Florian Witzmann

Larval ontogeny of Micromelerpeton credneri (Temnospondyli, Dissorophoidea)

Abstract A growth series of 97 specimens of the dissorophoid temnospondyl Micromelerpeton credneri from the Permo-Carboniferous of Central Europe is taken as a basis for ontogenetic investigations. Whereas the dermal skull roof is already ossified and sutured in the smallest specimen with a skull length of 6 mm, the ossification sequence of the postcranium can be reconstructed. Compared to branchiosaurids and Recent urodeles, the ossification of the postcranial skeleton is delayed. For the first time, external gills are described in Micromelerpeton credneri. Their three pairs of branches shorten proportionally during ontogeny. A Cartesian transformation and biometric analyses show allometric changes in the dermal skull roof. Whereas the preorbital region elongates slightly (due to positive allometric growth of nasal length and negative allometric growth of orbits) and grows in width isometrically, the postorbital skull table shows isometry in length (due to positive allometry of frontal length and negative allometry of parietal length) and distinct negative allometry in width (due to negative allometry of parietal and supratemporal width). The interorbital width relatively decreases. The cheek region shows positive allometry both in length and in width, shifting the jaw articulation posteriorly. In this way proportionally more space and attachment area for the adductor musculature are provided and the gape enlarges proportionally. The positive allometric growth of the diameter of the sclerotic ring indicates increased importance of the optical sense. Transformation into the adult stage took place gradually and in a longer period of time during ontogeny than in extant amphibians.

First direct evidence of a vertebrate three-level trophic chain in the fossil record

We describe the first known occurrence of a Permian shark specimen preserving two temnospondyl amphibians in its digestive tract as well as the remains of an acanthodian fish, which was ingested by one of the temnospondyls. This exceptional find provides for the first time direct evidence of a vertebrate three-level food chain in the fossil record with the simultaneous preservation of three trophic levels. Our analysis shows that small-sized Lower Permian xenacanthid sharks of the genus Triodus preyed on larval piscivorous amphibians. The recorded trophic interaction can be explained by the adaptation of certain xenacanthids to fully freshwater environments and the fact that in these same environments, large temnospondyls occupied the niche of modern crocodiles. This unique faunal association has not been documented after the Permian and Triassic. Therefore, this Palaeozoic three-level food chain provides strong and independent support for changes in aquatic trophic chain structures through time.

DEVELOPMENTAL PATTERNS AND OSSIFICATION SEQUENCE IN THE PERMO-CARBONIFEROUS TEMNOSPONDYL ARCHEGOSAURUS DECHENI (SAAR-NAHE BASIN, GERMANY)

Abstract A size series of 143 specimens of the Permo-Carboniferous temnospondyl Archegosaurus decheni from the Saar-Nahe Basin (south-west Germany), ranging in size from 18 to 280 mm skull length, can be interpreted as an extensive growth series. This study focuses on the reconstruction of ossification sequences and developmental patterns of skull, visceral skeleton, and postcranium in A. decheni. With respect to the dermal skull, the ossification of the postcranium is delayed. The basibranchial starts to ossify after formation of the dermal pectoral girdle, sclerotic ring, stapes, scales, and scapulocoracoid. Initial ossification of the ischium takes place distinctly later than that of the ilium, and the pubis remains entirely cartilaginous. Vertebral centra ossify late, after formation of the ischium. Branchial dentition is resorbed at a skull length of 150 mm, indicating a long larval phase. Carpals and tarsals start to ossify only in the largest individuals. Archegosaurus decheni exhibits no period of obvious metamorphosis, as indicated by the dissociation of developmental events during ontogeny. The delayed formation of scales, scapulocoracoid, and basibranchial, in comparison with the Permo-Carboniferous temnospondyls Sclerocephalus and Onchiodon, may be correlated with the secondary aquatic adaptation of A. decheni throughout its life history. The chronology of ossification of the endocranial elements can be reconstructed. The exoccipital ossifies first, followed by the quadrate, basioccipital, basisphenoid, sphenethmoid, and otic capsule. Comparison with other anamniotic tetrapods shows that the early ossification of the exoccipital and quadrate is a stable pattern, and that there is a tendency to eliminate ossification of the basioccipital and basisphenoid.

