A near‐tetrapod from the Baltic Middle Devonian

Ahlberg, Pererik; Lukševičs, Ervīns; Mark-Kurik, Elga

doi:10.1111/j.0031-0239.2000.00138.x

Cited by 41 publications

(43 citation statements)

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“…The recent redating of Metaxygnathus as late Frasnian 36 , in conjunction with the phylogenetic topologies recovered by our analysis, implies not only that Ventastega represents a lineage of Frasnian origin but that a substantial part of the Devonian tetrapod radiation occurred during the Frasnian. This is consistent with the occurrence of Livoniana, a fragmentary taxon apparently more derived than Tiktaalik, in the latest Givetian of the Baltic region 37 . It seems that the Famennian tetrapod record has only a poor stratophylogenetic fit, a contention that is further supported by the co-occurrence of the very primitive humerus ANSP 21350 (ref.…”

Section: The Postcranial Skeletonsupporting

confidence: 88%

Ventastega curonica and the origin of tetrapod morphology

Ahlberg

Clack

Lukševičs

et al. 2008

Nature

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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.The fossil record of Devonian tetrapods, the earliest and most primitive limb-bearing members of the tetrapod stem group, was for many decades restricted to the iconic 'four-legged fish' Ichthyostega from the Famennian (latest Devonian) of Greenland 1-5 and the fragmentary genus Acanthostega from the same strata 2 . During the last 20 years, intense collecting and research has produced complete skeletal material of Acanthostega 6-8 and a series of new taxa, greatly expanding the temporal and geographical range of these animals. Devonian tetrapods are now known from as early as the late Frasnian, the earlier part of the Late Devonian period, and have been recorded from Gondwana and north China as well as Laurussia 9-18 . However, most of these new forms remain very poorly known, typically represented by no more than lower jaw rami or isolated postcranial bones; Acanthostega and Ichthyostega are still the only Devonian tetrapods known from near-complete skeletons. We know less about the fishtetrapod transition than the taxic diversity suggests.Among the more fragmentary forms are five (Metaxygnathus, Densignathus, Elginerpeton, Obruchevichthys and Ventastega) that combine a characteristically tetrapod lower-jaw morphology with the retention of coronoid fangs and other 'fish' characters absent in Acanthostega, Ichthyostega and more crownward limbed members of the tetrapod stem group 19,20 . These genera seem to fall into the morphological gap between Acanthostega and Ichthyostega and the (paraphyletic) elpistostegids, but all except Ventastega are very incomplete. Ventastega was originally described in 1994 from the Pavāri locality in the late Famennian Ketleri Formation of Kurzeme, western Latvia 21 (Supplementary Information 1). Further excavations at this site up to 2001 have yielded an extensive body of material, including previously unknown or incompletely known elements such as a near-complete skull roof plus braincase and associated cheek (Fig. 1), scapulocoracoid, anocleithrum, interclavicle and ilium (Fig. 2). All come from a single horizon, and the occurrence of multiple identical examples of several elements (jaws, cheek plates, maxillae, clavicles, cleithra, nasals) indicates that only ...

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Section: The Postcranial Skeletonsupporting

confidence: 88%

Ventastega curonica and the origin of tetrapod morphology

Ahlberg

Clack

Lukševičs

et al. 2008

Nature

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“…Evidently, there was an extended period of coexistence between the two groups. From the mid-Devonian, fossils of the more primitive tetrapodomorph Eusthenopteron have been found in coastal marine sediments [2,13] (Eastern Canada), as have Panderichthys and Livoniana fossils (Latvia) [14]; Tiktaalik remains are found in non-marine fluvial deposits (Ellesmere Island, Canada) from the same period [15]. The former environment would very likely have been subject to tidal influences; the latter is less certain but by no means impossible.…”

Section: (B) a Brief Overview Of Devonian Tetrapodomorph Habitatsmentioning

confidence: 99%

Dynamical, biological and anthropic consequences of equal lunar and solar angular radii

Balbus

2014

Proc. R. Soc. A.

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The nearly equal lunar and solar angular sizes as subtended at the Earth is generally regarded as a coincidence. This is, however, an incidental consequence of the tidal forces from these bodies being comparable. Comparable magnitudes implies strong temporal modulation, as the forcing frequencies are nearly but not precisely equal. We suggest that on the basis of palaeogeographic reconstructions, in the Devonian period, when the first tetrapods appeared on land, a large tidal range would accompany these modulated tides. This would have been conducive to the formation of a network of isolated tidal pools, lending support to A. S. Romer's classic idea that the evaporation of shallow pools was an evolutionary impetus for the development of chiridian limbs in aquatic tetrapodomorphs. Romer saw this as the reason for the existence of limbs, but strong selection pressure for terrestrial navigation would have been present even if the limbs were aquatic in origin. Since even a modest difference in the Moon's angular size relative to the Sun's would lead to a qualitatively different tidal modulation, the fact that we live on a planet with a Sun and Moon of close apparent size is not entirely coincidental: it may have an anthropic basis.

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“…Dentary tusks appear to have evolved independently in the rhizodontids, the megalichthyids, and within`higher' tristi-chopterids (Platycephalichthys, Cabonnichthys, Mandageria, Eusthenodon and Notorhizodon; Johanson & Ahlberg 2001). In the [Panderichthys þ tetrapod] clade, the tusks are accompanied by marginal dentary dentition at the symphysis (Ahlberg & Clack 1998;Ahlberg et al 2000). In rhizodontids, the megalichthyids Cladarosymblema and Ectosteorhachis (Fox et al 1995), and the derived tristichopterids , the presence of a tusk more-orless excludes the marginal dentary dentition from reaching the symphysis.…”

Section: Tetrapod Stem-groupmentioning

confidence: 99%

Mandibles of rhizodontids: anatomy, function and evolution within the tetrapod stem-group

Jeffery¹

2002

Transactions of the Royal Society of Edinburgh: Earth Sciences

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The Rhizodontida (Pisces: Sarcopterygii) is a clade of predatory fishes from the Upper Devonian (Aztecia; ?Givetian of Antarctica) through to the Upper Carboniferous (Strepsodus; Moscovian of northern Europe and North America). They form the most basal plesion within the tetrapod stem-lineage. The mandibles were dominated by large symphysial tusks on the dentary. Not much else is known of the mandibles in primitive rhizodontids. However, later forms show several derived characters: the mandible is very deep dorsoventrally and narrow linguolabially; the coronoid fangs bear only a single fang and no other dentition; the Meckelian element was unossified, leaving the adductor fossa unfloored by bone; the prearticular produced a large dorsal process lingual to the adductor fossa, presumably for muscle attachment. These and other characters are discussed in the context of the evolution of the tetrapod stem-group.The mandible appears to have been split into two functional units, one comprising the firmly sutured prearticular, coronoids and dentary, the other comprising the firmly sutured infradentaries. The connection between the two units was weak, suggesting a longitudinal intramandibular hinge. The possibility that this acted as a ‘torsion grip’ during feeding is discussed.

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A near‐tetrapod from the Baltic Middle Devonian

Cited by 41 publications

References 8 publications

Ventastega curonica and the origin of tetrapod morphology

Ventastega curonica and the origin of tetrapod morphology

Dynamical, biological and anthropic consequences of equal lunar and solar angular radii

Mandibles of rhizodontids: anatomy, function and evolution within the tetrapod stem-group

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