Nathan J. Kley

Diffusible iodine-based contrast-enhanced computed tomography (diceCT) : an emerging tool for rapid, high-resolution, 3-D imaging of metazoan soft tissues.

Morphologists have historically had to rely on destructive procedures to visualize the three‐dimensional (3‐D) anatomy of animals. More recently, however, non‐destructive techniques have come to the forefront. These include X‐ray computed tomography (CT), which has been used most commonly to examine the mineralized, hard‐tissue anatomy of living and fossil metazoans. One relatively new and potentially transformative aspect of current CT‐based research is the use of chemical agents to render visible, and differentiate between, soft‐tissue structures in X‐ray images. Specifically, iodine has emerged as one of the most widely used of these contrast agents among animal morphologists due to its ease of handling, cost effectiveness, and differential affinities for major types of soft tissues. The rapid adoption of iodine‐based contrast agents has resulted in a proliferation of distinct specimen preparations and scanning parameter choices, as well as an increasing variety of imaging hardware and software preferences. Here we provide a critical review of the recent contributions to iodine‐based, contrast‐enhanced CT research to enable researchers just beginning to employ contrast enhancement to make sense of this complex new landscape of methodologies. We provide a detailed summary of recent case studies, assess factors that govern success at each step of the specimen storage, preparation, and imaging processes, and make recommendations for standardizing both techniques and reporting practices. Finally, we discuss potential cutting‐edge applications of diffusible iodine‐based contrast‐enhanced computed tomography (diceCT) and the issues that must still be overcome to facilitate the broader adoption of diceCT going forward.

Craniofacial Morphology of Simosuchus clarki (Crocodyliformes: Notosuchia) from the Late Cretaceous of Madagascar

ABSTRACT Simosuchus clarki is a small, pug-nosed notosuchian crocodyliform from the Late Cretaceous of Madagascar. Originally described on the basis of a single specimen including a remarkably complete and well-preserved skull and lower jaw, S. clarki is now known from five additional specimens that preserve portions of the craniofacial skeleton. Collectively, these six specimens represent all elements of the head skeleton except the stapedes, thus making the craniofacial skeleton of S. clarki one of the best and most completely preserved among all known basal mesoeucrocodylians. In this report, we provide a detailed description of the entire head skeleton of S. clarki, including a portion of the hyobranchial apparatus. The two most complete and well-preserved specimens differ substantially in several size and shape variables (e.g., projections, angulations, and areas of ornamentation), suggestive of sexual dimorphism. Assessment of both external and internal morphological features indicates a habitual head posture in which the preorbital portion of the dermal skull roof was tilted downward at an angle of ∼45°. Functional and comparative assessment of the feeding apparatus strongly indicates a predominantly if not exclusively herbivorous diet. Other features of the craniofacial skeleton of S. clarki are consistent with the interpretation developed from analysis of the postcranial skeleton of a terrestrial habitus, but the current working hypothesis of a burrowing lifestyle is not supported. The atypical appearance of the skull and lower jaw of S. clarki is underscored by the identification of at least 45 autapomorphic features, many of them related to the greatly foreshortened snout.

Iodine-enhanced micro-CT imaging: Methodological refinements for the study of the soft-tissue anatomy of post-embryonic vertebrates

The now widespread use of non-destructive X-ray computed tomography (CT) and micro-CT (µCT) has greatly augmented our ability to comprehensively detail and quantify the internal hard-tissue anatomy of vertebrates. However, the utility of X-ray imaging for gaining similar insights into vertebrate soft-tissue anatomy has yet to be fully realized due to the naturally low X-ray absorption of non-mineralized tissues. In this study, we show how a wide diversity of soft-tissue structures within the vertebrate head-including muscles, glands, fat deposits, perichondria, dural venous sinuses, white and gray matter of the brain, as well as cranial nerves and associated ganglia-can be rapidly visualized in their natural relationships with extraordinary levels of detail using iodine-enhanced (i-e) µCT imaging. To date, Lugols iodine solution (I2 KI) has been used as a contrast agent for µCT imaging of small invertebrates, vertebrate embryos, and certain isolated parts of larger, post-embryonic vertebrates. These previous studies have all yielded promising results, but visualization of soft tissues in smaller invertebrate and embryonic vertebrate specimens has generally been more complete than that for larger, post-embryonic vertebrates. Our research builds on these previous studies by using high-energy µCT together with more highly concentrated I2 KI solutions and longer staining times to optimize the imaging and differentiation of soft tissues within the heads of post-embryonic archosaurs (Alligator mississippiensis and Dromaius novaehollandiae). We systematically quantify the intensities of tissue staining, demonstrate the range of anatomical structures that can be visualized, and generate a partial three-dimensional reconstruction of alligator cephalic soft-tissue anatomy.

