Data from: New sharks and other Chondrichthyans from the latest Maastrichtian (Late Cretaceous) of North America

Cretaceous aquatic ecosystems were amazingly diverse, containing most
clades of extant aquatic vertebrates as well as an array of sharks and
rays not present today. Here we report on the chondrichthyan fauna from
the late Maastrichtian site that yielded the Tyrannosaurus rex skeleton
FMNH PR 2081 (“SUE”). Significant among the recovered fauna is an
unidentified species of carcharhinid shark that adds to the fossil record
of this family in the Cretaceous, aligning with estimates from molecular
evidence of clade originations. Additionally, a new orectolobiform shark,
here named Galagadon nordquisti n. gen n. sp., is diagnosed on the basis
on several autapomorphies from over two-dozen teeth. Common chondrichthyan
species found at the ‘SUE’ locality include Lonchidion selachos and
Myledaphus pustulosus. Two phylogenetic analyses (Maximum Parsimony and
Bayesian Inference) based on twelve original dental character traits
combined with 136 morphological traits from a prior study of 28 fossil and
extant taxa, posited Galagadon in two distinct positions: as part of a
clade inclusive of the fossil species Cretorectolobus olsoni and
Cederstroemia triangulata plus extant orectolobids from the Maximum
Parsimony analysis; and as the sister taxon to all extant hemiscyllids
from the Bayesian Inference. Model-based biogeographical reconstructions
based on both optimal trees suggest rapid island hopping-style dispersal
from the Western Pacific to the Western Interior Seaway of North America
where Galagadon lived. Alternatively, the next preferred model posits a
broader, near-global distribution of Orectolobiformes with Galagadon
dispersing into its geographic position from this large ancestral range.

白垩纪（Cretaceous）水生生态系统的多样性令人惊叹，囊括了现存绝大多数水生脊椎动物演化支，以及一众如今已绝迹的鲨类与鳐类。本文报道了产自产出霸王龙（Tyrannosaurus rex）标本FMNH PR 2081（俗称"SUE"）的马斯特里赫特阶晚期遗址的软骨鱼动物群。本次采集到的动物群中，一种未定名的真鲨科（Carcharhinidae）鲨鱼填补了该科在白垩纪的化石记录空白，其发现结果与基于分子证据得出的演化支起源时间估算结果一致。此外，本文还记述了一种全新的须鲨目（Orectolobiformes）鲨鱼，命名为Galagadon nordquisti（新属新种），其鉴定依据为24枚以上牙齿所具备的多项独有衍征。"SUE"遗址中常见的软骨鱼物种包括Lonchidion selachos与Myledaphus pustulosus。研究基于12项全新的牙齿形态性状，结合前人针对28个化石与现存类群建立的136项形态性状，开展了两项系统发育分析——最大简约法（Maximum Parsimony）与贝叶斯推断（Bayesian Inference）。结果显示，Galagadon的系统发育位置存在两种不同情形：在最大简约法分析中，它隶属于包含化石物种Cretorectolobus olsoni、Cederstroemia triangulata以及现存须鲨科类群的演化支；而在贝叶斯推断分析中，它则是所有现存竹鲨科（Hemiscylliidae）类群的姊妹群。基于最优树开展的模型驱动生物地理重建结果表明，Galagadon以跳岛式扩散的方式，从西太平洋快速抵达其栖息的北美西部内陆海道。另一套次优模型则提出须鲨目曾拥有更广的近全球性分布范围，Galagadon从这一广阔的祖先分布区扩散至其现今的地理分布区域。