Adelosaurus: transitional between Claudiosaurus and Atopodentatus

Another roadkill fossil gets nested
Adelosaurus huxleyi (Hancock and Howse 1870, Evans 1988, Figs. 1, 2) was originally considered to be a small protorosaur distinct from Protorosaurus (Watson 1914). It is the poster child for roadkill fossils, spread out on a plate and lacking a skull. Evans (1988) reported, “In the absence of the skull and ankle, classification remains tentative. The skeleton seems immature.” Otherwise there’s not much out there on Adelosaurus.

Phylogenetic analysis brings new insight
as Adelosaurus now nests between Claudiosaurus germaini (Carroll 1981, Late Permian) and the odd new kid on the block (not known to anyone before last year), Atopodentataus unicus (Cheng et al. 2014, early Middle Triassic).

Figure 1. Adelosaurus, a genuine roadkill fossil from the Late Permian together with a reconstruction of same. Note the dorsal expansion of the clavicle, and the robust scapulocoracoid.

Figure 1. Adelosaurus, a genuine roadkill fossil from the Late Permian together with a reconstruction of same. Note the dorsal expansion of the clavicle, and the robust scapulocoracoid.

The first step in understanding any roadkill, even if the only data is a crude drawing, is to rearrange the parts into its in vivo position, realizing that mistakes can be corrected later, following Steve Jobs guidelines.

Figure 2. Adelosaurus (middle) nests between Claudiosaurus (top) and Atopodentatus (bottom), all at the base of the Enaliosauria. Click to enlarge.

Figure 2. Adelosaurus (middle) nests between Claudiosaurus (top) and Atopodentatus (bottom), all at the base of the Enaliosauria. Click to enlarge.

Adelosaurus has a pectoral girdle, manus and carpus nearly identical to those of Claudiosaurus (Fig. 2). Digit 4 of the manus lacks two phalanges, unlike Claudiosaurus, but that’s an odd trait found  in Atopodentatus. The clavicle of Adelosaurus is interesting. Evidently it doesn’t have a broad medial portion. No sister taxa do either. That’s the dorsal portion, nearly identical to those odd clavicles in an Atopodentatus sister, Largocephalosaurus. Atopodentatus has standard straight clavicles, or so it appears. Adelosaurus is also the most basal taxon with a curved humerus, an enaliosaur trait.

Ultimately Adelosaurus is the ‘small plain brown sparrow’ from which all the odd and wonderful variations within the Enaliosauria appear. So it needs to appear in all future phylogenetic studies that employ member clades.

References
Cheng L, Chen XH,Shang QH and Wu XC 2014. A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Natur
Carroll RL 1981. Plesiosaur ancestors from the Upper Permian of Madagascar. Philosophical Transactions of the Royal Society London B 293: 315-383.
Currie PJ 1981. Hovasaurus bolei, an aquatic eosuchian from the Upper Permian of Madagascar. Palaeontologica Africana, 24: 99-163.
Evans 1988. The Upper Permian reptile Adelosaurus from Durham. Palaeontology 31(4): 957-964. online pdf
Hancock A and Howse R 1870. On Protorosaurus speneri von Meyer, and a new species, Protorosaurus huxleyi, from the Marl Slate of Middridge, Durham. Quarterly Journal of the geological Society of London 26, 565-572.
Watson DMS 1914. Broomia perplexa gen. et. sp. nov., a fossil reptile from South Africa. Proceedings of the Zoological Society, London 1914:995-1010

 

wiki/Claudiosaurus

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