THEROPODA

Lessner, Emily J., Parker, William G., Marsh, Adam D., Nesbitt, Sterling J., Irmis, Randall B. & Mueller, Bill D., 2022, New insights into Late Triassic dinosauromorph-bearing assemblages from Texas using apomorphy-based identifications, PaleoBios 35, pp. 1-41 : 10-17

THEROPODA

Femora Benton 1985

Panchen and Smithson 1987 Humeri Gauthier et al. 1988

Femur Pritchard 2015

Femur Pritchard 2015 Humeri Senter 2004

Femur Gauthier et al. 1988

Humeri Senter 2004 Pritchard et al. 2015 Ulna Ezcurra 2016 Nesbitt 2011

Femora Pritchard et al. 2015

Femora Ezcurra 2016 Nesbitt et al. 2015 Nesbitt 2011 Humerus Ezcurra 2016 Nesbitt et al. 2015

Humeri Ezcurra 2016 Nesbitt 2011

Humeri Li et al. 2016 Ezcurra 2016

Femur Nesbitt 2011

Pubis Nesbitt 2011

Tibiae Nesbitt 2011

Osteoderm Parker 2016a

Femora Nesbitt 2011

Femora Nesbitt 2011

Tibiae Novas 1996 Nesbitt 2011

Femora Nesbitt 2011

Femur Nesbitt 2011 Nesbitt et al. 2009c

Tibia Nesbitt 2011

Tibiae Novas 1992

Tibia Nesbitt 2011

Femora Nesbitt 2011

Tibiae Novas 1992 Nesbitt 2011

Figure 3. A–L. Tetrapod femora in posterior (A, C, E, G, I, K) and distal (B, D, F, H, J, L) views. A, B. TTU-P 11409F. C, D. TTU-P 11403. E, F. TTU-P 11273. G, H. TTU-P 11278. I, J. TTU-P 11390A. K, L. TTU-P 11390B. M–P. Tetrapod humeri in anterior (M), proximal (N, P), and posterior (O) views. M, N. TTU-P 11410B. O, P. TTU-P 11410C. Scale bar 1 cm. Abbreviations: ctf, crista tibiofibularis; dpc, deltopectoral crest; fc, fibular condyle; tc, tibial condyle. Arrows point anteriorly.

Localities— Femora: MOTT 3898 (Headquarters South); MOTT 3892 (Headquarters). Humeri: MOTT 3898 (Headquarters South).

Description and Rationale for Assignment—

Femora— The distal ends of the femora ( TTU-P 11409F, TTU-P 11403, TTU-P 11273, TTU-P 11278, TTU-P 11390A- B) preserve the distal expansions of each element as well as small portions of the midshafts proximally (Fig. 3A–L). The specimens are nearly identical, and therefore we describe them together. The femur preserves two distal condyles and the crista tibiofibularis (Fig. 3A–L). The fibular condyle is present as a small lateral crest on the anterolateral margin of the crista tibiofibularis. The crista tibiofibularis is circular in lateral view and extends further distally than the smaller medial, tibial condyle (Fig. 3A, C, E, G, I, K). This is in contrast to the neodiapsid character state of level distal articular surfaces ( Benton 1985; character B: state 14). The distal surface of the tibial condyle is flat, whereas the distal surface of the crista tibiofibularis is convex, with an anteroposteriorly-trending ridge on the lateral margin (Fig. 3B, D, F, H, J, L). There is a wide groove separating the crista tibiofibularis and the tibial condyle that continues onto the dorsal surface. This combination of femoral characters is similar to that of the drepanosauromorphs Hypuronector limnaios Colbert and Olsen, 2001 and Vallesaurus cenensis Wild, 1991 (Renesto et al. 2010). However, the absence of apomorphies specific to Reptilia, Diapsida, Sauria, or Drepanosauromorpha precludes referral to a more specific clade than Tetrapoda; however, this is the most-inclusive assignment and is based on the presence of distal condyles indicating a hinged knee-joint in the hindlimb (Panchen and Smithson 1987; character 62).

