| Paralititan | |
|---|---|
 | |
| Humeri (upper arm bones) ofParalititan at theEgyptian Geological Museum | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Clade: | †Titanosauria |
| Clade: | †Lithostrotia |
| Genus: | †Paralititan Smith et al., 2001 |
| Species: | †P. stromeri |
| Binomial name | |
| †Paralititan stromeri Smith et al., 2001 | |
Paralititan (meaning "tidal giant") is agenus ofsauropod dinosaur that lived in present-day Egypt during theLate Cretaceousperiod. It was described by Americanpaleontologist Joshua B. Smith and colleagues in 2001. The genus contains asingle species,Paralititan stromeri, named based on a fragmentary skeleton includingvertebrae andlimb bones. These fossils were unearthed by an American expedition to theBahariya Oasis in western Egypt in rock layers of theBahariya Formation. This formation dates to theCenomanianstage of the Late Cretaceous, which lasted101 to 94 million years ago. An incompletedorsal (back) vertebra that had been described by German paleontologistErnst Stromer in 1932 was also assigned toParalititan. However, this vertebra had been destroyed during theBombing of Munich inWorld War II.
Like other sauropods,Paralititan was afour-legged herbivore with a long neck ending in a small head. It was at one point considered one of the largest dinosaurs known. More recent estimates place it at 27 meters (89 feet) in length and 30 tonnes (33 short tons) in mass. This would make it a large sauropod, but not as huge as genera likeArgentinosaurus andPuertasaurus. Its robusthumerus (upper arm bone) is 1.69 meters (5.5 feet) in length and bears a largedeltopectoral crest (a forward directed bony flange). Thecaudal (tail) vertebrae are wider than tall and lackpleurocoels (large cavities that storedair sacs) on their sides.
Paralititan is a member of theSaltasauridae, afamily within the sauropod groupTitanosauria. Some saltasaurids, includingSaltasaurus itself, preserve dorsalosteoderms (bones formed in the skin), though such bones are unknown forParalititan.Paralititan coexisted with other dinosaurs such as the sauropodAegyptosaurus, thetheropodsTameryraptor,Spinosaurus, andBahariasaurus, and an unnamedabelisaurid theropod. During the Cenomanian, the Bahariya Formation was on the margin of theTethys Sea, and represented a large network ofmangrove swamps,rivers, andtidal flats.
In 1999, researcher Joshua Smith rediscovered a site in theBahariya Oasis of Egypt, known as Gebel el Dist, that had formerly been explored byAustro-HungarianpaleontologistRichard Markgraf between 1912 and 1914.[1][2][3] The fossils that Markgraf found, including those ofdinosaurs likeSpinosaurus andTameryraptor, had been shipped to Germany where they were described by German paleontologistErnst Stromer.[4][5] Markgraf had evidently removed all more complete skeletons, leaving only limited remains behind. In 2000, an American expedition was mounted to revisit the site but failed to find any dinosaur skeletons. At a new site, the nearby Gebel Fagga, the expedition succeeded in locating a partialsauropod skeleton.[6][3]
This incomplete skeleton consists of twosacrals (hip vertebrae, probably the 5th and 6th), the firstcaudal (tail vertebra), another caudal from the front portion of the tail,dorsal and sacral ribs, incompletescapulae (shoulder blades), a complete right and an incomplete lefthumerus (upper arm bone), the lower end of ametacarpal, and several additional elements. All of these fossils were transported to theEgyptian Geological Museum,Cairo and deposited under catalog number CGM 81119. Gebel Fagga and Gebel el Dist are sandstone outcrops of theBahariya Formation, dating to theCenomanianstage of theLate Cretaceousperiod. This makes these fossils around101 to 94 million years ago old.[3]
In 2001, an international crew made up of paleontologist Joshua B. Smith and colleagues described the partial skeleton as a newgenus andspecies of sauropod dinosaur, namedParalititan stromeri. They established this skeleton, CGM 81119, as theholotype (name-bearing) specimen. The generic name,Paralititan, derives from theGreekpara, meaning'near',halos'sea', andtitan, as in theGreek Titans. The specific name is in honor of Stromer, who first established the presence of dinosaur fossils in the Bahariya Oasis during a 1911 expedition.[1][2] The entire name therefore translates to "Stromer's tidal titan" or "Stromer's tidal giant", in reference to the paralictidal flats the dinosaur lived on.[3]
