38 results on '"Tiktaalik"'
Search Results
2. Axial Skeleton and Muscle Arrangement in Terrestrial Tetrapods
- Author
-
Preuschoft, Holger and Preuschoft, Holger
- Published
- 2022
- Full Text
- View/download PDF
Catalog
3. Sarcopterygians: From Lobe-Finned Fishes to the Tetrapod Stem Group
- Author
-
Clack, Jennifer A., Ahlberg, Per Erik, Fay, Richard R., Series editor, Popper, Arthur N., Series editor, Clack, Jennifer A., editor, and Fay, Richard R, editor
- Published
- 2016
- Full Text
- View/download PDF
4. Ancestral developmental potentials in early bony fish contributed to vertebrate water-to-land transition
- Author
-
Guo-Jie Zhang and Xu-Peng Bi
- Subjects
Tiktaalik ,Lineage (evolution) ,Heart Ventricles ,early bony fishes ,comparative genomics ,genetic regulation ,03 medical and health sciences ,CONUS ARTERIOSUS ,Mice ,0302 clinical medicine ,biology.animal ,lcsh:Zoology ,Basic Helix-Loop-Helix Transcription Factors ,Animals ,lcsh:QL1-991 ,Lung ,Ecology, Evolution, Behavior and Systematics ,030304 developmental biology ,Lungfish ,Gene Editing ,Mice, Knockout ,0303 health sciences ,Ichthyostega ,Ecology ,biology ,FIN ,Fishes ,ancestral developmental potential ,Vertebrate ,Extremities ,biology.organism_classification ,Biological Evolution ,Research Highlight ,EVOLUTION ,Gene Expression Regulation ,Evolutionary biology ,vertebrate landing ,Acanthostega ,HEART ,Animal Science and Zoology ,Adaptation ,030217 neurology & neurosurgery ,Psarolepis - Abstract
The water-to-land transition was a major step in vertebrate evolution and eventually gave rise to the tetrapods, including amphibians, reptiles, birds, and mammals. The first land invasion of our fish ancestors is considered to have occurred during the late Devonian period ~370 million years ago (Mya) (Daeschler et al., 2006). Many fossils from important transitional species, such as Tiktaalik, Acanthostega, and Ichthyostega, have helped to identify key morphological and anatomical structures crucial to vertebrate terrestrial adaptation (Coates, 1996; Johanson & Ahlberg, 2001; Shubin et al., 2006). However, homologous analyses of these body forms and structures in more ancient species have suggested that some of the morphologies related to vertebrate land dispersal were already present in early bony fish species. For instance, the presence of shoulder girdles on the articular surface of the endoskeleton in Late Lochkovian Psarolepis indicates that stem sarcopterygians already possessed an endoskeletal fin pattern similar to that of tetrapod stylopods (Zhu & Yu, 2009). In addition, primitive lungs, which originated from the respiratory pharynx and were located on the ventral side of the alimentary tracts, can be observed in several extant basal actinopterygians (bichirs, reedfish) and all extant sarcopterygians, as well as some fossils of coelacanths and salamanders (Cupello et al., 2017; Tissier et al., 2017) (Figure 1). This evidence suggests that, instead of relying on genetic innovations evolving after the first fish left their water habitat, this transition may have been accomplished by adopting physical traits and genetic components that already existed far earlier than when the transition occurred. Whether such an ancestral developmental regulatory network was present or not and how far this ancestral network can be traced in history are challenging questions for paleontologists. Three recent papers published in Cell provide new insights into this hypothesis. Wang et al. (2021) sequenced the giant genome of lungfish, the closest fish species to tetrapods, and Bi et al. (2021) sequenced the genomes of multiple early divergent ray-finned fish. Comparative genomic analyses from these two studies confirmed the presence of ancestral genetic regulatory networks that likely played essential roles in the development and evolution of various biological functions related to vertebrate land invasion. Although certain ancestral features have been lost in teleosts, the most derived fish lineage to evolve after whole-genome duplication (Sato & Nishida, 2010), they have been recreated in zebrafish by modifying their genetic makeup to reactivate the ancestral genetic network (Hawkins et al., 2021). more...
- Published
- 2021
- Full Text
- View/download PDF
5. Fin ray patterns at the fin-to-limb transition
- Author
-
Ihna Yoo, Natalia K Taft, Neil H. Shubin, Thomas A. Stewart, Edward B. Daeschler, and Justin B. Lemberg
- Subjects
0106 biological sciences ,endocrine system ,Tiktaalik ,Fin ,animal structures ,Evolution ,010603 evolutionary biology ,01 natural sciences ,dermal skeleton ,Amphibians ,03 medical and health sciences ,Endoskeleton ,Rhizodontida ,Extant taxon ,Elpistostegalia ,Animals ,14. Life underwater ,Eusthenopteron ,030304 developmental biology ,0303 health sciences ,Multidisciplinary ,biology ,Tristichopteridae ,Fossils ,Fishes ,Paleontology ,Extremities ,Anatomy ,Biological Sciences ,biology.organism_classification ,Biological Evolution ,body regions ,embryonic structures ,Animal Fins ,Tomography, X-Ray Computed ,human activities ,fin-to-limb transition - Abstract
Significance To explain how limbs evolved from fins, paleontologists have traditionally studied the endoskeleton. Here, we provide a comparative analysis of the other skeletal system of fins, the dermal skeleton. We describe dermal ray anatomy for 3 species of tetrapodomorph fishes. These data show that, prior to the origin of digits, dermal rays were simplified, the fin web became reduced in size, and the top and bottom of the fin became more asymmetric. These changes reveal how fins became adapted for interacting with the substrate prior to the fin-to-limb transition and that dorsoventral asymmetry is an important, understudied axis of diversification in paired fins., The fin-to-limb transition was marked by the origin of digits and the loss of dermal fin rays. Paleontological research into this transformation has focused on the evolution of the endoskeleton, with little attention paid to fin ray structure and function. To address this knowledge gap, we study the dermal rays of the pectoral fins of 3 key tetrapodomorph taxa—Sauripterus taylori (Rhizodontida), Eusthenopteron foordi (Tristichopteridae), and Tiktaalik roseae (Elpistostegalia)—using computed tomography. These data show several trends in the lineage leading to digited forms, including the consolidation of fin rays (e.g., reduced segmentation and branching), reduction of the fin web, and unexpectedly, the evolution of asymmetry between dorsal and ventral hemitrichia. In Eusthenopteron, dorsal rays cover the preaxial endoskeleton slightly more than ventral rays. In Tiktaalik, dorsal rays fully cover the third and fourth mesomeres, while ventral rays are restricted distal to these elements, suggesting the presence of ventralized musculature at the fin tip analogous to a fleshy “palm.” Asymmetry is also observed in cross-sectional areas of dorsal and ventral rays. Eusthenopteron dorsal rays are slightly larger than ventral rays; by contrast, Tiktaalik dorsal rays can be several times larger than ventral rays, and degree of asymmetry appears to be greater at larger sizes. Analysis of extant osteichthyans suggests that cross-sectional asymmetry in the dermal rays of paired fins is plesiomorphic to crown group osteichthyans. The evolution of dermal rays in crownward stem tetrapods reflects adaptation for a fin-supported elevated posture and resistance to substrate-based loading prior to the origin of digits. more...
