DOCSLIB.ORG

Paleoneurology: a Sight for Four Eyes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Paleoneurology: a Sight for Four Eyes Current Biology Dispatches Paleoneurology: A Sight for Four Eyes Lawrence M. Witmer Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, Ohio Center for Ecology and Evolutionary Studies, Athens, OH 45701, USA Correspondence: [email protected] https://doi.org/10.1016/j.cub.2018.02.071 The ‘third eye’ of the pineal complex is a curious component of the vertebrate brain associated with light sensation and melatonin production. A fossil lizard with a ‘fourth eye’ now calls for a reinterpretation of pineal evolution. ‘‘The part of the body in which perhaps few people today subscribe to mediating circadian and seasonal rhythms the soul directly exercises its Descartes’ view of the pineal organ as the via production of the hormone melatonin functions is not the heart at all, or ‘seat of the soul’, it retains an almost [2]. The mammalian pineal organ is the whole of the brain. It is mystical quality in some quarters. Pop complicated enough, but when other rather.a certain very small gland cultural references abound, suggesting vertebrates are taken into account, we now [the pineal organ] situated in the ways (and selling products, of course) to speak of a ‘pineal complex’ involving middle of the brain’s substance.’’ ‘activate the pineal’ with cannabis or multiple organs that emphasize the Rene Descartes, The Passions of ‘harmonic sound wave technology’ to photosensory component. That is, they the Soul, 1649 [1] achieve enlightenment (psychedelic or often are ‘eyes’ with structures spiritual). Fortunately, there is also a rich comparable to the cornea, lens, retina, and It’s perhaps understandable that our scientific literature on the neuroscience visual pigments (opsins) that we typically knowledge of the function and evolution of and clinical neuroendocrinology of the associate with our normal, lateral eyes and the pineal organ has been murky, because, pineal gland, revealing that the organ may which breach the skull to appear on the top as Descartes noted, it is indeed a very have less to do with the soul and of the head [3,4]. In fact, when considering small structure buried deep within the brain enlightenment and more to do with the pineal complex of vertebrates we now of humans and other mammals. Although responding to light/dark cycles and need to distinguish between ‘lateral eyes’ Current Biology 28, R306–R327, April 2, 2018 ª 2018 Elsevier Ltd. R311 Current Biology Dispatches the parapineal gland. The kicker is that there is a huge diversity of extinct tetrapods (land vertebrates), such as the famous sail-backed Dimetrodon, that often show a single large midline parietal foramen in their skull roofs [9–11]. Is this ‘third eye’ opening for a parapineal (parietal) eye or a pineal eye? Both ideas have been proposed [10,12]. Enter Saniwa ensidens, the 49-million- year-old fossil lizard that sparked Smith and colleagues’ [5] re-exploration — and indeed revision — of pineal-complex evolution in this issue of Current Biology. Fossils of this outwardly routine species, a close kin of extant monitor lizards (Varanus), have long been known and have been well studied recently [13,14]. Smith and colleagues [5], however, noticed a couple of specimens that showed something remarkable, which is not one midline opening in the skull roof as in other Figure 1. A four-eyed fossil lizard. lizards, but two. These fragmentary fossil The 49 million-year-old fossils of the extinct monitor lizard Saniwa ensidens uniquely and atavistically display both pineal and parapineal (parietal) eyes on the top of their heads, along with normal lateral specimens had sat in the Yale Peabody eyes. (Digital image based on microCT scan of extant Varanus monitor, modified to reflect the new Museum collection, barely noticed, for findings of S. ensidens [5]; by R. C. Ridgely of WitmerLab at Ohio University.) almost 150 years, but these authors had the insight to wonder whether they were (the eyes with which you’re reading these organs were almost certainly facing a ‘four-eyed’ animal. Indeed, at the words) and ‘median (midline) eyes’ within photosensory at their evolutionary origins end of their exhaustive studies, Smith and or on top of the head. Indeed, the median [6], and remain so to varying extents in the colleagues [5] came to the conclusion that eye formed by a component of the pineal species that retain them