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The skeleton of a juvenile Lanthanotus (Varanoidea)
Abstract
The cleared and stained skeleton of a juvenile Lanthanotus bomeensis provides additional evidence for the "cervicalization" of an anterior dorsal vertebra, resulting in the 9 cervical vertebrae thought to be diagnostic of the Varanidae. Lanthanotus shows two complete sternal ribs associated with the vertebral segments 10 and 11, and an incomplete sternal rib associated with the 9th segment; Varanus shows three complete sternal ribs associated with the vertebral segments 10, 11 and 12. The loss of a sternal rib associated with the 12th segment is autapomorphic for Lanthanotus. Nine cervical vertebrae may be diagnostic for the genus Varanus only, since Lanthanotus preserves a rudimentary sternal rib associated with the 9th vertebral segment, at least at some stage of its ontogeny. A free carpal "intermedium" is absent (or variably present) in Lanthanotus. The pattern of epiphyseal calcification in the carpus and tarsus of Lanthanotus is described and compared to Varanus.
... The interspecific variation of limb skeleton in lizards has been explored by different authors with different emphasis (e.g., Wellborn, 1933;Gasc, 1963;Renous-Lécuru, 1973;Mathur and Goel, 1976;Rieppel, 1992aRieppel, , 1992bRieppel, , 1992cRieppel, , 1993aMaisano, 2001Maisano, , 2002aMaisano, , 2002b. Nevertheless, data on early limb development in lizards *Correspondence to: Marissa Fabrezi, Instituto de Bio y Geociencias-Museo de Ciencias Naturales, Universidad Nacional de Salta, Mendoza 2, 4400-Salta, Argentina. ...
... An embryonic condensation representing the intermedium fuses with the radiale condensation in crocodiles and birds (Hinchliffe and Hecht, 1984;Mü ller and Alberch, 1990;Burke and Feduccia, 1997). In lizards, some authors have identified an ossified element as an intermedium in the carpus of some Anguidae (Renous-Lécuru, 1973), Iguanidae (Avery and Tanner, 1964), Lacertidae (Rieppel, 1992b;Maisano, 2001), Teiidae (Fischer and Tanner, 1979), Varanidae (Rieppel, 1992c), and Xantusiidae (Maisano, 2002b). Others (Mathur and Goel, 1976) have described this structure as a transient cartilage that disappears during the embryonic development of the lacertid Calotes versicolor. ...
... In some species of Scleroglossa (Panaspis breviceps and Gerrhosaurus nigrolineatus), we found a small ossified element between ulnare and radiale (Fig. 11B). A similar osseous element has been identified as the intermedium (Avery and Tanner, 1964;Renous-Lécuru, 1973;Fischer and Tanner, 1979;Rieppel, 1992bRieppel, , 1992cMaisano, 2001Maisano, , 2002b. ...
Shubin and Alberch (Evol Biol 1986;20:319-387) proposed a scheme of tetrapod limb development based on cartilage morphogenesis that provides the arguments to interpret the homologies of skeletal elements and sets the basis to explain limb specialization through later developmental modification. Morphogenetic evidence emerged from the study of some reptiles, but the availability of data for lizards is limited. Here, the study of adult skeletal variation in 41 lizard taxa and ontogeny in species of Liolaemus and Tupinambis attempts to fill in this gap and provides supporting evidence for the Shubin-Alberch scheme. Six questions are explored. Is there an intermedium in the carpus? Are there two centralia in the carpus? Is there homology among proximal tarsalia of reptiles? Does digit V belong to the digital arch? Is the pisiform an element of the autopodium plan? And should the ossification processes be similar to cartilage morphogenesis? We found the following answers. Some taxa exhibit an ossified element that could represent an intermedium. There is one centrale in the carpus. Development of proximal tarsalia seems to be equivalent with that observed among reptiles. Digit V could arise from the digital arch. Pisiform does not arise as part of the limb plan. And different patterns of ossification occur following a single and conservative cartilaginous configuration. Lizard limb development shows an early pattern common to other reptiles with clear primary axis and digital arch. The pattern then becomes lizard-specific with specialization involving some reduction in prechondrogenic elements.
... A fourth-third distal tarsal proportion of roughly two, as documented in this study and others (Rieppel, 1992;Conrad, 2006a;Rieppel and Grande, 2007; Smith and Buchy, 2008; Evans and Wang, 2010; Conrad et al., 2011b), can be recognized as exclusive to Squamata (Table 2), being also shared by MCD-8827 (Table 1). In this sense, the Sphenodon punctatus specimens analysed in this study show a fourth-third distal tarsal proportion of approximately three (see Table 2). ...