- Published
- 2020
6. New tetrapodomorph vertebrates from the Yam-Tesovo locality (Amata Regional Stage, Middle–Upper Devonian) of Leningrad Region, northwestern Russia
- Author
-
Oleg A. Lebedev and Gaël Clément
- Subjects
0106 biological sciences ,010506 paleontology ,Tiktaalik ,biology ,Livoniana ,Tetrapodomorpha ,Mandible ,Vertebrate ,biology.organism_classification ,010603 evolutionary biology ,01 natural sciences ,Devonian ,Paleontology ,biology.animal ,Elpistostegalia ,Tetrapod (structure) ,General Earth and Planetary Sciences ,Geology ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
Each piece of data is valuable for unearthing the earliest history of tetrapod origin. Despite frequently incomplete preservation, each skeletal element provides important information on the morphology, phylogeny and faunistic diversity of early tetrapodomorphs. We describe here new and earlier collected material from the fossil vertebrate site Yam-Tesovo on the Oredezh River (Leningrad Region, northwestern Russia) in the deposits of the Yam-Tesovo Formation within the Amata Regional Stage (?lowermost Frasnian, Upper Devonian). Upon similarity of their dermal ornamentation, two mandibular fragments are suggested to belong to the new tetrapodomorph taxon Rubrognathuskuleshovi n. gen. et sp. This species demonstrates a general ‘elpistostegalian' morphological pattern with some early tetrapod characters. The new taxon is characterised by an almost closed intercoronoid fossa, a prearticular that is strongly convex in section and bearing small teeth along its dorsal margin, low vertical coronoid laminae and coronoid fangs that enter the coronoid tooth row. The mandibular canal runs partly in open groove or opens to the surface by a row of large pores. The dermal ornament consists of a network of small ridges forming tubercles in the nodes. The postfrontal assigned to Tetrapodomorpha shows a ‘tetrapod-like' pits-and-ridges sculpturing and a supraorbital ridge characteristic of early tetrapods as well as ‘elpistostegalians'. Its long posterolateral bone margin demonstrates a lateral projection similar to that in Tiktaalik and unknown in other ‘elpistostegalians' and early tetrapods. An unusually flattened vomer is doubtfully related to the tetrapodomorph genus Livoniana Ahlberg, Lukševičs & Mark-Kurik, 2000, based upon characteristic multiple tooth rows. Teeth in rows decrease labially and show no clearly enlarged fang pairs. New finds of the last two decades present the earliest records of some tetrapod characters in non-limbed tetrapodomorphs. This challenges previous hypotheses on the origin of tetrapods. more...
- Published
- 2018
- Full Text
- View/download PDF
7. The Fish–Tetrapod Transition: New Fossils and Interpretations.
- Author
-
Clack, Jennifer
- Abstract
Our information on the transition between fish with fins and tetrapods with limbs and digits has increased manyfold in the last 15–20 years and especially in the last 5 or 10 years, with some spectacular finds of new material. Some of these include new tetrapod-like fish and very primitive tetrapods that help to resolve questions of the sequence of acquisition of tetrapod characters, the approximate timing of the events, the likely geographic location, and the circumstances under which it happened. Forelimbs and skulls became modified in advance of hind limbs, adapted for supporting the head and front of the body out of the water, probably in connection with air breathing. The likely time of origin for limbed tetrapods is between 385 and 380 million years ago, probably in the northern continent of Laurussia. The origin of limbed tetrapods did not coincide with the acquisition of full terrestriality, an outcome that probably arose in the Early Carboniferous. This later part of the story is documented by few fossils, though two in particular give key information. Studies of modern vertebrates, especially the evolutionary developmental genetics of Hox genes, are beginning to provide clues to the origin of digits. [ABSTRACT FROM AUTHOR] more...
- Published
- 2009
- Full Text
- View/download PDF
8. The Fin to Limb Transition: New Data, Interpretations, and Hypotheses from Paleontology and Developmental Biology.
- Author
-
Clack, Jennifer A.
- Subjects
- *
EXTREMITIES (Anatomy) , *FINS (Anatomy) , *TETRAPODS , *HUMERUS , *BIOLOGICAL evolution , *DEVELOPMENTAL biology , *FOSSILS - Abstract
After a brief historical review of the fin to limb transition and consideration of a theoretical "prototetrapod," this article considers new ideas generated from recent fossil finds and from developmental biology that bear on the question of how limbs, digits, limb joints, and pentadactyly evolved. Among the first changes to take place were those to the humerus, in concert with those to the breathing apparatus, and these adaptations were acquired while the animals were still basically aquatic with the evolution of digits occurring during this phase. Studies from developmental biology of modern taxa can be integrated with information from fossils to produce a fuller picture. The acquisition of pentadactyly was among the last changes to occur in the modification of a fin into a limb. This vision differs radically from older theoretical ideas which perceived land locomotion as the prime evolutionary force driving the transition. [ABSTRACT FROM AUTHOR] more...
- Published
- 2009
- Full Text
- View/download PDF
9. A Lungfish Walked into the Zoo: On the Origin of Limbs from Lobe-Fins
- Author
-
Ault, Charles R., Jr., author
- Published
- 2016
- Full Text
- View/download PDF
10. DESCRIBING THE LOWER JAW OF THE STEM TETRAPOD TIKTAALIK ROSEAE (LATE DEVONIAN: FRASNIAN) THROUGH COMPUTED TOMOGRAPHY DATA
- Author
-
Ted Daeschler and Kevin Sievers
- Subjects
Paleontology ,Tiktaalik ,medicine.diagnostic_test ,biology ,Tetrapod (structure) ,medicine ,Late Devonian extinction ,Computed tomography ,biology.organism_classification ,Geology - Published
- 2018
- Full Text
- View/download PDF
11. A tetrapod fauna from within the Devonian Antarctic Circle
- Author
-
Robert W. Gess and Per E. Ahlberg
- Subjects
010506 paleontology ,Multidisciplinary ,Tiktaalik ,biology ,Elpistostege ,Fossils ,Antarctic Regions ,010502 geochemistry & geophysics ,biology.organism_classification ,01 natural sciences ,Supercontinent ,Biological Evolution ,Devonian ,Gondwana ,Paleontology ,South Africa ,Geography ,Jaw ,Panderichthys ,Vertebrates ,Tetrapod (structure) ,Animals ,Late Devonian extinction ,0105 earth and related environmental sciences - Abstract
Out of Antarctica When we think of Devonian tetrapods, the ancestors of all modern vertebrates, we tend to picture amphibian-like creatures emerging from the water into a wet tropical forest or swamp. Indeed, all previously described specimens of this group have been recovered from the tropics. Gess and Ahlberg now describe two fossil tetrapods from Devonian Antarctica. Thus, the distribution of tetrapods may have been global, which encourages us to rethink the environments in which this important group was shaped. Science , this issue p. 1120 more...
- Published
- 2017
12. A Devonian tetrapod-like fish reveals substantial parallelism in stem tetrapod evolution
- Author
-
Liantao Jia, Wenjin Zhao, Per E. Ahlberg, and Min Zhu
- Subjects
0106 biological sciences ,010506 paleontology ,Tiktaalik ,Lineage (evolution) ,Zoology ,Biology ,010603 evolutionary biology ,01 natural sciences ,Devonian ,stomatognathic system ,Phylogenetics ,Tetrapod (structure) ,Animals ,Late Devonian extinction ,Ecology, Evolution, Behavior and Systematics ,Phylogeny ,0105 earth and related environmental sciences ,Ecology ,Fishes ,Bayes Theorem ,biology.organism_classification ,Biological Evolution ,Maximum parsimony ,body regions ,Evolutionary biology ,Parallel evolution - Abstract
The fossils assigned to the tetrapod stem group document the evolution of terrestrial vertebrates from lobe-finned fishes. During the past 18 years the phylogenetic structure of this stem group has remained remarkably stable, even when accommodating new discoveries such as the earliest known stem tetrapod Tungsenia and the elpistostegid (fish–tetrapod intermediate) Tiktaalik. Here we present a large lobe-finned fish from the Late Devonian period of China that disrupts this stability. It combines characteristics of rhizodont fishes (supposedly a basal branch in the stem group, distant from tetrapods) with derived elpistostegid-like and tetrapod-like characters. This melange of characters may reflect either detailed convergence between rhizodonts and elpistostegids plus tetrapods, under a phylogenetic scenario deduced from Bayesian inference analysis, or a previously unrecognized close relationship between these groups, as supported by maximum parsimony analysis. In either case, the overall result reveals a substantial increase in homoplasy in the tetrapod stem group. It also suggests that ecological diversity and biogeographical provinciality in the tetrapod stem group have been underestimated. A large, lobe-finned fish from the Late Devonian of China disrupts previously accepted stem-tetrapod phylogeny and reveals parallel evolution within the lineage. more...