today. Indeed, the larger normal-looking parietal foramen complex is widely known as ‘the third eye’ the evolutionary history of the pineal in the front must have been for the [3]. A new paper by Krister Smith and complex is complicated in that some parapineal organ as in other lizards, and colleagues in this issue of Current Biology extant groups (mammals and birds) have the smaller ‘accessory’ foramen behind [5] now presents evidence from a fossil lost the parapineal organ and one extant must have been for the pineal organ. lizard for the first identifiable case of a group (crocodilians) has apparently lost Moreover, the cup-like bone surface on jawed vertebrate with not just a third, but a both components almost entirely [6]. the outer part of the accessory foramen is fourth eye (Figure 1), both of which are part Thus, in most extant vertebrates, the consistent with the presence in life of of the pineal complex, thus shedding new pineal organ is the major component, and cornea- and lens-like structures. In other light, as it were, on the evolution of the its function largely centers on words, Saniwa ensidens had both parietal entire complex. photosensitive neuroendocrine (parapineal) and pineal eyes! Light-sensitive organs (in a broad production of melatonin. This completely unexpected finding has sense, visual organs) are widespread An exception would seem to be lizards. a number of important implications. For among invertebrates and vertebrates, and Most lizards have a prominent and example, there is no longer any debate pineal evolution extends back to the very externally visible ‘third eye’ (with cornea, that it is the parapineal component of the beginnings of vertebrates [6]. The pineal lens, etc.) in the midline of the tops of their pineal complex that forms the parietal eye complex is comprised of a pineal organ heads. This eye traverses an opening in in lizards, and that the parapineal/parietal and a parapineal organ, both of which the center of their bony skull roof, opening should no longer be termed the derive from a portion of the forebrain commonly called the parietal foramen in ‘pineal foramen’ in lizards as it still is called the diencephalon, specifically the which this eye sits (named for the parietal sometimes. It also tips the scales toward epithalamus. Anatomically, the parapineal bones that flank the opening). It turns out the notion that the pineal complex sits in front of the pineal on the midline, that this well-formed third or, as it’s probably is natively a midline system but debates have raged about whether commonly known, parietal eye of lizards is rather than a paired system that got they originally were paired organs (that is, thought to derive from the parapineal evolutionarily tugged into its midline left and right, like the lateral eyes) that organ, and the pineal organ sits behind it alignment. But, although it’s good to clean subsequently diverged in function and more deeply within the bony brain cavity, up the nomenclature and nail down the position [7] or whether they truly were as in other vertebrates [9,10]. So, most original anatomy, the truly remarkable always separate midline structures [8]. extant vertebrate groups emphasize the point is that Saniwa had a photoreceptive Regardless, both pineal and parapineal pineal gland whereas lizards emphasize pineal eye that peered out of the top of its R312 Current Biology 28, R306–R327, April 2, 2018 Current Biology Dispatches head. Such a feature was thought to have 4. Masuda, H., Oishi, T., Ohtani, M., Michinomae, 10. Quay, W.B. (1979). The parietal eye–pineal been lost hundreds of millions of years ago M., Fukada, Y., Shichida, Y., and Yoshizawa, complex. In Biology of the Reptilia, v. 9 T. (1994). Visual pigments in the pineal (Neurology A), C. Gans, R.G. Northcutt, and P. back when the earliest vertebrates with complex of the Japanese quail, Japanese Ulinski, eds. (London: Academic Press), jaws evolved, at which point the pineal grass lizard and bullfrog: pp. 245–406. Immunocytochemistry and HPLC analysis. gland sunk deeper into the brain cavity Tiss. Cell 26, 101–113. 11. Benoit, J., Abdala, F., Manger, P.R., and and lost its eyelike function. In 1893, Rubidge, B.S. (2016). The sixth sense in Belgian paleontologist Louis Dollo 5. Smith, K.T., Bhullar, B.