Cascocauda

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Cascocauda
Temporal range:
Ma
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order: Pterosauria
Family: Anurognathidae
Subfamily:
Batrachognathinae
Genus: Cascocauda
Yang et al., 2022
Species:
C. rong
Binomial name
Cascocauda rong
Yang et al., 2022

Cascocauda (meaning "ancient tail") is an

extinct genus of anurognathid pterosaur from the Late–⁠Middle Jurassic Tiaojishan Formation of Hebei Province, China. The genus contains a single species, C. rong, known from a complete skeleton belonging to a juvenile individual preserved with extensive soft-tissues, including wing membranes and a dense covering of pycnofibres.[1] Some of these pycnofibres appear to be branched, resembling the feathers of maniraptoran theropod dinosaurs, and suggesting that pterosaur pycnofibres may be closely related to feathers in dinosaurs.[2]

Discovery and naming

The

counter slab, and is housed in Nanjing University in Nanjing, China.[1]

The specimen was first reported as an unnamed anurognathid in December 2018 by Zixiao Yang and colleagues, along with another anurognathid specimen (CAGS-Z070), in a description and analysis of both specimens' integumentary structures.[2] NJU-57003 would not be fully described until 2022 by Yang and colleagues, wherein it was diagnosed as a new genus and species, Cascocauda rong. The generic name is derived from the Latin cascus, meaning 'ancient' or 'primitive', and cauda, meaning 'tail.' The specific name is from the Chinese character 'róng' (绒/絨), derived from the phrase "máo róng róng" (毛绒绒/毛絨絨) which means "a fluffy appearance." Thus, the full binomial name translates as "fluffy ancient tail."[1]

Description

Like other anurognathids, Cascocauda was a small pterosaur with a short, wide skull and "frog-like" jaws, large eyes, broad wings and a short tail. The only known specimen has a wingspan of 434 millimetres (17.1 in), although this individual was immature and likely not finished growing. The skull wider than it is long (22.2 mm long vs 31.7 mm wide) and poorly preserved, although the ascending processes of the jaw separating the

naris, antorbital fenestra and orbit appear visible on the right side. Its teeth were long (2.2-2.7 mm) and thin (~0.5 mm at their midpoint) with smooth surfaces and curved towards the tips, and at least nineteen teeth were present in the upper jaw.[1]

Most of the vertebrae are crushed or obscured, but the neck is visibly short and at least ten

vertebral centrum. This is similar to other Batrachognathinae, such as Sinomacrops, but unlike the shorter-tailed anurognathines.[1][2]

The

metacarpals are only a quarter the length of the radius.[1]

The bones of the hindlimb are long and straight, with a

cruropatagium between the legs, has a much shorter and more robust metatarsal, and while the first phalanx is robust and straight the second is slender and slightly curved. The claws on both the feet and wings are similar in shape and sharply curved, but the wing claws are larger and more robust.[1]

Integument and colouration

Cascocauda was almost entirely covered in an extensive coat of fur-like filaments known in pterosaurs as

human hair. These pycnofibres likely provided both insulation and may have helped streamline the body and wings during flight.[2]

The identity of these branching structures as pycnofibres or feathers was challenged by Unwin & Martill (2020), who interpreted them as bunched-up and degraded aktinofibrils–stiffening fibres found in the wing membrane of pterosaurs–and attributed the melanosomes and keratin to skin rather than filaments.[4] These claims were refuted by Yang and colleagues, who argue that Unwin and Martill's interpretations are inconsistent with the specimen's preservation. Namely, they argue that the consistent structure, regular spacing, and extension of the filaments beyond the wing membrane support their identification as pycnofibres. Further, they argue that the restriction of melanosomes and keratin to the fibres, as occurs in fossil dinosaur feathers, supports the case they are filaments and is not consistent with contamination from preserved skin.[5]

Compared to the coat of pycnofibres, the wing membranes (

patagia) are not as well preserved and are only locally discernible on the fossil.[2]

Classification

NJU-57003 was initially reported as an anurognathid of undetermined species in 2018, although Yang and colleagues recognised that the specimen showed similarities to

biota, and considered it likely to be a juvenile of one of these genera.[2] However, a later analysis of how anurognathid proportions change through growth (allometry) by Yang et al. (2022) demonstrated that the proportions of Cascocauda were distinct from all other anurognathids, irrespective of it being juvenile, and that it therefore belonged to a new taxon.[1]

A

phylogenetic analysis performed in the same study found Cascocauda to be a member of the subfamily Batrachognathinae in a clade of relatively long-tailed anurognathids, potentially a primitive trait compared to the short-tailed derived anurognathines.[1] A simplified version of their results is shown in the cladogram
below:

Anurognathidae
Batrachognathinae

Cascocauda rong

Sinomacrops bondei

Batrachognathus volans

Anurognathinae

Luopterus mutoudengensis

Dendrorhynchoides curvidentatus

Anurognathus ammoni

Vesperopterylus lamadongensis

CAGS-Z070

Jeholopterus ningchengensis

Palaeobiology

The only known specimen of Cascocauda is believed to be a juvenile, based on features of the skeleton that indicate immaturity. Namely, articular bones such as the

carpals in the wing and the scapula and coracoid of the shoulder are unfused, and the articular surfaces of the limb joints are rough and pitted, both indicative of incomplete bone growth. Based on allometric growth pattern, it is suggested that throughout their life, anurognathids like Cascocauda had little change in their lifestyle as flying arboreal insectivores, possibly consuming preys of consistent size, and that the ontogenetically consistent lifestyle would have retained the plesiomorphic traits as juvenile to later ontogeny.[1]

References