New remains of an ornithuromorph bird from Bajo de la Carpa Formation (Santonian, Upper Cretaceous), Paso Córdoba, Río Negro

LECUONA, A.; BAIANO, MATTIA A.; LEARDI, J. M.; POL, D.; SALGADO, L.

Trelew, Chubut (modalidad virtual)

Jornada; XXXV Jornadas Argentinas de Paleontología Vertebrados; 2022

Museo Paleontológico Egidio Feruglio

Theremains presented here correspond to an avian left tarsometatarsus (fieldnumber CCS-5) recovered from Bajo de la Carpa Formation (Santonian, UpperCretaceous), of Paso Córdoba locality, southwest of General Roca, Río Negro,Argentina. This element is 49.2 mm long, with incomplete proximal and distalends, and 10.4 mm midshaft width. The metatarsals (mtt) II to IV are fusedthrough its length, with shallow grooves between adjacent metatarsals on theirproximal halves, and even shallower ones along their distal halves. Thiscondition is similar to Patagopteryx deferrariisi, but the opposite isseen in Kaririavis mater and Neuquenornis volans, withmetatarsals almost fused proximally and unfused distally. The three metatarsalsare similar in width, where the IIIrd is 1.18 times the metatarsalIV. This condition differs from Patagopteryx that has a proportionatelynarrow metatarsal IV (mtt III/mtt IV width ratio = ca. 1.73) and Kaririaviswith a wider metatarsal III (mtt III/mtt IV width ratio = ca. 2). Theproximal vascular foramen is present between metatarsals III and IV, and openson the anterior and plantar surfaces, a condition shared with Patagopteryx, but absent in Kaririavis.The presence of a distal vascular foramen between the trochlea of metatarsalsIII and IV cannot be determined because the trochlea of metatarsal IV has notbeen preserved. No articular surface for metatarsal I is recognized on themetatarsal II, nor a swelling on the anterior surface of metatarsals II and IIIfor the attachment of the M. tibialis anterior. The plantar surface is somewhatexcavated on the proximal half, being shallower than in Patagopteryx(MACN-N-11) and Neuquenornis (MUCPv-142). A preliminary phylogeneticanalysis of Avialae recovers Kaririavis as the basal mostOrnithuromorpha and CCS-5 nested in a large polytomy within this clade alsoincluding Patagopteryx. This polytomy is probably due to the single remain of CCS-5 and thecombination of plesiomorphic (e.g.,trochlea of metatarsal II not medially curved) and apomorphic (e.g., metatarsal fusion) characters thatpresents. Several characters shared withPatagopteryx suggest it could represent a new specimen of this taxon; however,a more exhaustive phylogenetic analysis is needed. In any case, CCS-5 increasesknowledge about vertebrates from Bajo de la Carpa Formation at Paso Córdobalocality, where it is also known Velocisaurus, Achillesaurus, Notosuchus,Comahuesuchus, and Dinilysia, and tending to the fossil fauna diversityrepresented in the same levels of Neuquén city localities.