-A.S., Ko¨ hler, G., and mammalian forerunners: variability of the parietal Habersetzer, J. (2018). The only known jawed foramen and the evolution of the pineal eye in formulated the Law of the Irreversibility of vertebrate with four eyes and the Bauplan of South African Permo-Triassic eutheriodont Evolution, which simply states: that which the pineal complex. Curr. Biol. 28, 1101–1107. therapsids. Acta Palaeontol. Pol. 61, 777–789. is lost shall not be regained [15]. Some 6. Ekstro¨ m, P., and Meissl, H. (2003). Evolution 12. Kemp, T.S. (1969). On the functional laws are meant to be broken, and the re- of photosensory pineal organs in new morphology of the gorgonopsian skull. Philos. evolution of a pineal eye in Saniwa is not light: the fate of neuroendocrine Trans. R. Soc. Lond. B 256, 1–83. photoreceptors. Philos. Trans. R. Soc. Lond. B the first atavism to be reported. Still, it’s 358, 1679–1700. 13. Rieppel, O., and Grande, L. (2007). The not a common occurrence, and it’s so 7.
Load more

Recommended publications
  • Il/I,E,Icanjluseum
    il/i,e,icanJluseum PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK 24, N.Y. NUMBER 1870 FEBRUARY 26, 1958 The Role of the "Third Eye" in Reptilian Behavior BY ROBERT C. STEBBINS1 AND RICHARD M. EAKIN2 INTRODUCTION The pineal gland remains an organ of uncertain function despite extensive research (see summaries of literature: Pflugfelder, 1957; Kitay and Altschule, 1954; and Engel and Bergmann, 1952). Its study by means of pinealectomy has been hampered in the higher vertebrates by its recessed location and association with large blood vessels which have made difficult its removal without brain injury or serious hemorrhage. Lack of purified, standardized extracts, improper or inadequate extrac- tion techniques (Quay, 1956b), and lack of suitable assay methods to test biological activity have hindered the physiological approach. It seems probable that the activity of the gland varies among different species (Engel and Bergmann, 1952), between individuals of the same species, and within the same individual. This may also have contrib- uted to the variable results obtained with pinealectomy, injection, and implantation experiments. The morphology of the pineal apparatus is discussed in detail by Tilney and Warren (1919) and Gladstone and Wakely (1940). Only a brief survey is presented here for orientation. In living vertebrates the pineal system in its most complete form may be regarded as consisting of a series of outgrowths situated above the third ventricle in the roof of the diencephalon. In sequence these outgrowths are the paraphysis, dorsal sac, parapineal, and pineal bodies. The paraphysis, the most I University of California Museum of Vertebrate Zoology.
    [Show full text]
  • Anatomy and Relationships of the Triassic Temnospondyl Sclerothorax
    Anatomy and relationships of the Triassic temnospondyl Sclerothorax RAINER R. SCHOCH, MICHAEL FASTNACHT, JÜRGEN FICHTER, and THOMAS KELLER Schoch, R.R., Fastnacht, M., Fichter, J., and Keller, T. 2007. Anatomy and relationships of the Triassic temnospondyl Sclerothorax. Acta Palaeontologica Polonica 52 (1): 117–136. Recently, new material of the peculiar tetrapod Sclerothorax hypselonotus from the Middle Buntsandstein (Olenekian) of north−central Germany has emerged that reveals the anatomy of the skull and anterior postcranial skeleton in detail. Despite differences in preservation, all previous plus the new finds of Sclerothorax are identified as belonging to the same taxon. Sclerothorax is characterized by various autapomorphies (subquadrangular skull being widest in snout region, ex− treme height of thoracal neural spines in mid−trunk region, rhomboidal interclavicle longer than skull). Despite its pecu− liar skull roof, the palate and mandible are consistent with those of capitosauroid stereospondyls in the presence of large muscular pockets on the basal plate, a flattened edentulous parasphenoid, a long basicranial suture, a large hamate process in the mandible, and a falciform crest in the occipital part of the cheek. In order to elucidate the phylogenetic position of Sclerothorax, we performed a cladistic analysis of 18 taxa and 70 characters from all parts of the skeleton. According to our results, Sclerothorax is nested well within the higher stereospondyls, forming the sister taxon of capitosauroids. Palaeobiologically, Sclerothorax is interesting for its several characters believed to correlate with a terrestrial life, although this is contrasted by the possession of well−established lateral line sulci. Key words: Sclerothorax, Temnospondyli, Stereospondyli, Buntsandstein, Triassic, Germany.