Additionally, Smith and colleagues assigned a large anteriordorsal (vertebra from the front portion of the trunk), cataloged at thePaläontologisches Museum München (Bavarian State Collection of Paleontology) under SNSB-BSPG 1912V11164, toParalititan stromeri. Stromer, in 1932, assumed that this vertebra belonged to an undetermined "Giant Sauropod",[7] but it was destroyed alongside other fossils from the Bahariya Formation during theBombing of Munich inWorld War II.[2][3] Several isolated sauropod fossils, mainly consisting of caudal vertebrae, were assigned by Stromer to the other Bahariya sauropodAegyptosaurus,[7] but these may belong toParalititan instead.[3]
Only 5.1% ofParalititan's skeleton is known,[8] so its exact size is difficult to estimate. The limited material, especially the long humeri, suggested that it was one of the most massive dinosaurs ever discovered, with an estimated weight of 59 t (65 short tons) according to a 2011 study.[9] Joshua Smith, who informally led the research team that foundParalititan, told an interviewer, "It was a truly enormous dinosaur by any reckoning".[10] The complete right humerus measures 1.69 meters (5.5 feet) long which at the time of discovery was the longest known in a Cretaceous sauropod; this was surpassed in 2016 with the discovery of the titanosaurNotocolossus, which includes a 1.76 m (5 ft 9 in) humerus.[11] UsingSaltasaurus as a guide, American paleontologistKenneth Carpenter estimated its length at around 26 m (85 ft) in a 2006 study.[12]
American researcher Scott Hartman estimated that the animal was massive, but still smaller than the biggest titanosaurs such asPuertasaurus,Alamosaurus, andArgentinosaurus.[13] In the 2010 edition of his bookThe Princeton Field Guide to Dinosaurs, American researcherGregory S. Paul estimated its length at 20+ meters (66+ ft), and its weight at 20 tonnes (24.2 short tons).[14] In 2016, using equations that estimate body mass based on the circumference of the humerus and femur of quadrupedal animals, Argentine paleontologist Bernardo González Riga and colleagues gave a weight estimate of ~50 t (55 short tons) forParalititan.[11] In 2019, Paul estimatedParalititan between 30 and 55 tonnes (33–60.6 short tons) in weight.[15]
The sacral vertebrae ofParalititan lackpleurocoels, large spaces in the sides of the vertebra that stored pneumaticair sacs.[3] Air sacs made vertebrae lighter and were part of the respiratory system.[16][17] The absence of pleurocoels on the caudal vertebrae is common amongst titanosaurids, supporting its assignment to the group. One of the proximal (towards body) caudal vertebrae has a wider than tall, procoelouscentrum with a convex reararticularcondyle. In contrast to other titanosaurs likeAlamosaurus andNeuquensaurus, the centrum is not convex on both ends. The ventral (bottom) surface of the centrum has weakly pronounced ridges that border asagittal concavity. The other proximal caudal vertebra found has a stronglyprocoelus centrum with a well-developed distal condyle. Thescapula (shoulder blade) has a medial (inner) concavity that is bordered by a prominent rugosity, like in the titanosaursAeolosaurus,Lirainosaurus, Neuquensaurus, andSaltasaurus. As in thebrachiosauridBrachiosaurus,Paralititan bears a prominent tabularprocess on the caudoventral (rear-bottom) part of the scapula underneath theglenoid socket (the part of the scapula that articulates with the humerus). This feature is only found inBrachiosaurus andParalititan, demonstrating that it is a unique genus of titanosaur.[3]
Paralititan's humerus is huge at 1.69 meters (5.5 feet) in length, with greatly expanded upper and lower ends. The upper region of the proximal surface of the humerus bears a muscular depression (an area for muscle attachment). Thedeltopectoral crest is large, stretching for more than 53% of the length of the humerus. On the proximal surface of the distal end of the humerus is a largefossa (depression) that is bordered by two large ridges, a medial and a lateral one. The lateral ridge in particular expands into atuberosity relatively close to the upper margin of the humerus, as inSaltasaurus andLirainosaurus, whereas the medial ridge, one unique toParalititan, is relatively shorter and does not develop into a tuberosity. At thecondyles (area where the humerus articulates with theulna andradius) at the distal end of the humerus aresupracondylar ridges. These ridges extend over 1/3rd of the humerus' length and flank a largeolecranon fossa (area of the humerus that the ulna's olecranon process articulates), like in other titanosaurs. The metacarpal known fromParalititan has a rectangular, flattened surface indicativephalangeal reduction or absence on this digit. A second sauropod,Aegyptosaurus, is known from the Bahariya Formation.Paralititan differs fromAegyptosaurus in its larger size, possibly in not having pleurocoels in its front tail vertebrae, and in possessing a relatively longer deltopectoral crest on its humerus.[3]