Humeri— The proximal ends of the humeri (TTU- P11410B-C) preserve the proximal expansion and a small portion of the midshaft (Fig. 3M–P). TTU-P 11410B is smaller and more gracile than TTU-P 11410C, but otherwise the two specimens are identical and are therefore described together. The humerus is subrectangular in proximal view with slightly concave posterior and anterior margins (Fig. 3N, P). The concave anterior margin is formed by a triangular fossa on the anterior surface that tapers distally towards the midshaft. This fossa is bordered laterally by the deltopectoral crest, an anterolateral ridge extending along the length of the proximal end of the humerus from the proximal articular surface onto the midshaft distally (Fig. 3M, N, P). There is a small anteromedial protuberance just distal to the proximal end of the humerus. The lateral surface is flat, rounded proximally, and tapers distally in lateral view. There is another ridge along the posterolateral length of the proximal end of the humerus from the proximal end extending onto the midshaft distally. The ridge-like morphology of the deltopectoral crest and the combination of characters described above are similar to Hypuronector , Vallesaurus , Megalancosaurus Calzavara et al., 1980 , and Drepanosaurus Pinna, 1980 (Pritchard 2015). We assign TTU-P 11410B-C to Tetrapoda based the presence of a distinct humeral shaft ( Gauthier et al. 1988), and the absence of apomorphies specific to a more inclusive clade.

REPTILIA Linnaeus, 1758 sensu Gauthier et al., 1988

Referred Specimen— TTU-P 11287, complete right femur (Fig. 4A–C).

Locality— MOTT 3892 (Headquarters).

Description and Rationale for Assignment— TTU- P11287is rounded proximally and medially, lacks distinct proximal condyles, and tapers laterally in proximal view (Fig. 4A–C). The laterally tapering portion of the proximal end extends distally as a ridge on the lateral margin of the

midshaft, expanding dorsally into a rounded hump. The ventral surface of the femur preserves a ridge (=internal trochanter) that originates just distal to the proximal surface and extends distally (Fig. 4A). This ridge is present in nearly all early reptiles and diapsids (Pritchard 2015; 259:0). The proximal end of TTU-P 11287 is very similar to the proximal ends of other diapsid femora described later, although the internal trochanter is present as a ridge in TTU-P 11287, rather than a rounded knob as in the other specimens. However, the distal end of TTU-P 11287 is unique among the sample; two distal condyles are preserved, a larger lateral, fibular condyle and a smaller medial, tibial condyle (Fig. 4C). The lateral condyle extends slightly further distally than the medial condyle, similar to the condition in the early reptile Petrolacosaurus Reisz, 1981 . We assign TTU-P 11287 to Reptilia because of the presence of the ridge-like internal trochanter and the absence of apomorphies specific to a more inclusive clade.

DIAPSIDA Osborn, 1903 sensu Laurin, 1991

Referred Specimens— Femora: TTU-P 11407A, proximal end of left femur (Fig. 4D, E); TTU-P 11407B, proximal end of left femur (Fig. 4F, G); TTU-P 11408A, proximal end of right femur (Fig. 4H, I); TTU-P 11408B, proximal end of right femur (Fig. 4J, K); TTU-P 11408C, proximal end of left femur (Fig. 4L, M); TTU-P 11408D, proximal end of left femur (Fig. 4N, O); TTU-P 11288, proximal end of left femur (Fig. 4P, Q). Humeri: TTU-P 11404A, distal end of left humerus (Fig. 4R, S); TTU-P 11404B, distal end of left humerus (Fig. 4T, U); TTU-P 11404C, distal end of right humerus (Fig. 4V, W); TTU-P 11404D, distal end of right humerus (Fig. 4X, Y); TTU-P 11404E, distal end of right humerus (Fig. 4Z, AA); TTU-P 11394, distal end of right humerus (Fig. 4AB, AC); TTU-P 11410A, distal end of left humerus (Fig. 4AD, AE); TTU-P 11401, distal end of left humerus (Fig. 4AF, AG).