    [Show full text]
  • Variability of the Parietal Foramen and the Evolution of the Pineal Eye in South African Permo-Triassic Eutheriodont Therapsids
    The sixth sense in mammalian forerunners: Variability of the parietal foramen and the evolution of the pineal eye in South African Permo-Triassic eutheriodont therapsids JULIEN BENOIT, FERNANDO ABDALA, PAUL R. MANGER, and BRUCE S. RUBIDGE Benoit, J., Abdala, F., Manger, P.R., and Rubidge, B.S. 2016. The sixth sense in mammalian forerunners: Variability of the parietal foramen and the evolution of the pineal eye in South African Permo-Triassic eutheriodont therapsids. Acta Palaeontologica Polonica 61 (4): 777–789. In some extant ectotherms, the third eye (or pineal eye) is a photosensitive organ located in the parietal foramen on the midline of the skull roof. The pineal eye sends information regarding exposure to sunlight to the pineal complex, a region of the brain devoted to the regulation of body temperature, reproductive synchrony, and biological rhythms. The parietal foramen is absent in mammals but present in most of the closest extinct relatives of mammals, the Therapsida. A broad ranging survey of the occurrence and size of the parietal foramen in different South African therapsid taxa demonstrates that through time the parietal foramen tends, in a convergent manner, to become smaller and is absent more frequently in eutherocephalians (Akidnognathiidae, Whaitsiidae, and Baurioidea) and non-mammaliaform eucynodonts. Among the latter, the Probainognathia, the lineage leading to mammaliaforms, are the only one to achieve the complete loss of the parietal foramen. These results suggest a gradual and convergent loss of the photoreceptive function of the pineal organ and degeneration of the third eye. Given the role of the pineal organ to achieve fine-tuned thermoregulation in ecto- therms (i.e., “cold-blooded” vertebrates), the gradual loss of the parietal foramen through time in the Karoo stratigraphic succession may be correlated with the transition from a mesothermic metabolism to a high metabolic rate (endothermy) in mammalian ancestry.
    [Show full text]
  • Skull – Ii Dermatocranium
    BIOLOGY 524 ADVANCED VERTEBRTE MORPHOLOGY -OSTEOLOGY- SKULL – II DERMATOCRANIUM S. S. SUMIDA INTRODUCTION RECALL: SPLANCHNOCRANIUM – The splanchnocranium (sometimes called the viscerocranium) is the phylogenetically most ancient part of the skull. It arose even before vertebrates themselves to support the pharyngeal gill slits of protochordates. Within the vertebrates, it supports gill structures or their evolutionary derivatives. The cartilagenous or bony components are derived from neural crest, and form endochondrally. Components of the upper and lower jaw are derived from this. CHONDROCRANIUM – The chondrocranium is a cradle that supports the underside of the brain itself. Its components form endochondrally, and can be derived from either mesoderm or neural crest. The chondrocranium is derived from multiple individual structures that fuse to become this cradle. Not all components ossify, with some remaining as cartilage. DERMATOCRANIUM – The dermatocranium is slightly later in development and makes up the outer casing of the skull. It protects the brain above, and protects the entire braincase from below as the plate. Embryology of the Dermatocranium All components of the vertebrate dermatocranium form intramembranously from neural crest cells. In fact, it is unfortunate, as this type of formation used to be known as “dermal bone formation” (because of the proximity of the ne to the skin. However, even though we no longer use the term dermal formation, we still use the term dermatocranium. Notably, whereas the entire dermatocranium is derived from neural crest forms intramembranously, it is not the only part of the skeleton derived from neural crest (also the splanchnocranium, which forms endochondrally), and it is not the only part of the skeleton that forms intramembranously (also significant parts of the pectoral girdle, which is derived from mesoderm).
