Distal Tarsus Research Articles

Post-metamorphic development of Early Cretaceous frogs as a tool for taxonomic comparisons

ABSTRACT Specimens of a single but currently undetermined species of the anuran genus Liaobatrachus from the Lower Cretaceous of northeast China, including four articulated skeletons preserved on a single block of sediment plus two skulls and several additional adult skeletons on other slabs, illustrate post-metamorphic developmental stages from early juvenile to fully grown adult. The relative ages of the individuals were estimated based on body size combined with degree of ossification. Post-metamorphic developmental data not only provide a basis for comparisons with other fossil and recent anuran taxa, but also help to identify both age-independent (i.e., size-independent) characters that can be used for taxonomic comparisons among individuals of various sizes (i.e., ages) and age-dependent (i.e., size-dependent, ontogenetically variable) characters that can only be used for comparisons across corresponding developmental stages. Our study revealed that the following characters are independent of size in Liaobatrachus: frontoparietals with a fontanelle between their frontal portions; quadratojugal present; vertebral centra amphicoelous and pierced by a notochordal canal; and free (not ankylosed) ribs attached to diapophyses of second to fourth vertebrae. The tibiofibula/femur and presacral vertebral column/snout-vent length ratios were also found to be size independent. In contrast, ossification of the carpus, distal tarsals, and pubis appears to be ontogenetically variable (i.e., they vary with age), and this is presumably also true of fusion between the tibiale and fibulare. These characters should only be used for comparisons among individuals at a common developmental stage.

Extent With Modification: Leg Patterning in the BeetleTribolium castaneumand the Evolution of Serial Homologs

Serial homologs are similar structures that develop at different positions within a body plan. These structures share some, but not all, aspects of developmental patterning, and their evolution is thought to be constrained by shared, pleiotropic gene functions. Here we describe the functions of 17 developmental genes during metamorphic development of the legs in the red flour beetle, Tribolium castaneum. This study provides informative comparisons between appendage development in Drosophila melanogaster and T. castaneum, between embryonic and adult development in T. castaneum, and between the development of serially homologous appendages. The leg gap genes Distal-less and dachshund are conserved in function. Notch signaling, the zinc-finger transcription factors related to odd-skipped, and bric-à-brac have conserved functions in promoting joint development. homothorax knockdown alters the identity of proximal leg segments but does not reduce growth. Lim1 is required for intermediate leg development but not distal tarsus and pretarsus development as in D. melanogaster. Development of the tarsus requires decapentaplegic, rotund, spineless, abrupt, and bric-à-brac and the EGF ligand encoded by Keren. Metathoracic legs of T. castaneum have four tarsomeres, whereas other legs have five. Patterns of gene activity in the tarsus suggest that patterning in the middle of the tarsal region, not the proximal- or distal-most areas, is responsible for this difference in segment number. Through comparisons with other recent studies of T. castaneum appendage development, we test hypotheses for the modularity or interdependence of development during evolution of serial homologs.

MR imaging of the equine distal tarsus ‐ too much information?

MR imaging of the equine distal tarsus ‐ too much information?

Magnetic resonance imaging findings of bone marrow lesions in the equine distal tarsus

SummaryThree horses with sudden onset severe lameness were admitted for further diagnostic investigation. All horses had variable changes on radiographs in the distal tarsal region. Because of the sudden onset and severe degree of lameness, a magnetic resonance imaging (MRI) examination was performed. All horses showed areas of increased signal intensity in short tau inversion recovery (STIR) images involving the central and/or third tarsal bones. These lesions involved both the subchondral bone and bone marrow and are currently defined as bone marrow lesions (BML). Two horses were treated with shockwave therapy, one received intra‐articular medication. Two of the horses returned to previous athletic level and one is still in rehabilitation.

