Juratyrant langhami Benson, 2008

Brusatte, Stephen L. & Benson, Roger B. J., 2013, The systematics of Late Jurassic tyrannosauroid theropods from Europe and North America, Acta Palaeontologica Polonica 58 (1), pp. 47-54 : 52-53

Juratyrant langhami Benson, 2008

Figs. 1A , 3A, B .

Holotype: OUMNH J.3311−1–J.3311−30, an associated partial skeleton from a mature individual (see Benson [2008] for details). Individual bones include: one cervical vertebra ( OUMNH J.3311−1); five dorsal vertebrae ( OUMNH J.3311−2–J.3311−5 and J.3311−30); a complete sacrum ( OUMNH J.3311−6–J.3311−9); five caudal vertebrae ( OUMNH J.3311−10–J.3311−14); four isolated vertebral transverse processes ( OUMNH J.3311−16–J.3311−19); the complete pelvic girdle (left ilium, J.3311−20; right ilium, J.3311−21; right pubis, J.3311−22; left pubis, J.3311−23; right ischium, J.3311−24; left ischium, J.3311−25); both femora (left femur, J.3311−26; right femur, J.3311−27); both tibiae (right tibia, J.3311−28; left tibia, J.3311−29); and an unidentified bone fragment ( OUMNH J.3311−15).

Type horizon: The Pectinatites pectinatus Ammonite Zone , P. eatlecottensis Subzone, Kimmeridge Clay , Upper Jurassic: lower Tithonian.

Type locality: Dorset, England, United Kingdom. The specimen was recovered 6 miles west of Swanage between Rope Lake Head and Freshwater Steps (marked as Kimmeridge Ledges on Ordnance Survey maps, Ordinance Survey, 1979).

Emended diagnosis.—Tyrannosauroid theropod with four autapomorphies: ischial apron with a “folded” appearance ( Benson 2008); a fibular flange that continues as a distinct low ridge to the proximal end of the tibia ( Benson 2008); ischial tubercle of the ischium expressed as a convex bulge ( Brusatte et al. 2010); deep fossa on the lateral surface of the pubis ventral to the acetabulum (new character). Furthermore, Juratyrant langhami possesses two probable autapomorphies, which are difficult to assess in other taxa because of damage or non−preservation of the bone in question: a prominent hyposphene that extends posteriorly as a thin sheet on the fifth sacral vertebra ( Benson 2008) and an extensor groove of the femur expressed as a broad, concave outline in distal view ( Brusatte et al. 2010).

Remarks.— Benson (2008) considered a “folded” ischial apron (figured here in Fig. 3B ) and a proximally extensive fibular flange as autapomorphies of Juratyrant langhami , and we confirm that these still remain unique to this taxon among all known tyrannosauroids. Benson (2008) further regarded a prominent hyposphene on the fifth sacral vertebra to be unusual to J. langhami , and we tentatively consider this an autapomorphy here but note that it is difficult to assess in most other tyrannosauroids, especially basal taxa phylogenetically proximal to J. langhami (e.g., Dilong , Eotyrannus , Raptorex , Sinotyrannus , Xiongguanlong ). Guanlong also possesses a prominent hyposphene on the fifth sacral, and it projects even further posteriorly relative to the centrum face than in J. langhami , but it is not sheet−like as in J. langhami (IVPP V14531). Tyrannosaurids, on the other hand, do not possess a prominent hyposphene that projects far posterior to the centrum face (e.g., Alioramus IGM 100/1844, Brusatte et al. 2012; Tyrannosaurus, Brochu 2003 ).

We note three additional autapomorphies, two of which are definitive and one of which is probable. First, the ischial tubercle of J. langhami is present as a convex bulge on the posterior surface of the ischium. In Guanlong (IVPP V14531) and outgroup taxa it is expressed as a groove, whereas in more derived taxa such as Dryptosaurus ( Brusatte et al. 2011) , Raptorex ( Sereno et al. 2009) , Appalachiosaurus ( Carr et al. 2005) , and tyrannosaurids (e.g., Lambe 1917; Brochu 2003) it is present as a discrete, either ovoid or triangular, flange whose rugose lateral surface is depressed relative to the remainder of the ischium. J. langhami is the only taxon with a tubercle expressed as a bulge, which is not depressed or discretely offset from the posterior margin of the ischium. This unusual condition was noted by Brusatte et al. (2010) and treated as an intermediate morphology between the groove−like and flange−like states in an ordered character statement (character 278).

