A new pterosaur Pterosauria from Middle Jurassic Tiaojishan Formation of western Liaoning China

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1 Global Geology 13 3 / doi /j. issn / Article ID / A new pterosaur Pterosauria from Middle Jurassic Tiaojishan Formation of western Liaoning China L Junchang 1 and FUCHA Xiaohui 2 1. Institute of Geology Chinese Academy of Geological Sciences Beijing China 2. Jehol Paleontological Museum Chengde Hebei China Abstract A new pterosaur Archaeoistiodactylus linglongtaensis gen. et sp. nov. is erected based on an incomplete skeleton with a partial skull and lower jaw. The new taxon is characterized by circular tooth sockets of anterior mandibular teeth the anterior teeth of the upper jaw bearing posteriorly directed crowns a relatively short metacarpus and wing phalanges 2 and 3 and the tibia subequal in length. It possesses some plesiomorphic characters such as short metacarpals and circular tooth sockets. The pointed jaw tip present in the new taxon indicates that the expanded jaw tips of later istiodactylids are a derived character state and the new taxon represents the first istiodactylus-like pterosaur found from the pre-late Jurassic deposits which provides a key role in our understanding the origin and evolution of the known istiodactylid pterosaurs. Archaeoistiodactylus is regarded as the ancestor form of the known istiodactylid pterosaur. Key words Archaeoistiodactylus Pterosauria Middle Jurassic Tiaojishan Formation western Liaoning Introduction Until now all the known members of the Istiodactylidae an unusual group of pterodactyloids Howse et al Kellner 2003 are reported from the post-late Jurassic sediments mainly in the Early Cretaceous such as Istiodactylus latidens Seeley 1901 in the Vectis Formation of the Isle of Wight Howse et al Liaoxipterus brachyognathus Dong & Lü 2005 Lü et al Lü et al Nurhachius ignaciobritoi Wang et al Istiodactylus sinensis Andres & Ji 2006 Longchengpterus zhaoi = Nurhachius Lü et al Wang et al and Hongshanopterus lacustris Wang et al in the Lower Cretaceous Jiufotang Formation He et al of western Liaoning. Herein reported is a new istiodactylidlike pterosaur from the Middle Jurassic Tiaojishan Formation of Jianchang County western Liaoning of China Fig. 1. It is perhaps the ancestor form of the known istiodactylid pterosaur. 1 Systematic Palaeontology Pterosauria Kaup 1834 Breviquartossa Unwin 2003 Istiodactylidae Howse et al Archaeoistiodactylus gen. nov. Etymology Archaeo Greek word for ancient implying that the new pterosaur is an ancestor form of Istiodactylus. Diagnosis As for the type and only species. Fig. 2. Archaeoistiodactylus linglongtaensis sp. nov. Holotype A partial skeleton JPM is stored in the Jehol Paleontological Museum Chengde Received 20 July 2010 accepted 10 August 2010

2 114 Lü J. C. and Fucha X. H. Hebei Province. Type locality and horizon Linglongta Jianchang County of Liaoning Province Middle Jurassic Tiaojishan Formation BGMRLP 1989 L ü et al Fig. 1 Map of the fossil locality The solid pentagon indicating the fossil site

3 A new pterosaur Pterosauria from Middle Jurassic Tiaojishan Formation of western Liaoning China 115 A. whole skeleton JPM B. enlargement of the lower jaw and metacarpals with line drawings C. enlargement of a maxillary tooth. Scale bar = 10 cm in A and it is presented by mm in B and C. Fig. 2 The holotype of Archaeoistiodactylus linglongtaensis gen. et sp. nov.