A small alvarezsaurid from the eastern Gobi Desert offers insight into evolutionary patterns in the Alvarezsauroidea

ABSTRACT A partial postcranial skeleton of a small alvarezsaurid from the Late Cretaceous of the Mongolian eastern Gobi Desert locality of Khugenetslavkant represents the first reported articulated theropod material from that locality. The specimen is recognized as the holotype of a new taxon herein named Albinykus baatar, gen. et sp. nov. Phylogenetic analysis places Albinykus within Alvarezsauridae as the sister taxon of Shuvuuia, another Late Cretaceous Mongolian taxon from the slightly younger Djadokhta Formation. The complete coossification of the proximal tarsals with the tibia, and of the distal tarsals and proximal metatarsals, present in Albinykus are previously unknown in Alvarezsauridae. Extensive fusion is consistent with histological data from the tibia indicating that the individual was a subadult. These results are striking given that Albinykus is among the smallest known non-avian dinosaurs with a body mass no greater than 1 kg and ranks among the smallest known alvarezsaurids. Alvarezsauridae shows a decreasing size trend throughout its evolutionary history, a rarity among dinosaurian clades. Within maniraptoran dinosaurs, such a trend has thus far only been recognized within Avialae and at the origin of Paraves with respect to other coelurosaurs. The holotype was recovered articulated in a ‘seated’ position, with hind limbs aligned and the feet tucked under the body. This body posture, which is present in Aves, has been previously noted in other maniraptoran clades (i.e., Oviraptoridae Troodontidae) and is now recognized in Alvarezsauridae.

A small alvarezsaurid from the eastern Gobi Desert offers insight into evolutionary patterns in the Alvarezsauroidea

ABSTRACT A partial postcranial skeleton of a small alvarezsaurid from the Late Cretaceous of the Mongolian eastern Gobi Desert locality of Khugenetslavkant represents the first reported articulated theropod material from that locality. The specimen is recognized as the holotype of a new taxon herein named Albinykus baatar, gen. et sp. nov. Phylogenetic analysis places Albinykus within Alvarezsauridae as the sister taxon of Shuvuuia, another Late Cretaceous Mongolian taxon from the slightly younger Djadokhta Formation. The complete coossification of the proximal tarsals with the tibia, and of the distal tarsals and proximal metatarsals, present in Albinykus are previously unknown in Alvarezsauridae. Extensive fusion is consistent with histological data from the tibia indicating that the individual was a subadult. These results are striking given that Albinykus is among the smallest known non-avian dinosaurs with a body mass no greater than 1 kg and ranks among the smallest known alvarezsaurids. Alvarezsauridae shows a decreasing size trend throughout its evolutionary history, a rarity among dinosaurian clades. Within maniraptoran dinosaurs, such a trend has thus far only been recognized within Avialae and at the origin of Paraves with respect to other coelurosaurs. The holotype was recovered articulated in a ‘seated’ position, with hind limbs aligned and the feet tucked under the body. This body posture, which is present in Aves, has been previously noted in other maniraptoran clades (i.e., Oviraptoridae Troodontidae) and is now recognized in Alvarezsauridae.

Detecting substrate engagement: responses of tarsal campaniform sensilla in cockroaches

Sensory signals of contact and engagement with the substrate are important in the control and adaptation of posture and locomotion. We characterized responses of campaniform sensilla, receptors that encode forces as cuticular strains, in the tarsi (feet) of cockroaches using neurophysiological techniques and digital imaging. A campaniform sensillum on the fourth tarsal segment was readily identified by its large action potential in nerve recordings. The receptor discharged to contractions of the retractor unguis muscle, which engages the pretarsus (claws and arolium) with the substrate. We mimicked the effects of muscle contractions by applying displacements to the retractor apodeme (tendon). Sensillum firing did not occur to unopposed movements, but followed engagement of the claws with an object. Vector analysis of forces suggested that resisted muscle contractions produce counterforces that axially compress the tarsal segments. Close joint packing of tarsal segments was clearly observed following claw engagement. Physiological experiments showed that the sensillum responded vigorously to axial forces applied directly to the distal tarsus. Discharges of tarsal campaniform sensilla could effectively signal active substrate engagement when the pretarsal claws and arolium are used to grip the substrate in climbing, traversing irregular terrains or walking on inverted surfaces.