- Published
- 2017
13. Tooth replacement in early sarcopterygians
- Author
-
Philip C. J. Donoghue, Martin Rücklin, Mark Doeland, and Aidan M. C. Couzens
- Subjects
0106 biological sciences ,Tiktaalik ,Odontode ,micro-CT ,010603 evolutionary biology ,01 natural sciences ,dentition ,03 medical and health sciences ,stomatognathic system ,ancestral ,biology.animal ,lcsh:Science ,Eusthenopteron ,development ,Coelacanth ,Whorl (botany) ,030304 developmental biology ,0303 health sciences ,Multidisciplinary ,biology ,Dentition ,Latimeria ,Biology (Whole Organism) ,Vertebrate ,Anatomy ,biology.organism_classification ,stomatognathic diseases ,Osteichthyes ,lcsh:Q ,Research Article - Abstract
Teeth were an important innovation in vertebrate evolution but basic aspects of early dental evolution remain poorly understood. Teeth differ from other odontode organs, like scales, in their organized, sequential pattern of replacement. However, tooth replacement patterns also vary between the major groups of jawed vertebrates. Although tooth replacement in stem-osteichthyans and extant species has been intensively studied it has been difficult to resolve scenarios for the evolution of osteichthyan tooth replacement because of a dearth of evidence from living and fossil sarcopterygian fishes. Here we provide new anatomical data informing patterns of tooth replacement in the Devonian sarcopterygian fishes Onychodu s, Eusthenopteron and Tiktaalik and the living coelacanth Latimeria based on microfocus- and synchrotron radiation-based X-ray microtomography. Early sarcopterygians generated replacement teeth on the jaw surface in a pattern similar to stem-osteichthyans, with damaged teeth resorbed and replacement teeth developed on the surface of the bone. However, resorption grades and development of replacement teeth vary spatially and temporally within the jaw. Particularly in Onychodus , where teeth were also shed through anterior rotation and resorption of bone at the base of the parasymphyseal tooth whorl, with new teeth added posteriorly. As tooth whorls are also present in more stem-osteichthyans, and statodont tooth whorls are present among acanthodians (putative stem-chondrichthyans), rotational replacement of the anterior dentition may be a stem-osteichthyan character. Our results suggest a more complex evolutionary history of tooth replacement. more...
- Published
- 2019
- Full Text
- View/download PDF
14. Biomechanics and functional preconditions for terrestrial lifestyle in basal tetrapods, with special consideration ofTiktaalik roseae
- Author
-
Claudia Distler-Hoffmann, Bianca Hohn-Schulte, Holger Preuschoft, and Ulrich Witzel
- Subjects
Basal (phylogenetics) ,Tiktaalik ,biology ,Quadrupedalism ,Functional morphology ,Biomechanics ,Late Devonian extinction ,Anatomy ,General Agricultural and Biological Sciences ,biology.organism_classification - Abstract
The fossil Tiktaalik roseae from the Late Devonian induces clear definition of the biomechanical and functional preconditions for a terrestrial lifestyle including quadrupedal standing and locomoti... more...
- Published
- 2013
- Full Text
- View/download PDF
15. Evolution Is a 'Fact'
- Author
-
Francisco J. Ayala
- Subjects
geography ,Tiktaalik ,geography.geographical_feature_category ,Fossil Record ,biology ,Ecology (disciplines) ,Zoology ,biology.organism_classification ,Geographic distribution ,Divergent evolution ,Evolutionary biology ,Archipelago ,%22">Fish ,Archaeopteryx - Abstract
The evolution of organisms is at the core of all biological disciplines, from genetics and molecular biology to ecology and neurobiology. That organisms have evolved is a “fact” demonstrated by multiple sorts of evidence. The fossil record shows that organisms have evolved for hundreds of millions of years. Fossils have been found that are intermediate between fish and amphibians, between reptiles and birds, and, most importantly, between primates and humans. The geographic distribution of plants and animals displays their divergent evolution in different continents and islands. Notable examples are the Galapagos Islands and the Hawaiian archipelago, with some unique species of plants and animals and the absence of most others. The anatomy of organisms shows their evolutionary origins and the relationships between different species . Molecular biology, a recent discipline, provides the most definitive evidence of the evolution of life and the most precise information about the evolutionary relationships among living organisms. more...
- Published
- 2016
- Full Text
- View/download PDF
16. Land Vertebrates, the Origin and Evolution of
- Author
-
J.A. Clack
- Subjects
Ichthyostega ,Paleontology ,Pederpes ,Tiktaalik ,biology ,Acanthostega ,Tetrapod (structure) ,Terrestrial locomotion ,Evolution of tetrapods ,biology.organism_classification ,Eusthenopteron ,Geology - Abstract
This article introduces the tetrapods, both modern and extinct, and sets out what we know or can infer about the origin of the group. It introduces fossil members of the group that gave rise to tetrapods and discusses some of the conditions in which tetrapods developed limbs and walking. Terrestrial locomotion followed the evolution of limbs with digits once weight-bearing and flexible joints were developed. more...
- Published
- 2016
- Full Text
- View/download PDF
17. Sarcopterygians: From Lobe-Finned Fishes to the Tetrapod Stem Group
- Author
-
Jennifer A. Clack and Per E. Ahlberg
- Subjects
Tiktaalik ,stomatognathic system ,biology ,Latimeria ,Panderichthys ,Hyomandibula ,Tetrapod (structure) ,Youngolepis ,Anatomy ,biology.organism_classification ,Eusthenopteron ,Coelacanth - Abstract
The sarcopterygians or lobe-finned fishes is the group that gave rise to tetrapods, and they were the dominant bony fishes of the Devonian period. Their otic regions were constructed similarly to those of both the actinopterygians and chondrichthyans, their structure being the common inheritance of all jawed vertebrates. One distinguishing feature of the primitive sarcopterygian braincase was that the division between the anterior ethmosphenoid and posterior otoccipital sections of the braincase was marked by a flexible hinge joint, which is seen today in the modern coelacanth, Latimeria. The hyomandibular was long and projected ventrally with an opercular process that contacted the opercular bone and with the distal end associated indirectly with the jaw joint. It was a key component of the buccal pumping mechanism for breathing and feeding. The braincases of dipnoans (lungfishes) were the most highly modified of sarcopterygian braincases with consolidated fore and aft portions and reduction or loss of the hyomandibula. The utricle was enlarged in several fossil dipnoans, although the reason for this is not clear. The braincases of tetrapodomorph sarcopterygians differed little from the primitive condition in the group. The main modifications were to the more crownward and tetrapod-like forms from the Late Devonian. In these fishes, the hyomandibula was reduced in length, its contact with the opercular bone lost and, ultimately, the opercular bone itself disappeared. The spiracular notch and associated cleft increased in width and volume respectively, possibly resulting in increased air-breathing capacity and reduced use of the gill system. more...