... 3AeF, 5A). Besides, MCD-8827 also differs from the closest extant relative of Varanus, Lanthanotus borneensis, in the lateral plantar tubercle, which in the latter is placed distally, near the articulation condyle of the fifth metatarsal (Rieppel, 1980(Rieppel, , 1992Lee, 1997;Conrad, 2006a;Conrad et al., 2011b). ...
Appendicular remains of squamate reptiles are barely described in the fossil record due to their low preservational potential and generally poor diagnostic information. Not many squamate fossil individuals preserve appendicular bony elements, these being mainly restricted to the rare articulated specimens found in a limited number of localities with specific conditions that favor exceptional preservation. Detailed descriptions of these bones, especially tarsals and metatarsals, are thus scarce in the literature due to the lesser relevance given to these elements in most anatomical descriptions. In this study we analyze an unpublished fossil specimen from the Maastrichtian of Basturs-1 (Lleida, Catalonia, Spain) corresponding to several articulated appendicular pes bones of a possible member of Varaniformes. We also provide detailed insights on the anatomy of the tarsalia and metatarsalia, particularly in angui- morphs. The fossil specimen here described, with an estimated snout-vent length (SVL) of ~581 mm, reveals the putative varaniform from Basturs-1 as one of the largest Mesozoic terrestrial lizards, and possibly the largest from the European fossil record. Previous observations of an association between large lizards and dinosaur nesting sites are further supported by the find of this giant form in a locality known for the presence of numerous dinosaur eggs.
... Boulenger (1885Boulenger ( , 1889 subsequently affiliated them directly to Helodermatidae, but later studies (especially McDowell et Bogert 1954) confirmed the legitimacy of classifying earless monitor lizards into a special family and pointed to their specificity (e.g. Rieppel 1992). ...
... Boulenger (1885Boulenger ( , 1889 je následně přičlenil přímo ke korovcům, ale pozdější studie (zejména McDowell et Bogert 1954) potvrdily oprávněnost řazení varanovců do zvláštní čeledi a poukázaly na jejich specifičnost (např. Rieppel 1992). ...
Starting in 2014, members of the European Association of Zoos and Aquariums (EAZA) began to acquire earless monitor lizards. In this paper, the focus is on the ex situ population of Lanthanotus borneensis in EAZA, its origin, current status, role and perspectives.
... It is also frequently used in reptile groups outside Archosauria, including squamates (e.g. Rieppel, 1992b;Maisano, 2001Maisano, , 2002aSmith, 2009), rhynchocephalians (e.g. Jones et al., 2011;Cau, Baiano & Raia, 2014;Dong et al., 2019), and marine reptiles (e.g. ...
... Although the majority of this ossification occurs during prenatal ontogeny in most groups, ossification of skeletal cartilage continues throughout postnatal ontogeny in many saurians (e.g. Rieppel, 1992bRieppel, , 1993aMaisano, 2001;Mitgutsch et al., 2011). This occurs notably in the cartilage caps of long bone epiphyses, resulting in the ends of long bones possessing porous or spongy textures early in ontogeny in many reptiles (e.g. ...
Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.
... In CGS MJF 22, SAM-PK-K11126, and RC 55 individual cranial bones are disarticulated as most sutures are wide open, which is commonly interpreted as a juvenile trait (Estes, 1961;Kermack, 1984;Rieppel, 1992;Schaefer et al., 2009;Giere et al., 2010;Sekiya & Dong, 2010). CT images through the braincase and bony labyrinth of CGS MJF 22 (not preserved in SAM-PK-K11126 and RC 55) reveal that these anatomical structures Figure 18 Lemurosaurus pricei, NMQR 1702. ...
Biarmosuchia is a clade of basal therapsids that includes forms possessing plesiomorphic ‘pelycosaurian’ cranial characters as well as the highly derived Burnetiamorpha which are characterised by cranial pachyostosis and a variety of cranial bosses. Potential ontogenetic variation in these structures has been suggested based on growth series of other therapsids with pachyostosed crania, which complicates burnetiamorph taxonomic distinction and thus it is essential to better understand cranial ontogeny of the Burnetiamorpha. Here, three new juvenile biarmosuchian skulls from the late Permian of South Africa are described using X-ray micro computed tomography (CT). We found that juvenile biarmosuchians are distinguished from adults by their relatively large orbits, open cranial sutures, and incomplete ossification of the braincase and bony labyrinth. Also, they manifest multiple centres of ossification within the parietal and preparietal bones. CT examination reveals that the holotype of Lemurosaurus pricei (BP/1/816), previously alleged to be a juvenile, shows no evidence of juvenility and is thus probably an adult. This suggests that the larger skull NMQR 1702, previously considered to be an adult L. pricei , may represent a new taxon. This study provides, for the first time, a list of characters by which to recognise juvenile biarmosuchians.