Micro‐magnetic resonance imaging and embryological analysis of wild‐type and pma mutant mice with clubfoot

Gross similarities between the external appearance of the hind limbs of the peroneal muscle atrophy (pma) mouse mutant and congenital talipes equinovarus (CTEV), a human disorder historically referred to as ‘clubfoot’, suggested that this mutant could be a useful model. We used micro-magnetic resonance imaging to visualize the detailed anatomy of the hind limb defect in mutant pma mice and performed 3D comparisons between mutant and wild-type hind limbs. We found that the pma foot demonstrates supination (i.e. adduction and inversion of the mid foot and fore foot together with plantar flexion of the ankle and toes) and that the tibiale and distal tarsals display 3D abnormalities in positioning. The size and shape of the tibia, fibula, tarsal and metatarsal bones are similar to the wild-type. Hypoplasia of the muscles in the antero-lateral (peroneal) compartment was also demonstrated. The resemblance of these features to those seen in CTEV suggests that the pma mouse is a possibly useful model for the human condition. To understand how the observed deformities in the pma mouse hind foot arise during embryonic development, we followed the process of foot rotation in both wild-type and pma mutant mice. Rotation of the hind foot in mouse embryos of wild-type strains (CD-1 and C57/Black) occurs from embryonic day 14.5 onwards with rotation in C57/Black taking longer. In embryos from both strains, rotation of the right hind foot more commonly precedes rotation of the left. In pma mutants, the initiation of rotation is often delayed and rotation is slower and does not reach completion. If the usefulness of the pma mutant as a model is confirmed, then these findings on pma mouse embryos, when extrapolated to humans, would support a long-standing hypothesis that CTEV is due to the failure of completion of the normal process of rotation and angulation, historically known as the ‘arrested development hypothesis’.

Anatomy of the Early Cretaceous bird Rapaxavis pani, a new species from Liaoning Province, China

ABSTRACT The lacustrine deposits of the Jiufotang Formation, Liaoning Province, China have yielded a diverse avifauna representing a wide spectrum of basal lineages. Here we add to this diversity by describing the longirostrine enantiornithean taxon Rapaxavis pani gen. et sp. nov. The specimen possesses the following autapomorphies: (1) caudoateral processes of the sternum with two prominent branches and a smaller third branch, (2) paired triangular thoracic elements of unknown homology, and (3) the combination of six sacral vertebrae and six free caudal vertebrae. Otherwise, this genus is closely allied with the Yixian Formation species Longirostravis hani, sharing elongate, curving rostrum with teeth restricted to the premaxilla and rostral-most dentary, and a derived manus lacking unguals. The holotype of Rapaxavis is exquisitely preserved, with such details as distal tarsals, keratinous sheaths of the pedal unguals and some three-dimensional features of the bones intact. The holotype appears to lack a fused tibiotarsus and a fused carpometa-carpus. These features may indicate that the specimen is not yet fully grown, though the life stages of members of the Enantiornithes will not be clear until a complete ontogenetic series can be constructed. A comparison of the proportions of the pedal phalanges of Rapaxavis to modern birds shows Rapaxavis to be highly adapted to a grasping, arboreal lifestyle. The combination of strongly arboreal pedal adaptations and the probing adaptations in the rostrum is here confirmed in a member of the Enantiornithes for the first time in the literature, adding to their already impressive known functional diversity.

The histopathology of involutional ectropion and entropion

Objective: Involutional ectropion and entropion are characterized by excessive horizontal eyelid length, which is thought to be secondary to laxity of the medial and lateral canthal tendons and to the stretching of the tarsus. Histopathological features of the surgical eyelid specimens from patients with involutional ectropion and entropion were evaluated. Design: Prospective histopathological study. Participants: Eighteen full-thickness eyelid specimens from patients with involutional ectropion and entropion were obtained during horizontal eyelid shortening procedures performed at the Ministry of Health Ankara Training and Research Hospital. Methods: All specimens were fixed in 4% formaldehyde solution and sectioned sagittally. Hematoxylin-eosin, periodic acid-Schiff, and Masson's trichrome staining were done for all specimens. Histopathologic alterations of the tarsal plate, the palpebral portion of the orbicularis muscle, and the conjunctiva were examined. Results: The patients ranged in age from 60 to 80 years. The main histopathologic features of the ectropic eyelids included collagen degeneration and elastosis of the tarsal plate, increased amounts of adipose tissue in the distal tarsus, and subacute inflammation and epidermalization of the tarsal conjunctiva. Specimens from patients with involutional entropion generally had milder degrees of these histopathological features. Conclusions: The causes of the excessive horizontal length of the eyelid, which is thought to be secondary to laxity of the medial and lateral canthal tendons, may be collagen degeneration and elastosis of the tarsal plate and canthal tendons.