- Published
- 2016
- Full Text
- View/download PDF
18. The Fin to Limb Transition: New Data, Interpretations, and Hypotheses from Paleontology and Developmental Biology
- Author
-
Jennifer A. Clack
- Subjects
Ichthyostega ,Paleontology ,Tiktaalik ,Fin ,biology ,Space and Planetary Science ,Transition (fiction) ,Earth and Planetary Sciences (miscellaneous) ,Acanthostega ,Astronomy and Astrophysics ,biology.organism_classification ,Developmental biology - Abstract
After a brief historical review of the fin to limb transition and consideration of a theoretical “prototetrapod,” this article considers new ideas generated from recent fossil finds and from developmental biology that bear on the question of how limbs, digits, limb joints, and pentadactyly evolved. Among the first changes to take place were those to the humerus, in concert with those to the breathing apparatus, and these adaptations were acquired while the animals were still basically aquatic with the evolution of digits occurring during this phase. Studies from developmental biology of modern taxa can be integrated with information from fossils to produce a fuller picture. The acquisition of pentadactyly was among the last changes to occur in the modification of a fin into a limb. This vision differs radically from older theoretical ideas which perceived land locomotion as the prime evolutionary force driving the transition. more...
- Published
- 2009
- Full Text
- View/download PDF
19. On the phylogenetic position ofGogonasus andrewsae Long 1985, within the Tetrapodomorpha
- Author
-
Timothy Holland and John A. Long
- Subjects
Lungfish ,Tiktaalik ,Phylogenetic tree ,biology ,Tetrapodomorpha ,Fish fin ,Cell Biology ,biology.organism_classification ,Paleontology ,Evolutionary biology ,Osteolepis ,Gogo Formation ,Animal Science and Zoology ,Eusthenopteron ,Ecology, Evolution, Behavior and Systematics - Abstract
Within the Tetrapodomorpha, the Late Devonian Gogonasus andrewsae of the Gogo Formation, Gogo, Western Australia, has occupied an uncertain phylogenetic position. Following the description of several well-preserved three-dimensional skulls and pectoral girdles, the discovery of the first complete specimen (NMV P221807) made Gogonasus one of the best-known tetrapodomorph fish. Recent studies of pectoral fin structure and the spiracular opening of Gogonasus have suggested an unexpected affinity with ‘elpistostegalid’ fish such as Tiktaalik. Subsequent work has refuted characters linking these taxa, with phylogenetic analysis of the Tetrapodomorpha placing Gogonasus basal to megalichthyids and tristichopterids. In this paper we reanalyse characters linking Gogonasus with ‘elpistostegalid’ fish and those supporting the placement of Gogonasus crownward of Eusthenopteron. New phylogenetic analyses of the Tetrapodomorpha show a revised phylogenetic position of Gogonasus as being deeply nested within the Tetrapodomorpha, crownward of Osteolepis and Megalichthys, but basal to Eusthenopteron+‘elpistostegalids’. Functional consideration of the spiracular structure suggests a position of Gogonasus closer to ‘elpistostegalids’, although data is lacking from other less-well-preserved taxa to fully test the hypothesis. The humerus of the Late Devonian lungfish Chirodipterus from Gogo, Western Australia is figured for comparative purposes. more...
- Published
- 2009
- Full Text
- View/download PDF
20. Contrasting Developmental Trajectories in the Earliest Known Tetrapod Forelimbs
- Author
-
J. A. Clack, Per E. Ahlberg, and Viviane Callier
- Subjects
Ichthyostega ,Multidisciplinary ,Tiktaalik ,biology ,Fossils ,Ontogeny ,Fishes ,Anatomy ,Humerus ,biology.organism_classification ,Biological Evolution ,Species Specificity ,Forelimb ,Vertebrates ,Morphogenesis ,Tetrapod (structure) ,Acanthostega ,Muscle attachment ,Animals ,%22">Fish ,Muscle, Skeletal ,Biological sciences ,Locomotion ,Phylogeny - Abstract
Ichthyostega and Acanthostega are the earliest tetrapods known from multiple near-complete skeletons, with Acanthostega generally considered the more primitive. New material indicates differing ontogenetic trajectories for their forelimbs: In Ichthyostega , the pattern of muscle attachment processes on small humeri (upper arm bones) resembles that in “fish” members of the tetrapod stem group such as Tiktaalik , whereas large humeri approach (but fail to attain) the tetrapod crown-group condition; in Acanthostega , both small and large humeri exhibit the crown-group pattern. We infer that Ichthyostega underwent greater locomotory terrestrialization during ontogeny. The newly recognized primitive characteristics also suggest that Ichthyostega could be phylogenetically more basal than Acanthostega . more...
- Published
- 2009
- Full Text
- View/download PDF
21. The cranial endoskeleton of Tiktaalik roseae
- Author
-
Neil H. Shubin, Farish A. Jenkins, Jason P. Downs, and Edward B. Daeschler
- Subjects
Sarcopterygii ,Multidisciplinary ,Tiktaalik ,biology ,Fossils ,Skull ,Fishes ,Vertebrate ,Anatomy ,biology.organism_classification ,Palatoquadrate ,Biological Evolution ,Models, Biological ,Devonian ,body regions ,Endoskeleton ,stomatognathic system ,biology.animal ,Hyomandibula ,Animals ,Kinesis ,Ecosystem - Abstract
Among the morphological changes that occurred during the 'fish-to-tetrapod' transition was a marked reorganization of the cranial endoskeleton. Details of this transition, including the sequence of character acquisition, have not been evident from the fossil record. Here we describe the braincase, palatoquadrate and branchial skeleton of Tiktaalik roseae, the Late Devonian sarcopterygian fish most closely related to tetrapods. Although retaining a primitive configuration in many respects, the cranial endoskeleton of T. roseae shares derived features with tetrapods such as a large basal articulation and a flat, horizontally oriented entopterygoid. Other features in T. roseae, like the short, straight hyomandibula, show morphology intermediate between the condition observed in more primitive fish and that observed in tetrapods. The combination of characters in T. roseae helps to resolve the relative timing of modifications in the cranial endoskeleton. The sequence of modifications suggests changes in head mobility and intracranial kinesis that have ramifications for the origin of vertebrate terrestriality. more...
- Published
- 2008
- Full Text
- View/download PDF
22. 10. FISH OUT OF WATER
- Author
-
Donald R. Prothero
- Subjects
Fishery ,Tiktaalik ,biology ,%22">Fish ,biology.organism_classification ,Diversity of fish - Published
- 2015
- Full Text
- View/download PDF
23. A Devonian tetrapod-like fish and the evolution of the tetrapod body plan
- Author
-
Farish A. Jenkins, Edward B. Daeschler, and Neil H. Shubin
- Subjects
Sarcopterygii ,Tiktaalik ,Tetrapodomorpha ,Environment ,Paleontology ,stomatognathic system ,Elpistostegalia ,Morphogenesis ,Tetrapod (structure) ,medicine ,Animals ,Eusthenopteron ,History, Ancient ,Phylogeny ,Multidisciplinary ,biology ,Skull roof ,Fossils ,Skull ,Fishes ,Water ,Extremities ,biology.organism_classification ,Biological Evolution ,body regions ,medicine.anatomical_structure ,Acanthostega - Abstract
The relationship of limbed vertebrates (tetrapods) to lobe-finned fish (sarcopterygians) is well established, but the origin of major tetrapod features has remained obscure for lack of fossils that document the sequence of evolutionary changes. Here we report the discovery of a well-preserved species of fossil sarcopterygian fish from the Late Devonian of Arctic Canada that represents an intermediate between fish with fins and tetrapods with limbs, and provides unique insights into how and in what order important tetrapod characters arose. Although the body scales, fin rays, lower jaw and palate are comparable to those in more primitive sarcopterygians, the new species also has a shortened skull roof, a modified ear region, a mobile neck, a functional wrist joint, and other features that presage tetrapod conditions. The morphological features and geological setting of this new animal are suggestive of life in shallow-water, marginal and subaerial habitats. more...
