Ontogeny of the autopodial skeleton of the gecko Tarentola (Squamata: Phyllodactylidae)

Squamates exhibit evident diversity in their limb morphology. Gekkotans are a particularly diverse group in this respect. The appearance of toepads in gekkotans usually cooccurs with the reduction or loss of claws. The gecko Tarentola (Phyllodactylidae) shows a unique combination of features among geckos, with toepads, hyperphalangy, and dimorphism of claw expression (claws are retained on digits III and IV, but lost (manus) or strongly reduced (pes) on the remaining digits). Despite being a candidate model for studying embryonic skeletal development of the autopodium, no studies have investigated the autopodial development of the gecko Tarentola in detail. Here, we aim to follow up the development of the autopodial skeleton in T. annularis and T. mauritanica using acid-free double staining. The results indicate that the terminal phalanges of claw-bearing digits III and IV ossify earlier than in the remaining digits. This confirms the differential ossification as a result of claw regression in Tarentola. The strongly reduced second phalanges of digits IV in both the fore- and hindlimbs are the last ossifying phalanges. Such late ossification may precede the evolutionary loss of this phalanx. If this is correct, the autopodia of Tarentola would be an interesting example of both the hyperphalangy in digit I and the process of phalanx loss in digit IV. Delay in ossification of the miniaturised phalanx probably represents an example of paedomorphosis.

Embryonic development of the skull in a parthenogenetic lizard, the mourning gecko (Lepidodactylus lugubris)

Gekkotans are one of the major clades of squamate reptiles. As one of the earliest-diverging lineages, they are crucial in studying deep-level squamate phylogeny and evolution. Developmental studies can shed light on the origin of many important morphological characters, yet our knowledge of cranial development in gekkotans is very incomplete. Here, we describe the embryonic development of the skull in a parthenogenetic gekkonid, the mourning gecko (Lepidodactylus lugubris), studied using non-acidic double staining and histological sectioning. Our analysis indicates that the pterygoid is the first ossifying bone in the skull, as in almost all other studied squamates, followed closely by the surangular and prearticular. The next to appear are the dentary, frontal, parietal and squamosal. The tooth-bearing upper jaw bones, the premaxilla and maxilla, develop relatively late. In contrast to previous reports, the premaxilla starts ossifying from two distinct centres, reminiscent of the condition observed in diplodactylids and eublepharids. Only a single ossification centre of the postorbitofrontal is observed. Some of the endochondral bones of the braincase (prootic, opisthotic, supraoccipital) and the dermal parasphenoid are the last bones to appear. The skull roof is relatively poorly ossified near the time of hatching, with a large frontoparietal fontanelle still present. Many bones begin ossifying relatively later in L. lugubris than in the phyllodactylid Tarentola annularis, which suggests that its ossification sequence is heterochronic with respect to T. annularis.

Rediscovery and redescription of the only known mosasaur bone from the Turonian (Upper Cretaceous) of Poland

Mosasaur remains from Poland are very rare and are restricted mostly to the Campanian and Maastrichtian. The only currently known pre-Campanian records come from the Turonian strata in the Opole area, southwestern Poland. One of them is a single tooth which probably belongs to a yaguarasaurine while the other is an incomplete vertebra, for many years considered lost. The latter specimen has recently been found and is redescribed in this article. Its most characteristic feature is a strong dorsoventral compression of the articular surfaces. This is similar to the condition observed in basal mosasauroids such as halisaurines and tethysaurines. Unfortunately, due to its incompleteness, the rediscovered specimen cannot be confidently referred to any of these clades and can only be described as a probable non-mosasaurine, non-plioplatecarpine, non-tylosaurine mosasauroid. Despite its uncertain phylogenetic position, it is important from a historical point of view and as only the second record (and the only bone record) of mosasauroids from the Turonian of Poland.

