| Coahuilasaurus | |
|---|---|
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| Holotype photographs and line drawings | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Family: | †Hadrosauridae |
| Subfamily: | †Saurolophinae |
| Tribe: | †Kritosaurini |
| Genus: | †Coahuilasaurus Longrich et al., 2024 |
| Type species | |
| †Coahuilasaurus lipani Longrich et al.,2024 | |
Coahuilasaurus (meaning "Coahuila lizard") is an extinctgenus ofkritosaurinornithopod dinosaur from theLate Cretaceous (Campanian)Cerro del Pueblo Formation ofCoahuila, Mexico. The genus contains asingle species,C. lipani, known from the associated tips of the upper and lower jaw and other fragmentary skull bones. It is a large kritosaurin with an estimated body length of 8–9 metres (26–30 ft) and body mass of over 4 metric tons (4.4 short tons).[1][2]
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The holotype specimen, IGM 6685, is a partial skull. It was originally thought to belong to the same genus as PASAC 1, a large unnamed specimen known as the "Sabinas hadrosaurid", but this referral was later rejected. IGM 6685 was later referred to as a specimen ofKritosaurus.[3]
IGM 6685 was later named as a new genus and species of kritosaurin hadrosaurid in 2024. The generic name,Coahuilasaurus, honors the Mexican state of Coahuila, where the fossils were found. The specific name,lipani, honors the Lépai-Ndé or Lipani, a tribe ofApache Native Americans known from the area.[1]
Longrich et al. addedCoahuilasaurus to aphylogenetic analysis which found it to be a member of the Kritosaurini, while the Sabinas hadrosaur was found to be a member ofSaurolophini. A cladogram adapted from that analysis is shown below:[1]
TheCerro del Pueblo Formation is the oldest member of theDifunta Group, which is believed to have been deposited in theCampanian.[4][5][6] It is primarily made up of alternating layers ofsiltstones,sandstones, and grayshales. These rocks preservefluvial,lacustrine,coastal, andshallowmarine ecosystems. The shale layers primarily preserve marineinvertebrates such asammonites andgastropods and they interbedded with sandstone and siltstone layers, suggesting that sea levels were fluctuating over the time that the formation was deposited. The terrestrial deposits, in which the contemporary ornithomimosaurParaxenisaurus was found, are believed to represent a coastalfloodplain on the margin of anestuary. The presence of a diverse array of crocodiles, turtles, and freshwaterbivalves suggests a heavily vegetated riverine ecosystem. The abundance of dinosaur teeth and bone fragments also suggests that the region was replete with vegetation and supported a diverse assemblage ofmegafauna.[6]
Dinosaur remains are abundant in theCerro del Pueblo Formation, but most of the known remains are very incomplete. Many of these dinosaurs are known only from teeth, and are therefore very difficult to assign to any specificgenera. Teeth fromtheropods are very common and have shown thattyrannosaurids,dromaeosaurids,troodontids,[7] andcaenagnathids[8] lived in this environment in addition to the above-mentioned ornithomimosaurs.
Ornithischians were also common and diverse in the ecosystem, much like the contemporaneousDinosaur Park,Two Medicine,Kaiparowits, andKirtland formations.[7]Hadrosaur remains are the most common dinosaur fossil material found in the Cerro del Pueblo, being known fromvertebrae, limb bones,jawbones, teeth, and shoulder bones.[7] Some of these taxa have been named and described, such asTlatolophus,Velafrons, andLatirhinus,[9] but most remains have yet to be formally named or described, and additional species may have existed.[7]Ankylosaurs are represented by several unnamed taxa, andceratopsids likeCoahuilaceratops are known to have coexisted with bothchasmosaurines andcentrosaurines. Fossilized footprints from some kind ofpterosaur are also known from this formation.[7]
Like mostfluvialsediments from theCampanian ofLaramidia, the Cerro del Pueblo Formation was home to a wide array ofturtles includingpleurodires,paracryptodires,cheloniids,kinosternids, andtrionychids. These would have coexisted with bothgoniopholids andeusuchiancrocodyliformes in both freshwater and saltwater environments. There is also some evidence of snakes from this environment. Microfossils have also preservedgastropods,ammonites,bivalves, and other invertebrates.[6]
