Picking up the threads: Comparative osteology and associated cartilaginous elements for members of the genus Trilepida Hedges, 2011 (Serpentes, Leptotyphlopidae) with new insights on the Epictinae systematics.

The threadsnakes of the family Leptotyphlopidae have been historically neglected in terms of their natural history, ecology, systematics, and morphology. Given the relevance of morphological data for resolving systematic, evolutionary, and functional issues, we aimed to provide a detailed comparative description of osteology and associated cartilaginous elements for members of the genus Trilepida. Data were obtained through high-resolution computed tomography images, cleared and stained specimens, and radiography images of a total of 47 specimens and 12 species. Both cranial and axial osteology characters exhibited a relevant degree of intraspecific variation regarding qualitative and quantitative data associated with skull and vertebrae foramina and the shape of bony sutures and processes. The high representativeness of examined species and specimens allows us to provide a comprehensive discussion on the inter- and intraspecific osteological variation, as well as a compelling osteological diagnosis for the entire genus. Trilepida spp. differ from all Epictinae by the presence of the following combination of characters: paired nasals, fused supraoccipitals (distinct from parietal, prootics, and otooccipitals), a single (fused) parietal without a dorsal fontanelle, and the basioccipital participating in the foramen magnum (except in Trilepida nicefori). Our results reinforce the need for integration of detailed anatomical traits to usually conserved external morphological data to provide accurate diagnostic features for Epictinae. In addition, new phylogenetic hypotheses or even taxonomic re-allocations may broadly benefit from these detailed comparative studies.

Evolutionary treasures hidden in the West Indies: Comparative osteology and visceral morphology reveals intricate miniaturization in the insular genera Mitophis Hedges, Adalsteinsson, & Branch, 2009 and Tetracheilostoma Jan, 1861 (Leptotyphlopidae: Epictinae: Tetracheilostomina).

The genera Mitophis and Tetracheilostoma comprise two extant lineages of small-sized threadsnakes that exclusively inhabit several islands of the West Indies. Even though leptotyphlopids are known for their extremely reduced size, miniaturization has only been hypothesized to reflect insular dwarfism for the genus Tetracheilostoma. Herein, we aim to describe the comparative osteology and visceral morphology of both genera, investigating and discussing their several internal morphological simplifications and novelties. Our results indicate that these taxa exhibit several autapomorphies mostly concentrated in the dorsoposterior skull elements and maxillae, as well as in their axial skeleton and viscera. These novelties and simplifications are most likely a result of extreme miniaturization driven by the evolutionary constraints or ecological opportunities possibly imposed by the "island rule." Both Mitophis and Tetracheilostoma distinguish from all other Epictinae in lacking a dentigerous process in the maxillae, by having the prootic fused to the otooccipital, and by the lack (except in comparison to a few Epictia) of a cervical vertebrae intercentrum I. Additionally, Mitophis can be distinguished from other Epictinae by the participation of the unpaired supraoccipital in the dorsal border of the foramen magnum, by the absence of the pleurapophyses in the caudal vertebrae, by a higher number of liver segments, and by the extreme degeneration of the pelvic rudiments. Tetracheilostoma differs from other Epictinae by lacking a distinct supraoccipital, which is fused to the parietal. Thus, our results reinforce that morphological characters are extremely valuable for leptotyphlopid systematics given their extremely conserved external morphology.

Osteology of the enigmatic threadsnake species Epictia unicolor and Trilepida guayaquilensis (Serpentes, Leptotyphlopidae) with generic insights.

Since the rearrangement of all leptotyphlopid species previously known as "Leptotyphlops" in Adalsteinsson et al. (2009)'s paper, several taxa have remained untested regarding their generic identity and have been assigned to different genera based on phenotypic data or, in some cases, without any clear justification. Most of the difficulties in assigning some leptotyphlopid taxa are due to their conserved external morphology, summed with a relatively small number of available specimens, which complicate the recognition of a unique combination of characters for their reasonable generic allocation. On the other hand, recent osteological studies-especially those on the skull-provide relevant data combinations for species assignment and even for the recognition of new genera. In this work, we have attempted to determine the generic allocation of Epictia unicolor and Trilepida guayaquilensis-both species currently known only by their holotype-based on a detailed description of cranial and post-cranial osteology. We confirm the assignment of E. unicolor to the genus Epictia despite the divergent configuration of cephalic shields. Based mainly on data from the skull, suspensorium, and cervical vertebrae but supported by external morphology as well as a redescription of the holotype, we propose the assignment of Trilepida guayaquilensis to the genus Epictia. This study provides not only detailed data on the osteology of Epictia, but also a first approach to the putative combination of osteological characters for the genus.