    [Show full text]
  • Callibrachion and Datheosaurus, Two Historical and Previously Mistaken Basal Caseasaurian Synapsids from Europe
    Callibrachion and Datheosaurus, two historical and previously mistaken basal caseasaurian synapsids from Europe FREDERIK SPINDLER, JOCELYN FALCONNET, and JÖRG FRÖBISCH Spindler, F., Falconnet, J., and Fröbisch, J. 2016. Callibrachion and Datheosaurus, two historical and previously mis- taken basal caseasaurian synapsids from Europe. Acta Palaeontologica Polonica 61 (3): 597–616. This study represents a re-investigation of two historical fossil discoveries, Callibrachion gaudryi (Artinskian of France) and Datheosaurus macrourus (Gzhelian of Poland), that were originally classified as haptodontine-grade sphenaco- dontians and have been lately treated as nomina dubia. Both taxa are here identified as basal caseasaurs based on their overall proportions as well as dental and osteological characteristics that differentiate them from any other major syn- apsid subclade. As a result of poor preservation, no distinct autapomorphies can be recognized. However, our detailed investigations of the virtually complete skeletons in the light of recent progress in basal synapsid research allow a novel interpretation of their phylogenetic positions. Datheosaurus might represent an eothyridid or basal caseid. Callibrachion shares some similarities with the more derived North American genus Casea. These new observations on Datheosaurus and Callibrachion provide new insights into the early diversification of caseasaurs, reflecting an evolutionary stage that lacks spatulate teeth and broadened phalanges that are typical for other caseid species. Along with Eocasea, the former ghost lineage to the Late Pennsylvanian origin of Caseasauria is further closed. For the first time, the presence of basal caseasaurs in Europe is documented. Key words: Synapsida, Caseasauria, Carboniferous, Permian, Autun Basin, France, Intra-Sudetic Basin, Poland. Frederik Spindler [[email protected]], Dinosaurier-Park Altmühltal, Dinopark 1, 85095 Denkendorf, Germany.
    [Show full text]
  • The Cranial Anatomy and Relationships of the Synapsid Varanosaurus (Eupelycosauria: Ophiacodontidae) from the Early Permian of Texas and Oklahoma
    ANNALS OF CARNEGIE MUSEUM VOL 64, NUM~. 2, ..... 99-133 12 MAy 1995 THE CRANIAL ANATOMY AND RELATIONSHIPS OF THE SYNAPSID VARANOSAURUS (EUPELYCOSAURIA: OPHIACODONTIDAE) FROM THE EARLY PERMIAN OF TEXAS AND OKLAHOMA DAVID S BERMAN Curator, Section of Vertebrate Paleontology ROBERT R. REISZI JOHN R. BoLT2 DIANE ScoTTI ABsTRACT The cranial anatomy of the Early Permian synapsid Varanosaurus is restudied on the basis of preY iously described specimens from Texas, most importantly the holotype of the type species V. aCUlirostris. and a recently discovered, excellently preserved specimen from Oklahoma. Cladistic analysis of the Eupelycosauria, using a data matrix 0(95 characters, provides the following hYPOthesis of relationships of VaraIJosaurus: I) VaraIJosaurus is a member of the family Ophiacodontidae; 2) of the ophiacodonlid genera included in the analysis, Varanosaurus and OpniacodOIJ share a more recent common ancestor than either does with the more primitive Arcna('()tnyris; and 3) a clade containing the progressively more derived taxa Edaphosauridae, H aplodus. and Sphenacodontoidea (Sphena- . codontidae plus Therapsida), together with Varanopseidae and Caseasauria, are progressively more distant outgroups or sister taxa to Ophiacodontidae. A revised diagnosis is given for VaralJosQurus. INTRODUCTION Published accounts of the Early Permian synapsid Varanosaurus have been limited almost entirely to rather brief descriptions based on a few poorly preserved andlor incomplete skeletons collected from the Lower Permian of north-central Texas. The holotype of the type species Varanosaurus acutirostris was described originally by Broili (1904) and consists of an incomplete articulated skeleton (BSPHM 1901 XV 20), including most importantly the greater portion of the skull, collected from the Arroyo Formation, Clear Fork Group.
