Veterinary forensics is becoming more important in our society as a result of the growing demand for investigations related to crimes against animals or investigations of criminal deaths caused by animals. A veterinarian may participate as an expert witness or may be required to give forensic assistance, by providing knowledge of the specialty to establish a complete picture of the involvement of an animal and allowing the Courts to reach a verdict. By applying diverse dental profiling techniques, not only can species, sex, age-at-death, and body size of an animal be estimated, but also data about their geographical origin (provenance) and the post-mortem interval.
The work of the forensic medical pathologist and the forensic veterinary pathologist is similar; however, there is an enormous difference: while the work of the former focuses on a single species (the human being), the work of the latter encompasses multiple species, with cases involving household animals (including exotic species), farm animals, and wild animals. In this way, multispecies forensic pathology makes it a complex and difficult discipline to manage[4]. The forensic veterinary pathologist is not only specifically concerned with the post-mortem examination of a deceased animal and documents the findings of the examination but is also involved in the collection of evidence and court proceedings.
In veterinary forensics, the identification of carcasses is of less importance compared to its counterpart in human forensic medicine, although the reliable identification of live animals can be crucial (e.g., in the resolution of criminal investigations where the animal is the causative agent of the injuries or death of a human being). However, when it is necessary to identify dead animals or their remains, the following methods can be used[2]: (i) external markings, colour patterns, etc.; (ii) external morphological features (e.g., shape of antlers, abnormal coloration, or wear of hooves); (iii) presence of external collars, chains, ear tags, and other human-introduced devices (e.g., transponders); (iv) surgical evidence (e.g., docked tail, prosthesis); and (v) osteological characteristics. In the latter case, the ultimate goal of analysing a set of skeletal remains is to estimate the biological profile (i.e., to establish a set of characteristics that an animal specimen possessed during their life), which can be used to determine identity after death. In veterinary science, the biological profile would include the taxonomic classification (i.e., class, order, family, genus, and species identification), sex, age-at-death, body size, health/disease status, and individualising characteristics[5].The comparative dental anatomy analysis is a classical technique for species identification, and it also correlates to the inter-species relationship among members of the same family (e.g., family of Felidae: includes cheetah, leopard, tiger, domestic cat, lynx, among others)[9][10]. The number and types of teeth present in the oral cavity is useful in genus identification.
Species identification or the distinction of closely related species can also be done using the metric and morphological characteristics of the teeth, applying statistically robust techniques and using advanced tools (e.g., geometric morphometrics)[11][12][13][14][15][16][17]. Furthermore, the variation of simple metric characteristics such as tooth size or jaw length can be key in resolving debates about whether a sample comprises a single species or includes more than one morphologically similar species[18].
Non-metric dental traits (e.g., presence and size of cusps, form of fissures on occlusal surfaces of premolars and molars, form of ridges, presence of pits) also play a significant role in species identification. The variation of these non-metric traits is used to distinguish between species[14].
Thus, species identification is based primarily on macroscopic inspection of dental form (size + shape) (e.g.,[19]) and, in recent years, more complex tools (e.g., geometric morphometrics) and statistical procedures (e.g., machine learning algorithms, artificial intelligence) have allowed to analyse teeth and tooth marks with a higher precision[20][21][22]. However, when teeth are in a poor state of preservation, these traditional or advanced methods could be severely limited due to the difficulty or impossibility of observing species-specific dental anatomical characteristics. In this situation, histomorphometry of dental tissues (i.e., evaluating the organisation, composition, and structural components of enamel, dentine, and cementum)[23], immunological procedures[24], stable isotopes[25], genetic tools (such as DNA sequencing, Single Nucleotide Polymorphism, Polymerase Chain Reaction–Restriction Fragment Length Polymorphism, and microsatellite analysis)[26], and spectroscopy techniques (X-ray fluorescence[27][28] and Fourier transform infrared spectroscopy[29][30]) have become particularly useful and relatively applicative.
Sexual dimorphism is the term that refers to differences between males and females of the same species[31]. Sex is easily indicated by the presence/absence of the baculum/baubellum[32], but most frequently sexual dimorphism is identified by body measurements, particularly visible in body mass and size[33].