Paralititan belonged to the groupLithostrotia, a group of sauropods that existed during the Cretaceous period in every continent except for Australia.[18][3][19] This group includes a wide array of sauropods, including some of the largest dinosaurs known to ever live such asArgentinosaurus, Patagotitan, andPuertasaurus.Notocolossus andAlamosaurus were comparable in size toParalititan, being 24 m (79 ft)[20] and 26 metres (85 ft) long respectively.[15][21] The position ofParalititan within Lithostrotia has changed; Smith and colleagues (2001) consideredParalititan a member of Titanosauridae, a now unused clade name, alongsideSaltasaurus,Malawisaurus,Opisthocoelicaudia,Epachthosaurus, andAlamosaurus.[3] However, many later studies did not analyze thephylogenetic placement ofParalititan, likely on account of its fragmentary nature.[22] In studies by American paleontologist Kristina Curry Rogers (2005)[23] and British paleontologists Philip D. Mannion and Paul Upchurch (2011),[24]Paralititan was recovered as a basal titanosaurian in their phylogenetic analyses.Paralititan was also found to be distantly related to other African taxa likeMalawisaurus andRukwatitan, making the relationships ofParalititan relative to those of other African titanosaurs convoluted.[22]
In a 2022 phylogenetic analysis, Spanish paleontologist Bernat Villa and colleagues recoveredParalititan in the familySaltasauridae, a group of Asian, African, European, North American, and South American lithostrotian titanosaurs that lived during the Cretaceous period.[25][26][27][28] Some saltasaurids likeSaltasaurus had dorsalosteoderms on their backs,[29] though other saltasaurids likeParalititan have not been discovered with these osteoderms.[3] Based on the study,Paralititan was a member ofSaltasaurinae, a subfamily that is divided in two clades: Saltasaurini, endemic to South America, and an Afro-European clade formed byParalititan andAbditosaurus. The clade containing both the Afro-European and South American clades is backed by twosynapomorphies: divided humeral distal condyles and caudal centra that are wider than tall. Both of these features are found inParalititan.[28]
Below is acladogram by Villa et al. (2022), from the description of the European saltasaurineAbditosaurus.[28]
Theautochthonous (a fossil deposit with remains that were not moved by biological or physical processes), associated holotype skeleton was preserved intidal flat deposits with amangrove vegetation ofseed ferns,Weichselia reticulata, according to the occurrence of plant fossils and root marks in the sediments. The layer in which theParalititan fossils were found indicates a shallow water environment. Additionally, the associated nature of the holotype and presence of a shallow, vegetated tidal flat indicates that the skeleton was autochthonous. An isolatedtooth assigned toCarcharodontosaurus,[3] a genus formerly thought to be present in the Bahariya Formation but now assigned toTameryraptor,[4] was found associated with the skeleton. Smith and colleagues (2001) stated that this is evidence of the holotype being scavenged by a carnivorous dinosaur as the tooth is larger than theclasts that could be transported in the tidal flat channels, indicating that theCarcharodontosaurus individual moved towards the site and shed its tooth there.[3]
This mangrove system bordered theTethys Sea, which transformed the region into amangrove-dominated coastal environment filled with vasttidal flats andwaterways.[30]Paralititan is the first dinosaur demonstrated to have inhabited a mangrovehabitat. Alongside the earlier namedAegyptosaurus,Paralititan is one of the few sauropods known from the Bahariya Formation, alongside the coevaltheropodsBahariasaurus, Tameryraptor, andSpinosaurus, the latter being also known from the Kem Kem beds. AParalititan-sized titanosaur is known from the Kem Kem Beds, however it is only represented by fragmentary remains.[31][32] The faunal composition of both the Bahariya Formation and the Kem Kem Beds were thought to be similar in the past, but the describers ofTameryraptor suggested that such superficial comparisons require further examination.[4] Contemporaryabelisaurid dinosaurs from the Bahariya Formation were also terrestrial carnivores, preying on other terrestrial fauna.[33] A diverse fauna of aquatic animals is known from the Bahariya Formation. Underwater life diversity exploded during this period in the mangroves of North Africa, with turtles represented by thepleurodianApertotemporalis, large bony fish likeMawsonia[34] andParanogmius,[35]sawskatesOnchopristis andSchizorhiza,[36]sharks likeSqualicorax andCretolamna, and a broad selection ofinvertebrates.[37] Additionally, severalcrocodylomorphs like thestomatosuchidStomatosuchus[38] and theeunotosuchianLibycosuchus are known from the formation.[39][40][32]