... Di samping temuan kasus penyelundupan tersebut, sebuah artikel tentang penemuan Biawak Kalimantan di habitatnya di Kabupaten Landak telah dipublikasikan oleh seorang peneliti asing di sebuah majalah ilmiah Rusia (Langner, 2017) tanpa melibatkan peneliti ataupun mitra dari Indonesia. Beberapa peneliti lain yang menggunakan jenis kadal ini, di antaranya Rieppel (1992) tentang struktur tengkorak pada hewan muda, Ast (2001) tentang hubungan kekerabatan di antara biawak marga Varanus berdasarkan profil DNA, dan McCurry et al. (2015) tentang struktur tengkorak dan keanekaragaman ekologis biawak dan kerabat-kerabat dekatnya. Hal tersebut mengindikasikan minat di luar negeri akan jenis ini, baik sebagai komoditas perdagangan maupun subyek penelitian. ...
ABSTRAK. Biawak Kalimantan, Lanthanotus borneensis adalah jenis kadal yang dilindungi di Indonesia. Minat di luar negeri akan jenis endemik Borneo ini sebagai komoditas perdagangan maupun subyek penelitian cukup tinggi, sementara data populasinya di alam masih terbatas. Oleh karena itu, kami melakukan telaah populasi di habitatnya dan penelitian lanjutan untuk menunjang pengelolaan dalam rangka pemanfaatannya. Survei habitat dan populasi dilakukan di Kabupaten Landak, Provinsi Kalimantan Barat pada bulan Juni 2017 dan Juli 2018 dengan cara pengamatan langsung di lokasi dan wawancara dengan pihak-pihak terkait tentang keberadaan dan potensi perdagangannya di lokasi survei. Penelitian lanjutan tentang pilihan pakan berdasarkan mangsa alaminya dilakukan di Museum Zoologicum Bogoriense (MZB) di Kabupaten Bogor, Provinsi Jawa Barat dengan metode focal animal sampling dan analisis preferensi Neu. Penelitian kandungan nutrisi pakan terpilih juga dilakukan di MZB dengan metode proksimat untuk mengetahui kandungan protein kasar, lemak kasar, abu dan energi total. Kami menduga populasi Biawak Kalimantan berada di lokasi survei di sekitar Desa Semunti dan di kaki Gunung Nyiut, meskipun kami tidak menjumpai kadal ini selama periode survei. Karakteristik hutan tropis dengan aliran sungai kecil berair jernih dengan substrat lumpur berpasir di dasarnya mengindikasikan kesesuaian habitat dan ketersediaan mangsanya. Hasil uji pilihan pakan dan kandungan nutrisinya mengindikasikan sifat karnivora jenis kadal ini yang diduga memangsa hewan-hewan invertebrata berukuran kecil. Di dalam kandang, kadal ini mengkonsumsi pakan dengan kadar lemak dan protein yang relatif tinggi, misalnya cacing tanah dan daging udang. Hasil penelitian ini berguna untuk menunjang pengelolaan populasi Biawak Kalimantan di habitatnya (in-situ) maupun di luar habitatnya (ex-situ).
ABSTRACT. Biawak Kalimantan, Lanthanotus borneensis is a protected species of lizard in Indonesia. While wild population data still remain scarce, demands on this Borneo endemic for international trade is relatively high, as are interests on the species for scientific research. Thus, we planned a study on wild populations and habitats, as well as two further studies to provide data for management and utilization purposes. Field surveys were conducted in Landak, West Kalimantan in
... It is well documented the importance of skull intraspecific polymorphisms in vertebrate groups to understand the rapid morphological divergence conferred by heterochrony and by epigenetic development processes (De Beer, 1985). Surprisingly, there is a lack of studies concerning the ontogeny of the osteocranium in Squamates, especially in view of the importance of skull morphology either as a tool in developmental genetics or to phylogenetic reconstruction (Rieppel, 1992). Heterochronic changes in skull development of some primitive taxa of Lacertids, such as the fusion of the postfrontal and postorbital bones, appear to be a common source of evolutionary change in reptiles (Arnold, 1989). ...
