa were low (0.05-15 MPa). These results indicated that the transfer of major muscle and joint reaction take place predominantly through the thick bony ridges, whereas the fossa area act more as attachment sites of large muscles. During humeral abduction, coracoacromial ligament was stretched, and presumably will be under tension.     

The role of Emx2 during scapula formation

The scapula is subdivided into head, collum, and blade. Due to the expression pattern of Emx2 and the absence of the scapula blade in Emx2 knockout mice, it has been suggested that Emx2 is involved in the formation of the scapula. Micromanipulation experiments revealed that ectoderm ablation over the somites does not affect Emx2 expression but inhibits the formation of the scapula blade indicating that Emx2 is not sufficient to induce scapula blade formation. Furthermore, we show that the formation of the scapula head is dependent, scapula blade formation independent of FGFR-1-mediated signaling. Overexpression of Emx2 does not influence scapula blade formation but leads to the development of an additional posterior digit in the anterior border of the limb. Taken together, the data presented implicate that Emx2 expression is necessary but not sufficient for the development of the scapula blade. It is not a marker for scapula development but rather provides positional information along the proximodistal and anterior-posterior limb axes, whereas the specificity of the developing skeletal elements is determined by the concerted interaction of Emx2 with other factors.     

EMG of serratus anterior and trapezius in the chimpanzee: scapular rotators revisited.

The importance of arm-raising has been a major consideration in the functional interpretation of differences in shoulder morphology among species of nonhuman primates. Among the characters that have been associated with enhancement of the arm-raising mechanism in hominoid primates are the relative enlargement of cranial trapezius and caudal serratus anterior, as the main scapular rotators, as well as changes in scapular morphology associated with their improved leverage for scapular rotation. Yet in an EMG study of cranial trapezius and caudal serratus anterior function in the great apes, Tuttle and Basmajian (Yrbk. Phys. Anthropol. 20:491-497, 1977) found these muscles to be essentially inactive during arm-raising. Although Tuttle and Basmajian suggest that the cranial orientation of the glenoid fossa in apes has reduced the demand for scapular rotation during arm-raising, subsequent EMG studies on other primate species suggest that these muscles do play a significant role in arm motion during active locomotion. This paper presents a reexamination of muscle recruitment patterns for trapezius and caudal serratus anterior in the chimpanzee. All but the lowest parts of caudal serratus anterior were found to be highly active during arm-raising motions, justifying earlier morphological interpretations of differences in caudal serratus anterior development. The lowest digitations of this muscle, while inactive during arm-raising, displayed significant activity during suspensory postures and locomotion, presumably to control the tendency of the scapula to shift cranially relative to the rib cage. Cranial trapezius did not appear to be involved in arm-raising; instead, its recruitment was closely tied to head position.     

Postnatal allometry of the skeleton in Tupaia glis (Scandentia: Tupaiidae) and Galea musteloides (Rodentia: Caviidae)--a test of the three-segment limb hypothesis

During the evolution of therian mammals, the two-segmented, sprawled tetrapod limbs were transformed into three-segmented limbs in parasagittal zig-zag configuration (three-segment limb hypothesis). As a consequence, the functional correspondence of limb segments has changed (now: scapula to thigh, upper arm to shank, fore arm plus hand to foot). Therefore, the scapula was taken into account in the current study of the postnatal growth of the postcranial skeleton in two small mammalian species (Tupaia glis, Galea musteloides). Comparisons were made between the functionally equivalent elements and not in the traditional way between serially homologous segments. This study presents a test of the three-segment limb hypothesis which predicts a greater ontogenetic congruence in the functionally equivalent elements in fore and hind limbs than in the serially homologous elements. A growth sequence, with decreasing regression coefficients from proximal to distal, was observed in both species under study. This proximo-distal growth sequence is assumed to be ancestral in the ontogeny of eutherian mammals. Different reproductive modes have evolved within eutherian mammals. To test the influence of different life histories on ontogenetic scaling during postnatal growth, one species with altricial juveniles (Tupaia glis) assumed to be the ancestral mode of development for eutherians and one species with derived, precocial young (Galea musteloides) were selected. The growth series covered postnatal development from the first successive steps with a lifted belly to the adult locomotory pattern; thus, functionally equivalent developmental stages were compared. The higher number of allometrically positive or isometrically growing segments in the altricial mammalian species was interpreted as a remnant of the fast growth period in the nest without great locomotor demands, and the clearly negative allometry in nearly all segments in the precocial young was interpreted as a response to the demand on early locomotor activity. Different life histories seem to have a strong influence on postnatal ontogenetic scaling; the effects of the developmental differences are still observable when comparing adults of the two species.     