Developmental anomalies in the smooth snake, Coronella austriaca Laurenti, 1768 (Squamata, Colubridae) from Poland

We present four cases of rare developmental anomalies in the smooth snake Coronella austriaca Laurenti, 1768 from western Poland. These include brachycephaly, lordosis, a supernumerary row of ‘ventral’ scales, and the third reported case of dicephalism in snakes from Poland. All the cases are supported by X-ray radiography. One of the possible explanations for these anomalies is a low genetic variation in populations from western Poland.

Phylogenetic Diversity of Ossification Patterns in the Avian Vertebral Column: A Review and New Data from the Domestic Pigeon and Two Species of Grebes

Simple Summary

There are still many unknowns in the development of the skeleton in birds. Traditionally, the neck vertebrae were considered to be the first ossifying elements in the spine. Later studies have shown that this is not always the case. In some species, the thoracic vertebrae ossify even before them. Evolutionary analyses indicate that ancestrally the spine starts ossifying from two different sites, one located in the neck, the other in the thorax. However, the Neoaves, a group that includes all living birds except the palaeognaths, landfowl and waterfowl, are very poorly studied. In this article, we review the information about ossification patterns of the spine in birds. We also describe its development in three neoavians, the pigeon and two grebes. In the pigeon, the neck vertebrae were the first to ossify, but in the grebe, the thoracic vertebrae ossified earlier. Our analyses confirm the ancestral presence of two sites from which the ossification of the spine starts in birds.

Abstract

Despite many decades of studies, our knowledge of skeletal development in birds is limited in many aspects. One of them is the development of the vertebral column. For many years it was widely believed that the column ossifies anteroposteriorly. However, later studies indicated that such a pattern is not universal in birds and in many groups the ossification starts in the thoracic rather than cervical region. Recent analyses suggest that two loci, located in the cervical and thoracic vertebrae, were ancestrally present in birds. However, the data on skeletal development are very scarce in the Neoaves, a clade that includes approximately 95% of extant species. We review the available information about the vertebral column development in birds and describe the ossification pattern in three neoavians, the domestic pigeon (Columba livia domestica), the great crested grebe (Podiceps cristatus) and the red-necked grebe (Podiceps grisegena). In P. cristatus, the vertebral column starts ossifying in the thoracic region. The second locus is present in the cervical vertebrae. In the pigeon, the cervical vertebrae ossify before the thoracics, but both the thoracic and cervical loci are present. Our ancestral state reconstructions confirm that both these loci were ancestrally present in birds, but the thoracic locus was later lost in psittacopasserans and at least some galloanserans.

Embryonic development and perinatal skeleton in a limbless, viviparous lizard, Anguis fragilis (Squamata: Anguimorpha)

Despite the long history of embryological studies of squamates, many groups of this huge clade have received only limited attention. One such understudied group is the anguimorphs, a clade comprising morphologically and ecologically very diverse lizards. We describe several stages of embryonic development of Anguis fragilis, a limbless, viviparous anguimorph. Interestingly, in several clutches we observe high morphological variation in characters traditionally important in classifying embryos into developmental stages. The causes of this variation remain unknown but environmental factors do not seem to be very important. Additionally, we describe the state of ossification in several perinatal specimens of A. fragilis. The cranial skeleton is relatively poorly ossified around the time of birth, with all of the bones constituting the braincase unfused. On the other hand, the vertebral column is well ossified, with the neurocentral sutures closed and the neural arches fused in all postatlantal vertebrae. Such an advanced state of ossification may be related to the greater importance of the vertebral column in locomotion in limbless species than in ones with fully-developed limbs. Numerous factors seem to affect the state of ossification at the time of hatching or birth in squamates, including phylogenetic position, mode of reproduction and, potentially, limblessness. However, data from a greater number of species are needed to reach firmer conclusions about the relative importance of these variables in certain clades.

