A Pterosaur Without Limbs and Where to Find Them

BML-37012 (No. 85 in the Wellnhofer 1975 catalog) was considered to be a juvenile Rhamphorhynchus preserved largely without limbs (one femur listed). This small specimen (skull length: 2.8 cm) was also presented in Wellnhofer’s (1991) Encyclopedia of Pterosaurs. It appears to be unprepared.

BML-37012 (n45 in the Wellnhofer 1975 catalog) is a small and primitive Rhamphorhynchus

Figure 1. BML-37012 (n85 in the Wellnhofer 1975 catalog) is a small and primitive Rhamphorhynchus, phylogenetically close to the BMM specimen. Above: the in situ specimen, apparently without limbs. Below: A DGS tracing indicating where to dig for the limbs. Blanketing layers of Solnhofen limestone indicate where one will find more bone slightly beneath the surface. Determining where fossils may be just below the surface  by looking for bumps in the matrix is an age-old technique used by fossil preparators. Image from Wellnhofer 1991. Enlargements and overlays available by request. 

Solnhofen Preservation
When a fossil specimen is discovered by splitting Solnhofen limestones, typically many bones remain invisible, hidden beneath a thin blanket of limestone at the separation layer. Preparators can usually create a precise outline of the specimen, even when the bones are rather deep, because preparators can see the general direction of the fossil (head on one end, tail on the other) and the exact location of other elements are often betrayed by a slight rise in the matrix. Like a blanket over a child in bed, the limestone tells you exactly where to dig.

DGS Preview
The Digital Graphic Segregation (DGS) method permits an increase in contrast in the image of the matrix surrounding the fossil. This better indicates where the bumps and valleys are in the limestone blanketing the fossil. Doing so I was able to trace a complete and largely articulated forelimb disarticulated from the rest of the fossil and a complete hindlimb tucked close to the body. Another tibia and pedal digit 4 is twisted and tucked in behind the lumbar region of the fossil, visible without DGS. This particular tibia may be the previously identified femur. Pedal digit 4 was closely aligned with the deeper ilium and so was overlooked. While others dismiss and decry this method using Adobe Photoshop, it is exactly what preparators have been doing by eye for generations.

 

Figure 2. Reconstruction of Rhamphorhynchus specimen BML-37012 (n85 of Wellnhofer 1975).

Figure 2. Reconstruction of Rhamphorhynchus specimen BML-37012 (n85 of Wellnhofer 1975).

Reconstruction
A digital reconstruction of the fossil looks much like other similar Rhamphorhynchus specimens, like the BMM specimen and B St 1959 I 400 (n10 in the Wellnhofer 1975 catalog). Making such comparisons is one test that confirms the identification of the bones viewed through the blanketing limestone. It would also be a good test of the method if someone with the proper tools dug into the limestone to find the bones beneath the surface.

Description and Distinctions
The BML specimen has larger fingers 1-3 and very large eyes. So was it nocturnal? Did it compete with similarly built and sized anurognathids? Interesting questions that haven’t been brought up before under the false paradigm that such short-snouted rhamphs were simply juveniles of larger specimens. Smaller rhamphs have been dismissed as juveniles, but phylogenetic analysis does not match them to older adults. Rather it finds the small ones were related to each other. I know of no Rhamphorhynchus specimens that are identical to adults only smaller, as in Pterodaustro and PteranodonIf you know of any, please send the data.

Juvenile or Not?
As we learned earlier, hatchling pterosaurs, like juvenile tritosaur lizards in general, are virtual matches to adults. Phylogenetically smaller pterosaurs (those with larger ancestors) generally had a smaller rostrum and larger eyes because they developed in a shorter time in smaller eggs, thus retaining these more embryonic traits as hatchlings and adults. Later, as their descendants increased in utero development time, egg size increased and jaw length generally increased relative to overall size. This specimen, No. 85, matches sister taxa in morphology and is part of an uninterrupted size continuum and so it may be considered an adult. Hatchlings would have been one-eighth the size according to pelvic opening size.

References
Wellnhofer P 1975a. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. – Paleontographica A 148: 1-33.
1975b. Teil II. Systematische Beschreibung. – Paleontographica A 148: 132-186.
1975c. Teil III. Paläokolgie und Stammesgeschichte. – Palaeontographica 149: 1-30.
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. London, Salamander Books, Limited: 1-192.

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