Are ontogenetic shifts in diet linked to shifts in feeding mechanics? Scaling of the feeding apparatus in the banded watersnake Nerodia fasciata.

SUMMARY The effects of size on animal behaviour, ecology, and physiology are widespread. Theoretical models have been developed to predict how animal form, function, and performance should change with increasing size. Yet, numerous animals undergo dramatic shifts in ecology (e.g. habitat use, diet) that may directly influence the functioning and presumably the scaling of the musculoskeletal system. For example, previous studies have shown that banded watersnakes (Nerodia fasciata) switch from fish prey as juveniles to frog prey as adults, and that fish and frogs represent functionally distinct prey types to watersnakes. We therefore tested whether this ontogenetic shift in diet was coupled to changes in the scaling patterns of the cranial musculoskeletal system in an ontogenetic size series (70–600 mm snout–vent length) of banded watersnakes. We found that all cranial bones and gape size exhibited significant negative allometry, whereas the muscle physiological cross-sectional area (pCSAs) scaled either isometrically or with positive allometry against snout–vent length. By contrast, we found that gape size, most cranial bones, and muscle pCSAs exhibited highly significant positive allometry against head length. Furthermore, the mechanical advantage of the jaw-closing lever system remained constant over ontogeny. Overall, these cranial allometries should enable watersnakes to meet the functional requirements of switching from fusiform fish to bulky frog prey. However, recent studies have reported highly similar allometries in a wide diversity of vertebrate taxa, suggesting that positive allometry within the cranial musculoskeletal system may actually be a general characteristic of vertebrates.

Morphological integration and adaptation in the snake feeding system: a comparative phylogenetic study

A long‐standing hypothesis for the adaptive radiation of macrostomatan snakes is that their enlarged gape – compared to both lizards and basal snakes‐enables them to consume ‘large’ prey. At first glance, this hypothesis seems plausible, or even likely, given the wealth of studies showing a tight match between maximum consumed prey mass and head size in snakes. However, this hypothesis has never been tested within a comparative framework. We address this issue here by testing this hypothesis in 12 monophyletic clades of macrostomatan snakes using recently published phylogenies, published maximum consumed prey mass data and morphological measurements taken from a large sample of museum specimens. Our nonphylogenetically corrected analysis shows that head width – independent of body size – is significantly related to mean maximum consumed prey mass among these clades, and this relationship becomes even more significant when phylogeny is taken into account. Therefore, these data do support the hypothesis that head shape is adapted to prey size in snakes. Additionally, we calculated a phylogenetically corrected morphological variance–covariance matrix to examine the role of morphological integration during head shape evolution in snakes. This matrix shows that head width strongly covaries with both jaw length and out‐lever length of the lower jaw. As a result, selection on head width will likely be associated with concomitant changes in jaw length and lower jaw out‐lever length in snakes.

A Late Cretaceous (Maastrichtian) Snake Assemblage from the Maevarano Formation, Mahajanga Basin, Madagascar

ABSTRACT A Late Cretaceous (Maastrichtian) assemblage of snakes from the Maevarano Formation of the Mahajanga Basin, northwestern Madagascar, constitutes the only fossil record of snakes from the island. The assemblage, which lived in a highly seasonal, semi-arid climate, includes only archaic forms belonging to the Madtsoiidae and Nigerophiidae, and therefore no representatives of extant Malagasy clades. A large sample of exquisitely preserved vertebrae and several ribs are assigned to Madtsoia madagascariensis, a long (almost 8 m), heavy-bodied ambush predator inferred to have subdued its prey via constriction. A new madtsoiid genus and species, Menarana nosymena, is represented by several associated vertebrae and rib fragments, and part of the basicranium. It was approximately 2.4 m long and appears to have been a powerful, head-first burrower, or at least to have had a burrowing ancestry. Kelyophis hechti, by far the smallest snake in the assemblage (<1 m long), is a new genus and species of primitive nigerophiid based on six isolated vertebral specimens. It was not as specialized for the aquatic lifestyle inferred for other nigerophiids. Although recent molecular phylogeographic studies suggest an early colonization of Madagascar by snakes ancestral to modern Malagasy boids, with subsequent vicariant evolution, the Maevarano Formation assemblage offers no support for this hypothesis. The repeated pattern of extinct archaic lineages being replaced on Madagascar by basal stocks of extant clades (e.g., Anura, Crocodyliformes, Avialae, Mammalia) after the Late Cretaceous is also a plausible scenario for the origin of the extant Malagasy snake fauna.