    [Show full text]
  • The Many Faces of Synapsid Cranial Allometry
    Paleobiology, 45(4), 2019, pp. 531–545 DOI: 10.1017/pab.2019.26 Article The many faces of synapsid cranial allometry Isaac W. Krone , Christian F. Kammerer, and Kenneth D. Angielczyk Abstract.—Previous studies of cranial shape have established a consistent interspecific allometric pattern relating the relative lengths of the face and braincase regions of the skull within multiple families of mam- mals. In this interspecific allometry, the facial region of the skull is proportionally longer than the braincase in larger species. The regularity and broad taxonomic occurrence of this allometric pattern suggests that it may have an origin near the base of crown Mammalia, or even deeper in the synapsid or amniote forerun- ners of mammals. To investigate the possible origins of this allometric pattern, we used geometric morpho- metric techniques to analyze cranial shape in 194 species of nonmammalian synapsids, which constitute a set of successive outgroups to Mammalia. We recovered a much greater diversity of allometric patterns within nonmammalian synapsids than has been observed in mammals, including several instances similar to the mammalian pattern. However, we found no evidence of the mammalian pattern within Theroce- phalia and nonmammalian Cynodontia, the synapsids most closely related to mammals. This suggests that the mammalian allometric pattern arose somewhere within Mammaliaformes, rather than within nonmammalian synapsids. Further investigation using an ontogenetic series of the anomodont Diictodon feliceps shows that the pattern of interspecific allometry within anomodonts parallels the ontogenetic trajectory of Diictodon. This indicates that in at least some synapsids, allometric patterns associated with ontogeny may provide a “path of least resistance” for interspecific variation, a mechanism that we suggest produces the interspecific allometric pattern observed in mammals.
    [Show full text]
  • The Feeding System of Tiktaalik Roseae: an Intermediate Between Suction Feeding and Biting Downloaded by Guest on September 27, 2021 Pmx Pop AB 1 Cm Q
    The feeding system of Tiktaalik roseae:an intermediate between suction feeding and biting Justin B. Lemberga, Edward B. Daeschlerb, and Neil H. Shubina,1 aDepartment of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL 60637; and bDepartment of Vertebrate Zoology, Academy of Natural Sciences of Drexel University, Philadelphia, PA 19103 Contributed by Neil H. Shubin, December 17, 2020 (sent for review August 3, 2020; reviewed by Stephanie E. Pierce and Laura Beatriz Porro) Changes to feeding structures are a fundamental component of tall palatal elements, and a jointed neurocranium all thought to be the vertebrate transition from water to land. Classically, this event features that play a role in suction feeding (5, 9, 20). In contrast, has been characterized as a shift from an aquatic, suction-based theLateDevonianlimbedtetrapodomorphAcanthostega gunnari mode of prey capture involving cranial kinesis to a biting-based has a flat skull, interdigitating sutures between the bones of the feeding system utilizing a rigid skull capable of capturing prey on skull roof, absent gill covers, reduced hyomandibulae, horizontal land. Here we show that a key intermediate, Tiktaalik roseae, was palatal elements, and a consolidated neurocranium that are hy- capable of cranial kinesis despite significant restructuring of the pothesized to be derived adaptations for biting (5, 6, 21, 22). skull to facilitate biting and snapping. Lateral sliding joints be- Analyses of tetrapodomorph lower jaws have produced equivocal tween the cheek and dermal skull roof, as well as independent results, noting few differences between presumed aquatic and mobility between the hyomandibula and palatoquadrate, enable terrestrial forms (7, 8).