Localities— Femora: MOTT 3898 (Headquarters South); MOTT 3892 (Headquarters); MOTT 3900 (Headquarters North); MOTT 3901 (Green Tooth Arroyo). Humeri: MOTT 3898 (Headquarters South); MOTT 3892 (Headquarters).

<Figure 4. A. Reptilian femur in ventral (A), proximal (B), and distal (C) views. A–C. TTU-P 11287. D–Q. Diapsid femora in ventral (D, F, H, J, L, N, P) and proximal (E, G, I, K, M, O, Q) views. D,E. TTU-P 11407A. F,G. TTU-P 11407B. H, I. TTU-P 11408A. J, K. TTU-P 11408B. L, M. TTU-P 11408C. N, O. TTU-P 11408D. P,Q. TTU-P 11288. R–AG. Diapsid humeri in anterior (R, T, V, X, Z, AB, AD, AF) and distal (S, U, W, Y, AA, AC, AE, AG) views. R, S. TTU-P 11404A. T,U. TTU-P 11404B. V, W. TTU-P 11404C. X, Y. TTU-P 11404D. Z, AA. TTU-P 11404E. AB, AC. TTU- P11394. AD, AE. TTU-P 11410A. A F, AG. TTU-P 11401. Scale bar 1 cm. Abbreviations: ect, ectepicondyle; ent, entepicondyle; itr, internal trochanter; rc, radial condyle; uc, ulnar condyle. Arrows point anteriorly.

Description and Rationale for Assignment—

Femora— The specimens ( TTU-P 11407A-B, TTU- P11408A-D, TTU-P 11288) preserve the proximal expansions of the femora as well as a small portion of the midshafts distally (Fig. 4D–Q). The specimens are nearly identical, and therefore we describe them together. The femur is rounded proximally and medially, lacks distinct proximal condyles, and tapers laterally in proximal view (Fig. 4E, G, I, K, L, O, Q). The laterally-tapering portion extends distally as a ridge on the lateral margin of the midshaft, expanding dorsally into a rounded hump. The ventral surface of the femur preserves a rounded tuberosity, marking the internal trochanter, that originates just distal to the proximal end and extends distally as a ridge (Fig. 4D, F, H, J, L, N, P). The internal trochanter is observed as a rounded tuberosity in drepanosauromorphs and weigeltisaurids (Pritchard 2015; 259:1). Therefore, we assign TTU-P 11407A-B, TTU-P 11408A-D, and TTU- P11288 to Diapsida, the least inclusive clade that includes Drepanosauromorpha and Weigeltisauridae .

Humeri— The distal ends of the humeri (TTU- P11404A-E, TTU-P 11394, TTU-P 11410A, TTU-P 11401) preserve the distal expansion and a small portion of the midshaft in all specimens (Fig. 4R–AG). TTU-P 11410A and TTU-P 11404B are transversely narrow with less extensive epicondyles in comparison with the other specimens (Fig. 4T, AD). Otherwise, all specimens are nearly identical and are therefore described together. The entepicondyle originates on the medial side of the midshaft slightly more proximally than the ectepicondyle originates on the lateral side of the midshaft (Fig. 4R, T, V, X, Y, AB, AD, AF). Only TTU-P 11404C preserves an ectepicondylar foramen The ectepicondyle is broken away to differing degrees in some specimens, but it is complete in TTU-P 11404A, TTU-P 11404D, TTU-P 11410A, and TTU-P 11401, all of which lack an entepicondylar foramen, similar to the condition in drepanosaurs and archosauromorphs (Senter 2004; 63:1). There are two distal condyles: the large, lateral radial condyle and the smaller, medial ulnar condyle (Fig. 4S, U, W, Y, AA, AC, AE, AG). In anterior view, the radial condyle is elliptical and extends distally from the proximal end. The majority of the radial condyle is located on the anterior surface of the distal end of the humerus, and the condyle extends as a sharp ridge onto the distal surface. The ulnar condyle is elliptical in distal view and sits on the distal end of the humerus, slightly overhanging the posterior surface. A shallow groove separates the two condyles anterodistally and ends in a fossa just proximal to the radial condyle. The morphology and proportions of the ectepicondyle, entepicondyle, and radial condyle are comparable to Drepanosaurus , but because of incomplete preservation of our specimens and the compressed preservation of most drepanosauromorph specimens, we assign these specimens to Diapsida on the basis of the absence of an entepicondylar foramen and the absence of apomorphies specific to a more inclusive clade. The distal ends of the humeri discussed above compare favorably with a left distal end of a humerus ( NMMNH P-29044) from the Snyder Quarry in New Mexico, which was assigned to Cynodontia without using apomorphies (Zeigler et al. 2003).