Appendicular skeleton inBachia bicolor(Squamata: Gymnophthalmidae): osteology, limb reduction and postnatal skeletal ontogeny

Jerez, A. and Tarazona, O. A. 2009. Appendicular skeleton in Bachia bicolor (Squamata: Gymnophthalmidae): osteology, limb reduction and postnatal skeletal ontogeny. — Acta Zoologica (Stockhom) 90: 42‐50 The osteology of the appendicular skeleton and its postnatal development are described in Bachia bicolor , a serpentiform lizard with reduced limbs. The pectoral girdle is well developed and the forelimb consists of a humerus, ulna, radius, five carpal elements (ulnare, radiale, distal carpals 4‐3, centrale), four metacarpals (II, III, IV, V) and phalanges (phalangeal formula X-2-2-2-2). In the hindlimb, the femur is small and slender, and articulates distally with a series of ossified amorphous and extremely reduced elements that correspond to a fibula, tibia and proximal and distal tarsals 4 and 3. The pelvic girdle consists of ischium, pubis and ilium, but its two halves are widely separated; the ilium is the least reduced element. We describe the ossification and development during postnatal skeletal ontogeny, especially of epiphyseal secondary centres, ossifications of carpal elements, apophyseal ossifications and sesamoids. Compared to other squamates, B. bicolor shows an overall reduction in limb size, an absence of skeletal elements, a fusion of carpal elements, an early differentiation of apophyseal centres, and a low number of sesamoids and apophyseal centres. These observations suggest that the reductions are produced by heterochronic changes during postnatal development and probably during embryonic development; therefore the appendicular skeleton exhibits a pattern of paedomorphic features.

EGFR signaling is required for re-establishing the proximodistal axis during distal leg regeneration in the cricket Gryllus bimaculatus nymph

Nymphs of hemimetabolous insects, such as cockroaches and crickets, possess functional legs with a remarkable capacity for epimorphic regeneration. In this study, we have focused on the role of epidermal growth factor receptor (EGFR) signaling in regeneration of a nymphal leg in the cricket Gryllus bimaculatus. We performed loss-of-function analyses with a Gryllus Egfr homolog ( Gb' Egfr) and nymphal RNA interference (RNAi). After injection of double-stranded RNA for Gb' Egfr in the body cavity of the third instar cricket nymph, amputation of the leg at the distal tibia resulted in defects of normal distal regeneration. The regenerated leg lacked the distal tarsus and pretarsus. This result indicates that EGFR signaling is required for distal leg patterning in regeneration during the nymphal stage of the cricket. Furthermore, we demonstrated that EGFR signaling acts downstream of the canonical Wnt/Wg signaling and regulates appendage proximodistal (PD) patterning genes aristaless and dachshund during regeneration. Our results suggest that EGFR signaling influences positional information along the PD axis in distal leg patterning of insects, regardless of the leg formation mode.