To move or not to move? Skull and lower jaw morphology of the blindsnake Afrotyphlops punctatus (Leach, 1819) (Serpentes, Typhlopoidea, Typhlopidae) with comments on its previously advocated cranial kinesis.

"Scolecophidians" are traditionally known for their several skull and lower jaw autapomorphies, being conspicuously different from alethinophidian snakes in terms of skull shape and function. Although typically known for the absence of any kinetic joint in the skull dermatocranium and neurocranium-mostly due to an adaptation to fossorial habit, literature data have previously suggested a possible cranial kinesis for individuals of Afrotyphlops punctatus based on observations of live and preserved individuals. Given such observations, herein we aim to describe in detail the skull of A. punctatus based on CT-scan images of five specimens, evaluating the skull morphology and inferred function, and also providing valuable discussion on the skull osteology of the genus. Our results suggest that the skull of A. punctatus is similar to other blindsnakes in lacking any trace of snout, or even a frontal-parietal articulation. We also discuss possible osteological data that might be systematically relevant for Typhlopidae both interspecifically and intergenerically.

Digging into blindsnakes' morphology: Description of the skull, lower jaw, and cervical vertebrae of two Amerotyphlops (Hedges et al., 2014) (Serpentes, Typhlopidae) with comments on the typhlopoidean skull morphological diversity.

Scolecophidians are small fossorial snakes that exhibit several osteological innovations, most of which driven by their extreme body miniaturization. Considering that data on skull morphology has proven to be relevant in terms of scolecophidian systematics and morphofunctional evolution, herein, we aim to describe in detail the skull, lower jaw, and cervical vertebrae of Amerotyphlops brongersmianus and A. reticulatus. Our results suggest that the investigated osteology of Amerotyphlops resembles several new world typhlopid species, with reduced interspecific variation in the basicranium, lower jaw and cervical vertebrae. Both species exhibit characters states that are typically conserved intragenerically amongst typhlopoids, such as the presence of a single parietal, paired supraoccipitals, and otooccipitals that are in contact medially, and the basioccipital participating in the formation of the foramen magnum. We discuss possible systematically important osteological skull variations among typhlopoids and provide a comprehensive comparison of these taxa based on literature and data gathered herein.

Rediscovery of the rare Andean blindsnake Anomalepis colombia Marx 1953 (Serpentes: Anomalepididae) in the wild.

The fossorial snake genus Anomalepis Jan 1860 currently comprises four species with distribution restricted to the Neotropics, occurring from Nicaragua to trans-Andean Peru. Species of Anomalepis occur on the mainland from sea level to about 2,700 m elevation in habitats that range from xerophyte vegetation to tropical wet forests (Kofron 1988; McDiarmid et al. 1999; Uetz et al. 2019; Wallach et al. 2014). Kofron (1988) performed a taxonomic review of the genus Anomalepis, recognizing two phenotypic clusters of species: the A. mexicanus Jan 1860 composed exclusively by its nominal form, and the A. aspinosus Taylor 1939 group consisting of the former species, A. colombia Marx 1953 (Fig. 1) and A. flavapices Peters 1957. While Anomalepis aspinosus occurs in xerophytic formation from 500-2700 above sea level (asl hereafter) along the Peruvian Andes (Kofron 1988; McDiarmid et al. 1999; Wallach et al. 2014), and Anomalepis flavapices is found in the coastal rainforest plains of northwestern Ecuador (Kofron 1988; Wallach et al. 2014), Anomalepis mexicanus presents the most widespread distribution amongst its congeners, occurring in northeastern Honduras, Nicaragua, Costa Rica and Panama from sea level to 725 m altitude. Even though this species has previously been recorded for Peru (Kofron, 1988), it seems unlikely that this specimen belongs to A. mexicanus due to its distinct meristic features (see Kofron 1988) and its outlandish record (see Fig. 2). Marx (1953) described Anomalepis colombia based on a single specimen collected in 1946 by Kjell von Sneidern at La Selva (05º25'23N, 74º57'44W; 1700 m asl), municipality of Pueblo Rico, department of Caldas, Colombia. As far as we know, since its original description, no additional specimen of A. colombia has been reported in literature (cf. Kofron 1988; McDiarmid et al. 1999; Wallach et al. 2014).