SAURIA McCartney, 1802

Referred Specimen— TTU-P 11280, proximal end of right femur ( Fig. 5A, B).

Locality— MOTT 3898 (Headquarters South).

Description and Rationale for Assignment— The proximal end of the right femur, TTU-P 11280, preserves the expanded proximal condyles and a small portion of the midshaft ( Fig. 5A, B). The element is trapezoidal in proximal view, square anteriorly and dorsally, and tapers slightly posteriorly, very similar to Trilophosaurus buettneri Case, 1928 ( TMM 31025-140). The portion that tapers posteriorly extends distally as a ridge. In proximal view, the internal trochanter is present ventrally as a robust ridge ( Fig. 5B). The dorsal portion of the proximal surface is raised above the proximal extent of the internal trochanter on the ventral surface, similar to Malerisaurus robinsonae Chatterjee, 1980 , Trilophosaurus buettneri , Pamelaria dolichotrachela Sen, 2003 ( ISIR 316/55), and Prolacerta broomi Parrington, 1935 (BP/1/2676) ( Chatterjee 1980, Chatterjee 1986b, Sen 2003, Spielmann et al. 2008). In anterior and posterior views, the proximal border of the internal trochanter slopes proximally to meet the proximal surface of the femur as in Malerisaurus ( Chatterjee 1980, 1986b). The internal trochanter of TTU-P 11280 extends distally as a ridge on the ventral surface of the midshaft. A shallow, smooth intertrochanteric fossa is present, bordered by the internal trochanter ventrally and the posteriorly tapering ridge dorsally ( Fig. 5A, B). A shallow intertrochanteric fossa is present in Sauria ( Gauthier et al. 1988; 81:1). A rugose intertrochanteric fossa occurs only in Azendohsaurus madagaskarensis Flynn et al., 2010 , Erythrosuchus africanus Broom, 1905 , Proterosuchus alexanderi Hoffman, 1965 , and Prolacerta broomi (Nesbitt et al. 2015) , and these are deeper than that of TTU-P 11280. The morphology of the intertrochanteric fossa and absence of apomorphies specific to the taxa

listed above leads us to assign TTU-P 11280 to Sauria. ARCHOSAUROMORPHA Huene, 1946

sensu Benton, 1985

Referred Specimens— Humeri: TTU-P 11410E, distal end of right humerus ( Fig. 5C, D); TTU-P 11277, distal end of (right?) humerus ( Fig. 5E, F). Ulna: TTU-P 11386, proximal end of left ulna ( Fig. 5G).

Localities— Humer i: MOTT 3898 (Headquarters South). Ulna: MOTT 3869 (Boren Quarry).

Description and Rationale for Assignment—

Humeri— TTU-P 11410E and TTU-P 11277 preserve distal ends of humeri and are described below individually ( Fig. 5C–F).

