Introducing Jinguofortis perplexus.

Photograph of main slab of J. perplexus (Credit: Wang et al., 2018)

Birds originated from a theropod lineage more than 150 million years ago. By the Early Cretaceous, they diversified, evolving into a number of groups of varying anatomy and ecology. In recent years, several discovered fossils of theropods and early birds have filled the morphological, functional, and temporal gaps along the line to modern birds. Most of these fossils are from the Jehol Biota of northeastern China, dated between approximately 130.7 and 120 million years ago. The Jehol Biota provides an incredibly detailed picture of early birds, including Jeholornis, slightly more derived than Archaeopteryx, that lived with Sapeornis, Confuciusornis, and the earliest members of Enantiornithes and Ornithuromorpha. The clade Ornithothoraces (characterized by a keeled sternum, elongate coracoid, narrow furcula, and reduced hand) along with Jeholornithiformes, Confuciusornithiformes and Sapeornithiformes, form the clade Pygostylia. Basal members of this clade are essential to understand the evolution of the modern avian bauplan. The trait that gives the group its name is the presence of a pygostyle, a set of fused vertebrae at the end of the tail.

Jinguofortis perplexus gen. et sp. nov., from the Early Cretaceous of China, exhibits a mosaic combination of plesiomorphic nonavian theropod features like a fused scapulocoracoid and more derived traits, including the earliest evidence of reduction in manual digits among birds. The generic name is derived from “jinguo” (Mandarin), referring to female warrior, and “fortis” for brave (Latin). The specific name is derived from Latin “perplexus,” and highlights the combination of plesiomorphic and derived features present in the holotype specimen.

Holotype of J. perplexus. (Scale bar, 5 cm.) From Wang et al., 2018.

The holotype (IVPP V24194) was collected near the village of Shixia, Hebei Province, China. Biostratigraphic correlation confirms that the fossil-bearing horizon belongs to the Lower Cretaceous Dabeigou Formation of the Jehol Biota (127 ± 1.1 Ma). The holotype of Jinguofortis is subadult or adult given the bone histology, the presence of a fused carpometacarpus, tarsometatarsus, and pygostyle. The body mass estimated is 250.2 g, the wing span is 69.7 cm, with a wing area of 730 cm2.

Jinguofortis exhibits the following features: dentary with at least six closely packed teeth; scapula and coracoid fused into a scapulocoracoid in the adult; sternum ossified; deltopectoral crest of humerus large and not perforated; minor metacarpal strongly bowed caudally; minor digit reduced with manual phalangeal formula of 2–3-2; metatarsals III and IV subequal in distal extent; pedal phalanx II-2 with prominent heel proximally; and forelimb 1.15 times longer than hindlimb. The highly vascularized fibro-lamellar bone tissue indicates that Jinguofortis grew rapidly in early development, but the growth rate had slowed substantially by the time of death. The histology of Jinguofortis is comparable to that of Chongmingia and Confuciusornis, suggesting a similar growth pattern shared among these basal pygostylians. The phylogenetic analysis recovered Jinguofortis as the sister to Chongmingia. The clade uniting these two specimens is Jinguofortisidae, and constitutes the second most basal pygostylian lineage.

Forelimb of Jinguofortis. (A) Photograph. (B) Line drawing. (Scale bar, 1 cm.) From Wang et al., 2018.

Early avian flight clearly underwent a series of evolutionary experiments, as demonstrated by the diverse combination of plesiomorphic and derived features found among early extinct birds. The most striking primitive feature present in the flight apparatus of Jinguofortis is the fused scapulocoracoid, present predominantly in nonavian theropods. The convergently evolved scapulocoracoid in jinguornithids and confuciusornithiforms suggests that these basal clades likely reacquired a similar level of osteogenesis (or gene expression) present in their nonavian theropod ancestors.

 

References:

Wang, M., Stidham, T. A., & Zhou, Z. (2018). A new clade of basal Early Cretaceous pygostylian birds and developmental plasticity of the avian shoulder girdle. Proceedings of the National Academy of Sciences, 201812176. doi:10.1073/pnas.1812176115

The Tyrannosauroids from the Southern Hemisphere.

