[Paleontology • 2020] Allosaurus jimmadseni • A New Species of Theropod Dinosaur (Theropoda: Allosauroidea) from the lower part of the Morrison Formation (Upper Jurassic) of Western North America

Allosaurus jimmadseni

Chure​ & Loewen,​. 2020

 DOI: 10.7717/peerj.7803

Abstract 

Allosaurus is one of the best known theropod dinosaurs from the Jurassic and a crucial taxon in phylogenetic analyses. On the basis of an in-depth, firsthand study of the bulk of Allosaurus specimens housed in North American institutions, we describe here a new theropod dinosaur from the Upper Jurassic Morrison Formation of Western North America, Allosaurus jimmadseni sp. nov., based upon a remarkably complete articulated skeleton and skull and a second specimen with an articulated skull and associated skeleton. The present study also assigns several other specimens to this new species, Allosaurus jimmadseni, which is characterized by a number of autapomorphies present on the dermal skull roof and additional characters present in the postcrania. In particular, whereas the ventral margin of the jugal of Allosaurus fragilis has pronounced sigmoidal convexity, the ventral margin is virtually straight in Allosaurus jimmadseni. The paired nasals of Allosaurus jimmadseni possess bilateral, blade-like crests along the lateral margin, forming a pronounced nasolacrimal crest that is absent in Allosaurus fragilis.

Figure 4: Lateral view of the skull of the holotype specimen of Allosaurus jimmadseni (DINO 11541). Photograph of skull (A) in left lateral view and (B) explanatory line drawing. Matrix shown as stippled in B. Photo by Dan Chure.

 Scale bar equals 10 cm. Osteological abbreviations: a, articular; an, angular; aof, antorbital fossa; aofe, antorbital fenestra; d, dentary; emf, external mandibular fenestra; j, jugal; l, lacrimal; lv, lacrimal vacuity; ltf, laterotemporal fenestra; m, maxilla; mf, maxillary fenestra; n, nasal; na, naris; nf, narial fossa (external naris); o, orbit; pa, prearticular; pm, premaxilla; pnf, perinarial fossa; po, postorbital; q, quadrate; qj, quadratojugal; sa, surangular; sf, surangular foramen; scr, sclerotic ring; sq, squamosal.

Systematic paleontology

Dinosauria Owen, 1842; sensu Padian & May, 1993

Saurischia Seeley, 1887; sensu Gauthier, 1986

Theropoda Marsh, 1881; sensu Gauthier, 1986

Tetanurae Gauthier, 1986

Allosaurioidea Currie and Zhao, 1994; sensu Carrano, Benson & Sampson, 2012

Allosauria Paul, 1988

Allosauridae Marsh, 1878; sensu Sereno, 2005

Allosaurus Marsh, 1877

Allosaurus jimmadseni Chure and Loewen sp. nov. 

(previously inudum (Chure et al. 2006))

Etymology— In honor of the late James H. Madsen, Jr and in recognition of his outstanding contributions to our knowledge of Allosaurus through his herculean efforts of protecting, excavating, preparing, and curating of many thousands of Allosaurus bones from the Cleveland-Lloyd Dinosaur and his masterful monograph (Madsen, 1976) of that collection.

Figure 1: Quarry map of DINO 11541. Photograph of a painted cast of parts of the skeleton and skull of DINO 11541 in their original positions with respect to each other (A) and an explanatory line drawing taken from original quarry photos (B). Photos by Dan Chure. Scale bar equals one m.

Figure 3: Skull and skeletal reconstructions of Allosaurus jimmadseni.
 Idealized skull of Allosaurus jimmadseni in lateral (A), dorsal (B) and posterior (C) views. Skeletal reconstructions of DINO 11541 (D) and MOR 693 (E). Missing elements in indicated in gray. A–C original artwork by Samantha Zimmerman; D and E are modified from artwork by Scott Hartman. Scale bar equals 10 cm for A–C; one m for D and E.

  

Holotype locality—DINO 11541 was recovered from locality DNM 116, east of the enclosed Carnegie Quarry in the Utah part of Dinosaur National Monument. Exact locality data are on file at Dinosaur National Monument.

Holotype horizon—DINO 11541 was recovered from the Salt Wash Member of the Upper Jurassic (Kimmeridgian) Morrison Formation. All referred specimens occur in the stratigraphically equivalent lower part of the Morrison Formation in Wyoming.

Regional horizon—Allosaurus jimmadseni was found in the Salt Wash Member of the Morrison Formation in Utah and lower part of the Brushy Basin Member of the Morrison Formation in Wyoming and South Dakota. Allosaurus jimmadseni occurs below the “clay change” of Turner & Peterson (1999), except for at DMQ, which occurs only two m above the “clay change”.

Diagnosis—Allosaurus jimmadseni is distinguished from other basal tetanurans by the following unique combination of characters: (1) in lateral view, a row of neurovascular foramina pierce the medioventral wall of the maxillary antorbital fossa; (2) straight posteroventral jugal ramus of maxilla where it articulates with jugal; (3) laterodorsal margin of nasal “pinched” into low crest continuous from premaxilla to lacrimal; (4) posterior portion of dorsal surface of nasal cup-shaped, producing a median peak in region of nasofrontal contact; (5) relatively taller lacrimal horns than in Allosaurus fragilis; (6) jugal with relatively straight ventral margin and straight-to-slightly-curved outline in dorsal view; a well-developed distinct antarticular, and (7) axial intercentrum is rotated dorsally and has a flared rim in lateral view.

Figure 16: Skulls of Allosaurus in left lateral view.
(A) Allosaurus fragilis (DINO 2560). (B) Allosaurus jimmadseni (DINO 11541). (C) Allosaurus europeaus (ML 415). Scale bars equal 10 cm.

