Figure 1. Subset of the large pterosaur tree showing relationships among Darwinopterus and its predecessors among the Wukongopteridae and their predecessors.
Yesterday we looked at the phylogenetic ancestors (Fig. 1) of Darwinopterus. Today we’ll take a closer look at the five specimens assigned to this genus.
Lü et al. (2011) noted the alveoli have raised margins, the nasoantorbital fenestra were confluent [not true, if you look closely], inclined quadrate [plesiomorphic], elongate cervical vertebrae with low neural spine and reduced or absent cervical ribs [plesiomorphic], long tail of more than 20 caudals partially enclosed by filiform extensions of the pre- and post-zygopophyses [plesiomorphic] short metacarpus less than 60 percent length of humerus [plesiomorphic] fifth toe with two elongate phalanges [plesiomorphic] and curved second pedal phalanx with the angle of 130 degrees [plesiomorphic].
In the current analysis
the following traits distinguish Darwinopterus from outgroup taxa: Some are equivocal, subject to a change of score by virtue of taphonomic changes and exposure. Only the first two dorsal ribs are robust, not the first three. The humerus shape is straighter. The deltopectoral crest is wider than deep. Manual 1.1 is shorter relative to m2.1. Manual digit 3 is not longer than mt4. The prepubis is putter-shaped. So, really not much. Only 5 steps are added when the outgroup taxa are moved inside the clade.
The most basal taxon
is the female, ZMNH M8802 (Fig. 2) which is crestless, like its ancestors. The mandible tip is bent down.
Figure 2. Darwinoperus ZMNH8802 specimen, the female and most basal member of this genus.
On a side note:
The original ischium (Fig. 2a) was misidentified. It is hard to see on top of the right femur (on the left below as seen in ventral view). What was originally identified as a deep left ischium by Lü et al. is instead a second prepubis, identical to the correctly identified prepubis on the opposite side (Fig. 2a, b)
Figure 2a. Original identification by Lü et al. 2011a) of puboischium in Darwinopterus.
Figure 2b. Darwinopterus female pelvis (ZMNH 8802) with pelvic bones correctly identified. the ischium is best seen on the left in indigo. The prepubes are red. The egg has been flattened and deflated, like a balloon. The paired ischia are still deep enough to pass the egg in vivo.
The other four specimens have crests. The other four specimens have a shorter prepubis relative to the pelvis. Again, not much separates them.
The next clade
has two similar members, D. linglongtaensis (Fig. 3) and the YH2000 specimen (Fig. 4). Both are relatively gracile. The orbit is more upright. The mandible is gracile and slightly bent up distally. Some dentary teeth are taller than the mandible. The sacrum is mostly fused. The torso is longer relative to the humerus, separating the elbow from the ilium. The humerus is subequal to the femur. The ulna is longer relative to the humerus. Manual 2.1 and m3.1 are subequal. Manual 3.3 ≥ m3.1 + m3.2. When folded manual 4.1 extends only to the distal ulna, not the half point. Metatarsals 1 and 2 are the longest. Pedal 4.4 is shorter than p4.1.
Figure 3. Darwinopterus YH2000 specimen. It has a shorter ilium and a gracile build.
Minor differences, getting into the range of individual variation, separate the YH2000 and IVPP V 16049 specimens. The latter is more robust with a longer ilium and a shorter p5.1.
Figure 4. Darwinopterus linglongtaensis, IVPP V 16049. This is a robust specimen.
The third clade
has larger members, the Darwinopterus modulars holotype (ZMNH 8782, Fig. 5) and D. robustodens (41HIII-0309A, Fig. 6). The postorbital bar is lower and more robust. The coracoid is less than half the length of the humerus. The humerus is longer relative to the torso. The pubis depth is not shorter than the ischium.
Figure 5. Darwinopterus modularis (holotype) ZMNH 8782. A taller specimen with a longer neck and larger skull.
Again, minor differences separate these two, including the length of the neck, distribution of the teeth, a more robust tail in the holotype, and the pelvis shape.
Figure 6. Darwinopterus robustodens at the Henan Geological Museum (41HIII-0309A). The teeth tips are described (Lü et al. 2011) as sharper and are swollen between the crown and root. There are nine tooth pairs in the upper and eleven in the lower jaws, which are smaller than in D. modulars. Tomorrow we’ll take a closer look at the naris.
If we concentrate only the feet
We find a gradual evolution and a resulting variety in the pes of the included taxa (Fig. 7). Note the variation in p5.1 vs. mt4, the longest toe from the heel, the variety in metatarsal lengths and the relative lengths of metatarsus to digits.
Figure 7. Darwinopterus feet. If the gracile forms were female, would they have phylogenetically different feet? Or is it more parsimonious to consider the morphologically different forms a clade?
The wukongopterids were an interesting clade, evolving some pterodactyloid-grade traits, but not others. The multiple origin of the pterodactyloid-grade is a subject we handled earlier here. If you want to see all the wukongopterids together to scale, click here.
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