Size-related sexual dimorphism is a common phenomenon in carnivores, particularly in the size of the skull, mandible, and teeth, with males on average being significantly larger than females (e.g.,[34][35][36]), except in some animal species such as the spotted hyaena (Crocuta crocuta), where a reverse sexual dimorphism is observed[37]. In this order of mammals, sexual dimorphism in the size of the skull, canines, carnassial teeth, and molars is widespread, being more pronounced in the families of Felidae (e.g.,[38]), Canidae (e.g.,[33]), and Ursidae (e.g.,[39]). In general, dental sexual dimorphism of Primates centres on the canines[40][41][42] and, combined with the rest of the teeth in a discriminant analysis, can be used to assign a sex correctly in skeletal remains. Dental sexual dimorphism is also marked in tusks, including marine mammals such as narwhals, walruses, and dugongs, and herbivorous terrestrial mammals such as elephants and hippopotami[23].
Age-at-death estimation can be applied to living animals or skeletonised remains[43]. The examination of bones, horns, and dentition has been proposed in ageing of carcasses, as well as the length or height of animal and the colour of the pelage[44]. However, the study of animal dentition is one of the most practical and accurate methods for estimating their age-at-death[45]. Several methods have been proposed for the estimation of dental age-at-death in animal forensic investigations, such as those based on (i) dental development and eruption, (ii) occlusal tooth wear, (iii) dental cementum annuli, and (iv) secondary dentine deposition.
Since dental growth and mineralisation follow a consistent sequence and clear-cut changes occur over a brief period, age-at-death can be estimated with reasonable reliability from the state of development[23]. In veterinary practice, age-at-death can be estimated by visual examination evaluating dental eruption, since the sequence and timing of the eruption of teeth provides a reference scale for age-at-death estimation; it can be studied since the tooth begins the process when the crown emerges from the crypt until it reaches the occlusal plane[46].
After the dentition is fully erupted, several researchers have proposed age-at-death estimation methods based on dental wear[46]. Once a tooth emerges from the gingivae, dental wear initiates as a consequence of the grinding of teeth against one another, and the contact with food, cheeks, and tongue[23]. Dental attrition of the permanent teeth has been extensively studied and is considered a classic method for age-at-death estimation in adult animals[47], visually assessing the loss of enamel and the amount of the dentine exposed[23].
Another age-at-death estimation method is based on the analysis of incremental structures in dental cementum[46]. The deposition of cementum is continuous throughout the life of the animal, providing a longitudinal record of factors affecting its growth, resulting in incremental bands correlated with seasonal growth in most species. When longitudinal tooth sections are observed under a light-transmitting microscope using polarised light, translucent and opaque bands alternate as a result of the growth pattern; so, these bands can be related to the age of the animal and used to conduct the estimation of the age-at-death[48].
The study of secondary dentine deposition inside the pulp chamber is also applied for age-at-death estimation in animals[23]. Secondary dentine is the dental tissue formed after root completion and its deposition is continuous inside the pulp cavity in the form of layers while the pulp remains vital. As a result, the pulp cavity reduces in volume with age[49]. The relationship between the pulp/tooth area ratio using dental radiographic images is the basis of this age-at-death estimation method and has been applied in several animal species such as cat[50], dog[51], coyote[52], and lion[53].
Body size is described in terms of body length or mass, since these two variables provide the greatest predictive value for understanding the animal’s ecology[54]. Limb-based estimations of body mass are the most common methods using either lengths and/or midshaft cross-sectional dimensions of long bones[55]. They have the advantage that they are based on the relationship between body mass and the load borne by the limbs when they support the body on the ground[54]. However, because teeth are most frequently preserved in the skeletal record, their size is often used to estimate the body mass by biologists and palaeontologists[56][57]. While several studies use the post-canine tooth row length to infer allometric relationships with body mass (e.g.,[56][58][59]), other researchers have proven a strong relationship between body mass and the area of individual teeth, particularly the first molar (e.g.,[60][61][62][63]).
