Favreina babai, SCHLAGINTWEIT & TORROMÉ, 2025

Favreina babai ichnosp. nov.

Figs. 3-4 View Fig View Fig .

Derivatio nominis: The name is dedicated to the late Baba Senowbari-Daryan in recognition of his numerous contributions to the knowledge of fossil crustacean microcoprolites.

Holotype: Transverse section in Fig. 3A View Fig , sample M2_0_2 stored in the “ Museo de Ciencias Naturales de la Universidad de Zaragoza” under the depository number MPZ 2024 View Materials /323.

Stratum typicum: Santonian La Cañadilla Formation ( Fig. 2A View Fig ).

Type locality: Section exposed near Molinos ( Fig. 2B View Fig ).

Diagnosis: Rod-shaped microcoprolite, rounded to slightly oval in transverse sections (without any depression or cap), displaying a bilaterally symmetric pattern of numerous rounded canals. In the symmetry plane, a comparably thick longitudinally furrow, cylindrical to claviform in longitudinal section, is present. Interconnecting lines or fissural spaces between canals or connections between the latter and the median furrow are absent.

Description: Favreina babai represents a rod-like microcoprolite observed in different random sections. Transverse sections are rounded to slightly oval without any depression (“ventral groove”, e.g., Brönnimann and Masse, 1969). Rare ellipsoidal specimens are due to vertical compression/compaction and do not reflect the original morphology ( Fig. 3K View Fig ). The microcorpolite itself is homogeneously micritic without showing any differentiation of the material or texture (e.g., “ventral cap”). It is traversed by numerous longitudinal canals running parallel to one and another as discernible in longitudinal sections ( Fig. 3 View Fig E-F). As displayed in transverse sections, the canals are rounded in outline and display a bilaterally symmetric arrangement forming two groups which in turn are separated by a homogeneous median zone that lacks canals. The arrangement of canals allows differentiation between a straight longitudinal row parallel to the median axis (median canals), canals at the periphery forming a semicircle that follows the outline of the microcoprolite (peripheral canals) and internal canals between the two former groups. The last form two loops or arches ( Fig. 4 View Fig ). Interconnecting lines or fissural spaces between canals are poorly constrained to absent. The peripheral canals are only slightly offset from each other's without forming the zigzag pattern that is known from other ichnospecies of Favreina . With respect to size, the assemblage of microcoprolites is in a rather narrow range (see dimensions) not allowing any evidence of ichnogeny such as juvenile versus adult forms (e.g., Schweigert et al., 1997; Kopaska-Merkel, 2013; Belaústegui et al., 2016.)

Dimensions:

Diameter: 0.50-0.65 mm

Length: up to 1.20 mm

Number of median canals per side (1): 10-14 (= 20-28 in total)

Number of peripheral canals per side (2): 15-24 (= 30-48 in total)

Number of internal canals between (1) and (2): 18-25 (= 36-50)

Number of canals in total: ~88 to ~130

Diameter of canals: 0.014 -0.022 mm

Width of homogeneous median zone: ~ 0.05 mm Remarks: The arrangement and number of canals piercing microcoprolites in a longitudinal manner are used as the main distinguishing feature (e.g., Brönnimann, 1972; Senowbari-Daryan & Kuss, 1992). As the available transverse sections are neither ideally cut nor perfectly preserved, the reconstruction shown in Figure 4 View Fig is a combination obtained from various specimens ( Fig. 3 View Fig A-D). We differentiate three types of canals: (1) median canals, (2) peripheral canals, and (3) internal canals located between (1) and (2).

