Byronosaurus

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Byronosaurus
Temporal range: Late Cretaceous, 80–75  Ma
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Byronosaurus jaffei headden.jpg
Diagram showing known remains
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: Troodontidae
Subfamily: Troodontinae
Genus: Byronosaurus
Norell, Makovicky & Clark, 2000
Species:
B. jaffei
Binomial name
Byronosaurus jaffei
Norell, Makovicky & Clark, 2000

Byronosaurus is a genus of troodontid dinosaur from the Late Cretaceous Period of Mongolia.

Contents

Discovery and naming

In 1993, Michael Novacek, a member of an American Museum of Natural History expedition to the Gobi Desert, discovered the skeleton of a small theropod at Ukhaa Tolgod. This was further excavated in 1994 and 1995. The find was illustrated in a publication in 1994. [1] On 15 July 1996, at the Bolor's Hill site, about eight kilometers (five miles) away from the original location, a second specimen was discovered, a skull.

In 2000, Mark Norell, Peter Makovicky and James Clark named and described the type species Byronosaurus jaffei. The species name as a whole honoured Byron Jaffe, "in recognition of his family's support for the Mongolian Academy of Sciences-American Museum of Natural History Paleontological Expeditions". [2]

The holotype, IGM 100/983, was found in a layer of the Djadochta Formation dating from the late Campanian. It consists of a partial skeleton with skull. It contains a partial skull with lower jaws, three neck vertebrae, three back vertebrae, a piece of a sacral vertebra, four partial tail vertebrae, ribs, the lower end of a thighbone, the upper ends of a shinbone and calf bone, a second metatarsal and three toe phalanges. The paratype, specimen IGM 100/984, is the skull found in 1996, of which only the snout has been preserved. Both specimens are of adult individuals. [2]

In 2003, the type specimen of Byronosaurus was described in detail. Makovicky and his colleagues found that Byronosaurus had a pneumatised snout with a sinus in each maxilla. [3]

In 2009, two front skulls and lower jaws of very young, perhaps newly hatched, individuals, specimens IGM 100/972 and IGM 100/974, were referred to Byronosaurus, after originally having been identified as Velociraptor exemplars. Bever and Norell estimated that the skull length of IGM 100/972 and IGM 100/974 were about 22.6 cm (8.9 in) and 25.4 cm (10.0 in), respectively. [4]

In 2017, the researchers who described a troodontid Almas ukhaa suggested that the specimens described by Bever and Norell (2009) don't belong to Byronosaurus based on different features found in the skull such as the number of maxillary teeth in both specimens being significantly fewer than this genus. They argued that these specimens are more closely related to A. ukhaa than to B. jaffei. [5]

Description

Life restoration Byronosaurus.jpg
Life restoration

Byronosaurus was a small dinosaur, measuring about 1.5–2 m (4.9–6.6 ft) long and 50 cm (20 in) tall; it weighed only about 4–20 kg (8.8–44.1 lb). [6] [7] Unlike most other troodontids, its teeth seem to lack serrations just like its closest relative Xixiasaurus , probably a plesiomorphic trait among troodontids. [4] [8] The Ukhaa perinates show that Byronosaurus had a buccal maxillary groove and a recessed interfenestral bar. [4]

Classification

Maxillae of Byronosaurus compared with relatives Paraves maxillae.jpg
Maxillae of Byronosaurus compared with relatives

The following cladogram shows the position of Byronosaurus within Troodontidae according to a 2017 analysis by the palaeontologist Caizhi Shen and colleagues: [9]

MPC-D 100/44

Byronosaurus jaffei

Xixiasaurus henanensis

GM 100/1323 (now Almas ukhaa )

GM 100/1126

Jinfengopteryx elegans

Mei long

Sinovenator changii

Daliansaurus liaoningensis

Sinusonasus magnodens

Sinornithoides youngi

Troodon formosus

Zanabazar junior

Saurornithoides mongoliensis

Palaeobiology

Troodontids had some of the highest encephalization quotients (a measure of the ratio between actual brain size and the brain size predicted from body size) among non-avian dinosaurs. As suggested by their large eye-sockets and well-developed middle-ears, they appear to have had keen senses. They also had proportionately long legs, which indicates they were agile. [10] [8]

Diet

Comparison of troodontid teeth; L is Byronosaurus Troodontid teeth.jpg
Comparison of troodontid teeth; L is Byronosaurus