A century of waiting: description of a new Epictia Gray, 1845 (Serpentes: Leptotyphlopidae) based on specimens housed for more than 100 years in the collection of the Natural History Museum Vienna (NMW).

We describe a new species of Epictia based on eight specimens from Nicaragua collected and housed in the collection of the Natural History Museum Vienna for more than a century. The species differs from the congeners by the combination of external morphological characters: midtail scale rows 10; supralabials two, anterior one large and in broad contact with supraocular; infralabials four; subcaudals 14-19; middorsal scale rows 250-267; supraocular scales present; frontal scale distinct; striped dorsal color pattern with more or less triangular dark blotches on each scale; small white blotch in anterior part of dorsal surface of rostral present in five out of six specimens (two further specimens are lacking their heads); terminal spine and adjacent scales white. Eidonomic species separation from other Epictia spp. is also supported by a few qualitative and quantitative differences in vertebrae count and morphology. The new species is putatively assigned to the Epictia phenops species group based on external morphological characters and distribution.

Moving beyond the surface: Comparative head and neck myology of threadsnakes (Epictinae, Leptotyphlopidae, Serpentes), with comments on the 'scolecophidian' muscular system.

Studies on the cephalic myology of snakes provide a series of relevant data on their biology and systematics. Despite the great amount of descriptive studies currently available for the group, much of the knowledge remains obscure for most scolecophidian taxa. This study aimed to describe in detail the cephalic (head and neck) myology of members of the tribe Epictinae, Leptotyphlopidae. We provide the first report of the presence of extrinsic ocular muscles, and a double Musculus pterygoideus acessorius in Leptotyphlopidae. A well-developed M. levator anguli oris is exclusive to the subtribes Renina and Epictina, being reduced in Tetracheilostomina species. Both inter- and intraspecific variations are reported for the head and neck muscles, and such results provide additional data and raise an interesting discussion on the neck-trunk boundaries in snakes. We also provide a discussion on the terminology of a few head muscles in Leptoyphlopidae in comparison to the other lineages of ´Scolecophidia´ (Anomalepididae and Typhlopoidea).

Osteology and Cartilaginous Elements of Trilepida salgueiroi (Amaral, 1954) (Scolecophidia: Leptotyphlopidae).

Morphological and anatomical studies on the Leptotyphlopidae have increased in the past 10 years, providing important data on the systematics of this group, mainly focused on the skull and lower jaw morphology. However, most studies are based on a single specimen, rarely combining more than one single method of assessing morphological information. Therefore, several data on postcranial morphology, sexual dimorphism, and ontogenetic and intraspecific variation of leptotyphlopids remain poorly understood. Herein, we provide a detailed description of the cranial and postcranial skeleton of Trilepida salgueiroi based on more than 20 specimens (including males, females and juveniles), as well as a description of osteology and cartilaginous elements through the use of combined methodologies such as X-ray scanning, high resolution CT-scanning, and clearing and staining of articulated and disarticulated specimens. We also provide data on the presence/absence of dimorphic and intraspecific variation of the observed characters. The presence of a statolithic mass in the cavum vestibuli differs from the pattern found in other scolecophidians. A correlation of dorsal vertebrae with ventral and subcaudal scales was found (1:1), as well as total number of vertebrae with middorsal scales (1:1), thoracolumbar vertebrae and ventral scales (1:1), and a higher number of caudal vertebra with subcaudal scales (1.23:1). Intraspecific variation was found in several elements of the skull, lower jaw, pelvic girdle and vertebral number, but no evidence of sexual dimorphism was found in any of the species characters analysed. The homologies of several elements are discussed, although still remaining poorly understood and unknown.