Skeletal development of the temnospondyl Acanthostomatops vorax from the Lower Permian Döhlen Basin of Saxony

The development of the skeleton of the small temnospondyl Acanthostomatops vorax is described, based on 32 specimens from the Lower Rotliegend of Niederhaslich in Saxony. Both individually and ontogenetically, the skull table, length of gape, and dentition of the parasphenoid are broadly variable. The stapes has a short and straight shaft and a well-defined two-headed proximal region. Small specimens have three or four pairs of ossified ceratobranchials in the gill region, while the adult hyobranchium is composed of four pairs of hypobranchials and probably some additional elements. The postcranium is characterised by a stout and well-ossified humerus that is already large in small larvae, a minute rectangular interclavicle, a robust but short femur, a relatively short trunk with 21–22 presacrals and a moderate tail with 28 vertebrae. In adults, the trunk skeleton became proportionally shorter and the femur smaller with respect to skull length. Metamorphosis is best indicated by the disappearance of the larval gill skeleton, which was probably resorbed, while the structure of the limbs and axial skeleton as well as the absence of lateral line sulci suggest a terrestrial existence for adults.

A relict basal tetrapod from Germany: first evidence of a Triassic chroniosuchian outside Russia

Chroniosuchians are basal tetrapods nesting within the paraphyletic anthracosaurs and were so far only well known from the Permian and Triassic of Russia. In this study, we present evidence for their existence in the upper Middle Triassic of Germany, based on diagnostic osteoderms and vertebrae from the Kupferzell and Vellberg localities in southern Germany. The finds are most similar to Synesuchus, a Middle Triassic bystrowianid chroniosuchian from the Northern Ural Pechora region. They demonstrate that by Middle Triassic time, chroniosuchians were much more widespread than previously thought.

Amphibian development in the fossil record.

Ontogenetic series of extinct taxa are extremely rare and when preserved often incomplete and difficult to interpret. However, the fossil record of amphibians includes a number of well-preserved ontogenetic sequences for temnospondyl and lepospondyl taxa, which have provided valuable information about the development of these extinct groups. Here we summarize the current knowledge on fossil ontogenies of amphibians, their potential and limitations for relationship assessments, and discuss the insights they have provided for our understanding of the anatomy, life history, and ecology of extinct amphibians.

Deep-time evolution of regeneration and preaxial polarity in tetrapod limb development

Among extant tetrapods, salamanders are unique in showing a reversed preaxial polarity in patterning of the skeletal elements of the limbs, and in displaying the highest capacity for regeneration, including full limb and tail regeneration. These features are particularly striking as tetrapod limb development has otherwise been shown to be a highly conserved process. It remains elusive whether the capacity to regenerate limbs in salamanders is mechanistically and evolutionarily linked to the aberrant pattern of limb development; both are features classically regarded as unique to urodeles. New molecular data suggest that salamander-specific orphan genes play a central role in limb regeneration and may also be involved in the preaxial patterning during limb development. Here we show that preaxial polarity in limb development was present in various groups of temnospondyl amphibians of the Carboniferous and Permian periods, including the dissorophoids Apateon and Micromelerpeton, as well as the stereospondylomorph Sclerocephalus. Limb regeneration has also been reported in Micromelerpeton, demonstrating that both features were already present together in antecedents of modern salamanders 290 million years ago. Furthermore, data from lepospondyl ‘microsaurs’ on the amniote stem indicate that these taxa may have shown some capacity for limb regeneration and were capable of tail regeneration, including re-patterning of the caudal vertebral column that is otherwise only seen in salamander tail regeneration. The data from fossils suggest that salamander-like regeneration is an ancient feature of tetrapods that was subsequently lost at least once in the lineage leading to amniotes. Salamanders are the only modern tetrapods that retained regenerative capacities as well as preaxial polarity in limb development.