Conclusions: 

Based on all known data for specimens of Allosaurus, the genus contains two valid species from the Morrison Formation of North America, Allosaurus fragilis and Allosaurus jimmadseni, which are distinct from Allosaurus europeaus (Fig. 16). The jugal, maxilla and nasal of the two taxa differ in multiple characters, including features associated both with signaling structures (nasolacrimal crest in Allosaurus jimmadseni; lacrimal horn of Allosaurus fragilis) and with craniofacial modifications that more likely reflect modification under the direction of natural selection (e.g., transverse expansion of the rear portion of the skull in Allosaurus fragilis; dorsal displacement of the maxillary tooth row relative to the jaw joint in Allosaurus fragilis). Using these characters, this study assigns several specimens to Allosaurus jimmadseni. In a subsequent publication we will review all named species of Allosaurus from North America in support of our view that there are only two valid species of Allosaurus in North America, Allosaurus fragilis and Allosaurus jimmadseni.

    

Daniel J. Chure​ and Mark A. Loewen​​. 2020. Cranial Anatomy of Allosaurus jimmadseni, A New Species from the lower part of the Morrison Formation (Upper Jurassic) of Western North America. PeerJ. 8:e7803. DOI: 10.7717/peerj.7803

New species of Allosaurus discovered in Utah eurekalert.org/e/9ptg via @uofunews @EurekAlert

Remarkable New Species of Meat-Eating Jurassic Dinosaur Discovered in Utah - scitechdaily.com/remarkable-new-species-of-meat-eating-jurassic-dinosaur-discovered-in-utah/

      

   

[Paleontology • 2016] Gualicho shinyae • An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina

Gualicho shinyae 

Apesteguía, Smith, Valieri & Makovicky, 2016   DOI: 10.1371/journal.pone.0157793 

Abstract

Background

Late Cretaceous terrestrial strata of the Neuquén Basin, northern Patagonia, Argentina have yielded a rich fauna of dinosaurs and other vertebrates. The diversity of saurischian dinosaurs is particularly high, especially in the late Cenomanian-early Turonian Huincul Formation, which has yielded specimens of rebacchisaurid and titanosaurian sauropods, and abelisaurid and carcharodontosaurid theropods. Continued sampling is adding to the known vertebrate diversity of this unit.

Methodology/ Principal Findings

A new, partially articulated mid-sized theropod was found in rocks from the Huincul Formation. It exhibits a unique combination of traits that distinguish it from other known theropods justifying erection of a new taxon, Gualicho shinyae gen. et sp. nov. Gualicho possesses a didactyl manus with the third digit reduced to a metacarpal splint reminiscent of tyrannosaurids, but both phylogenetic and multivariate analyses indicate that didactyly is convergent in these groups. Derived characters of the scapula, femur, and fibula supports the new theropod as the sister taxon of the nearly coeval African theropod Deltadromeus and as a neovenatorid carcharodontosaurian. A number of these features are independently present in ceratosaurs, and Gualicho exhibits an unusual mosaic of ceratosaurian and tetanuran synapomorphies distributed throughout the skeleton.

Conclusions/ Significance

Gualicho shinyae gen. et sp. nov. increases the known theropod diversity of the Huincul Formation and also represents the first likely neovenatorid from this unit. It is the most basal tetatanuran to exhibit common patterns of digit III reduction that evolved independently in a number of other tetanuran lineages. A close relationship with Deltadromaeus from the Kem Kem beds of Niger adds to the already considerable biogeographic similarity between the Huincul Formation and coeval rock units in North Africa.

a pair of Gualicho dinosaurs pursuing prey.

illustration: Jorge Gonzalez and Pablo Lara 

Systematic paleontology

Dinosauria

Theropoda

Tetanurae

Avetheropoda

Gualicho shinyae gen. et sp. nov. 

(replaces Nototyrannus violantei Anonymous, 2011, nomen nudum)

Holotype: MPCN PV 0001, comprising four articulated centra from the dorsal vertebral column, an articulated gastral basket, a section of the tail distal to the transition point, the left scapulocoracoid and forelimb, the distal end of both pubes including the pubic boot, and parts of both hind limbs (Fig 1A). Much of the specimen had been lost to erosion when discovered, but the preserved parts including the forelimb, dorsal vertebrae, gastralia, and feet were articulated. Specimen measurements are provided in Table 1.

 Skeletal reconstruction of Gualicho shinyae showing recovered elements in white and missing elements in grey shading.

Artwork by J. González. 

Etymology: Gualicho, a Spanish name derived from the Gennaken (günün-a-künna or northern Tehuelche language) watsiltsüm, for a goddess who was considered the owner of animals and later, following the introduction of Christianity, reinterpreted as a demonic entity. She is now considered a source of misfortune by rural settlers (gauchos) of the Southern Cone. The name was chosen to reflect the difficult circumstances surrounding the discovery and study of the specimen, and its contentious history following excavation. The specific name honors Ms. Akiko Shinya, Chief Fossil Preparator at the Field Museum, for her many contributions to paleontology including discovery of the holotype of Gualicho on February 13th, 2007 (see S1 Fig).

Sebastián Apesteguía, Nathan D. Smith, Rubén Juárez Valieri and Peter J. Makovicky. 2016. An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina. PLoS ONE. 11(7): e0157793.   DOI: 10.1371/journal.pone.0157793

Meet Gualicho shinyae, the puny-armed distant relative of T. rex https://www.theguardian.com/science/2016/jul/13/meet-gualicho-shinyae-the-puny-armed-distant-relative-of-t-rex