Due to their large brains, possible stereoscopic vision, grasping hands, and enlarged sickle-claws, troodontids were generally assumed to have been predatory. In 1998, the palaeontologist Thomas R. Holtz and colleagues pointed out that the serrations on the teeth of troodontids were different from those of typical, carnivorous theropods in their large size and wide spacing, which is similar to the condition in herbivorous dinosaurs (including therizinosaurid theropods) and lizards rather than carnivorous dinosaurs. They suggested that this difference in coarseness may be related to the size and resistance of plant and meat fibres, and that troodontids may have been herbivorous or omnivorous. They also pointed out that some features that had been interpreted as predatory adaptations in troodontids were also found in herbivorous and omnivorous animals, such as primates and raccoons. [11] [8]

In 2001, the palaeontologists Philip J. Currie and Dong Zhiming rejected the idea that troodontids could have been herbivorous. They stated that troodontid anatomy was consistent with a carnivorous lifestyle, and pointed out that the structure of their serrations was not much different from those of other theropods. They noted that troodontid features such as sharply pointed serrations that curved up towards the tip of the teeth, razor sharp enamel between the serrations, and blood grooves at the bases, were not seen in herbivorous dinosaurs, which had simpler, cone shaped serrations. [12] Lü and colleagues discussed the previous studies of troodontid diet, and suggested that the loss of serrations in the teeth of Byronosaurus and some other troodontids was related to a change in their diet. Since the teeth would appear to have lost their typical ability to slice meat, at least these troodontids may therefore have been either herbivorous or omnivorous. [8] In 2015, the palaeontologist Christophe Hendrickx and colleagues suggested that basal (or "primitive") troodontids with unserrated teeth were herbivorous, whereas more derived troodontids with serrated teeth were carnivorous or omnivorous. [13]

Reproduction

Hatchling specimen IGM 100/972 at the AMNH Dromaeosaurid juvenile AMNH 28506 cast.jpg
Hatchling specimen IGM 100/972 at the AMNH

Mark Norell and colleagues described two "perinate" (hatchlings or embryos close to hatching) specimens of Byronosaurus (specimens IGM 100/972 and IGM 100/974) in 1994. The two specimens were found in a nest of oviraptorid eggs in the Late Cretaceous "Flaming Cliffs" of the Djadochta Formation of Mongolia. The nest is quite certainly that of an oviraptorosaur, since an oviraptorid embryo is still preserved inside one of the eggs. The two partial skulls were first described by Norell et al. (1994) as dromaeosaurids, but reassigned to Byronosaurus after further study. [4] [14] [15] The juvenile skulls were either from hatchlings or embryos, and fragments of eggshell are adhered to them although it seems to be oviraptorid eggshell.

The presence of tiny Byronosaurus skulls in an oviraptorid nest was considered an enigma. Hypotheses explaining how they came to be there included that they were the prey of the adult oviraptorid, that they were there to prey on oviraptorid hatchlings, or that an adult Byronosaurus may have laid eggs in a Citipati nest (see nest parasite). [14] However, these interpretations have all been shown to not be the case. In 2011, Norell stated that the Byronosaurus nest was found two metres uphill from the oviraptorid nest, with the oviraptorid nest at the end of a drainage course from the Byronosaurus nest, suggesting that the baby Byronosaurus skulls must have been washed from one nest to the other. [16] This claim has been already confirmed in 2005 by Gerald Grellet-Tinner who noted the presence of a troodontid nest (IGM 100/1003x) close to the Citipati nest containing the juvenile troodontid skulls. [17] Norell is officially preparing to publish this information with more important details. [16]

Not only is the claim regarding nest parasitism considered dubious, but other researchers have pointed out the differences in skull morphology, suggesting that these specimens do not belong to this genus. [5] The eggs of Byronosaurus and other troodontids are not paired unlike oviraptorids like Citipati, but are "nearly vertically embedded with their round poles" up and are exposed barely above the sediment. [18]

See also

Related Research Articles

<i>Deinonychus</i> Genus of theropod dinosaur

Deinonychus is a genus of dromaeosaurid theropod dinosaur with one described species, Deinonychus antirrhopus. This species, which could grow up to 3.4 meters (11 ft) long, lived during the early Cretaceous Period, about 115–108 million years ago. Fossils have been recovered from the U.S. states of Montana, Utah, Wyoming, and Oklahoma, in rocks of the Cloverly Formation and Antlers Formation, though teeth that may belong to Deinonychus have been found much farther east in Maryland.