TTU-P 11410E preserves the distal end of a right humerus and a portion of the midshaft ( Fig. 5C, D. It is likely that this specimen is associated with TTU-P 11410D described below ( Fig. 6C), the proximal end of a right humerus assigned to Archosauriformes because the specimens are from the same locality, of similar preservation and size, and the midshafts have similar cross sections. The distal end of the humerus is mediolaterally elongate in distal view ( Fig. 5D). The distal end expands medially, whereas the lateral edge is vertical. The distal end preserves two condyles, the larger medial condyle (=ulnar) and the smaller lateral condyle (=radial). The lateral condyle tapers anterolaterally. The medial condyle expands slightly anteriorly and is rounded from the proximal surface onto the medial edge. The ectepicondyle is flat, whereas the entepicondyle is present as a flange proximal to the medial condyle ( Fig. 5C). The absence of an entepicondylar foramen is a character state shared by drepanosaurs and archosauromorphs (Senter 2004; 46:1). The obvious difference in morphology from the specialized drepanosauromorph humeri (e.g., the distal condyles are elliptical and the epicondyles are blade-like in drepanosauromorph humeri) and the absence of a preaxial crest on the lateral surface precludes referral to Drepanosauromorpha (Pritchard et al. 2015; 152:1). Therefore, we assign TTU-P 11410E to Archosauromorpha.

TTU-P 11277 preserves the distal end of a (right?) humerus and a portion of the midshaft ( Fig. 5E, F). Our description of this specimen is preliminary because we are unable to determine its exact medial-lateral orientation. The distal end of the humerus expands mediolaterally and posteriorly and has two condyles, one descending further distally than the other ( Fig. 5E). The descending condyle (=medial/ulnar?)is smaller and triangular in distal view, whereas the more proximal condyle (=lateral/ radial?) is larger and rectangular in distal view ( Fig. 5F). There is an intercondylar groove that shallows anteroposteriorly and widens mediolaterally from the posterior edge of the distal surface onto the anterior surface. The non-descending condyle has a flat epicondyle, but there is a small ridge on the posterolateral edge of the descending condyle (=entepicondyle?) ( Fig. 5E). The posterior surface is concave on the distally descending condyle. Because of the absence of any epicondylar foramina and the obvious difference in morphology from drepanosauromorph humeri (e.g., the distal condyles are elliptical and the epicondyles are blade-like in drepanosauromorph humeri) we assign TTU-P 11277 to Archosauromorpha. This humerus is identical to the known distal end of a humerus ( UMMP 10604) that has been assigned both to Hesperosuchus agilis Colbert, 1952 (Long and Murry 1995) and a phytosaur ( Case 1929) but is now believed to be shuvosaurid on the basis of an associated femur (personal observation, e.g., proximal end of femur with posteriorly-projecting hook on anteromedial tuber and the absence of an anterolateral tuber on proximal end of femur; Nesbitt 2011; 300:3, 302:1).

