SILESAURIDAE NESBITT ET AL., 2010

Marsh, Adam D. & Parker, William G., 2020, New dinosauromorph specimens from Petrified Forest National Park and a global biostratigraphic review of Triassic dinosauromorph body fossils, PaleoBios 37, pp. 1-56 : 11-13

SILESAURIDAE NESBITT ET AL., 2010

FIG 5A–R

Referred specimens and localities — PEFO 44460 ( Fig. 5A–C), proximal end of right femur, PFV 451: Black Knoll E, PFM; PEFO 34347 ( Fig. 5D–F), proximal end of right femur, PFV 122: The Dying Grounds, UCMP V 7038, BMM; PEFO 38279 ( Fig. 5G–I), proximal end of right femur, PFV 288: Lot’s Wife, BMM; PEFO 39373/ UWBM 108379 ( Fig. 5J–L), proximal end of left femur, PFV 410: Kaye Quarry, UWBM C2226, Jim Camp Wash beds, SM; PEFO 43474 ( Fig. 5M–O), proximal end of left femur, PFV 354: Flattops NE, Martha’s Butte beds, SM; PEFO 35117 ( Fig. 5P–R), proximal end of left femur, PFV 337: Valley of the Dead, BMM.

Description and rationale for assignment— All of these specimens represent proximal ends of femora. PEFO 44460 ( Fig. 5A–C) is nearly the same size as the large silesaurid reported from the Middle Triassic of Tanzania (NHMUK R16303, Barrett et al. 2015). The PEFO femora have the three proximal condyles that are present plesiomorphically in ornithodirans (the lateral tuber, anteromedial tuber, and posteromedial tuber) (Nesbitt 2011), and the posteromedial tuber is small (Nesbitt 2011:301-0), unlike the relatively large posteromedial tuber found in lagerpetid dinosauromorphs, e.g., Dromomeron romeri (GR 218) and D. gregorii (TMM 31100- 1306, Nesbitt et al. 2009b: figs. 1C, 2c, respectively), and some suchian archosaurs such as Revueltosaurus callenderi (PEFO 34561), aetosaurs, e.g., Typothorax coccinarum Cope (1875) (UCMP 34238, Nesbitt 2011: fig. 38a), and ornithosuchids, e.g., NHMUK PV R 3561 (Walker 1964: fig. 12d). The posteromedial tuber is so reduced (e.g., Fig. 5D) that it is identical to those that have been scored as ‘absent’ in Silesaurus opolensis (ZPAL Ab III/361/23, Dzik 2003: fig. 13a) and Eucoelophysis baldwini (NMMNH P-22298, Sullivan and Lucas 1999: fig. 6c), which is apormorphic for Silesauridae and creates a subtriangular proximal outline of the femur (Nesbitt 2011:301-2).

A straight transverse groove is present on the proximal surface of the femora (Nesbitt 2011:314-1) ( Fig. 5D), similar to that of silesaurids, e.g., Si. opolensis (ZPAL Ab III/361/23, Dzik 2003: fig. 13a), and Asilisaurus kongwe (NMT RB159, Nesbitt et al. 2019: fig. 42a), herrerasaurids, e.g., Staurikosaurus pricei Colbert (1970) (MCZ 1669, Bittencourt and Kellner 2009: fig. 26a), and early sauropodomorphs, e.g., Saturnalia tupiniquim (MCP PV 3844, Langer et al. 2003: fig. 4c) and Buriolestes schultzi Cabreira et al. (2016, ULBRA-PVT280: fig. s2d). The development of this groove is owing to the presence of a cartilaginous cone on the proximal end of the femur in

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archosaurs (Tsai et al. 2018), which is ontogenetically variable (Griffin 2018). All PEFO specimens except PEFO 43474 and PEFO 39373/UWBM 108379preserve a sharp ridge-like dorsolateral trochanter, or attachment for the m. ischiotrochantericus (Piechowski et al. 2020), on the anterolateral surface of the femur (Nesbitt 2011:307-1) ( Fig. 5E), which is found in silesaurids, e.g., E. baldwini (NMMNH P-22298, Sullivan and Lucas 1999: fig. 6a), Kwanasaurus williamparkeri Martz and Small (2019, DMNH EPV.54828: fig. 17e), and Si. opolensis (ZPAL Ab III/361/21, Piechowski et al. 2020: fig. 19b), and some early ornithischian dinosaurs, e.g., Lesothosaurus diagnosticus Galton (1978, NHMUK RU B17) (Baron et al. 2017a: fig. 14a), Eocursor parvus (SAM-PK-K8025, Butler 2009: fig. 15e), and Scutellosaurus lawleri Colbert (1981, MNA V1752: fig. 25). The development of this feature is also ontogenetically variable (Piechowski et al. 2014, Griffin and Nesbitt 2016).

Perhaps the most obvious apomorphy of Silesauridae present in the PEFO femora, excluding the heavily weathered PEFO 43474, is the notch presented ventromedial to the femoral head (Nesbitt 2011:304-1) ( Fig. 5F), which is present in early silesaurids such as As. kongwe (NMT RB19, Nesbitt et al. 2010: fig. 2k), as well as later-diverging silesaurids such as K. williamparkeri (DMNH EPV 54828, Martz and Small 2019: fig. 17b) and E. baldwini (NMMNH P-22298, Sullivan and Lucas 1999: fig. 6a). The only PEFO specimen complete enough to preserve the anterior trochanter is PEFO 44460 ( Fig. 5B). In that specimen, that trochanter is a raised, rounded knob. We assign these femora to the Silesauridae owing to the presence of a ventral notch under the femoral head when preserved and a highly reduced posteromedial proximal tuber that forms a subtriangular proximal outline.