Hyobranchial and postcranial ontogeny of the temnospondylOnchiodon labyrinthicus (Geinitz, 1861) from Niederhäslich (Dohlen Basin, Autunian, Saxony)

KurzfassungEs werden das Hyobranchium, das Postcranialskelett sowie die Entwicklungsereignisse in der Ontogenese des TemnospondylenOnchiodon labyrinthicus aus dem Döhlen-Becken (Autun, Sachsen) beschrieben. Ab einer Schädellänge von etwa 20 mm ist das Scapulocoracoid nachzuweisen, verknöchert aber sehr langsam. Deutlich später als das stämmige Ilium und später als das Scapulocoracoid verknöchert das Ischium, das sich schnell ausdifferenziert. Der Stapes verknöchert bei 26 mm Schädellänge, und die Exoccipitalia wahrscheinlich bei 40 mm, gefolgt vom Quadratum. Die Wirbelzentren verknöchern erst in der juvenilen Phase bei etwa 50 mm Schädellänge. Der larvale Hyobranchialapparat, in welchem sowohl Basibranchiale als auch Ceratobranchialia verknöcherten, deutet auf starkes Saugschnappen hin. Nach der Larvalperiode wurden die knöchernen Ceratobranchialia resorbiert. Das schwach verknöcherte Postcranium deutet daraufhin, dass die Juvenilen semiterrestrisch gelebt haben.AbstractHyobranchium, postcranial skeleton, and developmental events during ontogeny of the temnospondylOnchiodon labyrinthicus from the Dohlen Basin (Autunian, Saxony) are described. At a skull length of approximately 20 mm, the scapulocoracoid appeared, but ossified very slowly. The ischium ossified distinctly later than the stout ilium and later than the scapulocoracoid. The stapes can be determined in specimens beyond 26 mm skull length, and the exoccipitals started to ossify probably at 40 mm, followed by the quadrate. Vertebral centra ossified in early juveniles at approximately 50 mm skull length. The larval hyobranchium with ossified basibranchial and ceratobranchials indicates strong suction feeding. The bony ceratobranchials were resorbed after the larval period. The poorly ossified postcranium suggests that juveniles lived semiterrestrially.

Vertebral Pathology in an Ornithopod Dinosaur: A Hemivertebra in Dysalotosaurus lettowvorbecki from the Jurassic of Tanzania

A vertebral fragment of the Late Jurassic ornithopod dinosaur Dysalotosaurus lettowvorbecki from Tanzania is described. It consists of a hemivertebra that is co‐ossified with a complete vertebral centrum. The hemivertebra causes a hyperkyphotic posture of the vertebral column with an angle of approximately 35° between the end plates of the vertebra, that is, a dorsal bending of the vertebral column. Associated with this is a 15° lateral bending, which suggests a scoliosis. Micro‐CT scans reveal thickening of the cortical bone in the hemivertebra and the complete vertebral centrum as compared to a “normal” vertebra. This can be interpreted as a reaction of the bone to the abnormal direction of forces arising from the defective configuration of the vertebral column. No signs of vertebral fracture are present. The arrangement of the Foramina venosa and the trapezoidal outline of the complete centrum that is co‐ossified with the hemivertebra indicate that the hemivertebra in Dysalotosaurus developed early in embryogenesis probably by “hemimetameric segmental shift”, that is, a defect of the fusion of the paired vertebral anlagen. This finding illustrates that hemivertebrae represent a fundamental defect of the vertebrate ontogenetic program. Anat Rec, 291:1149‐1155, 2008.

Metoposaurid and mastodonsaurid stereospondyls from the Triassic – Jurassic boundary of Portugal

Witzmann, F. & Gassner, T., March, 2008. Metoposaurid and mastodonsaurid stereospondyls from the Triassic – Jurassic boundary of Portugal. Alcheringa 32, 37–51. ISSN 0311-5518. Remains of stereospondyl amphibians from the Triassic – Jurassic boundary of the Algarve, southern Portugal, are described for the first time. They consist of several intercentra of different sizes, ribs and fragments of the scapular girdle and the skull. The opisthocoelous morphology of some of the disc-like intercentra and the presence of a lateral flange on the clavicle indicate that parts of the material can be referred unambiguously to metoposaurid stereospondyls, representing the first evidence of this group from the Iberian Peninsula. Several other disc-like intercentra that are amphicoelous and thinner than those of the metoposaurids can be referred to mastodonsaurid stereospondyls (either Mastodonsaurus or Cyclotosaurus). The fossil locality is situated in a palaeorift system that linked the known metoposaurid localities in eastern North America, Morocco, and Central Europe.