Lacerta dugesii es un lacertido con distribución amplia en los archipielagos de Madeira y Selvagens, habitando una gran variedad de habitats. Se analizaron 371 animales de siete islas (Madeira, Porto Santo, Ilhéu Chão, Deserta Galeto, Bugio, Selvagem Grande y Selvagem Pequena). El objetivo de este trabajo es documentar una situación de elevado polimorfismo en la disposición de las escamas de la región occipital, correspondientes a cuatro patrones de escamas distintos. Uno de los cuales fue considerado normal y encontrado en la mayoría de los animales. Otro se caracterizaba por la presencia de una escama occipital fragmentada. Un tercer tipo por la presencia de una diminuta escama occipital. Por fin la ausencia de escama occipital caracterizaba el cuarto patrón y sólo se encontró en las dos pequeñas islas Selvagens. Ninguna población presentaba los cuatro patrones, faltando siempre uno o dos de ellos.
... Known only from Sarawak, Malaysia and West Kalimantan, Indonesia (Yaap et al., 2012), Pianka (2004) estimated that only around 100 specimens of the species had ever been collected. Although several museum-based investigations have focused on its morphology and systematics (Mcdowell & Bogert, 1954;Underwood, 1957;Olivier, 1980Olivier, , 1992Maisano et al., 2002), field studies have been lacking, and basic information on its natural history and occurrence remains scarce (Mertens, 1966;Proud, 1978;Harrisson, , 1965Harrisson & Haile, 1961;Das, 2003;Auliya, 2006;Yaap et al., 2012). From limited encounters with the species in the wild, it is believed to be nocturnal (Das, 2003), and has been collected in both terrestrial and aquatic environments (e.g., Harrisson & Haile, 1961;Pianka, 2004;Yaap et al., 2012). ...
Until very recently, the Bornean earless monitor, Lanthanotus borneensis, has rarely been kept in captivity, and published accounts on the habits of captive individuals and their husbandry are scarce. In this account, we detail aspects of the husbandry and behavior of a single L. borneensis maintained in captivity by the Bronx Zoo from 1968 to 1976, in the hopes that this information may contribute towards an improved understanding of the species' biology and captive management.
... Xenosaurus grandis appears to lack the fontanelle basicranialis in adult specimens. The fenestra basicranialis is persis-tent in juvenile Lanthanotus (Rieppel, 1992), but nothing remains of it in the adult (McDowell & Bogert, 1954;Rieppel, 1980Rieppel, , 1983 Basisphenoid: The basisphenoid (Figs 1C, 2C, 14, 15B) is a midline element contacting the pterygoids, prootics, and basioccipital. It forms the anteroventral portion of the osseous braincase and the connection between the palate and the braincase. ...
Shinisaurus crocodilurus Ahl is an endangered lizard of uncertain phylogenetic affinities with a very restricted geographic distribution within southern China and northern Vietnam. Available cranial descriptions are brief and based on incomplete or immature specimens. Consequently, the cranial structure of this important species remains poorly documented. This paper provides a detailed redescription based on several well-preserved adult and subadult skeletons. Description of individual bones corrects errors in previous studies. Comparisons with extant and fossil anguimorphs, especially Xenosaurus, allow a new diagnosis of cranial autapomorphies for Shinisaurus. The significance of Shinisaurus for anguimorph interrelationships is discussed briefly. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 141, 399–434.
... Within extant reptiles, recent work by Rieppel (1992a Rieppel ( ,b,c, 1993a Rieppel ( ,b, 1994b) has outlined a very precise and consistent developmental sequence for the ossification of the carpus. In squamates the sequence of ossification in Lacerta vivipara (Rieppel, 1992a), Cyrtodactylus pubisulcus (Rieppel, 1992b), and Lanthanotus borneensis (Rieppel, 1992c) is virtually identical and in all cases the first element to ossify is the ulnare followed by the fourth distal carpal and only then the intermedium. The 'radiale' described by Rieppel for these taxa is actually derived from the intermedium and is developmentally not a true radiale but a centrale (Shubin & Alberch, 1986; Caldwell, 1994). ...
A comprehensive analysis of amniote interrelationships is presented in an attempt to test turtle interrelationships. The results refute earlier hypotheses that turtles are related to parareptiles, i.e. to procolophonids or pareiasaurs. Instead, turtles are shown to be the sister-group of Sauropterygia, the two clades being nested within Sauria as sister-group of Lepidosauriformes. This scenario is also supported by several developmental and soft tissue characters which are shown to be congruent with the current phylogeny. The analysis strongly supports a monophyletic Parareptilia, sister-group of a monophylctic Eurcptilia. The Diapsida, however, is paraphyletic unless it includes turtles and sauropterygians. Additionally, the position of turtles within Diapsida has major implications for the evolutionary history and/or significance of many characters, i.e. temporal fenestration.