4 116 Lü J. C. and Fucha X. H. Etymology The specific name refers to the fossil site Linglongta of Jianchang County Liaoning Province. Diagnosis A new istiodactylid-related pterosaur bears the following characters circular tooth sockets of anterior mandibular teeth relatively short metacarpus metacarpal IV is approximate 60% of the length of the humerus and wing phalanges 2 and 3 and the tibia are all subequal in length. The posteriorly directed crown of the preserved tooth of the upper jaw is similar to that of Hongshanopterus Wang et al Description The specimen is not well preserved Table 1. The anterior part of the lower jaw and posterior part of the upper jaw are preserved. Partial limb bones such as wing phalanges humerus and metacarpals are preserved. Only some limb bones are articulated the rest are spread across the slab. The skull is badly damaged. The posterior portion of the skull is preserved but the anterior portion is missing. Elements are preserved either as bones or impressions in the matrix. A thin narrow long bone extends posteriorly should be the premaxilla. A long bone with tooth socket should be the maxilla. The large elongate space between the maxilla and the premaxilla indicates that the nasoantorbital opening is large similar to those of other istiodactylids such as Istiodactylus sinensis Andres & Ji 2006 Nurhachius ignaciobritoi Wang et al and Longchengopterus Wang et al Lü et al The parietal and frontal are preserved. Both the quadrates are preserved. The distal end of the quadrate is round in lateral view. Its proximal end is wider thanthe distal one with a clear articular surface for the lower jaw. The jugual process for contacting postorbital is narrow and long. A partial braincase is exposed in ventral view. There is a complete maxillary tooth preserved. It is labiolingually compressed with pointed triangular crown and the crown curves posteriorly similar to that of Hongshanopterus lacustris Wang et al Table 1 Measurements of Archaeoistiodactylus linglongtaensis gen. et sp. nov. JPM /mm Elements Length Width Humerus 47 5 Ulna / Radius 70 4 Metacarpal IV 28 4 Wph1 35 as preserved 4 Wph Wph Wph Femur 44 4 Tibia 62 3 The anterior portion of the lower jaw is also preserved as either bone or impressions. The tip of lower jaw is narrow and pointed. One anterior lower jaw teeth belonging to each side are preserved and they are labiolingually compressed. There is a bony process between the teeth similar to the state seen in Longchengpterus zhaoi Wang et al Lü et al The posterior teeth are missing but tooth sockets are present. These sockets are circular which are different from other isiodactylid pterosaurs where they are anteroposteriorly elongated Dong & Lü 2005 Wang et al Wang et al Wang et al Lü et al One cervical vertebra is present and covers a part of the humerus. The cervical vertebra is relatively short and preserved in dorsoventral view. The neural spine is weakly developed and no pleuroceols are visible on the centrum. Five isolated dorsal vertebrae are scattered in the slab. They are short and no detailed information can be obtained. The sternum is not well-preserved but its outline can be traced. It is rectangular in shape with a short cristospine. The shaft of the humerus is straight with expanded proximal and distal ends. The deltopectoral crest is warped and it is as proportionally short as in Longchengpterus zhaoi. The morphology of the humerus is almost identical to that of Longchengpterus zhaoi Wang et al

5 A new pterosaur Pterosauria from Middle Jurassic Tiaojishan Formation of western Liaoning China 117 The radius and ulna are preserved except for some small distal portions. Both ulna and radius are slightly curved. The diameter of the ulna is the same as that of the radius. The proximal end of the ulna is triangular in shape. The distal carpals are fused they are rectangular in shape. Metacarpals I-IV are almost the same in length as each other. Compared to the length of the humerus metacarpal IV is short is about 60% of the length of the humerus. The proximal portion of the wing phalanx 1 is missing thus its exact length is uncertain. The lengths of the wing phalanges 2 and 3 are nearly the same. Wing phalanx 4 is circular in cross-section and the distal end is curved posteriorly. The ilium is not preserved. The pubis is fan-like with a pubic foramen. The ischium is covered by the anterior part of the frontal. A small portion of the proximal end of the femur is missing but the length can be measured. The shaft of the femur is straight with slightly expanded distal end. The articular surface of proximal end of the tibia is concave. The length ratio of tibia to femur is The distal end of the tibia is missing. The distal end of the fibula is fused to the shaft of the tibia. The tarsals and metatarsals are not well preserved. A curved thin bones preserved near the distal portion of the tibia may be the second phalanx of the fifth toe. One small pedal ungual is present. 3 Comparison and discussion Archaeoistiodactylus linglongtaensis gen. et sp. nov. shares the following characters with istiodactylid pterosaurs the shape of the tooth crown and the warped deltopectoral crest as in Nurhachius and Longchengpterus = Nurhachius Lü et al Wang et al Wang et al However it differs from istiodactylid pterosaurs in having a shorter metacarpal IV compared to the humerus Circular tooth sockets of the anterior teeth and having subequal wing phalanges 2 and 3 and the tibia. The tip of the upper jaw is pointed implying that the expanded tip of the jaws such as in Istiodactylus latidens Seeley 1901 Howse et al and Liaoxipterus brachyognathus Dong & Lü 2005 Lü et al is the derived character. The pointed jaw present in Longchengpterus zhaoi = Nurhachius Lü et al Wang et al indicates that the pointed jaw is a primitive character state as the case in Hongshanopterus lacustris Wang et al At present almost all the reported istiodactylid pterosaurs were discovered from Early Cretaceous deposits. Till now four kinds of pterosaurs were found from the Middle Jurassic deposits from western Liaoning and its surrounding areas they are Pterorhynchus wellnhoferi Czerkas & Ji 2002 Changchengopterus pani Lü 2009 Darwinopterus modularis Lü et al and Fenghuangopterus lii Lü et al Archaeoistiodactylus linglongtaensis qen. et sp. nov. differs from the above-mentioned pterosaurs. Pterorhynchus wellnhoferi Czerkas & Ji 2002 in that the teeth are long sharp and a smaller ratio of metacarpal IV to humerus in Pterorhynchus wellnhoferi. Changchengopterus pani Lü 2009 in that the larger ratio of tibia to femur It is in Changchengopterus and the similar lengths of wing phalanges 2 and 3 in the new faxon. Fenghuangopterus lii Lü et al in the tooth morphology and the ratio of humerus to metacarpal IV. The ratio of metacarpal IV to humerus is about 55% in Fenghuangopterus but it is 60% in Archaeoistiodactylus. Darwinopterus modularis Lü et al in the tooth morphology. The same ratio of metacarpal IV to humerus present in different taxa such as in Changchengopterus ratio of metacarpal IV to humerus is Lü 2009 Darwinopterus Lü et al and Archaeoistiodactylus indicates that the grow speeds of both metacarpal IV and humerus is constant in these pterosaurs. Although Archaeoistiodactylus gen. nov. shares characters with some istiodactylids such as Hongshan-