- Published
- 2006
- Full Text
- View/download PDF
24. Tetrapod-like middle ear architecture in a Devonian fish
- Author
-
Per E. Ahlberg and Martin D. Brazeau
- Subjects
Tiktaalik ,Ear, Middle ,stomatognathic system ,biology.animal ,Gill slit ,medicine ,Tetrapod (structure) ,Animals ,Gait ,History, Ancient ,Multidisciplinary ,biology ,Fossils ,Respiration ,Fishes ,Vertebrate ,Extremities ,Anatomy ,biology.organism_classification ,Biological Evolution ,body regions ,medicine.anatomical_structure ,Panderichthys ,Hyomandibula ,Middle ear ,Acanthostega - Abstract
Detailed study of Panderichthys, a lobe-finned fish closely related to the first amphibians, suggests that the early stages in the evolution of the vertebrate middle ear were related to breathing, rather than detecting sound. Our middle ear corresponds to a reduced gill slit called the ‘spiracle’ in fishes. In a well preserved Panderichthys fossil specimen held in the Latvian Natural History Museum in Riga, this gill slit is much larger than in other ancient fish species and has vertebrate-like architecture, yet was probably used to inhale water or air. It seems that a rudimentary auditory role for the stapes and other middle-ear components first developed in primitive land vertebrates. Few fossils show the incipient stages of complex morphological transformations1. For example, the earliest stages in the remodelling of the spiracular tract and suspensorium (jaw suspension) of osteolepiform fishes2,3,4 into the middle ear of tetrapods have remained elusive3. The most primitive known tetrapods show a middle ear architecture that is very different from osteolepiforms such as Eusthenopteron3, with little indication of how this transformation took place. Here we present an analysis of tetrapod middle ear origins that is based on a detailed study of Panderichthys, the immediate sister taxon of tetrapods. We show that the spiracular region is radically transformed from osteolepiforms and represents the earliest stages in the origin of the tetrapod middle ear architecture. The posterior palatoquadrate of Panderichthys is completely tetrapod-like and defines a similarly tetrapod-like spiracular tract. The hyomandibula has lost its distal portion, representing a previously unrecognized advance towards a stapes-like morphology. This spiracular specialization suggests that the middle ear of early tetrapods evolved initially as part of a spiracular breathing apparatus5,6. more...
- Published
- 2006
- Full Text
- View/download PDF
25. Pelvic girdle and fin of Tiktaalik roseae
- Author
-
Neil H. Shubin, Edward B. Daeschler, and Farish A. Jenkins
- Subjects
Canada ,Fin ,Tiktaalik ,Biology ,Pelvis ,Amphibians ,stomatognathic system ,Species Specificity ,medicine ,Animals ,Appendage ,Multidisciplinary ,Pelvic girdle ,Fossils ,Animal Fins ,Fishes ,Paleontology ,Anatomy ,Biological Sciences ,biology.organism_classification ,Ischium ,Biological Evolution ,Closest relatives ,body regions ,medicine.anatomical_structure ,Vertebrates - Abstract
A major challenge in understanding the origin of terrestrial vertebrates has been knowledge of the pelvis and hind appendage of their closest fish relatives. The pelvic girdle and appendage of tetrapods is dramatically larger and more robust than that of fish and contains a number of structures that provide greater musculoskeletal support for posture and locomotion. The discovery of pelvic material of the finned elpistostegalian, Tiktaalik roseae, bridges some of these differences. Multiple isolated pelves have been recovered, each of which has been prepared in three dimensions. Likewise, a complete pelvis and partial pelvic fin have been recovered in association with the type specimen. The pelves of Tiktaalik are paired and have broad iliac processes, flat and elongate pubes, and acetabulae that form a deep socket rimmed by a robust lip of bone. The pelvis is greatly enlarged relative to other finned tetrapodomorphs. Despite the enlargement and robusticity of the pelvis of Tiktaalik, it retains primitive features such as the lack of both an attachment for the sacral rib and an ischium. The pelvic fin of Tiktaalik (NUFV 108) is represented by fin rays and three endochondral elements: other elements are not preserved. The mosaic of primitive and derived features in Tiktaalik reveals that the enhancement of the pelvic appendage of tetrapods and, indeed, a trend toward hind limb-based propulsion have antecedents in the fins of their closest relatives. more...
- Published
- 2014
26. Fins, Fossils and Fingers
- Author
-
Göran Lundborg
- Subjects
Fishery ,Transitional phase ,Waves and shallow water ,Tiktaalik ,Geography ,Fin ,biology ,Fish species ,Forearm bone ,%22">Fish ,biology.organism_classification ,Devonian - Abstract
Three hundred and seventy-five million years ago, many different types of big fish lived in the sea. Gradually, some of them began approaching shallow water close to land. It became advantageous for these fishes to be able to support themselves on the seabed with their fins so they could raise their heads above the water’s surface in an amphibian-like way. In this transitional phase between life in the water and life on land, the fins of some fish species showed an obvious development towards an arm and a hand. The Tiktaalik, discovered on Ellesmere Island in northern Canada and dating back to about 375 million years ago, has been regarded as a missing link between fish and land animals, showing a first hint of a human hand in its fin. more...
- Published
- 2013
- Full Text
- View/download PDF
27. Do mudskippers and lungfishes elucidate the early evolution of four-limbed vertebrates?
- Author
-
J. Malcolm Elliott and Ulrich Kutschera
- Subjects
Ichthyostega ,Tiktaalik ,biology ,Ecology ,Panderichthys ,Tetrapod (structure) ,Acanthostega ,Periophthalmus ,Evolution of tetrapods ,biology.organism_classification ,Ecology, Evolution, Behavior and Systematics ,Devonian ,Education - Abstract
Recently, the origin of four-limbed vertebrates (tetrapods) was re-assessed, based on footprints and trackways that were made by early land animals almost 400 million years (my) ago. That is 18 my earlier than the oldest known tetrapod body fossils, such as Acanthostega and Ichthyostega from Greenland, and 10 my older than the earliest ‘tetrapodomorph fishes’ (Panderichthys, Tiktaalik etc.). These and other facts suggest that the first tetrapods may have thrived in the marine-influenced intertidal and/or lagoon zone as well as in brackish and freshwater environments associated with land vegetation, as previously thought. Here, we discuss the controversial question whether or not extant air-breathing fishes, such as mudskippers, amphibious gobioids that inhabit mangrove swamps, can be interpreted as living model organisms, with reference to the earliest land plants. In addition, recent developmental and behavioural studies on lungfishes (Dipnoi) are summarized and evaluated. We conclude that mudskipping ‘walking fishes’ (Periophthalmus sp.) and Dipnoi (Protopterus sp.) shed light on the gradual evolutionary transition of ancient fishes to early tetrapods that occurred during the Devonian in muddy, salty waters. However, they are not the ancestors of tetrapods, because extant organisms cannot be progenitors of other living beings. more...