Blind snakes represent the most basal group of extant snakes and include fossorial species with unusual skeletal traits. Despite their known phylogenetic position, little is known about their ontogeny and what it might reveal about the origin of their skull anatomy. Here we describe for the first time the ontogenetic transformations of the skull of a blind snake, the typhlopid Amerotyphlops brongersmianus, including embryos and postnatal individuals. Furthermore, we provide data on the size changes relative to skull growth of the main elements of the gnathic complex. We observed that the skull of this blind snake undergoes considerable morphological change during late ontogeny. Additionally, we detected delayed development of some traits (closure of the skull roof, opisthotic-exoccipital suture, ossification of the posterior trabeculae) simultaneously with clearly peramorphic traits (development of the crista circumfenestralis, growth of the pterygoid bar). Our analysis suggests that the unique skull anatomy of blind snakes displays plesiomorphic and highly autapomorphic features, as an outcome of heterochronic processes and miniaturization, and is shaped by functional constraints related to a highly specialized feeding mechanism under the selective pressures of a fossorial lifestyle.
Se describe la variación ontogenética del esqueleto de 13 embriones de Tupinambis merianae y 11 de Tupinambis rufescens, detectándose heterocronías entre ambas especies. Los resultados muestran que los elementos dermales (tanto del cráneo como de la cintura pectoral) osifican antes que los elementos condrales, siendo los elementos que forman la mandíbula inferior, el paladar (especialmente los palatinos y los pterigoides) y la clavícula los primeros en osificarse, mientras que los elementos del dermatocráneo más tardíos en osificarse son los del arco temporal superior (lacrimal, postorbital, postfrontal). Las principales diferencias en los tiempos de aparición y osificación se producen en algunos huesos del cráneo y en el autopodio (carpo/tarso), pero estas heterocronías no alteran la arquitectura final del esqueleto. Los resultados encontrados son comparados y discutidos con el conocimiento existente sobre otros linajes de Squamata. We describe the ontogenetic variation of skeleton of 13 Tupinambis meriane embryos and 11 Tupinambis rufescens embryos. Furthermore heterochronies in ossification sequence between both species are recorded. Results show that dermal elements (belonging to the skull and the pectoral girdle) ossify before the chondral elements, being the elements that constitute the lower jaw, the palate (especially the palatine and the pterygoid), and the clavicle the first ones to ossify. The elements belonging to the dermatocranium which ossify later are the ones of the upper temporal arch (lacrimal, postorbital and postfrontal). The main differences present in timing of onset and ossification are produced in some bones of the skull and of the autopodium (carpus / tarsus); though, these heterochronies do not alter the final structure of the skeleton. Results achieved are compared and discussed with the available knowledge of other squamate lineages.
Current phylogenies of mosasauroid reptiles are reviewed and a new phylogeny examining aigialosaur interrelationships presented. Patterns of mesopodial ossification and overall limb morphology are described for adult mosasauroids. Ossification sequences are mapped onto a phylogeny in order to assess the distribution of ontogenetic characters. Consistent and ordered distributions are found. Based on the phylogenetic distribution of ossification patterns, an overall mesopodial ossification sequence for mosasaurs is proposed. Carpal sequence: ulnare - distal carpal four (dc4) - intermedium - dc3 - radiale or dc2 - del or pisiform and dc5. Tarsal sequence: astragalus - distal tarsal four or calcaneum. Skeletal paedomorphosis is recognized as a dominant pattern in the evolution of mosasauroid limbs. Apomorphic characters of skeletal paedomorphosis, apparent in most taxa, reach extremes in tylosaurs. Arguments for the presence of a single proximal cartilage in the tarsus of mosasaurs are made. This cartilage is presumed to include ossification centres from which both the astragalus and calcaneum will ossify.
The state of ossification of the skeleton at hatching or birth and shortly thereafter is described and compared for 21 squamate species. The presence in the neonate of metapodial ossification centers and epiphyseal secondary centers varies among species, whereas the appearance of apophyseal ossifications and endochondral calcifications and the ossification of sesamoid precursors are predominantly postnatal phenomena. The data suggest a possible causal relationship between viviparity and skeletally immature neonates, whereas state of ossification at hatching or birth is probably attributable to phylogeny overall. Of the clades represented in this investigation, phrynosomatids, teiioids, and amphisbaenians exhibit the most skeletally mature neonates, whereas the reverse is true of gekkotans, xantusiids, and anguids.
