The Family Tree of the Pterosauria 17 – The Ornithocheiridae part 1 of 3

We just looked at one branch of descendants from Scaphognathus (No. 110) and Gmu 10157 that ultimately produced Cycnorhamphus and Feilongus. Here we look at the other branch of Scaphognathus No. 110 descendants, the Ornithocheiridae in three parts. Part 1 (below) will look at basal taxa. Part 2 will look at Coloborhynchus, Istiodactylus and their kin. Part 3 will look at more derived taxa such as Anhanguera and Liaoningopterus.

The Ornithocheiridae.

Figure 1. The Ornithocheiridae. Click to enlarge and expand.

We’ll start with Yixianopterus
Yixianopterus jingangshanensis JZMP-V12 (Lü et al. 2006) ~20 cm skull length, Barremian/Aptian Early Cretaceous ~125 mya, was overall 8x larger than and distinct from it tiny phylogenetic predecessor, Gmu-10157. The skull of Yixianopterus was longer judging by the pre-antorbital fenestra portion and the mandible. The teeth were more widely spaced. The caudals were shorter. Fingers 1-3 were smaller, but the wing finger was much more robust. Manual 4.1 approached the elbow when folded and the wingtip was higher than the skull when quadrupedal. The pelvis and tibia were more robust.

JZMP embryo

Figure 2. Click to enlarge DGS tracings. The JZMP ornithocheirid embryo, in situ and reconstructed.

We Haven’t Met the Adult Yet, But We Know This Embryo
The JZMP pterosaur embryo JZMP-03-03-2 (Ji et al. 2004) was found inside an eggshell, so we know it’s age precisely: zero. Considering the size of its pelvic opening one can estimate the size of the adult at 8x larger, which is consistent with Pterodaustro and its embryo/hatchling. The hypothetical adult size is also consistent with sister taxa. The embryo was originally compared to Beipiaopterus. Distinct from Yixianopterus, the skull of JZMP-03-03-2 was deeper anteriorly with an upturned premaxilla in which all of the premaxillary teeth were oriented chiefly anteriorly. The dentary was downturned at the tip. The antorbital fenestra was larger.The cervicals were longer posteriorly and shorter anteriorly. The sacrals were as long as the dorsals. The sternal complex was a wide rectangle with a transverse leading edge and a short cristospine. The scapula and coracoid were robust and oriented more laterally. The humerus was relatively smaller. The metacarpus was subequal to the ulna. The wing finger was robust proximally, but less so distally. Both m4.2 and m4.3 were longer than m4.1. The anterior ilium was much longer than the posterior process. The femur was shorter and the tibia was relatively longer. The pes was similar in size to that of Yixianopterus.

Note the long rostrum and small eye, as in the embryo of Pterodaustro. All of the small pedal bones were ossified. These facts falsify the hypothesis of pterosaur allometric growth (Wellnhofer 1970, Bennett 1991, 1992, 1994, 2001) and support the isometric hypothesis in which embryos and juveniles were almost identical to adults in morphology.

From Lebanon, a Nameless Pterosaur
The Lebanon ornithocheirid MSNM V 3881 (Dalla Vecchia, Adruini & Kellner 2001) A small, robust wing from Lebanon has a radius less than half the diameter of the ulna and manual digit 2 is subequal to 3. At present there is little else to distinguish it from Haopterus, except that it had a longer metacarpus relative to the ulna. The humerus, although incomplete, was small, as in the JZMP embryo.

The First Classic Ornithocheirid
Boreopterus cuiae JZMP 04-07-3 (Lü and Ji 2005) Distinct from the JZMP embryo, the skull of Boreopterus had at least 27 teeth in each upper jaw. They were long, slender and closely spaced. The rostrum was relatively longer and lower with a larger portion anterior to the antorbital fenestra. The postorbital portion was reduced with a posteriorly leaning orbit, as in Istiodactylus. The suborbital skull descended and the quadrate leaned posteriorly. The cervicals were longer with higher neural spines. The sacrals were shorter by more than half. The caudals were more robust. The humerus was larger, extending nearly to the acetabulum. The ulna and radius were also larger relative to the metacarpus. Fingers I-III were smaller. When folded the wing tip was no taller than the skull. The distal wing phalanges were shorter. The pelvis was tiny. The hind limb was more gracile, inluding a tiny foot.