<span class="mw-page-title-main">Troodontidae</span> Extinct family of bird-like dinosaurs

Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discoveries of complete and articulated specimens, have helped to increase understanding about this group. Anatomical studies, particularly studies of the most primitive troodontids, like Sinovenator, demonstrate striking anatomical similarities with Archaeopteryx and primitive dromaeosaurids, and demonstrate that they are relatives comprising a clade called Paraves.

<i>Oviraptor</i> Extinct genus of dinosaurs

Oviraptor is a genus of oviraptorid dinosaur that lived in Asia during the Late Cretaceous period. The first remains were collected from the Djadokhta Formation of Mongolia in 1923 during a paleontological expedition led by Roy Chapman Andrews, and in the following year the genus and type species Oviraptor philoceratops were named by Henry Fairfield Osborn. The genus name refers to the initial thought of egg-stealing habits, and the specific name was intended to reinforce this view indicating a preference over ceratopsian eggs. Despite the fact that numerous specimens have been referred to the genus, Oviraptor is only known from a single partial skeleton regarded as the holotype, as well as a nest of about fifteen eggs and several small fragments from a juvenile.

<span class="mw-page-title-main">Deinonychosauria</span> Extinct clade of dinosaurs

Deinonychosauria is a clade of paravian dinosaurs which lived from the Late Jurassic to the Late Cretaceous periods. Fossils have been found across the globe in North America, Europe, Africa, Asia, South America, and Antarctica, with fossilized teeth giving credence to the possibility that they inhabited Australia as well. This group of dinosaurs are known for their sickle-shaped toe claws and features in the shoulder bones.

<span class="mw-page-title-main">Oviraptoridae</span> Extinct family of dinosaurs

Oviraptoridae is a group of bird-like, herbivorous and omnivorous maniraptoran dinosaurs. Oviraptorids are characterized by their toothless, parrot-like beaks and, in some cases, elaborate crests. They were generally small, measuring between one and two metres long in most cases, though some possible oviraptorids were enormous. Oviraptorids are currently known only from the Late Cretaceous of Asia, with the most well-known species and complete specimens found only in the Gobi Desert of Mongolia and northwestern China.

<i>Khaan</i> Extinct genus of dinosaurs

Khaan was an oviraptorid dinosaur that was found in the Djadochta Formation of Mongolia and lived in the Late Cretaceous Period (Campanian), 75-71 million years ago.

<i>Saurornithoides</i> Extinct genus of dinosaurs

Saurornithoides is a genus of troodontid maniraptoran dinosaur, which lived during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing. The name is derived from the Greek stems saur~ (lizard), ornith~ (bird) and eides (form), referring to its bird-like skull.

<i>Archaeornithoides</i> Extinct genus of dinosaurs

Archaeornithoides is a genus of maniraptoran theropod dinosaur of the Late Cretaceous of Mongolia.

<i>Conchoraptor</i> Extinct genus of dinosaurs

Conchoraptor is a genus of oviraptorid dinosaurs that lived in Asia during the Late Cretaceous epoch, about 70 million years ago. It is known from the Barun Goyot and Nemegt formations of Mongolia.

<i>Sinornithoides</i> Extinct genus of dinosaurs

Sinornithoides is a genus of troodontid theropod dinosaurs containing the single species Sinornithoides youngi. S. youngi lived during the Early Cretaceous. It measured approximately one meter long (3.3 ft). It lived in Inner Mongolia, China, and probably ate invertebrates and other small prey. They lived in what is now Mongolia, which was part of Laurasia.

<i>Citipati</i> Genus of oviraptorid dinosaur

Citipati is a genus of oviraptorid dinosaur that lived in Asia during the Late Cretaceous period, about 75 million to 71 million years ago. It is mainly known from the Ukhaa Tolgod locality at the Djadochta Formation, where the first remains were collected during the 1990s. The genus and type species Citipati osmolskae were named and described in 2001. A second species from the adjacent Zamyn Khondt locality may also exist. Citipati is one of the best-known oviraptorids thanks to a number of well-preserved specimens, including individuals found in brooding positions atop nests of eggs, though most of them were initially referred to the related Oviraptor. These nesting specimens have helped to solidify the link between non-avian dinosaurs and birds.

