Adaptations and significance of the cranial feeding apparatus of the sunbeam snake (Xenopeltis unicolor): Part I. Anatomy of the skull

Frazzetta, T. H.

doi:10.1002/(sici)1097-4687(199901)239:1<27::aid-jmor2>3.0.co;2-z

Cited by 14 publications

(15 citation statements)

References 9 publications

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“…The stapes of Dinilysia patagonica is large and massive, and connects the quadrate with the oval window, making possible transmission of environment vibration to the inner ear through it. This characteristic was also observed by Frazzetta () in Xenopeltis unicolor , where the stapes has a foot plate of large diameter, which is greater than the total length of the bone. In addition, X. unicolor is a medium‐sized snake that grows up to 1 m (Greene, 2000), and has a relatively robust body, a posteriorly wide braincase, with short and triangular quadrates, and relatively large orbits in dorsal position (Frazzetta, ), all characteristics also found in D. patagonica .…”

Section: Discussionsupporting

confidence: 72%

“…This characteristic was also observed by Frazzetta () in Xenopeltis unicolor , where the stapes has a foot plate of large diameter, which is greater than the total length of the bone. In addition, X. unicolor is a medium‐sized snake that grows up to 1 m (Greene, 2000), and has a relatively robust body, a posteriorly wide braincase, with short and triangular quadrates, and relatively large orbits in dorsal position (Frazzetta, ), all characteristics also found in D. patagonica . Taking into account that X. unicolor is one of the largest semifossorial extant snake; thus, D. patagonica could have developed similar habits with a partly fossorial lifestyle.…”

Section: Discussionmentioning

confidence: 95%

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First Natural Endocranial Cast of a Fossil Snake (Cretaceous of Patagonia, Argentina)

Triviño

Albino

Dozo

et al. 2017

The Anatomical Record

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In this study, we describe a natural endocranial cast included in a partially preserved medium-sized skull of the Upper Cretaceous South American snake Dinilysia patagonica. The endocast is composed of sedimentary filling of the cranial cavity in which the posterior brain, the vessels, the cranial nerves, and the inner ear surrounded by delicate semicircular canals, are represented. It is simple in form, with little differentiation between the three main areas (Forebrain, Midbrain, and Hindbrain), and without flexures. The nervous system is well preserved. The posterior brain surface is smooth, except for two small prominences that make up the cerebellum. A large inner ear is preserved on the right side; it consists of a voluminous central mass, the vestibule, which occupies most of the space defined by the three semicircular canals. In particular, the lateral semicircular canal is very close to the vestibule. This characteristic, in combination with the medium to large body size of Dinilysia, its large skull and dorsally exposed orbits, and vertebrae bearing a rather high neural spine on a depressed neural arch, suggests that this snake would have had a semifossorial lifestyle. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:9-20, 2018. © 2017 Wiley Periodicals, Inc.

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Section: Discussionsupporting

confidence: 72%

Section: Discussionmentioning

confidence: 95%

First Natural Endocranial Cast of a Fossil Snake (Cretaceous of Patagonia, Argentina)

Triviño

Albino

Dozo

et al. 2017

The Anatomical Record

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“…At least one species of snake, Xenopeltis unicolor (not closely related to bolyerines), has flattened maxillaries that are vertically thin enough to bend (Frazzetta 1999), and to allow some depression of the front ends of these bones to grip prey (pers observation). Quite clearly the downward flexion of the front of the maxillae seen in Xenopeltis is subtle compared to the much sharper maxillary declination permitted by a synovial joint; and the arrangement of bones impinging upon the maxillae in Xenopeltis, that allows and supports their flexion, is distinctly different from that of pythons, boas, bolyerines, and most other snakes (Frazzetta 1999).…”

Section: Bolyerine Snakesmentioning

confidence: 95%

“…Quite clearly the downward flexion of the front of the maxillae seen in Xenopeltis is subtle compared to the much sharper maxillary declination permitted by a synovial joint; and the arrangement of bones impinging upon the maxillae in Xenopeltis, that allows and supports their flexion, is distinctly different from that of pythons, boas, bolyerines, and most other snakes (Frazzetta 1999). A hypothetical proto-bolyerine, whose maxillae were under selection for increased thinness, could go only so far in that direction before a breaking threshold of the maxillae was reached.…”

Section: Bolyerine Snakesmentioning

confidence: 99%

“…He shows that various skeletal anomalies are known to occur throughout many vertebrates involving their long bones, which normally are of a single piece but which can acquire anomalous joints dividing the bone into two sections. Reif's statement that there is no all-or-none characteristic of a bone divided by a joint, because variation in mineralization of bones allow them to be flexible without an articular intervention, harks back (see above) to the condition in Xenopeltis (Frazzetta 1999) with a bendable maxilla. There is, however, no adaptive or functional continuity between a flexible beam and one interrupted by a full-blown joint, as the mechanical implications are greatly different.…”

Section: Bolyerine Snakesmentioning

confidence: 99%

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Flatfishes, Turtles, and Bolyerine Snakes: Evolution by Small Steps or Large, or Both?