Feeding by mandibular raking in a snake

Most snakes transport prey through the mouth by using asynchronous ratcheting movements of their upper jaws. In contrast, we have found that threadsnakes (members of the basal snake clade Scolecophidia) have a unique feeding mechanism in which the tooth-bearing elements of the lower jaw rotate synchronously in and out of the mouth, dragging prey into the oesophagus. This mechanism, which we call ‘mandibular raking’, is the only vertebrate feeding mechanism known in which prey is transported exclusively by movements of the lower jaw.

Morphology of the skull of the white-nosed blindsnake, Liotyphlops albirostris (Scolecophidia: Anomalepididae)

This article presents a detailed description and illustration of the skull of Liotyphlops albirostris in comparison to the skulls of Typhlophis squamosus, Leptotyphlops dulcis, and Typhlops jamaicensis, based on high‐resolution X‐ray computed tomography (HRXCT). The skull of T. squamosus is illustrated and discussed in detail for the first time. A number of uniquely shared derived characters is identified that support the monophyly of the clade Anomalepididae. Anomalepidids retain some features that are plesiomorphic relative to other scolecophidians, such as the presence of a supratemporal (except in Anomalepis) and ectopterygoid. The homology of the element located posteroventral to the eyeball in anomalepidids and variably referred to as a jugal or postorbital (or a fusion of both in Anomalepis) remains unknown. Scolecophidians exhibit a highly derived skull morphology adapted to head‐first burrowing. Both anomalepidids and typhlopids evolved a condition known as an “outer shell design,” but did so in different ways. Leptotyphlopids combine elements of both the anomalepidid and typhlopid snout morphologies. J. Morphol., 2009.

Post-cranial prey transport mechanisms in the black pinesnake, Pituophis melanoleucus lodingi: an x-ray videographic study

Most previous studies of snake feeding mechanisms have focused on the functional morphology of the highly specialized ophidian jaw apparatus. Although some of these studies have included observations of post-cranial movements during feeding, the functional roles of these movements have remained poorly understood. In this study, we used x-ray videography to examine post-cranial prey transport mechanisms in a colubrid snake, Pituophis melanoleucus lodingi. We found that prey transport in this species progresses through four distinct phases, three of which are characterized by either undulatory or concertina-like movements of the anterior portion of the trunk. In the first phase of transport (the oral phase), unilateral movements of the jaws are used to pull the head forward around the prey. In the second phase (the orocervical phase), unilateral jaw movements continue, but are augmented by concertina-like movements of the anterior portion of the trunk. In the third phase (the cervical phase), prey transport occurs exclusively through concertina-like movements of the neck. Finally, in the fourth phase (the thoracic phase), prey is transported to the stomach via undulatory movements of the trunk. Our observations of feeding behavior in a phylogenetically diverse sample of fourteen other snake species demonstrate that similar post-cranial transport mechanisms are used by a wide variety of alethinophidian snakes that feed on large, bulky prey.

New Snakes from the Upper Cretaceous (Maastrichtian) Maevarano Formation, Mahajanga Basin, Madagascar

ABSTRACT We describe three new fossil snakes on the basis of recently discovered vertebrae collected from the Upper Cretaceous (Maastrichtian) Maevarano Formation of Madagascar. One represents a new genus and species of madtsoiid, Adinophis fisaka, the third member of this family recognized from the Maevarano Formation. It exhibits dorsoventrally compressed centra and dorsally placed synapophyses. The second taxon is a new species of the nigerophiid genus Indophis, I. fanambinana, representing the second nigerophiid taxon known from the Maevarano Formation. It shares numerous features with the Indian nigerophiid I. sahnii, including small synapophyses positioned ventrolaterally on distinct synapophyseal processes and a unique cotylar shape in posterior trunk vertebrae. The discovery of I. fanambinana demonstrates a strong biogeographic link with penecontemporaneous snake faunas from India. A third new taxon is represented by a partial centrum that cannot be assessed thoroughly due to its incompleteness; this specimen is conservatively assigned to Serpentes incertae sedis, gen. et sp. indeterminate. It is distinct from other snakes known from the Late Cretaceous of Madagascar in possessing a strongly depressed condyle and relatively large lateral foramina. These new discoveries, together with previous descriptions of snakes from the Maevarano Formation, make the Maevarano snake fauna one of the most taxonomically diverse snake assemblages known from the Mesozoic and the most diverse in terms of body size range.