    [Show full text]
  • The Skull Roof Tracks the Brain During the Evolution and Development of Reptiles Including Birds
    ARTICLES DOI: 10.1038/s41559-017-0288-2 The skull roof tracks the brain during the evolution and development of reptiles including birds Matteo Fabbri1*, Nicolás Mongiardino Koch! !1, Adam C. Pritchard1, Michael Hanson1, Eva Hoffman1,9, Gabriel S. Bever2, Amy M. Balanoff2, Zachary S. Morris3, Daniel J. Field! !1,4, Jasmin Camacho3, Timothy B. Rowe9, Mark A. Norell5, Roger M. Smith6, Arhat Abzhanov7,8* and Bhart-Anjan S. Bhullar1* Major transformations in brain size and proportions, such as the enlargement of the brain during the evolution of birds, are accompanied by profound modifications to the skull roof. However, the hypothesis of concerted evolution of shape between brain and skull roof over major phylogenetic transitions, and in particular of an ontogenetic relationship between specific regions of the brain and the skull roof, has never been formally tested. We performed 3D morphometric analyses to examine the deep history of brain and skull-roof morphology in Reptilia, focusing on changes during the well-documented transition from early reptiles through archosauromorphs, including nonavian dinosaurs, to birds. Non-avialan taxa cluster tightly together in mor- phospace, whereas Archaeopteryx and crown birds occupy a separate region. There is a one-to-one correspondence between the forebrain and frontal bone and the midbrain and parietal bone. Furthermore, the position of the forebrain–midbrain bound- ary correlates significantly with the position of the frontoparietal suture across the phylogenetic breadth of Reptilia and during the ontogeny of individual taxa. Conservation of position and identity in the skull roof is apparent, and there is no support for previous hypotheses that the avian parietal is a transformed postparietal.
    [Show full text]
  • First Evidence of Convergent Lifestyle Signal in Reptile Skull Roof
    Ebel et al. BMC Biology (2020) 18:185 https://doi.org/10.1186/s12915-020-00908-y RESEARCH ARTICLE Open Access First evidence of convergent lifestyle signal in reptile skull roof microanatomy Roy Ebel1,2* , Johannes Müller1,2 , Till Ramm1,2,3,4 , Christy Hipsley3,4 and Eli Amson1 Abstract Background: The study of convergently acquired adaptations allows fundamental insight into life’s evolutionary history. Within lepidosaur reptiles—i.e. lizards, tuatara, and snakes—a fully fossorial (‘burrowing’) lifestyle has independently evolved in most major clades. However, despite their consistent use of the skull as a digging tool, cranial modifications common to all these lineages are yet to be found. In particular, bone microanatomy, although highly diagnostic for lifestyle, remains unexplored in the lepidosaur cranium. This constitutes a key gap in our understanding of their complexly interwoven ecology, morphology, and evolution. In order to bridge this gap, we reconstructed the acquisition of a fossorial lifestyle in 2813 lepidosaurs and assessed the skull roof compactness from microCT cross-sections in a representative subset (n = 99). We tested this and five macroscopic morphological traits for their convergent evolution. Results: We found that fossoriality evolved independently in 54 lepidosaur lineages. Furthermore, a highly compact skull roof, small skull diameter, elongate cranium, and low length ratio of frontal and parietal were repeatedly acquired in concert with a fossorial lifestyle. Conclusions: We report a novel case of convergence that concerns lepidosaur diversity as a whole. Our findings further indicate an early evolution of fossorial modifications in the amphisbaenian ‘worm-lizards’ and support a fossorial origin for snakes.