- Published
- 2013
- Full Text
- View/download PDF
28. The earliest known stem-tetrapod from the Lower Devonian of China
- Author
-
Liantao Jia, Timothy Senden, Min Zhu, Tuo Qiao, Wenjin Zhao, John A. Long, and Jing Lu
- Subjects
Sarcopterygii ,China ,Tiktaalik ,General Physics and Astronomy ,General Biochemistry, Genetics and Molecular Biology ,Devonian ,Paleontology ,Tetrapod (structure) ,medicine ,Animals ,History, Ancient ,Phylogeny ,Lungfish ,Multidisciplinary ,biology ,Fossils ,Fishes ,Extremities ,General Chemistry ,biology.organism_classification ,Biological Evolution ,Skull ,medicine.anatomical_structure ,Panderichthys ,Tungsenia ,Animal Fins - Abstract
Recent discoveries of advanced fish-like stem-tetrapods (for example, Panderichthys and Tiktaalik) have greatly improved our knowledge of the fin-to-limb transition. However, a paucity of fossil data from primitive finned tetrapods prevents profound understanding of the acquisition sequence of tetrapod characters. Here we report a new stem-tetrapod (Tungsenia paradoxa gen. et sp. nov.) from the Lower Devonian (Pragian, ∼409 million years ago) of China, which extends the earliest record of tetrapods by some 10 million years. Sharing many primitive features with stem-lungfishes, the new taxon further fills in the morphological gap between tetrapods and lungfishes. The X-ray tomography study of the skull depicts the plesiomorphic condition of the brain in the tetrapods. The enlargement of the cerebral hemispheres and the possible presence of the pars tuberalis in this stem-tetrapod indicate that some important brain modifications related to terrestrial life had occurred at the beginning of the tetrapod evolution, much earlier than previously thought. more...
- Published
- 2012
29. QnAs with Neil Shubin
- Author
-
Prashant Nair
- Subjects
QnAs ,musculoskeletal diseases ,Multidisciplinary ,Tiktaalik ,biology ,media_common.quotation_subject ,Art history ,Anatomy ,Biological evolution ,Art ,equipment and supplies ,biology.organism_classification ,humanities ,body regions ,media_common - Abstract
Neil Shubin regards the socket in the hip joint of Tiktaalik’s pelvic appendage. Image courtesy of John Westlund, University of Chicago.
- Published
- 2014
- Full Text
- View/download PDF
30. The pectoral fin of Panderichthys and the origin of digits
- Author
-
Elga Mark-Kurik, Per E. Ahlberg, and Catherine A. Boisvert
- Subjects
Sarcopterygii ,Fin ,Tiktaalik ,fin ,Zoology ,Devonian ,stomatognathic system ,evolution ,Tetrapod (structure) ,Animals ,limb ,Lungfish ,Multidisciplinary ,biology ,Fossils ,palaeontology ,Fishes ,Fish fin ,Extremities ,Geology ,Anatomy ,biology.organism_classification ,Biological Evolution ,Skeleton (computer programming) ,body regions ,Panderichthys ,Geologi ,elpistostegid - Abstract
One of the identifying characteristics of tetrapods (limbed vertebrates) is the presence of fingers and toes. Whereas the proximal part of the tetrapod limb skeleton can easily be homologized with the paired fin skeletons of sarcopterygian (lobe-finned) fish, there has been much debate about the origin of digits. Early hypotheses1 interpreted digits as derivatives of fin radials, but during the 1990s the idea gained acceptance that digits are evolutionary novelties without direct equivalents in fish fin skeletons. This was partly based on developmental genetic data2, but also substantially on the pectoral fin skeleton of the elpistostegid (transitional fish/tetrapod) Panderichthys, which appeared to lack distal digit-like radials3. Here we present a CT scan study of an undisturbed pectoral fin of Panderichthys demonstrating that the plate-like 'ulnare' of previous reconstructions is an artefact and that distal radials are in fact present. This distal portion is more tetrapod-like than that found in Tiktaalik 4 and, in combination with new data about fin development in basal actinopterygians5, sharks6 and lungfish7, makes a strong case for fingers not being a novelty of tetrapods but derived from pre-existing distal radials present in all sarcopterygian fish. more...
- Published
- 2008
31. Ventastega curonica and the origin of tetrapod morphology
- Author
-
Ivars Zupiņš, Per E. Ahlberg, Ervīns Lukševičs, Henning Blom, and Jennifer A. Clack
- Subjects
Shoulder ,Tiktaalik ,Biologisk systematik ,Ventastega ,Morphology (biology) ,Devonian ,tetrapod ,Biological Systematics ,Biology ,Paleontology ,Phylogenetics ,evolution ,Tetrapod (structure) ,Animals ,Pelvic Bones ,Biological sciences ,Phylogeny ,Multidisciplinary ,palaeontology ,Fossils ,Skull ,Fishes ,Evolutionary transitions ,biology.organism_classification ,Biological Evolution ,%22">Fish - Abstract
The gap in our understanding of the evolutionary transition from fish to tetrapod is beginning to close thanks to the discovery of new intermediate forms such as Tiktaalik roseae. Here we narrow it further by presenting the skull, exceptionally preserved braincase, shoulder girdle and partial pelvis of Ventastega curonica from the Late Devonian of Latvia, a transitional intermediate form between the 'elpistostegids' Panderichthys and Tiktaalik and the Devonian tetrapods (limbed vertebrates) Acanthostega and Ichthyostega. Ventastega is the most primitive Devonian tetrapod represented by extensive remains, and casts light on a part of the phylogeny otherwise only represented by fragmentary taxa: it illuminates the origin of principal tetrapod structures and the extent of morphological diversity among the transitional forms. more...
- Published
- 2007
32. Tiktaalik roseaeat the Academy of Natural Sciences of Philadelphia
- Author
-
Edward B. Daeschler
- Subjects
Tiktaalik ,History ,Ecology ,biology ,Arctic ,Sister group ,Tree of life (biology) ,Natural science ,Late Devonian extinction ,biology.organism_classification ,Archaeology ,Ecology, Evolution, Behavior and Systematics - Abstract
Paleontological research occasionally reveals species with far-reaching consequences for reconstructing the tree of life and exploring the processes that shaped the diversity of life on Earth. Concurrent with the release of this volume of the Proceedings of the Academy of Natural Sciences, the research group at the Academy said farewell to a suite of fossils that have modernized our understanding of the “fish-to-tetrapod” transition. Over the past 15 years, a project co-led by the Academy’s Ted Daeschler and Neil Shubin of the University of Chicago has endeavored to discover Late Devonian vertebrate fossils from the Nunavut Territory of Arctic Canada. Their ultimate goal was realized in 2004 and subsequent field seasons with the collection and description of the tetrapodomorph sarcopterygian, Tiktaalik roseae, now recognized as belonging to the sister group of Tetrapoda. more...