Normalization procedures using maximum voluntary isometric contractions for the serratus anterior and trapezius muscles during surface EMG analysis.

The serratus anterior and trapezius muscles are considered to be the only upward rotators of the scapula and are very important for normal shoulder function. A variety of methods have been used to produce a maximum voluntary isometric contraction (MVIC) of these muscles for normalization of EMG data. The purpose of this study was to quantify the surface EMG activity of the serratus anterior muscle and the upper, middle, and lower parts of the trapezius during 9 manual muscle tests performed with maximum effort in 30 subjects. It was found that no one muscle test produced a MVIC for all individuals. Therefore, to perform normalization within each subject, it is suggested that the 2 or 3 tests identified in this study that produce high levels of EMG activity for each muscle be performed. The scapular protraction muscle test that is often used to normalize data for the serratus anterior muscle produced relatively low levels of EMG activity and was not found to be an optimal test. Muscle tests in which an attempt was made to de-rotate the scapula from an upwardly rotated position produced much higher levels of EMG activity in the serratus anterior muscle.     

Visual field of cultured striped trumpeter Latris lineata (Teleostei) larvae feeding on rotifer prey

The visual field of striped trumpeter Latris lineata larvae fed rotifer prey was determined from analysis of feeding behaviour in the horizontal plane. The visual field was forward and laterally directed, characterised by maximum reactive distances (distance at which the predator first detects and reacts to the prey) of 5.07 mm and 5.25 mm on days 13 and 17 post-hatching, respectively, 97% of mean larval length. This confirmed the predicted horizontal visual field, forward and laterally directed, derived from higher cone cell densities in the dorso-temporal and medial regions of the retina compared with ventral regions. The visual field of prey detection expanded laterally with ontogeny as a wider range of reactive angles was used by 17 day-old than 13 day-old larvae. Larvae displayed a saltatory searching pattern, periodically stopping to scan for prey throughout the visual field, and exhibited a side-to-side movement of the head as they approached and stopped, prior to striking at a detected prey item. Larvae on day 17 post-hatching terminated 35% of feeding sequences at the pre-strike position, at a mean distance from prey of 0.58 mm.     

Crouched posture and high fulcrum, a principle in the locomotion of small mammals: The example of the rock hyrax (Procavia capensis) (Mammalia: Hyracoidea)

The cineradiographic study of the locomotion of the rock hyrax (Procavia capensis) and the functional interpretation of its locomotory system, reveals that the main action of proximal segments is combined with flexed position and low movements of limb joints. This observation can be applied to the locomotion of other small mammals. In the forelimb, scapular rotation and translation account for more than 60% of step length. Effective shoulder joint movements are mostly restricted to less than 20°, and elbow movements range mainly between 20°-50°. The detachment of the shoulder girdle of therian mammals from the axial skeleton, and development of a supraspinous fossa, are correlated with movements at a high scapular fulcrum. Movements at such a high fulcrum are in interdependency with a crouched posture. Only flexed limbs can act as shock absorbers and prevent vertical changes in the center of gravity. Basic differences in forelimb movements exist between larger primates (humeral retraction) and smaller mammals (scapula retraction). In the hyrax, propulsion is due mainly to hip joint movements in symmetrical gaits, but sagittal lumbar spine movements play the dominant role at in-phase gaits. Joint and muscular anatomy, especially of the shoulder region, are discussed in view of the kinematic data.     

Comparative macro- and microscopic anatomy of the nasal cavity of European insectivores]

