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Labocania anomala - DinoFan83 - 01-30-2021
Labocania was a species of carnivorous theropod, previously considered a tyrannosauroid or abelisaurid but almost certainly a carcharodontosaurid.
Labocania anomala, the type species, was described and named by Ralph Molnar in 1974. The generic name references the La Bocana Roja locality where it was found, named after la Bocana Roja, "the red estuary". The species name means "anomalous" in Latin, in reference to the distinctive and very robust build.
The holotype (LACM 20877) was found in a layer of the La Bocana Roja Formation, dating from the late Campanian of the late Cretaceous period about 73 million years old. It consists of a very fragmentary skeleton with skull elements, including a right quadrate, a left frontal, a piece of the left maxilla, a fragment of the dentarium, a chevrom, the upper parts of both ischia, the middle shaft of the right pubis, most of the second right metatarsal, a pedal phalanx and several loose teeth. The elements were not articulated, dispersed over a surface of about two square metres, and strongly weathered. The remains were mixed with the ribs of hadrosauroids.
Although it is not very complete, Labocania was probably an extremely large theropod, despite popular estimates not implying this. Gregory S. Paul estimated it at 7 meters and 1500 kg in 2010, while Ruben Molina-Pérez and Asier Larramendi gave a higher estimation of 8.2 meters and 2600 kg in 2016, with both estimates made under the assumption that it was a tyrannosauroid.
However, because Labocania looks to have been a carcharodontosaurid instead of a tyrannosauroid, it would almost certainly have been far larger (and in fact one of the largest known land predators of all), with a skull size estimate restored as such equaling or exceeding in size the skull of the giant Carcharodontosaurus specimen SGM-DIN 1 (itself estimated at 13-13.7 meters and 9000-9800 kg). An estimate based on the fairly complete carcharodontosaurid Acrocanthosaurus also supports a gigantic size, at 12.9 meters and 9500 kg.
The cranial elements are very robust, and the frontals in particular are strongly thickened. The teeth of the maxilla are gradually recurving and rather flat (just like those of carcharodontosaurids) and those of the premaxilla do not have a D-shaped cross-section, unlike tyrannosaurids.
Given how fragmented known specimens are, the affinities have been hard to establish before the animal was placed in phylogenetic analyses by experts. Molnar especially compared Labocania with the carcharodontosaurid Shaochilong (then known as "Chilantaisaurus" maortuensis and thought to be a basal tyrannosauroid at the time), and found the two to be rather similar.
Additionally, similarity between Labocania and tyrannosaurids was found in the form of the ischium which features a low triangular obturator process and a circular lateral scar on the upper end. These features, however, are also known in both species of Giganotosaurus, further supporting Labocania as a carcharodontosaurid.
Labocania did not end up assigned to any family in the original description, placed as Theropoda incertae sedis. Based on further comparisons with Shaochilong under the old assumption that the latter was a tyrannosauroid, Labocania was considered as a possible tyrannosauroid in the 2004 edition of The Dinosauria by Thomas Holtz, but now that it is known what Shaochilong is, these comparisons support carcharodontosaurid affinities for Labocania.
However, even in 2004, Holtz pointed out that the similarities with the Tyrannosauridae were shared with the Coelurosauria in general—no tyrannosauroid synapomorphies were present—and that Labocania also showed some abelisaurid traits such as the thick frontals and a reclining quadrate. On the other hand, the L-shaped chevron and the flattened outer side of the second metatarsal indicated a position in the Tetanurae.
Later phylogenetic analyses by experts Mickey Mortimer and Andrea Cau have yielded strong support carcharodontosaurid Labocania, in a very close position to Shaochilong.
The recognition of Labocania as a carcharodontosaurid indicates, contrary to popular belief, that allosauroids neither died out in the Cenomanian-Turonian extinction event nor were outcompeted by tyrannosauroids. They would instead have survived to at least the latest Campanian - therefore it being within the realm of possibility that some allosauroids lived to see the asteroid that killed off the dinosaurs - and most certainly would not have been outcompeted by tyrannosauroids, instead very likely being ecologically dominant over them in at least Labocania's case.