[D] Byronosaurus jaffei [Su] [sG] [T]
Describer
Norell, Makovicky & Clark, 2000
Time
Cretaceous Late Campanian
Classification
Saurischia Theropoda Tetanurae Coelurosauria Troodontidae
Diet
Carnivore
Fossilsite
Ukhaa Tolgod, Mongolia
Length
1,5 meter
Info
Genus - Typespecies - Skull
Described in the March 2000 issue (published April 17, 2000) of the Journal of Vertebrate Paleontology.
B. jaffei was an extremely lightly built and agile animal with big eyes and relative big brains during the Campanian two were entombed in Mongolian sand dunes. One of the dino specimens was found in 1993 at Ukhaa Tolgod, a rich deposit of fossils in southern Mongolia, a second was unearthed nearby three years later. Included among the remains is a good skull. It is the first troodontid known to have unserrated teeth, like those of birds. Byronosaurus jaffei itself cannot be an ancestor of birds, which evolved some 70 million years earlier, but could have shared a common ancestor with them.
Like its North American reletive, Troodon formosus, Byronosaurus jaffei was a predator of small animals. Its large, forward-facing eyes gave Byronosaurus jaffei a sterioscopic view. Unlike other troodonts, however, Byronosaurus jaffei has a large and sensetive nose, the new dinosaur possesses two birdlike features: teeth that lack steak-knife-like serrations and a chamber in the snout where air enters from the nostrils before passing through to the mouth. Among dinosaurs, troodontids also had large brains relative to their size, approaching the brain-to-size ratio of birds.
Holotype
IGM (Institute of Geology, Mongolia) 100/983, a fragmentary skull and postcranial bones. The skull of IGM 100/983 is preserved in two parts. The rostral fragment and the braincase were found in place adjacent to one another in life position separated by a zone of weathering. The anterior section is composed of the muzzle and articulated mandible which have been mediolaterally flattened. The skull is broken at the anterior margin of the orbits and the three dimensionally preserved braincase is separate. The roof of the braincase is missing, exposing an eroded endocast. Postcranial elements were collected as surface float below the skull along with the partial remains of an ornithomimid (see Makovicky and Norell, 1998 for details). Additional remains were collected during the 1994 and 1995 field seasons as float.
Etymology
Named in honor of Byron Jaffe in recognition of his family’s support for the Mongolian Academy of Sciences-American Museum of Natural History Paleontological Expeditions.
Locality
The type specimen (IGM 100/983) was collected at Ukhaa Tolgod.
Diagnosis
Byronosaurus jaffei can be assigned to the Troodontidae on the basis of the following combination of derived characters:
1. Numerous tightly packed teeth on the anterior part of the tooth row (Currie, 1987);
2. Maxillary participation in the posterior margin of the nares (Barsbold and Osmolska, 1990) (also present in therizinosaurs [e.g., Erlikosaurus]);
3. Otosphenoidal crest large and prominent (Currie and Zhao , 1994);
4. Dentaries that are roughly triangular in side view with mental foramina in a deep groove (Currie, 1987); and
5. A lacrimal with an elongate anterior process dorsal to the antorbital fossa.
Byronosaurus jaffei can be differentiated from all other troodontids species reported to date on the basis of the following derived characters:
6. Teeth devoid of serrations on the anterior and posterior carinae (also found in Spinosauridae, Pelecanimimus and some basal Avialae);
7. The presence of a large interfenestral bar that is not inset medially from the lateral surface of the maxilla;
8. The presence of a connection between the nasal passage and the antorbital fenestra through the interfenestral bar; and
9. A horizontal groove on the maxilla adjacent, and parallel to the tooth row, containing small foramina.
Referred Specimen
A second specimen (IGM 100/984), collected July 15, 1996 at a locality called Bolor’s Hill, approximately 5 km away from the main Ukhaa Tolgod exposure, can be referred to Byronosaurus jaffei. The fragmentary rostrum preserves some important features not preserved on the type, including a secondary bony palate formed by both the premaxillary and maxillary shelves and the vomer. It is referred to Byronosaurus jaffei on the basis of the derived characters 6, 7, and 8.