Frazzetta

2011

Evol Biol

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Step size in evolution is rapidly becoming a major subject of interest to biologists. Traditionally, small changes alone were seen as significant in evolution, and any large differences between an ancestor and its descendant could be explained entirely by the accumulation of many small steps. Whether the evolution of major adaptations is mainly a matter of amassing such small increments of change, or if a significant proportion occurs through the inclusion of one or more large steps, is vital to the understanding of how evolution works. This paper begins by examining four ''classic'' examples of animalsflatfishes, turtles, bolyerine snakes, and gastropod molluscs-each of which has seemed difficult to interpret as resulting from a continuous series of tiny increments. Recently, however, arguments have appeared to contradict those views, and to propose instead that each of these animal groups arose through continuous adaptive modifications. While some of these arguments are more plausible than others, the view of the present author is that in none of them is there convincing evidence to conclude that the groups arose solely through gradual changes. More specifically, there is no basis to reject an evolutionary origin of the major traits in each group that included at least one principal inovation, occurring in a large, discontinuous step, preceded and followed by relatively small, more gradual changes. The broader question of how discontinuous evolution may occur is addressed through several means. These include considerations of epigenetic (sensu Waddington) development, comparative embryology, population genetics, and other approaches. Overall the phenomenon of adaptive accommodation is seen as of major importance, and its implications for ameliorating possible deleterious attributes of novel phenotypes are discussed. In the course of these analyses the doctrine that all adaptive evolution is driven by external environmental change is reviewed. It is suggested that while small adaptive changes are often closely related to shifts in specific environmental facets, the modifications associated with more major adaptations may be less so.

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To Move or Not to Move: Cranial Joints in European Gekkotans and Lacertids, an Osteological and Histological Perspective

Mezzasalma

Maio

Guarino

2013

The Anatomical Record

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Lepidosaurs are frequently described as having highly kinetic skulls, and different forms of cranial kinesis have been described as being characteristic of their radiation. The model of amphikinesis proposed by Frazzetta, J Morphol 1962; 111:287-319, which was long considered a synapomorphy of the large suborder Sauria, is now much debated given its uncertain distribution among the various lizard taxa and the lack of data about its morphological correlates. In this article, we analyze the anatomical correlates of different forms of cranial kinesis, with particular regard to the putative saurian amphikinesis, describing the possible diverse skull movements of several species of European gekkotans (Hemidactylus turcicus, Mediodactylus kotschyi, and Tarentola mauritanica) and lacertids (Lacerta agilis, L. bilineata, Podarcis muralis, P. siculus, and Teira dugesii). Using serial and whole-mount histology, we found clear differences between gekkotans and lacertids in the structure of several cranial joints underlining the existence of two degrees of intracranial mobility. The lacertid species possess the anatomical features for streptostyly (quadrate joints) and metakinesis (parietal-supraoccipital and parabasisphenoid-pterygoid joints) and lack the anatomical correlates for mesokinesis (mobility of frontal-parietal and palatine-pterygoid joints) and amphikinesis (coupled mesokinesis, metakinesis, and streptostyly). In contrast, geckos present all the anatomical correlates for amphikinesis as described by the traditional quadratic crank model. Finally, we present a comprehensive summary of the different forms of squamate cranial kinesis, advancing two alternative hypotheses about the evolutionary origin of amphikinesis. Anat Rec, 297:463-472, 2014. V C 2013 Wiley Periodicals, Inc.

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Adaptations and significance of the cranial feeding apparatus of the sunbeam snake (Xenopeltis unicolor): Part I. Anatomy of the skull

Cited by 14 publications

References 9 publications

First Natural Endocranial Cast of a Fossil Snake (Cretaceous of Patagonia, Argentina)

First Natural Endocranial Cast of a Fossil Snake (Cretaceous of Patagonia, Argentina)

Flatfishes, Turtles, and Bolyerine Snakes: Evolution by Small Steps or Large, or Both?

To Move or Not to Move: Cranial Joints in European Gekkotans and Lacertids, an Osteological and Histological Perspective

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