Introducing Notatesseraeraptor frickensis.

Notatesseraeraptor frickensis at the Sauriermuseum Frick. (From Wikimedia Commons)

Over the last two decades our knowledge of the fossil record of early theropod dinosaurs has greatly improved. However, there are different hypotheses about their relationships. Theropods are relatively abundant in post-Carnian Triassic faunas, including the European Liliensternus, the South American Zupaysaurus, and the North American Coelophysis. Those taxons represent the earliest major radiation of Neotheropoda. Two primitive branches of this clade are the Coelophysoidea and the Dilophosauridae. More recent studies suggest that at least some members of the ‘traditional Coelophsoidea’ are more closely related to the tetanurans and that the Dilophosauridae may represent a second clade of early non-averostran neotheropods. Notatesseraeraptor frickensis gen. et sp, from the Late Triassic of Switzerland, provides new clues about the relationships of the early theropods.

The new specimen belong to an immature individual of length 2.6–3.0 m, and it was collected in 2006 from Gruhalde clay pit in Frick (Aargau, Switzerland), a place well known for its abundant, articulated Plateosaurus material. The genus name derives from the Latin “nota” meaning feature and “tesserae”, a word used to describe glass, or other material used in the construction of a mosaic, in reference to the interesting mixture of characters found in the fossil.

Skeletal anatomy of N. frickensis gen. et sp. nov. From Zahner and Brinkmann, 2019.

The new specimen was described based on a cranium (SMF 09-2) and partial postcranial skeleton (SMF 06-1). The cranium is proportionally long and low as is commonly found in traditional coelophysoid-grade neotheropods. But in contrast to coelophysids, the premaxillary tooth crowns of N. frickensis are all strongly recurved, laterally compressed and bear fine serrations. The postcranial skeleton includes two articulated forelimbs, 13 dorsal, four sacral and four proximal caudal vertebrae; cervical, dorsal and sacral ribs; chevrons; gastralia; and even stomach contents ( a well-preserved maxilla of the rhynchocephalian Clevosaurus). The preserved postcranial elements share most of their morphological similarities with ‘Syntarsus’ kayentakatae. N. frickensis has plesiomorphically long forelimbs. The radius is about three-quarters of the length of the humerus. The manus is composed of four digits, whereas the fourth is reduced to a very slim metacarpal. The shape of the ilium are similar to those found in Coelophysis.  

The phylogenetic analyses, with emphasis on early neotheropods, suggests that Notatesseraeraptor is a basal member of Dilophosauridae, a clade that comprises Dilophosaurus, and Cryolophosaurus.

 

References:

Marion Zahner; Winand Brinkmann (2019). “A Triassic averostran-line theropod from Switzerland and the early evolution of dinosaurs”. Nature Ecology & Evolution. doi:10.1038/s41559-019-0941-z

Martín D. Ezcurra, and Federico L. Agnolín (2017). Gondwanan perspectives: Theropod dinosaurs from western Gondwana. A brief historical overview on the research of Mesozoic theropods in Gondwana. Ameghiniana 54: 483–487. https://doi.org/10.5710/102.054.0501

 

Hesperornithoides miessleriis and the evolution of flight.

Primary blocks of Hesperornithoides specimen WYDICE-DML-001. Images taken by Levi Shinkle. From Hartman et al., 2019.

Birds originated from a theropod lineage more than 150 million years ago. Their evolutionary history is one of the most enduring and fascinating debates in paleontology. In recent years, several discovered fossils as well as innovative studies of living bird behavior, have enriched our understanding of early paravian evolution and flight origins. The discovered fossils demonstrate that distinctive bird characteristics such as feathers, flight, endothermic physiology, unique strategies for reproduction and growth, and a novel pulmonary system have a sequential and stepwise transformational pattern, with many arising early in dinosaur evolution, like the unusually crouched hindlimb for bipedal locomotion,the furcula and the “semilunate” carpal that appeared early in the theropod lineage.

The new paravian theropod, Hesperornithoides miessleriis, from the Late Jurassic Morrison Formation of east–central Wyoming, provides new clues about paravian relationships, as well as the acquisition of flight-related characters in stem avians. Nicknamed “Lori”, and with an estimated length of 89 cm, the new specimen is significantly smaller than other relatively complete theropods from the Morrison Formation. Hesperornithoides lived in a wetland environments with herbaceous plants, but no trees. The habitat, combined with limb proportions indicate that the new specimen was clearly terrestrial.

Association of skeletal elements of Hesperornithoides miessleriis assembled from 3D scans of specimen blocks. Scale bar = 6 cm. From Hartman et al., 2019

Hesperornithoides exhibits the following combination of characters: pneumatic jugal; short posterior lacrimal process; quadrate forms part of lateral margin of paraquadrate foramen; small external mandibular fenestra, humeral entepicondyle >15% of distal humeral width; manual ungual III subequal in size to ungual II; mediodistal corner of tibia exposed anteriorly. The holotype (WYDICE-DML-001) is a partially articulated skeleton consisting of an almost articulated skull, five cervical vertebrae, isolated anterior dorsal rib, portions of 12 caudal vertebrae, five chevrons, partial left scapula and coracoid, portions of the proximal left humerus and distal right humerus, left ulna and radius, radiale, semilunate carpal, left metacarpals I–III, manual phalanges III-2 and 3, manual unguals I, II, and III, ilial fragment, most of an incomplete femur, right and left tibiae and fibulae, left astragalus and calcaneum, portions of right and left metatarsal packets, left pedal phalanges III-1, III-2, III-3, IV-1, IV-2, IV-3, IV-4, and pedal unguals II and III and the proximal portion of IV. The cranial elements are preserved in a separate “skull block”, whereas the axial skeleton is distributed across three blocks.

The acquisition of powered flight in birds was preceded in the course of paravian evolution by a complex sequence of anatomical and functional innovations, and many characters associated with avian flight evolved in a terrestrial context. For this reason, a refined and robust phylogeny of paravians is imperative in order to elucidate the sequence of evolutionary stages that resulted in the acquisition of major avian traits.

 

References:

Hartman S, Mortimer M, Wahl WR, Lomax DR, Lippincott J, Lovelace DM. 2019. A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ 7:e7247 https://doi.org/10.7717/peerj.7247

Agnolin FL, Motta MJ, Egli FB, Lo Coco G, Novas FE. 2019. Paravian phylogeny and the dinosaur-bird transition: an overview. Frontiers in Earth Science 6:252 https://www.frontiersin.org/articles/10.3389/feart.2018.00252/full