The anatomy and ultrastructure of the suctorial organ of Solifugae (Arachnida)

Solifugae possess an evertable, adhesive pedipalpal organ (suctorial organ) at the tip of the distal tarsus of each pedipalp that is unique among arachnids. When inverted inside the pedipalp, the suctorial organ is covered with two cuticular lips, a dorsal upper lip and a ventral lower lip, but it can be protruded rapidly in order to facilitate grasping prey or climbing on bushes or even climbing on smooth surfaces due to its remarkable adhesive properties. In this study, the suctorial organs of different species from old world families Galeodidae and Karschiidae and new world families Ammotrechidae and Eremobatidae were investigated by means of light microscopy, scanning and transmission electron microscopy. In all representatives, the suctorial organ is formed by an evertable, cuticular pad with a complex internal stabilizing structure. The procuticle of this pad consists of a lattice-like basal plate and numerous stalked structures connected to this basal plate. The shafts of the stalked structures are regularly organized and ramify apically. The surface of the suctorial organ is constituted of a very thin epicuticle overlaying the ramifying apices forming ridges and furrows on the ventral side of the suctorial organ.

A new protorosaur (Diapsida) from the Upper Buntsandstein of the Black Forest, Germany

ABSTRACT A new genus and species of protorosaur is described on the basis of material originally referred to Tanystropheus antiquus from the Upper Buntsandstein of the Black Forest, Germany. The new taxon is characterized by eight cervical vertebrae that bear markedly elongate cervical ribs, a shagreen of denticles covering the vomers, palatines and pterygoids, a bifurcate second sacral rib, a well-ossified tarsus with three distal tarsals, and an elongate proximal phalanx on digit five. The status of Tanystropheus antiquus is discussed and, while it is retained, its validity is questioned.

A concerted action of a paired-type homeobox gene, aristaless, and a homolog of Hox11/tlx homeobox gene, clawless, is essential for the distal tip development of the Drosophila leg

The subdivision of the developing field by region-specific expression of genes encoding transcription factors is an essential step during appendage development in arthropod and vertebrates. In Drosophila leg development, the distal-most region (pretarsus) is specified by the expression of homeobox genes, aristaless and Lim1, and its immediate neighbor (distal tarsus) is specified by the expression of a pair of Bar homeobox genes. Here, we show that one additional gene, clawless, which is a homolog of vertebrate Hox11/tlx homeobox gene family and formerly known as C15, is specifically expressed in the pretarsus and cooperatively acts with aristaless to repress Bar and possibly to activate Lim1. Similar to aristaless, the maximal expression of clawless requires Lim1 and its co-factor, Chip. Bar attenuates aristaless and clawless expression through Lim1 repression. Aristaless and Clawless proteins form a complex capable of binding to specific DNA targets, which cannot be well recognized solely by Aristaless or Clawless.

Chapter 2: The Ankle Structure of Two Pterodactyloid Pterosaurs from the Santana Formation (Lower Cretaceous), Brazil

Abstract The extremely well-preserved tarsus of the tapejarid Tapejara sp. and the anhanguerid Anhanguera piscator (Pterosauria, Pterodactyloidea) are described and regarded as representative of the ankle structure of Pterosauria. The pterosaur ankle joint (PAJ) shows the following features: astragalus mediolaterally elongated forming a hemicylinder; proximal part of the astragalocalcaneal contact characterized by a ridge bordered on each side by a depression on the astragalus that has a perfect counterpart in the calcaneum, and distal part that is concavo-convex, with the concavity present in the astragalus; calcaneum extremely reduced not reaching the posterior portion of the tarsus; absence of an astragalar posterior groove, perforating foramen, calcaneal tuber, and astragalar ascending process; proximal tarsals fusing very early in ontogeny, forming a tibiotarsus. The main movement between the crus and foot in the PAJ occurs between the proximal and distal tarsals as in the advanced mesotarsal-reverse...

The hind limb ofCaptorhinus agutiand the step cycle of basal amniotes

Exquisitely preserved limb elements of Captorhinus aguti from the Lower Permian locality of Richards Spur, Oklahoma, form an excellent basis for analysing the step cycle of the hind limb of basal amniotes. An articulated composite hind limb skeleton is moved through the step cycle. These movements are constrained by the intrinsic skeletal anatomy and data from fossilized footprints attributed to Palaeozoic amniotes. Two well-defined hinge joints are evident: a distal tarsometatarsal joint, and a mesotarsal joint between the calcaneum–astragalus–centrale unit and distal tarsals. A strict homology between the latter and mesotarsal joint in lepidosaurs is uncertain. The conspicuous size disparity between the distal end of the tibia and the much larger tibial facet of the astragalus, a widespread feature of archaic amniotes, permits considerable movement between the distal end of the tibia and astragalus during the stance phase. Differential dorsoflexion, concentrated at the preaxial side of the mesotarsal joint, allows the pes to remain stationary (rather than slide laterally) on the substrate as the femur is retracted and the tarsus shifts from an anterior to lateral orientation. The distal end of the femur describes an arc of only ~60° during the stance phase, but could rotate about 60° about its long axis, a figure comparable to that recorded for living lizards.