The topography of the nasal fossa and its epithelium were studied in 4 European Insectivores, Sorex araneus L., Crocidura russula (Hermann), Talpa europaea L. and Erinaceus europaeus L. The following results were obtained: 1. The length of the nasal capsules is in relation to the length of the head in all 4 species the same. 2. The noses of all forms studies, except E. europaeus are very similar because of the trunk-shaped pars anterior nasi. 3. The numbers of turbinals are constant. 4. Of all turbinals the atrio-turbinal is ventrally the rostral one, and in the shrews it is considerably longer than in E. europaeus and T. europaea. 5. There is a maxillo-turbinal caudal of the atrio-turbinal. Both of these turbinals can be found separated by an incisura atrio-maxillo-turbinalis in T. europaea and the shrews. In E. europaeus the skeleton of the 2 turbinals is bridged by a fold of mucous membrane. 6. The maxillo-turbinal is bilamellar in T. europaea and the shrews, with each of the laminae rolled up in opposite direction. The surface of the maxillo-turbinal of E. europaeus is increased enormously by means of secondary folds. 7. The naso-turbinal begins almost at the tip of the nose and approaches the lamina cribrosa, where it disappears. One can discern 3 differently shaped parts of the naso-turbinal: Crus orale, crus intermedium and crus aborale. The nasoturbinal originates out of 2 different structures (the crus orale of the naso-turbinal and the lamina semicircularis) which are ontogenetically different, however, they have become fused during ontogeny, thus forming a structure which seems to be homogenous. 8. There are 3 ethmo-turbinals. The 1st ethmo-turbinal is the largest one and its free anterior tip is found in the intermediate part of the nasal fossa. Its epi-turbinal is an accessory lamella found in the aboral part of the first ethmoturbinal. Except in S. araneus it always appears in paraseptal views between the ethmo-turbinal I and II. 9. There are 3 ecto-turbinals. 2 ecto-turbinals are situated between the naso-turbinal and the ethmo-turbinal I, whereas the 3rd ecto-turbinal appears between ethmo-turbinal I and II. 10. There are 3 recesses of the lateral parts of the nasal fossa: The recessus frontalis anterior is found rostral-dorsally of the pars intermediate of the nasal fossa. The recessus frontalis posterior communicates with the former, but is located caudal of it. The 3rd recessus sphenoidalis is actually a subcerebral niche of the nasal fossa in the os sphenoidale. 11. There is only one pneumatic cavity in Insectivores, the sinus maxillaris. 12. The nasal fossa can be divided into a regio vestibularis, regio respiratoria and regio olfactoria. The epithelium of the nasal fossa is similar in all forms studied. 13. The anterior part of the oral regio vestibularis is outlined by keratinized epithelium; posteriorly, by loosing its stratum corneum, it changes into unkeratinized pseudostratified epithelium. 14...     

Outcomes of scapula stabilization in obstetrical brachial plexus palsy: a novel dynamic procedure for correction of the winged scapula

Among the late consequences of obstetrical brachial plexus palsy is winging of the scapula, a functional and aesthetic deformity. This article introduces a novel surgical procedure for the dynamic correction of this clinical entity that involves the dynamic transfer of the contralateral trapezius muscle and/or rhomboid muscles and anchoring to the affected scapula. In more severe cases of scapula winging, the contralateral latissimus dorsi muscle may also need to be transferred to achieve dynamic scapula stabilization. The outcomes of this novel surgical procedure were analyzed in relation to the effect on abduction, external rotation, growth of the scapula, and distance of the scapula from the posterior midline. The results were analyzed in 26 patients who underwent this procedure and had adequate follow-up. The mean patient age was 6.39 years. Fourteen (54 percent) had a diagnosis of Erb palsy, and 12 (46 percent) had a diagnosis of global paralysis. All 26 patients had an additional secondary procedure performed prior to or simultaneously with the scapula stabilization procedure. In 19 patients, the contralateral trapezius was transferred and anchored to the medial border of the winged scapula alone, but in seven cases the underlying rhomboid major was transferred along with the trapezius muscle to provide sufficient scapula stabilization. In five cases in which the scapula winging was severe, the contralateral latissimus dorsi muscle was transferred at a second stage. After this procedure, all patients demonstrated improved scapula symmetry. The mean increase in abduction was 18 degrees (p < 0.001), the mean increase in external rotation was 19 degrees (p < 0.001), and the mean increase in anterior flexion was 12 degrees (p = 0.015). The improvement of the relative position of the winged scapula on the posterior thorax was analyzed by measuring the distance of the inferior angle of both scapulae from the midline, then calculating the difference between normal and affected sides and comparing this value before and after the scapula stabilization procedure. This value preoperatively was 3.24 cm; postoperatively it decreased to 0.36 cm (p < 0.001), demonstrating a statistically significant improvement.     

Assessment of scapular morphology and bone quality with statistical models

The design of total shoulder arthroplasty implants are guided by anatomy. The objective of this study was to develop statistical models to quantify shape and material property variation in the scapula. Material-mapped models were reconstructed from CT scans for a training set of subjects. Statistical shape (SSM) and intensity (SIM) models were created; SSM modes described scaling, changes in the medial border and acromial process, and elongation of the scapular blade. SIM modes captured bone quality changes in the anterior and inferior glenoid. Bone quality was independent of scapular morphology. Variation described by the statistical representations can inform implant design and sizing.     

