Field of Science

End of 2009 Literature

Two last minute papers for 2009 from Palaeodiversity. This is an open access journal so these papers and others can be downloaded for free from here.

Maisch, M.V., Vega, C.S., and R.R. Schoch. 2009. No dicynodont in the Keuper – a reconsideration of the occurrence of aff. Dinodontosaurus in the Middle Triassic of Southern Germany. Palaeodiversity 2:271-278.

Abstract - An isolated humerus, attributed to a dicynodont therapsid and identified as aff. Dinodontosaurus, from the Lower Keuper (Middle Ladinian, Middle Triassic) of southwestern Germany is redescribed. An additional but smaller humerus that is similar in morphology might pertain to the same taxon. Several morphological features preclude an identification of the material as either aff. Dinodontosaurus, a dicynodont, or even a synapsid. The deltopectoral crest shows a number of tubercles, probably for muscle attachment. The supinator process is strongly developed and clearly offset from the rest of the bone. The distal articulation facet is very narrow transversely. There is no foramen entepicondyloideum. The ectepicondyle has a deeply concave distal surface, at least in the large and presumably adult specimen. An alternative identification for the two humeri proves difficult, as they do not agree with any other known tetrapod from the Lower Keuper. They bear close resemblance, however, to the humerus of the Permian temnospondyl Eryops, suggesting the presence of an as yet unknown temnospondyl.

This paper also emphasizes the importance of correctly determining taxonomic identity when using incomplete or unique specimens for biostratigraphic correlations.

Spielmann, J.A., Lucas, S.G., Heckert, A.B., Rinehart, L.F., and H. R. Richards III. 2009. Redescription of Spinosuchus caseanus (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America. Palaeodiversity 2: 283–313.

Abstract - Our reexamination of the holotype of Spinosuchus caseanus from the Upper Triassic of West Texas, in addition to the recognition of additional records of this taxon, demonstrates that it is closely related to the trilophosaurid archosauromorph Trilophosaurus and thus is included in a revised Trilophosauridae. Previous arguments suggesting that features that unite Spinosuchus and Trilophosaurus are not limited to these two taxa or are symplesiomorphies shared with a wide variety of contemporaneous Triassic archosauromorphs are not substantiated based on a detailed comparative analysis of the two taxa. The distinctive neural spine morphology of Spinosuchus allows for recognition of this taxon based on isolated vertebrae and thus increases its biostratigraphic value. Spinosuchus is restricted to strata of Adamanian age and is therefore an index taxon of the Adamanian land-vertebrate faunachron.

One interesting aspect of the new referred specimens of Spinosuchus is that they co-occur in a quarry in which the only other recovered material (cranial and postcranial) has been referred to Trilophosaurus jacobsi (Spielmann et al., 2007). Dorsal and sacral vertebrae from the quarry represent Spinosuchus, whereas all of the other material (that does not include dorsal and sacral vertebrae) where referred to T. jacobsi (i.e. there is no duplication of elements). Thus, although discounted by Spielmann et al. (2009) is seems possible that all of the material may indeed belong to a single taxon and that T. jacobsi would be a junior synonym of S. caseanus. Spielmann et al. (2009) claim that dorsal vertebrae from the quarry exist that are more similar to Trilophosaurus buettneri and not Spinosuchus, thus the taxa are not the same, but this will have to await future description of this material.

It also seems strange (and unstable) to diagnose Trilophosauridae based solely on shared vertebral laminae and not including characters of the unique skull and tooth morphology that has historically diagnosed the taxon, but again this determination will rely on future material being recovered.

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