6 118 Lü J. C. and Fucha X. H. opterus Longchengpterus zhaoi = Nurhachius Lü et al Wang et al rather than to any other pterosaurs which indicates that it is more related to istiodactylids than to other pterosaurs it does not belong to the pterodactyloid istiodactylid pterosaurs. The relatively small ratio of wing metacarpal to humerus lower jaw tip and tooth morphologies indicates that it is more primitive than the Cretaceous istiodactylids. Considering the geological age of the Archaeoistiodactylus-bearing stratum Middle Jurassic and the primitive characters present in Archaeoistiodactylus Archaeoistiodactylus is regarded as an ancestor of istiodactylid pterosaurs. The discovery of Archaeoistiodactylus gen. nov. and other monofenestratid pterosaurs from the Middle Jurassic Tiaojishan Formation of Jianchang County western part of Liaoning and northern Hebei provinces indicates that western Liaoning and its surrounding areas may be an evolutionary center of pterosaur radiation although the exact mechanism is not clear. However the high frequency of paleomagnetic reversal during this period See Gradstein et al may affect the normal activities of organisms thus may accelerate the biological changes. Acknowledgements This research was supported by grants from the Natural Science Foundation of China the 973 Project 2006CB and the Basic Outlay of Scientific Research Work from the Ministry of Science and Technology J1003 J0703. References Andres B Ji Q A new species of Istiodactylus Pterosauria Pterodactyloidea from the Lower Cretaceous of Liaoning China. Journal of Vertebrate Paleontology Bureau of Geology and Mineral Resources of Liaoning Province BGMRLP Regional Geology of Liaoning Province. Beijing Geological Publishing House. Czerkas S A Ji Q A new rhamphorhynchoid with a headcrest and complex integumentary structures. Dinosaur Museum Journal Dong Z M Lü J C A new ctenochasmatid pterosaur from the Early Cretaceous of Liaoning Province. Acta Geologica Sinica Gradstein F M Ogg J G Smith A G A Geological Timescale Cambridge Cambridge University Press. He HY Wang X L Zhou Z H et al Timing of the Jiufotang Formation Jehol Group in Liaoning northeastern China and its implications. Geophysical Research Letters 31 L Howse S C B Milner A R Martill D M Pterosaurs / / Martill D M Naish D. Eds. Dinosaurs of the Isle of Wight. London The Palaeontological Association Kaup J J Versuch einer eintheilung der s ugethiere in 6 st mme und der amphibien in 6 ordnungen. Isis Kellner A W A Pterosaur phylogeny and comments on the evolutionary history of the group / / Buffetaut E Mazin J M. Eds. Evolution and Palaeobiology of Pterosaurs. London Geological Society Special Publications Lü J C Fucha X H Chen J M A new scaphognathine pterosaur from the Middle Jurassic of Western Liaoning China. Acta Geoscientica Sinica Lü J C Ji S A Yuan C X et al Pterosaurs from China. Beijing Geological Publishing House 147. Lü J C Unwin D M Jin X S et al Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society B Lü J C Xu L Ji Q Restudy of Liaoxipterus Istiodactylidae Pterosauria with comments on the Chinese istiodactylid pterosaurs. Zitteliana B Lü J C A new non-pterodactyloid pterosaur from Qinglong County Hebei Province of China. Acta Geologica Sinica Seeley H G Dragons of the Air. London Methuen & Co Unwin D M On the phylogeny and evolutionary history of pterosaurs / / Buffetaut E Mazin J M. Eds. Evolution and Palaeobiology of Pterosaurs. London Geological Society Special Publications Wang L Li L Duan Y et al A new istiodactylid pterosaur from western Liaoning. Geological Bulletin of China Wang X L Campos D Zhou Z H et al A primitive istiodactylid pterosaur Pterodactyloidea from the Jiufotang Formation Early Cretaceous northeast China. Zootaxa Wang X L Kellner A W A Zhou Z H et al Pterosaur diversity and faunal turnover in Cretaceous terrestrial ecosystems in China. Nature