Postnatal ossification sequences in Acrocephalus scirpaceus and Chroicocephalus ridibundus (Aves: Neognathae): The precocial-altricial spectrum and evolution of compound bones in birds

Although the development of the avian skeleton has attracted considerable attention, most of the studies have been concentrated on the embryonic period, while studies on the postnatal period are rare. We studied the postnatal development of the skeleton in two phylogenetically distant birds, an altricial passerine Acrocephalus scirpaceus and a semiprecocial charadriiform Chroicocephalus ridibundus. The neonates of the former, despite being altricial, have well-ossified skeleton-the degree of development approaches that of the semiprecocial gull. However, after hatching the limb bones (particularly those of the hind limb) ossify earlier in the gull which is probably related to faster acquisition of locomotor abilities. We have observed that, in contrast to previous reports from neognathous birds, in the ankle of the gull, the ascending process fuses with the astragalus rather than with the calcaneum. This type of development is present in palaeognaths and nonavian dinosaurs but has not yet been reported in neognaths. This indicates a greater diversity within Neognathae and suggests a more complex scenario for the evolution of the avian ankle. However, data from a greater number of species are needed to establish the developmental sequence ancestral for neognathous birds. Furthermore, the sequence of bone fusions in the wrist of Acrocephalus is similar to the fossil-documented evolutionary sequence observed in the phylogeny of early birds, with the semilunate carpal and major metacarpal fusing first, followed by the alular metacarpal fusing with the major metacarpal and then the major and minor metacarpal fusing proximally. These data underscore the importance of developmental studies for reconstructing the evolutionary history.

Biology and origin of isolated north-easternmost populations of the common wall lizard, Podarcis muralis

The common wall lizard, Podarcis muralis, is a widely distributed European lizard which has been often introduced across the continent, including north of the continuous species range. Three such populations were recently discovered in the Strzelin Hills in Poland, but no information is available about their origin. We studied the morphological variation, demographic structure and ecology of these populations, as well as their possible origin based on cytochrome b mtDNA sequences. Between 2011 and 2019, the lizards were annually active from the first half of March to mid-October. Males attained significantly larger snout-vent length than females and had relatively larger heads. Almost half of all captured individuals exhibited at least one pileus scale anomaly. Analysis of colour polymorphism revealed the occurrence of three morphs: white, white-red and red. The oldest lizards reached the age of 8 years. These parameters of Polish populations do not deviate from those of other populations from similar latitudes. Molecular analysis revealed that they belong to the most common haplotype of Central European haplogroup I of the Central Balkan clade. This haplotype is widely distributed across the Czech Republic and Slovakia; however, genetic data do not allow determination of the exact origin of the Polish population. Human-mediated introduction from the closest localities, the Czech Republic or Slovakia, is probable but the relict status cannot at present be excluded.

Ventral scale width in snakes depends on habitat but not hunting strategy

Environment and lifestyle induce substantial variation in the mechanisms of locomotion in vertebrates. A spectrum of adaptations related to locomotion is also present in limbless taxa, especially snakes, which have radiated successfully into a wide range of habitats. The majority of studies concerning habitat-driven variation in locomotor mechanisms of snakes have focused on the musculoskeletal system. Far less recognized is the variation in the morphology of ventral scales, which are another pivotal component of the locomotor system in snakes. Here, we investigated patterns of interspecific variation in the width of ventral scales in terms of lifestyle (hunting mode) and habitat occupied in 55 species of snakes belonging to eight families. We found that increasing terrestriality was associated with enlarged ventral scales. Reduction instead of maintenance of the width of ventral scales was observed in aquatic species, suggesting that wide ventral scales set constraints on aquatic locomotion. In terrestrial species, no significant differences were observed in terms of arboreality or hunting mode, which suggests overall optimization in the size of ventral scales towards terrestrial locomotion. Association between the width of ventral scales and locomotion can result in a habitat-dependent costs of abnormalities in ventral scale morphology, commonly observed in snakes.