Numerous studies have performed regression equations based on post-canine tooth row length and/or mandibular first molar crown area (i.e., crown area = mesiodistal × buccolingual diameter) and have been developed for a variety of species of the class Mammalia, including ungulates (e.g.,[57][63]), marsupials (e.g.,[61]), carnivores (e.g.,[58][62][64]), rodents (e.g.,[59][65]), Primates (e.g.,[56][66][67]), and even sharks (e.g.,[68]). Although the first molar is considered the tooth that has the least variation in its adjustment to body mass and, therefore, would be the ideal tooth to estimate body mass from a single tooth, regression equations are available for the other tooth classes of the dentition (e.g.,[61][64][67]).
Stable isotope ratios vary among biomes that animals inhabit and are incorporated into organism tissues from its diet. In this way, animals moving between isotopically different biomes can retain information of previous feeding locations for periods of time that depend on the turnover rates for the different organism tissues[69].
In the case of teeth, stable isotope analysis can be performed on either the organic or inorganic fraction. The organic fraction preserves proteins such as collagen, so the collagen contained in dentine can be used to assess short-term changes that occurred during puppyhood, as these tissues form in early life and undergo little remodelling[70]. The inorganic fraction is primarily formed by hydroxyapatite. The dense crystalline structure of enamel makes it the preferred tissue for isotopic analysis, as it is less susceptible to diagenetic alterations compared to bone tissue[71][72]. Furthermore, dental enamel, unlike bone, is not remodelled during life, and therefore the isotopic signature of dental enamel is directly related to the environment and diet during the period of tooth formation[72].
The post-mortem interval is the time between the death of an animal and the discovery of the body[73]. In human forensic medicine, the study of the post-mortem interval is one of the most popular topics; however, in veterinary forensics, the number of studies is extremely limited[73][74][75][76]. Researchers must face a deficiency in the development of methodologies for a large number of species and, therefore, the obligation to apply methods developed in humans, lacking the appropriate validation to be applied in crimes against animals[74][75][77].
The most used methods of relevance to forensic veterinary pathology for estimating the post-mortem interval in animals’ dead bodies are mainly based on temperature changes, muscular stiffening (also called rigor mortis), ocular changes, cadaveric lividity (livor mortis), decomposition processes, and entomology[75][77]. In the case of studies conducted on animal dentition, there is a limited amount of research based on morphological, histological, or molecular analysis[78][79][80][81]. The small number and the results of the studies conducted on animal dentition for estimation of the post-mortem interval show the need to increase the analysis on this topic. All the studies point out the potential of their methods but emphasise the need for further research to give greater solidity to the results[78][79][80][81].
In forensic sciences, recognising and correctly identifying the actions of animals on human remains, but also on other faunal remains, is crucial, as this allows the collection of data about events that may have affected the body over a time, which may have ranged from the ante-mortem to post-mortem period[82]. In certain contexts or situations, animals can cause severe injuries that, on one hand, may lead to the death of the individual attacked and, on the other hand, can alter the corpse in the post-mortem period, either in relation to soft or hard tissues[83]. To reconstruct the forensic scene as reliably as possible and define how certain animal species acted on a human body, it is essential to correctly identify the nature of the injuries, the anatomical region affected, the circumstances in which they occurred and the agent that caused them, in order to avoid possible misjudgements with very disastrous implications in the forensic framework. At a macroscopic level, bite marks are among the signs most frequently found on the body of a victim, whether it is exposed in an open, outdoor, or enclosed environment. Bite marks can be defined as both superficial and deep marks left by teeth that affect, in diverse ways, both soft and hard tissues whose morphology varies depending on the size and shape of the maxillary/mandibular dental arches and the force exerted by the bite[84].
Determining which predator species is responsible for killing a human is important, especially when there is the possibility of overlapping bite marks, as is the case with many carnivore species[85]. For example, in bite mark comparisons of sympatric animals, measurements of the maxillary and mandibular intercanine distance are frequently used as an aid in identifying the different animal species responsible for a predatory or scavenging attack[86][87].
There is no doubt that veterinary forensics is becoming increasingly important in our modern society, increasing the demand for investigations related to crimes against animals or investigations of criminal deaths of human beings involving animals. The potential of dentition in the identification process in forensic contexts emphasises the need for further research to give greater solidity to the results, helping the Courts in answering questions of interest to the legal system to reach a reliable verdict.
This entry is adapted from the peer-reviewed paper 10.3390/ani12162038