Comparisons: Senowbari-Daryan & Kuss (1992, tab. 1) provided a comparison table comprising the 19 different Favreina ichnospecies described till then. Since that time, the following nine ichnotaxa have been added: Favreina prima Herbig, 1993 , Favreina peruvensis Blau et al., 1994 , Favreina belandoi Fels in Schweigert et al., 1997, Favreina omanensis Senowbari-Daryan & Bernecker, 2000 , F. lahngangkogelensis Schlagintweit et al., 2005 , F. fontana Senowbari-Daryan et al., 2007 , F. tosaensis Senowbari-Daryan et al., 2010 , F. carpatica Senowbari-Daryan et al., 2013 , and F. iranensis Dalvand et al., 2015 . This amounts to a total of 28 ichnospecies of Favreina . F. babai is among those forms that may display more than 100 longitudinal canals till now comprising just one Cretaceous representative, F. angulata Senowbari-Daryan & Kuss, 1992 , and is therefore compared with this group ( Tab. 2; Fig. 5 View Fig ). Among these, we note that the three ichnospecies F. prusensis Paréjas, 1948 (Upper Jurassic of Switzerland), F. lahngangkogelensis Schlagintweit et al., 2005 (Upper Jurassic of Austria) and F. iranensis Dalvand et al., 2015 exhibit a striking correspondence between the pattern of the longitudinal canals in transverse section ( Fig. 5 View Fig A-E). They have several rows of zigzagging canals parallel to the median plane (the innermost row) and the lateral periphery. In addition, all three may reach diameters larger than 1 millimetre as a further characteristic while most others have diameters between 0.50 mm and 0.80 mm. Here, we propose the synonymy of the three ichnotaxa with F. prusensis Paréjas, 1948 having priority. As another distinguishing criterion, F. babai shows a distinct and well-delimited median zone lacking any canals. These features distinguish F. babai from ichnotaxa such as F. angulata Senowbari-Daryan & Kuss, 1992 ( Fig. 5G View Fig ), F. carpatica Senowbari-Daryan, Lazăr & Bucur, 2013 ( Fig. 5H View Fig ), and F. multicanalis Förster in Förster & von Hillebrandt, 1984 ( Fig. 5J View Fig ). The diameter of the canals is not a practical feature to separate different ichnospecies of Favreina (e.g., Senowbari-Daryan & Kuss, 1992, tab. 1). Most have diameters in a range between 10 and 30 µm. Only F. cuvillieri Brönnimann, 1955 and F. radiata Senowbari-Daryan & Kuss, 1992 have greater canal diameters of 40 and 50 µm respectively ( Senowbari-Daryan & Kuss, 1992, tab. 1). The differences in the pattern of the canal arrangement in transverse section is evident from the provided reconstruction ( Fig. 4 View Fig ) and the compilation shown in Figure 5 View Fig . For example, some just have an indistinct arrangement ( Fig. 5H View Fig , J-K), while others lack peripheral canals that run parallel to the external surface ( Fig. 5I View Fig ).

Last but not least, comparison is made to Favreina murciensis Cuvillier et al., 1969 from the ‘Sénonien inferieur’ of the Murcia region of south- eastern Spain. With a diameter of 0.30 mm it is smaller than F. babai and exhibits a much reduced number of canals (about 30). Both share in common the ‘sillon “dorsal” médian’, that is the median stripe in the middle of the microcoprolite lacking canals. F. murciensis was described from the Sierra de Utiel Formation, a shallow-marine coastal geological unit characterized by well-preserved cyclicity in the form of shallowing-up sequences ( Martín-Chivelet & Giménez, 1992). This formation was initially assigned to the early Campanian in the first regional reviews ( Gil et al., 2004); however, more updated studies suggest a Coniacian-Santonian age ( Martín-Chivelet et al., 2019). This time interval, along with paleogeography and similarities in paleoenvironment, facies, and eustatic influence, suggests that the upper part of the Sierra de Utiel Formation is coeval with the La Cañadilla Formation.

Palaeoenvironent: The La Cañadilla Formation represents a transitional setting from shallow-marine to coastal and can be subdivided into three distinct belts ( Torromé et al., 2022): (1) a low-energy lagoon colonized by rudists, green algae (Dasycladales), and foraminifera (mainly miliolids); (2) a transitional belt with a patchy distribution of carbonate mudbanks and ponds, featuring a variable proportion of charophytes, gastropods, and foraminifera; and (3) a vegetated coastal plain exhibiting intense brecciation and root bioturbation, mainly colonized by charophytes and gastropods ( Fig. 6 View Fig ).

Evidence of crustaceans in the La Cañadilla Formation is scarce, with only fragmented crab claws identified in the more energetic areas of the lagoon, adjacent to the mudbanks of the second belt. Similarly, Favreina babaensis ichnosp. nov. has only been recognized in the low-energy lagoon. Fossil remains from the original bed (M2_0, M2_1, M2_2, M2_7) are associated with wackestone accumulations, while remains from the newly sampled overlying bed (M2_3) are more characteristic of packstone accumulations.