    [Show full text]
  • Biology 3315 – Comparative Vertebrate Morphology Skulls and Visceral Skeletons
    Biology 3315 – Comparative Vertebrate Morphology Skulls and Visceral Skeletons 1. Head skeleton of lamprey Cyclostomes are highly specialized in both the construction of the chondrocranium and visceral skeleton. The main mass of cartilage surrounding the brain is broadly homologous with the neurocranium (= chondrocranium) of other fishes, but a number of accessory cartilages, including the “piston” of the “tongue”, are also present; these cannot be adequately homologized with any structure in other vertebrates. The visceral skeleton is atypical in consisting of a fused latticework of branchial cartilages. This “branchial basket” has special elastic properties important to the peculiar mode of respiration used by cyclostomes. Observe the well-developed notochord. 2. Chondrocranium of the Chondrichthyes Because the cartilagenous fishes lack the dermal bones that gave protection to the brain, the chondrocranium is very solid, with complete lateral walls and a roof. The chondrocranium of the shark is not typical of that structure for vertebrates in general. Although it never ossifies, it is sometimes so hardened with granules of calcium salts that it cannot be cut with a knife. Examine the shark chondrocrania on display. 3. Chondrocranium of bony fish These specimens are of the holostean Amia and the chondrostean Ascipeuser (sturgeon). Note the general form of the isolated chondrocranium and its several centers of ossification. How does it compare with that of the shark? Examine the sturgeon to see the relationship of the overlying dermatocranium to the chondrocranium. Notice the unossified member between some of the dermal bones. Which portions of the visceral component of the skull are visible in this specimen? 4.
    [Show full text]
  • Cranial Anatomy of Two New Late Devonian Lungfishes (Pisces: Dipnoi) from Mount Howitt, Victoria
    AUSTRALIAN MUSEUM SCIENTIFIC PUBLICATIONS Long, John A., 1992. Cranial anatomy of two new Late Devonian lungfishes (Pisces: Dipnoi) from Mount Howitt, Victoria. Records of the Australian Museum 44(3): 299–318. [5 December 1992]. doi:10.3853/j.0067-1975.44.1992.37 ISSN 0067-1975 Published by the Australian Museum, Sydney naturenature cultureculture discover discover AustralianAustralian Museum Museum science science is is freely freely accessible accessible online online at at www.australianmuseum.net.au/publications/www.australianmuseum.net.au/publications/ 66 CollegeCollege Street,Street, SydneySydney NSWNSW 2010,2010, AustraliaAustralia Records of the Australian Museum (1992) Vo1.44: 299-318. ISSN 0067-1975 299 Cranial Anatomy of Two New Late Devonian Lungfishes (Pisces: Dipnoi) from Mount Howitt, Victoria JOHN A. LONG Western Australian Museum, Francis Street, Perth, W A 6000, Australia ABSTRACT. Two new lungfishes are described from the Frasnian lacustrine sediments near Mount Howitt, eastern Victoria. Howidipterus donnae n.gen., n.sp. has toothplates with well-developed marginal teeth, and has a skull roof pattern similar to Scaumenacia but with a D bone present and large paired rostral bones anterior to the E bones. The cheek has moderately deep infraorbitals. The scales have a coarse ornament with widely spaced ridges. Barwickia downunda n.gen., n.sp. has a skull roof pattern characterised by a narrow, small D bone, narrow E bones as long as the C bones, and I bones which are indented well into the rear of the B bone and on occasion may contact each other. The dentition is denticulate as in Fleurantia. The cheek has a narrow, bar-like bone 6 + 7.
    [Show full text]