Figure 1.
Skeletal reconstruction of Talos sampsoni (UMNH VP 19479).
Talos is known from the upper Campanian Kaiparowits Formation, southern Utah, USA. Skeletal drawing illustrates the distribution of elements preserved with the holotype (in red). Missing elements based on Troodon formosus and/or Saurornithoides mongoliensis. Drawing © Scott Hartman 2010.
Figure 2.
Stylized stratigraphic section of the middle and lower units of the Kaiparowits Formation [46].
Section indicates relative chronostratigraphic positions of Talos sampsoni UMNH VP 19479, troodontid indet. UMNH VP 16303, and Hagryphus giganteus (UMNH VP 12765). Radiometric dates derived from 40Ar/39Ar dating of bentonites [46], undated bentonite horizons also shown.
Figure 3.
Skeletal elements of Talos and Troodon illustrating select diagnostic characters of Talos sampsoni (UMNH VP 19479).
(A) left astragalus of Talos (on left) and right astragalus of Troodon (on right, reversed, MOR 553S-8.20.92.311) in lateral view, (B) and in proximal view, (C) distal aspect of left metatarsal III of Talos (on left) and Troodon (right two elements, MOR 553S-8.69.406, 7.29.92.113) in extensor view, and (D) distal aspect of left metatarsal IV of Talos (left two elements) and Troodon (on right, reversed, MOR 553S-11.1.01.8) in oblique distal and extensor, and extensor views respectively. Abbreviations: dd, dorsolateral depression on metatarsal IV; dp, dorsolateral tuberosity on metatarsal IV; dg, dorsolateral groove on metatarsal IV; ib, intercondylar bridge on astragalus; ln, lateral notch on astragalus; lt, lateral tab on metatarsal III; pg, proximal groove on astragalus; sc, subequal lateral and medial condyles of astragalus.
Figure 4.
Linear regression of length-to-width ratio in the second and fourth metatarsals of Talos sampsoni and Troodon formosus.
Regressions quantify the taxonomic significance of metatarsal slenderness in the holotype of Talos (UMNH VP 19479) based on transverse width of the second metatarsal (p<0.05) and craniocaudal width of the fourth metatarsal (p<0.05), despite its juvenile ontogenetic stage. Troodon specimens represented: metatarsal II (MOR 553S-7.8.91.28; MOR 553S-7.18.92.5; and MOR 748); metatarsal IV (MOR 553S-11.1.01.8; MOR 553S7.28.8.102; MOR 553S-7.1.9.9, MOR 553S-92.260, MOR 748).
Figure 5.
Axial elements of Talos sampsoni (UMNH VP 19479).
Dorsal vertebra in left lateral (A), caudal (B), and dorsal (E) views; sacral centrum in ventral view (C), and dorsal centrum in ventral view (D). Abbreviations: ipdf, infrapostzygapophyseal fossa; nc, neural canal; ns, neural spine; poz, postzygapophysis; pp, parapophysis; tp, transverse process. Scale bar equals 5 cm.
Figure 6.
Left ulna of Talos sampsoni (UMNH VP 19479).
Ulna in medial (A) and dorsal (B) views. Abbreviations: er, extensor ridge; lc, lateral aspect of the distal condyle condyle; mc, medial aspect of the distal condyle; paf, proximal articular facet. Scale bar equals 5 cm.
Figure 7.
Pelvic girdle elements of Talos sampsoni (UMNH VP 19479).
Right ischium in proximal (A), medial (B), and lateral (C) views; left ischium in medial (D) and lateral (E) views; right (F) and left (G) pubic shafts in cranial view. Abbreviations: ac, acetabulum; cdr, caudolateral ridge; ip, iliac peduncle; op, obturator process; pa, pubic apron; pdt, proximodorsal tuberosity; pp, pubic peduncle. Scale bar equals 10 cm.
Figure 8.
Femur, tibia, and fibula of Talos sampsoni (UMNH VP 19479).
Left femur in lateral view (A); left tibia in cranial view (B); left fibula in lateral view (C). Dotted line illustrates impression of ascending process of ipsilateral astragalus. Abbreviations: ca, caudal aspect; cr, cranial aspect; gt, greater trochanter; lc, lateral condyle; lr, lateral ridge; lt, lesser trochanter; mc, medial condyle; pt, posterior trochanter, ttc, lateral tubercle of trochanteric crest. Scale bar equals 10 cm.
Figure 9.
Tarsal elements of Talos sampsoni (UMNH VP 19479).
