Hauffiopteryx (BRLSI M1399): a CT-scanned Jurassic ichthyosaur skull

Figure 1. BRLSI M1399 is a new ichthyosaur that has been subjected to CT scanning and colorizing. It had huge eyeballs evidently not spherical in shape (there was no room in the skull). The original paper did not put the palate together. That is remedied here. Click to enlarge.

Figure 1. Hauffiopteryx, BRLSI M1399, is a new ichthyosaur that has been subjected to CT scanning and colorizing. It had huge eyeballs evidently not spherical in shape (there was no room in the skull). The original paper did not put the palate together or separate the posterior mandibles. Those are remedied here. At lower left are hypothetical eyeballs. A short F-stop is ideal for light gathering. Click to enlarge.

A new ichthyosaur, Hauffiopteryx, has been CT scanned.
You can see a rotating image of that Marek et al. (2015) scan here.

From the abstract: “New information on the braincase, palate and occiput are provided from three-dimensional scans of an exceptionally preserved ichthyosaur (‘Hauffiopteryx’ typicus) skull from the Toarcian (183–174 Ma, Lower Jurassic) of Strawberry Bank, England. This ichthyosaur has unusual, hollow, tubular hyoid bars. The occipital and braincase region is fully reconstructed, creating the first digital cranial endocast of an ichthyosaur. Enlarged optic lobes and an enlarged cerebellum suggest neuroanatomical adaptations that allowed it to be a highly mobile, visual predator. The olfactory region also appears to be enlarged, suggesting that olfaction was more important for ichthyosaurs than has been assumed. Phylogenetic analysis suggests this ichthyosaur is closely related to, but distinct from, Hauffiopteryx, and positioned within Thunnosauria, a more derived position than previously recovered. These results further our knowledge of ichthyosaur cranial anatomy in three dimensions and provide a platform in which to study the anatomical adaptations that allowed ichthyosaurs to dominate the marine realm during the Mesozoic.”

Figure 2. From Marek et al. (2015), a cladogram of the higher ichthyosaurs. Pink arrow points to Eurhinosaurus and Leptonectes where Hauffiopteryx nests when the more derived taxa are not included on the large reptile tree.

Figure 2. From Marek et al. (2015), a cladogram of the higher ichthyosaurs. Pink arrow points to Eurhinosaurus and Leptonectes where Hauffiopteryx nests when the more derived taxa are not included on the large reptile tree.

The authors report, “Most post-Triassic ichthyosaurs belong to the clade Thunnosauria, with Hauffiopteryx typicus recovered as the immediate out-group to this clade (Fischer et al. 2013). Therefore, this species is an important marker in the transition to the great majority of advanced ichthyosaurs.”

Figure 2. Subset of the large reptile tree focusing on ichthyosaurs. Note most of the more derived ichthyosaurs from Marek et al. 2015, are not listed here. So we're not comparing apples to apples here.

Figure 3. Subset of the large reptile tree focusing on ichthyosaurs. Note most of the more derived ichthyosaurs from Marek et al. 2015 (Fig. 2), are not listed here. So we’re not comparing apples to apples here.

The authors further report, “Most Lower Jurassic ichthyosaur specimens are preserved in flattened and compressed form. This is especially true of exceptionally preserved specimens from Holzmaden, southern Germany (Toarcian, Lower Jurassic), which may show soft tissues and body outlines, but the skeletons are flattened and conceal details, especially within the skull. Other ichthyosaurs may be three dimensional, but disarticulated.”

Figure 4. A more complete but crushed specimen of Hauffiopteryx along with tracings and reconstructions of key parts.

Figure 4. A more complete but crushed specimen of Hauffiopteryx along with tracings and reconstructions of key parts. Click to enlarge. Black hand bones are metacarpals. Note the differences in maxilla length. The 3D specimen appears to have a shorter maxilla no further forward than the naris, unlike the crushed specimen or Eurhinosaurus. Two species of Ophthalmosaurus show the same sort of variation.

Both specimens
of Hauffiopteryx have a box-like cranium housing huge eyes along with a small, sharp rostrum. Ophthalmosaurus, Leptonectes and Eurhinosaurus (Fig. 6) more or less share these traits and, give the taxon list of the large reptile tree, they all nest together. This may change with the addition of more taxa, as shown in figure 2.

The lacrimal question
In the CT scanned specimen (Fig.1) a slender bone extends along the ventral naris and extends slightly outside of it. In the crushed specimen (Fig. 2) the area ventral to the naris is crushed and broken. In sister taxa the lacrimal extends along the lower rim of the naris, but it was not colorized that way in figure 1. So I wonder about it.

The maxilla question
In the 3D specimen (Fig. 1) the yellow maxilla does not extend anteriorly beyond the large narrow naris. That’s not the case in the crushed specimen or Eurhinosaurus. Similarly in various species of Ophthalmosaurus the maxilla may be long or short. In the 3D specimen (Figs. 1, 5) there is a depression aligned with what would have been the pmx/mx suture. So I wonder if part of the maxilla in the 3D specimen was improperly colorized originally?The tiny teeth at the anterior of the possible maxilla suggest that may be the actual maxilla Marek et al. may have misidentified a splintered break as a suture.

Figure 5. The disputed maxilla in BRLSI M1399. Marek et al. colorized the maxilla only to the anterior naris, but that might be a break. Some sister taxa extend the maxilla beyond the the naris and the tiny teeth at the thin anterior of the new maxilla both indicate a possible error was made, mistaking a break for a suture. If valid, this is what DGS can do. Click to enlarge.

Figure 5. The disputed maxilla in BRLSI M1399. Marek et al. colorized the maxilla only to the anterior naris, but that might be a break. Some sister taxa extend the maxilla beyond the the naris and the tiny teeth at the thin anterior of the new maxilla both indicate a possible error was made, mistaking a break for a suture. If valid, this is what DGS can do. Click to enlarge.

If the traits identified here are valid, Hauffiopteryx and its new sister are closer to Eurhinosaurus (Fig. 6) than Marek et al. nested them. Though relatively smaller, the crescent-shaped tail of the crushed Hauffiopteryx (Fig. 4) is also similar to that of Eurhinosaurus (Fig. 6).

Figure 1. Eurhinosaurus, a derived ichthyosaur, in several views.

Figure 6. Eurhinosaurus, a derived ichthyosaur, in several views.

 

References
Marek RD, Moon BC, Wiliams M and Benton MJ 2015. The skull and endocranium of a Lower Jurassic ichthyosaur base on digital reconstructions. Palaeontology 2015: 1-20.

 

 

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