Norell, Makovicky & Clark, 2000
Norell, Makovicky & Clark, 2000
Time
Cretaceous Late Campanian
Classification
Saurischia Theropoda Tetanurae Coelurosauria Troodontidae
Diet
Carnivore
Fossilsite
Ukhaa Tolgod, Mongolia
Length
1,5 meter
Info
Genus - Typespecies - Skull
Described in the March 2000 issue (published April 17, 2000) of the Journal of Vertebrate Paleontology.
B. jaffei was an extremely lightly built and agile animal with big eyes and relative big brains during the Campanian two were entombed in Mongolian sand dunes. One of the dino specimens was found in 1993 at Ukhaa Tolgod, a rich deposit of fossils in southern Mongolia, a second was unearthed nearby three years later. Included among the remains is a good skull. It is the first troodontid known to have unserrated teeth, like those of birds. Byronosaurus jaffei itself cannot be an ancestor of birds, which evolved some 70 million years earlier, but could have shared a common ancestor with them.
Like its North American reletive, Troodon formosus, Byronosaurus jaffei was a predator of small animals. Its large, forward-facing eyes gave Byronosaurus jaffei a sterioscopic view. Unlike other troodonts, however, Byronosaurus jaffei has a large and sensetive nose, the new dinosaur possesses two birdlike features: teeth that lack steak-knife-like serrations and a chamber in the snout where air enters from the nostrils before passing through to the mouth. Among dinosaurs, troodontids also had large brains relative to their size, approaching the brain-to-size ratio of birds.
Holotype
IGM (Institute of Geology, Mongolia) 100/983, a fragmentary skull and postcranial bones. The skull of IGM 100/983 is preserved in two parts. The rostral fragment and the braincase were found in place adjacent to one another in life position separated by a zone of weathering. The anterior section is composed of the muzzle and articulated mandible which have been mediolaterally flattened. The skull is broken at the anterior margin of the orbits and the three dimensionally preserved braincase is separate. The roof of the braincase is missing, exposing an eroded endocast. Postcranial elements were collected as surface float below the skull along with the partial remains of an ornithomimid (see Makovicky and Norell, 1998 for details). Additional remains were collected during the 1994 and 1995 field seasons as float.
Etymology
Named in honor of Byron Jaffe in recognition of his family’s support for the Mongolian Academy of Sciences-American Museum of Natural History Paleontological Expeditions.
Locality
The type specimen (IGM 100/983) was collected at Ukhaa Tolgod.
Diagnosis
Byronosaurus jaffei can be assigned to the Troodontidae on the basis of the following combination of derived characters:
1. Numerous tightly packed teeth on the anterior part of the tooth row (Currie, 1987);
2. Maxillary participation in the posterior margin of the nares (Barsbold and Osmolska, 1990) (also present in therizinosaurs [e.g., Erlikosaurus]);
3. Otosphenoidal crest large and prominent (Currie and Zhao , 1994);
4. Dentaries that are roughly triangular in side view with mental foramina in a deep groove (Currie, 1987); and
5. A lacrimal with an elongate anterior process dorsal to the antorbital fossa.
Byronosaurus jaffei can be differentiated from all other troodontids species reported to date on the basis of the following derived characters:
6. Teeth devoid of serrations on the anterior and posterior carinae (also found in Spinosauridae, Pelecanimimus and some basal Avialae);
7. The presence of a large interfenestral bar that is not inset medially from the lateral surface of the maxilla;
8. The presence of a connection between the nasal passage and the antorbital fenestra through the interfenestral bar; and
9. A horizontal groove on the maxilla adjacent, and parallel to the tooth row, containing small foramina.
Referred Specimen
A second specimen (IGM 100/984), collected July 15, 1996 at a locality called Bolor’s Hill, approximately 5 km away from the main Ukhaa Tolgod exposure, can be referred to Byronosaurus jaffei. The fragmentary rostrum preserves some important features not preserved on the type, including a secondary bony palate formed by both the premaxillary and maxillary shelves and the vomer. It is referred to Byronosaurus jaffei on the basis of the derived characters 6, 7, and 8.
Norell, Makovicky & Clark, 2000