Second, we note that there is a deep fossa on the lateral surface of the pubis ventral to the acetabulum, which is bordered anteriorly by a stout ridge ( Fig. 3A ). This ridge separates the fossa from the rugose pubic tubercle on the anterior surface of the pubis. The fossa and corresponding ridge are absent in all other tyrannosauroids known from well preserved pubes, including Guanlong , Raptorex , and tyrannosaurids (e.g., Brochu 2003).

Third, J. langhami possesses a uniquely−shaped extensor groove on the anterior surface of the distal femur, in which the groove is present, but shallow, and expressed as a broad concave margin in distal view ( Benson 2008: fig. 11F). In more basal taxa such as Guanlong (IVPP V14531) and Dilong (IVPP V14243) the extensor groove is absent and the anterior surface of the femur is flat, and in more derived taxa ( Xiongguanlong , Dryptosaurus , Raptorex , tyrannosaurids) the groove is present and expressed as a deep, U−shaped cleft in distal view. J. langhami , therefore, is unique in possessing a shallow and broad extensor groove, and this was noted by Brusatte et al. (2010) who scored J. langhami for its own intermediate character in an ordered character statement related to the presence and depth of the groove (character 290). We acknowledge, however, that the femora of OUMNH J.3311 (the holotype and only specimen of J. langhami ) are deformed; the right femur is crushed mediolaterally and does not exhibit an extensor groove whereas the left is crushed anteroposteriorly and shows a broadly curved groove ( Benson 2008). Thus, this feature is only proposed hesitantly as an autapomorphy.

Finally, Benson (2008) described Juratyrant langhami as possessing an autapomorphic condition of the posterior dorsal vertebrae, in which the postzygapophyses are reduced and raised dorsally relative to the prezygapophyses ( Benson 2008: fig. 3). This condition is not present in the basal tyrannosauroid Guanlong (IVPP V14531), but is present in Xiongguanlong ( Li et al. 2010; FRDC−GS JB16−2−1), Raptorex ( Sereno et al. 2009; LH PV18), and tyrannosaurids (e.g., Alioramus, IGM 100/1844; Tarbosaurus, Maleev 1974 ; Tyrannosaurus, Brochu 2003 ). We include this character in our revised phylogenetic analysis and recover the derived state (dorsally elevated postzygapophyses) as a synapomorphy of the clade of all tyrannosauroids more derived than, and including, J. langhami .

Figures

Fig. 1. Ilia of basal non−tyrannosaurid tyrannosauroids with a posterodorsally inclined ridge on the lateral surface of the ilium. A. Right ilium (reversed) of Juratyrant langhami Benson, 2008 (OUMNH J.3311−21), Kimmeridge Clay, Dorset England, Late Jurassic (early Tithonian). B. Left ilium of Stokesosaurus clevelandi, Madsen 1974 (UMNH VP 7473), Morrison Formation, Utah, USA, Late Jurassic (early Tithonian). C. Left ilium of Eotyrannus lengi Hutt, Naish, Martill, Barker, and Newberry, 2001 (MIWG 1997.550), Wessex Formation, Isle of Wight, England, Early Cretaceous (Barremian). All in lateral view. Arrows denote the lateral ridge.

Fig. 3. Autapomorphies of tyrannosauroids Juratyrant langhami Benson, 2008, Kimmeridge Clay, Dorset England, Late Jurassic (early Tithonian) (A, B) and Stokesosaurus clevelandi Madsen, 1974, Morrison Formation, Utah, USA, Late Jurassic (early Tithonian) (C). A. Right pubis (OUMNH J.3311−22) in lateral view, with the autapomorphic lateral fossa denoted. B. Left ischium (OUMNH J.3311−25) in lateral (B1) and anterior (B2) views, with an inset close up (2.5× magnification) of the autapomorphic folded proximal region of the ischial apron (B3). The autapomorphic convex ischial tubercle is also denoted. C. Pubic peduncle of the left ilium (UMNH 2938) in medial view, with the autapomorphic swollen rim indicated.