Santanaraptor lived in South America during the Early Cretaceous about 112 million years ago (From Wikimedia Commons).

Tyrannosauroidea, the superfamily of carnivorous dinosaurs that includes the iconic Tyrannosaurus rex, was mainly distributed in the Northern Hemisphere. However, a few specimens from Australia (Timimus hermani and the articulated pubes NMV P186046) and Brazil (Santanaraptor placidus), have been referred to this clade.

Santanaraptor was unearthed in 1996 in the Romualdo Group (Santana Formation). The holotype is a juvenile partial skeleton that may have reached 1.25 metres (4.1 ft) in length, and it was presumed to be similar to Dilong and Guanlong. It was first described as a coelurosaurian theropod by Alexander Kellner in 1999, but in 2014 Thomas Holtz classified Santanaraptor as the first tyrannosauroid known from Gondwana. Delcourt and Grillo (2018), also placed Santanaraptor within Tyrannosauroidea based on the following features: the absence of an accessory ridge on the lateral surface of the cnemial crest; the absence of a horizontal groove across the astragalar condyles anteriorly; a deep fossa on the medial surface of the femoral head, lateral to the trochanteric fossa; an ischial medial apron positioned along the anterior margin of its shaft in medial view; the lesser trochanter and the greater trochanter extending to approximately the same level proximally; the proximal margin of the femur is concave in posterior view due to a greater trochanter that is elevated substantially relative to the lateral portion of the proximal surface of the head; and a shallow femoral extensor groove on the anterior surface of the distal end that is expressed as a broad concave anterior margin in distal view but present as an extensive depression on the anterior surface of the femur.

Holotypic left femur of Timimus hermani (From Wikimedia Commons)

Timimus was unearthed in 1994 from Eumeralla Formation and shares similar features with Tyrannosauroidea, but due to the incompleteness of the Timimus holotype, is difficult to properly evaluate its phylogenetic position. The same applies to NMV P186046. It was suggested (Benson et al., 2012) that NMV P186046 and the Timimus holotype may represent a single taxon given their similar phylogenetic positions and congruent sizes, although they did not come from the same site.

Time-calibrated phylogeny of Tyrannosauroidea. From Delcourt and Grillo, 2018.

Tyrannosauroidea had a Eurasian distribution, but basal lineages of the newly proposed clade, Pantyrannosauria (the most inclusive clade, containing Tyrannosaurus rex and Dilong paradoxus, but not Proceratosaurus bradleyi), were distributed across Europe (Juratyrant, Eotyrannus and Aviatyrannis), North America (Stokesosaurus), South America (Santanaraptor), Australia (Timimus), and Asia (Dilong and Xiongguanlong). It was hypothesized that all basal lineages of Pantyrannosauria were already established in the Late Jurassic before the complete separation of Gondwana and Laurasia.

The fact that Santanaraptor and Timimus were relatively small suggests that Gondwanan tyrannosauroids remained small in comparison to northern species. The presence of Santanaraptor in a semi-arid environment with marine incursion also suggests that tyrannosauroids were not only found in humid paleoenvironments.

References:

Rafael Delcourt, Orlando Nelson Grillo , Tyrannosauroids from the Southern Hemisphere: Implications for biogeography, evolution, and taxonomy. Palaeo (2018), doi: 10.1016/j.palaeo.2018.09.003

Apesteguía, S., Smith, N.D., Juárez Valieri, R., Makovicky, P.J., 2016. An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina. PLoS One 11, 1–41. doi:10.1371/journal.pone.0157793

Benson, R.B.J., Rich, T.H., Vickers-Rich, P., Hall, M., 2012. Theropod fauna from southern Australia indicates high polar diversity and climate-driven dinosaur provinciality. PLoS One 7, e37122. doi:10.1371/journal.pone.0037122

Porfiri, J. D., Novas, F. E., Calvo, J. O., Agnolín, F. L., Ezcurra, M. D. & Cerda, I. A. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research 51: 35-55. https://doi.org/10.1016/j.cretres.2014.04.007

Holtz Jr, T.R., 2004. Tyrannosauroidea, in: Weishampel, D.B., Dodson, P., Osm (Eds.), The Dinosauria. University of California Press, Berkeley, pp. 111–136.