Құрып кеткен динозаврлар туысы: Aletopelta коомбси

Extinct genus of dinosaurs

Aletopelta (/ə/,/l//iː//t//oʊ /'/p//ɛ//l//t//ə// /'/k//oʊ//m//z//i/; meaning 'wanderer shield') is a monospecific genus of basal ankylosaurid dinosaur from Southern California that lived during the Late Cretaceous (upper Campanian stage, 75.5 Ma) in what is now the Point Loma Formation. The type and only species, Aletopelta coombsi, is known from a partial skeleton preserving osteoderms. It was originally described in 1996 by W. P. Coombs, Jr. and T. A. Deméré before being named in 2001 by Tracy Ford and James Kirkland. Aletopelta has an estimated size of 5 metres (16 feet) and weight of 2 tonnes (4,409 lbs). The holotype formed a miniature reef and was scavenged upon by invertebrates and sharks.

In 1987, construction work was done on the College Boulevard near Carlsbad at the Californian coast. While paleontologically surveying the work, Bradford Riney noted that a skeleton had been uncovered by a ditch dug for a sewage pipe. Within days, the specimen was secured by the San Diego Natural History Museum. It was dubbed the "Carlsbad Ankylosaur". The skeleton was later described, but not named, in 1996 by Thomas Deméré and Walter Preston Coombs before being named in 2001 by Tracy Lee Ford and James Kirkland. The skeleton originated from a layer of the marine Point Loma Formation which dates to the upper Campanian stage, 75.5 Ma. The formation has yielded specimens pertaining to calcareous nannoplankton, foraminifers, scaphopods, pelecypods, gastropods, cephalopods, ostracods, decapods, echinoids, elasmobranchs, and actinopterygians, with the addition of a femur, right dentary containing teeth and cervical vertebrae of a hadrosaur. The type and only known specimen of Aletopelta was once a bloated carcass that had been washed out to sea, likely by a stream, which sank to the bottom with its underside facing upwards and became a miniature reef, as evidence by Pelecypoda such as Ostrea sp. and Spondylus sp. being attached to the bones and the presence of ammonites and gastropods found in association with the skeleton. The carcass was also scavenged upon by marine invertebrates and sharks such as Squalicorax and Scapanorhynchus, which resulted with most of the long bones being hollow and many shallow pits on the osteoderms and ribs. Ford and Kirkland (2001) originally diagnosed Aletopelta based on the teeth being wider than tall; the femur being much longer than both the tibia and fibula; the presence of three metatarsals; a pelvic shield composed of polygonal, low peaked osteoderms; a large short pointed spike in the shoulder region; the presence of hollow cap like osteoderms across dorsum; the presence of hollow pup tent like osteoderms over neck and shoulders; triangular, dorsally compressed caudal osteoderms that are highly asymmetrical from top to bottom; and hollow and thin osteoderms. Ford & Kirkland (2001) also reinterpreted it as an ankylosaurid and considered it to be taxonomically distinct enough to be warranted as a new genus and species. Arbour & Currie (2015), however, considered it as a valid genus based on new characteristics and found Stegopeltinae to not be a valid clade. Arbour & Currie (2015) additionally recovered Aletopelta within a polytomy containing Liaoningosaurus, Cedarpelta, Chuanqilong and more derived ankylosaurids. A similar position was recovered by Arbour & Evans (2017) and Rivera Sylva et al. (2018) but also placed Hylaeosaurus, Crichtonpelta, Gobisaurus and Shamosaurus within the polytomy. Park et al. (2019) also placed Aletopelta within a polytomy but with the inclusion of Jinyunpelta, Nodosaurus and Kunbarrasaurus. Although most often being recovered as a basal ankylosaurid, Frauenfelder et al. (2022) found it to be the basalmost nodosaurid. The results of a phylogenetic analysis conducted by Arbour & Currie (2015) is reproduced below.