<i>Nemegtomaia</i> Extinct genus of dinosaurs

Nemegtomaia is a genus of oviraptorid dinosaur from what is now Mongolia that lived in the Late Cretaceous Period, about 70 million years ago. The first specimen was found in 1996, and became the basis of the new genus and species N. barsboldi in 2004. The original genus name was Nemegtia, but this was changed to Nemegtomaia in 2005, as the former name was preoccupied. The first part of the generic name refers to the Nemegt Basin, where the animal was found, and the second part means "good mother", in reference to the fact that oviraptorids are known to have brooded their eggs. The specific name honours the palaeontologist Rinchen Barsbold. Two more specimens were found in 2007, one of which was found on top of a nest with eggs, but the dinosaur had received its genus name before it was found associated with eggs.

<span class="mw-page-title-main">Djadochta Formation</span> Geologic formation in Mongolia

The Djadochta Formation is a highly fossiliferous geological formation situated in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 million to 71 million years ago. The type locality is the Bayn Dzak locality, famously known as the Flaming Cliffs. Reptile and mammal remains are among the fossils recovered from the formation.

<i>Tsaagan</i> Extinct genus of dinosaurs

Tsaagan is a genus of dromaeosaurid dinosaur from the Djadokhta Formation of the Late Cretaceous of Mongolia.

<i>Minotaurasaurus</i> Extinct genus of dinosaurs

Minotaurasaurus is a monospecific genus of ankylosaurid dinosaur that lived in Mongolia during the Late Cretaceous in what is now the Djadochta Formation. The type and only species, Minotaurasaurus ramachandrani, is known from two skulls, a cervical vertebra and a cervical half ring. It was named and described in 2009 by Clifford Miles and Clark Miles. The first fossils of Minotaurasaurus were illegally exported out of Mongolia.It has been suggested to be a synonym of Tarchia but more recent publications consider it as a distinct genus.

<i>Xixiasaurus</i> Genus of dinosaur

Xixiasaurus is a genus of troodontid dinosaur that lived during the Late Cretaceous Period in what is now China. The only known specimen was discovered in Xixia County, Henan Province, in central China, and became the holotype of the new genus and species Xixiasaurus henanensis in 2010. The names refer to the areas of discovery, and can be translated as "Henan Xixia lizard". The specimen consists of an almost complete skull, part of the lower jaw, and teeth, as well as a partial right forelimb.

<span class="mw-page-title-main">Jinfengopteryginae</span> Extinct subfamily of dinosaurs

Jinfengopteryginae is a subfamily of bird-like theropod dinosaurs known from the Cretaceous of Eurasia. This group includes relatively few genera, with members discovered in 2005 but the name erected in 2012. Like other troodontids, this group of dinosaurs resided in the Paraves potentially close to the Avialae.

Mark Allen Norell is an American vertebrate paleontologist. He is currently the chairman of paleontology and a research associate at the American Museum of Natural History. He is best known as the discoverer of the first theropod embryo and for the description of feathered dinosaurs. Norell is credited with the naming of the genera Apsaravis, Byronosaurus, Citipati, Tsaagan, and Achillobator. His work regularly appears in major scientific journals and was listed by Time magazine as one of the ten most significant science stories of 1993, 1994 and 1996.

<span class="mw-page-title-main">Timeline of troodontid research</span> Events in the history of paleontology

This timeline of troodontid research is a chronological listing of events in the history of paleontology focused on the troodontids, a group of bird-like theropod dinosaurs including animals like Troodon. Troodontid remains were among the first dinosaur fossils to be reported from North America after paleontologists began performing research on the continent, specifically the genus Troodon itself. Since the type specimen of this genus was only a tooth and Troodon teeth are unusually similar to those of the unrelated thick-headed pachycephalosaurs, Troodon and its relatives would be embroiled in taxonomic confusion for over a century. Troodon was finally recognized as distinct from the pachycephalosaurs by Phil Currie in 1987. By that time many other species now recognized as troodontid had been discovered but had been classified in the family Saurornithoididae. Since these families were the same but the Troodontidae named first, it carries scientific legitimacy.

<i>Almas ukhaa</i> Genus of reptiles (fossil)

Almas is a genus of troodontid theropod dinosaur from the Late Cretaceous of Mongolia. It contains a single species, Almas ukhaa, named in 2017 by Pei Rui and colleagues, based on a partial articulated skeleton. The only known specimen was found in the Djadochta Formation, which is late Campanian in age.

References

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