Ontogeny and morphology of the round window and aqueduct of cochlea in Tupaia and other mammals

Studied the morphogenesis of the Fenestra rotunda and of the Aquaeductus cochleae in a series of 23 dated embryos and postnatal stages of Tupaia belangeri. The ontogeny of the Fenestra rotunda is the result of the caudal growth of the Processus recessus (DE BEER 1937). The Processus arises from the caudal ridge of the floor of the cochlear part of the otic capsule. On the 28th d of ontogeny (the gestation period of Tupaia belangeri is 43 d), it is fused with the lateral edge of the parachordal plate. On the 40th d, the Processus recessus joins the ventral surface of the canalicular part of the otic capsule, which develops a small cartilaginous process to meet it. In Tupaia, the Processus recessus is a large cartilaginous plate in a nearly horizontal position. It does not reach the plane of the Foramen perilymphaticum. The Processus recessus can be regarded as a part of the parachordal plate that was shifted laterally together with the Recessus scalae tympani by the enlargement of the cochlear part of the otic capsule in the ancestors of living mammals. The Processus forms the floor of the Aquaeductus cochleae, by which the laterally shifted Recessus scalae tympani of mammals remains connected with the cranial cavity. The Aquaeductus cochleae contains the Ductus perilymphaticus connecting the Cavum perilymphaticum of the inner ear with the Cavum leptomeningeum. The Fenestra rotunda of mammals is homologous with the lateral aperture of the Recessus scalae tympani of reptiles. In some mammals (e.g. Micropotamogale), the Membrana tympani secundaria spans the lateral aperture of the Recessus scalae tympani, as in many reptiles. Both the Membrana tympani secundaria of reptiles and that of mammals are homologous. Secondarily, in a large number of therian mammals (e.g. Myotis [Frick 1952]), the tympanic cavity extends into the Recessus scalae tympani displacing the Membrana tympani secundaria medially from the lateral aperture of the Recessus scalae tympani (= Fenestra rotunda of mammals) and even into the plane of the Foramen perilymphaticum. Thereby the Fossula fenestrae rotundae is formed, which in bounded medially by the Membrana tympani secundaria.     

The development of the septum primum relative to atrial septation in the mouse heart

The septum primum in the mouse originates as a thickened primordium with a straight rather than a sickle-shaped ventral border. It is covered on its ventral border by anterior cushion material which is continuous over the roof of the atrium with the principal anterior cushion mass. A process of cavitation thins the septum primum and precedes actual fenestration. This process shifts the membranous septum to the left thereby providing room for the septum secundum to overlap on the right side. The septum primum cannot contact the posterior cushion until closure of the sinus venosus gutter which is described. The closure of the interatrial foramen, later the foramen primum, is accomplished by cell growth of the anterior cushion material. The ventral thick border of the septum primum contributes to the ventral limbus and the caudal thickened boundary of the fossa ovalis with some contribution from the left venous valve. These boundaries as well as the membranous portion of the interatrial septum are derived from the same primordium, namely the septum primum.     

云南兽(三列齿类爬行动物)的耳区结构

本文介绍了以短吻云南兽为代表的一种耳区结构.它表明在三列齿类爬行动物里已经出现有发育的耳蜗壳以及在其内侧通过的颈内动脉等进步性质,听腔亦趋封闭.云南兽的中耳腔外侧出现了一条曲折的骨质外耳道,侧枕骨突外侧明显的沟可能表明方骨后耳膜之存在.     

ONTOGENY AND RELATIONSHIPS OF THE TRILOBITE PSEUDOPETIGURUS PRANTL AND PŘIBYL

Abstract:  The ontogeny of Pseudopetigurus deprati Turvey et al ., 2006 from the Ordovician Dawan Formation (Arenigian), Anhui Province, South China, is described. The presence of an anterior cranidial border in Pseudopetigurus is recognized for the first time. On account of the short (tr.), spindle-shaped anterior border, and the distinct, steeply inclined, wall-like pygidial margin, Pseudopetigurus is assigned to the family Dimeropygidae, the first genus of this family endemic to Gondwana. It has previously been regarded as a member of family Isocolidae. Cladistic analysis of species assigned to Dimeropygidae supports the monophyly of a clade including Dimeropyge , Dimeropygiella , Ischyrotoma , Pseudohystricurus and Pseudopetigurus , which may represent a subfamily Dimeropyginae. The distribution of Dimeropyginae shows a predominantly palaeotropical distribution, while the Gondwana Pseudopetigurus must have diverged from the dimeropygine common ancestor in pre-Arenigian time.