Haopterus

Figure 3. Click to enlarge. Haopterus, the smallest ornithocheirid

Haopterus
Haopterus gracilis IVPP V11726 (Wang and Lü 2001) was overall smaller than and distinct from Boreopterus, the skull of Haopterus was shorter and relatively taller. The cervicals, dorsal, sacrals and caudals were all shorter. The scapula and coracoid were shorter. The humerus was extremely roubst with a deltopectoral crest extending for ~33% of the length. As in the Lebanon ornithocheirid, the radius and ulna were relatively short. Manual 4.1 approached the elbow. The relatively longer wing would have extended far above the head when folded. The pelvis was gracile and smaller. The femur was shorter. The metatarsals were shorter. Ornithocheirids, like Haopterus, were evidently spending more time in the air and less on the ground, judging by their wing/leg proportions.

Zhenyuanopterus

Figure 4. Click to enlarge. Zhenyuanopterus

Zhenyuanopterus
Zhenyuanopterus longirostris (Lü et alk. 2010) GLGMV 0001 Early Cretaceous. Distinct from Boreopterus, the skull of Zhenyuanopterus was longer, especially in the pre-antorobital fenestra region. The teeth were more widely spaced and continued erupting closer to the orbit, which was smaller. A squarish crest surmounted the mid rostrum. The cranium was crest-like, probably for muscle attachments. The cervicals were more robust. The torso was smaller and shallower, as in Haopterus. The caudals were more robust. The sternal complex did not have lateral ‘wings’. The scapula and coracoid were fused. The coracoids were laterally oriented. The humerus was as long as the torso. The ulna and radius were more robust and relatively shorter. The hind limbs were longer, as in Haopterus. The feet were extremely tiny with robust metatarsals and slender digits.

 

Arthurdactylus dorsal view.

Figure 5. Click to enlarge. Arthurdactylus dorsal view.

Arthurdactylus from South America
Arthurdactylus conandoylei 
(Frey and Martill 1994) SMNK 1132 PAL Early Cretaceous. Distinct from Zhenyuanopterus, the torso of Arthurdactylus was deeper, as in Boreopterus. The sacrals were all unfused. The caudals were vestigial. The coracoids were much longer than the scapula, producing a very high shoulder joint. The ulna was massive. Manual 4.1 approached the elbow when folded. The short pubis was directly beneath the actebulum. The ischium was slender. The foot was slightly larger than in Zhenyuanopterus with more slender metatarsals and longer digits.

In summary
Taxa at the base of the Ornithocheiridae are those closest to cycnorhamphids in their morphology. Yixianopterus is at the base followed by the JZMP embryo. Due to isometric growth in pterosaurs we can enlarge it eight times to gauge what the adult was like. A trend toward a longer snout, more and longer teeth, larger wings and smaller feet is apparent.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1994. Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153
Dalla Vecchia FM, Arduin P and Kellner AWA 2001. The first pterosaur from the Cenomanian (Late Cretaceous) Lagerstätten of Lebanon. Cretaceous Research 22: 219-225.
Frey E and Martill DM 1994. A new Pterosaur from the Crato Formation (Lower Cretaceous, Aptian) of Brazil. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 194: 379–412.
Ji Q, Ji S-A, Cheng Y-N, You HL, Lü J-C, Liu Y-Q and Yuan CX 2004. Pterosaur egg with leathery shell. Nature 432:572.
Lü J 2010. A new boreopterid pterodactyloid pterosaur from the Early Cretaceous Yixian Formation of Liaoning Province, northeastern China. Acta Geologica Sinica 24: 241–246.
Lü J and Ji Q 2005. A new ornithocheirid from the Early Cretaceous of Liaoning Province, China. Acta Geologica Sinica 79 (2): 157–163.
Lü J, Ji S, Yuan C, Gao Y, Sun Z and Ji Q 2006. New pterodactyloid pterosaur from the Lower Cretaceous Yixian Formation of Western Liaoning. In J. Lü, Y. Kobayashi, D. Huang, Y.-N. Lee (eds.), Papers from the 2005 Heyuan International Dinosaur Symposium. Geological Publishing House, Beijing 195-203.
Wang X and Lü J 2001. Discovery of a pterodactylid pterosaur from the Yixian Formation of western Liaoning, China. Chinese Science Bulletin 46(13):1-6.

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