Ulna— TTU-P 11386 preserves the expanded proximal end of a left ulna ( Fig. 5G). The olecranon process is elongate and projects further proximally than the rest of the element. The olecranon process is firmly co-ossified to the rest of the ulna, but a suture is visible, indicating that the process is a separate ossification. The large olecranon process is similar to the condition in the stem-sauropodomorph dinosaur Saturnalia tupiniquim Langer et al., 1999 (Langer et al. 2007). A separately-ossified olecranon process is present in the archosauromorphs Protorosaurus speneri Meyer, 1832 and Amotosaurus rotfeldensis Fraser and Rieppel, 2006 ( Ezcurra 2016; 423:1). It is also present in some kannemeyeriiform dicynodonts (e.g., Maisch 2001; 33:1), including the Late Triassic, North American taxon Placerias Camp and Welles, 1956 ( Camp and Welles 1956: fig. 33). However, these taxa differ from TTU-P 11386 because the separate ossification of the olecranon is proportionally much larger than that of TTU-P 11386, comprising more than half the length of the proximal ulna. This ossification in dicynodonts also possesses a large fossa on the medial surface ( Camp and Welles 1956: fig. 33b), whereas this surface is convex in TTU-P 11386. However, a poorly developed or absent olecranon process is the more basal synapsid morphology (Reisz 1986). In TTU-P 11386, the olecranon is attached on the posterior surface of the proximal end at the same level as of the anterodorsallyfacing articular surfaces. The olecranon process is convex posteriorly and thickens proximally on the medial edge ( Fig.5G). There is no lateral tuber (=radius tuber)present on the proximal end of the ulna. Distinct lateral tubera are present in aetosaurs, Revueltosaurus , most paracrocodylomorphs, and early dinosauriforms (Nesbitt 2011; 237). The proximal surface of the element is divisible into three sections: a proximally raised, rounded posterior section, a flat anterolateral surface, and a proximally concave anteromedial surface. The two anterior proximal surfaces are separated by an anteroposteriorly trending ridge. The posterolateral edge of the ulna is rounded, whereas the posteromedial edge of the ulna is formed by a proximodistal ridge. The medial surface of TTU-P 11386 is flat. TTU-P 11386 is triangular in distal view, tapering anteriorly. A proportionately small, separately-ossified olecranon is only present in some archosauromorphs and so we assign TTU-P 11386 to Archosauromorpha.

TANYSTROPHEIDAE Gervais, 1859 sensu Pritchard et al., 2015

Referred Specimens— Femora: TTU-P 11344, complete right femur ( Fig. 5H–J); TTU-P 11281, distal end of right femur ( Fig. 5K, L).

Localities— MOTT 3869 (Boren Quarry); MOTT 3628 (Kirkpatrick Quarry).

Description and Rationale for Assignment— The complete femur ( TTU-P 11344) is approximately 129 mm in length, and when viewed in medial and lateral perspective TTU-P 11344 is nearly straight with only the slightest sigmoid curvature ( Fig. 5H–J). The lack of a proximodorsal incline in the proximal head of the femur is a character state diagnosing a clade comprising the tanystropheids Langobardisaurus Renesto, 1994 , Tanytrachelos Olsen, 1979 , and the Hayden Quarry taxon (Pritchard et al. 2015; 177:1). The proximal surface of TTU-P 11344 is slightly concave ( Fig. 5H). The internal trochanter projects from the proximal end and tapers distally along the ventromedial surface of the shaft of TTU-P 11344 ( Fig. 5J). The posterior trochanter of TTU-P 11344 does not extend as far distally along the ventrolateral shaft as the internal trochanter and is not as wide mediolaterally as the internal trochanter. The posterior and internal trochanters comprise the borders for the intertrochanteric fossa on the ventral surface of the proximal end of TTU-P 11344 ( Fig. 5H). The element tapers distally and both TTU-P 11344 and TTU-P 11281 broaden mediolaterally just proximal to three distal condyles ( Fig.5K). Both specimens preserve a medial and lateral tibial condyle on the ventral side of the distal femur and a fibular condyle on the dorsolateral surface of the lateral tibial condyle ( Fig. 5I, L). There is a fossa present on the medial distal surface of both TTU-P 11344 and TTU-P 11281, between the lateral tibial condyle and the fibular condyle; this depression that extends proximally onto the medial shaft. The lateral tibial condyle is larger than both the medial tibial and fibular condyles in both specimens,and the fibular condyle in both specimens has a flat ventral surface. These character states (e.g., larger lateral tibial condyle and flat ventral surface of fibular condyle) are shared with the Hayden Quarry femora assigned to Archosauromorpha by Pritchard et al. (2015) and are not present in most early archosauriforms. We assign TTU-P 11344 to Tanystropheidae based on the lack of curvature discussed above and tentatively assign TTU-P 11281 to the clade based on the character states present on the distal end.