Left astragalus in medial (A), cranial (B), lateral (C), and proximal (D) views; left calcaneum in lateral view (E). Abbreviations: ap, ascending process; as, astragalar sulcus; g, groove at base of ascending process; ib, intercondylar bridge; mc, medial condyle; lc, lateral condyle. Scale bar equals 3 cm.
Figure 10.
Articulated pes of Talos sampsoni (UMNH VP 19479).
Digit one reversed from right pes. Abbreviations: DI, digit one; DII, digit two; DIII, digit three; DIV, digit four; MT1, metatarsal one; MT2, metatarsal two; MT3 metatarsal three; MT4, metatarsal four. Scale bar equals 10 mm.
Figure 11.
Metatarsus of Talos sampsoni (UMNH VP 19479).
Right metatarsal I in lateral (G) and medial (H) views; left metatarsal II in extensor (A), medial (B), flexor (C), lateral (D), proximal (E), and distal (F) views; left metatarsal III in extensor (J), medial (K), and distal (I) views; left metatarsal IV in flexor (N), lateral (O), medial (P), proximal (L), and distal (M) views. Abbreviations: lc, lateral condyle, mc, medial condyle; m3t, tab on extensor surface of metatarsal three; m4t, tab on flexor surface of metatarsal four; MT1, metatarsal one; MT2, metatarsal two; MT3 metatarsal three; MT4, metatarsal four. Scale bar equals 10 mm.
Figure 12.
Pedal phalanges of Talos sampsoni (UMNH VP 19479).
Digit one of right pes in lateral (A) and medial (B) views; digit two of left pes in medial (C), lateral (D), and extensor (E) views; digit three of left pes in medial (F), lateral (G), and extensor (H) views; digit four of left pes in medial (I), lateral (J), and extensor (K) views. Abbreviations: er, extensor ridge; dl, dorsal “lip”; ird, dorsal intercondylar ridge; irv, ventral intercondylar ridge; p, pathology; pp, proximal pit; PI-1, first phalanx of digit 1; PI-2, second phalanx of digit 1; PII-1, first phalanx of digit 2; PII-2, second phalanx of digit 2; PII-3, third phalanx of digit 2; PIII-1, first phalanx of digit 3; PIII-2, second phalanx of digit 3; PIII-3, third phalanx of digit 3; PIII-4, fourth phalanx of digit 3; PIV-1, first phalanx of digit 4; PIV-2, second phalanx of digit 4; PIV-3, third phalanx of digit 4; PIV-4, fourth phalanx of digit 4; PIV-5, fifth phalanx of digit 4. Scale bar equals 5 mm.
Figure 13.
Micro-CT renderings of the pathological first phalanx of the left second pedal digit (II-1) of Talos sampsoni (UMNH VP 19479).
Phalanx II-1 in lateral (A, H), flexor (C–D). extensor (F–G) views. Cross-sectional images of Talos taken through axial (B), transverse (E), and parasagittal (I) planes. Hashed lines in A and F represent the plane of section for images in B (1), E (2), and I (3). Anatomical reference lines show position of axial cross section (B) only. Green arrows in B, E, and I depict the boundary between the original cortical contour (shown in purple on C, G, and H) and the exostotic bone. Abbreviations: bc, bony collar; Ic, lateral condyle; mc, medial condyle; oc, original cortical surface.
Figure 14.
Proximal (A) and midshaft (B) histologic cross-sections of the fibula of Talos sampsoni (UMNH VP 19479).
Medullary spaces are towards the bottom. Bands representing slowed growth including lamellar bone and lines of arrested growth are marked with “<”. The proximal section preserves five or six bands, whereas the midshaft has three. The third band of the midshaft section is not represented in this view due to taphonomic loss of the bone periphery. Between these bands, bone consists primarily of fibrolamellar bone with longitudinally oriented osteons. Episodes of endosteal deposition and erosion occur in the medullary regions of both sections. Abbreviations: do, developing osteons; el, endosteal deposition of lamellar bone; fl, fibrolamellar bone; mc, medullary cavity. Scale bars equal 0.3 mm.
Figure 15.
Evolutionary relationships of Talos sampsoni (in red).
Tree illustrates combined topology of six MPTs (Tree Length = 48). Dashed lines indicate equally parsimonious positions for T. sampsoni (three alternates) and Sinovenator changi (two alternates). Node numbers represent support values (black = Bremer; blue = standard bootstrapping, GC values; green = symmetrical resampling, GC values).