[D] Talos sampsoni [sG] [T]
Describer
Zanno, Varricchio, O\\\'Connor, Titus & Knell 2011
Time
Cretaceous Late Campanian
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Troodontidae
Diet
Carnivore
Fossilsite
Kaiparowits Formation, Utah, US
Info
Abstract
Background
Troodontids are a predominantly small-bodied group of feathered theropod dinosaurs notable for their close evolutionary relationship with Avialae. Despite a diverse Asian representation with remarkable growth in recent years, the North American record of the clade remains poor, with only one controversial species Troodon formosus presently known from substantial skeletal remains.
Methodology/Principal Findings
Here we report a gracile new troodontid theropod Talos sampsoni gen. et sp. nov. from the Upper Cretaceous Kaiparowits Formation, Utah, USA, representing one of the most complete troodontid skeletons described from North America to date. Histological assessment of the holotype specimen indicates that the adult body size of Talos was notably smaller than that of the contemporary genus Troodon. Phylogenetic analysis recovers Talos as a member of a derived, latest Cretaceous subclade, minimally containing Troodon, Saurornithoides, and Zanabazar. MicroCT scans reveal extreme pathological remodeling on pedal phalanx II-1 of the holotype specimen likely resulting from physical trauma and subsequent infectious processes.
Conclusion/Significance
Talos sampsoni adds to the singularity of the Kaiparowits Formation dinosaur fauna, which is represented by at least 10 previously unrecognized species including the recently named ceratopsids Utahceratops and Kosmoceratops, the hadrosaurine Gryposaurus monumentensis, the tyrannosaurid Teratophoneus, and the oviraptorosaurian Hagryphus. The presence of a distinct troodontid taxon in the Kaiparowits Formation supports the hypothesis that late Campanian dinosaurs of the Western Interior Basin exhibited restricted geographic ranges and suggests that the taxonomic diversity of Late Cretaceous troodontids from North America is currently underestimated. An apparent traumatic injury to the foot of Talos with evidence of subsequent healing sheds new light on the paleobiology of deinonychosaurians by bolstering functional interpretations of prey grapp ling and/or intraspecific combat for the second pedal digit, and supporting trackway evidence indicating a minimal role in weight bearing.
Etymology
Talos, (Greek) referring to the mythological, fleetfooted protector of Crete, often depicted as winged, who succumbed to a wound on the ankle. The name is also a play on the English word ‘‘talon’’ meaning a sharply hooked claw. The specific epithet honors Scott D. Sampson, architect of the Kaiparowits Basin Project.
Holotype
UMNH VP 19479, partial postcranial skeleton, including fragmentary portions of the dorsal, sacral, and caudal axial column, left ulna, additional forelimb fragments, a partial pelvis, and partial left and right hind limbs.
Type Horizon, Locality, and Age
UMNH VP 19479 was collected in Grand Staircase-Escalante National Monument from a region known as ‘‘The Blues,’’ within the northern portion of the Kaiparowits Plateau. The specimen was entombed in a lightgreenish gray siltstone/fine sandstone unit exposed in the middle portion of the ‘‘middle unit’’ of the Kaiparowits Formation, approximately 260 meters above the base. Small freshwater gastropod and bivalve shells (not collected) were observed associated with the skeleton and support the interpretation of the type horizon as overbank or possibly crevasse splay. A couple of small fragments of compactituberculate ornamented dinosaur eggshell were also observed at the locality. Small, 1–2 cm diameter calcium carbonate pedogenic nodules present at the bone level, as well as the blocky weathering nature of the host matrix, indicate that the horizon was a hypomature paleosol by the time it was buried deep enough to be isolated from soil forming processes. A bentonite located approximately 185 meters above the base of the Kaiparowits in this area (75 meters below the specimen) yielded a single crystal 40Ar/39Ar date of 75.95 +/2 0.18 Ma, indicating a late Campanian age for UMNH VP 19479.
Diagnosis
A troodontid dinosaur exhibiting the following combination of characters (autapomorphies marked with asterisk): acetabular margin of ischium strongly concave dorsally; notch between lateral condyle and ascending process of astragalus in lateral view, poorly developed intercondylar bridge of astragalus hyperconstricted proximal groove separating astragalar body and ascending process craniocaudally wide and v-shaped cranioproximal groove on astragalar condyles absent; astragalar condyles subequal in cranial extent; shaft of metatarsal II markedly compressed (midshaft length-to-transverse width ratio 38.8; metatarsal III distally ginglymoid; pronounced, rounded tab on dorsolateral aspect of metatarsal III proximal to distal condyle distal corner of lateral collateral ligament pit on metatarsal IV with small protuberance, creating rounded depression between extensor aspects of distal condyles.