- Published
- 2015
- Full Text
- View/download PDF
33. An exceptional Devonian fish from Australia sheds light on tetrapod origins
- Author
-
Erich M. G. Fitzgerald, Timothy Senden, Timothy Holland, John A. Long, and Gavin C. Young
- Subjects
Multidisciplinary ,Tiktaalik ,Time Factors ,biology ,Fossils ,Skull ,Australia ,Fishes ,Zoology ,Extremities ,biology.organism_classification ,Devonian ,Transitional fossil ,Elpistostegalia ,Hyomandibula ,Tetrapod (structure) ,Animals ,Eusthenopteron ,History, Ancient ,Phylogeny ,Kenichthys - Abstract
The evolutionary transition from water to land exerts a continuing fascination, heightened by recent discoveries of transitional fossils in Canada and the reinterpretation as tetrapods (or near-tetrapods) of fossils once classified as fishes. But signs of land life are detectable even further back. A spectacularly preserved 380-million-year old fossil of the fish Gogonasus from the Devonian of Australia is fish-like in many respects, yet features of its ear and limbs are unexpectedly advanced. The transition from fishes to tetrapods was one of the most dramatic events in the evolution of vertebrates, but many pivotal fossils are incomplete, resulting in gaps in the data that are used for phylogenetic reconstruction. Here we present new observations from the most complete, acid-prepared Devonian tetrapodomorph fish yet discovered, Gogonasus1,2, which was previously placed just crownward of Kenichthys and rhizodontids3,4, the most primitive taxa on the tetrapod lineage. Unexpectedly, Gogonasus shows a mosaic of plesiomorphic and derived tetrapod-like features. Whereas the braincase and dermal cranial skeleton exhibit generalized morphologies with respect to Eusthenopteron5 or Panderichthys6, taxa that are traditionally considered to be phyletically close to tetrapods7,8, the presence of a deeply invaginated, wide spiracle, advanced internal spiracular architecture and near-horizontal hyomandibula are specialized features that are absent from Eusthenopteron9. Furthermore, the pectoral fin skeleton of Gogonasus shares several features with that of Tiktaalik, the most tetrapod-like fish10. A new phylogenetic analysis places Gogonasus crownward of Eusthenopteron as the sister taxon to the Elpistostegalia. Aspects of the basic tetrapod limb skeleton and middle ear architecture can now be traced further back within the tetrapodomorph radiation. more...
- Published
- 2006
34. Transitions between Major Classes: Vertebrates
- Author
-
Kathleen R Devlin and Stuart S. Sumida
- Subjects
Tiktaalik ,stomatognathic system ,biology ,Permian ,Carboniferous ,biology.animal ,Lineage (evolution) ,Ventastega ,Vertebrate ,Zoology ,Taxonomic rank ,Diadectomorpha ,biology.organism_classification - Abstract
The advent of cladistic analyses of relationships between organisms has provided more rigorous means of defining lineages, although fossil records suggest that boundaries between vertebrate clades are not always distinct. At the beginning of the transition from water to land, the earliest tetrapods retain many fish-like features, and at the end of this continuum numerous terrestrial adaptations may be seen in groups not traditionally classified as amniotes. Characters of the jaw and middle ear, classically associated with Mammalia, differentiated as a functional complex that developed across the therapsid–mammal transition. Feathers and features associated with lightening the skeleton are also found in terrestrial dromaeosaurid dinosaurs, and are not exclusive to birds. That each of these transitions took place through a series of graded steps suggests that they should be considered more as a process than as a point in time or geologic history. Key Concepts: The transitions between what are considered major taxonomic groups of vertebrates are not distinct, but rather are ‘blurry’ as they reflect processes and the gradual accumulation of suites functional anatomical and physiological complexes. The water-to-land transition is not a single event. It is a continuum ranging across nearly 50 My from the first tetrapods to the first amniotes. With new information including the details of transitional forms such as Tiktaalik and Ventastega, understanding of the changes in the limb skeleton from sarcopterygian fishes to the earliest tetrapods has been refined significantly. The Late Carboniferous to Early Permian Diadectomorpha have emerged as the closest relatives of crown-group amniotes, sharing numerous anatomical features with them. Dromaeosaurid dinosaurs demonstrate a variety of experiments in feather distribution and potential flight adaptations as the group from which Aves evolved. The lineage leading to extant mammals began the process of transformation of the feeding apparatus, associated modifications of the middle ear and (probable) soft tissue associations in groups generally considered to be closely related but outside of traditionally defined mammals. Keywords: evolution; palaeontology; vertebrata; tetrapoda; amniota; mammalia; aves more...
- Published
- 2006
- Full Text
- View/download PDF
35. Fins into Limbs - Edited by B. K. Hall
- Author
-
Jonathan Bard
- Subjects
Recapitulation theory ,Histology ,Tiktaalik ,biology ,Computer science ,business.industry ,media_common.quotation_subject ,Anatomical structures ,Cell Biology ,biology.organism_classification ,Epistemology ,Origin of species ,Instinct ,Feeling ,First person ,Artificial intelligence ,Anatomy ,business ,Molecular Biology ,Erasmus+ ,Ecology, Evolution, Behavior and Systematics ,Developmental Biology ,media_common - Abstract
For those of us whose careers in developmental biology stretch back a long way, the most exciting insights in the last forty years have, without doubt, been in the area of evolutional developmental biology, or evo-devo. The story has a history. Erasmus Darwin and others at the end of the 18th century advanced the possibility of evolution and in 1859, Charles Darwin published the core mechanism in The Origin of Species. He was, however, very thin on the relationship between evolution and embryology and was not always right, for example: ‘From what we know of the embryos of mammals, birds, fishes and vertebrates, these animals are the modified descendents of some ancient progenitor, which was furnished in its adult state with branchiae, a swim-bladder, four fish-like limbs, and a long tail, all fitted for aquatic life’. Haeckel, the major comparative anatomist at the end of the 19th century, got it wrong with his biogenetic law, which essentially states that evolution adds to, rather than modifies, embryonic development. It seems to have been Waddington, harking back to von Baer, who was the first person to emphasize that the roots of anatomical variation lay in mutations that affected development. At a more practical level, a great deal of anatomical and palaeontological data on the relationships between development and evolution has been collected during the last two centuries. It was not until the early 1980s, however, with the rise of eukaryotic molecular genetics and the recognition that hox patterning underpinned so much of axial organization across the Bilateria, that the field could start to put molecular flesh on the bare bones of the earlier theoretical and anatomical insights. From these beginnings, the results of a lot of hard work over the last 25 years linking molecular biology, palaeontology, bioinformatics, evolutional homologies and experimental embryology have been that we now understand something of the molecular details of the development and evolution of biological structure. Nowhere, however, have the successes been as great as in the evolution of fins into limbs, a homology that first seems to have been pointed out by Carl Gegenbaur in 1865 and most recently analysed in Jenny Clack's monograph Gaining Ground. The publication of the multi-authored Fins into Limbs carries on where Gaining Ground ended: its three sections and 19 chapters explore almost every aspect of limb evolution and development. The first section discusses evolutional history, skeletal changes in the fin-to-limb transition (obviously written before the publication of Tiktaalik roseae), locomotion and evolutional novelties. The eight chapters on development (the only section with molecular data) cover everything in the area from patterning mechanisms to postnatal growth to regeneration. The last section on transformation has seven chapters that review the evolution of the amphibian and mammalian appendicular skeletons, sesamoids and ossicles, limb diversity, and adaptations for flying, digging and swimming. Let me not beat about the bush: I think Fins into Limbs is the best and most enjoyable multi-author book that I have come across in years. It will be a standard in the field for some time and anyone with the slightest interest in evo-devo, as well as anyone with even a passing interest in fins and/or limbs, should read it. Why am I so enthusiastic? There are several reasons and the first is the general high scientific quality of the chapters, several of which contain important reference material. The second is the way that the chapters cohere to give such a rich picture of a fascinating area, building on their historical roots where appropriate while being, so far as I can see, pretty well up to date. The third is the way that knowledge in so many areas of science is brought together to illuminate one or another aspect of the story – it is a very modern book. For all this, much credit goes of course to the editor, but to use the quote from William Harvey that Joseph Needham cites in the dedication of his wonderful book A History of Embryology, ‘all did well’. Actually there is a different sort of reason for being so uncritical: if something is enjoyable to read, it disarms the critical instincts of the reader, and I felt disarmed! Many of the chapters are of general interest (evolution, development), although this may just mean that I had the appropriate background to read them without the need to run to my reference books and wikis. Some seemed to me to be more specialized (almost anything to do with the anatomical details of adaptation was new to me) but I enjoyed finding out about some wonderful obscurities: there are, for example, more than 20 sesamoids and inconstant ossicles in the human foot, the first time-lapse study of aquatic motion was first carried out by Marey in 1890 on a tethered skate (the pictures were good!), and there are four types and three grades of joints – a challenge to those who investigate molecular pathways and systems. Given that so much is good in this book, it may seem ungenerous for a reviewer to think about the next edition and what it will contain, but, with the intention of encouraging it, I will. It is hard to think that there is much more to be said on the anatomical side but I did come away with the feeling that our knowledge of the molecular underpinnings of limb development is still rudimentary. On the basis of expression and transgenic studies, we know the roles of many genes involved in limb development and understand the basics of the networks in which they participate, but there is a large gap between our knowledge of the regulatory pathways and the anatomical structures that they generate. Similarly, we have little insight into how mutation leads to the quantitative changes in pathway kinetics that, in turn, lead to the wide range of limb forms among vertebrates. It is not unreasonable to expect, in the near future, a great deal of research into the dynamics of the molecular events downstream of transcriptional activation and in pathway kinetics. It is only in this area of computational biology that Fins into Limbs is thin. Network dynamics is one aspect where we can expect progress; modelling of mutation rates to changes in phenotype will be another and the linking of anatomical change to functional change will be a third. The considerable progress currently being made in the quantitative modelling of musculo-skeletal anatomy to predict running and jumping activity is allowing us to link changes in limb anatomy to changes in behaviour, and this in turn will increase our knowledge of how extinct animals lived and evolved. We can look forward to real progress being made in this area of biomechanics in the next few years, and incorporated into the next edition of Fins into Limbs– for now, it is enough to enjoy a very good and important book. more...