New morphological observations on Triassic pterosaurs

Abstract Since 1973, about 20 specimens of Triassic pterosaurs have been found in northern Italy, Austria and Greenland, belonging to Eudimorphodon, Peteinosaurus, Preondactylus and Austriadactylus . Their age is middle to late Norian and Eudimorphodon is the most common genus. The restudy of the specimens shows that Peteinosaurus presents trimorphodonty in the lower jaw and a fibula unreduced in length, distally expanded and fused to the tibiotarsus above the lateral condyle. Specimen MCSNB 3359 does not show diagnostic features of Peteinosaurus and is referred to it with doubt, whereas MCSNB 3496 is not Eudimorphodon but Peteinosaurus. Preondactylus, Peteinosaurus, ?Peteinosaurus and Dimorphodon could form a monophyletic group. The tarsus of Triassic pterosaurs consists of two proximal tarsals, which fuse to the tibia during ontogeny, forming a tibiotarsus, and two distal tarsals. The larger of the two proximal tarsals was probably the calcaneum. The lateral condyle of the tibiotarsus is larger or more well formed than the medial one. The shape of the distal tarsals is similar to that of the distal tarsals in Dimorphodon . The metatarsals did not spread and the foot was ectaxonic; metacarpal length increases from metacarpal I to IV. This suggests that footprints of Triassic pterosaurs were different from Pteraichnus -like footprints. Some features are unique to Triassic pterosaurs. and Austriadactylus have a multicuspid dentition, Peteinosaurus has cuspules in the distal teeth of the lower jaw and Preondactylus has serrated maxillary teeth. This could be a convergent feature or symplesiomorphic for their clade. and Austriadactylus have very large maxillary teeth below the ascending process of the maxilla. and possibly Preondactylus do not have the bundles of elongated caudal zygapophyseal and haemapophyseal processes which are present in Peteinosaurus and in the Jurassic long-tailed pterosaurs.

Heritability of age-at-onset of bone spavin in Icelandic horses estimated by survival analysis

Age-at-onset of bone spavin (BS) in horses was defined as a double-censored survival variable. A small material of binary responses to a radiographic examination of the distal tarsus in 439 Icelandic horses sired by 17 stallions was analysed. In order to test different models larger simulated data were generated according to an exponential proportional hazard model and subject to censoring. The resulting survivor functions were similar. The bias in survivor functions caused by double censoring in the material was reduced by use of the self-consistency (S-C) algorithm. Using a binary threshold model and the Weibull regression model, an analysis of age-at-onset of spavin resulted in severe underestimation of sire variance components in the simulated data. Survival analysis with Prentice and Gloeckler’s (1978) model led to less biased estimates. Application of this method on the real data resulted in an effective heritability estimate of h 2=0.33, which can be compared with an estimate of h 2=0.1 based on an analysis of radiographic signs (RS) using the binary threshold model. These results indicate that the age-at-onset of RS, which reflect the predisposition of BS, is a trait with medium-high heritability.

The ground state of the ventral appendage in Drosophila.

In Drosophila melanogaster, the antennae, legs, genitalia, and analia make up a serially homologous set of ventral appendages that depend on different selector genes for their unique identities. The diversity among these structures implies that there is a common ground state that selector genes modify to generate these different appendage morphologies. Here we show that the ventral appendage that forms in the absence of selector gene activity is leglike but consists of only two segments along its proximo-distal axis: a proximal segment and a distal tarsus. These results raise the possibility that, during evolution, leglike appendages could have developed without selector gene activity.