The hitherto poorly known forefin of
Chensaurus chaoxianensis
(Ichthyosauria) from the Lower Triassic (Spathian) is redescribed on the basis of the holotype and two new specimens. The humerus resembles that of
Utatsusaurus hataii
but is distinctive in having an emarginated anterior margin. The anteroproximal prominence of the radius is well developed, unlike that of other ichthyosaurs. All three specimens have five metacarpals and many phalanges, but only three carpals, which are identified as the ulnare, intermedium, and fourth distal carpal. These specimens show that delayed mesopodial ossification occurred in ichthyosaurs, at least in an early evolutionary stage. Because delayed mesopodial ossification is common among diapsids and is unknown in Jurassic ichthyosaurs, it was lost during the evolution of the Ichthyosauria. The osteogenic developmental axis appears to have continued into the fourth digit, as in other amniotes. The ossification pattern provides conclusive evidence to support the suggestion that the basal element of the fifth digit in Early Triassic ichthyosaurs is a metacarpal, rather than a carpal.
Having been described in 1710, the first specimen of Protorosaurus speneri is one of the first fossil reptiles ever described. The only major monograph of the species was published in 1856, based on the 25 specimens available at that time. However, the skull anatomy remained almost unknown. Although the monograph on Protorosaurus contains very detailed descriptions, many anatomical features of the postcranium remained unclear due to extreme crushing of most specimens. Recently discovered material, especially a complete skull, the first juvenile, and a less crushed almost complete skeleton, provided the incentive to revise the anatomy of Protorosaurus. The new material allows a reconstruction of the skull for the first time as well as that of several postcranial elements, e.g. a complete interclavicle and a complete pubis. Furthermore, several anatomical features e.g. the well developed humerus and the number and arrangement of tarsal elements, can be described in more detail. The first juvenile specimen of Protorosaurus provides new insights into the ontogeny of the pelvic region and the tarsal elements. Protorosaurus is a member of the archosauromorph group Prolacertiformes, a group generally considered to be monophyletic. The anatomy of Protorosaurus will therefore be compared to that of other well known representatives of the group. The comparison shows that the skull anatomy of Protorosaurus closely resembles that of Prolacerta broomi, Macrocnetnus bassanii, and Pamelaria dolichotrachela. The postcranium is similar to that of Prolacerta broomi and Pamelaria dolichotrachela. Because the phylogenetic status and make-up of the Prolacertiformes is currently discussed controversially, a preliminary computer-aided, cladistic analysis is performed based on the dataset of the first author postulating a paraphyletic Prolacertiformes. Over 30% of the original codings were corrected for Protorosaurus, and the analysis was also modified with regard to the included taxa. The new analysis includes 17 taxa and 144 characters. Protorosaurus turns out to be a basal archosauromorph and the direct sister taxon of Megalancosaurus. The Prolacertiformes themselves are paraphyletic with Prolacerta and Pamelaria being more closely related to the Archosauriformes. The anatomical similarities between Protorosaurus, Prolacerta and Pamelaria must hence be interpreted as convergent. If Megalancosaurus is deleted from the analysis, Protorosaurus falls into an unresolved trichotomy with (Tanystropheus plus Macrocnemus), which becomes the direct sister taxon to the monophylum consisting of (Pamerlaria plus Prolacerta plus (Euparkeria plus Proterosuchus)). Furthermore, in this case the Choristodera fall outside the Sauria.
The evolution of forefins within the Ichthyopterygia is re-evaluated based on the largest set of data available up to present, including recently reported Early Triassic forms. Three humeral morphotypes are recognized; one is plesiomorphic, and the other two characterize two of the major clades. The forefin elements of various ichthyopterygians are identified, based on osteogenetic sequences and topological arrangements. Both lines of evidence, ontogenetic and morphological, support a single conclusion that Stenopterygius, and all other ichthyopterygians belonging to the clade that survived into the Jurassic, lack digit I of the forelimb. Digits I and II are probably absent in Shastasaurus and closely related forms. The topology along the primary axis and digital arch is conservative among all ichthyopterygians examined, as expected from the underlying mechanism of limb development.
Three of the six earliest ichthyosaurs, namely, Chaohusaurus geishanensis, Chensaurus chaoxianensis, and Chensaurus faciles, occur in the Lower Triassic (Spathian) of the Chaohu area, Anhui Province, China. A reexamination of the three holotypes and two referred specimens indicates that the three species share derived features; however, the characters originally used to distinguish among the three are either growth-related or absent. Measurements of the specimens suggest that they represent a growth series of a single species, Chaohusaurus geishanensis Young and Dong 1972. The forefin of this species shows a strongly positive allometry, leading to the unusually large forefin in the largest specimen (the holotype). The use of the standard allometric equation may be problematic when two structures compared start their developments asynchronically. However, the alternative equation of Schmalhausen is also problematic, and therefore more scrutiny is required. The lunate fin elements, which commonly occur in the first and fifth digits of Early Triassic ichthyosaurs, first become ossified as biconcave elements, as in other metacarpals and phalanges.