Zanno, Varricchio, O\\\'Connor, Titus & Knell 2011
Time
Cretaceous Late Campanian
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Troodontidae
Diet
Carnivore
Fossilsite
Kaiparowits Formation, Utah, US
Info
Abstract
Background
Troodontids are a predominantly small-bodied group of feathered theropod dinosaurs notable for their close evolutionary relationship with Avialae. Despite a diverse Asian representation with remarkable growth in recent years, the North American record of the clade remains poor, with only one controversial species Troodon formosus presently known from substantial skeletal remains.
Methodology/Principal Findings
Here we report a gracile new troodontid theropod Talos sampsoni gen. et sp. nov. from the Upper Cretaceous Kaiparowits Formation, Utah, USA, representing one of the most complete troodontid skeletons described from North America to date. Histological assessment of the holotype specimen indicates that the adult body size of Talos was notably smaller than that of the contemporary genus Troodon. Phylogenetic analysis recovers Talos as a member of a derived, latest Cretaceous subclade, minimally containing Troodon, Saurornithoides, and Zanabazar. MicroCT scans reveal extreme pathological remodeling on pedal phalanx II-1 of the holotype specimen likely resulting from physical trauma and subsequent infectious processes.
Conclusion/Significance
Talos sampsoni adds to the singularity of the Kaiparowits Formation dinosaur fauna, which is represented by at least 10 previously unrecognized species including the recently named ceratopsids Utahceratops and Kosmoceratops, the hadrosaurine Gryposaurus monumentensis, the tyrannosaurid Teratophoneus, and the oviraptorosaurian Hagryphus. The presence of a distinct troodontid taxon in the Kaiparowits Formation supports the hypothesis that late Campanian dinosaurs of the Western Interior Basin exhibited restricted geographic ranges and suggests that the taxonomic diversity of Late Cretaceous troodontids from North America is currently underestimated. An apparent traumatic injury to the foot of Talos with evidence of subsequent healing sheds new light on the paleobiology of deinonychosaurians by bolstering functional interpretations of prey grapp ling and/or intraspecific combat for the second pedal digit, and supporting trackway evidence indicating a minimal role in weight bearing.
Etymology
Talos, (Greek) referring to the mythological, fleetfooted protector of Crete, often depicted as winged, who succumbed to a wound on the ankle. The name is also a play on the English word ‘‘talon’’ meaning a sharply hooked claw. The specific epithet honors Scott D. Sampson, architect of the Kaiparowits Basin Project.
Holotype
UMNH VP 19479, partial postcranial skeleton, including fragmentary portions of the dorsal, sacral, and caudal axial column, left ulna, additional forelimb fragments, a partial pelvis, and partial left and right hind limbs.
Type Horizon, Locality, and Age
UMNH VP 19479 was collected in Grand Staircase-Escalante National Monument from a region known as ‘‘The Blues,’’ within the northern portion of the Kaiparowits Plateau. The specimen was entombed in a lightgreenish gray siltstone/fine sandstone unit exposed in the middle portion of the ‘‘middle unit’’ of the Kaiparowits Formation, approximately 260 meters above the base. Small freshwater gastropod and bivalve shells (not collected) were observed associated with the skeleton and support the interpretation of the type horizon as overbank or possibly crevasse splay. A couple of small fragments of compactituberculate ornamented dinosaur eggshell were also observed at the locality. Small, 1–2 cm diameter calcium carbonate pedogenic nodules present at the bone level, as well as the blocky weathering nature of the host matrix, indicate that the horizon was a hypomature paleosol by the time it was buried deep enough to be isolated from soil forming processes. A bentonite located approximately 185 meters above the base of the Kaiparowits in this area (75 meters below the specimen) yielded a single crystal 40Ar/39Ar date of 75.95 +/2 0.18 Ma, indicating a late Campanian age for UMNH VP 19479.
Diagnosis
A troodontid dinosaur exhibiting the following combination of characters (autapomorphies marked with asterisk): acetabular margin of ischium strongly concave dorsally; notch between lateral condyle and ascending process of astragalus in lateral view, poorly developed intercondylar bridge of astragalus hyperconstricted proximal groove separating astragalar body and ascending process craniocaudally wide and v-shaped cranioproximal groove on astragalar condyles absent; astragalar condyles subequal in cranial extent; shaft of metatarsal II markedly compressed (midshaft length-to-transverse width ratio 38.8; metatarsal III distally ginglymoid; pronounced, rounded tab on dorsolateral aspect of metatarsal III proximal to distal condyle distal corner of lateral collateral ligament pit on metatarsal IV with small protuberance, creating rounded depression between extensor aspects of distal condyles.