Tracking down the lizards from Gravenhorst's collection at the University of Wrocław: type specimens of Callopistes maculatus Gravenhorst, 1838 and three Liolaemus species rediscovered

Johann Ludwig Christian Gravenhorst's herpetological collection at the Museum of Natural History, University of Wrocław included numerous important specimens of amphibians and reptiles. The majority, if not the entirety, of this collection has long been thought to be lost. However, we were able to rediscover some type specimens of lizards. The rediscovered specimens include the holotypes of Liolaemus conspersus and L. hieroglyphicus, one syntype of Callopistes maculatus (here designated as the lectotype) and two syntypes of L. lineatus (one of which is herein designated as the lectotype). Reexamination of these specimens indicates that previous synonymies proposed for L. conspersus and two syntypes of L. hieroglyphicus are problematic; furthermore, more complex taxonomic work is needed to resolve this issue. Two rediscovered syntypes of L. lineatus differ in several scalation traits and are possibly not conspecific. The type specimens of several other species of lizards from Gravenhorst's collection (Liolaemus marmoratus, L. unicolor and two other syntypes of L. lineatus, Leiocephalus schreibersii and Chalcides viridanus) were not found and are probably lost.

Variability of pterygoid teeth in three species of Podarcis lizards and the utility of palatal dentition in lizard systematics

Palatal dentition in lizards is incompletely known, especially data on its variability are scarce. We studied variation in the number of pterygoid teeth in three species of Podarcis, a species-rich genus of lacertid lizards: terrestrial, P. siculus and saxicolous, P. erhardii and P. cretensis. In contrast to some previous studies, we found no sexual dimorphism in the number of palatal teeth in any of these species. The number of teeth was not correlated to lizard size. In our sample, P. cretensis on average had more teeth than did P. erhardii but fewer than did P. siculus. In addition, some specimens of P. cretensis and P. siculus showed asymmetry in the number of pterygoid teeth, which may be a result of anthropogenic pressure. The observed variability in the occurrence of palatal dentition illustrates the importance of scoring this character in phylogenetic analyses only on the basis of a sufficient sample.

Evolution of developmental sequences in lepidosaurs

BACKGROUND

Lepidosaurs, a group including rhynchocephalians and squamates, are one of the major clades of extant vertebrates. Although there has been extensive phylogenetic work on this clade, its interrelationships are a matter of debate. Morphological and molecular data suggest very different relationships within squamates. Despite this, relatively few studies have assessed the utility of other types of data for inferring squamate phylogeny.

METHODS

We used developmental sequences of 20 events in 29 species of lepidosaurs. These sequences were analysed using event-pairing and continuous analysis. They were transformed into cladistic characters and analysed in TNT. Ancestral state reconstructions were performed on two main phylogenetic hypotheses of squamates (morphological and molecular).

RESULTS

Cladistic analyses conducted using characters generated by these methods do not resemble any previously published phylogeny. Ancestral state reconstructions are equally consistent with both morphological and molecular hypotheses of squamate phylogeny. Only several inferred heterochronic events are common to all methods and phylogenies.

DISCUSSION

Results of the cladistic analyses, and the fact that reconstructions of heterochronic events show more similarities between certain methods rather than phylogenetic hypotheses, suggest that phylogenetic signal is at best weak in the studied developmental events. Possibly the developmental sequences analysed here evolve too quickly to recover deep divergences within Squamata.

Integrating developmental biology and the fossil record of reptiles

Numerous new discoveries and new research techniques have influenced our understanding of reptile development from a palaeontological perspective. They suggest for example that transition from mineralized to leathery eggshells and from oviparity to viviparity appeared much more often in the evolution of reptiles than was previously thought. Most marine reptiles evolved from viviparous terrestrial ancestors and had probably genetic sex determination. Fossil forms often display developmental traits absent or rare among modern ones such as polydactyly, hyperphalangy, the presence of ribcage armour, reduction of head ornamentation during ontogeny, extreme modifications of vertebral count or a wide range of feather-like structures. Thus, they provide an empirical background for many morphogenetic considerations.