Evidence from studies of chondrogenic and osteogenic patterns in extant lepidosaurs is used to analyze skeletal pattern formation in ontogenetic series of three primitive Permian diapsids: Hovasaurus boulei: Thadeosaurus colcanapi; and Claudiosaurus germaini. The ossification of proximal and postaxial carpals proceeds according to the sequence: 1) ulnare; 2) distal carpal four; 3) intermedium; 4) lateral centrale; 5) distal carpal three or one. The sequence of ossification of the remaining carpals is highly variable. Tarsal ossification proceeds according to the sequences: 1) astragalus/calcaneum; 2) distal tarsal four; 3) distal tarsal three; 4) centrale; 5) distal tarsals two, one, or five. C. germaini shows great intraspecific variation in the sequence of distal tarsal ossification after ossification of the centrale. Limb ossification is highly constrained along the primary limb axis and at the beginning of the digital arch. Variation is observed preaxially along the digital arch and with respect to the development of the fifth digit. The conserved sequences are the same as those seen in living lepidosaurs; sequence variation in living lepidosaurs is noted in the preaxial region of the digital arch. The evolution of the terrestrial limb in lepidosauromorphs is interpreted as having been constrained by the processes of limb development. The fossil diapsids illustrate a primitive condition for lepidosauromorphs and provide a basis for comparison of change among other diapsids.
The skeleton of a newly discovered, exceptionally preserved specimen of Saniwa ensidens is described in detail. The fossil consists of a complete articulated skeleton exposed in dorsal view. It adds important additional information to our knowledge of the anatomy of this fossil varanoid taxon, including a detailed description of the dermatocranium in dorsal view, complete vertebral counts, and a detailed account of the appendicular skeleton. Cartilage preservation allows the identification of treacheal rings, sternum, inscriptional ribs, epicoracoid and suprascapula. Patches of skin are preserved on dermal skull bones, and scattered scales surround the entire skeleton. Incomplete ossification of carpal and tarsal elements, as well as of epiphyses, indicate that the specimen is not fully mature.
Evolution of paddle-like limbs in ichthyosaurs and plesiosaurs is correlated with loss of perichondral bone from the shafts of long bones. Among ichthyosaurs, loss of perichondral bone is first observed on the shafts of digit bones of Early Triassic taxa. Late Triassic ichthyosaurs show perichondral bone loss on the postaxial margins of the ulna and fibula. Among plesiosaurs, loss of perichondral bone is first observed on the postaxial margins of the ulna and fibula of Lower Jurassic taxa. In geologically later species of both groups, perichondral bone is progressively lost on all margins of the ulna and radius, and fibula and tibia. Late Triassic and Jurassic ichthyosaurs show an absence of perichondral ossifications on all limb bones distal to the humerus and femur. Delayed ossification of the mesopodium is not observed in ichthyosaurs. Evolutionary changes to the ossification of perichondral tissues appear to affect the sequence of limb ossification as long bones lose perichondral bone. Limb bones of ichthyosaurs and plesiosaurs resemble mesopodial elements through loss of perichondral bone. The proportion of endochondral bone found on these transformed bones is increased, resulting in an increased articular surface area and increased articular complexity.
Limb osteology and ontogenetic patterns of limb ossification are described for the plesiosaur Cryptoclidus eurymerus (Upper Jurassic: Callovian), and compared to those of other sauropterygians. Major features of limb ossification in Cryptoclidus are identified: 1) delayed mesopodial ossification; 2) alterations to the ossification sequence of the radius/ulna, tibia/fibula, and some metacarpals and metatarsals; 3) the loss of perichondral bone from the margins of the radius/ulna, tibia/fibula, and some metacarpals and metatarsals; 4) altered bone morphology is correlated with loss of perichondral bone. Recognition of some of these features in basal sauropterygians, and their application to the study of limb elements in derived sauropterygians such as Cryptoclidus, alters traditional identifications of several bones. The conventional intermedium is re-identified as a centrale. The ‘true’ intermedium is found to be a small bone that is variably free, ossifies to the base of the radius forming a distinct process, or ossifies to the base of the ulna. Additional endochondral ossifications are found along the preaxial and postaxial margins of the limb. These bones have perichondral bone on some margins, articulate with distinct facets on other limb elements, and therefore cannot be dismissed as sesamoid ossifications. Bones conventionally identified as the 4th distal carpal, 4th distal tarsal, and calcaneum, are re-identified as the 4th metacarpal, and the 4th and 5th metatarsals, respectively.