- Published
- 2008
- Full Text
- View/download PDF
36. Your inner fish
- Author
-
Jennifer A. Clack
- Subjects
Ichthyostega ,Tiktaalik ,Magic (illusion) ,biology ,Zoology ,Vertebrate ,Context (language use) ,General Medicine ,Human body ,biology.organism_classification ,Vertebrate Biology ,Genealogy ,biology.animal ,Acanthostega - Abstract
I once heard of a medical doctor who “didn’t believe in evolution” because he “could not see the connection between a human and a giraffe.” In Your inner fish, University of Chicago paleontologist Neil Shubin combines information from the worlds of paleontology, embryology, and developmental genetics to explain the evolutionary connection not only between humans and giraffes (that is to say, all other mammals) but also between ourselves and all vertebrates and indeed nonvertebrates too. Written largely in the first person, this lively and convincing account begins with an exposition of the logic underlying the fields of anatomy and stratigraphy (geological study of the stratification of sediment and rock) mixed with Shubin’s experiences of the terrors and triumphs of paleontological field work. I empathize with those descriptions, which illustrate the serendipitous nature of finding fossils and also the predictability that is possible when researchers have done their homework. Shubin describes the magic of anatomical dissection and the fundamental homologies among limbs of different vertebrates. Shubin and colleagues have contributed much to our understanding of the origin of vertebrate limbs with digits. In 2006, Shubin’s group reported their discovery of a fossilized Tiktaalik skeleton in northern Canada. This fish, with fins possessing basic wrist-like joints that could support the front of the body out of water, is believed to be a transitional animal whose existence partly bridges the gaps in our understanding of the emergence of tetrapods (four-legged animals) from their fish ancestors. Subsequent chapters focus on the history of discoveries of the embryonic origins and genetic control mechanisms at work in different regions of the body. This historical background brings home to the reader that science is performed by people in the context of their times. Shubin’s description of patterns common in the development of appendages, teeth, the vertebrate head, body plans, and sensory systems are extolled with quirky and little-known facts that add interest and intrigue. More deeply, he reveals the connections between humans and multicellular organisms at the cellular and molecular levels and the relationship of those connections to features prefigured in unicellular organisms. In the last chapter, which expounds the logic of phylogenetic analysis, the author’s explanation of sets within sets and how cladistic methodology (classification of organisms by common ancestry) works to produce a phylogeny is unclear and may be confusing for nonspecialist readers. Some minor mistakes and omissions detract from the overall appeal of the book. More substantially, the role played by Acanthostega — an extinct tetrapod and among the first vertebrate animals to have recognizable limbs — is played down, whereas it was a key to unlocking this field. While Shubin mentions earlier that this genus displayed a primitive, flipper-like limb, he fails to mention the astonishing fact (at the time of its discovery) that it possessed eight digits per limb and that this, among other factors, initiated a revolution in the way the origin of limbs was viewed. Additionally, and also to relegate the significance of Acanthostega, Shubin uses an old reconstruction of Ichthyostega (another early tetrapod genus contemporary with Acanthostega) to illustrate a Devonian tetrapod, when this is known to be substantially incorrect. There are good reconstructions of Acanthostega that would have provided a better model. This is also the case in a later chapter on ears, in which Ichthyostega is again used to illustrate an early tetrapod, when its ear is known to be highly unrepresentative of any other early tetrapod ear. Acanthostega is well known in this regard and should have been used. I was also surprised to find no mention of Michael Coates, a fellow professor at the University of Chicago who did much of the key work on Acanthostega and is now working in Shubin’s lab, nor of Shubin’s postdoctoral mentor, the late Pere Alberch, with whom Shubin did some key embryological work. Most surprising of all is the lack of any mention of the importance of neural crest cell populations in the development of vertebrates, in particular the evolution of the head, jaws, sense organs, and dermal skeleton, the latter two apparently intimately connected in their origins from neural crest ectodermal tissues. The reason may be that it is one of those issues that is so much at the heart of things that it gets taken for granted by those in the field. Despite some of my disagreements with statements made in this book, I recommend it for anyone who wants a user-friendly guide to the concepts underlying the evolution of animals, including humans, and especially to those readers who are unclear about the basis for ideas about organic evolution and who would like to know more about what connects us to the rest of the animal kingdom and indeed the rest of the organic world. It’s an exciting, sometimes breathless read in an accessible style, though the more staid might find the tone grating. I will, despite some reservations, put it on the reading list for students studying vertebrate biology. more...
- Published
- 2008
- Full Text
- View/download PDF
37. We Are All Fish.
- Author
-
Lemonick, Michael D.
- Published
- 2014
38. The Fish–Tetrapod Transition: New Fossils and Interpretations
- Author
-
Jennifer A. Clack
- Subjects
Tiktaalik ,biology ,Ventastega ,biology.organism_classification ,Education ,body regions ,Tulerpeton ,Paleontology ,Pederpes ,stomatognathic system ,Evolutionary biology ,Panderichthys ,Acanthostega ,Tetrapod (structure) ,Casineria ,Ecology, Evolution, Behavior and Systematics - Abstract
Our information on the transition between fish with fins and tetrapods with limbs and digits has increased manyfold in the last 15–20 years and especially in the last 5 or 10 years, with some spectacular finds of new material. Some of these include new tetrapod-like fish and very primitive tetrapods that help to resolve questions of the sequence of acquisition of tetrapod characters, the approximate timing of the events, the likely geographic location, and the circumstances under which it happened. Forelimbs and skulls became modified in advance of hind limbs, adapted for supporting the head and front of the body out of the water, probably in connection with air breathing. The likely time of origin for limbed tetrapods is between 385 and 380 million years ago, probably in the northern continent of Laurussia. The origin of limbed tetrapods did not coincide with the acquisition of full terrestriality, an outcome that probably arose in the Early Carboniferous. This later part of the story is documented by few fossils, though two in particular give key information. Studies of modern vertebrates, especially the evolutionary developmental genetics of Hox genes, are beginning to provide clues to the origin of digits. more...
- Full Text
- View/download PDF
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.