Fuyuansaurus – a Baby Tanystropheid or a Mother?

A tiny new tanystropheid was recently described by Fraser et al. (2013). Complete and articulated, but unfortunately too big for its slab, despite its tiny size, the holotype fossil of  Fuyuansaurus lacks a tail and limbs, though undoubtedly limbs were present in vivo (phylogenetic bracketing).

Figure 1. Fuyuansaurus in situ and close to full scale. Unfortunately this tiny tanystropheid is too large for its tinier slab and so lacks legs and a tail.

Figure 1. Fuyuansaurus in situ and close to full scale. Unfortunately this tiny tanystropheid is too large for its even tinier slab and so legs and a tail extend off the slab. If your screen resolution is 72pdi, the upper image is full scale. The light blue structure is a possible egg and the red structure is a possible pubis more like that of sister taxa. There is a mass of soft tissue preservation from the torso covering the posterior nasals, too. The orange structure in the egg may be a displaced hemal arch (chevron).

It always helps when a reconstruction is made,
in this case to literally unwind the specimen.

Figure 2. Click to enlarge. Reconstruction of Fuyuanasaurus. Fraser et al. identified a strange circular object as the pubis, but no sister taxa have a circular pubis. Here it is tentatively ID'd as an egg because a standard pubis is found  nearby.

Figure 2. Click to enlarge. Reconstruction of Fuyuanasaurus slightly smaller than full scale. Yes=, it’s that tiny. Fraser et al. identified a strange circular object as the pubis, but no sister taxa have a circular pubis. Here it is tentatively ID’d as an egg/embryo because a standard pubis is found nearby and another soft tissue mass is also preserved anteriorly. Oddly, cervical #8 is shorter than #7 or #9. Orange in the cheek area is not the coronoid, but a portion of the pterygoid. Purple on the upper jaw margin below the cheek is not the dentary but the surangular.

Phylogenetic analysis nests Fuyuansaurus between the small Tanystropheus with multi-cusped teeth and the large one with simple stabbers. So does that make this another Tanystropheus species? Or do we need to separate the two Tanys generically? Depends if you’re a lumper or splitter. Fraser et al. did not publish their analysis if one was made.

That strange circular “pubis”.
Fraser et al. identified a round structure with ridge-like process terminating in a hollow bone end as a pubis, but noted that it was unlike the pubis of Tanystropheus or Macrocnemus. No kidding… Autapomorphies like this often have a different reality, as we learned earlier. I wonder if the flat round object was an egg because I found a regular strut-like pubis nearby on the inner mandible and the narrow structure that penetrates the soft ellipse could have been a chevron or a lumbar rib. So the possible tiny juvenile could actually be a possible tiny mother. And that ridge along the rim of the egg could be an embryo vertebral series. Hard to tell with available materials, but an interesting thought nevertheless that could pan out with higher resolution.

References
Fraser NC, Rieppel O and Chun L 2013. A long-snouted protorosaur from the Middle Triassic of southern China, Journal of Vertebrate Paleontology, 33:(5):1120-1126.

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