The aigialosaur Carsosaurus marchesetti is represented by a nearly complete skeleton from the Upper Cretaceous (Cenomanian-Turonian) of Slovenia. Dermal girdle elements include portions of the clavicles and a small interclavicle with a short anterior process. Endochondral girdle elements include a small scapula and large unfenestrated coracoid. A mineralized sternum is also present. The carpus is anguid-like and consists of ten ossified elements. Reduction of the procoelous nature of centrum articular surfaces is restricted to the caudal series. The type of C. marchesetti is the largest aigialosaur specimen known (> 1.5 m) and has proportionally larger propodials than any other aigialosaur. Phylogenetic reconstruction places Carsosaurus within a polytomous clade composed of all known aigialosaurs. Aigialosaurs are the sister-group to Mosasauridae, forming the Mosasauroidea, and are within Anguimorpha but distinct from Varanoidea. Supposed synapomorphies of varanids and mosasauroids are identified as either plesiomorphies of Anguimorpha, or as misidentified homologs. Results of a principal component analysis of limb measurements suggest that aigialosaurs occupy a position on a functional continuum reflective of terrestrial not aquatic animals. Morphometric criteria cannot validate the exclusion of Carsosaurus from the Aigialosauridae.
Limb ossification patterns for the Lower Jurassic (Toarcian) ichthyosaur, Stenopterygius, are described. It is found that limb ossification follows a continuous proximal to distal sequence from the propodial elements through to the terminal elements of 1st to 4th digit in the manus and the 1st to 3rd digit in the pes. The 5th manal and 4th pedal digit begin ossification later than more preaxial digits and also show evidence of proximal addition of elements near the distal mesopodial row in a manner consistent with delayed ossification of the 5th distal mesopodial in other diapsids. Ossification of manal elements in the Supernumerary 3–4 (S3-4) digit and the 5th digit appear interdependent; if one or the other is highly ossified, ossification of the other is retarded. The 1st pedal digit is considered to be lost in Stenopterygius and the 4th pedal digit is identified as the 5th digit. Delayed ossification of the mesopodium is not observed. The most preaxial proximal tarsal is identified as the centralc; the remaining proximal tarsals are the astragalus and calcaneum, and it is inferred that the astragalus and calcaneum ossified from within a single proximal cartilage.
Current phylogenics of mosasauroid reptiles are reviewed and a new phylogeny examining aigialosaur interrelationships presented. Patterns of mesopodial ossification and overall limb morphology are described for adult mosasauroids. Ossification sequences are mapped onto a phylogeny in order to assess the distribution of ontogenetic characters. Consistent and ordered distributions are found. Based on the phylogenetic distribution of ossification patterns, an overall mesopodial ossification sequence for mosasaurs is proposed. Carpal sequence: ulnare—distal carpal four (dc4)—intermedium—dc3—radiale or dc2—de1 or pisiform and dc5. Tarsal sequence: astragalus—distal tarsal four or calcaneum. Skeletal paedomorphosis is recognized as a dominant pattern in the evolution of mosasauroid limbs. Apomorphic characters of skeletal paedomorphosis, apparent in most taxa, reach extremes in tylosaurs. Arguments for the presence of a single proximal cartilage in the tarsus of mosasaurs are made. This cartilage is presumed to include ossification centres from which both the astragalus and calcaneum will ossify.
The mineralization of the skeleton from hatching to near maximum size in two phrynosomatid lizards, Callisaurus draconoides and Uta stansburiana, is described in detail. Observed patterns in the appearance of epiphyseal secondary centers, ossification centers, apophyseal ossifications, and calcifications, the distribution of sesamoids, and the timing of fusions, are compared and contrasted with observations of other squamates available in the literature. Overall, Callisaurus and Uta exhibit an advanced state of ossification in the hatchling relative to other squamate neonates and share a similar sequence of braincase fusions and appearance of secondary centers. Preliminary observations suggest that patterns of postnatal skeletal development are highly conserved and independent of patterns of prenatal morphogenesis, and thus a potentially rich source of character data for systematic investigations.
The construction of a comparative database of squamate postnatal skeletal development is continued with the detailed description of the mineralization of the skeleton from birth to near maximum size in Lepidophyma gaigeae and four Xantusia taxa. Observed patterns in the sequence of appearance of epiphyseal secondary centers, ossification centers, apophyseal ossifications, and calcifications, the distribution of sesamoids, and the timing of fusions are compared and contrasted with other squamates. Xantusiids share a similar sequence of braincase fusions, but differ in the sequence of appearance of ossification centers and epiphyseal secondary centers. Relative to other squamates they exhibit an immature neonatal state of ossification, a delayed appearance of ossification centers and epiphyseal secondary centers, and an accelerated appearance of apophyses. All five xantusiid taxa possess two sesamoids previously unreported in squamates. These observations add to the growing body of evidence that morphogenesis and osteogenesis are largely independent developmental phenomena.
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